Conveners
Heavy Ion Physics
- You Zhou (University of Copenhagen (DK))
- Yen-Jie Lee (Massachusetts Institute of Technology)
- Iwona Grabowska-Bold (AGH University of Science and Technology (PL))
- Guilherme Milhano (LIP-Lisbon & CERN TH)
Heavy Ion Physics
- Yen-Jie Lee (Massachusetts Institute of Technology)
- You Zhou (University of Copenhagen (DK))
- Guilherme Milhano (LIP-Lisbon & CERN TH)
- Iwona Grabowska-Bold (AGH University of Science and Technology (PL))
Heavy Ion Physics
- Yen-Jie Lee (Massachusetts Institute of Technology)
- You Zhou (University of Copenhagen (DK))
- Guilherme Milhano (LIP-Lisbon & CERN TH)
- Iwona Grabowska-Bold (AGH University of Science and Technology (PL))
Heavy Ion Physics
- There are no conveners in this block
Jets are produced by a high momentum transfer of initial partons at high energies. Comparing jet production in pp and nucleus-nucleus collisions will allow us to study the jet-quenching effect caused by the hot and dense QCD medium produced in nucleus-nucleus collisions when energetic partons traverse the medium. In particular, systematic studies of jet production in different multiplicity...
This talk presents the latest jet measurements in 5.02 TeV Pb+Pb collisions with the ATLAS Experiment at the LHC. Jets are direct probes of the quark-gluon plasma produced in heavy-ion collisions and studying how they are modified in the heavy-ion collisions compared to the pp collisions provides insight into their interactions with this QCD medium. The latest jet results from ATLAS shown in...
We demonstrate that the recent forward-forward dijet correlation data measured by the ATLAS collaboration for proton-proton and proton-lead collisions are consistent with the broadening effects due to both the gluon saturation and the resummation of large logarithms of the hard scale (the so-called Sudakov logarithms). We find that both effects are necessary to describe the experimental results.
The presence of a hot and dense medium, produced in ultra-relativistic heavy-ion collisions, is known to modify the parton shower evolution. Several observations of the resulting intra-jet activity show significant modifications of what can be considered as a medium-modified jet from a โvacuumโ (proton-proton) reference. These modifications, generically known as jet quenching effects, are the...
The quenching of jets in heavy-ion collisions probes the transport properties of the quark-gluon plasma. We present selected recent inclusive jet and photon+jet measurements from the CMS experiment.
It is known already for some time that the leading power limit of the Color Glass Condensate (CGC) expressions for dijet production can be identified with the (generalized) Transverse Momentum Dependent (TMD) factorization in the small x regime. In the latter formalism, there are several TMD gluon distributions containing distinct Wilson line operators, and corresponding on-shell hard...
The precise reconstruction of jet transverse momenta in heavy-ion collisions is a challenging task. A major obstacle is the large number of uncorrelated (mainly) low-$p_{\rm T}$ particles overlaying the jets. Strong region-to-region fluctuations of this background complicate the jet measurement and lead to significant uncertainties.
We developed a novel approach to correct jet momenta (or...
The phenomenological structure of inclusive cross-sections of the production of two neutral $K$ mesons in hadron--hadron, hadron--nucleus and nucleus--nucleus collisions is theoretically studied taking into account the strangeness conservation in strong and electromagnetic interactions. Relations for the dependence of correlations of two short-lived and two long-lived neutral kaons
$K^0_S...
The production of light neutral mesons in different collision systems is interesting for a variety of reasons: In AA collisions the measurements can provide important information on the energy loss of partons traversing the Quark-Gluon Plasma (QGP) which is formed in heavy-ion collisions at the LHC. Measured in pp collisions, neutral meson spectra serve as a reference for pA and AA collisions....
Our presentation will be largely based on our recent paper [1].
The centrality and energy dependence of rapidity distributions of pions in Pb+Pb reactions can be understood by imposing local energy-momentum conservation in the longitudinal โfire-streaksโ of excited matter. With no tuning nor adjustment to the experimental data, the rapidity distribution of pions produced by the fire-streak...
A semi-classical Hamiltonian approach can be used to describe the quark-gluon plasma (QGP) production mechanism in heavy-ion collisions in real physical 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 can be thought as a...
Studies of the production of light- and heavy-flavour baryons are of prominent importance to characterise the partonic phase created in ultrarelativistic heavy ion collisions and to investigate hadronisation mechanisms at the LHC. Studies performed in p--Pb and pp collisions have revealed unexpected features, qualitatively similar to what is observed in larger collision systems and, in the...
High energy pp, p-Pb, and Pb-Pb collisions at the LHC offer a unique opportunity to study the production of light (anti-)nuclei. The study of the production yield of (anti-)nuclei in heavy-ion collisions at LHC energies probes the late stages in the evolution of the hot, dense nuclear matter created in the collision and serves as baseline in the search for exotic multi-baryon states. ...
The study of identified hadron production as a function of event multiplicity is a key tool for understanding the similarities and differences between large and small colliding systems.
The multiplicity-dependence of the total yields of identified hadrons as a function of event activity shows a remarkable scaling that covers all the collision systems considered.
The production rates of strange...
We review our studies of spectator-induced electromagnetic (EM) effects on charged pion emission. For heavy-ion Pb+Pb and Au+Au reactions, we formulate a model which associates the size of EM effect with the space-time properties of the system of hot and dense matter formed in the collision. As a result we obtain an estimate for the pion decoupling time which agrees with pion decoupling times...
The first measurements of event-by-event correlated fluctuations of neutral and charged kaons are reported in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV, which are proposed to be related to isospin fluctuations in the kaon sector. These dynamic fluctuations affect the mechanism of correlated productions of neutral and charged kaons in heavy ion collisions. In this work we have used the...
Identified hadron spectra from relativistic heavy-ion collisions allow
one to reconstruct the final state of the fireball. In principle, one
could deduce its previous evolution from a back extrapolation of the
final state. It is also important to study the collisions at different
energies, since hot matter at different energy and baryon densities is
created that way. One is then...
A rich set of open heavy flavour states is observed by LHCb in pPb collisions collected at 5 and 8.16 TeV nucleon-nucleon centre-of-mass energies. Thanks to the LHCb forward acceptance that is complementary to general purpose detectors, heavy-flavor hadrons can be studied down to zero transverse momentum. This talk presents production measurements of beauty hadrons and open charm states...
Heavy quarks (charm and beauty) constitute unique probes for the hot and dense QCD medium produced in heavy-ion collisions: the Quark-Gluon Plasma (QGP). They are mainly produced in hard scattering processes among partons, which occur immediately after the nuclei crossing with a time-scale shorter than the QGP formation time. Therefore, they witness the full evolution of the medium loosing...
In ultrarelativistic heavy-ion collisions at RHIC energies, the charm quarks are predominantly produced in initial hard partonic scatterings. Therefore, they experience the entire evolution of the hot and dense medium produced in these collisions, known as the Quark-Gluon Plasma (QGP), and make a very valuable probe. The STAR experiment is capable of studying the production of charm quarks and...
Measurements of heavy flavour hadrons in PbPb collisions provide information about the heavy quark dynamics inside the quark-gluon plasma (QGP). Heavy quarks are sensitive to the transport properties of the medium and may interact with the QCD matter differently from light quarks. At low pT, heavy quarks provide a direct window on the in-medium QCD force. At high pT, the comparison of results...
Unexpectedly strong suppression of heavy flavored mesons, produced with high transverse momenta in heavy ion collisions, is caused by final state interactions in the created dense medium. Gluon bremsstrahlung by a highly virtual heavy quark ceases shortly after the hard collision in accordance with perturbative QCD calculations and LEP measurements of the fragmentation function....
The LHC heavy-ion physics program aims at investigating the properties of the Quark-Gluon Plasma (QGP) formed in such collisions. Heavy quarks (charm and beauty) are regarded as efficient probes to study and characterize the QGP, as they are created on a very short time scale in initial hard processes and subsequently experience the entire system evolution interacting with the medium...
The study of heavy-flavour (charm and beauty) production is important to understand the properties of the Quark-Gluon Plasma (QGP) formed in ultra-relativistic heavy-ion collisions, since heavy quarks are produced in the initial stages of the collisions and subsequently interact with the medium throughout its evolution.
In the QGP, strange quarks are expected to be abundantly produced and...
In this presentation we discuss the contribution of the three-pomeron configurations to quarkonia production in proton-proton collisions. This mechanism provides a natural explanation of the elevated multiplicities of the produced charged hadrons in the events with production of charmonia. The suggested mechanism gets dominant contribution from the region which can be theoretically described...
We present LHCb results on quarkonia production in proton-lead collisions, using the data collected at 5.02 and 8.16 TeV nucleon-nucleon centre-of-mass energies, covering forward (pPb configuration) and backward (Pbp configuration) rapidities. Measurements include charmonia, where the prompt and from-b-decay components are disentangled, and bottomonia states. The large increase in size of the...
Quark-gluon plasma and it's properties can be studied with quarkonium states used as a probe. Both $J/\psi$ and $\Upsilon$ states dissociate if a sufficiently high temperature is reached in the plasma. Since these quarkonium states have different binding energies, they are expected to dissociate at different temperatures, which is expected to lead to the so-called sequential suppression...
Heavy quarks are produced at the first instant of a nucleus-nucleus collision and therefore are an important tool to study the subsequent high energy-density medium formed in ultra-relativistic heavy-ion collisions. A series of experimental efforts for understanding the properties of the Quark-Gluon Plasma (QGP), a medium consisting of a deconfined state of quarks and gluons, are based on...
J/$\psi$ production provides a particular sensitivity to the medium which can be produced in heavy-ion collisions at ultrarelativistic energies as delivered by the LHC. The vacuum production is modelled by a reference measured in proton-proton collisions and potential initial-state effects can be constrained using p--Pb collisions in the same collision-energy regime.
In this contribution...
LHCb has the unique capability to study collisions of the LHC beams on fixed targets. Internal gas targets of helium, neon and argon have been used so far to collect samples corresponding to integrated luminosities up to 0.1 pb-1. An upgraded target, allowing a wider choice of target gas species and an increase in the gas density by up to two orders of magnitude, is planned to be installed for...
We report on our study showing that heavy-flavour production at the LHC can strongly improve our knowledge of the gluon content of the heavy nuclei. We have indeed observed that the nuclear effects encoded in both most recent global fits of nuclear parton densities at next-to-leading order (nCTEQ15 and EPPS16) gives a good account of the LHC proton-lead data. Thanks to a Bayesian-reweighting...
Electroweak bosons produced in ultrarelativistic heavy-ion collisions serve as excellent probes of the collision geometry and centrality. Their production rates should be unaffected by initial-state effects. Due to the correlation between the kinematics of quarks from incoming nuclei and the rapidity of produced electroweak bosons, they also provide insight into nuclear modifications of parton...
The production of low-mass dielectrons is the most promising tools for the understanding of the chiral symmetry restoration and of the thermodynamical properties of the Quark-Gluon Plasma (QGP) created in ultra-relativistic heavy-ion collisions. Since dielectrons are unaffected by strong final-state interactions and emitted during all stages of the collision, they carry information about the...
The Large Hadron-electron Collider (LHeC) is a proposed upgrade of the LHC at CERN. It consists of an ERL providing electrons to collide with the HL-LHC, HE-LHC and the FCC-hh ion beams. It will achieve per nucleon centre-of-mass energies 0.8-2.2 TeV, respectively, and luminosities about $10^{33}$ cm$^{โ2}$ s$^{โ1}$ The LHeC and its possible successors will extend the kinematic plane in...
Light-by-light (LbyL) scattering, $\gamma\gamma\rightarrow\gamma\gamma$, is a very rare process allowed in Quantum Electrodynamics via a loop diagram. The precise measurement of this process is potentially sensitive to contributions from Beyond Standard Model. Despite the small cross-section, the LbyL scattering can be observed in ultra-peripheral high energy heavy-ion collisions due to strong...
So far light-by-light scattering ($\gamma\gamma\to\gamma\gamma$) was not accessible for experiments because the corresponding cross section is rather low. Measurements of diphotons in ultra-peripheral collisions (UPCs) of lead-lead have been reported recently by the ATLAS [1] and CMS Collaborations [2]. Our theoretical results based on equivalent photon approximation in the impact parameter...
We present a calculation of the cross section of inclusive dijet photoproduction in ultraperipheral Pb-Pb collisions at the LHC using next-to-leading order perturbative QCD. We demonstrate that our theoretical calculations provide a good description of various kinematic distributions measured by the ATLAS collaboration. We find that the calculated dijet photoproduction cross section is...
We calculate cross sections for di-lepton photoproduction in ultrarelativistic heavy-ion collisions from low (SPS) to high (LHC) energy.
We study the invariant-mass distributions of dileptons produced in ultrarelativistic heavy-ion collisions at very low pair transverse momenta, $P_T< 0.15$ GeV. Specifically, we investigate the interplay of thermal radiation with initial photon annihilation...
Recent observations at RHIC and the LHC of two- and multi-particle correlations in high multiplicity relativistic proton-proton and proton-ion collisions and similarity of the results to those observed in central heavy-ion collisions are often interpreted as an evidence for collective particle production in small collision systems. These results motivate a study in even smaller systems, such...
The observed azimuthal modulations of long-range correlations in pseudorapidity in small systems like pp or p-Pb collisions show strikingly similar features to those seen in heavy ion collisions. Many theoretical approaches to interpreting this effect have been developed. However, it is still unclear whether these long-range correlations are due to final
or initial state effects. To further...
One of the primary goals of the NA61/SHINE experiment at CERN SPS is the detection of the critical point (CP) of strongly interacting matter. In the interests of this search, an energy (beam momentum 13A โ 150A GeV/c) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La) scan is being performed.
A number of observables are being considered as possible signatures of the CP. These include...
ATLAS measurements of differential and global Fourier harmonics of charged particles ($v_{n}$) in 5.02 TeV Pb+Pb and 5.44 TeV Xe+Xe collisions in a wide range of transverse momenta (up to 60 GeV), pseudorapidity (|$\eta$|<2.5) and collision centrality (0-80%) are presented. The higher order harmonics, sensitive to fluctuations in the initial state, are measured up to n=7 using the two-particle...
Anisotropic flow coefficients $v_n$ have been used as a tool to probe the initial conditions and transport properties of the strongly interacting matter produced in heavy-ion collisions. In this talk we report on the measurements of $p_{\rm T}$-differential $v_2$ and $v_3$ coefficients for charged hadrons using two-and multi-particle cumulants in Pb-Pb collisions at...
Anisotropic flow, characterised by the flow coefficients $v_n$, is one of the probes used to study the properties of the strongly interacting Quark-Gluon Plasma formed in ultra-relativitic heavy-ion collisions. These flow coefficients are usually measured by correlations between two or more particles.
We present results on the pseudorapidity ($\eta$) dependence of...
The study of flow coefficients and in particular their higher orders, provides important constraints on the initial conditions and transport properties of the QGP. It has been shown that higher order flow coefficients ($n > 3$) have significant contribution from lower order initial spatial anisotropies giving rise to non-linear flow modes. Thus, these non-linear observables probe the...
