12th International workshop on Multiple Partonic Interactions at the LHC

Auditorium (LIP Lisbon)


LIP Lisbon

Av. Prof. Gama Pinto 2 1649-003 Lisbon
Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF) , Jonathan Hollar (LIP) , Michele Gallinaro (LIP) , Ricardo Gonçalo (UC/LIP)

Zoom: Zoom link

Meeting ID: 649 7066 1694
Passcode: 87654321


MPI@LHC 2021 is the twelfth conference of a series of successful joint theory/experiment workshops that bring together the world's leading experts from theory and LHC experiments to discuss the latest progress on the physics relevant to the Multiple Partonic Interactions. 

This year it will take place in a hybrid mode (online and in-person) in Lisbon and hosted by LIP, Laboratório de Instrumentação e Física Experimental de Partículas. A mandatory Green Pass is required for all attendees of the workshop.

The conference will cover the following topics, divided in working groups:

  • WG1: Minimum Bias, Underlying Event and Monte Carlo generators
  • WG2: Double Parton Scattering
  • WG3: High multiplicities and small systems
  • WG4: Diffraction and small-x
  • WG5: Heavy Ion collisions 

Previous editions of the workshop

Registration for the workshop
  • Albert Bursche
  • Alessandro Gavardi
  • Alexander Kovner
  • Andrea Dainese
  • Andreas Morsch
  • Ankita Mehta
  • Antoni Szczurek
  • Armando Bermudez Martinez
  • Arthur Moraes
  • Benjamin Nachman
  • boris blok
  • Bronislav Zakharov
  • Cesar da Silva
  • Chiara Oppedisano
  • Chris Flett
  • Christopher Plumberg
  • Daniel Tapia Takaki
  • Danish Farooq Meer
  • David d'Enterria
  • Debasish Das
  • Dhevan Gangadharan
  • Dong Jo Kim
  • Farid Salazar
  • Federico Alberto Ceccopieri
  • Florian Fabry
  • Francesco Giovanni Celiberto
  • Francesco Giuli
  • Gabriel Corrêa
  • giulia manca
  • Giulia Marinelli
  • Giulia Pancheri
  • Grigorios Chachamis
  • Gustavo Gil da Silveira
  • Gösta Gustafson
  • Hassane Hamdaoui
  • Heikki Mäntysaari
  • Jasmine Brewer
  • Javira Altmann
  • Jochen Bartels
  • Jonathan Hollar
  • João A. Gonçalves
  • Julia Velkovska
  • Julian Alexander Boelhauve
  • Krista Smith
  • Laszlo Jenkovszky
  • Laurent Schoeffel
  • Leif Lönnblad
  • Liliana Apolinário
  • Luca Micheletti
  • Lucia Anna Tarasovicova
  • Lucian Harland-Lang
  • Marcelo Munhoz
  • Marcos Venício Gonçalves Sales
  • Marek Bombara
  • Maria Vittoria Garzelli
  • Marius Utheim
  • Mark Strikman
  • Mark Sutton
  • Markus Diehl
  • Martin Hentschinski
  • Matteo Rinaldi
  • Matthew Kelsey
  • Mees van Kampen
  • Michal Meres
  • Michele Gallinaro
  • Mike Sas
  • Mikel Mendizabal
  • Ming Liu
  • Miroslav Myska
  • Natalia Dzalaiova
  • Nestor Armesto
  • Nodoka Yamanaka
  • Oldrich Kepka
  • Oleh Fedkevych
  • Olga Piskounova
  • Ophir Ruimi
  • Oskar Grocholski
  • Peter Skands
  • Prabhat Pujahari
  • Raghav Kunnawalkam Elayavalli
  • Rajat Gupta
  • Randhir Singh
  • Ricardo Gonçalo
  • Riccardo Nagar
  • Sergey Levonian
  • Simon Plätzer
  • Simone Amoroso
  • Smbat Grigoryan
  • Smita Chakraborty
  • Soumya Mohapatra
  • Stefanos Leontsinis
  • Suman Kumar Kundu
  • sunil bansal
  • Theraa Tork
  • Uliana Dmitrieva
  • Umit Sozbilir
  • Victor Paulo Goncalves
  • Vlasios Petousis
  • Walter Luiz Alda Junior
  • Xiaoxuan Chu
  • Xin-Nian Wang
  • Xueli Hua
  • You Zhou
  • Yue Hang Leung
  • Yuri Kulchitsky
  • Zaida Conesa del Valle
    • 09:30 09:50
      coffee 20m
    • 09:50 10:00
      Welcome and Introduction 10m
      Speakers: Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF) , Jonathan Hollar (LIP) , Michele Gallinaro (LIP) , Ricardo Gonçalo (UC/LIP)
    • 10:00 11:00
      WG1: MB and UE
      Conveners: Armando Bermudez Martinez (CMS-DESY) , Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF)
      • 10:00
        Soft QCD and Phenomenology with Herwig 7 15m
        Speaker: Simon Platzer
      • 10:20
        Predicting strangeness yields in small and large systems with PYTHIA/Angantyr 15m
        Speaker: Smita Chakraborty (Lund University)
      • 10:40
        A PYTHIA 8 Underlying Event Tune For RHIC Energies 15m
        Speaker: Matthew Kelsey (Wayne State University)
    • 11:00 12:00
      WG2: Double Parton Scattering
      Conveners: Ankita Mehta (UHH) , Jonathan Hollar (LIP)
      • 11:00
        ATLAS measurements of Double Parton Scattering (15+3) 15m
        Speaker: Ranjit Nayak (Tel Aviv University (IL))
      • 11:20
        Double parton scattering studies using gauge bosons and jets at CMS (15+3) 15m
        Speaker: Rajat Gupta (Panjab University (IN))
      • 11:40
        Importance of jet fragmentation properties to study DPS (15+3) 15m
        Speaker: Dr Ramandeep Kumar (Akal University, India)
    • 12:00 13:30
      lunch 1h 30m
    • 13:30 14:30
      WG2: Double Parton Scattering
      Conveners: Ankita Mehta (UHH) , Jonathan Hollar (LIP)
      • 13:30
        Review of DPS in perturbative QCD (20+5) 20m
        Speaker: Riccardo Nagar (DESY)
      • 13:55
        Double parton distributions in colour space: perturbative splitting and positivity bounds (20+5) 20m
        Speaker: Peter Plößl (Deutsches Elektronen-Synchrotron DESY)
    • 14:30 15:40
      WG1: MB and UE
      Conveners: Armando Bermudez Martinez (CMS-DESY) , Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF)
    • 15:45 16:00
      coffee break 15m
    • 16:00 16:45
      WG1: MB and UE
      Conveners: Armando Bermudez Martinez (CMS-DESY) , Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF)
      • 16:00
        MB & UE: review of measurements at LHCb 20m
        Speaker: Julian Alexander Boelhauve
      • 16:25
        MB & UE: review of measurements and MC tuning at CMS 20m
        Speaker: Saptaparna Bhattacharya (Northwestern University (US))
    • 16:45 17:35
      WG4: small-x and diffraction: WG4: Small x & Diffraction
      Conveners: Albert Bursche (South China Normal University) , Martin Hentschinski (Universidad de las Americas Puebla) , Michele Gallinaro (LIP)
      • 16:45
        Measurement of lepton-jet correlation in deep-inelastic scattering with the H1 detector using machine learning for unfolding 20m

        The first measurement of lepton-jet momentum imbalance and azimuthal correlation in lepton-proton scattering at high momentum transfer is presented. These data, taken with the H1 detector at HERA, are corrected for detector effects using an unbinned machine learning algorithm (OmniFold), which considers eight observables simultaneously in this first application. The unfolded cross sections are compared to calculations performed within the context of collinear or transverse-momentum-dependent (TMD) factorization in Quantum Chromodynamics (QCD) as well as Monte Carlo event generators. The measurement probes a wide range of QCD phenomena, including TMD parton distribution functions and their evolution with energy in so far unexplored kinematic regions.

        arxiv:2108.12376, submitted to PRL

        Speaker: Ben Nachman (LBNL)
      • 17:10
        Forward dijet production at the EIC: beyond the TMD factorization 15m

        The measurement of azimuthal correlations in the production of forward dijet in deep inelastic scattering provides a unique channel to access the small-x regime of the Weizsäcker-Williams gluon TMD. Its study could potentially provide signatures of gluon saturation at the future Electron-Ion Collider.

        While the TMD factorization for semi-inclusive dijet production is expected to hold in the exact back-to-back kinematics, there are important kinematic (perturbative power) and genuine saturation contributions that must be resummed for more controlled phenomenological predictions. The latter contributions account for higher physical degrees of freedom, beyond the TMD distributions, inside hadronic matter. In this talk, I will compare the results of the TMD and the improved TMD factorization framework to those in the CGC EFT, and report on the expected size of kinematic and genuine saturation corrections at different kinematics accessible at the EIC [1]. If time allows, I will discuss recent progress towards the computation of dijet production at the next-to-leading order in the CGC EFT [2].


        [1] The importance of kinematic twists and genuine saturation effects in dijet production at the Electron-Ion Collider. R. Boussarie, F. Salazar, H. Mäntysaari, and B. Schenke.

        [2] Dijet impact factor in DIS at next-to-leading order in the Color Glass Condensate. P. Caucal, F. Salazar, and R. Venugopalan.

        Speaker: Farid Salazar (Stony Brook University)
    • 09:30 10:00
      coffee 30m
    • 10:00 11:00
      WG2: Double Parton Scattering
      Conveners: Ankita Mehta (UHH) , Jonathan Hollar (LIP)
      • 10:00
        First observation of triple-J/psi production in pp collisions, and constraints on double and triple parton scatterings (15+3) 15m
        Speaker: David d'Enterria (CERN)
      • 10:20
        LHCb measurement of double parton scattering in pPb collisions (15+3) 15m
        Speaker: Albert Bursche (South China Normal University)
      • 10:40
        Double-parton effects in production of fully heavy tetraquarks in proton-proton collisions (15+3) 15m
        Speaker: Prof. Antoni Szczurek (IFJ Krakow & University of Rzeszow)
    • 11:00 12:00
      WG3: High multiplicities and small systems
      Conveners: Grigorios Chachamis (LIP) , Simone Amoroso (DESY)
      • 11:00
        Leptons from HF decays : measurements and inferences towards small systems (15+3) 15m

        Briefly after the Big Bang, the early universe was in a high temperature and high density environment. In order to recreate this state of matter in the laboratory, mini bangs are created by colliding heavy ions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and subsequently at the Large Hadron Collider (LHC) at CERN. In this talk I shall be covering on the selected results from LHC and RHIC. I shall be covering spectra and correlations (flow) and also nuclear modification factor. I shall be discussing quarkonia flow in further detail. Due to the larger mass of the bottomonium states compared to the charmonium ones,the measurement of bottomonia production in proton-nucleus collisions allows a study of CNM effects in a different kinematic regime, therefore complementing the J/Psi studies[1]. For smaller systems like p+A and p+p we have less deeply bound bottomonia states and thus a comparatively larger chance to escape. This means that more states become measurable, which is a positive feature. On the other hand,it also means that the escape mechanism which underlies the anisotropic flow of bottomonia may become largely ineffective, in particular for the Upsilon(1S). Accordingly,the measurement of a sizable flow for Upsilon(1S) in small systems[2] would probably hint at the importance of initial-state correlations. Hence understanding small systems becomes very important and such studies will be also stressed and presented including the opportunities which will be possible in LHC Run-3 small system data-sets.
        [1] D. Das and N. Dutta, Int. J. Mod. Phys. A 33, no. 16, 1850092 (2018)
        [2] D.Das , Nucl.Phys.A 1007 (2021) 122132

        Speaker: Debasish Das (Saha Institute of Nuclear Physics)
      • 11:20
        ALICE strange particles and fragmentation measurements (15+3) 15m

        The results from the ALICE pp and p-Pb program show intriguing trends resembling those of nucleus-nucleus collisions usually attributed to quark-gluon plasma formation. One of these measured effects is enhanced production of (multi-)strange particles with respect to pions (a.k.a. the strangeness enhancement) gradually rising from low-multiplicity to high-multiplicity pp or p-Pb collisions where production rates of (multi-)strange particles similar to peripheral Pb-Pb collisions are reached.
        In pp or p-Pb collisions, the strange quarks can be created either in hard processes (jets) or soft processes (underlying events). Two experimental approaches can address the strange quark production in the jet fragmentation: direct one using strange hadron tagged jet reconstruction or via two-particle correlations with strange particles. Both the approaches benefit from excellent identification of strange hadrons up to high transverse momentum in the ALICE detector. In the presentation, we report on strange mesons and baryons production in the jet and out-of-the jet and the role of particles produced from jet fragmentation in the strangeness production in high-multiplicity pp or p-Pb collisions.

        Speaker: Marek Bombara (Pavol Jozef Šafárik University)
      • 11:40
        The three point asymmetric cumulants in high multiplicity pp collisions (15+3) 15m

        We study the inuence of quantum interference and colour flow on three point correlations described by asymmetric cumulants in high multiplicity events in pp collisions. We use the model previously developed for the study of the collectivity in symmetric cumulants. We show that the resulting three point asymmetric cumulant is in qualitative agreement with the experimental data for the same parameters of the model as it was with the symmetric cumulants. Our results show that the initial state correlations must play a major role and may be even dominant in the explanation of the correlations in high multiplicity pp events.

        Speaker: Ran Segev
    • 12:00 13:30
      lunch 1h 30m
    • 13:30 14:30
      WG2: Double Parton Scattering
      Conveners: Ankita Mehta (UHH) , Jonathan Hollar (LIP)
      • 13:30
        Study of parton correlations via DPSs in associated quarkonium production in high energy accelerator experiments (20+5) 20m
        Speaker: Nodoka Yanamaka
      • 14:00
        Sum rules for triple parton distribution function (20+5) 20m
        Speaker: Oleh Fedkevych (University of Genoa)
    • 14:30 15:30
      WG3: High multiplicities and small systems
      Conveners: Grigorios Chachamis (LIP) , Simone Amoroso (DESY)
      • 14:30
        Search for collective behaviour and multiparton interactions in ep scattering at HERA (20+5) 20m

        Collective behaviour of final-state hadrons is studied in ep scattering using the H1 and ZEUS detectors at HERA. Measurements of two- and four-particle azimuthal correlations in both DIS and photoproduction are presented. Ridge yields are extracted from fits to two-particle correlations with H1 data. Comparisons of the magnitudes and signs of the first- and second-harmonic of two-particle correlations are made with ZEUS data. Four-particle cumulant correlations are observed to be positive. The results do not indicate the kind of collective behaviour observed at RHIC and the LHC in high-multiplicity hadronic collisions. The possibility of multiparton interactions are studied in photoproduction with ZEUS. Comparisons of PYTHIA predictions with the measurements strongly indicate the presence of multiparton interactions from hadronic fluctuations of the exchanged photon.

        Speaker: Dhevan Gangadharan
      • 15:00
        Collectivity in small systems: the initial state perspective (20+5) 20m

        I discuss the physical origin of collective like signals in collisions of small systems from the perspective of initial state structure. Recent theoretical developments and directions of CGC inspired research are described.

        Speaker: Alex Kovner (University of Connecticut)
    • 15:30 15:45
      coffee break 15m
    • 15:45 17:55
      WG3: High multiplicities and small systems
      Conveners: Grigorios Chachamis (LIP) , Simone Amoroso (DESY)
      • 15:45
        Collectivity in small systems at RHIC (20+5) 20m

        The quark-gluon plasma (QGP) produced in ultra-relativistic collisions between large nuclei, such as gold or lead has vanishingly small specific viscosity making it one of the most “perfect” liquids known. Experimentally, the near-perfect liquid manifests itself in a collective flow of the produced particles, and measurements of the collective flow patterns have been a key to extracting the QGP properties. However, collective effects are also observed in small collision systems, such as proton-nucleus or even proton-proton collisions, which were originally not expected to produce QGP. In the quest for understanding how the perfect liquid behavior emerges, the PHENIX and STAR collaborations at RHIC performed a series of measurements in several small systems. Gold nuclei were collided with protons, deuterons, and 3He nuclei at a nucleon-nucleon center-of-mass energy of 200 GeV, and a beam energy scan was performed with deuteron-gold collisions. This talk will review the RHIC results from the small-system geometry and beam-energy scans and discuss our current understanding of the various effects that contribute to the observed collectivity in small collision systems at RHIC.

        Speaker: Julia Velkovska (Vanderbilt University)
      • 16:10
        ALICE results on long- and short-range correlations in high multiplicity pp collisions (15+3) 15m

        In this talk, we present the latest results on two-particle correlations in high-multiplicity pp events from the ALICE Collaboration. In addition to the traditional long-range ridge studies, we present a new differential study in high-multiplicity pp collisions which contain a high-momentum charged particle or reconstructed jet, in order to determine whether long-range correlations are correlated with hard processes [1]. Furthermore, we perform a flow-extraction method using a low-multiplicity template, and present the non-flow free flow harmonics. The results are compared to the Pythia and EPOS Monte Carlo models which employ different mechanisms to generate ridge-like features, and to the results obtained in other LHC experiments.

        [1] JHEP 05 (2021) 290, arXiv:2101.03110

        Speaker: Jasper Parkkila (University of Jyväskylä)
      • 16:30
        Event-shapes and the presence of jets in e+e-and pp collisions (15+3) 15m

        Event-shape observables such as transverse sphericity are widely being used by the particle and nuclear physics community to characterize events and study the underlying physics mechanisms.
        In earlier studies these observables proved useful in e+e- collisions to discriminate between di-jet and multi-jet topologies, and more recently were exploited in pp collisions.
        However, by using events produced with the PYTHIA event generator, we have found that in pp collisions the correlation between event-shape observables and jets is far weaker than is the case in e+e- collisions. Rather, there is an indication that event-shapes in pp collisions are sensitive to the amount of multi-parton interactions, which motivates further investigation of the use of these observables in a new way.
        In this talk we present results that support our claim that event-shapes in pp collisions are sensitive to fundamentally different event characteristics and physics mechanisms compared to the same observables in e+e- collisions, which is contrary to what the community has claimed thus far.

        Speaker: Mike Sas (Yale)
      • 16:50
        Jet quenching in small systems (20+5) 20m

        We discuss recent results on possible jet quenching in collisions of small
        systems: in $pp$, $pA$ and oxygen-oxygen collisions. Calculations of the radiative and collisional parton energy loss are performed for the temperature dependent running QCD coupling. We use parametrization of $\alpha_s(Q,T)$ which has a plateau around $Q \sim \kappa T$ (it is motivated by the lattice calculation of the effective QCD coupling in the QGP). The parameter $\kappa$ has been fitted to the LHC data on the nuclear modification factor $R_{AA}$ in heavy ion collisions. Using the optimal $\kappa$ we perform calculations of $R_{pp}$, $R_{pPb}$, and $R_{AA}$ and $v_2$ for O+O collisions. We find that predictions for $R_{OO}$ may differ substantially for scenarios with and without mini-QGP formation in $pp$ collisions.
        We show that the available data on $R_{pPb}$ may be consistent with the QGP formation in $pp$ and $pPb$ collisions. However, a scenario with the QGP formation only in $pPb$ collisions is excluded.

        Speaker: Bronislav Zakharov (L.D. Landau Institute for Theoretical Physics)
      • 17:15
        ATLAS and CMS results on collectivity in small-systems (20+5) 20m

        This talk presents an overview of recent measurements from the ATLAS and CMS collaborations that study collective behavior in $p$+Pb and $pp$ collisions.For $p$+Pb collisions, measurements of collective behavior involving strange, charm and bottom hadrons are presented. Measurements of elliptic anisotropy in Ultra-peripheral $p$+Pb collisions, which are
        in fact $p$+$\gamma$ collisions, are presented and compared to corresponding measurements in hadronic $p$+Pb collisions. Several measurements that investigate the long-range correlations observed in $pp$ collisions, commonly called the ``ridge'', are presented. A study of the dependence of the ridge on the presence of a hard process in the event, namely a $Z$-boson, is presented, and its implications are discussed. Studies of the long-range correlations in $pp$ collisions involving heavy-flavor hadrons are presented. Finally, correlation measurements with an active rejection of particles associated with semi-hard processes, such as low-pT jets, are also discussed. These measurements can give further insight into the origin of the $pp$ ridge.

        Speaker: Soumya MOHAPATRA (Columbia University)
    • 09:30 10:00
      coffee 30m
    • 10:00 11:00
      WG3+WG5 common session: WG3+WG5
      Conveners: Daniel Tapia Takaki (University of Kansas) , Grigorios Chachamis (LIP) , Liliana Apolinário (LIP) , Simone Amoroso (DESY)
      • 10:00
        Opportunities of OO and pO collisions at the LHC (20+5) 20m

        I will discuss the opportunities of the upcoming oxygen-oxygen (OO) and proton-oxygen (pO) run at the LHC. I will briefly present results and projections from the recent dedicated workshop and highlight the unique physics accessible in this run. Measuring partonic energy loss (through suppression of hadron or jet spectra) in OO would be ground-breaking but poses challenges since there is likely not time in the short run for a pp reference measurement at the same energy. I will discuss the precision and accuracy of constructing a pp baseline for the oxygen run, either from perturbative QCD or from interpolation of spectra measurements at nearby energies. I will finally highlight a new proposal to bypass the need for constructing a pp reference by measuring the ratio of OO or pO spectra to pp spectra at a different center-of-mass energy.

        Speaker: Jasmine Brewer (CERN)
      • 10:30
        QCD and Relativistic Hydrodynamics from pp to AA (20+5) 20m

        One of the biggest open questions in the study of nuclear collisions is the proper understanding of collective behavior and, in particular, whether a unified framework can be found which simultaneously describes the relevant features of this behavior in all collision systems. To date, a number of such frameworks have been proposed, including that of relativistic hydrodynamics. This approach models a collision's evolution using the equations of relativistic fluid dynamics, thereby attributing the observed collective behavior to the fluid-like evolution of the quark-gluon plasma (QGP).

        In this talk I will review some recent challenges to the applicability of the hydrodynamic framework in nuclear collisions. These challenges, which become particularly acute in small systems, arise from the large gradients and non-equilibrium corrections present in nuclear collisions and the fact that, as recently demonstrated, these lead readily to violations of the hyperbolic character of the hydrodynamic equations of motion and/or of relativistic causality itself. Moreover, these challenges turn out to be present even in models which have been explicitly tuned to match the experimental data. I will suggest some broad implications of these results for the ongoing debate about the nature and origins of collectivity in nuclear collisions.

        Speaker: Christopher Plumberg (University of Illinois at Urbana-Champaign (USA))
    • 11:00 12:00
      WG4: small-x and diffraction
      Conveners: Albert Bursche (South China Normal University) , Martin Hentschinski (Universidad de las Americas Puebla) , Michele Gallinaro (LIP)
      • 11:00
        Double parton scattering via photon-proton interactions and the transverse proton structure 20m

        In this contribution, we present possible appealing advantages offered by double parton scattering (DPS) processes via photon-proton interactions. In fact, as discussed in the proton-proton collisions framework, the DPS cross section depends on the double parton distribution functions (dPDFs) of the protons. These new quantities encode new information on the 3D partonic structure of the proton, complementary to TMDs and GPDs. In fact, dPDFs are sensitive to unknown double parton correlations in hadrons which cannot be accessed through, e.g., GPDs. However, dPDFs are almost unknown and, in particular, their dependence on the transverse distance of partons. In our analyses [1, 2, 3, 4] we investigated the relevance of both perturbative and non perturbative double parton correlations in dPDFs. Moreover, our collaboration studied the impact of these effects on the experimental observable called effective cross section, $\sigma_{eff}$ [5, 6]. However, as proved in Refs. [7, 8] in proton-proton collisions, only limited information on the partonic proton structure can be extracted from data due to the lack of information on dPDFs and their relative first moment called effective form factor (eff), the latter entering the definition of $\sigma_{eff}$. Therefore, in Ref. [12], we studied the possibilities offered by DPS initiated by quasireal photons. In fact, in this case, the offshellness of the photons is controlled by measuring leptons, proton or ions from the impinging beam scattered at low angle. At such low virtualities, the photon will fuctuate hadronically and/or electromagnetically in a $q−\bar q$ pair which then initiates the double parton scattering with the proton. In this scenario, the photon transverse size could be almost controlled by measuring the virtuality and, in turn, the interaction rate in the DPS mechanism. Such a condition leads to the extraction of information on the transverse proton structure. In Ref. [12] we prove that the dependence of $\sigma^{\gamma p}_{eff}(Q^2)$ on the photon virtuality $Q^2$ could be related to the mean transverse distance between two partons in the proton active in the DPS process. In addition, different models of the photon and proton effs have been used to calculate, for the first time, $\sigma_{eff}^{\gamma p}(Q^2)$. These results have been then used to estimate the DPS cross section for the four jets production via DPS for the HERA kinematics. In fact, the ZEUS collaboration reported significant MPI effects in this channel for the four jets cross sections, and exposed in their analyses possible contamination of the DPS processes. By estimating the expected number of events at given integrated luminosity, we conclude that DPS process in photoproduction gives a significant fraction of the four jet production cross section if cuts on transverse momenta of the jets are low enough.

        [1] M. Rinaldi, S. Scopetta and V. Vento, Phys. Rev. D 87, 114021 (2013)
        [2] M. Rinaldi, S. Scopetta, M. Traini and V. Vento, JHEP 1412, 028 (2014)
        [3] M. Rinaldi, S. Scopetta, M. C. Traini and V. Vento, JHEP 1610, 063 (2016)
        [4] M. Rinaldi and F. A. Ceccopieri, Phys. Rev. D 95, no. 3, 034040 (2017)
        [5] F. A. Ceccopieri, M. Rinaldi and S. Scopetta, Phys. Rev. D 95, no. 11, 114030 (2017)
        [6] M. Rinaldi, S. Scopetta, M. Traini and V. Vento, Phys. Lett. B 752, 40 (2016)
        [7] M. Rinaldi and F. A. Ceccopieri, JHEP 1909, 097 (2019)
        [8] M. Rinaldi and F. A. Ceccopieri, Phys. Rev. D 97, no. 7, 071501 (2018)
        [9] G. S. Bali et al., JHEP 1812, 061 (2018)
        [10] M. Rinaldi, S. Scopetta, M. Traini and V. Vento, Eur. Phys. J. C 78, no. 9, 781 (2018)
        [11] M. Rinaldi, Eur. Phys. J. C 80, no. 7, 678 (2020)
        [12] M. Rinaldi and F. A. Ceccopieri, arXiv:2103.13480.

        Speaker: Matteo Rinaldi (Dipartimento di Fisica e Geologia. Università degli studi di Perugia. Istituto Nazionale di Fisica Nucleare, sezione di Perugia.)
      • 11:30
        Very forward particle production and searches (FASER, etc) 20m
        Speaker: Maria Vittoria Garzelli (Universitaat Hamburg (DE))
    • 12:00 13:30
      lunch 1h 30m
    • 13:30 15:00
      WG4: small-x and diffraction
      Conveners: Albert Bursche (South China Normal University) , Martin Hentschinski (Universidad de las Americas Puebla) , Michele Gallinaro (LIP)
      • 13:30
        Elastic photon-initiated production at the LHC: the role of hadron-hadron interactions 20m

        We discuss the role of additional hadron-hadron interactions in elastic photon-initiated production at the LHC, both in proton and heavy ion collisions. We in particular assess different sources of uncertainty associated with these cross sections, and compare with other calculations in the literature. A key result of our analysis is that the uncertainty associated with the survival factor is small, and it is only by taking very extreme and rather unphysical variations in the modelling of the survival factor that significant differences in the predicted cross sections. This underlines the basic, rather model independent, point that a significant fraction of elastic photon-initatied scattering occurs for hadron-hadron impact parameters that are simply outside the range of QCD interactions, and hence this sets a lower bound on the survival factor in any physically reasonable approach.

        Speaker: Lucian Harland-Lang (University of Oxford)
      • 14:00
        Parton distribution functions: measurements and interpretations 20m
        Speaker: Mark Sutton (ATLAS Collaboration)
      • 14:30
        Results on diffraction and exclusive production 20m
        Speaker: Gustavo Gil Da Silveira (Universidade do Estado do Rio de Janeiro)
    • 15:00 15:15
      coffee break 15m
    • 15:15 16:30
      WG4: small-x and diffraction
      Conveners: Albert Bursche (South China Normal University) , Martin Hentschinski (Universidad de las Americas Puebla) , Michele Gallinaro (LIP)
      • 15:15
        The Electron Ion Collider and gluon imaging using azimuthal correlations at the EIC 20m

        We calculate azimuthal correlations between the exclusively produced virtual photon or vector meson and the scattered electron in Deep Inelastic Scattering processes at the future Electron-Ion Collider (EIC). We identify "kinematical" and "intrinsic" contributions to these correlations. Performing explicit calculations within the Color Glass Condensate framework we show that the correlations are sensitive to the non-trivial spatial correlations in the gluon distribution of the target, and that significant azimuthal modulations could be measured at the future EIC.

        Speaker: Heikki Mäntysaari (University of Jyväskylä)
      • 15:40
        Results from peripheral and ultra-peripheral collisions at the LHC 20m
        Speaker: Giulia Manca (Universita` degli studi di Cagliari and INFN, Cagliari, IT)
    • 17:40 18:00
      directions to excursion and dinner 20m
    • 18:00 20:30
      Excursion 2h 30m

      We will go on a boat trip on the river Tagus. The boat leaves at 18:30.
      We will meet at 18:00-18:15 at the "Terreiro do Paço" subway station (blue line).

    • 20:45 22:15
      Dinner 1h 30m

      Dinner at 21h:
      Restaurant “A Muralha”
      address: R. Jardim do Tabaco 112 (it is near the Fado museum)

    • 09:30 10:00
      coffee 30m
    • 10:00 11:00
      WG5: Heavy ions
      Conveners: Daniel Tapia Takaki (University of Kansas) , Liliana Apolinário (LIP)
      • 10:00
        Accessing the initial conditions of ultrarelativistic heavy-ion collisions 25m

        The primary goal of the ultrarelativistic heavy-ion collision program at the LHC is to study the quark-gluon plasma (QGP) properties, a state of strongly interacting matter that exists at high temperatures and energy densities. However, the lack of knowledge on the initial conditions of heavy-ion collision results in a significant uncertainty of the extraction of the transport properties of QGP.

        In this talk, I will present the latest developments of multi-particle correlations. I will show that the newly proposed mixed harmonic correlation of various moments of anisotropic flow coefficients can provide strong constraints on the correlations between various moments of eccentricity coefficients in the initial conditions. Both hydrodynamic model predictions and ALICE measurements will be discussed. In addition, I will discuss the newly proposed correlation between mean transverse momentum and anisotropic flow coefficients, which could reflect the size and shape of the initial state and give direct access to the initial conditions. I will present the newest experimental measurements from both RHIC and the LHC experiments, as well as several recent theoretical model predictions. I will further show that the current state-of-the-art understanding of the initial conditions and the QGP properties relies on the Bayesian analyses, which are all based on the TRENTo initial state model and fail completely in describing the experimental data. The potential solutions will be discussed in the end.

        Speaker: You Zhou (Niels Bohr Institute)
      • 10:30
        Overview on quarkonia and heavy-flavor physics at the LHC 25m

        The production of quarkonia and open heavy-flavor hadrons in relativistic heavy-ion collisions has been widely explored by all LHC experiments and represents a valuable tool for probing the properties of the quark-gluon plasma (QGP). In fact, since heavy quarks, charm and beauty, are produced during the hard parton-parton scattering, they experience the entire evolution of the fireball. On one side, the suppression of quarkonium bound states by the QGP, as well as the charmonium regeneration by (re)combination of charm quarks in a strongly interacting medium, are sensitive to the medium properties. On the other, the measurement of open heavy-flavor hadron production can provide us important information on the heavy quarks' energy loss and hadronization mechanism. Moreover, the measurement of the azimuthal anisotropy coefficients ($v_{2}$, $v_{3}$) for different hadron species allows to assess the collective behavior of heavy quarks in an expanding medium.\

        In this contribution, recent quarkonium and heavy flavor measurements in nucleus-nucleus collisions obtained at the LHC. In particular, the nuclear modification factor for various hadrons and particle species ratios will be shown as a function of transverse momentum, centrality and multiplicity. The latest measurements of flow coefficients for quarkonia and heavy-flavor hadrons will be also presented.

        Speaker: Luca Micheletti (INFN Torino (IT))
    • 11:00 12:00
      WG4: small-x and diffraction
      Conveners: Albert Bursche (South China Normal University) , Martin Hentschinski (Universidad de las Americas Puebla) , Michele Gallinaro (LIP)
      • 11:00
        Small x gluon PDF from LHCb exclusive J/psi data 15m

        The exclusive J/psi production process within a `tamed’ collinear factorisation approach to NLO is described, giving a stable and reliable theoretical prediction owing to the resummation of a class of large logarithms and implementation of a crucial low Q_0 subtraction. A comparison with data from HERA and LHCb is made, before an extraction of a low x ~ 3*10^{-6} and low scale mu^2 ~ 2.4 GeV^2 gluon PDF is obtained via profiling of global PDF sets. The significance of this result for low x global gluon PDF fits is quantified.

        Speaker: Chris Flett (The University of Jyväskylä)
      • 11:20
        Accessing the proton UGD via exclusive polarized rho-meson leptoproduction at HERA and the EIC 15m

        We study the exclusive polarized leptoproduction of ρ-mesons within the framework of high-energy factorization. Cross sections for longitudinally and transversally polarized mesons are presented. We employ a wide variety of unintegrated gluon distributions available in the literature and compare to HERA data. The resulting cross sections strongly depend on the choice of unintegrated gluon distribution. We also present predictions for the proton target in the kinematics of the Brookhaven EIC.

        Speaker: Francesco Giovanni Celiberto (ECT*/FBK Trento & INFN-TIFPA)
      • 11:40
        Measurement of exclusive pi+pi- and rho0 meson photoproduction at HERA 15m

        Exclusive photoproduction of $\rho^0(770)$ mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900000 events is used to measure single- and double-differential cross sections for the reaction $\gamma{}p\to\pi^{+}\pi^{-}Y$. Reactions where the proton stays intact ($m_Y=m_p$) are statistically separated from those where the proton dissociates to a low-mass hadronic system ($m_p< m_Y < 10$ GeV). The double-differential cross sections are measured as a function of the invariant mass $m_{\pi\pi}$ of the decay pions and the squared 4-momentum transfer $t$ at the proton vertex. The measurements are presented in various bins of the photon-proton collision energy $W_{\gamma{}p}$. The phase space restrictions are $0.5< m_{\pi\pi}< 2.2$ GeV, $|t|< 1.5$ GeV$^2$, and $20< W_{\gamma{}p}< 80$ GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the $m_{\pi\pi}$ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the $\rho^0(770)$ meson mass and width at $m_\rho=770.8^{+2.6}_{−2.7}$ (tot.) MeV and $\Gamma_\rho=151.3^{+2.7}_{−3.6}$ (tot.) MeV, respectively. The model is used to extract the $\rho^0(770)$ contribution to the $\pi^{+}\pi^{−}$ cross sections and measure it as a function of $t$ and $W_{\gamma{}p}$. In a Regge asymptotic limit in which one Regge trajectory $\alpha(t)$ dominates, the intercept $\alpha(t=0)=1.0654^{+0.0098}_{−0.0067}$ (tot.) and the slope $\alpha′(t=0)=0.233^{+0.067}_{−0.074}$ (tot.) GeV$^{−2}$ of the $t$ dependence are extracted for the case $m_Y=m_p$.

        Eur.Phys.J.C80 (2020), 1189 [arxiv:2005.14471]

        Speaker: Sergey Levonian (DESY)
    • 12:00 13:20
      lunch 1h 20m
    • 13:20 13:55
      WG2: Double Parton Scattering
      Conveners: Ankita Mehta (UHH) , Jonathan Hollar (LIP)
    • 13:55 15:15
      WG5: Heavy ions
      Conveners: Daniel Tapia Takaki (University of Kansas) , Liliana Apolinário (LIP)
      • 13:55
        Recent results on soft and hard probes at RHIC 25m

        In this talk, recent results from selected topics on soft and hard probes by experiments STAR and PHENIX at RHIC will be presented. Besides heavy-ion collisions at $\sqrt{s_{\rm{NN}}}=200$ GeV, RHIC has delivered collisions at lower energies in recent years, driven by the STAR BES-II program, ranging from $\sqrt{s_{\rm{NN}}}=27$ GeV to $\sqrt{s_{\rm{NN}}}=3$ GeV.

        At top RHIC energies, heavy flavor hadrons are a valuable probe to study properties of the quark gluon plasma created in large systems, while their measurements in smaller systems can help us study cold nuclear matter effects. At lower energies, measurements of strange and light flavor hadrons can help systematically investigate the properties of QCD matter at finite baryon densities. Finally, at the lowest energy achieved from the STAR fixed target setup, $\sqrt{s_{\rm{NN}}}=3$ GeV, measurements on the collective flow of light and strange hadrons, particle yield ratios, hypernuclei lifetime and binding energy will be presented, and implications on the produced QCD medium properties will be discussed.

        Speaker: Yue Hang Leung (Lawrence Berkeley National Laboratory)
      • 14:25
        Overview talk on recent soft probes in heavy-ion physics at the LHC 25m
        Speaker: Prabhat Ranjan Pujahari (CERN)
      • 14:55
        Two-particle correlations triggered with strange hadrons in pp collisions at 13 TeV measured with ALICE 15m

        Angular correlations between particles can be utilised to study soft fragmentation and production processes as well as the role of multiple parton interactions. Moreover, a study of the multiplicity dependence can further differentiate between the connection of bulk particles and strangeness production in a more dense environment and the potential role of collective effects.
        In this talk, we present results on the two-particle correlation studies in pp collisions at 13 TeV measured with ALICE where strange hadrons ($\mathrm{K_{S}^0}$,$\Lambda$ and $\Xi$) are used as trigger particles.
        The comparison of the correlation functions of the $\Xi$ hyperon associated with different strange and non-strange mesons and baryons with different models such as PYTHIA8 or EPOS provides an insight into the strangeness production mechanism. The ratios of the per-trigger yields from $\mathrm{K_{S}^0}$-h and $\Lambda$-h to the yields extracted from the h-h correlation function are sensitive to the difference between quark and gluon jets hadronisation mechanism. The multiplicity and $p_{\mathrm{T}}^{\mathrm{trigg}}$ dependence of the per-trigger yields and balanced yields will be shown.

        Speaker: Lucia Anna Tarasovicova (Westfälische Wilhelms-Universität Münster (DE))
    • 15:15 15:40
      coffee break 25m
    • 15:40 17:30
      WG5: Heavy ions
      Conveners: Daniel Tapia Takaki (University of Kansas) , Liliana Apolinário (LIP)
      • 15:45
        Neutron production in ZDC as a probe of the dynamics of hard gamma A and pA interactions 15m

        Neutron production in ZDC as a probe of the dynamics of hard gamma A and pA interactions.

        Speaker: Mark Strikman (PSU (USA))
      • 16:05
        Heavy-Ion Physics at the LHCb 15m
        Speaker: Cesar Luis da Silva (CERN)
      • 16:25
        MPI & Jet Physics in Heavy-Ion Collisions 25m
        Speaker: Xin-nian Wang (LBL)
      • 16:55
        Jets and UPC physics in heavy-ion collisions at the LHC 25m
        Speaker: Hassane HAMDAOUI (Rabat)
    • 09:30 10:00
      coffee 30m
    • 10:00 11:00
      WG1: MB and UE
      Conveners: Armando Bermudez Martinez (CMS-DESY) , Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF)
      • 10:00
        Status of the GENEVA Monte Carlo event generator 20m
        Speaker: Alessandro Gavardi (Università degli studi di Milano-Bicocca)
      • 10:25
        The intrinsic kT in LO and NLO parton showers 20m
        Speaker: Mikel Mendizabal (DESY)
    • 11:00 12:00
      WG5: Heavy ions
      Conveners: Daniel Tapia Takaki (University of Kansas) , Liliana Apolinário (LIP)
      • 11:00
        Role of MPI to HI 10m

        10 min talk as input for round-table discussion.

        Speaker: Nestor Armesto (Universidade de Santiago de Compostela)
      • 11:10
        Double and triple parton scatterings in heavy-ion collisions 10m

        This is a 10' presentation requested for the WG5 discussion session on Friday Oct. 15th.

        Speaker: David d'Enterria (CERN)
      • 11:20
        Role of MPI to HI 10m

        10 min talk as input for round-table discussion.

        Speaker: Leif Lonnblad
      • 11:30
        Role of MPI to HI 10m

        10 min talk as input for round-table discussion.

        Speaker: Andreas Morsch (CERN)
      • 11:40
        Round-table discussion 20m
        Speakers: Andreas Morsch (CERN) , David d'Enterria (CERN) , Leif Lonnblad (Lund) , Nestor Armesto (Universidade de Santiago de Compostela)
    • 12:00 13:30
      lunch 1h 30m
    • 13:30 14:10
      WG1: MB and UE: summary and discussion
      Conveners: Armando Bermudez Martinez (CMS-DESY) , Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF)
      • 13:30
        WG1: summary and discussion (20´+15´) 20m
        Speakers: Armando Bermudez Martinez (CMS-DESY) , Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF)
    • 14:10 14:50
      WG2: Double Parton Scattering: summary and discussion
      Conveners: Ankita Mehta (UHH) , Jonathan Hollar (LIP)
      • 14:10
        WG2: summary and discussion (20´+15´) 20m
        Speakers: Ankita Mehta (UHH) , Jonathan Hollar (LIP)
    • 14:50 15:30
      WG4: small-x and diffraction: summary and discussion
      Conveners: Albert Bursche (South China Normal University) , Martin Hentschinski (Universidad de las Americas Puebla) , Michele Gallinaro (LIP)
      • 14:50
        WG4: summary and discussion (20´+15´) 20m
        Speakers: Albert Bursche (South China Normal University) , Martin Hentschinski (Universidad de las Americas Puebla) , Michele Gallinaro (LIP)
    • 15:30 15:45
      coffee break 15m
    • 15:45 16:25
      WG3: High multiplicities and small systems: summary and discussion
      Conveners: Grigorios Chachamis (LIP) , Simone Amoroso (DESY)
      • 15:45
        WG3: summary and discussion (20´+15´) 20m
        Speakers: Grigorios Chachamis (LIP) , Simone Amoroso (DESY)
    • 16:25 17:05
      WG5: Heavy ions: summary and discussion
      Conveners: Daniel Tapia Takaki (University of Kansas) , Liliana Apolinário (LIP)
      • 16:25
        WG5: summary and discussion (20´+15´) 20m
        Speakers: Daniel Tapia Takaki (University of Kansas) , Liliana Apolinário (LIP)
    • 17:15 17:55
      International Advisory Board 40m
      Speaker: Arthur Marques Moraes (Centro Brasileiro de Pesquisas Físicas - CBPF)