Conveners
Parallel 4: Electroweak: Photon-induced processes (UPC)
- Alexander Milov (Weizmann Institute of Science (IL))
Parallel 4: Electroweak: Photon-induced processes (UPC)
- Axel Drees
Parallel 4: Novel theoretical developments
- Francois Arleo (Centre National de la Recherche Scientifique (FR))
Parallel 4: HF & QQbar: Heavy flavour flow
- Silvia Masciocchi (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
Parallel 4: Electroweak: Photons
- Jean-Philippe Guillet (LAPTh CNRS)
Parallel 4: Electroweak: Photons & dileptons
- Itzhak Tserruya (Weizmann Institute of Science (IL))
Parallel 4: Novel experimental developments
- Thomas Peitzmann (Nikhef National institute for subatomic physics (NL))
Parallel 4: HF & QQbar
- Peter Alan Steinberg (Brookhaven National Laboratory (US))
At the LHC, the highly boosted electromagnetic field of the beam
particles represents a source of quasi-real photon. Vector meson
photo-production measurements in pp/Pb-Pb collisions are sensitive to
the gluon parton distribution functions in the proton/nucleus. LHCb
results on charmonium production in ultra-peripheral Pb-Pb collisions at
5.02 TeV and in pp at 13 TeV will be presented.
In high-energy heavy-ion collisions, dileptons can be produced via photon-photon and photonuclear processes, induced by the strong electromagnetic field accompanying highly charged relativistic heavy ions. These two processes were conventionally and extensively studied in ultra-peripheral collisions (UPCs). Recently, a significant excess of $J/\psi$ yields at low transverse momenta ($p_T$) was...
The photo-production of heavy vector mesons in the electromagnetic interactions
of ultra-relativistic nuclei is thought to be sensitive to the gluon parton
distribution functions in the nucleus and thus to cold nuclear effects like shadowing
or gluon saturation. Besides the well known observations of vector meson
production in ultra-peripheral collisions (UPC), recently there were reports...
The aim of this study is to measure exclusive photoproduction of three resonant particles, $\bf \Upsilon(1S)$, $\bf \Upsilon(2S)$ and $\bf \Upsilon(3S)$ mesons, in their $\mu^{+}\mu^{-}$ decay modes, in ultraperipheral pPb collisions. The $\bf \Upsilon(1S)$ photoproduction cross section are measured, over the rapidity range $| y | < 2.2$, as a function of the photon-proton center-of-mass...
The coherent photon-nucleus and photon-photon interactions has been studied in detail to probe the gluon distribution in nucleus and to test QED via relativistic heavy-ion collisions. These kind of interactions are traditionally thought to be only exist in ultra-peripheral collisions (UPC), where there is no hadronic interactions. Recently, significant excess of $J/\psi$ yield and dielectron...
In ultra-relativistic heavy-ion collisions the intense electromagnetic fields of the nuclei provide a large flux of equivalent photons. This flux leads to photon-photon and photon-nucleus reactions at high center-of-mass energies. In ultra-peripheral collisions (UPCs), the nuclei have large impact parameter, and the dominant interaction mechanism is through these photon-induced processes. This...
A measurement of light-by-light scattering, γγ → γγ, in ultraperipheral PbPb collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is reported. The analysis is conducted using a data sample corresponding to an integrated luminosity of 390 μb − 1 recorded by the CMS experiment at the LHC. Light-by-light scattering processes are selected in events with two photons exclusively...
We discuss the physics case related to the studies of ultra-peripheral $p$+(H,$^3$He) and Pb+(H,$^3$He) collisions in the fixed-target mode at the LHC. In particular, we show how one can measure the gluon GPD $E_g(x,\xi)$ in exclusive $J/\psi$ photoproduction with a transversely polarised hydrogen target.
We present a study the two-photon production of the Higgs boson, gamma-gamma->H, at the LHC and Future Circular Collider (FCC) in ultraperipheral PbPb and pPb collisions at sqrt(s_NN) = 5.5, 8.8, 39 and 63 TeV. Signal and background events are generated with MADGRAPH 5, including gamma fluxes from the proton and lead ions in the equivalent photon approximation, yielding sigma(gamma-gamma->H) =...
The final-state interactions of a Higgs boson with a dense quark-gluon medium are studied. The dominant Higgs-parton scattering processes, $g\,H\to\,g\,g,Q\,\bar{Q}$, have a total cross section $\sigma_{Hg}\approx $1-10$ \mu b$, in the kinematical range of relevance at current and future hadron colliders. Such medium-induced enhancement of the Higgs decays into a pair of jets leads to an...
The jet energy loss coefficient $\hat{q}$ serves as one of the most important transport coefficients that characterize the modification of hard jets in a QGP. A quantitative extraction of $\hat{q}$ requires sophisticated jet quenching theory, precise and extensive experimental data, as well as an advanced statistical framework that compares theory to data. Within the JETSCAPE collaboration,...
We have developed a hybrid hadronization model with two well-defined limits: string fragmentation for dilute systems, and quark recombination for dense sytems of partons. The model smoothly interpolates in between those limits by evaluating the probability of quark wave packets to coalesce with each other into hadronic wave functions as a deciding factor. We will discuss a new implementation...
We derive a diffusion coefficient of quarks propagating through a strongly coupled plasma from the AdS/CFT correspondence. This diffusion coefficient interpolates between light and heavy flavour. In contradistinction to past results, this diffusion coefficient does not increase with quark velocity. Taking our diffusion coefficient derivation as fundamental, we use the fluctuation-dissipation...
We compute for the first time the suppression of bottomonia in a strongly coupled QGP and compare the results to those from a weakly coupled QGP and to data. Using imaginary time techniques we numerically determine the real and imaginary parts of the ground state binding energy of the $\Upsilon$(1S) in a $p_T$-independent potential computed from AdS/CFT and another computed from pQCD. We...
Beyond 2020 we will enter the High-Luminosity era of the LHC, right after the upgrades of the second Long Shutdown of the Large Hadron Collider (LHC). The ongoing state-of-the-art experimental instrument upgrades require high-performance simulation framework in the background, which is modern, robust, and comes with long term support.
Here we present the HIJING++ (Heavy Ion Jet INteraction...
The experimentally observed dissociation and regeneration of bound charmonium states in heavy-ion collisions provide a powerful tool to probe the dynamics of the hot, dense plasma. These measurements are sensitive to the effects of color screening, color recombination, and possibly to other, new phenomena affecting dynamics of heavy quarks in the QCD medium. In the large-statistics Run 2...
In pp collisions such as the ones delivered by the LHC since 2010, the production of heavy quarks proceeds dominantly from the hard scattering of two gluons. These quarks then hadronize in either open heavy-flavor hadrons or quarkonia (e.g. $J/\psi$, $\Upsilon$). The study of quarkonium production as a function of the charged particle multiplicity therefore naturally links soft and hard...
Measurements of open heavy flavour production in p--A collisions offer a way to study so called Cold Nuclear Matter (CNM) effects, which include gluon shadowing, gluon saturation, $k_{\rm T}$ broadening, and energy loss in CNM, that can affect the production rate and the kinematic properties of charm and beauty hadrons in nuclear collisions.
In addition, in recent years, in pp and p--Pb...
Heavy flavor production and collectivity in A+A and $p$+A collisions provide insight into the energy loss mechanism and transport properties of heavy quarks in QGP regions of varying sizes and temperatures. This talk presents a comprehensive overview of the latest ATLAS heavy flavor results in different collision systems. Final results on the production of muons from heavy flavor decays in...
The measurement of heavy quark collective motion in heavy ion collisions is a powerful tool to reveal key QGP properties, such as shear viscosity and quark diffusion. PHENIX has new measurements of the second Fourier harmonic, v2, of separated charm and bottom quarks at mid-rapidity |y|<0.35 in Au+Au collisions at sqrt(sNN)=200 GeV. The technique utilized in these measurements makes use of the...
Photons are penetrating probes of the strongly-coupled nuclear plasma created in relativistic heavy-ion collisions. The entire spacetime evolution of the Quark-Gluon Plasma (QGP) is imprinted in their spectrum and momentum anisotropies, making them effective probes the earlier stage of heavy ion collisions. In this talk we use photons to study the complex initial dynamics of lower energy...
In recent years data from small collision systems at LHC and RHIC have revealed evidence for collective behavior of the produced hadrons, and indications that a hot strongly-coupled system is being formed in these collisions. If so, the matter formed must also radiate thermal or low momentum direct photons. The versatility of RHIC puts PHENIX in an ideal position to search for any indications...
Direct photons are a powerful tool for elucidating the properties of the hot QCD matter in heavy-ion collisions. They are estimated by assuming that the scaled baseline of proton-proton collision result, which exhibits fair agreement with perturbative QCD calculations, represents prompt photons. On the other hand, recent analyses on azimuthal momentum anisotropy show that a primordial fluid...
Direct photons are produced by various processes in pp, p–A and A–A collisions and are sensitive to details of the space-time evolution the medium produced in heavy-ion collisions. In A-A collisions the low $p_{\rm T}$ part of the direct photon spectrum is expected to be dominated by thermal direct photons - thermal radiation of hot matter, i.e., of the quark-gluon plasma and the...
PHENIX has observed that a large number of direct photons are radiated during the evolution of the strongly coupled QGP produced in Au+Au collision at 200 GeV to hadron resonance matter. The direct photons are emitted with a large azimuthal anisotropy. PHENIX has extended this study using large data samples from Au+Au collisions at 39, 62.4, and 200 GeV, and Cu+Cu collisions at 200 GeV. For a...
Measurements of photon and jet production in small collision systems are of great interest to understanding the partonic structure of heavy nuclei, and serve as a constraint on the initial state in large collision systems. These channels are sensitive to a broad set of physics effects such as the modification of the parton densities in nuclei, including the onset of non-linear QCD or...
The intensive synchrotron radiation resulting from the quarks interacting with a collective confining color field in the heavy ion collisions is discussed. The spectrum of hard photons is presented and is compared with experimental data showing a feasibility of this magnetic bremsstrahlung-like radiation. The study of the predicted early specific anisotropy in the angle distribution of leptons...
Dileptons (l$^+$l$^-$) are produced during all stages of heavy-ion collisions (HIC) via various production mechanisms. Since leptons interact through the electromagnetic force, not via the strong force, they carry pristine information about the produced medium. For this reason, dileptons provide an essential tool for studying the properties of the strongly interacting medium produced in HICs. ...
The production of low-mass dielectrons is one of 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. At low invariant mass ($m_{\rm ee} <$ 1.1 GeV/$c^{2}$), the dielectron invariant-mass spectrum is sensitive to the properties of short-lived...
The ALICE Collaboration is preparing a major upgrade of the detector apparatus during the second LHC long shutdown (LS2, 2019-20) in view of the LHC Runs 3 and 4 (2021 to 2029).
The objective of the ALICE upgrade for LS2 is two-fold: i) an improvement of the tracking precision and efficiency, in particular in the low-momentum range; ii) an improvement of the readout capabilities of the...
sPHENIX is the next generation heavy ion physics experiment designed to collect a suite of unique jet and Upsilon observables with unprecedented statistics and kinematic reach at RHIC. The sPHENIX inner most tracking detector, MVTX (MAPS-based vertex detector), will provide a precise determination of the impact parameter of tracks to the primary vertex in high multiplicity heavy ion...
By extracting the beam with a bent crystal or by using an internal gas target, the multi-TeV proton and lead LHC beams allow one to perform the most energetic fixed-target experiments ever and to study $pp$, $pd$ and $pA$ collisions at $\sqrt{s_{NN}}=115$ GeV and Pb$p$ and PbA collisions at $\sqrt{s_{NN}}=72$ GeV with high precision and modern detection techniques. In this talk, we will review...
The proposed sPHENIX detector at the Relativistic Heavy Ion Collider (RHIC), designed to take advantage of technological advances from the Large Hadron Collider (LHC), will allow measurements of jets and jet correlations with a kinematic reach that will overlap with measurements made at the LHC. This is made possible by taking advantage of the increased luminosity due to accelerator upgrades...
To quantify parton-medium interactions in the presence of a hot-and-dense medium, jets are studied as a function of parton flavor. In particular, gluon initiated jets are expected to lose more energy than corresponding quark jets. Inclusive jets are produced with a high gluon fraction at LHC energies, while boson-tagged jets have a strong enhancement of light-quark initiated jets....
We will present our newly developed DREENA framework, which allows predicting energy loss of high $p_\perp$ partons traversing quark gluon plasma (QGP). The framework is based on dynamical energy loss formalism, and is applied to both the medium with constant temperature (DREENA-C) [1] and to evolving medium modeled by Bjorken 1+1D expansion (DREENA-B) [2]. The formalism allows making...
The production of open heavy flavor in ultrarelativistic heavy ions collisions is known to be one of the best probes of the QGP phase before freeze out as well as of its coupling strength. One of the most topical issues is whether non perturbative effects could increase this strength around the critical temperature and hence communicate a stronger elliptical flow to heavy quarks. In [1], it...
Heavy quarks (charm and beauty) are produced in hard parton scatterings in the early stages of hadronic collisions. Therefore, they are ideal probes to investigate the properties of the Quark-Gluon Plasma (QGP) produced in ultra-relativistic heavy-ion collisions. The study of angular correlations between heavy-flavour particles and charged particles allows us to characterize the heavy-quark...
The dissociation of quarkonia in the medium created in heavy ion collisions is still one of the most debated topics in the heavy ion community. Progress in understanding the effect relies on a broad range of measurement in collisions with different nuclear sizes, covering a broad rapidity coverage. This presentation will report the J/Psi measurements performed by the PHENIX collaboration at...
We study the propagation of charm and bottom quarks in the quark-gluon plasma (QGP) by means of a relativistic Boltzmann transport approach. The non-perturbative interaction between heavy quarks and light quarks is described by means of a quasi-particle approach in which light partons are dressed with thermal masses. It permits to have an Equation of State close to lattice QCD thermodynamics...
