Spring Institute 2014: High-energy physics after LHC Run I

12 Mar 2014, 10:30 → 14 Mar 2014, 13:00 Europe/Rome

Aula Seminari (LNF, Alte Energie)

Gennaro Corcella (LNF)

The Spring Institute 2014-1 will focus on several hot topics of high-energy physics, with a special emphasis on LHC phenomenology. Beyond the discovery of the Higgs boson, certainly a breakthrough in particle physics, the LHC has carried out a number of outstanding Standard Model measurements, in both electroweak and strong sectors, and severely constrained a number of new physics models.The forthcoming run at 14 TeV will allow more refined precision studies, thus giving us the chance to make clear statements on many scenarios beyond the Standard Model. The Spring Institute will try to address some of such topics, by reviewing the state of the art of theoretical calculations and predictions, and presenting a few recent experimental measurements. The miniworkshop `Hunting for Supersymmetry at the LHC' will deal with the searches for supersymmetry after the 8 TeV LHC run, with a theory review, along with updated results on behalf of CMS and ATLAS experiments. Besides supersymmetry, we will also discuss the challenges for new physics searches in Higgs decays into a Z and a lepton pair, as well as the lesson which can be learned, in the flavour sector, from the latest LHCb measurements. Also, the implications of the found value for the Higgs mass on the vacuum metastability will be debated. From the Standard Model viewpoint, special care will be taken about the phenomenology of top quarks, such as the production of top pairs with a Higgs boson, yielding a direct access to the top Yukawa coupling, and higher-order calculations of the cross-section ratio ttbb/ttjj. Recent computations of diphoton production, the main background for Higgs searches, will also be investigated, paying special attention to the inclusion of NNLO corrections. Furthermore, the predictions of models for proton-proton scattering at the LHC will be presented, and compared with the total, elastic and inelastic cross sections measured at TOTEM, CMS, ATLAS and ALICE. Finally, the role of the running coupling constant at the intersection of perturbative and non-perturbative QCD regimes will be investigated in the context of the quark-hadron duality.

Wednesday, 12 March

1 ttH production at the LHC

The associated production of a Higgs boson with top quarks is going to give direct access to the top-Higgs Yukawa coupling and will play a crucial role in constraining new physics from a combined measurement of Higgs-boson couplings. In this talk we will review the theoretical work done to provide reliable tools for present and future experimental analyses.

Speaker: Laura Reina (Florida State University)

Slides frascati14.pdf

2 Improving the ttH signal at the LHC through spin-polarization effects

New strategies to improve the signal-to-background ratio for Higgs production in association with a top-quark pair at the LHC, based on top-quark spin properties, will be presented.

Speaker: Barbara Mele (INFN Roma)

Slides LNF_Mele.pdf

3 Diphoton production at LHC: the main background for Higgs boson searches

Diphoton production is the main background in searches and studies for a low mass Higgs boson, decaying in a pair of photons. Due to current searches and studies at the LHC, it is desirable to count with the best theoretical tool to describe this background. In this talk we will present the details behind the calculation, which is based on the transverse momentum subtraction formalism, and show different results obtained using a code that calculates diphoton production at NNLO in perturbative QCD. We will talk about the comparison with the LHC data and Tevatron data and discuss why the NNLO is necessary to understand the phenomenology of this process.

Speaker: Leandro Cieri (INFN Roma)

Slides Lean_Frascati_G.pdf

Thursday, 13 March

4 The Higgs->Zll spectrum at low Q2: SM vs. light new physics

We analyse the H->Zll spectrum at low values of the dilepton pair invariant mass. First we present precise predictions of the spectrum within the Standard Model, taking into account the effects due to QCD resonances. Then we illustrate the sensitivity of this spectrum to New Physics models with exotic light states and the natural connection with the (g - 2) anomaly.

Speaker: Martin Alonso-Gonzalez (INFN LNF)

Slides Gonzalez-Alonso.pdf

5 (Meta) stability of the electroweak vacuum

Since the discovery of the Higgs boson at LHC, experimentalists and theorists have studied its properties in the hope of finding some hints of new physics. Unfortunately the data appear to converge toward Standard Model predictions, therefore it could be reasonable to investigate the behavior of the SM beyond its natural range of energy. We find that the measured Higgs and top masses put the SM in a near-critical situation, where the minimum of the EW vacuum is at the border between the stable and the unstable phases. In order to distinguish between these two states, we made a NNLO calculation of the corrections to the Higgs quartic coupling. I will illustrate the results of our calculations.

Speaker: Pier Paolo Giardino (INFN Roma 3)

Slides MetaStability.pdf

6 Overview of the latest LHCb results

During the first LHC run in 2011 and 2012, the LHCb experiment has collected a total of 3/fb of proton-proton collision data at a centre-of-mass energy of 7 and 8 TeV. These data has allowed to perform a wide variety of analysis in B, D and Kaon decays as well as electroweak and QCD measurements in the unique rapidity region 2 < eta < 5 covered by the LHCb detector. An overview of the latest LHCb results will be given, covering rare meson decays, CP violation in B mesons, charm physics, spectroscopy, QCD and electroweak measurements

Speaker: Ricardo Vazquez-Gomez (INFN LNF)

Slides VazquezGomez.pdf

MINIWORKSHOP: HUNTING FOR SUSY AT THE LHC

7 Status of SUSY after the 8 TeV LHC run

I will review the implications of the direct SUSY and Higgs search results at the LHC and emphasize on the differences between constrained scenarios, such as mSUGRA, and more general MSSM scenarios. Complementary information can also be obtained using monojet searches at the LHC, as well as from Dark Matter experiments and flavour physics data, that will be described briefly. Finally, I will present projected results for the next LHC run.

Speaker: Nazila Mahmoudi (CERN &amp; LPC Clermont-Ferrand)

Slides Nazila_Frascati_March14.pdf

8 SUSY searches status with the CMS detector

The LHC first run came to an end in February 2013 after three years of extraordinary performance. Major advances in physics have been achieved, including the discovery of a new light Higgs particle. This discovery is in agreement with many predictions from simple SuperSymmetric (SUSY) theories, which also predict light super-partners particles. The mass of some of these particles is required to be within the LHC reach by naturalness, therefore an extensive program of searches for new physics phenomena beyond the Standard Model is pursued by the major experiments. In this talk, the most recent results on SUSY searches from the CMS collaboration are presented, covering a broad number of models and scenarios.

Speaker: Ferdinando Giordano (INFN Catania)

Slides FG_FrascatiSUSYWorkshop.pdf

9 Long Lived Particles Searches in SUSY and BSM in the ATLAS experiment

Many models of physics beyond the Standard Model predict new particles with long lifetimes. Examples include Supersymmetry with R-parity violation, suppressed decays of the next-to-lightest supersymmetric particle, or models with hidden sectors. The Large Hadron Collider has extended the reach of particle-physics experiments with a potential for discovery of new physics at the TeV scale and many searches have been carried out by both ATLAS and CMS. The methodology of the searches (reconstruction techniques, background suppression, etc.) and the sensitivity of these searches in the ATLAS experiment are reviewed.

Speaker: Monica Verducci (INFN Roma)

Friday, 14 March

10 Models for proton-proton scattering at LHC: asymptotic limits, black-disk limit and geometrical scaling

We discuss recent LHC measurements for the total, elastic and inelastic cross-sections, by TOTEM, CMS, ATLAS and ALICE collaborations in the light of present phenomenological predictions. We present result of various models, including an empirical model for elastic pp scattering at LHC, which indicates that the asymptotic black-disk limit R=(elastic cross section)/(total cross section) =1/2 is far from being reached, and discuss the implications on classical geometrical scaling behaviour. We propose a geometrical scaling law for the position of the dip in the differential elastic cross-section. The new scaling law allows to make predictions valid both for intermediate and asymptotic energies.

Speaker: Giulia Pancheri (INFN LNF)

Slides pancheri.pdf

11 NLO theoretical predictions for the cross-section ratio ttbb/ttjj at the LHC

Triggered by ongoing experimental searches at the LHC, we present updated NLO QCD predictions on the ratio of ttbb and ttjj production rates for present and future collider energies. We perform a detailed study of the kinematics and scale uncertainties of the two processes with the goal of assessing if and how much possible correlations help to reduce the theoretical uncertainty of the ratio, thus enhancing the predictive power of this observable.

Speaker: Giuseppe Bevilacqua (INFN LNF)

Slides bevilacqua_LNF2014.pdf

12 Quark-hadron duality and large-x PDFs

We present an analysis of the role of the running coupling constant at the intersection of perturbative and non-perturbative QCD. A unified description of the 2 regimes (pQCD and NP QCD) might derive through the definition of the effective coupling, as they both provide ways of analyzing its freezing in the IR region. We extract the effective coupling from all available experimental data on the unpolarized structure function of the proton at large values of Bjorken x, including the resonance region. We suggest that parton-hadron duality observed in this region can be explained if non-perturbative effects are included in the coupling constant. The outcome of our analysis is a smooth transition from perturbative to non-perturbative QCD physics, embodied in the running of the coupling constant at intermediate scales. While our approach is purely perturbative, we compare our result to various non-perturbative schemes.

Speaker: Aurore Courtoy (Université de Liège)

Slides si_courtoy.pdf