11th International Workshop on Multiple Partonic Interactions at the LHC

Miroslav Myska (Czech Technical University (CZ))

MPI@LHC 2019 is the eleventh 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 is hosted at Department of PhysicsFaculty of Nuclear Sciences and Physical EngineeringCzech Technical University in Prague

The conference will cover the following topics:

  • Minimum Bias, Underlying Event and Monte Carlo generators
  • Double Parton Scattering
  • High multiplicities and small system
  • Diffraction and small x physics
  • Heavy Ion collisions 

Previous editions of the workshop

MPI@LHC'18 Perugia, Italyhttps://indico.cern.ch/event/736470/

MPI@LHC'17 Shimla, Indiahttps://indico.cern.ch/event/625304/

MPI@LHC'16 San Cristóbal de las Casas, Mexicohttps://indico.nucleares.unam.mx/event/1100/timetable/#20161128

MPI@LHC’15 Trieste, Italyhttp://indico.ictp.it/event/a14280/

MPI@LHC'14 Krakow, Polandhttps://indico.cern.ch/event/305160/

MPI@LHC'13 Antwerp, Belgiumhttp://indico.cern.ch/event/231843/

MPI@LHC'12 CERN Geneva, Switzerland:  http://indico.cern.ch/conferenceDisplay.py?confId=184925

MPI@LHC'11 DESY Hamburg, Germany:  http://mpi11.desy.de/

MPI@LHC'10 Glasgow, Scotland:  http://www.mpi2010.physics.gla.ac.uk/

MPI@LHC'08 Perugia, Italy:  http://www.pg.infn.it/mpi08/






This workshop is supported by the project Centre of Advanced Applied Sciences (CAAS) with the number CZ.02.1.01/0.0/0.0/16-019/0000778. CAAS is co-financed by European Union.

    • 09:00 09:10
      Welcome/Introduction 10m
      Speakers: Igor Jex, Dean of FNSPE, CTU in Prague, Miroslav Myska (Czech Technical University (CZ))
    • 09:10 10:30
      Double Parton Scattering
      Convener: Rafal Maciula (Institute of Nuclear Physics PAN)
      • 09:10
        Double parton scattering at CMS 20m

        A summary of results on double parton scattering processes from CMS will be presented. The focus of the talk will lie on the latest result on WW production via double parton scattering. The data set in use is from the Run-II data taking periods in 2016 and 2017, corresponding to an integrated luminosity of 77.4 fb-1. The result constitutes the first evidence of this process, with an observed significance of 3.9 standard deviations. An outlook will be given on this interesting process in order to spark discussion on its interpretation in terms of theoretically more sophisticated models of double parton interactions.

        Speaker: Marc Dünser for the CMS Collaboration (CERN)
      • 09:30
        Studies of double parton scattering at the LHCb 20m

        The talk is going to include the latest LHCb results on searches of double parton scattering (DPS) effects in the data, taken by the experiment in proton-proton collisions during Run1 and Run2 of the LHC operation. The measurements are performed for the different final states and mainly focused on the processes involving heavy quarks, which provide the most precise probing of factorization hypothesis for DPS for gluon-mediated processes.

        Speaker: Daria Savrina for the LHCb Collaboration (M.V. Lomonosov Moscow State University (RU))
      • 09:50
        Double parton scattering in jet production processes 20m

        A composite nature of hadrons leads to a complicated structure of the underlying event in hadronic collisions. In particular it give rise to a possibility to have two hard interactions per one hadron-hadron collision, so called double parton scattering (DPS) phenomenon. Among different possible DPS production processes the four-jet DPS production is of particular interest due to a high jet abundance in proton-proton collisions at the LHC.
        In this talk, I will consider the four-jet DPS production in proton-proton collisions. In particular, I will discuss the impact of the initial and final state radiation on various DPS sensitive distributions as well as various sets of cuts to increase the fraction of DPS events.

        Speaker: Oleh Fedkevych (INFN - National Institute for Nuclear Physics)
      • 10:10
        Models for the energy behaviour of MPS effective cross-section 20m

        We examine currently available data for Double Parton Scattering and discuss the energy behaviour of the extracted effective cross-section. A variety of models is compared with different data sets. We find that processes dominated by gluons initiated DPS, such as 4 jet production, exhibit a rising behaviour as the energy increases. Eikonal models as well as models based on empirical fits to pp elastic cross-section are compared with data.

        Speaker: Dr Giulia Pancheri (INFN Frascati Laboratories)
    • 10:30 11:00
      Break: Coffee Break
    • 11:00 12:30
      MPI & Small-x & diffraction
      Convener: Christine Overgaard Rasmussen (Lund University)
      • 11:00
        MC developments in small-x and diffraction 35m

        In this talk we review current developments regarding small-x and diffractive physics from the viewpoint of Monte Carlo Event Generators. Besides highlighting advances in describing diffractive events we also point out where further work is necessary.

        Speaker: Patrick Kirchgaesser
      • 11:35
        The electron-ion collider – A collider to unravel the mysteries of hadron structure 25m

        Understanding the properties of nuclear matter and its emergence through the underlying partonic structure and dynamics of quarks and gluons requires a new experimental facility in hadronic physics known as the Electron-Ion Collider (EIC). The EIC will address some of the most profound questions concerning the emergence of nuclear properties by precisely imaging gluons and quarks inside protons and nuclei such as the distribution of gluons and quarks in space and momentum, their role in building the nucleon spin and the properties of gluons in nuclei at high energies. This presentation will highlight the capabilities of an EIC to unravel the mysteries of hadron structure at low-x.

        Speaker: Elke-Caroline Aschenauer (BNL)
      • 12:00
        Diffractive Bremsstrahlung in hadronic collisions 30m

        Production of heavy photons (Drell-Yan), gauge bosons, Higgs bosons, heavy flavors and dijets, which is treated within the QCD parton model as a result of hard parton-parton collision, can be considered as a bremsstrahlung process in the target rest frame. In this talk, I will discuss the recent progress and the basic features of the diffractive channels of these processes in the framework of color dipole approach. The main observation is a dramatic breakdown of diffractive QCD factorisation due to the interplay between soft and hard interactions, which dominates these processes. This observation is crucial for phenomenological studies of diffractive reactions in high-energy hadronic collisions.

        Speaker: Roman Pasechnik (Lund university)
    • 12:30 14:00
      Break: Lunch
    • 14:00 15:40
      Monte Carlo, MB & UE
      Convener: Guy Paic (Universidad Nacional Autonoma (MX))
      • 14:00
        Mueller dipole evolution in Pythia 8 20m

        This talk focuses on the recent implementation of the Mueller dipole formalism in Pythia 8. We show how the dipole formalism can be used to assign spatial vertices to the MPIs in Pythia 8. This allows us to study geometric quantities such as initial state eccentricities, connected to flow coefficients measured at the LHC. In this work we show comparisons to pp, pPb and PbPb data from the LHC and briefly discuss the forthcoming extensions to UPCs and eA collisions.

        Speaker: Christine Overgaard Rasmussen (Lund University)
      • 14:20
        MC study of high multiplicity jet- and UE-biased pp collisions at the LHC energies 20m

        New measurements on particle production as a function of the charged-particle multiplicity in pp collisions have been reported by the ALICE Collaboration. The novelty of the results relies on the use of transverse spherocity for event classification in either pencil-like or isotropic events, which turn out to be sensitive to the main hard scattering or underlying event, respectively. Results indicate that the average transverse momentum as a function of multiplicity is higher in jetty-like (low spherocity) events than in isotropic (high spherocity) events. While QCD-inspired generators like EPOS LHC and PYTHIA 8 describe the data for minimum bias and isotropic events, the average $p_{\rm T}$ is overestimated by PYTHIA 8 in high multiplicity jetty-like events.

        In this work the charged particle production in the toward and transverse regions, relative to the leading-charged particle ($p_{\rm T}^{\rm leading}>4$\,GeV/$c$), are studied as a function of the event multiplicity and event transverse spherocity in pp collisions at $\sqrt{s}=13$ TeV. The study is conducted using EPOS LHC and PYTHIA 8. We will show that in the 0-10\% most jetty-like events, the UE is not negligible. The contributions of the jet and underlying event to the average $p_{\rm T}$ of high multiplicity jetty-like and isotropic events will be shown. The auto-correlation effects in both two models will be discussed. In this context, the observed tension between data and PYTHIA 8 will be explained.

        Speaker: Antonio Ortiz Velasquez for the ALICE Collaboration (Universidad Nacional Autonoma (MX))
      • 14:40
        Run 2 results on Minimum Bias and Underlying Event by CMS 20m

        The talk will present the results obtained by the CMS collaboration on minimum bias processes and the so-called underlying event. An overview of what we learned during the whole Run 2 of the LHC will be provided.

        Speaker: Ankita Mehta for the CMS Collaboration (Eötvös University, Budapest)
      • 15:00
        Shoving mechanism in PYTHIA8 20m

        The interaction force between Lund strings contributes to the flow effects in high-multiplicity pp and AA collisions. Hence, it is important to know how much push can this force exert on the strings, whose effects might be observed in the system as a whole. In this talk, we present our shoving mechanism implemented in the Lund string model. This mechanism, along with rope hadronization and colour reconnection processes, makes PYTHIA better equipped to explain collectivity effects in high-multiplicity p-p, p-A and A-A collisions. We present preliminary results of our shoving model on e+e- and p-p angular correlation studies.

        Speaker: Ms Smita Chakraborty (Lund University)
      • 15:20
        MB and MC tuning at LHCb 20m

        Results from LHCb measuring bulk properties of minimum bias events, as well the inelastic cross-section will be summarized. Using these results, a tuning campaign for Pythia 8, specific to the LHCb fiducial volume, is underway and explores some of the newly available colour reconnection models. Some highlights from this tuning campaign will be presented.

        Speaker: Philip Ilten for the LHCb Collaboration (University of Birmingham (GB))
    • 15:40 16:10
      Break: Coffee Break
    • 16:10 17:40
      Heavy Ions
      Convener: Antonin Maire (IPHC - Strasbourg (CNRS-In2p3/Unistra))
      • 16:10
        Rivet as an experiment-theory interface for the heavy-ion community 30m

        The comparison of experimental data and theoretical predictions is crucial for our understanding of the mechanisms for particle production and interactions in hadron collisions at the LHC. The Rivet (Robust Independent Validation of Experiment and Theory) framework was developed for this purpose and is used as a generator-independent system for event generator validation and tuning. It provides a large set of experimental analysis algorithms (called plugins) going along with the published data. Thus, Rivet allows a direct comparison of different generators and experimental data, as well as the preservation of the MC analysis algorithms used.

        Originally developed for validation and tuning of models in high energy physics in pp(bar) and ee collisions, Rivet did not fulfill the requirements of many of the heavy-ion analyses: the latter require features like in-situ calibration steps, comparisons of AA and pp collisions, and binning in global event observables. A dedicated effort of the ALICE collaboration together with the Rivet core team and theorists resulted in the first Rivet release with heavy-ion functionalities. It provides the mentioned features as well as more than 10 analyses implemented as heavy-ion plugins using these features. While the development of Rivet is continuing in order to deal with other conceptual and technical difficulties of such analyses, it already provides an interface for the heavy-ion community to start writing their own analysis plugins.

        Speaker: Przemyslaw Karczmarczyk for the ALICE Collaboration (Warsaw University of Technology (PL))
      • 16:40
        Azimuthal anisotropy of heavy-flavour production with ALICE at the LHC 20m

        Heavy quarks are sensitive probes to test the properties of the Quark-Gluon Plasma (QGP) state formed in heavy-ion collisions since, due to their large masses, they are formed on timescales shorter than the QGP formation time.
        In particular, the measurement of the azimuthal anisotropy of hadrons containing heavy quarks gives insight into the participation of low-momentum heavy quarks in the collective expansion of the system and their possible thermalisation in the medium. Recent measurements of the azimuthal anisotropy in high-multiplicity pp and p–Pb collisions show remarkable similarities with Pb–Pb collisions and suggest the presence of collectivity, whose origin is still debated.
        In addition, due to their formation time, heavy quarks are also ideal candidates to probe the strong magnetic field created in heavy-ion collisions by the charged nucleons of the colliding nuclei that do not participate in the collision. In this context, the measurement of the direct flow coefficient of D mesons will give access to fundamental properties of the QGP.

        In this contribution, the latest measurements of heavy-flavour azimuthal anisotropies in Pb–Pb collisions and in p–Pb collisions at √s_{NN} = 5.02 TeV with ALICE will be presented. The D-meson azimuthal anisotropy measured with an Event-Shape Engineering technique will be also shown to investigate the influence of initial geometry fluctuations on heavy-flavour production.

        Speakers: Dr Grazia Luparello for the ALICE Collaboration (INFN Trieste), Grazia Luparello (Universita e INFN Trieste (IT))
      • 17:00
        Overview of hard and soft probe measurements with STAR at RHIC 40m

        Studies of hot and dense QCD matter created in high energy heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) revealed that the matter resembles properties of strongly coupled liquid with very low viscosity. High statistics data and major upgrades of the STAR experiment opened recently a new era of tomography of the QCD matter at RHIC using hard probes. In particular, the Heavy Flavor Tracker enables precision measurements of open heavy flavor hadrons and the Muon Telescope Detector greatly improves quarkonium measurements. Studies in the heavy flavor sector are accompanied by measurements of jet 
        properties that provide further insights into the partonic energy loss in the QCD matter. RHIC is also uniquely positioned to map the QCD phase diagram by varying the energy as well as species of collided nuclei and dedicated studies to look for the critical point of the QCD phase diagram are pursued. In this talk, an overview of recent results on hard and soft probes in heavy-ion collisions measured by the STAR experiment will be presented.

        Speaker: Jana Bielcikova for the STAR Collaboration (Czech Academy of Sciences (CZ))
    • 17:40 19:10
      Break: Welcome drink
    • 09:00 10:20
      High Multiplicities (small system)
      Convener: Christian Bierlich (Lund University (SE))
      • 09:00
        Particle production and event shape studies: status and new ideas 20m

        Results on hadron production in high-multiplicity proton-proton (pp) and proton-lead (p--Pb) collisions at the LHC energies have revealed the presence of collective phenomena reminiscent to those observed in lead-lead (Pb--Pb) collisions. The bulk particle production in Pb--Pb collisions cannot be calculated from first principles of QCD and instead relies on thermodynamic and hydrodynamic modelling, which assumes a system in a kinetic and chemical equilibrium. On the other hand, some of the collective effects observed in pp collisions can be qualitatively described by phenomenological models, such as multi-partonic interactions (MPI) and color reconnection (CR), or color ropes and shoving. In order to understand the origins of collectivity in pp collisions it is important to isolate the soft regime of QCD, where such effects are pronounced, from the collisions where hard QCD scatterings dominate. Experimentally this can be done using event shape observables such as transverse spherocity $S_{\rm O}$ or self-normalized charged-particle density $R_{\rm T}$. In this talk I will overview the current results from double-differential studies of pp collisions and compare them to predictions from several Monte Carlo generators. In addition, I will discuss the future prospects of the event shape studies.

        Speaker: Vytautas Vislavicius (University of Copenhagen (DK))
      • 09:20
        Improving the selection on MPI using multiplicity and leading charged-particle transverse momentum 20m

        We present a phenomenological study of the number of Multiple Parton Interactions (MPI) as a function of mid-rapidity charged-particle multiplicity and leading transverse momentum ($\it{p_{\rm T}^{\rm {leading}}}$) in proton-proton collisions at $\sqrt{s}$ = 13 TeV using the event generator PYTHIA 8.240. We observe important correlations between leading charged particle $\it{p_{\rm T}}$ and charged particles multiplicity with MPI. Namely, when we combine both quantities the details of the MPI become more visible compared with the selection based purely on multiplicity. The observed effects survive even when the pseudorapidity interval is increased from $|\eta| <$ 1 to $|\eta| <$ 4. Similar results are obtained when a selection on the leading partonic transverse momentum is implemented. We have complemented the study documenting the contribution of quarks and gluons collisions to the different $\it{p_{\rm T}^{{\rm leading}}}$/multiplicity classes.

        Speaker: Dr Aditya Nath Mishra (ICN-UNAM)
      • 09:40
        Particle production of charged and light flavor hadrons, $\pi$, K, $\phi$, p and $\Xi$, as a function of Transverse Spherocity in pp collisions $\sqrt(s) = 13$ TeV with ALICE at the LHC 20m

        The underlying mechanisms of light flavour production are currently not well understood, although they can be described in the framework of different phenomenological models. pQCD models based on hard scatterings,
        such as PYTHIA, describe light flavour production via string-breakings and rope-hadronization.
        Statistical thermal models predict that the production of light flavour particles is driven by extensive quantities (i.e temperature) and by the hadron masses. The results presented here aim to isolate the different components of hadron production via a differential analysis based on the transverse spherocity using data collected with the ALICE detector at the LHC. The transverse spherocity allows one to perform a topological selection of events that are "isotropic" (dominated by multiple soft processes) and "jetty" (where a single hard process is responsible for a significant part of the multiplicity).

        In this contribution we present a study of inclusive charged-particle production, as well as
        identified $\pi$, K, $\phi$, p, and $\Xi$ particle production as a function of charged-particle
        multiplicity density and transverse spherocity at mid-rapidity, $|\eta|<0.8$, in pp collisions at
        $\sqrt(s) = 13$ TeV. The results are presented for two multiplicity estimators covering
        different pseudorapidity regions. The focus of the inclusive charged-particle measurements is average
        $p_{\textrm{T}}$ as a function of multiplicity and transverse spherocity. For identified hadrons,
        transverse momentum spectra and ratios will be presented for high multiplicity events for both
        Finally, the results obtained with ALICE are compared to different model calculations.

        Speaker: Adrian Fereydon Nassirpour (ALICE Collaboration, Lund University (SE))
      • 10:00
        Multiplicity dependent hadron chemistry from dynamical core--corona initialisation 20m

        Strangeness enhancement reported from the ALICE Collaboration [1] is referred to as an indication of the existence of quark-gluon plasma (QGP) in small colliding systems such as p+p and p+Pb collisions. Yield ratios of strange hadron show continuous increase as a function of multiplicity and saturation in averaged Pb+Pb events when the QGP is supposed to be formed. Motivated by this data, we develop a unified and phenomenological description of QGP formation under the ``dynamical initialisation model [2]''. We describe the formation of QGP fluids using the hydrodynamic equation with source terms. Just after the collision of nuclei, partons start traversing in vacuum and depositing their four-momentum dynamically. We generate the QGP fluids assuming the deposited four-momentum suddenly get thermalised, i.e. converted into the source of the QGP fluids.

        In this work, we develop the dynamical initialisation introducing the core--corona picture:
        Local equilibrium is likely to be achieved among highly populated partons due to multi-secondary scatterings, while partons tend to traverse without being QGP components when these are in low-density regions. Under this picture, we dynamically separate the initial partons into the QGP fluids (core: dense/soft components) and surviving partons (corona: dilute/hard components). We utilise the Cooper--Frye formula to obtain final hadron yield from the core, while we perform string fragmentation with PYTHIA [3] for the corona.

        We show the (multi-)strangeness yield ratios monotonically increase with multiplicity due to the competition between core and corona components and successfully reproduce the tendency of experimental data [4]. We also calculate the fraction of fluidized energy as a function of multiplicity from small to large systems and find that if we try to describe the experimental data with our model, there should be sizable contributions from the QGP fluids even in averaged p+p collision events.

        [1] J. Adam et al. [ALICE Collaboration], Nature Phys. 13, 535 (2017).
        [2] M. Okai, K. Kawaguchi, Y. Tachibana and T. Hirano, Phys. Rev. C 95, no. 5, 054914 (2017).
        [3] T. Sjöstrand, S. Mrenna, and P. Z. Skands, Comput. Phys. Commun. 178, 852 (2008)
        [4] Y. Kanakubo, M. Okai, Y. Tachibana and T. Hirano, Progress of Theoretical and Experimental Physics 2018, no.12, 121D01 (2018).

        Speaker: Yuuka Kanakubo (Sophia Univ.)
    • 10:20 10:50
      Break: Coffee Break
    • 10:50 12:40
      Double Parton Scattering
      Convener: Arthur Moraes (CBPF - Brazilian Center for Physics Research (BR))
      • 10:50
        ATLAS results on quarkonia and its associated production 20m

        The associated production of vector boson with quarkonia is a key observable for understanding the quarkonium production mechanisms, including the separation of single and double parton scattering components.
        This talk will present the latest measurements from ATLAS on quarkonium production, including the associated production of W+J/psi.

        Speaker: Maria Smizanska for the ATLAS Collaboration (Lancaster University (GB))
      • 11:10
        Probing double parton scattering via associated open charm and bottom production in ultraperipheral pA collisions 30m

        I will discuss a novel channel for phenomenological studies of the double-parton scattering (DPS) based upon associated production of charm and bottom quark-antiquark pairs in well-separated rapidity intervals in ultra-peripheral high-energy proton-nucleus collisions. This process provides a direct access to the double-gluon distribution in the proton at small-x and enables one to test the factorised DPS pocket formula. I will present the corresponding theoretical predictions for the DPS contribution to this process at typical LHC energies and beyond and validate the use of the energy-independent (but photon momentum fraction dependent) effective cross section.

        Speaker: Roman Pasechnik (Lund university)
      • 11:40
        Double-Parton-Scattering studies with quarkonia 20m

        I will review the status and prospects of studies of Double Parton Scatterings with associated and pair production of quarkonia. This includes J/psi pairs, Upsilon pairs, Upsilon+J/psi, J/Psi+D, Upsilon+D, J/psi+Z and J/psi+W at the LHC and the Tevatron.

        Speaker: Jean-Philippe Lansberg (IPN Orsay, Paris Saclay U. / IN2P3-CNRS)
      • 12:00
        J/psi + Upsilon associated production and prospects to observe a new heavy tetraquark state 20m

        We consider a new mechanism for prompt simultaneous production of $J/\psi$ and $\Upsilon$ mesons in high energy hadronic collisions. The process is considered as a perturbative production of $B_c^{(*)}$ mesons $g{+}g\to B_c^{(*)} {+}\bar{B_c}^{\!\!(*)}$ followed by a long-distance final state interaction that rearranges the quarks to form $J/\psi$ and $\Upsilon$ mesons. Passing from $B_c^{(*)}{+}\bar{B_c}^{\!\!(*)}$ configuration to $J/\psi{+}\Upsilon$ configuration may proceed via a hypothetical resonance state, the tetraquark. The goal of this work is to examine whether the respective cross section is large enough to encourage a direct detection of the tetraquark at the LHC conditions (yes), and whether this hypothesis can help to explain the D0 data without assigning an unusually low value to $\sigma_{\rm eff}$ in the double parton scattering mechanism (no).

        Speaker: Dr Sergey Baranov (P.N.Lebedev Institute of Physics)
      • 12:20
        Double parton distributions and heavy-quark mass effects 20m

        Double parton distributions (DPDs) are an essentialingredient in the computation of the full DPS cross sections. Their numerical handling is complicated by their structure, which depends on more than twice the number of parameters with respect to regular PDFs. Furthermore, in order to make phenomenological predictions for DPS, it is necessary to also include heavy-quark contributions in the calculations, and in some cases the effects of their masses.

        We developed a library called ChiliPDF, which is able to perform the interpolation and evolution of single and double parton distributions with arbitrary input and in a precise and efficient way. Using this library, we produce for the first time evolved DPDs using NNLO DGLAP evolution and matching at the flavor transition scales. We also present some studies and developments regarding the effect of the heavy-quark masses on DPDs, specifically in the case of perturbative splitting from regular PDFs, which happens in the limit of small interpartonic transverse distance.

        Speaker: Mr Riccardo Nagar (Deutsches Elektronen-Synchrotron DESY)
    • 12:40 14:00
      Break: Lunch
    • 14:00 15:00
      Monte Carlo, MB & UE
      Convener: Valentina Mariani (Universita e INFN, Perugia (IT))
      • 14:00
        Bose–Einstein correlations of charged hadrons in proton-proton collisions at the CMS experiment 20m

        Bose-Einstein correlations of charged hadrons provide a tool to investigate the space-time structure of the hadron emitting source. In CMS we measure charged hadrons over a broad multiplicity range, from a few particles up to about 250 reconstructed charged hadrons in proton-proton collisions 13 TeV. Different analysis techniques were used to investigate the dependence on simulations when removing the non-Bose-Einstein background from the correlation functions. The measured correlation radii were studied as functions of particle multiplicity and average pair transverse momentum. The results were compared to theoretical predictions, pointing out interesting similarities and differences in hadron production in heavy ion collisions as well.

        Speaker: Mate Csanad for the CMS Collaboration (Eotvos University, Budapest)
      • 14:20
        Monte Carlo Modelling and Tuning in CMS 20m

        A new set of CMS underlying-event tunes is presented for the PYTHIA 8 event generator. The tunes use the NNPDF3.1 parton distribution functions at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) order in perturbative QCD, and the strong coupling amd PDF evolution at LO or NLO. Comparisons of the predictions of the new tunes are provided for observables sensitive to the global underlying event, to soft multiparton interactions, and to double-parton scattering contributions, as well as for observables measured in various final states, such as multijet, Drell-Yan, and top quark-antiquark pair production. The measurements characterizing the properties of the underlying event in top quark pair production and the Drell-Yan processes are also presented.

        Speaker: Dr Vieri Candelise for the CMS Collaboration (Universita e INFN Trieste (IT))
      • 14:40
        Spacetime Colour Reconnection in Herwig 7 20m

        We present a model for generating spacetime coordinates in the Monte Carlo event generator Herwig 7, and perform colour reconnection by minimizing a boost-invariant distance measure of the system. We compare the model to a series of soft physics observables. We find reasonable agreement with the data, suggesting that pp-collider colour reconnection may be able to be applied in larger systems.

        Speaker: Andrzej Konrad Siodmok (Polish Academy of Sciences (PL))
    • 15:00 15:25
      MPI & Small-x & diffraction
      Convener: Christine Overgaard Rasmussen (Lund University)
      • 15:00
        Measurements of single diffraction using forward proton tagging at ATLAS 25m

        Inclusive single diffractive dissociation (pp->pX) is studied using data collected by the
        ATLAS experiment at the LHC. The intact proton is reconstructed and measured in the
        ALFA forward spectrometer, while charged particles from the dissociative system (X)
        are reconstructed and measured using the ATLAS inner tracking detector and
        calorimeters. Differential cross sections are presented as a function of the proton
        fractional momentum loss, the four-momentum transfer squared, and the size of a
        rapidity gap measured from the edge of the ATLAS calorimeters. The results are
        interpreted in the framework of Regge phenomenology.

        Speaker: Maciej Trzebinski for the ATLAS Collaboration (Polish Academy of Sciences (PL))
    • 15:25 15:55
      Break: Coffee Break
    • 15:55 17:35
      MPI & Small-x & diffraction
      Convener: Christine Overgaard Rasmussen (Lund University)
      • 15:55
        Diffractive excitation in pp and pA scattering at high energies 25m

        We present an update of the Miettinen-Pumplim (MP) model for diffractive excitation for proton-proton ($pp$) and antiproton-proton ($\bar{p}p$) scattering considering recent LHC data. The energy dependence of the total, elastic, and diffractive cross sections are analyzed and compared to data. The implications of the diffractive excitation in proton-nucleus ($pA$) collisions are also discussed for different nuclei. We used the MP model to derive the main quantities present in the treatment of the diffractive excitation in $pA$ collisions. We demonstrate that the effect of fluctuations decreases at larger energies and heavier nuclei. We also compare our results with the predictions for the proton dissociation induced by photon interactions.

        Speaker: Dr P.V.R.G. Silva (Universidade Federal de Pelotas)
      • 16:20
        CMS results on diffraction and exclusive production 25m

        An overview of recent diffractive and exclusive measurements with CMS is given. Results on jet-gap-jet event topologies are shown, together with central exclusive p-p production. Diffractive dijet production is measured with proton tagging in pp collisions. In addition, recent results on exclusive rho0 and upsilon production in pPb collisions at 5.02 TeV are presented.

        Speaker: Ankita Mehta for the CMS Collaboration (Eötvös University, Budapest)
      • 16:45
        A complete picture of photon-initiated production at the LHC 25m

        In this talk we present results of a new calculation and Monte Carlo implementation of photon-initiated production in LHC proton-proton collisions. This includes a precise, differential evaluation of both inclusive and semi-exclusive channels, that is with and without rapidity gaps in the final state. Details of the underlying formalism as well as phenomenological results will be presented.

        Speaker: Dr Lucian Harland-Lang (University of Oxford)
      • 17:10
        Very-forward neutral particles production measured by the LHCf experiment 25m

        The LHC-forward (LHCf) experiment is dedicated to the measurement of the very forward neutral particle production cross section in proton-proton and proton-lead collisions at the Large Hadron Collider at CERN. The experiment employs two independent detectors, named Arm1 and Arm2, which are placed on opposite sides along the beam line approximately 140 meters away from the interaction point of the ATLAS experiment. Both detectors are composed of two sampling calorimeters. Each calorimeter employs 16 Gd$_2$SiO$_5$ (GSO) scintillator layers alternated with tungsten layers. The transverse impact position of the incident particle is measured with GSO bars in Arm1 and silicon micro-strip detectors in Arm2. The experiment can measure particles with pseudorapidity greater than 8.4, up to zero-degree.
        The measurement of the very forward secondary particles produced in high energy hadronic collisions is strictly correlated with the study of the ultra-high-energy cosmic rays (UHECRs). Since UHECRs can only be measured with ground-based experiments, detailed Monte Carlo simulations of the shower of secondary particles produced by the interaction of the primary cosmic ray with the atmosphere (the so called “air-showers”) must be employed. Most of the energy flow of an air-shower is concentrated in the very-forward region where soft quantum chromodynamics processes dominate, so phenomenological hadronic interaction models must be used in the simulations. The discrepancy between the predictions of different models gives the main contribution to the uncertainty on the measurements of UHECRs spectrum and mass composition. The tuning of hadronic interaction models in the very-forward region with data of accelerator experiments can therefore reduce the systematic uncertainty of UHECRs measurements.
        In this contribution the LHCf main physics results from the Run II of LHC will be presented. At first, the results on photon and neutron production cross section in p-p collisions at 13 TeV will be shown. The comparison of the experimental data with some of the commonly used hadronic interaction models (DPMJET, EPOS, PYTHIA, QGSJET and SIBYLL) will be also discussed. Then, the motivation of the combined analysis of LHCf with the ATLAS experiment will be explained. In particular, the number of tracks recorded in ATLAS central detectors are used to discriminate low-mass diffraction interactions. The preliminary results of LHCf-ATLAS combined photon analysis will then be presented and compared with models predictions. Finally, the first preliminary results of π0 transverse momentum spectrum in proton-proton collisions at 13 TeV will be shown.
        Even if there is not a single hadronic interaction model with a good agreement with data in the whole energy and pseudorapidity range, measured data lie mostly between models predictions. The tuning of hadronic interaction models using the experimental data from accelerator experiments, in particular in the very-forward region, can improve the precision of the Monte Carlo simulations and reduce the discrepancy between different models.

        Speaker: Alessio Tiberio for the LHCf Collaboration (INFN, Firenze (IT))
    • 09:00 10:40
      High Multiplicities (small system)
      Convener: Christian Bierlich (Lund University (SE))
      • 09:00
        Collectivity in small systems with the CMS experiment 20m

        Collectivity in small systems with the CMS experiment

        Speaker: Prabhat Ranjan Pujahari for the CMS Collaboration (Indian Institute of Technology Madras (IN))
      • 09:20
        Interferometric Signatures of Hydrodynamics in Small Systems 20m

        Particle interferometry has proven to be an indispensable tool in probing the space-time evolution of femtoscopic collision systems. In this talk, I show how hydrodynamic predictions for the space-time evolution of high-multiplicity $pp$ and $p+$Pb collisions can be tested against interferometric observables designed to probe their size and shape. In particular, I consider how the dependence of these observables on the transverse momentum $K_T$ and the multiplicity $dN^{\mathrm{ch}}/d\eta$ may reflect the hydrodynamic nature of the evolving system.

        Speaker: Christopher Plumberg
      • 09:40
        Measurement of colour flow using jet-pull observables in top-quark-antiquark events with the ATLAS experiment at √s = 13 TeV 20m

        Measurements of distributions of two weighted angular moments derived from jet
        constituents are presented. The jet-pull angle and the jet-pull magnitude, both of
        which are derived from the jet-pull angular moment, encode the colour connections between
        partons that seed the jets.
        The measurements are performed in top-quark-antiquark events with one leptonically
        decaying W boson and one hadronically decaying W boson, using 36.1 fb-1 of pp collision
        data recorded by the ATLAS detector at a centre-of-mass energy of 13 TeV delivered by the
        Large Hadron Collider. The observables are measured for two dijet systems, corresponding
        to the colour-connected daughters of the W boson and the two b-jets from the top-quark
        decays. To allow the comparison of the measured distributions to colour model predictions,
        the measured distributions are unfolded to particle level, after correcting for experimental
        effects introduced by the detector. While good agreement can be found for some
        combinations of predictions and observables, none of the predictions describes the data well
        across all observables.
        Reference: TOPQ-2017-13,

        Speaker: Yvonne Reinhild Peters for the ATLAS Collaboration
      • 10:00
        Hadronic Rescattering in Pythia 20m

        We have developed a framework for hadronic rescattering in Pythia. Our goal is to study how rescattering can account for observed phenomena such as flow, jet quenching, etc. In this presentation I will outline our algorithm and present some preliminary results.

        Speaker: Marius Utheim (Lund University)
      • 10:20
        Bulk vs Shear viscosity on high multiplicity small collision systems 20m

        High multiplicity events in heavy-ion collisions are still under debate whether they produce an extremely hot and dense matter similar to the QGP formed on heavy atomic nuclei collisions. One of the main characteristics of the formation of this state is that it behaves like a near-perfect fluid, with very tiny shear viscosity. We present an estimate of the shear and bulk viscosity properties of the high multiplicity events in p-Pb and p-p collisions at the current LHC energies in the framework of the color of sources. Moreover, the effects of non-thermal equilibrium shown to be relevant. A comparison among the predictions of the relativistic hydrodynamics and the limits in conformal theory is also shown.

        Speaker: Irais Bautista Guzman (Autonomous University of Puebla (MX))
    • 10:40 11:10
      Break: Coffee Break
    • 11:10 12:40
      Heavy Ions
      Convener: Karel Safarik (Czech Technical University (CZ))
      • 11:10
        Multi-particle Bose-Einstein correlations in Au+Au collisions at PHENIX 20m

        Exploration of the rich structure of the QCD phase diagram is an important topic in the RHIC heavy ion program whose ultimate goal is to discover the critical endpoint. Investigation of the space-time structure of hadron emissions at various phase transition points using Bose-Einstein correlation of identical bosons will provide insight on the location of the critical endpoint. PHENIX has performed comprehensive measurements of the Bose-Einstein correlation in Au+Au collisions at $\sqrt{s_{NN}}$ = 15, 19, 27, 39, 62.4, and 200 GeV, where we incorporated Levy-type source function to describe the measured correlation functions. We also extended our analysis from two particles to three particle correlations to characterize the nature of the hadron emission source. We put particular focus on one of the parameters in the Levy-type source function, the index of stability $\alpha$, which is related to one of the critical exponents (the so-called correlation exponent $\eta$). We have measured its collision energy and centrality dependence. The three particle correlations confirmed the findings of the two-particle correlations, and also provided insight on pion production mechanism beyond Core-Halo models. We will present the latest PHENIX results on the multi-particle Bose-Einstein correlation, and discuss its physics interpretation.

        Speaker: Mate Csanad for the PHENIX Collaboration (Eotvos University, Budapest)
      • 11:30
        Dynamical description of heavy quarks and electromagnetic probes in heavy-ion collisions at ultra-relativistic energies 20m

        Relativistic heavy-ion collisions produce extremely hot dense matter.
        Heavy flavor and electromagnetic particles are promising probes to
        investigate the properties of the hot dense matter. The
        parton-hadron-string dynamics (PHSD) is a Boltzmann-type transport code,
        but it further includes the off-shellness of particles based on
        Kadanoff-Baym equations. The equation-of-state and shear viscosity of a
        partonic matter from lattice QCD calculations are implemented in the PHSD.
        We use the PHSD to show how heavy flavor mesons and dileptons are produced
        and modified through the interactions with hot dense matter in
        relativistic heavy-ion collisions from the SPS to the LHC energies. We
        have found that not only cold nuclear matter effects such as
        (anti)shadowing but also hot nuclear matter effects significantly modify
        the production of heavy flavor particles in relativistic heavy-ion
        collisions. While intermediate-mass dilepton is mainly contributed from
        heavy flavor pair in high-energy heavy-ion collisions, the contribution
        from partonic interactions becomes more dominant as collision energy
        decreases. It implies that intermediate-mass dilepton in low-energy
        heavy-ion collisions has a possibility to carry the information of
        partonic matter.

        Speaker: Dr Taesoo Song (GSI)
      • 11:50
        Flow as an interplay of fluid-like and non-fluid like excitations 20m

        To study the microscopic structure of quark-gluon plasma produced in hadronic collisions, data must be confronted with models that go beyond fluid dynamics. In order to illustrate the importance of non-fluid like excitations in small systems such as pp and pA collisions, I shall discuss the interplay of fluid-like and non-fluid like excitations in a simple kinetic theory model that encompasses fluid dynamics but contains also particle-like excitations in a boost invariant setting with no symmetries in the transverse plane and with large initial momentum asymmetries. This kinetic theory is confronted with data on azimuthal flow coefficients over a wide centrality range in PbPb collisions at the LHC, in AuAu collisions at RHIC, and in pPb collisions at the LHC. In this way, I shall present the evidence that non-hydrodynamic excitations make the dominant contribution to collective flow signals in pPb collisions at the LHC and contribute significantly to flow in peripheral nucleus-nucleus collisions, while fluid-like excitations dominate collectivity in central nucleus-nucleus collisions at collider energies.

        Speaker: Bin Wu (CERN)
      • 12:10
        Overlapping interests between heavy ions and small systems 30m

        Open discussion.

        Speakers: Antonin Maire (IPHC - Strasbourg (CNRS-In2p3/Unistra)), Christian Bierlich (Lund University (SE)), Karel Safarik (Czech Technical University (CZ)), Valentina Zaccolo (Universita e INFN Trieste (IT))
    • 12:40 13:30
      Break: Lunch
    • 13:30 15:30
      Guided Tour 2h
    • 18:00 19:00
      Staropramen Brewery - exhibition & beer tasting 1h

      Visitor Center of Staropramen Brewery, Pivovarska 9

    • 19:00 22:00
      Staropramen Brewery - Conference Dinner 3h

      Visitor Center of Staropramen Brewery, Pivovarska 9

    • 08:40 11:00
      Monte Carlo, MB & UE
      Convener: Philip Ilten (University of Birmingham (GB))
      • 09:30
        Particle physics in extensive air shower cascades 30m

        With current large cosmic ray observatories, precise data of extensive air shower cascades is recorded up to primary particle energies of 10^{20}eV. While there is significant progress in understanding cosmic rays in general, and also particle physics in the air shower cascades, there are also tantalizing open questions. The most interesting one is the "muon mystery", which is a strong hint for particle physics beyond the standard description in these cascades at ultra-high energies. The connection between particle physics and cosmic ray air shower observations is presented and discussed. The relation to relevant LHC measurements is highlighted.

        Speaker: Ralf Ulrich (KIT - Karlsruhe Institute of Technology (DE))
      • 10:00
        Production of identified light flavour hadrons as a function of underlying event activity in pp collisions with the ALICE detetector 20m

        Various recent measurements of high-multiplicity pp and p-A collisions at LHC energies have revealed, surprisingly, that these small collision systems exhibit some features of the quark-gluon-plasma, e.g. collective behaviour and strangeness enhancement, formerly thought to be achievable only in heavy-ion collisions. A promising method to narrow down the origin of this behaviour is to study the effect of Multi-Parton Interactions (MPIs). As proposed in: “Probing collective effects in hadronisation with the extremes of the underlying event” by T. Martin, P. Skands, and S. Farrington (Eur. Phys. J. C (2016) 76, 299), the mean number of MPIs can be accessed experimentally through the self-normalised charged particle density in the Transverse region where the Underlying Event (UE) dominates: $R_{\rm T} = N_{\rm Ch,Transverse}/\langle N_{\rm Ch,Transverse} \rangle$.

        The study of particle production as a function of $R_{\rm T}$ would reveal whether, e.g., the properties of “low-UE” events $(R_{\rm T}\rightarrow 0)$ are compatible with equivalent measurements in $e^{+}e^{-}$ collisions (jet universality) and whether the scaling behaviour towards “high-UE” $(R_{\rm T}\rightarrow 1)$ events exhibits properties of non-trivial soft-QCD dynamics.
        In this contribution, the $p_{\rm T}$ spectra of $\pi,{\rm K},{\rm p},\phi~{\rm and}~\Xi$ as function of $R_{\rm T}$ are presented in pp collisions at $\sqrt{s}=13~{\rm TeV}$. Moreover, the $p_{\rm T}$-differential particle ratios as function of $R_{\rm T}$ in the Towards (jet region) and Transverse regions are contrasted. This discussion will be complemented with UE measurements at the same collision energy.

        Speaker: Omar Vazquez Rueda for the ALICE Collaboration (Lund University (SE))
      • 10:20
        Update on Herwig 7 20m

        Recent progress in the development of the general purpose Monte Carlo generator Herwig 7 will be presented. A focus will be given to progress in modeling underlying event and minimum bias.

        Speaker: Stefan Gieseke (Karlsruhe Institute of Technology)
      • 10:40
        The underlying event in Pythia in function of multiplicity at 13 TeV 20m

        The correlation between the near side and transverse side has been studied with Pythia. Strong correlations between the two regions occur at high multiplicities of above dN/deta of 50 charged particles. The changes occurring in the spectra obtained subtracting the transverse side spectra are reported. We conclude that the results indicate the possibility of parton energy loss in pp collisions.

        Speaker: Guy Paic (Universidad Nacional Autonoma (MX))
    • 11:00 11:30
      Break: Coffee Break
    • 11:30 12:45
      MPI & Small-x & diffraction
      Convener: Radek Zlebcik (Deutsches Elektronen-Synchrotron (DE))
      • 11:30
        Saturation in the impact-parameter plane through vector meson photoproduction 25m

        Up to now, searches for saturation have concentrated in the the small-x behaviour of QCD. Here we add the transverse dimension to this type of studies. We present a model of hadrons with an energy-dependent structure in the transverse plane made of hot spot, regions of high gluonic density. Using this model and the colour-dipole formalism we compute the diffractive photoproduction of vector mesons off protons and show that the dissociative cross section offers a new signature of saturation in the impact-parameter plane. We compare our results to HERA and LHC data and predict that future electron-ion colliders, like JLEIC, eRHIC and LHeC, will be able to map the scale dependece of the associated saturation scale using real and virtual photons as well as different vector mesons.
        This work is based on results published in Phys.Lett. B766 (2017) 186-191, Nucl.Phys. B934 (2018) 330-340, and Phys. Rev. D 99, 034025 (2019).

        Speaker: Prof. Jesus Guillermo Contreras Nuno (Czech Technical University (CZ))
      • 11:55
        Determination of proton parton distribution functions using ATLAS data 25m

        We present fits to determine parton distribution functions (PDFs) using top-antitop,
        inclusive W/Z-boson, as well as W+ and W− boson production measurements in
        association with jets from ATLAS, in combination with deep-inelastic scattering data
        from HERA. The ATLAS W and Z boson data exhibit sensitivity to the valence quark
        distributions and the light quark sea composition, whereas the top-quark pair production
        data have sensitivity to the gluon distribution. The impact of the top-antitop production
        data is increased by fitting several distributions simultaneously, with the full information
        on the systematic and statistical correlations between data points. The parton
        distribution functions extracted using W+jets data show an improved determination of
        the high-x sea-quark densities, while confirming the unsuppressed strange-quark
        density at lower x<0.02 found by previous ATLAS analyses.

        Speaker: Josef Pacalt for the ATLAS Collaboration (Palacky University (CZ))
      • 12:20
        $\eta_c$(1S) and $\eta_c$(2S) production at the LHC 25m

        We present results of calculations of cross sections for production of $\eta_c$(1S)
        and $\eta_c$(2S) for the LHC for $\sqrt{s}$ = 7, 8, 13 TeV.
        The calculations are performed within $k_t$-factorization approach
        for different unintegrated gluon distributions from the literature.
        Some of UGDFs include saturation effects.
        We discuss effect of the transition $g^* g^* \to \eta_c$ form factors obtained
        from $c \bar c$ wave functions.
        The results are compared with existing LHCb data for $\eta_c$(1S).
        A range of $x_1, x_2$ and $k_{1t}, k_{2t}$ will be discussed.
        A comment on UGDFs will be made.

        Speaker: Antoni Szczurek (Institute of Nuclear Physics)
    • 12:45 14:00
      Break: Lunch
    • 14:00 15:45
      Double Parton Scattering
      Convener: Daria Savrina (M.V. Lomonosov Moscow State University (RU))
      • 14:00
        Transverse partonic proton structure via double parton scattering at the LHC 25m

        Here we present our studies on the so called double parton distribution functions (dPDFs) and transverse proton structure. Double PDFs appear in the double parton scattering (DPS) cross section in high energy proton-proton and proton nucleus collisions. These new distributions represent a novel and promising complementary tool, w.r.t. TMDs and GPDs, to access the 3D partonic structure of the proton. In fact, dPDFs encode double parton correlations in hadrons which cannot be accessed through, e.g., GPDs. However, up to date, dPDFs are almost unknown, in particular, in its dependence on the transverse distance of partons. In this scenario we consider model calculations in order to investigate the impact of double correlations in dPDFs. We considered a fully relativistic treatment by using the Light-Front approach [1]. In this framework, we showed how dynamical
        correlations, induced by the used model, prevent the factorisation of dPDFs in terms of standard PDFs, a common assumption in experimental analyses. We focus our attention also in correlations induced by relativistic effects [2]. However, since dPDFs cannot be directly observed in DPS, we investigated the impact of double correlations effects in the so called effective cross section, $\sigma_{eff}$, an essential experimental ingredient for the comprehension of the role of DPS in proton-proton collisions. To this aim, dPDFs have been evolved at the experimental momentum scales through the pQCD evolution procedure. We show how the $x$ dependence of $\sigma_{eff}$, being $x$ the longitudinal momentum fraction carried by a parton inside the hadron, can be interpreted as the cleanest evidence of partonic correlations [3]. We have also calculated the DPS cross section for the same sign $W$ pair production process, a golden channel to observe DPS at the LHC. In this analysis, as non perturbative input, dPDFs, evaluated within a constituent quark model, have been used. We showed that partonic correlations could be observed in next LHC run [4]. Furthermore, since indications on the magnitudo of $\sigma_{eff}$ are available, we also demonstrated how the mean value of $\sigma_{eff}$ can be related to the mean partonic distance between two parton active in a DPS process [5,6]. Such a procedure allows to link the mean value of an experimental observable to the transverse proton structure.

        [1] M. Rinaldi et al PRD 87, 114021 (2013); M. Rinaldi et al JHEP 12, 028 (2015); M. Rinaldi et al JHEP 10, 063 (2016) and M. Rinaldi et al PRD 95, 034040 (2017).
        [2] M. Rinaldi and F. A. Ceccopieri, Phys. Rev. D 95, no. 3, 034040 (2017)
        [3] M. Rinaldi et al PLB 752,40 (2016) and M. Traini et al PLB 768, 270 (2017)
        [4] F. A. Ceccopieri et al PRD 95, 114030 (2017).
        [5] M. Rinaldi et al, PRD 97, 071501 (2018).
        [6] M. Rinaldi and F. A. Ceccopieri, JHEP 09, 097 (2019).

        Speaker: Dr Matteo Rinaldi (Perugia University and INFN, Perugia)
      • 14:25
        Double Parton Distributions for the Nucleon on the Lattice 20m

        Double parton distributions (DPDs) are an important piece in the descriptions of double hard interactions. On the lattice we calculate correlation functions of two local quark currents, which can be related to Mellin moments of DPDs. For the first moment we calculate all contributing Wick contractions for the nucleon (proton), considering several channels corresponding to the quark polarisation. Furthermore, we test to what extend a factorization into a convolution of generalized parton distributions (GPDs) is valid.

        Speaker: Christian Zimmermann
      • 14:45
        W+dijet production in pA collisions via DPS revisited 20m

        W boson creation associated with dijet production is a promising channel to study double parton interactions at the LHC. In this talk we review and update predictions for the W+jets signal in proton lead collisions and discuss a new method which could give access to longitudinal and/or transverse structure of the proton.

        Speaker: Federico Alberto Ceccopieri (Universita & INFN, Milano-Bicocca (IT))
      • 15:05
        Double parton distributions: evolution, initial conditions and transverse momentum dependence 20m

        I will present results of my investigations on the topics enumerated in the title based on my joint work with my collaborators.

        Speaker: Krzysztof Golec-Biernat (Institute of Nuclear Physics, Cracow)
      • 15:25
        Simulating Double Parton Scattering with dShower 20m

        In this talk, a new Monte-Carlo simulation of double parton scattering (DPS) at parton level is presented. In this simulation, the dynamics of the 1→2 perturbative splittings is consistently included, with the impact-parameter dependence taken into account. The evolution is performed using an angular-ordered parton shower which is combined with a set of double parton distributions that depend explicitly on the inter-parton distance. We present some results from an illustrative study in the context of same-sign WW production at the LHC. In several distributions we see differences compared to DPS models in Herwig, Pythia, and the DPS "pocket formula".

        Speakers: Baptiste Cabouat (University of Manchester), Jonathan Richard Gaunt (CERN)
    • 15:45 16:15
      Break: Coffee Break
    • 16:15 18:05
      High Multiplicities (small system)
      Convener: Valentina Zaccolo (Universita e INFN Trieste (IT))
      • 16:15
        Hadronization of Deconfinement Matter in Terms of First-Order Phase Transition 30m

        The hadronization of the deconfined matter arising in high-energy particle collisions is considered in terms of the first kind phase transition in the multiple flux tube approach. Based on the compactification of the standard (3+1) chromodynamics into $ QCD_{xy} + QCD_{zt}$, the rate of hadron production in particle collisions with respect to both the rapidity and $p_T$ distributions is derived in the flux tube approach. The obtained rate strongly depends on the energy of the colliding particles, number of tubes, hadron mass as well as on the temperature of the confinement-deconfinement phase transition. Under the concept of the longitudinal dominance and the transverse confinement in a flux tube, and provided that the hadronization process is governed by the phase transition of the first kind, the hadron rate is obtained in the explicit form in the multiple tube approach. In the case of the pion production in $pp$ collisions we obtain a good agreement to the experimental results on the pion yield with respect to both the rapidity and $p_T$ distributions.

        Speaker: Prof. Andrew Koshelkin (National Research Nuclear University)
      • 16:45
        Charged particle multiplicity dependence of quarkonium production measured by the STAR experiment 20m

        Recently, an interesting faster than linear dependence of quarkonium production on charged particle multiplicity in p+p collisions has been observed. This can be used to study basic particle production mechanism and relation between soft and hard QCD processes. Such a strong increase of normalized particle yield from hard processes with respect to normalized charged particle multiplicity may be a sign of saturation effects, string percolation or multiple parton interactions. In order to distinguish among these scenarios, the dependence of quarkonium production on charged particle multiplicity needs to be measured in different $p_{T}$ ranges and at different collision energies.

        In this presentation, the studies of relation between normalized quarkonium yields and normalized charged particle multiplicity in p+p collisions, measured by the STAR experiment, will be presented. These include the results on $J/\psi$ production both at $\sqrt{s}=200\:\mathrm{GeV}$ and at $\sqrt{s}=500\:\mathrm{GeV}$. At $\sqrt{s}=500\:\mathrm{GeV}$ measurements of $\Upsilon$ production will also be shown. The data are shown for different integrated $p_{T}$ ranges $p_{T}>0, p_{T}>1.5$ and $p_{T}>4\:\mathrm{GeV/c}$. All these results will be compared to model calculations. In addition, prospects for further studies at the STAR experiment will also be discussed.

        Speaker: Dr Leszek Kosarzewski for the STAR Collaboration (Czech Technical University in Prague)
      • 17:05
        Quarkonium measurements in small systems at the LHC 20m

        At the LHC energies Multiple Parton Interactions (MPI) are expected to affect not only processes involving soft particle production, but also the hard momentum scales relevant for the production of heavy quarks, such as charm and beauty. Quarkonium measurements in high-multiplicity proton-proton (pp) collisions can shed light on the role of MPI at such hard momentum scales, as well as on the interplay between hard and soft particle production mechanisms.
        In this contribution we will discuss the latest results from LHC collaborations on quarkonium production measurements as a function of the charged particle multiplicity in small systems. In particular we will focus on results in pp collisions for center-of-mass energies ranging from 2.76 TeV to 13 TeV and based on multiplicity estimators covering different pseudorapidity regions, in several rapidity and transverse momentum ranges of quarkonium states. Similar measurements in p--Pb collisions at center-of-mass energies of $\sqrt{s_{\rm NN}} =$ 5.02 and 8.16 TeV will also be shown. We will discuss these results together with models that implement MPI and some other different theoretical calculations.

        Speaker: Fiorella Fionda (University of Bergen (NO))
      • 17:25
        Evolution of light- and heavy-flavor hadron production in pp collisions from low to high multiplicity at ALICE 20m

        Measurements of the production of light- and heavy-flavor hadrons are of great importance for studies of the matter produced in high-energy collisions. The ALICE experiment has excellent tracking and particle identification capabilities, which have been used to measure a wide variety of hadrons as a function of multiplicity in pp collisions. Studies of light- and heavy-flavor hadrons in high-multiplicity pp collisions have revealed intriguing qualitative similarities to observations in larger collision systems. An overview of the multiplicity dependence of light- and heavy-flavor hadron production in pp collisions at LHC energies will be presented. Topics covered will include strangeness enhancement, the production of light (anti-)nuclei and hadronic resonances, the enhancement of baryon production at intermediate transverse momenta, and charm production. These results will be compared to phenomenological models, with an emphasis on the effects of multiple partonic interactions, as well as results from other collision systems and energy regimes.

        Speaker: Dr Barbara Antonina Trzeciak for the ALICE Collaboration (Czech Technical University in Prague)
      • 17:45
        Identified-hadron pt spectra and collectivity in small systems 20m

        Certain data features that were attributed to quark-gluon plasma (QGP) formation in more-central A-A collisions -- evidence for radial flow and jet quenching in pt spectra, v2, v3, etc. in azimuth correlations, one or two "ridge" structures in long-range angular correlations -- have more recently been observed in high-multiplicity p-A and even p-p collisions. Arguing by analogy with A-A collisions it is suggested that a flowing dense medium or QGP may be formed even in small collision systems. Alternatively, one could argue that data features appearing in small low-density systems should not be associated with QGP, and alternative explanations are required for any collision system. In this talk I focus on evidence (or not) for radial flow and jet modification in pt spectra from several collision systems. I present a comparison of identified-hadron (PID) pt spectra from p-p, p-Pb, Au-Au and Pb-Pb collisions. The PID spectra are described with a two-component (soft + hard) model of hadron production. To the statistical limits of spectrum data radial flow is excluded from p-p and p-Pb spectra for any charge multiplicity, and is unlikely in A-A collisions as well. Jet modification is also excluded from p-p and p-Pb collisions, whereas strong modification is evident in more-central A-A collisions as has long been evident. The combined results suggest that QGP formation can be questioned for any collision system and that an alternative non-QGP explanation is required for v2 data.

        Speaker: Thomas Trainor
    • 09:00 09:30
      MPI & Small-x & diffraction
      • 09:00
        WG4 (MPI&Low-x&Diffraction) - Summary 15m
        Speakers: Christine Overgaard Rasmussen (Lund University), Radek Zlebcik (Deutsches Elektronen-Synchrotron (DE))
      • 09:15
        WG4 (MPI&Low-x&Diffraction) - Discussion 15m
        Speakers: Christine Overgaard Rasmussen (Lund University), Radek Zlebcik (Deutsches Elektronen-Synchrotron (DE))
    • 09:30 10:00
      Double Parton Scattering
      • 09:30
        WG2 (Double Parton Scattering) - Summary 15m
        Speakers: Arthur Moraes (CBPF - Brazilian Center for Physics Research (BR)), Daria Savrina (M.V. Lomonosov Moscow State University (RU)), Rafal Maciula (Institute of Nuclear Physics PAN)
      • 09:45
        WG2 (Double Parton Scattering) - Discussion 15m
        Speakers: Arthur Moraes (CBPF - Brazilian Center for Physics Research (BR)), Daria Savrina (M.V. Lomonosov Moscow State University (RU)), Rafal Maciula (Institute of Nuclear Physics PAN)
    • 10:00 10:30
      Monte Carlo, MB & UE
      • 10:00
        WG1 (MC&UE&MB) - Summary 15m
        Speakers: Guy Paic (Universidad Nacional Autonoma (MX)), Philip Ilten (University of Birmingham (GB)), Valentina Mariani (Universita e INFN, Perugia (IT))
      • 10:15
        WG1 (MC&UE&MB) - Discussion 15m
        Speakers: Guy Paic (Universidad Nacional Autonoma (MX)), Philip Ilten (University of Birmingham (GB)), Valentina Mariani (Universita e INFN, Perugia (IT))
    • 10:30 11:00
      Break: Coffee Break
    • 11:00 11:30
      Heavy Ions
      • 11:00
        WG5 (Heavy Ion) - Summary 15m
        Speakers: Antonin Maire (IPHC - Strasbourg (CNRS-In2p3/Unistra)), Karel Safarik (Czech Technical University (CZ))
      • 11:15
        WG5 (Heavy Ion) - Discussion 15m
        Speakers: Antonin Maire (IPHC - Strasbourg (CNRS-In2p3/Unistra)), Karel Safarik (Czech Technical University (CZ))
    • 11:30 12:00
      High Multiplicities (small system)
      • 11:30
        WG3 (High Multiplicity) - Summary 15m
        Speakers: Christian Bierlich (Lund University (SE)), Valentina Zaccolo (Universita e INFN Trieste (IT))
      • 11:45
        WG3 (High Multiplicity) - Discussion 15m
        Speakers: Christian Bierlich (Lund University (SE)), Valentina Zaccolo (Universita e INFN Trieste (IT))
    • 12:00 13:00
      Break: Lunch