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This workshop is included in the activities of the working package WP25 (Light-and heavy-quark hadron spectroscopy) of the project STRONG-2020. It has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 824093.
The major topics of the workshop will cover:
1) Precision calculations in non-perturbative QCD: Effective Field Theories, analyticity, dispersion relations and Lattice QCD
2) Spectroscopy & Exotic states
3) Hadron Decays & Production
4) Form factors, LECs, fundamental parameters of QCD and light nuclei
spectroscopy
The meeting will be held online via Zoom; passcode 137632
The poster session will be organised via gather.town There are also several rooms at the gather.town allocated for small group discussions. [Poster session instructions].
I will discuss the possibilities to study exotic hadron spectroscopy at a Super-CEBAF facility with a beam of about 24 GeV
In order to understand the nature of the XYZ particles, theoretical predictions of the various XYZ decay modes are essential. In this work, we focus on the semi-inclusive decay of heavy quarkonium hybrids into traditional quarkonium in the Born Oppenheimer EFT (BOEFT) framework. We present results of the decay rates for several heavy quark hybrids. We also develop a systematic framework in which the theoretical uncertainty can be systematically improved.
We present the results of a coupled-channel analysis of the J/Ψp invariant mass distribution, in which the Pc states measured by the LHCb collaboration are treated as Σ(∗)cD¯(∗) molecules, for details see [Phys. Rev. Lett., 124, 072001 (2020)] and its recent update [arXiv:2102.07159 [hep-ph], accepted for publication in JHEP]. The approach incorporates the Σ(∗)cD¯(∗) elastic channels and all potentially important inelastic channels, i.e. J/Ψp, ΛcD¯(∗) and ηcp, with the interactions constrained by heavy quark spin symmetry (HQSS). The effects of three-body unitarity from the πΛD¯ intermediate state are also investigated. A special care is taken to constraints from renormalisation-group invariance in the presence of the one-pion exchange potential, which are shown to be extremely important for obtaining sensible results and even for distinguishing between the quantum numbers of the Pc states.
The proposed EFT approach yields a very good description of the data. Apart from the three established states, a new state, associated with the JP=3/2−Σ∗cD¯ molecule and predicted from HQSS, reveals itself already in the current data. The line shapes in the elastic and inelastic channels are predicted and should play the key role in revealing the decay properties of the Pc states and their quantum numbers, once new data become available.
The heavy quark diffusion coefficient is encoded in the spectral functions of the chromo-electric and the chromo-magnetic correlators that are calculable on the lattice. We study the chromo-electric and the chromo-magnetic correlator in the deconfined phase of SU(3) gauge theory at wide range of temperatures.
Several new findings in the four, five and six quark systems have catalysed new interest in the field of multiquark states. Very significant progress has recently been made in the 6q sector, on both the theoretical and experimental fronts. The first theoretical work on di-baryonic states can be dated back to Dyson and Xoung (1964) when they predicted an existence of six non-strange dibaryons based on SU(6) symmetry. Finally, we were able to identify the last members of this sextet experimentally, by detecting isotensor dibaryon.
Major progress has been made by extending di-baryonic studies from hadronic beams to electromagnetic probes. Latest results from ELPH and MAMI facilities confirm the feasibility of dibaryon production in photo-induced reactions. Clean and controlled environment of photon beams allows to pin down our knowledge about the size and internal structure of di-baryonic states.
A lot of progress has been made by heavy-ion experiments in extracting baryon-baryon interaction strength in the strange quark sector.
A progress in experimental part was complimented by the theoretical studies. Latest results in quark models and lattice QCD calculations demonstrated significant improvement in our understanding of di-baryonic physics.
The results on di-baryonic states also got a new pace in astrophysical direction, where the property of the lightest genuine hexaquark state was linked to a neutron star dynamics and the limits on heaviest possible neutron star mass.
In my talk I will review recent experimental results and outline future perspectives in di-baryonic sector.
We study the two step sequential one pion production mechanism, np(I=0)→π−pp, followed by the fusion reaction pp→π+d, in order to describe the np→π+π−d reaction with π+π− in I=0, where a narrow peak, so far identified with a "d(2380)" dibaryon, has been observed. We find that the second step pp→π+d is driven by a triangle singularity that determines the position of the peak of the reaction and the large strength of the cross section. The combined cross section of these two mechanisms produce a narrow peak with the position, width and strength compatible with the experimental observation within the approximations done. This novel interpretation of the peak without invoking a dibaryon explains why the peak is not observed in other reactions where it has been searched for.
Understanding the nucleon-nucleon and the hyperon-nucleon interaction is essential in obtaining a comprehensive picture of the strong interaction. The former has been extensively studied in the past decades, whereas details of the interaction involving strangeness degrees of freedom is very sparse. This is partly attributed to difficulties performing high-precision scattering experiments with hyperons, which decay quickly. Hyperons are expected to play a key role in the composition of Neutron stars, and obtaining constraints on the fundamental two (and three) body forces between hyperons and nucleons will allow us to better understand the key properties of neutron stars. Recent advancements in accelerator and detector technologies allow us to performed detailed studies of this interaction utilising final state interactions in exclusive hyperon photoproduction experiments. In this talk, I will provide an overview of the experimental programme carried out at Thomas Jefferson accelerator facility for studying the hyperon-nucleon interaction.
We determine the existence and much debated parameters of the f0(1300) light scalar resonance. We establish the existence of its associated pole in the complex plane, determining its parameters by means of analytic continuation method on a model-independent dispersively constrained analysis of ππ→ππ and ππ→K¯K data. We show how this pole appears consistently using Forward Dispersion Relations or Roy equations and different continuation methods. We also provide a simple parameterization of the ππ scattering data and their uncertainties up to ∼1.8 GeV, consistent with dispersion relations up to ∼1.4 GeV and with the poles of the f0(500), f0(980) and f0(1300) found in these dispersive studies.
The study of baryonic excited states provides fundamental information on the internal structure of the nucleon and on the degrees of freedom that are relevant for QCD at low energies. N are composite states and are sensitive to details of the how quarks are confined.
One of the still open problems in the description of the baryon spectrum by Quark Models or lattice QCD is the missing observation of a sizable number of nucleonic resonances.
Significant progress has been made in recent years and is evident in several new entries of N and ∆ states in the latest editions of the Review of Particle Properties (PDG), as well as the inclusion of the transition form factor measurement for several excited states.
Most of the newly discovered states have masses in the range 1.85 GeV to 2.1 GeV where precise photoproduction data were driving the new observations, however the mass region above 2.1 GeV has hardly been studied. This is the region where the gluonic excitations are expected to occur, representing the focus of the task in the search of exotic baryons.
The availability of polarized photon beams impinging on polarized targets provide access to single and double polarization observables of meson photo-production processes, which strongly constrain the reaction amplitudes and proved to be the new key information in the discovery of the new resonances.
Electro-production of the same mesons-baryon final states produced in photo-reactions allows for the extraction of the resonance electro-couplings and the study of their evolution as a function of the Q2 photon virtuality. This additional information allows to picture the evolution of the effective-degrees N freedom as a function of the distance scale and to assess the possible hybrid nature of new resonances.
Our understanding of the physics of baryonic systems containing strangeness is limited by the scarcity of experimental data. Aiming at alleviating this deficit is Lattice QCD (LQCD), a numerical approach to solve the complex dynamics of strongly interacting systems of hadrons and nuclei. I will present the results obtained by the NPLQCD collaboration for two octet-baryon systems, with strangeness ranging from 0 to -4, at two sets of quark masses that are heavier than those in nature. In particular, I will present their binding energies and scattering parameters, as well as the low-energy coefficients appearing in the effective field theory Lagrangian describing the interaction of two non-relativistic octet baryons. The findings point to interesting symmetries observed in hypernuclear forces as predicted in the limit of QCD with a large number of colors.
We study the two body decay of mesons using the covariant helicity formalism. We find that to explain the ratio of partial wave amplitudes of the decay processes, the Lagrangian must include operators with dimension>4. We estimate the coupling constants in the cases of 1++→1−−0−, 1+−→1−−0−, 2−+→2++0−, and 2−+→1−−0− decays by fitting the ratio of the derived partial wave amplitudes and the partial decay widths to the available data. We estimate the ratios of the partial waves for the like decays where data are not available.
The main goal for modern nuclear physics is to build a fundamental understanding of the nuclear structure and dynamics from fundamental principles of the strong nuclear force (QCD). A plethora of experimental data exist on light and heavier nuclei utilizing experiments at Thomas Jefferson laboratory (JLAB) and the CEBAF Large Acceptance Spectrometer that can be used to study nuclear reactions in great detail. In this poster we will present our work in which we utilize a real photon beam to studying many proton knock-out reactions. Our preliminary results are compared with predictions from theoretical models and specifically from Giessen Boltzmann-Uehling-Uhlenbeck project (GiBUU), to obtain a better understanding of the underlying dynamics in such many-body systems.
Jefferson Lab, Virginia, USA, is a world leading international facility in nuclear and particle physics. JLab houses a superconducting RF particle accelerator known as CEBAF (Continuous Electron Beam Accelerator Facility) and had an almost hermetic detector known as CLAS (CEBAF large acceptance spectrometer). CLAS was composed of many detection systems, including the start counter, which is a set of scintillators used to determine the time at when an event originated within the target in photo induced reactions. Presented in this poster are studies in which we investigate the utilization of the start counter as a neutron polarimeter. This study will pave the way for further analyses where polarization determinations can provide an insight to underlying physics, allowing us to shed light in hexaquark states.
For a general Hb→Hcτν− decay we analyze the role of the τ polarization vector in the context of LFU violation studies. We use a general phenomenological that includes several new physics terms. We show that both in the laboratory frame and in the center of mass, a P component is only possible for complex Wilson coefficients. We make specific evaluations of the polarization vector components for some decays, specially for Λb→Λc transitions.
Matter at high densities is still a relatively unsolved mystery and significant work is being conducted in an attempt to gain some knowledge about it and the role played by the nuclear forces and QCD. This research is employing the use of the A2@MAMI facility to investigate the 6 quark configuration, aka. dibaryons, in a state of high density within the nucleus of Ca-40 and Ca-48. The poster is presenting the experimental procedure employed in obtaining the data using A2’s Crystal Ball and TAPS setup, the current progress of the analysis, a brief background of the theory and link to Neutron Stars and the implications the results may have on current models of Neutron Stars.
CLAS12 has been performing experiments at Thomas Jefferson National Laboratory (JLab) in which electrons of energy up to 11 GeV is impinging on liquid hydrogen or deuterium targets. One of the important physics programs of these experiments is the search for exotic particles, like hybrids, tetraquarks, pentaquarks, and hexaquarks. CLAS12@JLab has a unique possibility to study hexaquarks, including the recently discovered d(2380).
Hexaquarks could have a great impact on our understanding of strong interactions, especially many-body effects within Quantum Chromo Dynamics (QCD), but also our models of neutron stars. This work is searching for a candidate for a very strange hexaquark (d_sss) (with the strangeness of -3), very negative (electric charge of -2) and with the highest possible spin, J=3. If found the d_sss hexaquark could potentially have implications on “strange stars”. The first steps of this analysis will be presented together with the studies of various conventional background channels, such as N resonances with larger decay branches to states with strangeness and evidence of excited Λ*s states.
The scalar glueball G is the lightest particle of the
Yang-Mills sector of QCD, with a lattice predicted mass of about
mG≃1.7 GeV. It is natural to investigate glueball-glueball
scattering and studying the possible emergence of a bound state,
that we call glueballonium. We perform this study in the context of a
widely used dilaton potential, that depends on a single parameter ΛG. We consider a unitarization prescription that allows us to predict the lowest partial waves in the elastic window. These quantities can be in principle calculated on the
lattice, thus offering possibility for testing the validity of the dilaton
potential and an independent determination of its parameter. Moreover, we
also show that a stable glueballonium exists if ΛG is small enough. In particular, for
ΛG compatible with the expectations from the gluon condensate, the glueballonium has a mass of about 3.4 GeV.
Quantum Chromo Dynamics (QCD) is our current best description of interactions between quarks and gluons and it not only predicts the existence of the well understood meson (two-quark) and baryon (three-quark) states it also predicts exotic Tetra-, Penta- and Hexaquarks.
Experiments taking place at Thomas Jefferson Lab in Virginia, USA using the upgraded CLAS12 detector system allows a detailed investigation of exotic hadron systems. In our experiment electrons accelerated to an energy of 10.6GeV, scatter off either a liquid hydrogen or deuterium target. Various interesting effects can be explored in these reactions, including production of exotic hadrons, such as hybrids, pentaquarks or hexaquarks the latter being the subject of my research.
In my poster I will present the analysis of data recently collected at CLAS12, which provides the first search for a ds hexaquark, a particle with quark content uuudds or uuddds and quantum numbers Jp=3+. Preliminary results on most promising decay channels, e.g. ed→e’K+ds→ e’K+Λn and ed→e’K+ds→ e’K+dK- will be shown. To enhance analysis sensitivity to these rare channels an improved PID (Particle Identification) method was developed. All experimental methods were verified utilizing more conventional reactions with similar final states, in particular ep→e’K+Λ, ep→e’ρ0p and ep→e’ωp. These reactions on proton target were used as benchmarks to tune analysis techniques applied for the experiment’s with deuterons. First results on ds searches will be confronted with analysis of empirical and simulated data of the most prominent background channels.
A profound theoretical study utilizing Monte Carlo calculations to simulate different decay branches acquiring the branching ratios and partial decay widths was also carried out to clarify the reaction dynamics for the ds hexaquark. The results of these calculations will be discussed as well.
Experimental data for pion photoproduction including
differential cross sections and various polarization observables
from four reaction channels, γp→π0p, γp→π+n, γn→π−p and γn→π0n from
threshold up to W=2.2~GeV have been used in order to perform a
single-energy partial wave analysis with minimal model dependence by
imposing constraints from unitarity and fixed-t analyticity in an
iterative procedure. Reaction models were only used as starting
point in the very first iteration. We demonstrate that with this
procedure partial wave amplitudes can be obtained which show only a
minimal dependence on the initial model assumptions.
We have performed a fixed-t single-energy partial wave analysis of pion
photoproduction in full isospin on the world collection of data. In
an iterative two-step process the single-energy multipoles are
constrained by fixed-t Pietarinen expansions fitted to
experimental data. This leads to a partial wave expansion that obeys
fixed-t analyticity with a least model dependence. In the energy
range of W=1.09−2.20~GeV we have obtained electric and magnetic
multipoles Eℓ±,Mℓ±, up to F waves.
We compared our four SE solutions in their predictions for unmeasured
polarization observables. At lower energies the spread of these
predictions is rather small, but it becomes larger at higher
energies, where it will help to propose new measurements in order to
get a unique PWA.
Strangeness production at intermediate energies in p+p collisions is of particular importance to the field of hadron physics, since investigating the creation mechanism of strange baryons near threshold deepens our understating of its internal structure. This study presents the exclusive reconstruction of the p+p→p+K++Σ0 at beam energy 3.5 GeV with the HADES detector setup. The daughter Lambda hyperon Σ0→Λγ (BR ≈ 100 \%) was reconstructed with the decay mode Λ→pπ− (BR ≈ 63.9 \%) partly within the main HADES acceptance and partly within the forward wall acceptance. A kinematic refit was applied by constraining the secondary proton and the pion to the nominal Λ mass and the overall missing mass to the photon mass. In total, 2613 events were reconstructed and used to investigate the dynamics of the reaction p+p→p+K++Σ0 by studying the angular distributions in the CMS, Gottfried-Jackson and helicity frames. The acceptance corrected CMS distributions of the Σ0 and the proton show anisotropies. This is more pronounced in the case of the proton, which is the expected behavior if pion exchange dominates the Σ0 production process. In addition, the helicity angular distributions are far different from isotropy, which is a clear indication that there is a resonant component of the Σ0 production. In order to provide a better description of the experimental distributions, a partial wave analysis using Bo-Ga PWA has been performed. The Bo-Ga PWA determines the contribution of different non-resonant and resonant partial waves to the pK+Σ0 production. However, due to the poor statistics, it was not possible to obtain an exact contributions of nucleon resonances. Nevertheless, resonances with mass around 1.710 GeV/c2 (N∗(1710)) and 1.900 GeV/c2 (N∗(1900) or Δ∗(1900)) are certainly required by the PWA fit. The total production cross section of the Σ0 hyperon was obtained by integrating the yield for the different angular distributions and found to be σ=18.50±2.32(stat)±1.70(syst) μb. In addition, the ratio R(pK+Λ/pK+Σ0) was found to be 1.91 ± 0.35 in agreement with the general trend towards the high energy limit of 2.2, which has been determined experimentally for ϵ> 700 MeV.
We study the strong and radiative decays of the antiquark-quark ground state nonet{ρ3(1690),K⋆3(1780),ϕ3(1850),ω3(1670)} in the framework of an effective quantum field theory approach, based on the SUV(3) flavor symmetry. The effective model is fitted
to experimental data listed by the Particle Data Group . We predict numerous experimentally
unknown decay widths and branching ratios. An overall agreement of theory (fit and predictions)
with experimental data confirms the qq¯¯ nature of the states and qualitatively validates the effective
approach.
MesonEx experiment at CLAS12 studies exotic mesons production. Investigating exclusive π0 production is crucial to understand the viability of the fundamental ηπ reaction. These studies aim to the beam asymmetry Σ calculation and the comparison of the latter with the same obtained by GlueX and SLAC experiments.(Phys. Rev.C, 95:042201, Apr 2017) As the outcomes of these experiments shows significant discrepancies, the results provided by CLAS12 can be critical in the exotic meson production studies.
Thanks to data analysis, it has been possible to clearly identify the reserched reaction, improving the Signal/Background ratio and selecting π0 exclusive reaction only.
The beam asymmetry calculation are ongoing, focusing on the different intervals selection.
Studies on the variation of the cross section with transferred p are also ongoing.
In recent years, hadron spectroscopy has led to the discovery of some exotic states found in the hidden-charm and hidden-bottom sectors, like the Zc(3900), Zc(4020), Zb(10610) and Zb(10650). These states do not fit the conventional constituent-quark models given that they are expected to contain hidden-charm or hidden-bottom components respectively, but they are also found to be charged. The most recently discovered one, reported by the BESIII collaboration at the end of last year, has even been found to contain a strange component. Although there exist several exotic structures which could describe these states, the molecular one is prominent due to the closeness of these states to the thresholds of some D(∗)D¯(∗) and B(∗)B¯(∗) channels. The molecular picture also permits an analytic treatment of these states via Heavy Quark Effective Field Theory (HQEFT). Within this framework and making use of SU(3) light flavor symmetry, we have been able to describe all the measured Zc and Zb states mentioned before, as well as predict the masses and widths of some of their yet-to-be-seen symmetric partners.
Recent observations in heavy-quark spectroscopy have provided numerous candidates for hadronic resonances which are exotic in nature. The Electron Ion Collider (EIC) has the potential to produce such resonances in photoproduction reactions, which would confirm the observations in previous experiments and provide complementary insight into their composition. This opportunity has inspired recent work on theoretical models for exclusive production of so-called XYZ states in electron-hadron collisions as well as detector simulations to meet the requirements of such a program at the EIC. The status of these studies and potential detector configurations will be presented.
The spectrum of mesons holds important information about the interaction of quarks and gluons. Of special interest are so called hybrid mesons which have gluonic degrees of freedom. Over the years various candidates have been identified but most evidence comes from pion beam experiments. To further the understanding of these states it would be beneficial to measure them in other production mechanisms. After upgrading the CEBAF accelerator to 12 GeV, Jefferson Lab is ideally placed to fill this gap.
This talk will present the ongoing efforts of the CLAS12 MesonEx program running in Hall B and GlueX experiment in Hall D. Both are dedicated to study the spectrum of exotic mesons in electro- and photoproduction, respectively.
An important tool to experimentally probe the nucleon excitation spectrum is the study
of meson photoproduction reactions. Partial wave analyses are used to extract the baryon resonances from the experimental data. For an unambiguous solution it is not enough to only measure the unpolarized cross section, but several single and carefully chosen double polarization observables are needed in addition.
Several experimental facilities have dedicated programs to measure these polarization observables in different photoproduction reactions using e.g. a polarized photon beam and a polarized target, like the Crystal Ball experiment located at the accelerator facility MAMI in Mainz.
This talk will present recent results concerning the polarization observables G and E in the γp→pπ0 and γp→nπ+ reactions.
One of the open challenges in subnuclear physics is to understand the
non-perturbative regime of Quantum Chromodynamics, including the world
of the nucleon and its excitations.
A necessary step towards this aim is a precise knowledge
of the experimental spectrum and the properties of baryon resonances.
Recently, large progress has been made based on photoproduction
experiments providing not only differential cross section
measurements but also high quality single and double polarization
observables.
Radiative transition of an excited baryon to a nucleon with emission of a virtual massive photon converting to dielectron pair (RNe+e- Dalitz decays) provides important information about baryon-photon coupling at low q2 =(me+e- )2 in time-like region. Enhancements in electromagnetic Transition Form-Factors (eTFF) at q2 close to vector mesons (/) poles have been predicted for N(1520/1535) and (1232) by various calculations reflecting important role of pion cloud (see for example [1]). The understanding of these couplings is also of primary importance for interpretation of the emissivity of QCD matter studied in heavy ion collisions via dilepton emission [2]. Indeed, low mass dilepton distributions measured in Heavy ion collisions indicate the dominant role played by rho meson with the spectral function strongly modified by interactions with baryons in fireball. Understanding of the role played by vector mesons in eTFF of baryons and in the emissivity of QCD matter plays prominent role in the physics programme of HADES experiment at GSI/FAIR.
The first measurements of the + pe+e- and Dalitz decays of higher mass resonances in p+p collisions have been already concluded [3, 4], confirming the important role played by meson in baryon transitions. Those measurements were followed by studies of pion- proton reactions using secondary pion beam available at GSI. Two pion and , for the first time, dielectron production in the second resonance region were studied . The two pion data have been analysed with Bonn-Gatchina PWA together with results of other experiments allowing for the separation of N(1520/1535) resonance contributions and their various decay channels . In particular off-shell meson contribution has been extracted providing important constraint for the interpretation of dielectron spectra measured in the same experiment. In the latter case electron angular distributions in the virtual photon rest frame have been analysed allowing for extraction of the hadronic spin density matrix elements as a function of virtual photon emission angle providing independent information about spin and parity of the involved resonances, as proposed in [6]. This presentation will summarize most important results obtained in proton and pion induced reactions . In the outlook HADES plans to extend studies of Baryon Dalitz decays to hyperons in p+p collisions will be presented, too [7].
[1] G. Ramalho and M. T. Pena Phys. Rev. D 85, 113014
[2] P. Salabura and J. Stroth Prog.Part.Nucl.Phys. 120 (2021)
[3] J. Adamczewski-Musch et al. [HADES Collaboration], Eur.Phys.J. A53 (2017) no.9, 188
[4] J. Adamczewski-Musch et al. [HADES Collaboration], Phys. Rev. C 95 (2017) no.6, 065205
[5] J. Adamczewski-Musch et al. [HADES Collaboration], Phys.Rev.C 102 (2020) 2, 024001
[6] E. Speranza, M. Zetenyi, B. Friman PLB764(2017) 282
[7] J. Adamczewski-Musch et al. [HADES Collaboration] Eur.Phys.J.A 57 (2021) 4, 138
We present a data-driven analysis of the resonant S-wave ππ→ππ and πK→πK reactions using the partial-wave dispersion relation. The contributions from the left-hand cuts are accounted for using the Taylor expansion in a suitably constructed conformal variable. The fits are performed to experimental and lattice data as well as Roy analyses. For the ππ scattering we present both a single- and coupled-channel analysis by including additionally the KK¯ channel. For the latter the central result is the Omn`es matrix, which is consistent with the most recent Roy and Roy-Steiner results on ππ→ππ and ππ→KK¯, respectively. By the analytic continuation to the complex plane, we found poles associated with the lightest scalar resonances σ/f0(500), f0(980), and κ/K∗0(700) for the physical pion mass value and in the case of σ/f0(500), κ/K∗0(700) also for unphysical pion mass values.
Nowadays, we are experimentally and theoretically pushing the boundaries of our understanding of particle physics to progressively higher energies and precisions. When searching for physics beyond the Standard model, including in CP violating observables, one often encounters observables involving multi-hadron final states, e.g., in semi-leptonic, D- and B-meson decays. In addition, the identification of exotic resonances in such final states requires control over rescattering effects. Especially for heavy particles decaying with net strangeness, it thus becomes increasingly important to also describe the abundantly appearing final state interactions of kaons and pions up to high energies. In particular a consistent description of πK scattering and production can serve as a test of Standard Model physics, can be used to search for exotic hadronic states in crossed channels and can improve the spectroscopy of exited kaon resonances.
In this talk I want to present the results of Ref. [1]. In this paper, we constructed a representation of the πK S-wave form factor using the elastic πK scattering phase shifts via dispersion relations in the elastic region, as demanded by Watson's theorem, and extended this model into the inelastic region using resonance exchange, while maintaining unitarity and the correct analytic structure.
As a first application, we successfully described the τ→KSπντ spectrum, including the highly overlapping S-wave resonance K∗0(1430) and P-wave resonance K∗(1410). In contrast to common Breit-Wigner parametrisations, which violate unitarity, our parametrisation has the correct phase behaviour build-in and fulfils unitarity by construction. For an improved separation of these resonances using future measurements, which could potentially be measured at Belle II, we further calculated forward-backward asymmetries for the different fit scenarios. In addition, we could use our results to refine the estimate of the CP asymmetry generated by tensor operators. Finally, we were able to extract the resonance properties of the K∗0(1430) and K∗0(1950) via Padé approximants.
[1] Von Detten, L. and Noël, F. and Hanhart, C. and Hoferichter, M. and Kubis, B.
"On the scalar πK form factor beyond the elastic region"
Eur. Phys. J. C 81, 420 (2021); DOI: 10.1140/epjc/s10052-021-09169-7
The excitation spectrum of light mesons, which are composed of up, down, and strange quarks, is studied since decades. However, it still holds a number of puzzles and surprises that provide new insights into the nature of the strong interaction.
Recent high-quality data samples from the COMPASS experiment at CERN allow us to not only study the properties of established mesons with unprecedented precision but to also search for new states. These searches aim in particular to resolve the question of the existence of so-called exotic states, such as four-quark states or states with excited gluon fields. Since light mesons have often large widths and are overlapping, the mapping of their spectrum is challenging and requires large quantities of data. The data are analyzed using partial-wave analysis (PWA) techniques. Most excited meson states decay preferentially into multi-particle final states, for which the PWA requires extensive modeling of the dynamics of the final-state hadrons.
In this talk, I will give an overview of the ongoing experimental studies of light mesons at COMPASS. I will also touch on novel analysis techniques and the prospects for future progress.
We have investigated the thermal effects on the properties of open heavy-flavor mesons using a unitarized effective hadronic theory in coupled channels based on chiral and heavy-quark symmetries at finite temperature below Tc within the imaginary-time formalism. The in-medium amplitudes of the scattering of the heavy mesons with the light mesons and the ground-state self-energies and spectral functions are calculated in a self-consistent manner. I will present our findings for the thermal masses and widths of the open heavy-flavor ground states, as well as for the dynamically generated states [1]. I will also show our results for the meson Euclidean correlators obtained from the thermal spectral functions and their comparison with lattice QCD simulations [2]. In addition I will show our recent calculations of transport coefficients below Tc [3].
Short-lived hadronic resonances are good probes to investigate the late-stage evolution of ultra-relativistic heavy ion collisions. Since they have lifetimes comparable to that of the fireball, the measured yields may be affected by rescattering and regeneration processes in the hadronic phase, which modifies the particle's momentum distributions after hadronization. Measurements of the production of resonances characterized by different lifetimes, masses, quark content, and quantum numbers can be used to explore the different mechanisms that influence the shape of particle momentum spectra, the dynamical evolution and lifetime of the hadronic phase, strangeness production, and collective effects. Furthermore, a multiplicity dependent analysis on resonance production in pp and p--Pb collisions could highlight the possible onset of collective-like phenomena even in small systems. The ALICE experiment has collected data from several collision systems at LHC energies and the latest results on hadronic resonance production will be presented.
We present a unified QCD-based description of elastic and transition form factors involving the nucleon and its resonances. We compare predictions made using a framework built upon a Faddeev equation kernel and interaction vertices that possess QCD-like momentum dependence with results obtained using a confining, symmetry-preserving treatment of a vector ⊗ vector contact-interaction in a widely-used leading-order (rainbow-ladder) truncation of QCD’s Dyson-Schwinger equations. This comparison explains that the contact-interaction framework produces hard form factors, curtails some quark orbital angular momentum correlations within a baryon, and suppresses two-loop diagrams in the elastic and transition electromagnetic currents. Such defects are rectified in our QCD-based approach and, by contrasting the results obtained for the same observables in both theoretical schemes, shows those objects which are most sensitive to the momentum dependence of elementary quantities in QCD.
Measurements of the total cross section for the production of vector mesons off the proton allow the determination, using a Vector-Meson Dominance model, of absolute values of the vector meson - proton scattering lengths. A comparative analysis of the recently determined scattering lengths for omega-p, phi-p, and J/psi-p using the A2, CLAS, and GlueX experimental data respectively are reported. Following these results and by using quasi-data from a theoretical approach, we predicted Upsilon-p scattering length. The role of the "young" vector-meson effect is evaluated. We propose to measure the total cross section for Upsilon production off the proton at the threshold with EIC and/or EicC.
Recently a method of measuring static force from the lattice using an insertion of chromoelectric field to an Wilson loop has been proposed to tackle the ambiguities of taking derivative of the static potential. We present the current status of testing the viability of this approach and also expand the calculation for the first time to use gradient flow, which solves the problems with the renormalization of chromoelectric field on the lattice.