PHOTON 2019 - International Conference on the Structure and the Interactions of the Photon. Satellite Workshop: Photon Physics and Simulation at Hadron Colliders.

3 Jun 2019, 08:30 → 7 Jun 2019, 19:15 Europe/Rome

Bruno Touschek Auditorium (INFN-LNF, Italy)

This conference is part of the series initiated in 1973 in Paris, as an International Colloquium on Photon-Photon Collisions at Electron-Positron Storage Rings. The latest Photon conferences took place in CERN-Geneva (2017), Novosibirsk (2015), Paris (2013), Spa (2011), Hamburg (2009), Paris (2007), Warsaw (2005), Frascati (2003), Ascona (2001), Freiburg (2000), Ambleside (1999), and Egmond aan Zee (1997).

 

This year edition will feature a two-day workshop on Photon Physics and Simulation at Hadron Colliders, focused on photon phenomenology at the LHC, on June 6-7.
More info on this workshop can be found at:
https://indico.cern.ch/event/783361/

 

The conference scientific program will include topics related to photon-photon and photon-hadron collisions as well as final-state photon production at current and future colliders. In addition, high-energy astrophysics gamma-rays, and photon-related searches of new physics (axions, dark/hidden photons, ...) will also be discussed. The conference format consists of talks in plenary sessions only. The LOC offers a number of young researcher grants to attend the conference. Interested participants are invited to send an e-mail to photon19_loc@lists.lnf.infn.it with their motivated request for support.

The 2019 Edition of the Colloquium will be hosted in the first established laboratory of the Italian National Institute of Nuclear Physics (awarded also as EPS historical site) the place where in 1959, exactly 60 years ago, the first Italian Electro-Syncroton started its operations. Here, the year after, the first matter-antimatter collider (AdA) ever built saw the light.

 

1st Circular.pdf

2nd_Circular.pdf

final_circular.pdf

FPS_Photon.zip

Monday, 3 June

08:45 Registration

1 Welcome Speech

Speakers: Pierluigi Campana (LNF), Giulia Pancheri (LNF)

photon2019-June3.pdf

General Talks

Convener: Pasquale Di Nezza (LNF)

2 The Synchrotron: father of the Frascati particle accelerators

On 9 February 1959 it was announced that the 1 GeV energy was reached by the Frascati synchrotron. This great achievement, considering the Italy of the post-war period, started the Frascati history on particle physics experiments and on development of particle accelerators and detectors. The synchrotron team then developed the accelerator concept by building the first electron and positrons collider in the world, ADA: subsequently the ADONE colliders and the first Phi-Factory DAPHNE have been realized in Frascati.

Speaker: Andrea Ghigo (LNF)

ghigo - Sincrotrone_father_last.pdf

3 Standard Model measurements with photons

In this talk I will discuss photon measurements i) as tests of pQCD and
used to tune PDFs ii) providing important information for BSM searches, and
iii) related with the Higgs Boson. I will go over LHC and non-LHC results
and give prospects for HL-LHC and beyond.

Speaker: Niki Saoulidou (University of Athens, Greece)

Photon_19_NS_v3.pdf

4 Parton distribution functions and EW corrections

Precision phenomenology at the LHC requires accounting for both higher-order QCD and electroweak corrections as well as for photon-initiated subprocesses. In this talk I summarise the development history concerning: the inclusion of electroweak effects in parton distribution functions, the evolution of PDF algorithms for the determination of the photon PDF during the past decade, and the impact of photon-initiated contributions to several processes.

Speaker: Stefano Carrazza (MI)

carrazza.pdf

11:00 Coffee Break

Gamma-Hadron Collisions

Conveners: Aurore Courtoy (Instituto de Física, UNAM), Marco Battaglieri (GE)

5 Spectroscopy of light quarks

In this talk we will review some recent progress on light quark spectroscopy
coming from $\eta$ and $\eta$' physics.

Speaker: Emilie Passemar (Indiana University/JLab)

EPassemar_Photon2019.pdf

6 Heavy quark spectroscopy

I will review the status of heavy quark spectroscopy, in particular the XYZ and pentaquark candidates.

Speaker: Alessandro Pilloni (ROMA1)

heavy.pdf

7 Nucleon structure in lepton-nucleon interactions

Various measurements of photoproduction in lepton-nucleon interactions are presented, along with their theoretical interpretations. These include spin-independent measurements of inclusive charm and beauty production, isolated photons and jets as well as exclusively produced hadrons. Results of hadron photoproduction in data taken with polarised leptons and nucleons are shown also.

Speaker: Charlotte Van Hulse

photon_ep_charlotte.pdf

8 Light dark states with electromagnetic form factors

There may exist new sub-GeV particles, χ, which are electrically neutral but couple to the electromagnetic current via higher-dimensional operators. This talk focus on the possible detection of light state coupled to the photon through magnetic- and electric-dipole moments, or carrying an anapole moment or charge radius.
New constraints, as well as future sensitivities, on the existence of such states are derived from a number of high-intensity experiments and other collider observations, since no positive signals have been found. The second half of the talk discusses the possibility that χ is dark matter (or very long-lived) and study ensuing astrophysical and cosmological constraints, and shows that a combination of all considered probes rule out χ particles with dimensional five and six operators as dark matter when assuming a standard freeze-out abundance.

Speaker: Xiaoyong Chu (Institute of High Energy Physics, Vienna)

PHOTON_CHU.pdf

13:30 Lunch Break

Gamma-Hadron Collisions

Conveners: Aurore Courtoy (Instituto de Física, UNAM), Marco Battaglieri (GE)

9 Status of the anomalous magnetic moment of the muon in spring 2019

In this talk we review the recent progress on the numerical determination of the hadronic contributions to the anomalous magnetic moment of the muon and we discuss the role of experimental data on the accuracy of its determination. Special emphasis on the light-by-light scattering contribution and on its main contribution, the pseudoscalar piece, is made. A state-of-the-art deviation between theory and experiment for the $(g-2)_{\mu}$ is discussed and an outlook for the near future made.

Speaker: Pere Masjuan (Johannes Gutenberg-Universität Mainz, Institute für Kernphysik)

HLBL_Photon19.pdf

10 Gravitational form factors & internal forces in hadrons

The gravitational form factors of hadrons can be studied through hard-exclusive reactions, give access to the "last global unknown property" D-term, and promise insights on the internal forces inside hadrons from a unique perspective through their interpretation in terms of energy-momentum tensor densities. The current experimental and theoretical status is reviewed.

Speaker: Peter Schweitzer (UConn)

Peter-Schweitzer-PHOTON2019.pdf

11 Combination and QCD analysis of charm and beauty production cross-section measurements in deep inelastic ep scattering at HERA

Measurement of open charm and beauty production cross sections in ep deep inelastic scattering (DIS) at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections are obtained in a restricted kinematic range. Perturbative QCD calculations are compared to the combined data. Next-to-leading order QCD analysis is performed using these data together with combined inclusive HERA DIS cross sections. The running charm and beauty quark masses are determined.

Speaker: Uri Karshon (Weizmann Institute)

karshon - charm_beauty_DIS.pdf

16:30 Coffee Break

Gamma-Gamma Collisions

Convener: Lucian Harland-Lang (IPPP Durham)

12 Recent results from two-photon processes at Belle

In this talk, I will talk about recent progresses by two-photon processes at Belle. (a) meson transition form factor (TFF), a important input for calculation of hadronic light-by-light scattering contribution, which is one of dominant theory uncertainty source to muon g-2. With single tag method, the pi0/f0(980)/f2(1270) TFF is presented in this talk. (b) The cross section of hadron pair production in no-tag measurements, is a good place to test (p)QCD prediction. The results of KsKs via gamma gamma fusion in low-W region is presented, and compared with that of pQCD calculation. (c) Similar to J/psi p, the phi p is interesting channel for exotic baryons. A search for exotic baryons is presented in gamma gamma -> p p-bar K+ K-.

Speaker: Wenbiao Yan (USTC)

wenbiao.pdf

13 Recent results on two-photons processes at BaBar

We study process e+e- -> e+e-eta' in the double-tag mode and measure for the first time the gamma gamma -> eta' formfactor
F(Q^2_1,Q^2_2) in the momentum-range 2 < Q^2_1,Q^2_2 < 60 GeV^2. The analysis is based on data with an integrated luminosity
469 fb^-1 collected at the PEP-II e+e- collider with the BABAR detector at center-of-mass energies near 10.6 GeV. The results for the formfactor are compare with the predictions based on pQCD and VMD.

Speaker: Peter Lukin (Budker Institute of Nuclear Physics and Novosibirsk State University)

BaBar_Lukin_Talk_v2.pdf

14 gamma-gamma physics at KLOE-2

The KLOE-2 experiment completed its data-taking at the e+e- DAPHNE collider in Frascati, achieving the integrated luminosity goal of more than 5 fb-1 at the phi peak. KLOE-2 represents the continuation of KLOE with an upgraded detector and an extended physics program. The new four stations installed to tag electrons and positrons from the reaction e+e- -> e+e-gammagamma -> e+e-X, give the opportunity to investigate gamma-gamma physics at the phi resonance. Single pseudoscalar production will improve the determination of the two-photon decay widths of these mesons. An accuracy of O(1%) for the pi0 is reachable with 5 fb-1, matching the current theory precision. With the same amount of data, the measurement of the pi0 -> gamma gamma* TFF in the space-like region with 5-6% accuracy could be reached in a region not yet exploited of the low momentum transfer. Preliminary results and perspectives on gamma-gamma physics will be presented.

Speaker: Dario Moricciani (LNF)

talk.pdf

15 Transition Form Factor Measurements at BESIII

Motivated by the recent developments in data-driven approaches to improve the hadronic light-by-light scattering calculations of the Standard Model prediction of the anomalous magnetic moment of the muon $a_\mu$, the BESIII collaboration has embarked on a dedicated two-photon physics program. The momentum dependence of transition form factors of single pseudoscalar mesons, as well as of multi-meson systems is studied. Based on the high statistics data, collected at the $\tau$-charm factory BESIII operated at the BEPCII accelerator in Beijing, the information can be provided in the relevant momentum region for $a_\mu$. In this presentation we discuss recent results, the current status of ongoing measurements, and the prospects for $\gamma\gamma$ collision studies at BESIII.

Speaker: Christoph Florian Redmer (Institute for Nuclear Physics, Johannes Gutenberg - University Mainz)

CFR190603.pdf

18:20 Welcome Dinner

Tuesday, 4 June

Gamma-Gamma Collisions

Convener: Lucian Harland-Lang (IPPP Durham)

16 Observation of light-by-light scattering and measurements of photon-photon collisions at ATLAS

We present the observation of the light-by-light scattering process, γγ → γγ, in lead-lead collisions at √sNN = 5.02 TeV. The analysis is conducted using 1.73nb-1 of data collected in November 2018 by the ATLAS experiment at the LHC. Light-by-light scattering event candidates are selected in events with two photons produced exclusively, with small diphoton transverse momentum and small acoplanarity. After applying all selection criteria, 59 candidate events are observed for a background expectation of 12 ± 3 events. An excess of events over the expected background is found with an observed significance of 8.2 standard deviations. The fiducial cross section is also measured and compared to the theoretical predictions.
In addition, we present the measurements of γγ → W+W- and γγ → 𝜇+𝜇- in proton-proton collisions at ATLAS. The production of γγ → 𝜇+𝜇- was measured at a centre- of-mass energy of 13 TeV using 3.2 fb-1. Fiducial and differential cross sections are compared to theoretical predictions both with and without corrections for absorptive effects. Exclusive production of W+W- consistent with the Standard Model prediction was found with 3𝜎 significance using 20.2 fb-1 of data at a centre-of-mass energy of 8 TeV. The fiducial cross section was measured and found to be in agreement with Standard Model predictions. Constraints were placed on anomalous quartic gauge boson interactions.

Speaker: Iwona Grabowska-Bold (AGH University of Science and Technology)

Photon2019-AtlasLbyL-062019.pdf

17 Measurements with photon-photon collisions in CMS

Measurements with photon-photon collisions in CMS are reviewed.

Speaker: Justin Williams (CERN)

williams.pdf

18 Magnetic monopoles in heavy ion collisions

Magnetic monopoles are present in generic classes of models beyond the Standard Model and there are currently searches underway for them at the LHC. The strong magnetic fields present in peripheral heavy ion collisions can produce monopoles by the (dual) Schwinger effect. I will outline recent progress in understanding this process and argue that heavy ion collisions may be the most promising place to carry out searches for monopoles.

Speaker: Oliver Gould (University of Helsinki)

frascati_talk.pdf

19 Diphoton elastic scattering in UPC at smaller $W_{\gamma\gamma}$

So far light-by-light scattering ($\gamma\gamma\to\gamma\gamma$) was not accessible for experiments because the corresponding cross section is rather low. Measurements of diphotons in ultra-peripheral collisions (UPCs) of lead-lead have been reported recently by the ATLAS [1] and CMS Collaborations [2]. Our theoretical results based on equivalent photon approximation in the impact parameter space [3] are in agreement with the current data [1, 2].
We will discuss how to extend such studies to lower $\gamma\gamma$ energies where photoproduction of pseudoscalar and scalar resonances contribute to the two-photon final state. In addition, we consider the dominant background that arises from $\gamma\gamma$ fusion into pairs of neutral pions [4]. Such $\pi^0$-pairs contribute to the background when only two of the four decay photons are within the experimental acceptance, the other two photons escape undetected. We will discuss in detail how to reduce the unwanted background. We will present differential distributions and total cross section in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{NN}}=5.05$ and $5.52$ TeV [5] and cross section for Ar-Ar collisions at the energy equal to $6.3$ TeV [6]. Results for ALICE and LHCb acceptance will be presented.

[1] ATLAS Collaboration, Nature Phys. 13 (2017) 852 & arXiv:1904.03536 [hep-ex]
[2] CMS Collaboration, arXiv:1810.04602
[3] M.Kłusek-Gawenda, P.Lebiedowicz, A.Szczurek, Phys. Rev. C93 (2016) 044907
[4] M.Kłusek-Gawenda, A.Szczurek, Phys. Rev. C87 (2013) 054908
[5] M.Kłusek-Gawenda, R.McNulty, R.Schicker, A.Szczurek, 1904.01243 [hep-ph]
[6] Z.Citron et al., arXiv:1812.06772

Speaker: Antoni Szczurek (Institute of Nuclear Physics, Krakow and Rzeszow University, Rzeszow)

szczurek1.pdf

20 Particle production in $\gamma \gamma$ interactions at hadronic colliders: Recent results and prospects

In this talk we will present a brief review of the recent results for the particle production by $\gamma \gamma$ interactions at $pp/pA/AA$ collisions. In particular, the dilepton production will be discussed, as well the background associated to pomeron induced interactions. Finally, the probe of the X(4350) in $\gamma \gamma$ interactions at the LHC will be discussed.

Speaker: Victor Goncalves (Universidade Federal de Pelotas)

Talk_Dileptons_Photon19.pdf

10:55 Coffee Break

Gamma-Gamma Collisions

Convener: Lucian Harland-Lang (IPPP Durham)

21 Study of QED in strong field regime at LUXE experiment

The talk presents the LUXE experiment which plans on using the European XFEL electron beam at DESY with an energy of 17.5 GeV and a high intensity optical laser to study non-perturbative QED phenomena. The main focus of the experiment will be the measurement of the rate of laser assisted electron-positron pair production in collisions of high energy photons with an intensive laser beam and high intensity Compton scattering in electron-laser interaction. The design of the experimental setup, detector systems requirements and simulation results will be presented and discussed.

Speaker: Oleksandr Borysov (Deutsches Elektronen-Synchrotron DESY)

luxe_photon2019.pdf

22 Production of $W^+ W^-$ and $t \bar t$ pairs in photon-photon mechanism in proton-proton scattering

Photon-induced processes in proton-proton interactions have become recently very topical. The large energy at the LHC, when combined with relatively large luminosity at run II, allows to start the exploration of such processes.

We discuss production of $W^+ W^-$ pairs and $t \bar t$ quark-antiquark pairs in proton-proton collisions induced by two-photon fusion including, for a first time, transverse momenta of incoming photons. The unintegrated inelastic fluxes (related to proton dissociation) of photons are calculated based on modern parametrizations of deep inelastic structure functions in a broad range of $x$ and $Q^2$.

We focus on processes with single and double proton dissociation. Highly excited remnant systems hadronise producing particles that can be vetoed in the calorimeter. We calculate associated effective gap survival factors. The gap survival factors depend on the process, mass of the remnant system and collision energy. The rapidity gap survival factor due to remnant fragmentation for double
dissociative (DD) collisions is smaller than that for single dissociative (SD) process. We observe approximate factorisation: $S_{R,DD} \approx S_{R,SD}^2$ when imposing rapidity veto. For the $W^+W^-$ final state, the remnant fragmentation leads to a taming of the cross section when the rapidity gap requirement is imposed. Also for $t \bar t$ quark-antiquark pairs such a condition reverses the hierarchy observed for the case when such condition is taken into account.

Our results imply that for the production of such heavy objects as $t$ quark and $\bar t$ antiquark the virtuality of the photons attached to the dissociative system are very large ($Q^2 <$ 10$^{4}$ GeV$^2$). A similar effect was observed for the $W^+ W^-$ system.

1. M. Luszczak, L. Forthomme, W. Schafer, A. Szczurek,
   arXiv:1810.12432; JHEP (2019) in print.

2. L. Forthomme, M. Luszczak, W. Schafer, A. Szczurek,
   Phys.Lett. B789 (2019) 300-307.

3. M. Luszczak, W. Schafer, A. Szczurek,
   JHEP 1805 (2018) 064.

4. M. Luszczak, W. Schafer and A. Szczurek,
   Phys. Rev. D93 (2016) 7, 074018.

5. M. Luszczak, A. Szczurek, Ch. Royon,
   JHEP 1502 (2015) 098.

Speakers: Antoni Szczurek (Institute of Nuclear Physics, Krakow and Rzeszow University, Rzeszow), Dr Marta Łuszczak (Faculty of Mathematics and Natural Sciences, University of Rzeszow, Poland), Dr Forthomme Laurent (Helsinki Institute of Physics), Wolfgang Schaefer (Institute of Nuclear Physics PAN)

szczurek2.pdf

23 Searches for Dark Matter at the LHC in forward proton mode

We analyze in detail the LHC prospects for charged electroweakino searches, decaying to leptons, in compressed supersymmetry scenarios, via exclusive photon-initiated pair production. This provides a potentially increased sensitivity in comparison to inclusive channels, where the background is often overwhelming. We pay particular attention to the challenges that such searches would face in the hostile high pile-up environment of the LHC, giving close consideration to the backgrounds that will be present. The signal we focus on is the exclusive production of same-flavour muon and electron pairs, with missing energy in the final state, and with two outgoing intact protons registered by the dedicated forward proton detectors installed in association with ATLAS and CMS. We present results for slepton masses of 120--300 GeV and slepton-neutralino mass splitting of 10--20 GeV, and find that the relevant backgrounds can be controlled to the level of the expected signal yields. The most significant such backgrounds are due to semi-exclusive lepton pair production at lower masses, with a proton produced in the initial proton dissociation system registering in the forward detectors, and from the coincidence of forward protons produced in pile-up events with an inclusive central event that mimics the signal. We also outline a range of potential methods to further suppress these backgrounds as well as to enlarge the signal yields.

Speaker: Lucian Harland-Lang (University of Oxford)

lhlDM.pdf

24 Towards an analytical threshold function of the two lepton pair production in gamma-gamma collisions

The analytical asymptotic cross section for arbitrary masses was given a few years ago.
Obtaining an analytical approach of the onset of the asymptotic regime is an interesting challenge.
The current status will be reviewed.

Speaker: Dr Frédéric Kapusta (LPNHE Paris)

FK-2019.pdf

25 The ${\gamma^* \gamma^* \to \eta_c (1S,2S)}$ transition form factor

We discuss $\gamma^* \gamma^* \to \eta_c(1S)\, , \,\eta_c(2S)$ transition form factor for both virtual photons. The general formula is given. We use different models for the $c \bar c$ wave function (LFQM or the ones obtained from the solution of the Schr\"odinger equation for different $c \bar c$ potentials: harmonic oscillator, Cornell, logarithmic, power-law and Buchm\"uller-Tye).
We compare our results to the BaBar experimental data for $\eta_c(1S)$, for one real and one virtual photon. We discuss approaching of $Q_1^2 F(Q_1^2,0)$ or $Q_2^2 F(0,Q_2^2)$ to their asymptotic value $\frac{8}{3}f_{\eta_{c}}$
predicted by Brodsky and Lepage formalizm.We discuss applicability of the collinear and/or massless limit and delayed onset of asymptotic behaviour.
We present some examples of two-dimensional distributions for $F_{\gamma^* \gamma^* \to \eta_c}(Q_1^2,Q_2^2)$.
A factorization breaking measure is proposed and factorization breaking effects are quantified and shown to be almost model independent.

Speakers: Izabela Babiarz (Institute of Nuclear Physics, Polish Academy of Sciences), Prof. Victor P. Goncalves (Instituto de Fisica e Matematica Universidade Federal de Pelotas (UFPel)), Dr Roman Pasechnik (Department of Astronomy and Theoretical Physics, Lund University), Dr Wolgang Sch\"afer (nstitute of Nuclear Physics, Polish Academy of Sciences), Prof. Antoni Szczurek (Institute of Nuclear Physics, Krakow and Rzeszow University, Rzeszow)

Babiarz_photon2019.pdf

13:15 Lunch Break

Gamma-Hadron Collisions

Conveners: Aurore Courtoy (Instituto de Física, UNAM), Marco Battaglieri (GE)

26 Photoproduction of penta-quark states: a theoretical perspective

The 2015 LHCb discovery of an exotic structure (denoted by $P_c^+$) decaying in $J/\psi \,p$ and conjectured to be a penta-quark state has triggered a renewed interest in the possible existence of multiquark states not predicted by the naive quark model. In this talk we present some considerations on $P_c$ photo-production experiments, aimed at testing its multi-quark interpretation in the framework of a 40-years-old ''string-junction'' picture that allows a unified description of baryons, tetra-, and penta-quark states.

Speaker: Giancarlo Rossi (University of Roma Tor Vergata)

photon_LNF.pdf

27 Vector meson photoproduction in ultra-peripheral p-Pb and Pb-Pb collisions at the LHC with ALICE

Vector mesons are plenteously produced in ultra-peripheral collisions where the impact parameter is larger than the sum of the radii of the two projectiles, implying that electromagnetic induced processes become dominant.

Light vector meson photoproduction cross sections can be used to study Glauber-Gribov shadowing effects at the hadronic level while the photoproduction of heavy vector mesons is expected to be sensitive to the poorly known gluon structure function and gluon shadowing effects at low Bjorken x.

The ALICE Collaboration has published the first measurements of the ρ0, J/ψ and ψ(2S) photoproduction cross section in ultra-peripheral Pb-Pb collisions and that for exclusive J/ψ photoproduction off protons in ultra-peripheral proton-lead collisions at the LHC and has obtained a substantially larger data set in 2015-2018 from LHC Run 2, allowing much more detailed studies of the production mechanism to be performed. In particular, the increased energy and more detailed measurements in the forward region in Run 2 give access to lower values of Bjorken-x than in previous studies. In this talk, an overview of the past results from Run 1 and the latest available results from Run 2 will be given. The results are compared to theoretical models.

Speaker: Michal Broz (CTU Prague)

UPC.Photon2019.pdf

28 Central exclusive production at LHCb

The LHCb collaboration has measured central exclusive production of J/ψ, ψ(2S), and Υ mesons as well as J/ψJ/ψ and J/ψψ(2S) meson pairs in proton-proton collisions. The analyses of Υ and charmonium pairs are performed at the centre-of-mass energies of 7 TeV and 8 TeV, and those of J/ψ and ψ(2S) are done at 7 TeV and 13 TeV. The analysis at 13 TeV involves the usage of new shower counters. These allow to reduce background by vetoing events with activity in an extended region in rapidity. The measurements of central exclusive production at LHCb are sensitive to gluon distributions for x-Bjorken values down to 2 × 10^{−6} (at 13 TeV). An overview of the LHCb results is presented and compared to existing measurements of other experiments.

Speaker: Charlotte Van Hulse

photon_lhcb_charlotte.pdf

16:15 Coffee Break

Astrophysical Gamma

Convener: Luca Latronico (TO)

29 Evidence for a New Component of Solar Gamma-Ray Emission

The Sun is not expected to be a bright gamma-ray source above 1 GeV, due to the moderate strength of solar magnetic fields. However, the Sun may act as a passive gamma-ray source, through the hadronic interaction of galactic cosmic rays with the Solar atmosphere. The Fermi-LAT has detected a bright solar gamma-ray flux, which implies that solar magnetic fields efficiently redirect incoming cosmic rays and produce outgoing gamma-ray emission. Here, I will show new observations, including the first resolved imaging of this gamma-ray signal across the solar surface, that find three surprising results. First, the gamma-ray emission extends to energies exceeding 200 GeV, implying that Solar magnetic fields can redirect TeV protons. Second, the morphology and spectrum of gamma-ray emission varies significantly over the solar cycle. Third, a significant “spectral-dip” appears between energies of 30-50 GeV. These observations are in significant tension with all current models of solar gamma-ray production. I will conclude by focusing on possible theoretical interpretations of these results, and their implications for our understanding of our nearest stellar neighbor.

Speaker: Tim Linden (The Ohio State University)

photon2019.pdf

30 Indirect searches for dark matter from radio to gamma rays

The particle nature of dark matter remains one of the most mysterious and urgent research questions of modern particle physics and cosmology. Despite decades of research, the mass of possible dark matter particles is only constrained to within 80 orders of magnitude or so. Astronomical observations spanning the full electromagnetic spectrum allow to search for dark matter particles across the mass scales. I will briefly review the most popular models for dark matter, including axions, sterile neutrinos, WIMPs and primordial black holes, discuss the current status of astrophysical searches, and highlight opportunities for the upcoming years.

Speaker: Christoph Weniger (GRAPPA, University of Amsterdam)

ID_detection-Weniger.pdf

31 Axion-like particles and high energy astrophysics

Axion-like particles (ALPs) are light, neutral, (pseudo-)scalar bosons predicted by several extensions of the Standard Model of particle physics such as the String Theory and are supposed to interact primarily only with two photons. In the presence of an external magnetic field photon-ALP oscillations may occur and produce sizable astrophysical effects in the very-high energy (VHE) band. Photon-ALP oscillations increase the transparency of the Universe to VHE photons partially preventing the gamma-gamma absorption due to the Extragalactic Background Light (EBL). Furthermore, they have important implications for active galactic nuclei (AGNs) by modifying their observed spectra both for flat spectrum radio quasars (FSRQs) and BL Lacs. Many attempts have been made in order to constrain the ALP parameter space (two-photon coupling, ALP mass) by studying irregularities in spectra due to photon-ALP conversion in galaxy clusters, consequences of ALP emission by main sequence stars and by supernovae but the debate is still open. Future observational data in an extended energy band (like with the Cherenkov Telescope Array) might give an answer.

Speaker: Giorgio Galanti (INAF, Osservatorio Astronomico di Brera)

Galanti-PHOTON2019.pdf

Wednesday, 5 June

Astrophysical Gamma

Convener: Luca Latronico (TO)

32 Recent results from the Pierre Auger Observatory

In this talk some recent results from the Pierre Auger Collaboration
will be presented. These include the measurement of the energy
spectrum of cosmic rays over a wide range of energies, studies of the
cosmic-ray mass composition with the fluorescence and surface detector
of the Observatory, studies on the anisotropies in the arrival
direction of cosmic rays at different scales and the searches for
photons and neutrinos. The astrophysical implications of the spectrum
and composition results are also discussed. Finally the progress of
the upgrade of the Observatory, AugerPrime is presented.

Speaker: Sergio Petrera (INFN and Gran Sasso Science Institute )

Petrera-Photon2019.pdf

33 Unveiling the unresolved gamma-ray sky through its anisotropies

The gamma-ray sky has been revealed in the last decade by the Fermi Large Area Telescope (LAT), offering an outstanding picture of our Universe at the highest energies. The majority of this gamma-ray emission has been attributed to known processes involving cosmic-ray interactions with the interstellar medium within our Galaxy. Another important contribution is represented by the gamma-ray emission of known Galactic and extragalactic astrophysical sources. However, still an important fraction (~ 20%) of the total gamma-ray emission remains unresolved, and therefore we referred to it as the unresolved gamma-ray background (UGRB). Guaranteed contribution to this componend is the cumulative emission of gamma-ray sources that are too faint to be resolved separately and hence lie below the current instrumental sensitivity. On the other hand, even more exotic scenarios involving dark matter particles may contribute as well, making the exact composition of the UGRB one of the main unanswered questions in gamma-ray astrophysics. The unprecedented large sample of high quality gamma-ray photons provided by the Fermi-LAT opened a new window on this study: the measurement and characterization of UGRB spatial anisotropies. In this talk I will give an overview of all the different techniques employed in the effort to give a definitive answer to the question of the UGRB composition.

Speaker: Michela Negro (TO)

Negro_gammaaniso_PHOTON2019.pdf

34 Detection of a gamma-ray halo around Geminga with the Fermi-LAT and implications for the positron flux

An excess in the flux of cosmic positrons at Earth above 10 GeV has been measured by Pamela, Fermi-LAT and with unprecedented precision by AMS-02. The observed flux cannot be explained by the production of positrons in the spallation reaction of hadronic cosmic rays (CRs) with the interstellar medium. Various interpretations have been invoked to explain this excess, such as the production in Galactic supernova remnants and pulsar wind nebulae (PWNe) or, intriguingly, in the dark matter halo of the Milky Way. However, a dominant contribution from dark matter is ruled out by the complementary bounds found in other indirect searches. Models where supernova remnants produce secondary CRs struggle to explain the other species of CR fluxes observed by AMS-02. Recently, Milagro and HAWC experiments reported the detection of an extended gamma-ray emission from Geminga and Monogem PWNe at TeV energies. These nearby and powerful PWNe have been widely considered as the main candidates to contribute to the cosmic positrons at Earth. Severe constraints for a significant PWNe contribution to the positron excess can be derived from this gamma-ray emission, which has been interpreted as coming from the electrons and positrons accelerated in the PWNe and undergoing inverse Compton scattering in the interstellar medium.
In this contribution we will report the first detection of a significant extended emission from Geminga at GeV energies in Fermi-LAT data, derived by including the proper motion of its pulsar. We will present a detailed study of the gamma-ray halo around Geminga and Monogem, and show the constraints found for the contribution of these PWNe to the positron excess, combining Milagro and HAWC data with measurements from the Fermi-LAT for the first time. Then we will demonstrate that using gamma-ray data from the LAT is of central importance to provide a precise estimate for the PWN contribution to the cosmic positron flux.

Speaker: Silvia Manconi (Università degli Studi di Torino)

manconi_photon19.pdf

10:45 Coffee Break

Astrophysical Gamma

Convener: Luca Latronico (TO)

35 Multi-messenger astronomy of gravitational-wave transients in the "Automatic Public Alert" Era

The search for electromagnetic counterparts or neutrino emissions from gravitational-wave sources engages a wide scientific community. Here, we outline the pathway that led to the birth of multi-messenger astronomy with the first direct observations of the gravitational-wave signals measured to date, focusing on the new challenges of LIGO and Virgo Observing Run 3 (O3) and the beginning of the public gravitational-wave alert era.

Speaker: Giuseppe Greco (Urbino University/INFN-Firenze)

Greco_photon2019_v4.pdf

36 The multi-messenger approach for current and future transient searches at very high energies

The very high energy sky comprises many astrophysical sources originating from explosive or flaring events on different timescales, from fraction of seconds to years. These transient sources are largely observed and monitored in different bands of the electromagnetic spectrum, including very high energy (VHE, $E>100$ GeV) gamma rays. Furthermore, transient sources are associated with systems of compact objects like black holes and neutron stars. Other non-photonic messengers, like gravitational waves and neutrinos, are expected to be produced in these extreme environments. Therefore the detailed characterization of the sources and environments of transient events should benefit from a multi-messenger approach for such searches.
In this context, Cherenkov telescopes like MAGIC face many challenges in the observation of transient sources at VHE, stemming in particular from their low duty cycle and limited field of view. Nonetheless, the planning of targeted follow-up strategies proved to be successful in the observation of transients. In this contribution, a particular highlight will be given to the synergies between MAGIC and facilities like LIGO/Virgo and IceCube, providing alerts on GW and neutrino events respectively. Such synergies are the key to many outstanding results, as demonstrated by the detection of the flaring blazar TXS 0506+06 in coincidence with a high energy neutrino and the first time detection of a Gamma-Ray Burst at VHE by MAGIC, GRB 190114C.
Finally, the future CTA experiment will open a new window in transient searches, thanks to its improved sensitivity, especially for short timescales.

Speaker: Alessio Berti (TO)

berti_transients_photon2019_20190605_149.pdf

37 Gamma-ray and neutrino astrophysics connection

The recent discovery of a diffuse neutrino flux of astrophysical origin by IceCube started the search to identify the cosmic sources of this emission. Synergy with other experiments could be a useful mean of investigation and in particular, the combination of neutrino/gamma-ray information is motivated by the fact that both radiations may be produced in the same astrophysical particle-cascades scenario, arriving to us undeflected from the source.
With these assumptions, we can place limit on the known astrophysical source classes contribution to the diffuse neutrino flux.
Another ground of discovery in this field is the search for transient and variable neutrino/electromagnetic sources, in which case the atmospheric neutrino and muon backgrounds can be reduced by taking time- and space-coincidence. Recent results with Fermi will be presented.

Speaker: Dario Gasparrini (ROMA2)

Photon2019_gasparrini.pdf

38 Observation of high-energy cosmic photons with new-generation space telescopes

While the Fermi gamma-ray telescope lives its 11th year in orbit, new particle and gamma-ray space detectors are in operation as DAMPE (DArk Matter Particle Explorer), or are in the development stage as HERD (High Energy Cosmic Radiation Detector) and e-Astrogam. DAMPE was launched in 2015 by a collaboration of Chinese, Italian and Swiss scientific institutions and performs high-quality observations of cosmic electrons, protons, nuclei and also gamma rays up to 10 TeV with good angular and energy resolution. HERD will be installed on board the Chinese Space Station to be launched in 2022 and will perform accurate measurements of energy and direction of cosmic rays and photons. An overview on these and other future experiments and a summary of the main gamma-ray results and expectations will be presented.

Speaker: Piergiorgio Fusco (BA)

Photon_2019_Frascati_Fusco.pdf

13:15 Lunch Break

Future Perspectives

Convener: David d'Enterria (CERN)

39 Prospects for photon-photon measurements with tagged protons in ATLAS

In 2017, ATLAS has been equipped with a new, dedicated detector system
allowing measurements of forward protons scattered at small angles in
diffractive and electromagnetic processes. These ATLAS Forward Proton
detectors (AFP) can operate during standard high-luminosity LHC runs
and collect large amounts of integrated luminosity. This gives a
possibility to study rare interactions, in particular, the two-photon processes.
The physics programme includes measurements of photon-photon interactions
present in the Standard Model, as well as using searches for new physics.
During the talk, the AFP detectors and their performance during 2017
and 2018 operations will be presented. Physics goals and first results
will be discussed.

Speaker: Maciej Trzebinski (IFJ PAN)

ATL-COM-PHYS-2019-638.pdf

40 Prospects for photon-photon measurements with CMS/TOTEM

Prospects for photon-photon measurements with CMS and TOTEM will be reviewed.

Speaker: Justin Williams (CERN)

prospects_williams.pdf

41 Photon detection with the CMS ECAL in the present and at the HL-LHC and its impact on Higgs boson measurements

The CMS experiment at the LHC features a high-resolution homogeneous electromagnetic calorimeter (ECAL). Its excellent performance in the reconstruction of high-energy photons has played a key role in the discovery of the Higgs boson and the measurement of its properties. The High-Luminosity LHC (HL- LHC) is expected to deliver an integrated luminosity 20 times larger than the LHC, allowing to study rare processes such as Higgs boson pair production and self-coupling. During HL-LHC operations, up to 200 concurrent interactions per-bunch collision are expected. In order to maintain its current performance in the harsher environment of the HL-LHC, an upgrade of the ECAL is planned. This contribution describes the ECAL performance in photon reconstruction and its impact on the measurement of the Higgs boson properties during the LHC Run II. Prospects for Higgs boson measurements at the HL-LHC are presented as well.

Speaker: Marco Cipriani (ROMA1)

cipriani_photonCMS_andHiggs_v2.pdf

16:15 Coffee Break

Future Perspectives

Convener: David d'Enterria (CERN)

42 Higgs boson production in photon-photon interactions with proton, light-ion, and heavy-ion beams at current and future colliders

The production of the Higgs boson in photon-photon interactions with proton and nucleus beams at three colliders planned or proposed at CERN --- the high-luminosity Large Hadron Collider (HL-LHC), the high-energy LHC (HE-LHC), and the Future Circular Collider (FCC) --- is studied. The cross sections for the process A$\,\gamma\gamma\,$A$\rightarrow$(A)$\,$H$\,$(A), with the ions A surviving the interaction and the Higgs scalar exclusively produced, are computed with Madgraph 5 modified to include the corresponding elastic $\gamma$ fluxes, for Pb-Pb, Xe-Xe, Kr-Kr, Ar-Ar, O-O, p-Pb, and p-p over the nucleon-nucleon collision energy range $\sqrt{s_{_{\rm{NN}}}}\approx 3$--$100$ TeV. Simulations of the $\gamma \gamma \rightarrow \,$H$\,\rightarrow b\bar{b}$ decay mode --- including realistic (mis)tagging and reconstruction efficiencies for the final-state b-jets, as well as appropriate kinematical selection criteria to reduce the similarly computed $\gamma \gamma \rightarrow b\bar{b},c\bar{c},q\bar{q}$ continuum backgrounds --- have been carried out. Taking into account the expected luminosities for all systems, the yields and significances for observing the Higgs boson in ultraperipheral collisions (UPCs) are estimated. At HL-LHC and HE-LHC, the colliding systems with larger Higgs significance are Ar-Ar(6.3 TeV) and Kr-Kr(12.5 TeV) respectively, but $3\sigma$ evidence for two-photon Higgs production would require 200 and 30 times larger integrated luminosities than those planned today at both machines. Factors of ten can be gained by running for a year, rather than the typical 1-month heavy-ion operation at the LHC, but the process will likely remain unobserved until a higher energy hadron collider, such as the FCC, is built. In the latter machine, the $5\sigma$ observation of Higgs production in UPCs is feasible in just the first nominal run of Pb-Pb and p-Pb collisions at $\sqrt{s_{_{\rm{NN}}}} = 39$ and $63$ TeV respectively.

Speaker: David d'Enterria (CERN)

dde_UPC_Higgs_photon19_frascati.pdf

43 SuperKEKB and Belle II status, and prospects on two-photon physics

At present experiments with a new Belle II detector at SuperKEKB collider has started at KEK (Japan). These new experiments will continue and widen the studies began at the previous experiments with the Belle detector. The luminosity of the SuperKEKB collider will exceed the previous one by about 40 times, amounting to $8\times 10^{35}$cm$^{-2}$s$^{-1}$. The main features of the collider and detector as well as the current status of the SuperKEKB/Belle II project are reported in this talk. Main physics motivations, goals and perspectives of this experiment for two-photon physics are discussed as well.

Speaker: Boris Shwartz (Budker Institute of Nuclear Physics, Novosibirsk State University)

talk-belle5.pdf

44 "Coherent photoproduction of J/ψ in nucleus-nucleus collisions and future perspectives for electron-ion collider "

We investigate the exclusive photoproduction of J/ψ mesons in ultraperipheral heavy-ion collisions in the color dipole approach.
We use the color dipole formulation of Glauber-Gribov theory to calculate the diffractive amplitude on the
nuclear target. We compare our results to recent published data on exclusive J/ψ production in ultraperipheral
lead-lead collisions at √sNN=2.76 and √sNN=5.02TeV. We describe these data well, however at high-γA
energies there is room for additional shadowing corrections, corresponding to triple-Pomeron terms or shadowing from large mass diffraction.
It is very interesting to investigate this issue at future measurements at electron-ion collider (EIC) .
It will be crucial for a deeper understanding of the nuclear glue.

Based on Phys.Rev. C99 (2019) no.4, 04490

Speaker: Agnieszka Luszczak (Cracow University of Technology)

photon2019-A.L.pdf

45 Electroweak Precision Tests on the SM

A global survey of weak mixing angle measurements at low and high energies is presented first. Then I will discuss theoretical uncertainties in precision observables with special emphasis on their correlations. The important role of vacuum polarization in global fits will also be addressed before fit results are presented.

Speaker: Jens Erler (IF-UNAM)

Erler.PHOTON 2019.pdf

Thursday, 6 June

Gamma Final States

Convener: German Fabricio Roberto Sborlini (M)

46 Dark Photons

Dark photons

G.A. Kozlov
Bogolyubov Laboratory of Theoretical Physics Joint Institute for Nuclear Research, Joliot Curie st., 6, Dubna, Moscow region, 141980 Russia

Abstract
The couplings of the Standard Model sector to the scale invariant degrees of freedom can open the possibility to study dark photons (DP). The model for the DP particle solvable in 4-dimensional space-time is presented at the lowest order of perturbative theory using canonical quantization. The model is gauge and scale invariant and the associated symmetries are spontaneously broken with the following properties: dark photons are massive and can be clarified through their final states. The Dalitz-like decay of the (Higgs-like) scalar boson into a single photon and DP is studied. The interaction between DP and quarks is mediated by the derivative of the scalar field - the dilaton. The mass of the dilaton does not enter the final solutions. The limits are set on the DP mass, the mixing strength between the standard photon and DP. This study can be used to probe the DP sector since the emitted energy of the single photon is encoded with measuring of the missing of the recoil DP.

Speaker: Gennady Kozlov (JINR)

Kozlov_DP_2019_3.pdf

47 The PADME experiment at LNF

Among the theoretical models addressing the dark matter problem, the category based on a secluded sector is attracting increasing interest. The PADME experiment, at the Laboratori Nazionali di Frascati (LNF) of INFN, is designed to be sensitive to the production of a low mass gauge boson A’ of a new U(1) symmetry holding for dark particles. This 'dark photon’ is weakly coupled to the photon of the Standard Model, and it provides an experimental signature for one of the simplest implementations of the dark sector paradigm. The DAΦNE Beam-Test Facility of LNF provides a high intensity, mono-energetic positron beam impacting on a low Z target. The PADME detectors are designed to measure with high precision the momentum of a photon, produced along with A’ boson in e+e- annihilation in the target, thus allowing to measure the A’ mass as the missing mass in the final state. This technique, particularly useful in case of invisible decays of the A’ boson, is adopted for the first time in a fixed target experiment. Simulation studies predict a sensitivity on the interaction strength (ε^2 parameter) down to 10−6, in the mass region 1 MeV<M_A’<22.5 MeV, for one year of data taking with a 550 MeV beam. In Winter 2018-2019 the first run took place, providing useful data to study the detector performance, along with the beam and background conditions. Intense activity is taking place to deliver preliminary results on the PADME data quality. This talk will review the status of the experiment and the prospects.

Speaker: Clara Taruggi (LNF)

Taruggi_PHOTON2019.pdf

48 Search for an invisible vector boson from pi0 decays at NA62

The high-intensity setup, trigger system flexibility and detector performance make the NA62
experiment at CERN particularly suitable to perform direct searches for long-lived hidden-sector particles, such as dark photons, dark scalars, axion-like particles, and heavy neutral leptons, using kaon and pion decays as well as operating the experiment in dump mode.
Results from NA62 will be presented on a search for pi0 decays to one photon and an invisible massive dark photon. From about 400 million pi0 decays, no signal is observed beyond the expected fluctuation of the background and limits are set in the plane of the dark photon coupling to ordinary photon vs the dark photon mass. The analysis has been also interpreted in terms of the branching ratio BR for the electroweak decay pi0 to gamma nu nu-bar: the null result implies a limit on the BR at the level of 2 x 10^{-7}.

Speaker: Letizia Peruzzo (JGU Mainz)

49 Fully neutral final states at KLOE/KLOE-2

In March 2018, the KLOE-2 experiment completed its data-taking at the e+e- DAPHNE collider in Frascati, collecting more than 5 fb-1 at the phi peak, thus extending the KLOE physics program with an upgraded detector. The KLOE detector is well suited for the study of fully neutral final states due to its large radius and a hermetic electromagnetic calorimeter, providing excellent timing and position resolution (50 ps and O(cm), respectively, at 1 GeV). The calorimeter energy resolution (5%/sqrt(E)) is greatly improved when kinematic constraints are applied. The upgraded KLOE-2 detector extends its acceptance coverage thanks to the new small angle calorimeters placed near the interaction region.

The latest results on prompt neutral final states will be presented, with particular emphasis on five photon final state, which is used to study the eta -> pi0 gamma gamma decay. This process provides an important test of ChPT because of its sensitivity to the p^6 term on both the branching ratio and the M(gg) spectrum. A preliminary KLOE measurement, based on 450 pb-1, provided a much lower BR value than the most accurate determination from Crystal Ball. A new analysis with a larger data sample is in progress to confirm this result. The same five photon final state is also used to search for the B boson, a postulated leptophobic mediator of dark forces.

Speaker: Marcin Berlowski

10:35 Coffee Break

Gamma Final States

Convener: German Fabricio Roberto Sborlini (M)

50 A Light Dark Matter Portal: the axion-like particle

The nature of the dark matter is still an unsolved mystery and its identification represent a big challenge for model builders and experimentalists. For many years the WIMP miracle has been considered the most promising solution among the Dark Matter candidates. Recently lower energy scales have attracted increasing interest. I will present the axion-like particle (ALP) as a possible candidate for a Portal to a Light Dark Sector, with particular attention to the phenomenology at low energy
electron positron colliders.

Speaker: Federica Giacchino (LNF)

PHOTON 2019.pdf

51 Isolated Photon Production in pp and p–Pb Collisions at the LHC measured with the ALICE experiment

In high-energy hadron collisions, direct photons can be produced at different stages and are of particular interest to study the hot QCD medium since they escape it without being affected.

At high transverse momentum ($p_{\text{T}}$), their production is dominated by high-$p_{\text{T}}$ parton fragmentation and hard-scattering processes between partons. The latter can be accessed experimentally using an isolation procedure leading to reduce both the fragmentation contribution and the large decay photon background. Their measurement in proton-proton collisions allows to test pQCD calculations and put constraints on parton distribution functions (PDFs). In addition, in proton-ion collisions (e.g., proton-lead) cold nuclear matter effects can be studied and especially nuclear PDFs can be tested. Their knowledge is crucial to understand the global picture of direct photon production in the context of hot nuclear matter where other mechanisms can occur in addition.

In this talk, recent results from the ALICE experiment on the isolated photon production in proton-proton and proton-lead collisions at the LHC will be presented.

Speaker: Erwann Masson (Subatech, IN2P3-CNRS (FR))

2019_PHOTON_ErwannMasson.pdf

52 Light neutral meson production at the LHC measured by ALICE

We review production of light neutral mesons, neutral pions and eta mesons, measured in pp, pA and AA collisions at LHC energies. Neutral meson production provides exploration of various physics topics: In pp collisions one can test pQCD predictions, study structure function in proton and fragmentation functions, and build a reference for pA and AA collisions; In pA collisions, it enables to study cold nuclear matter effects; In AA collisions, high transverse momentum neutral mesons give insights of the parton energy loss in hot quark-gluon plasma. Furthermore, these two mesons are the dominant source of decay photons which need to be precisely dertemined in order to measure direct photons.
In ALICE, neutral mesons are reconstructed in the two-photon decay channel. Photons can be reconstructed via several methods, using electromagnetic calorimeters and utilizing dielectrons from photon conversion in a detector material. This allows to provide spectra in a very wide transverse momenta range and cross check of results among them. In this talk, experimental results on the light neutral meson production in pp, p--Pb and Pb--Pb collisions at LHC energies will be presented.

Speaker: Daiki Sekihata (Center for Nuclear Study, the University of Tokyo)

20190603_PHOTON2019_v6.pdf

53 Isolated photon and photon+jet production at NNLO QCD accuracy

Based on [1904.01044], I present recent results of a Next-to-Next-to-leading order (NNLO) calculation of inclusive isolated photon and photon-plus-jet production using the Monte-Carlo event generator NNLOJET. In order to mimic experimental photon isolation criteria we apply a staged isolation procedure. A Frixione-type isolation with small cone size is used to ensure numerical stability, followed by a hard-cone isolation with larger cone size, tailored to the actual experimental setup. We compare the results to recent $13\mathrm{TeV}$ data by ATLAS [1701.06882,1801.00112] and CMS [1807.00782]. We observe substantial corrections in certain kinematical regions, leading to a significant improvement of theory uncertainty and description of the data.

Speaker: Marius Höfer (Universität Zürich)

Talk_Photon_M_Hoefer.pdf

54 Very-forward photon production in p-p and p-Pb collisions measured by the LHCf experiment

The main purpose of the LHCf experiment is to test the hadronic interaction models used in ground based cosmic rays experiments to simulate air-showers induced by ultra-high-energy cosmic rays in the Earth atmosphere. Since most of the air-shower energy flow is contained in the very forward region (where soft-QCD processes dominate), Monte Carlo simulations must rely on phenomenological models. The data from accelerator experiments are therefore very important for the tuning of these hadronic interaction models.
The LHCf experiment, situated at the LHC accelerator, is composed of two independent detectors located at 140 metres from the ATLAS interaction point (IP1) on opposite sides along the beam axis: the particular position of the detectors allows LHCf to measure neutral particles up to zero-degree with respect to the beam, with a pseudorapidity coverage of η > 8.4. Each detector is composed by two sampling and position sensitive calorimeters.
In this contribution the latest photon production measurements from LHCf will be compared with the predictions of DPMJET, EPOS, PYTHIA, QGSJET and SIBYLL Monte Carlo event generators, commonly used in air-shower simulations. The photon production cross section in proton-proton collisions at $\sqrt{s}$ = 13 TeV and the preliminary results in proton-lead collisions at $\sqrt{s_{NN}}$ = 8.16 TeV will be shown. Furthermore, the LHCf-ATLAS combined results on photon production cross section in p-p collisions at $\sqrt{s}$ = 13 TeV will be presented: using ATLAS information on central particles production the type of the interaction (diffractive or non-diffractive) can be discriminated experimentally and it is possible to study in particular the low-mass diffractive interactions.
There is not any hadronic interaction model well reproducing all the experimental data measured by the LHCf experiment. However, these data in the very-forward region will be useful in the tuning of the models and consequently reducing the discrepancy between their predictions.

Speaker: Alessio Tiberio (Università degli Studi di Firenze & INFN)

PHOTON2019_tiberio_v2.pdf

55 Rare and radiative B decays at LHCb

Rare and radiative b-hadron decays are sensitive probes of New Physics through the study of branching fractions, angular observables, CP asymmetries and measurements of the polarisation of the photon emitted in the decay.
The LHCb experiment is ideally suited for the analysis of these decays due to its high trigger efficiency, as well as excellent tracking and particle identification performance.
Recent results from the LHCb experiment are presented and their interpretation is discussed.

Speaker: Miriam Calvo Gomez (La Salle. Universitat Ramon Llull)

Rare and radiative B decays at LHCb.pdf

13:15 Lunch Break

Workshop on Photon Physics and Simulation at Hadron Colliders

Conveners: Giancarlo Ferrera (MI), Leandro Javier Cieri (Istituto Nazionale di Fisica Nucleare - Sez. Milano Bicocca), Leonardo Carminati (MI)

Workshop timetable

16:20 Coffee Break

Workshop on Photon Physics and Simulation at Hadron Colliders

Conveners: Giancarlo Ferrera (MI), Leandro Javier Cieri (Istituto Nazionale di Fisica Nucleare - Sez. Milano Bicocca), Leonardo Carminati (MI)

Workshop timetable

20:00 Conference Dinner

Friday, 7 June

Future Perspectives

Convener: David d'Enterria (CERN)

56 The Muon g-2 Experiment at Fermilab

The muon anomalous magnetic moment, $a_\mu=\frac{g-2}{2}$, is a low energy observable that can be both measured and computed with high precision. Therefore it provides an important test of the Standard Model (SM) and it is a sensitive probe for new physics. In particular, any deviation from the Standard Model theoretical value can be due to Beyond Standard Model Physics contribution, such as SUSY, Dark Matter, or new unknown contributions.
The $a_\mu$ value has been measured to a precision of $0.54$ ppm by the E821 experiment at the Brookhaven National Laboratory (BNL). This result shows a ${\sim}3.6\, \sigma$ difference compared to the SM prediction. In an effort to clarify this discrepancy between experimental measurement and theoretical calculation, the Muon g-2 (E989) experiment at Fermilab aims to reduce the experimental error on $a_\mu$ by a factor of four.
E989 collected a dataset with the same statistical power of the BNL experiment during the Run 1 data taking (2018). The data are under analysis and the first result will most likely be published next summer. In this talk I will discuss the experimental setup and report on the status of the Run 1 analysis.

Speaker: Matteo Sorbara (Università degli Studi di Roma Tor Vergata & INFN Sezione Roma Tor Vergata)

MS_muon_g-2.pdf

57 Project of the Charm-Tau factory in Novosibirsk

The project of the Super C-Tau factory (SCTF) is under development now at BINP in Novosibirsk. This electron-positron collider is intended for experiments in the energy range from 2 to 6 GeV with a luminosity of $10^{35}$ cm$^{-2}$s$^{-1}$. The high luminosity will provide a wide physical program that includes many fundamental issues like a study of mixing in the D meson system, search for CP-violating effects in decays of charmed particles, and search for "new physics" in rare and Standard Model-forbidden decays of charmed particles and tau lepton. Other important fields including two photon physics is also presented in the researches plans.

Speaker: Boris Shwartz (Budker Institute of Nuclear Physics)

talk-photon19-4.pdf

58 Gamma-gamma collider based on European XFEL

Using Compton scattering of 0.5 \mum laser photons on existing 17.5 GeV (spent) electron beams from European XFEL one can obtain a gamma-gamma collider with W<12 GeV . This energy region is not covered by Super-B collider or LHC (the later due QCD backgrounds). Such a collider will be a nice place for application of modern technologies: powerful lasers, optical cavities, SC linacs and low-emittance electron sources. Physics program: spectroscopy of C+ resonances in various J^P states (b\bar{b}, four quark states, quark molecules and other exotics). Variable circular and linear photon polarization will help to determine quantum numbers. Using a large distance between the interaction and the conversion point, it is possible to obtain quasi-monochromatic collisions and thus to measure the total gamma-gamma section in the region below 12 GeV with a high accuracy. Variable photon polarization allows you to measure separately polarization components of the cross section (σ_perp,σ_paral, σ_0, σ_2).

Speaker: Valery Telnov (Budker INP)

telnov-PHOTON-2019.pdf

10:45 Coffee Break

General Talks

Convener: Paola Gianotti (LNF)

59 The EuPRAXIA@SPARC_LAB project

On the wake of the results obtained so far at the SPARC_LAB test-facility at LNF, we are currently investigating the possibility to design and build a new multi-disciplinary user-facility, equipped with a soft X-ray Free Electron Laser (FEL) driven by a ~1 GeV high brightness linac based on plasma accelerator modules. EuPRAXIA@SPARC_LAB is conceived as an innovative and evolutionary tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. It could be progressively extended to be a high brightness “particle beams factory” able to produce electrons, photons (from THz to γ-rays), neutrons, protons and positrons, that will be available for a wide national and international scientific community interested to take profit of advanced particle and radiation sources. This fundamental goals will be integrated in the LNF facility by using a high gradient X-band RF linac and the high power laser FLAME to drive Plasma Oscillations in the accelerator module. This activity is performed in synergy and in the framework of the H2020 Design Studies EuPRAXIA and CompactLight. In this talk we report about the recent progresses in the on going design study and about opportunities and perspectives for the high brightness beam physics scientific community.

Speaker: Massimo Ferrario (INFN-LNF)

Photon_019.pptx.pdf

60 Photon-induced processes at high energy hadron colliders

I discuss the possibilities for using the LHC as a photon colliding
machine. The photon parton
density is quite precisely known and I consider the
implications for the LHC phenomenology. In addition, the colour singlet
nature of the photon means that it can readily lead to exclusive or
semi-exclusive events, with limited or no extra particle production in
the final state. I will show how such exclusive processes, in particular
in combination with proton tagging measurements, provide a well
understood environment in which to test the Standard Model and search
for the BSM physics. I shall focus on a few topical examples.

Speaker: Valeri Khoze (IPPP, University of Durham)

khoze-Photon-19.pdf

khoze-Photon-19.ppt

61 The electron-ion collider – A collider to unravel the mysteries of hadron structure

Understanding the properties of nuclear matter and its emergence through the underlying partonic structure and dynamics of quarks and gluons requires a new experimental facility in hadronic physics known as the Electron-Ion Collider (EIC). The EIC will address some of the most profound questions concerning the emergence of nuclear properties by precisely imaging gluons and quarks inside protons and nuclei such as the distribution of gluons and quarks in space and momentum, their role in building the nucleon spin and the properties of gluons in nuclei at high energies. Two facility concepts have been presented to address these conditions, at Brookhaven National Laboratory and Jefferson Laboratory taking advantage of existing accelerator infrastructure and accelerator expertise. This presentation will highlight the capabilities of an EIC and discuss its status.

Speaker: Elke-Caroline Aschenauer (BNL)

EIC.US.eca.pptx

62 Perspectives of photon physics at future colliders

We discuss recent highlights in SM photon physics at the LHC, new opportunities at its forthcoming high-luminosity runs, and perspectives for its possible high-energy upgrade and a future electron-ion collider (EIC). Particular emphasis is put on the role of photoproduction processes in understanding the nuclear structure and interactions at high energies and on searches for photon-like particles in extensions of the SM motivated e.g. by dark matter.

Speaker: Michael Klasen

klasen.pdf

63 Final Remarks

Speaker: Pasquale Di Nezza (LNF)

Pas-FinalRemarks.pdf

13:20 Lunch Break

Workshop on Photon Physics and Simulation at Hadron Colliders

Conveners: Giancarlo Ferrera (MI), Leandro Javier Cieri (Istituto Nazionale di Fisica Nucleare - Sez. Milano Bicocca), Leonardo Carminati (MI)

Workshop timetable

17:15 Coffee Break