International Workshop on Hadron Structure and Spectroscopy - 2022

29 Aug 2022, 08:00 → 31 Aug 2022, 23:00 Europe/Zurich

40/S2-A01 - Salle Anderson (CERN)

Bakur Parsamyan (CERN, JINR and Turin section of INFN), Fulvio Tessarotto (Universita e INFN Trieste (IT))

The three day long "International Workshop on Hadron Structure and Spectroscopy - 2022" (IWHSS-2022) will take place at CERN in Geneva, Switzerland, from August 29th to 31st, 2022.

IWHSS-2022 is the 18th workshop in the series of annual workshops on Hadron Structure and Spectroscopy, with most recent editions being the IWHSS-2020 (remote due to COVID-19),
IWHSS-2019 (Aveiro, Portugal) and IWHSS-2018 (Bonn, Germany).
This year the workshop is planned to be organized in fully in-person mode.

The scientific programme of the workshop will be traditionally focused on the following topics:

• Spin and 3D Structure Structure of the Nucleon
• TMDs, GPDs and GTMDs
• Fragmentation Functions
• Fixed Target and Collider Experiments
• Meson Structure and Spectroscopy
• Search for Exotics
• Future Measurements and Experimental proposals

The opening session of the workshop will be dedicated to double-anniversary of COMPASS experiment:
25 years since approval and 20 years since first data-taking.

 

              

Monday, 29 August

08:30 Registration

COMPASS Legacy: Morning Session 1

Convener: Dr Bakur Parsamyan (CERN, JINR and Turin section of INFN)

1 Welcome

Speakers: Dr Bakur Parsamyan (CERN, JINR and Turin section of INFN), Fulvio Tessarotto (Universita e INFN Trieste (IT))

2 Welcome address from CERN

Speaker: Pippa Wells (CERN)

IWHSS2022_Wecome_CERN.pdf

IWHSS2022_Wecome_CERN.pptx

3 COMPASS Legacy: Nucleon spin structure and gluon polarization

The spin puzzle started with the discovery in 1987 by the European Muon Collaboration at CERN that quark spins contribute little to the proton spin. Subsequently the result was confirmed by the Spin Muon Collaboration and extended to the deuteron. At that time it was widely assumed that a large gluon polarisation would mask the quark spin contribution to the nucleon via the axial anomaly. Thus an experimental determination of the gluon polarisation became essential to understand the nucleon spin. This was one of the key objectives when proposing the COMPASS experiment. The talk will give a short history of the beginnings of COMPASS and summarise its contributions to the longitudinal spin structure of the nucleon.

Speaker: Gerhard Mallot (Albert Ludwigs Universitaet Freiburg (DE))

2022_iwhss_mallot.pdf

4 COMPASS Legacy: transverse spin phenomena

COMPASS has been one of the first experiments to look for experimental verification of the new ideas coming from the USA in the '90s on the possible correlations between the transverse spin of the quarks and the transverse spin of the parent nucleon, or between the intrinsic quark transverse momentum and the nucleon spin. These conjectures turned out to be right, and a new chapter of hadron physics opened up. This talk will review the COMPASS contribution to this new field.

Speaker: Franco Bradamante (Universita e INFN Trieste (IT))

Bradamante_IWHSS2022.pdf

Bradamante_IWHSS2022.pdf

Bradamante_IWHSS2022.pptx

5 Hadron spectroscopy - The COMPASS Legacy as seen in 2022

The spectroscopy of light hadrons has been one of the scientific pillars of the COMPASS experiment. Based on several data taking periods, the COMPASS experiment
has accumulated the worlds largest data sets for numerous studies for hadrons with light and strange quarks. The wealth of data stimulated the development of new analysis technologies, which have revealed unknown issues from previous experiments. The analyses have allowed to precisely determine mass and with of established resonances but in particular showed the existence of new and partly exotic mesons. These observations have also led to new interpretations for resonance structures. This presentation will sketch the progress made in hadron spectroscopy in the last 20 years, presents numerous scientific results and exemplarily point to some analysis techniques, which have and will impact also other spectroscopy experiments.

Speaker: Prof. Stephan Paul (Technische Universitat Munchen (DE))

IWHSS 2022 - Spectroscopy.pdf

11:00 Coffee break

Theory overview: Morning Session 2

Convener: Fulvio Tessarotto (Universita e INFN Trieste (IT))

6 A 3D overview of the last 20 years

COMPASS has been one of the pioneering experiments in the study of the 3D structure of the proton in momentum space, encoded in Transverse Momentum Distributions (TMDs). This talk will offer a brief overview of the main theory and phenomenological advances that took place in the last 20 years in this field of research, with emphasis on the topics where COMPASS has given (and will continue giving) invaluable contributions.

Speaker: Prof. Alessandro Bacchetta

COMPASS2022_Bacchetta.pdf

7 Theory and phenomenology of Generalized Parton Distributions

An overview of the theoretical and phenomenological aspects of generalized
parton distributions will be given, including recent results, extractions
from available experimental data and prospects for the future.

Speaker: Kresimir Kumericki

kumericki-cern22.pdf

8 Developments in understanding of hadron spectrum

Research in particle physics of the last two decades dramatically changed the landscape of the field of hadron spectroscopy. Large data sets and advanced analysis techniques in the light-meson sector lead to establishment of the lightest hybrid meson, where gluons play the principal role. Long-anticipated scalar glueball have been traced in the radiative decays of $J/\psi$. We have witnessed groundbreaking discoveries of unexpected states in the heavy-flavour sector: the pentaquarks showing up as heavy-flavour atoms, and a variety of tetraquarks spanning the new classes of hadrons. The traditional spectral analysis is complemented nowadays by lattice computations that experienced tremendous development over the last years. New calculations give access not only to the stable hadrons in a clean isolated setup, but also to hadronic resonances via scattering amplitudes. The spectroscopy field is tightly connected to different branches of particles physics including the studies of CP violation, studies of flavour anomalies, and correlation analysis in the heavy-ion collisions. Tight cooperation between theory and experiment has become a common practice to reassure coherent progress to deep understanding of the inner working of QCD at low energy.

Speaker: Mikhail Mikhasenko (Excellence Cluster ORIGINS)

development_mikhasenko_v0.pdf

13:05 Lunch break

Experimental results: Afternoon Session 1

Convener: Barbara Badelek (University of Warsaw (PL))

9 The HERMES experiment and its view on the nucleon's spin and 3D structure

In this talk, the HERMES experiment, which took data from 1995 until 2007 at HERA, and its contribution to unravelling the spin and momentum structure of the nucleon will be reviewed. The focus will be on transverse momentum distributions, especially from its data-taking campaign with transversely polarized protons as target, shedding light on such novel effects as the Sivers and Collins asymmetries but also providing evidence for sizeable quark-gluon correlations via twist-3 observables.

Speaker: Gunar Schnell

IWHSS2022_gunar.schnell.pdf

10 JLab physics programme: overview

In this talk, we summarize the ongoing scientific program of the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and give an outlook into future opportunities. The program addresses important topics in nuclear, hadronic, and electroweak physics, including nuclear femtography, meson and baryon spectroscopy, quarks and gluons in nuclei, precision tests of the standard model, and dark sector searches.

Speaker: Stepan Stepanyan

Stepanyan_JLAB_IWHSS22.pdf

Stepanyan_JLAB_IWHSS22.pdf

Stepanyan_JLAB_IWHSS22.pptx

11 Highlights from RHIC: Cold QCD & Spin

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is the world's only polarized proton collider with center-of-mass energies up to 500 GeV. It provides unique opportunities to study the spin structure in hadronic systems and opens new kinematic regions compared to deep inelastic scattering. The three pillars of the RHIC spin program cover the gluon polarization, sea quark helicity distributions, and transverse spin effects in hadronic systems. We will summarize recent results and discuss near term plans and their implications on parton distribution functions in the collinear and transverse momentum dependent frameworks.

Speaker: Oleg Eyser (Brookhaven National Laboratory)

2022-08-29_IWHSS2022_ColdQCDatRHIC.pdf

16:15 Coffee break

Future experiments: Afternoon Session 2

Convener: Prof. Andrea Bressan (Universita e INFN Trieste (IT))

12 Science and Status of the US Electron Ion Collider

The US department of Energy announced in 2020 that a high-luminosity, high-energy electron-ion collider (EIC) with polarized beams would be built at Brookhaven National Laboratory (BNL), jointly by BNL and Jefferson Laboratory (JLab). Since then an EIC project has been setup and it is marching towards the realization of collisions in the early 2030's with significant international involvement. In the meanwhile, an enthusiastic world-wide EIC Users Group is gearing up to design and construct the first EIC detector and started planning for a second one. In this talk, I will present the original core science motivation for the EIC and some new avenues that have developed since its approval. I will also present the current status of the detector organization, planning and design.

Speaker: Prof. Abhay Deshpande (Stony Brook and BNL)

EIC-Overview-IHWSS22-present.pdf

EIC-Overview-IHWSS22-present.pdf

EIC-Overview-IHWSS22-present.pptx

13 3D Structure of the Nucleon: from JLab12 to JLab24

The quark-gluon dynamics manifests itself in a set of non-perturbative functions describing all possible spin-spin and spin-orbit correlations. Single and di-hadron semi-inclusive and hard exclusive production, both in current and target fragmentation regions, provide a variety of spin and azimuthal angle dependent observables, sensitive to the dynamics of quark-gluon interactions. Studies of evolution properties of observables in SIDIS, and validation of the existing theory, is a challenging task, which will require high precision measurements in multidimensional bins.
In this talk, we present an overview of the current status and some planned measurements of the orbital structure of nucleons at JLab, and possible extensions to future physics program of upgraded to 20-24 GeV JLab .

Speaker: harut avakian

avakian-2022-IWHSS.pdf

14 AMBER PRM measurements programme: status and perspectives

The proton radius can be determined by measuring the slope of the electric form factor $G_\text{E}$ at small squared four-momentum transfer $Q^2$. Numerous elastic scattering and laser spectroscopy measurements of the proton radius have been performed with contradicting results ---the so-called proton radius puzzle. We propose to measure the proton radius in high-energy elastic muon-proton scattering at the M2 beam line of CERN's Super Proton Synchrotron in the year 2023. A high-precision measurement at low $Q^2$ realized with a high-pressure hydrogen TPC can contribute to a solution of the puzzle, especially in view of the systematics of this approach compared to electron scattering.

Speaker: Christian Dreisbach (Technische Universitaet Muenchen (DE))

2022.08.29. - IWHSS2022 AMBER PRM Dreisbach.pdf

15 LHC fixed-target experiments

New physics frontiers can be opened by using internal gas targets at the LHC. The various collision systems like pp, pA, and PbA at energies varying from √s_NN=72 GeV to √s=115 GeV, and the implicit forward kinematic of the collisions, make accessible a broad program of measurements, from the large-x frontier for particle and astroparticle physics to spin and heavy-ion physics. A first step into this new technology has been tested successfully at LHCb, specifically designed for Drell-Yan, quarkonia, and heavy-flavour studies, with the SMOG system. Based on a storage cell (SMOG2), an improved gas target has been installed in the LHC Long Shutdown 2. This will pave the way for quantitative searches in QCD through the study of the nucleon’s internal dynamics in terms of both quarks and gluons' degrees of freedom. Furthermore, in LHCb, final states with c- or b-quarks (e.g. inclusive quarkonia production) will be efficiently reconstructed, thus providing precious information on the so-far unknown gluon TMDs. In addition, SMOG2 will also act as R&D for the already proposed Polarised Gas Target (LHCspin). Here, with the use of the transversely polarized H and D targets, among several measurements, the quark TMDs in pp collisions, at unique kinematic conditions, can be determined. The status of the LHCb project and proposals related to the ALICE experiment will be presented.

Speaker: Pasquale Di Nezza (INFN e Laboratori Nazionali di Frascati (IT))

IWHSS-2022 P.DiNezza.pdf

19:30 Welcome Cocktail

Tuesday, 30 August

QCD, GTMDs and TMDs: Morning Session 1

Convener: Marco Radici

16 Chiral Entanglement and Emergence of Hadron Structure

The standard model (SM) of particle physics is around for about 50 years and is highly successful with families of leptons and quark coming in multiplets of at first sight ad-hoc electroweak and strong symmetry groups with an intriguing discrete chirality and triality structure. These play a role both for space-time symmetries and internal symmetries with chirality maximally broken in the electroweak sector and chiral symmetry restoration in the strong sector linked to the confining triality structure.
The chiral structure in a context of a tripartite qubit Hilbert space as basis for SM allows for different classes of maximally entangled quantum states identified as leptons and quarks as basis for electroweak and strong sectors, emerging with a different symmetry structure. Chiral entanglement could be an emerging principle in the SM that can provide guidance for its extension but that also can help in understanding features within the standard model such as mass patterns, universality breaking, partonic structure with distribution and fragmentation phenomena for confined systems or the role of gluonic Wilson lines for non-collinearity.

Speaker: Piet Mulders (Nikhef/VU)

2022-IWHSS-Mulders.pdf

17 GTMDs and Wigner functions

Generalized TMDs (GTMDs) of hadrons are the most general two-parton correlation functions. The Fourier transforms of GTMDs are partonic Wigner functions. In this talk, we give a brief overview of these objects and the various developments that has taken place over the last few years, including, in particular, the state-of-the-art of observables for these quantities.

Speaker: Shohini Bhattacharya

IWHSS2022_Shohini.pdf

18 PDF bias and flavor dependence in TMD distributions

We study the influence of collinear parton distribution functions (PDFs) and
their uncertainties on the determination of unpolarized transverse momentum
dependent (TMD) distributions. We take into account, for the first time,
flavor-dependent non-perturbative TMD profiles. We carry out a Bayesian analysis
to incorporate the propagation of PDF uncertainties into TMD extractions. We find
that collinear PDF uncertainties and non-perturbative TMD flavor dependence are
both essential to obtain reliable TMD determinations, and should be included in
future global analyses.

Speaker: Francesco Hautmann (Institute of Theoretical Physics)

tk_iwhss22_aug30.pdf

19 Gluon TMDs and J/ψ polarization in SIDIS

We study the polar and azimuthal decay angular distributions of J/ψ mesons produced in semi-inclusive, deep-inelastic electron-proton scattering. For the description of the quarkonium formation mechanism, we adopt the framework of nonrelativistic QCD, with the inclusion of the intermediate color-octet channels that are suppressed at most by a factor $v^4$ in the velocity parameter $v$ relative to the leading color-singlet channel. We put forward factorized expressions for the helicity structure functions in terms of transverse momentum dependent gluon distributions and shape functions, which are valid when the $J/\psi$ transverse momentum is small with respect to the hard scale of the process. By requiring that such expressions correctly match with the collinear factorization results at high transverse momentum, we determine the perturbative tails of the shape functions and find them to be independent of the $J/\psi$ polarization. In particular, we focus on the $\cos2\phi$ azimuthal decay asymmetry, which originates from the distribution of linearly polarized gluons inside an unpolarized proton. We therefore suggest a novel experiment for the extraction of this so-far unknown parton density that could be performed, in principle, at the future Electron-Ion Collider.

Speaker: Cristian Pisano

IWHSS-2022-pisano.pdf

10:40 Coffee break

TMD PDFs and FFs: Morning Session 2

Convener: Prof. Alessandro Bacchetta

20 A new global (SIDIS-DY) fit of unpolarised proton TMDs at N3LL

We show results from the latest unpolarised proton TMD fit, performed at the N3LL perturbative accuracy by the MAP (Multidimensional Analysis of Partonoc distributions) collaboration.

Speaker: Giuseppe Bozzi (University of Cagliari and INFN, Cagliari)

MAP22.pdf

21 Phenomenological Analyses of TMD processes: a focus on rapidity and thrust dependeces

In this talk I will give a brief overview of the state of the art of TMD factorization theorems with special focus on the treatment of rapidity divergences and thrust dependence. I will then highlight some recent phenomenological progress especially regarding the non perturbative aspects of thrust resummation in e+e- --> hX.

Speaker: Mariaelena Boglione

Boglione_IWHSS_2022.pdf

22 Pion and kaon fragmentation functions at NNLO

In this contribution I wil present a new determination of unpolarised charged pion and kaon fragmentation functions from a set of single-inclusive electron-positron annihilation and lepton-nucleon semi-inclusive deep-inelastic scattering data. The determination includes next-to-next-to-leading order QCD corrections to both processes, and is carried out in a framework that combines a neural-network parametrisation of fragmentation functions with a Monte Carlo representation of their uncertainties.

Speaker: Valerio Bertone (C.E.A. Paris-Saclay)

bertone_IWHSS2022_30_08_2022.pdf

23 Spin effects in unpolarized SIDIS using the string+${}^3P_0$ model

The spin effects in fragmentation have been recently introduced in the Pythia 8 event generator for the simulation of the transversely polarized SIDIS process by using the string+${}^3P_0$ model of hadronization. This is achieved with the StringSpinner package, which currently uses parametrizations of the transversity PDFs and enables spin effects in the generator for pseudoscalar and vector meson production. The promising comparisons obtained between simulations and data on transverse spin asymmetries have stimulated further work.
The package is presently being extended to the study of quark spin effects in unpolarized SIDIS as induced by the Boer-Mulders TMD PDF, still an unknown and haunted function describing the correlation between the quark transverse spin and its intrinsic transverse momentum in the nucleon. The status and preliminary results are presented here.

Speaker: Albi Kerbizi (Universita e INFN Trieste (IT))

Kerbizi_IWHSS-2022.pdf

12:40 Lunch break

SIDIS and Drell-Yan measurements: Afternoon Session 1

Convener: Fabienne Kunne (Université Paris-Saclay (FR))

24 COMPASS unpolarised SIDIS results: TMDs

An important part of the COMPASS program concerns the study of transverse spin and momentum dependent parton distribution and fragmentation functions. In the last decade unpolarised results either as azimuthal modulations or as $P_{hT}$-dependent multiplicities have gain particular interest by both theoreticians and experimentalists. A review of recent results of these TMD-dependent observables as obtained by COMPASS using hadrons produced by a high energy muon beam scattering off unpolarised and polarized targets will be given.

Speaker: Andrea Bressan (Universita e INFN Trieste (IT))

Unpolxs_Bressan.pdf

Unpolxs_Bressan.pptx

25 COMPASS Drell-Yan programme: recent results

In 2015 and 2018 COMPASS collected data with 190 GeV $\pi^-$ beam and with transversely polarised proton target followed by a hadron absorber. The data offer a unique opportunity to study the structure of the proton and of the pion in the Drell–Yan pair and J/$\psi$ production, in particular the universality of the Sivers function and of the other TMD PDFs.

Speaker: Jan Matousek (Charles University (Prague, CZ), CERN)

Matousek_20220830.pdf

26 SpinQuest project: status and perspectives

The SpinQuest/E1039 experiment at the Fermi National Accelerator Laboratory aims to perform the first Sivers function measurement for sea quarks using the Drell-Yan process in proton-proton scattering transverse single spin asymmetry to find evidence for non-zero orbital angular momentum of light antiquarks in the nucleon. The experiment employs a 120-GeV extracted proton beam colliding with transversely-polarized NH3 and ND3 cryogenic targets, and a spectrometer that detects pairs of positive and negative muons from Drell-Yan production on polarized nucleons. This will allow a measurement of the transverse single spin asymmetry for a number of physics processes, including J/ψ and Drell-Yan production. In this presentation, an overview of the SpinQuest experiment as well as the physics goals and current status will be discussed.

Speaker: Ievgen Lavrukhin

SpinQuest_IWHSS_2022_Ievgen_Lavrukhin.pdf

15:15 Coffee break

Hadron Spectroscopy: Afternoon Session 2

Convener: Prof. Bernhard Ketzer (University of Bonn (DE))

27 Hadron spectroscopy theory and phenomenology

I'll discuss the recent developments obtained in hadron spectroscopy (light and heavy exotic mesons), in collaboration with the JPAC, GlueX and COMPASS collaborations.

Speaker: Vincent Mathieu (University of Barcelona)

COMPASS-Aug22.pdf

28 Spectroscopy results from LHCb

The measurements of heavy hadron spectroscopy can provide invaluable experimental input to improve our knowledge of QCD. With unique coverage of heavy-hadron enriched kinematic region and excellent performance in reconstructing and identifying heavy-hadron decays, the LHCb experiment has been making leading efforts in such studies. In this talk, the latest results on heavy-hadron spectroscopy, including both exotic and conventional hadrons will be presented.

Speaker: Liupan An (CERN)

LHCbSpectroscopy_20220830.pdf

29 Testing the chiral anomaly and measuring the radiative width of the $\rho$(770) in Primakoff reactions at COMPASS

The COMPASS experiment at CERN has collected an extensive data set with a pion beam impinging on nuclear targets during the years 2009 and 2012. In this data set, Primakoff events are recorded, which are characterized by a single-photon interaction between beam pion and target nucleus. Primakoff events with $\pi^-\pi^0$ in the final state allow us to measure the direct coupling of three pions two one photon - a process, which is driven by the chiral anomaly and described by the anomalous form factor $F_{3\pi}$. Besides the contribution from $F_{3\pi}$, the invariant mass distribution of the final state shows a dominant contribution from the $\rho$(770) resonance appearing in the $s$-channel. Previous analysis date back to the 80ies and extract either $F_{3\pi}$ or the radiative width of the $\rho$ independently. We will present new results from the COMPASS measurement, which for the first time combines the extraction of $F_{3\pi}$ and $\Gamma_{\rho\rightarrow\pi\gamma}$.

Speaker: Dominik Ecker (Technische Universitaet Muenchen (DE))

Ecker_20220830.pdf

18:30 Conference Dinner

Wednesday, 31 August

GPDs, Form Factors: Morning Session 1

Convener: Andrzej Sandacz (National Centre for Nuclear Research (PL))

30 Recent developments obtained with PARTONS framework

We discuss recent developments in the field of generalised parton distributions (GPDs), which were obtained with the PARTONS framework (https://partons.cea.fr). This includes in particular addressing the problem of model dependency, which spoils both the modelling of GPDs, and the extraction of quantities like D-term and amplitudes of exclusive processes. A bunch of other recent results, and a new Monte Carlo generator called EpIC, will be presented as well.

Speaker: Paweł Sznajder (National Centre for Nuclear Research)

sznajder_iwhss0822_2.pdf

31 Exclusive Processes and GPDs with CLAS/CLAS12

Hard exclusive processes allow the study of the 3D structure of the nucleon through the Generalized Parton Distributions (GPDs), which goes beyond what can be achieved with Elastic and Deep Inelastic ScaIering. In this talk, recent developments with CLAS/CLAS12 will be presented.

Speaker: Prof. Kyungseon Joo (University of Connecticut)

IWHSS-2022-JOO.pdf

32 Deeply virtual meson electroproduction: selected topics

I will address selected topics in deeply virtual meson electroproduction including the scale and flavor dependence, from light to charmed quarks.

Speaker: Prof. Simonetta Liuti

liuti_IWHSS22 [Autosaved].pdf

liuti_IWHSS22 [Autosaved].pptx

33 COMPASS GPD program

Deeply Virtual Compton Scattering (DVCS) and Hard Exclusive Meson Production (HEMP) are valuable processes to study Generalized Parton Distributions (GPDs), which help to reveal the 3-dimensional structure of the nucleon in QCD. Following a test run in 2012, exclusive measurements were performed at COMPASS in 2016 and 2017 at the M2 beamline of the CERN SPS. The 160 GeV muon beam impinged on a 2.5m long liquid hydrogen target that was surrounded by a barrel-shaped time-of-flight system to detect the recoiling target proton. The scattered muons and the particles produced were detected by the COMPASS spectrometer, which was supplemented by an additional electromagnetic calorimeter for the large-angle-photon detection.
The DVCS cross section is extracted from the sum of cross sections measured with opposite beam charge and polarization. Special emphasis was put on the investigation of the pi0 background. In the COMPASS kinematic domain, the DVCS cross section is closely related to the GPD H and gives a measure of the transverse extension of the partons in the proton in the sea-quark regime of Bjorken-x. In parallel, the measurement of the cross section of exclusive production of pi0, ρ0 and ω meson can provide important inputs for the understanding of chiral-even and chiral-odd GPDs, as well as insights into the reaction mechanisms involved. Recent results on exclusive ρ0 and ω production will be presented while exclusive pi0 production will be described in detail in Markéta Pešková’s presentation.

Speaker: Nicole D'Hose (Université Paris-Saclay (FR))

NdH_IWHSS_2022.pdf

34 The space-time electromagnetic structure of hadrons

The space-time electromagnetic structure of hadrons

The structure of hadrons is conveniently described in terms of form factors, that are accessible through electron-positron annihilation into a hadron and anti-hadron pair and its time reverse reaction, respectively in the space and time-like regions of transferred squared momenta. The fact (established by the JLab-GEp collaboration using the Akhiezer-Rekalo recoil polarization method) that the electric and magnetic distributions inside the proton are different contrary to what previously assumed, may lead to the observation of a zero crossing or a negative electric proton form factor at large momenta. Precise results were recently obtained at electron-positron colliders by the BESIII collaboration. They confirm the irregularities in the annihilation cross section previously observed at BaBar. These were fitted by a damped regular oscillation on the top of a monotone decreasing function, and interpreted as an interference between two phenomena or classes of phenomena occurring at the quark and at the hadron scales. A similar analysis done by the BESIII collaboration highlights such behaviour also in the neutron case. Interesting correlations appear among proton, neutron and hyperon form factors. A dynamical picture that coherently describes all these observations can be drawn, giving the scale of a diquark component of the hadron wave function and the hint of a neutral screened region at very small distances.
[on the basis of Refs. 2205.09171 [nucl-th], Phys.Rev.C 105 (2022) 065206, Phys.Rev.C 103 (2021) 3, 035203]

Speaker: Egle Tomasi (CEA Saclay)

ETG-SLTL.pdf

11:05 Coffee break

New/ongoing studies: Morning Session 2

Convener: Jan Matousek (Charles University (Prague, CZ), CERN)

35 Recent COMPASS TMD results: ongoing studies

In the context of the Transverse-Momentum-Dependent (TMD) description of the nucleon structure,of particular interest are the distributions of the transverse-momentum squared P_T^2 and the amplitudes of the azimuthal modulations (azimuthal asymmetries) of charged hadrons and of hadron pairs produced in Semi-Inclusive DIS off an unpolarized nucleon target. The P_T^2 – distributions and the azimuthal asymmetries can both be related to the intrinsic transverse momentum k_T of the quarks, while the azimuthal asymmetries also include contributions related to the still unknown Boer-Mulders TMD parton distribution function.
In 2016 and 2017, the COMPASS experiment at CERN collected a large sample of DIS events using a longitudinally polarized 160 GeV/c muon beam scattering off a liquid hydrogen target. Part of the collected data has been analysed to study the P_T^2 – distributions and the azimuthal asymmetries of charged hadrons and of hadron pairs, that will be shown and discussed in this talk.

Speaker: Andrea Moretti (Universita e INFN Trieste (IT))

Moretti_220831_IWHSS.pdf

36 Extraction of Pion TMDs from Drell-Yan data

In this talk we present our extraction of unpolarized quark-pion transverse-momentum-dependent parton distribution functions (TMD-PDFs) from a fit of all the existing Drell-Yan data. The fit is performed at the N3LL logarithmic accuracy in the resummation of qT-logarithms.

Speaker: Lorenzo Rossi (University of Pavia & INFN)

IWHSS_22_Rossi.pdf

37 Exclusive \pi^{0} muoproduction measurements at COMPASS

Hard Exclusive Meson Production and Deeply Virtual Compton Scattering (DVCS) are most commonly used reactions to study Generalised Parton Distributions (GPDs). Investigation of GPDs represents one of the main goals of the COMPASS-II program. Measurements of the exclusive processes were performed at COMPASS in 2016 and 2017 at the M2 beamline of the CERN SPS using the 160 GeV/$c$ muon beam scattering off a 2.5m long liquid hydrogen target surrounded by a barrel-shaped time-of-flight system to detect a recoiling target proton. The scattered muons and the produced real photons were detected by the COMPASS spectrometre, supplemented by an additional electromagnetic calorimetre for the detection of large-angle photons.

Exclusive $\pi^{0}$ production is the main source of background for DVCS process, while it provides complementary information for parametrisation of GPDs. We will report on preliminary results on exclusive $\pi^{0}$ production cross-section from 2016 data and its dependence on the squared four-momentum transfer $|t|$ and on the azimuthal angle $\phi$ between the scattering plane and the $\pi^{0}$ production plane. The results will provide a further input to phenomenological models for constraining GPDs, in particular chiral-odd (“transversity”) GPDs.

Speaker: Marketa Peskova (Charles University (CZ))

IWHSS22_Peskova.pdf

38 Investigating cold nuclear matter effects in charmonia at the fixed-target COMPASS experiment

Suppression of charmonia is one of the most distinctive signatures of Quark Gluon Plasma (QGP) in heavy-ion collisions. Suppression can also take place in hadron-nucleus collisions due to cold nuclear matter(CNM) effects where the presence of QGP is not expected. The hadron-nucleus collisions are therefore important as they help disentangling the effects of the QGP from those due to CNM. Charmonium production in hA collisions at fixed-target energies is sensitive to the effects of nPDF and the partonic energy loss in nuclear matter.
The double differential ($x_F$, $p_T$) cross sections of J/$\psi$ production have been measured by the COMPASS collaboration in hA collisions at $\sqrt s$ = 18.9 GeV. A negative pion beam with momentum of 190 GeV/c was impinging on ammonia, aluminum and tungsten targets. The preliminary results for the ratios of heavy to light targets (Al/W) for J/$\psi$ production show a sizable suppression towards high $x_F$. A dependence with $p_T$ is also investigated, which might indicate the presence of energy loss effects. The results will be compared to the available fixed-target and collider measurements in order to explore scaling behavior and energy dependence and will be followed by the comparison with theoretical model predictions.

Speaker: Dr Anisa Khatun (Université Paris-Saclay (FR))

Khatun_IWHSS_2022.pdf

12:45 Lunch break

Future experiments: Afternoon Session 1

Convener: Dr Michela Chiosso (University of Torino and INFN)

39 NICA-SPD project

The Spin Physics Detector is a multipurpose experiment foreseen to run at the NICA collider (JINR, Dubna). The main purpose of the experiment is the study of the nucleon spin structure in collisions of polarized protons and deuterons as well as other spin-related phenomena. The SPD physics program and the detector concept will be presented.

Speaker: Alexey Guskov (Joint Institute for Nuclear Research (RU))

SPD_project_IWHSS22.pdf

40 RF separated and conventional hadron beam in CERN’s secondary M2 beam line

The AMBER collaboration is planning measurements of the inner structure and the excitation spectrum of the kaon. For this purpose it is very important to have a kaon beam of high intensity as the results will be statistics-limited. The M2 beam line of the CERN SPS delivers a high intensity secondary mixed hadron beam consisting mainly of pions, so it is crucial to tag the vast majority of the kaons that reach the experiment. The kaon tagging is done by so-called CEDAR Čerenkov detectors short distance upstream of the experiment target. The efficiency to detect the kaons depends critically on the parallelism of the beam traversing the CEDAR counters.
Moreover, in order to overcome the disadvantage of the low fraction of kaons in the mixed beam, investigations are planned employing an radio-frequency (RF) separated beam. This technique enriches the content of a certain particle type within a beam consisting of different species at a fixed momentum by exploiting their different velocities.
In the present contribution, we discuss possible improvements of the conventional beam optics to achieve a better parallelism and hence better performance of the CEDARs for AMBER Drell-Yan and diffractive measurements. We focus especially on the investigation of multiple scattering in the present setup in the regions where the beam runs through air at atmospheric pressure. We will show the possible improvement of the parallelism by reducing the amount of multiple scattering and adapting the beam optics in consequence.
Additionally, we introduce the principle of RF separation and explain its dependence on different parameters of beam optics and hardware. We discuss particle production rates, beam transmission for the specific options studied, as well as limitations for beam intensity and purity posed by the beam line layout and acceptance as well as by radiation protection considerations. Different beam optics settings have been examined, providing either focused or parallel beams inside the RF cavities. We will discuss the separation and transmission capability of the different optics settings for given characteristics of the RF cavities and show preliminary results of the potential purity and intensity of the RF separated beam.

Speaker: Fabian Metzger (CERN; HISKP, University of Bonn (DE))

IWHSS2022_Metzger.pdf

IWHSS2022_Metzger.pptx

41 AMBER spectroscopy program with RF separated beams

The excitation spectrum of light mesons; which are composed of up, down, and strange quarks; allows us to study QCD at low energies. While the non-strange light-meson spectrum is already mapped out rather well, many predicted strange mesons have not yet been observed experimentally and many potentially observed states still need further confirmation. Hence, the strange-meson spectrum still holds many surprises that need to be discovered. The COMPASS experiment at CERN has studied so far mainly non-strange mesons of the $a_J$ and $\pi_J$ families with high precision, using the dominating $\pi^-$ component of the beam. Using the smaller $K^-$ component allows us to investigate also the spectrum of strange mesons. The flagship channel is the $K^-\pi^-\pi^+$ final state, for which COMPASS has acquired the so-far world's largest data set. Based on this data set, we performed a partial-wave analysis in order to disentangle the produced mesons by their spin-parity quantum numbers. However, strange-meson spectroscopy at COMPASS is limited by blind spots in the experimental acceptance due to the limited final-state particle identification.
In this talk, we will show recent results from this analysis of COMPASS data and we will give prospects for a high-precision measurement of the strange-meson spectrum at AMBER -- a new QCD facility at CERN, in which we can overcome the limitations of the COMPASS measurement.

Speaker: Stefan Wallner (Max Planck Institute for Physics)

2022-08-31_IWHSS_Wallner_AMBER-Program-with-RF-Separated-Beams_fixed.pdf

42 Pion and Kaon Structure Studies with AMBER

The main objectives of the AMBER experimental program are presented. Emphasis is given to measurements of the pion and kaon structure as a tool for understanding the emergence of the hadronic mass mechanism. The complementarity aspects of Drell-Yan, charmonium and direct-photon production experiments are reviewed. The benefits expected from the foreseen RF-separated meson beam facility are discussed.

Speaker: Dr Stephane Platchkov (Université Paris-Saclay (FR))

Platchkov_IWHSS22.pdf

Platchkov_IWHSS22.pptx

16:20 Visit to COMPASS experimental hall