COST Workshop on Interplay of hard and soft QCD probes for collectivity in heavy-ion collisions

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Monday, 25 February 201911:0011:00 - 12:30Room: Lundmarksalen12:30 Jets in pQCD - Stefan Prestel (Lund U.)Jets in pQCD
- Stefan Prestel (Lund U.)

12:30 - 13:30Room: Lundmarksalen13:30 PYTHIA and other MC generators for pp physics - Torbjörn Sjöstrand (Lund U.)PYTHIA and other MC generators for pp physics- Torbjörn Sjöstrand (Lund U.)

13:30 - 14:30Room: Lundmarksalen14:30 Coffee breakCoffee break14:30 - 15:00Room: Lundmarksalen15:00 Angantyr - Leif Lönnblad (Lund U.)Angantyr- Leif Lönnblad (Lund U.)

15:00 - 16:00Room: Lundmarksalen16:00 Rivet hands on session - Christian Bierlich (Lund U.)Rivet hands on session- Christian Bierlich (Lund U.)

16:00 - 18:00Room: Lundmarksalen18:0018:00 - 19:00 -
Tuesday, 26 February 201908:30 From micro to macro QCD phenomena - Christopher Plumberg (Lund U.)From micro to macro QCD phenomena
- Christopher Plumberg (Lund U.)

08:30 - 09:30Room: Lundmarksalen09:30 Coffee breakCoffee break09:30 - 10:00Room: Lundmarksalen10:00 Statistical thermal model - Volodymyr Vovchenko (FIAS)Statistical thermal model- Volodymyr Vovchenko (FIAS)

10:00 - 11:00Room: Lundmarksalen11:00 EPOS - Klaus Werner (SUBATECH)EPOS- Klaus Werner (SUBATECH)

11:00 - 12:00Room: Lundmarksalen12:00 LunchLunch12:00 - 13:3013:30 Nuclear Parton Distribution Functions - Ilkka Helenius (Jyvaskyla U.)Nuclear Parton Distribution Functions- Ilkka Helenius (Jyvaskyla U.)

13:30 - 14:30Room: Lundmarksalen14:30 Photon induced processes from semi-central to ultraperipher collisions: introduction - Wolfgang Schafer (IFJ Krakow)Photon induced processes from semi-central to ultraperipher collisions: introduction- Wolfgang Schafer (IFJ Krakow)

14:30 - 15:30Room: Lundmarksalen15:30 Coffee breakCoffee break15:30 - 16:00Room: Lundmarksalen16:00 Jet quenching - Liliana Apolinário (LIP Lisbon)Jet quenching- Liliana Apolinário (LIP Lisbon)

16:00 - 17:00Room: Lundmarksalen17:0017:00 - 18:00Room: Lundmarksalen -
Wednesday, 27 February 201909:00 From small to large systems - What can we learn about the QGP? - Jurgen Schukraft (NBI)From small to large systems - What can we learn about the QGP?
- Jurgen Schukraft (NBI)

09:00 - 09:35Room: Lundmarksalen09:35 Recent flow results from LHC - You Zhou (NBI)Recent flow results from LHC- You Zhou (NBI)

09:35 - 10:00Room: Lundmarksalen10:00 Overview of jet physics results from ALICE - Filip Krizek (NPI Prague)Overview of jet physics results from ALICE- Filip Krizek (NPI Prague)

10:00 - 10:25Room: Lundmarksalen Collisions of ultra-relativistic heavy ions are used to create strongly interacting matter in the regime of high-energy densities and temperatures. Under these conditions color confinement of quarks and gluons in hadrons breaks down and a new state of matter called Quark-Gluon Plasma is formed. Properties of this medium can be inferred based on observed modifications of produced jets. Recently, jet analyses have developed new tools to study jet properties more differentially. These observables are based on hadron-jet correlations or jet-shape and jet-substructure measurements. The talk will review recent results from these jet analyses peformed in ALICE.10:25 Coffee breakCoffee break10:25 - 10:45Room: Lundmarksalen10:45 Does dN/deta scale as Npart or Ncoll - Christian Holm Christensen (NBI)Does dN/deta scale as Npart or Ncoll- Christian Holm Christensen (NBI)

10:45 - 11:10Room: Lundmarksalen11:10 Quark Gluon Plasma: the fastest rotating fluid - Michal Sumbera (NPI Prague)Quark Gluon Plasma: the fastest rotating fluid- Michal Sumbera (NPI Prague)

11:10 - 11:35Room: Lundmarksalen The extreme energy densities generated in ultra-relativistic heavy ion collisions produce a state of matter that behaves surprisingly like a fluid, with exceptionally high temperature and low viscosity. Non-central collisions have angular momenta of the order of 1,000ћ, and the resulting fluid may have a strong local rotational structure. Spin–orbit coupling can lead to preferential orientation of particle spins along the direction of rotation. I will present STAR measurements (Nature 548 (2017) 62, arXiv:1701.06657) of an alignment between the global angular momentum of a non-central collision and the spin of emitted particles, revealing that the fluid produced in heavy ion collisions is the most vortical system so far observed. I will also briefly discuss observable effects due to strong magnetic fields produced in ultra-relativistic heavy ion collisions related to the restoration of fundamental symmetries of quantum chromodynamics.11:35 Multiplicity and center-of-mass energy dependence of light-flavor hadron production in pp collisions - Vytautas Vislavicius (NBI)Multiplicity and center-of-mass energy dependence of light-flavor hadron production in pp collisions- Vytautas Vislavicius (NBI)

11:35 - 12:00Room: Lundmarksalen Measurements of particle production in proton-proton collisions as a function of multiplicity have revealed intriguing signs of collective behaviour in small systems. In this talk the recent results on light-flavour hadron production in pp collisions will be compared to larger systems, such as p-Pb, Pb-Pb and Au-Au. In addition, the importance of $\sqrt{s}$ to the observed trends will be addressed and tools to separate the soft and hard scattering regimes of the QCD will be discussed.12:00 LunchLunch12:00 - 13:3013:30 The final state swing - Leif Lönnblad (Lund U.)The final state swing- Leif Lönnblad (Lund U.)

13:30 - 13:55Room: Lundmarksalen13:55 Influence of electromagnetic fields on small systems - Lucia Oliva (GSI, Darmstadt)Influence of electromagnetic fields on small systems- Lucia Oliva (GSI, Darmstadt)

13:55 - 14:20Room: Lundmarksalen The recent experimental observations at RHIC and LHC indicate the formation of quark-gluon plasma even in small systems such as proton-nucleus collisions. In the early stage of relativistic heavy ion collisions extremely intense magnetic fields, with a magnitude up to 5-50 m_π^2, are produced; in asymmetric collisions, and in proton-induced reactions in particular, not only the magnetic field but also the electric field is very high. Moreover, in asymmetric colliding systems the particle rapidity distributions are strongly asymmetric inside the overlap region. By means of microscopic calculations within the Parton-Hadron-String Dynamics (PHSD) approach we study the distributions of electromagnetic fields in central p+Au collisions and investigate the influence of these fields on final hadronic observables, such as particle distributions and flow harmonics.14:20 Colour evolution - Patrick Kirchgaeßer (KIT)Colour evolution- Patrick Kirchgaeßer (KIT)

14:20 - 14:45Room: Lundmarksalen We consider soft gluon evolution of a system of clusters forming the initial state of the cluster hadronization model, in order to constrain colour reconnection models from a perturbative point of view. We show that this ansatz produces clusters with properties attributed to a colour pre-confined state and find strong evidence for formerly investigated colour reconnection models based on geometric properties. We also explore the possibility of colour flows giving rise to baryonic clusters and propose simple parametrizations in order to incorporate the effects of soft gluon evolution in a Monte Carlo Event Generator. In the first part of my talk I will explain the underlying theory, while in the second part I will focus on the implementation in the Monte Carlo Event Generator Herwig.14:45 Non-flow Effects on Q-cumulants - Kristjan Gulbrandsen (NBI)Non-flow Effects on Q-cumulants- Kristjan Gulbrandsen (NBI)

14:45 - 15:10Room: Lundmarksalen One of the most used methods to compute flow coefficients in high-energy particle collisions is the Q-cumulant method. The method employs the mathematical concept of a cumulant which is meant to identify correlations to some order (between more particles in this case). For this reason, it is often said that the method removes lower order non-flow effects. A semi-theoretical study has been done to show that this is not (by design) true. Additionally, other effects of the particle distribution function can produce artificial flow signals. Such effects are demonstrated and discussed.15:10 Coffee breakCoffee break15:10 - 15:40Room: Lundmarksalen15:40 Multiplicity dependence of particle production at the LHC in (canonical) statistical model - Volodymyr Vovchenko (FIAS)Multiplicity dependence of particle production at the LHC in (canonical) statistical model- Volodymyr Vovchenko (FIAS)

15:40 - 16:05Room: Lundmarksalen System-size dependence of hadrochemistry at vanishing baryon density is studied within the statistical model in the context of p-p, p-Pb, and Pb-Pb data of the ALICE collaboration. Evaluations are done in the framework of a new Thermal-FIST package. Effects of exact conservation of charges, incomplete equilibration of strangeness, finite resonance widths, are multiplicity dependence of the chemical freeze-out temperature are covered.16:05 In what way is a QGP interacting? - Peter Christiansen (Lund U.)In what way is a QGP interacting?- Peter Christiansen (Lund U.)

16:05 - 16:30Room: Lundmarksalen It is often thought that if the anisotropic flow in small systems is due to final state interactions then one should also observe significant jet quenching in the same systems. In this talk, I will discuss this statement based on ideas of Kinetic theory and results from the new Angantyr generator and show that one can have final state interactions that does not give significant jet quenching. Finally, I will try to relate this to perfect fluidity.16:30 Strangeness and space-time model in Herwig - Stefan Gieseke (KIT)Strangeness and space-time model in Herwig- Stefan Gieseke (KIT)

16:30 - 16:55Room: Lundmarksalen16:55 Role of string collectivity and semihard process in multiplicity-dependent transverse momentum and the strangeness enhancement - Vladimir Kovalenko (St.Petersburg State U.)Role of string collectivity and semihard process in multiplicity-dependent transverse momentum and the strangeness enhancement- Vladimir Kovalenko (St.Petersburg State U.)

16:55 - 17:20Room: Lundmarksalen The multiplicity dependence of the mean transverse momentum as well as strangeness and multi-strangeness production is studied in the framework of two models: dipole-based Monte Carlo model with string fusion [1-2], and extended multi-pomeron exchange model [3-4]. The first model allows the unifying description of pp, pA and AA collisions [5]. The partonic interactions are described as collisions of dipoles. The hardness of the collision is determined by transverse size of the colliding dipoles. The production of the observed particles is implemented in the string mechanism, taking into account string fusion [6-7]. The second model [3-4] is based on Regge-Gribov approach. The model includes string collectivity, parametrized by one parameter, beta, which is determined by data on pt-multiplicity correlation at wide energy range. For the particles species discrimination, both models use the modified Schwinger mechanism [8], where the effective string tension, according to the string fusion prescription, depends on the string density. We show that two effects contribute to the transverse momentum: the hardness of the partonic collision, and the modification of the string tension. Only second effect leads to the modification of strangeness and multi-strangeness production. Taking it into account allows one to describe the experimental data [9] at LHC energy. [1] V. N. Kovalenko, Phys. Atom. Nucl. 76, 1189 (2013), arXiv:1211.6209 [hep-ph]. [2] V. Kovalenko, V. Vechernin, PoS (Baldin ISHEPP XXI) 077, arXiv:1212.2590 [nucl-th], (2012). [3] E. Bodnia, D. Derkach, G. Feofilov, V. Kovalenko, A. Puchkov, PoS (QFTHEP 2013) 060 (2013), arXiv:1310.1627 [hep-ph]. [4] E. O. Bodnia, V. N. Kovalenko, A. M. Puchkov, G. A. Feofilov, AIP Conf. Proc. 1606, 273-282 (2014), arXiv:1401.7534 [hep-ph]. [5] V. N. Kovalenko, Phys. Part. Nucl, 48, 945 (2017). [6] M. A. Braun, C. Pajares, Nucl. Phys. B 390, 542 (1993). [7] N. S. Amelin, N. Armesto, M. A. Braun, et al., Phys. Rev. Lett. 73, 2813 (1994). [8] J. Schwinger, Phys. Rev. 82, 664 (1951); T. S. Biro, et al, Nucl. Phys. B. 245, 449 (1984). [9] J. Adam, et al (ALICE Collaboration), Nature Physics 13, 535-539 (2017).19:0019:00 - 21:00 -
Thursday, 28 February 201909:00 Generating functional for quenched observables - Konrad Tywoniuk (Bergen U.)Generating functional for quenched observables
- Konrad Tywoniuk (Bergen U.)

09:00 - 09:25Room: Lundmarksalen Hard probes, and in particular jets, are at the same time both promising and challenging tools for probing the hot and dense nuclear matter created in high-energy heavy-ion collisions at the RHIC and LHC. Radiative processes in the medium lead to a redistribution of energy within the jet cone and an enhanced energy leakage out of it. These modifications are governed by the interplay of the relevant momentum- and time-scales, and are sensitive to the way partonic fluctuations within the jet are resolved by the medium. Mapping out all relevant regimes of jet-medium interactions onto the Lund kinematical plane, we establish a probabilistic picture of the fragmentation in the form of a generating functional (GF). In contrast to the GF in vacuum, in medium it contains terms describing fragmentation at short and long time-scales, compared to the medium scales, and the transition between them. Due to the mismatch between real and virtual emissions, the GF is normalized to the collimator function that describes how jet substructures are quenched and can be measured from the inclusive jet spectrum in heavy-ion collisions. We put a special emphasis on the role of color coherence for hard, small-angle fluctuations.09:25 Soft modifications to pp fragmentation: The shoving model - Christian Bierlich (Lund U.)Soft modifications to pp fragmentation: The shoving model- Christian Bierlich (Lund U.)

09:25 - 09:50Room: Lundmarksalen In this talk the recently developed shoving model, based on interacting Lund strings, is discussed. The model is developed with soft collective effects in pp in mind, most prominently a description of the ridge in pp collisions. Since Lund strings also connect the hardest fragment of a jet to beam remnants, shoving the connecting strings will affect jet observables as well. Similarities to jet quenching in AA collisions are highlighted in this connection.09:50 Probing the QGP time structure from large to small(er) systems with top quarks - Liliana Apolinário (LIP Lisbon)Probing the QGP time structure from large to small(er) systems with top quarks- Liliana Apolinário (LIP Lisbon)

09:50 - 10:15Room: Lundmarksalen Top quarks have been recently proposed as a unique probe to determine the space-time evolution of the medium that is created in heavy-ion collisions [1]. In particular, they allow an approximate determination of the time at which the top’s decay products start interacting with the QGP, making this channel most sensitive to the late time dynamics of the produced medium. This is achieved by using the hadronic decay chain of the top quark: in addition to the finite lifetimes of the top and W-boson, the time-delay in the interaction of the (colour-singlet) W-boson’s decay products with the medium adds to a finite total time-delay that can be applied to probe different QGP timescales. Top quarks have already been measured in nuclear collisions. With the forthcoming HL-LHC and HE-LHC, the increase in luminosity and energy can be further explored to use top quark observables as a unique probe of the QGP. In this talk, we show the latest projections for the use of this particular channel in both PbPb and lighter ions collisions in these two setups. [1] L. Apolinário, J. G. Milhano, G. Salam, C. Salgado, Phys.Rev.Lett. 120 (2018) no.23, 23230110:15 Coffee breakCoffee break10:15 - 10:45Room: Lundmarksalen10:45 Suppression of anisotropic flow without viscosity - Adam Takacs (Bergen U.)Suppression of anisotropic flow without viscosity- Adam Takacs (Bergen U.)

10:45 - 11:10Room: Lundmarksalen Relativistic viscous hydrodynamics calculations can describe a wide range of observables in relativistic heavy ion collisions. However, many studies suggest that the hot and dense system created is not in local thermal equilibrium, resulting in a contradiction for the applicability of hydrodynamics. In hydrodynamic calculations, a crucial step is to convert the fluid fields into observable particles. The most common approach is to use the Cooper-Frye formula, which assumes thermal (Boltzmann/Bose/Fermi) distributions at the conversion. In this talk, I show how local equilibrium distributions of the Tsallis form can affect observables, resulting in non-exponential particle distributions and a viscous-like suppression of the anisotropic flow. By comparing the calculation to experimental data, I will estimate the degree of non- Boltzmann effects on the freeze-out surface.11:10 A Monte Carlo study of in-medium quark and gluon jet colour scaling - Joao Barata (Santiago de Compostela)A Monte Carlo study of in-medium quark and gluon jet colour scaling- Joao Barata (Santiago de Compostela)

11:10 - 11:35Room: Lundmarksalen Most jet quenching models predict that, at the parton level, the quark to gluon energy loss due to in-medium interactions scales with the ratio of the corresponding Casimirs $C_F/C_A$. However, in the jet framework, one expects a violation of this scaling due to the finite extension of the jet. In this talk, I will present results from a Monte Carlo study of calibrated Z+jets events which allow addressing this problem. The results presented here show an interesting scaling violation which indicates that gluon and quark jets are much more similar in medium than the corresponding partons. In addition, a parametrization of the average energy loss for quarks and gluons and for its variance is provided. Such a parametrization can prove useful to computing observables for in-medium events without needing a full Monte Carlo simulation.11:35 The future of JEWEL - Korinna Zapp (Lund U.)The future of JEWEL- Korinna Zapp (Lund U.)

11:35 - 12:00Room: Lundmarksalen12:00 LunchLunch12:00 - 13:3013:30 Dynamical description of heavy-ion collisions - Elena Bratkovskaya (GSI, Darmstadt)Dynamical description of heavy-ion collisions- Elena Bratkovskaya (GSI, Darmstadt)

13:30 - 14:05Room: Rydbergsalen We present the basic ideas of the Parton-Hadron-String Dynamics (PHSD) transport approach which is a microscopic covariant dynamical model for strongly interacting systems formulated on the basis of Kadanoff-Baym equations for Green's functions in phase-space representation (in 1st order gradient expansion beyond the quasi-particle approximation). The approach consistently describes the full evolution of a relativistic heavy-ion collision from the initial hard scatterings and string formation (based on LUND string model) through the dynamical deconfinement phase transition to the strongly-interacting quark-gluon plasma (sQGP) as well as hadronization and the subsequent interactions in the expanding hadronic phase. The PHSD approach has been applied to p+p, p+A and A+A collisions from lower SIS to LHC energies and been successful in describing a large number of experimental data including single-particle spectra, collective flow and electromagnetic probes. The highlights of the PHSD results will be presented with the focus on charm production.14:05 Particle Interferometry from Hydrodynamics and Event Generators - Christopher Plumberg (Lund U.)Particle Interferometry from Hydrodynamics and Event Generators- Christopher Plumberg (Lund U.)

14:05 - 14:30Room: Rydbergsalen Particle interferometry - also known as Hanbury Brown-Twiss (HBT) interferometry - is a measurement technique based on momentum-space correlations between identical particles which has proven to be an indispensable tool in studying the space-time evolution of femtoscopic collision systems. In particular, HBT interferometry allows one to classify these collision systems on the basis of their collision geometry. This, in turn, provides a useful aid to calibrating things such as jet-quenching analyses in both large and small collision systems, where the precise geometry of the system plays a crucial role in the interpretation of experimental results. In this talk, I describe some recent and ongoing efforts to connect the techniques of HBT interferometry with the question of QGP medium formation in heavy-ion collisions and high multiplicity hadron-hadron collisions, some of which are directly relevant to the goal of understanding jet-quenching in collision systems of various sizes. Specifically, I will show how hydrodynamic predictions for the space-time geometry can be tested using HBT, and I will discuss some current work to enable similar predictions to be made using the MC event generator formalism of Pythia/Angantyr for the modeling of high-energy collision systems.14:30 New exact solutions of relativistic hydrodynamics and their applications - Tamás Csörgő (Wigner RCP)New exact solutions of relativistic hydrodynamics and their applications- Tamás Csörgő (Wigner RCP)

14:30 - 14:55Room: Rydbergsalen A recently found new family of exact solutions of 1+1 dimensional relativistic hydrodynamics will be presented, and its applications to describe the pseudorapidity density, the HBT radii and the estimation of the initial energy density in proton-proton and heavy ion collisions at LHC, RHIC and SPS energies will be reviewed. The talk will focus on a recently discovered signal of a non-monotonic behaviour of the initial energy densities in heavy ion collisions at RHIC energies. References: 1) Lifetime estimations from RHIC Au+Au data. G. Kasza and T. Csörgő, [arXiv:1811.09990]. 2) A new and finite family of solutions of hydrodynamics: Part III: Advanced estimate of the life-time parameter. T. Csörgő and G. Kasza, [arXiv:1810.00154]. 3) A new and finite family of solutions of hydrodynamics: Part II: Advanced estimate of initial energy densities. G. Kasza and T. Csörgő, [arXiv:1806.11309 [nucl-th]]. 4) A new and finite family of solutions of hydrodynamics. Part I: Fits to pseudorapidity distributions. T. Csörgő, G. Kasza, M. Csanád and Z.F. Jiang, [arXiv:1806.06794]. 5) New exact solutions of relativistic hydrodynamics for longitudinally expanding fireballs. T. Csörgö, G. Kasza, M. Csanád, Z.F. Jiang, [arXiv:1805.01427]. 10.3390/universe4060069, Universe 4 (2018) 69.14:55 QGP from the quantum ground-state of QCD? - Roman Pasechnik (Lund U.)QGP from the quantum ground-state of QCD?- Roman Pasechnik (Lund U.)

14:55 - 15:20Room: Rydbergsalen In this talk, I will elaborate on a semi-classical Hamiltonian approach to describe the QGP production mechanism in real time based upon the existence of a homogeneous initial state being a non-trivial QCD ground-state. An effect ala parametric resonance leading to a decay of the homogeneous gluon condensate into inhomogeneous gluon plasma is thought to be a possible driver of QGP production in QCD.15:20 Coffee breakCoffee break15:20 - 15:50Room: Rydbergsalen15:50 Creation of quark–gluon plasma droplets with three distinct geometries - Tamás Csörgő (Wigner RCP)Creation of quark–gluon plasma droplets with three distinct geometries- Tamás Csörgő (Wigner RCP)

15:50 - 16:15Room: Rydbergsalen Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark–gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons. In this state, matter behaves as a nearly inviscid fluid that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton–proton (p+p) and proton–nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton–gold (p+Au), deuteron–gold (d+Au) and helium–gold (3He+Au) collisions at a nucleon–nucleon centre-of-mass energy sqrt(s_NN)=200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide the best simultaneous description of these measurements.16:15 Effect of Rope hadronisation on Strangness enhancement in pp collisions at the LHC - Ranjit Nayak (IIT Bombay)Effect of Rope hadronisation on Strangness enhancement in pp collisions at the LHC- Ranjit Nayak (IIT Bombay)

16:15 - 16:40Room: Rydbergsalen The p-p collisions at high multiplicity at LHC show small scale collective effects similar to that observed in heavy ion collisions such as enhanced production of strange and multi-strange hadrons, long range azimuthal correlations, etc. The observation of strangeness enhancement in p-p collisions at 7 TeV and 13 TeV as measured by ALICE experiment is explored using Pythia8 event generator within the framework of microscopic rope hadronization model which assumes the formation of ropes due to overlapping of strings in high multiplicity environment. The spectral shape and its hardening with multiplicity is well described by the model. The mechanism of formation of ropes also described the observed experimental strangeness enhancement for higher multiplicity classes in p-p collisions at 7 TeV and 13 TeV. The enhancement with multiplicity is further investigated by studying the mean pT (< pT >) and the integrated yields (< dN/dy >) of strange and multi-strange hadrons and comparing the predictions to the mea- sured data at LHC for 7 TeV and 13 TeV.16:40 Jet production in ultra-peripheral collisions with Pythia 8 - Ilkka HeleniusJet production in ultra-peripheral collisions with Pythia 8- Ilkka Helenius

16:40 - 17:05Room: Rydbergsalen Traditionally jet production in different collision systems has been used to study different physics: jet quenching in AA, initial-state nuclear modifications in pA and pQCD baseline in pp. There are, however, recent observations of similar collective effects in all these systems. This challenges the picture where the measurements in these different systems would provide information only on well-separated physics phenomena. In addition to these widely-studied collision systems, it is also possible to study photon-proton and photon-nucleus interactions in ultra-peripheral collisions (UPCs) at the LHC. These photon-induced processes could offer new insights on the collective phenomena and provide a clean environment to study purely initial-state effects. In this talk we discuss how these processes can be simulated with Pythia 8 general-purpose Monte Carlo event generator by applying the recent photoproduction framework. As an application, we study the potential of photo-nuclear dijets in PbPb collisions at the LHC to further constrain nuclear PDFs. In addition, we introduce our dynamical rapidity gap survival model for hard diffraction which is now implemented also for photoproduction in Pythia 8, and present predictions for diffractive dijet production in UPCs at the LHC.17:05 Hadron yields and fluctuations at the CERN Super Proton Synchrotron: system size dependence from Pb+Pb to p+p collisions - Anton Motornenko (Frankfurt U.)Hadron yields and fluctuations at the CERN Super Proton Synchrotron: system size dependence from Pb+Pb to p+p collisions- Anton Motornenko (Frankfurt U.)

17:05 - 17:30Room: Rydbergsalen The kaon to pion ratio K^+/\pi^+ and the scaled variance \omega^- for fluctuations of negatively charged particles are studied within the statistical hadron resonance gas (HRG) model and the Ultra relativistic Quantum Molecular Dynamics (UrQMD) transport model. The calculations are done for p+p, Be+Be, Ar+Sc, and Pb+Pb collisions at the CERN Super Proton Synchrotron energy range to reveal the system size dependence of hadron production. For the HRG calculations the canonical ensemble is imposed for all conserved charges. In the UrQMD simulations the centrality selection in nucleus-nucleus collisions is done by calculating the forward energy E_{\rm F} deposited in the Projectile Spectator Detector, and the acceptance maps of the NA61/SHINE detectors are used. The role of centrality selection on fluctuation measures is studied in detail. A comparison of the HRG and UrQMD results with the data of the NA61/SHINE Collaboration is done. To understand a difference of the event-by-event fluctuations in p+p and heavy ion collisions the centrality selection procedure in the sample of all inelastic p+p events is proposed and analyzed within the UrQMD simulations. References: [1] A. Motornenko, K. Grebieszkow, E. Bratkovskaya, M.I.Gorenstein, M.Bleicher and K.Werner, J. Phys. G 45, no. 11, 115104 (2018), arXiv:1711.07789 [nucl-th] [2] A. Motornenko, V.V. Begun, V. Vovchenko, M.I. Gorenstein and H. Stoecker, arXiv:1811.10645 [nucl-th]. -
Friday, 1 March 201909:00 Parton tomography: Wigner distributions in nucleon and nuclear targets - Emmanuel de Oliveira (UFSC Florianopolis)Parton tomography: Wigner distributions in nucleon and nuclear targets
- Emmanuel de Oliveira (UFSC Florianopolis)

09:00 - 09:35Room: Lundmarksalen09:35 Vector meson production by photon - induced interactions in heavy ion collisions: Recent results and prospects - Victor Goncalves (Universidade Federal de Pelotas)Vector meson production by photon - induced interactions in heavy ion collisions: Recent results and prospects- Victor Goncalves (Universidade Federal de Pelotas)

09:35 - 10:00Room: Lundmarksalen In this contribution we will present a brief review of the recent results that demonstrate that the single and double vector meson production by photon - induced interactions in heavy ion collisions can be used to constrain the QCD dynamics at high energies and improve our understanding about the gluon Sivers function.10:00 Photon induced production of J/psi and dilepton pairs in semi-central nucleus-nucleus collisions - Antoni Szczurek (IFJ Krakow)Photon induced production of J/psi and dilepton pairs in semi-central nucleus-nucleus collisions- Antoni Szczurek (IFJ Krakow)

10:00 - 10:25Room: Lundmarksalen We calculate total and differential cross sections for J/\psi photoproduction in ultrarelativistic lead-lead collisions at the LHC energy \sqrt{s_{NN}}=2.76 TeV. In the present approach we use a simple model based on vector dominance picture and multiple scattering of the hadronic (c \bar c) state in a cold nucleus as an example. In our analysis we use both the classical mechanics and quantum (Glauber) formulae for calculating \sigma_{tot, J/psi Pb} which is a building block of our model. We compare our UPC results with ALICE and CMS data. For semi-central collisions (b < R_A+R_B) a modification of the photon flux is necessary. We discuss different motivated by physics approximations. We try to estimate the cross sections for different centrality bins and for J/psi mesons emitted in forward rapidity range (2.5 < y < 4) corresponding to recent ALICE experimental results. Reasonable results are obtained and open questions are discussed. We study the invariant-mass distributions of dileptons produced in ultrarelativistic heavy-ion collisions at very low pair transverse momenta, P_T\leq 0.15 GeV. Specifically, we investigate the interplay of thermal radiation with initial photon annihilation processes, \gamma \gamma \to l^+ l^-, triggered by the coherent electromagnetic fields of the incoming nuclei. For the thermal radiation, we employ the emission from the QGP and hadronic phases with in-medium vector spectral functions which describes the inclusive excess radiation observed over a wide range of collision energies. For the coherent photon fusion processes, whose spectrum is much softer than for thermal radiation, we employ initial fluxes from the Fourier transform of charge distributions of the colliding nuclei in the equivalent-photon approximation. We first verify that the combination of photon fusion, thermal radiation and final-state hadron decays gives a fair description of the low-P_T invariant-mass as well as P_T spectra as recently measured by the STAR collaboration in \sqrt{s_{NN}}=200 GeV Au+Au collisions for different centrality classes, including experimental acceptance cuts. The coherent contribution dominates in peripheral collisions, while thermal radiation shows a markedly stronger increase with centrality. We extend the calculations to lower collision energies (\sqrt{s_{NN}}=17.3 GeV) and compare to the acceptance-corrected dimuon excess spectra measured by the NA60 experiment at the CERN SPS; the contribution from photoproduction turns out to be subleading. We also provide predictions for the ALICE experiment at the LHC. The resulting excitation function from SPS to LHC energies reveals a nontrivial interplay of photoproduction and thermal radiation.10:25 Coffee breakCoffee break10:25 - 10:55Room: Lundmarksalen10:55 What must we learn about QGP-like effects in small systems from Run 3+ - Naghmeh Mohammadi (CERN)What must we learn about QGP-like effects in small systems from Run 3+- Naghmeh Mohammadi (CERN)

10:55 - 11:30Room: Lundmarksalen11:30 ALICE upgrade and prospects - David Silvermyr (Lund U.)ALICE upgrade and prospects- David Silvermyr (Lund U.)

11:30 - 11:55Room: Lundmarksalen11:55 The CLASH project - Leif Lönnblad (Lunds universitet) Peter Christiansen (Lunds universitet)The CLASH project- Leif Lönnblad (Lunds universitet)
- Peter Christiansen (Lunds universitet)

11:55 - 12:20Room: Lundmarksalen In this talk, the KAW sponsored CLASH project will be described. CLASH is a 5 year project started summer 2018 where experimentalists and theorists in Lund aims to pin down the origin of collective effects in small systems.