Cold Nuclear Matter Effects Research Articles

Measurement of J/ψ at forward and backward rapidity in p+p , p+Al , p+Au , and He3+Au collisions at sNN=200 GeV

Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of $J/\psi$ measurements at forward and backward rapidity in various small collision systems, $p$$+$$p$, $p$$+$Al, $p$$+$Au and $^3$He$+$Au, at $\sqrt{s_{_{NN}}}$=200 GeV. The results are presented in the form of the observable $R_{AB}$, the nuclear modification factor, a measure of the ratio of the $J/\psi$ invariant yield compared to the scaled yield in $p$$+$$p$ collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on $J/\psi$ production with different projectile sizes $p$ and $^3$He, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for $p$$+$Au and $^{3}$He$+$Au. However, for 0%--20% central collisions at backward rapidity, the modification for $^{3}$He$+$Au is found to be smaller than that for $p$$+$Au, with a mean fit to the ratio of $0.89\pm0.03$(stat)${\pm}0.08$(syst), possibly indicating final state effects due to the larger projectile size.

Reconstruction of D0 meson in d+Au collisions at = 200 GeV by the STAR experiment

Owing to their large masses, charm quarks are predominantly produced through initial hard scatterings in heavy-ion collisions. Therefore, they can serve as penetrating probes to study the intrinsic properties of the hot medium created in heavy-ion collisions. However, Cold Nuclear Matter effects can also affect the charm quark production in nuclear collisions with respect to p + p collisions. These effects can be measured in small collision systems such as d/p+Au. In these proceedings, D0 meson reconstruction in d+Au collisions at at the STAR experiment is described. Thanks to the excellent impact parameter resolution provided by the Heavy Flavor Tracker detector, D0() mesons are topologically reconstructed from their hadronic decay channel D0 () (). The Boosted Decision Trees machine learning algorithm from the TMVA package is applied in order to improve signal/background separation.

Jet angularities in photoproduction at the Electron-Ion Collider

We consider the one-parameter family of jet substructure observables known as angularities using the specific case of inclusive jets arising from photoproduction events at an Electron-Ion Collider (EIC). We perform numerical calculations at next-to-leading logarithmic accuracy within perturbative QCD and compare our results to PYTHIA 6 predictions. Overall, we find good agreement and conclude that jet substructure observables are feasible at the EIC despite the relatively low jet transverse momentum and particle multiplicities. We investigate the size of subleading power corrections relevant at low energies within the Monte Carlo setup. In order to establish the validity of the Monte Carlo tune, we also perform comparisons to jet shape data at HERA. We further discuss detector requirements necessary for angularity measurements at an EIC, focusing on hadron calorimeter energy and spatial resolutions. Possible applications of precision jet substructure measurements at the EIC include the tuning of Monte Carlo event generators, the extraction of nonperturbative parameters and studies of cold nuclear matter effects.

Measurement of electrons from heavy-flavour hadron decays as a function of multiplicity in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV

The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval −1.07 < ycms< 0.14 and transverse momentum interval 2 < pT< 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (Qcp). The QpPb results obtained are consistent with unity within uncertainties in the measured pT interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions.

Measurements of heavy-flavor jets with ALICE at the LHC

Heavy quarks created in ultra-relativistic heavy-ion collisions are mostly produced in hard QCD processes during the early stages of the reaction. They interact with the hot and cold nuclear matter throughout the evolution of the medium via semi-hard and soft processes such as energy loss via gluon radiations and collisions. Nuclear modification of heavy flavors in p-A systems provides insight into cold nuclear matter effects such as (anti)shadowing and kT- broadening, and serves as a baseline for A-A studies. In addition to that the fully reconstructed heavy-flavor jets provide additional information on the flavor (or mass) dependence of fragmentation, color charge effects as well as insight into the contribution of late gluon splitting. In this contribution, we present the measurements of b-jet production in p–Pb collisions at sNN=5.02 TeV and c-jet production in pp, p–Pb and Pb–Pb collisions measured by the ALICE experiment at the LHC. The measurements of the nuclear modification factors for c-jet in p–Pb and Pb–Pb collisions are also presented. The experimental measurements are compared with the results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and the NLO pQCD calculations (POWHEG+PYTHIA6). We find good agreement of the measurements with the results from Monte Carlo event generators and from NLO pQCD calculations.

Measurements of quarkonia and open heavy-flavour production in heavy-ion collisions with the ATLAS detector

Measurements of quarkonia produced in ultrarelativistic Pb+Pb collisions provide a means to probe the properties and evolution of the hot and dense medium created in those collisions. Promptly produced quarkonia are directly affected by the interaction with the hot nuclear matter, while non-prompt production allows for the study of b-quark energy loss. The studies of quarkonia production are complemented by measurements of the azimuthal modulation of J/ψ production. Studies of quarkonia and open-charm production in p+Pb collisions provide an additional insight, as they directly probe cold nuclear matter effects. This report will present the most recent ATLAS measurements of charmonia production and flow in Pb+Pb collisions, as well as charmonia and bottomonia production in p+Pb collisions. In addition, results on D meson production and flow will be presented.

Quarkonium Production Measurements with the ALICE Detector at the LHC

In (ultra-)relativistic heavy-ion collisions, the strongly interactingmatter is predicted to undergo a phase transition into a plasma of deconfinedquarks and gluons (QGP) and quarkonia probe different aspects of this medium.However, the medium modification of quarkonium production includes also the contribution of cold nuclear matter effects (CNM), such as shadowing or nuclear break-up in addition to QGP effects. Proton--nucleus collisions, where no QGP is expected, are used to measure cold nuclear matter effects on quarkonium production. Vacuum production of quarkonia is modelled in proton--proton (pp) collisions, which are used as reference for both heavy-ion and proton--nucleus collisions. Besides serving as reference, results in pp collisions represent a benchmark test of QCD based models in both perturbative and non-perturbative regimes. The ALICE detector has unique capabilities at the LHC for measuring quarkonia down to zero transverse momentum. Measurements are carried out at both central and forward rapidity, in the dielectron and dimuon decay channel, respectively. In this contribution the latest quarkonium measurements for various energies and colliding systems, performed by the ALICE Collaboration during the LHC Run-2 period, will be discussed.

Recent progress of quarkonium measurements in heavy-ion collisions at RHIC energies from STAR

One of the primary goals of relativistic heavy-ion collisions is searching for quark-gluon plasma and studying its properties. Among the probes of QGP, the suppression of heavy quarkonium, due to color screening, in heavy-ion collisions has been proposed as a direct signature of QGP formation. However, other effects, such as regeneration and cold nuclear matter effect, would also significantly modify the production of heavy quarkonium in heavy-ion collisions. Recently, the STAR collaboration has installed a new detector, the Muon Telescope Detector. It enables the STAR collaboration to measure quarkonium precisely via di-muon decay channel to constrain the motion of heavy quarkonium in QGP. In this article, the recent progress of quarkonium measurements in p+Au and Au+Au collisions at 200 GeV will be reviewed. Moreover, the measurement of very-low- p T J/ψ, which is likely from coherent photoproduction in heavy-ion collisions, and its physics implication will be discussed.

Inclusive heavy flavor jet production with semi-inclusive jet functions: from proton to heavy-ion collisions

The past several years have witnessed important developments in the QCD theory of jet production and jet substructure in hadronic collisions. In the framework of soft-collinear effective theory, semi-inclusive jet functions and semi-inclusive fragmenting jet functions have allowed us to combine higher order calculations with resummation of potentially large logarithms of the jet radius, ln R. Very recently, the semi-inclusive jet functions for partons fragmenting into heavy flavor jets were computed by Dai, Kim and Leibovich. In this paper we show how the formalism can be extended to c-jet and b-jet production in heavy ion collisions. The semi-inclusive jet functions for heavy flavor jets in a QCD medium are evaluated up to the next-to-leading order in αs and first order in opacity. For phenomenological applications, we also consider the inclusion of the cold nuclear matter effects and the jet energy dissipation due to collisional interactions in matter. We present the numerical predictions for the cross sections and the corresponding nuclear modification factors in proton-nucleus and nucleus-nucleus collisions and compare our results to data from the Large Hadron Collider.

Lepton-Jet Correlations in Deep Inelastic Scattering at the Electron-Ion Collider.

We propose the lepton-jet correlation in deep inelastic scattering as a unique tool for the tomography of nucleons and nuclei at the electron-ion collider (EIC). The azimuthal angular correlation between the final state lepton and jet depends on the transverse momentum dependent quark distributions. We take the example of single transverse spin asymmetries to show the sensitivity to the quark Sivers function. When the correlation is studied in lepton-nucleus collisions, transverse momentum broadening effects can be used to explore cold nuclear matter effects. These features make lepton-jet correlations an important new hard probe at the EIC.

Nuclear Physics at the Energy Frontier: Recent Heavy Ion Results from the Perspective of the Electron Ion Collider

Quarks and gluons are the fundamental constituents of nucleons. Their interactions rather than their mass are responsible for 99 % of the mass of all visible matter in the universe. Measuring the fundamental properties of matter has had a large impact on our understanding of the nucleon structure and it has given us decades of research and technological innovation. Despite the large number of discoveries made, many fundamental questions remain open and in need of a new and more precise generation of measurements. The future Electron Ion Collider (EIC) will be a machine dedicated to hadron structure research. It will study the content of protons and neutrons in a largely unexplored regime in which gluons are expected to dominate and eventually saturate. While the EIC will be the machine of choice to quantify this regime, recent surprising results from the heavy ion community have begun to exhibit similar signatures as those expected from a regime dominated by gluons. Many of the heavy ion results that will be discussed in this document highlight the kinematic limitations of hadron–hadron and hadron–nucleus collisions. The reliability of using as a reference proton–proton (pp) and proton–ion (pA) collisions to quantify and disentangle vacuum and Cold Nuclear Matter (CNM) effects from those proceeding from a Quark Gluon Plasma (QGP) may be under question. A selection of relevant pp and pA results which highlight the need of an EIC will be presented.

Probing cold nuclear matter effects with the productions of isolated- and +jet in p+Pb collisions at 8.16 TeV * * Supported by the NSFC of China (11435004, 11322546, 11805167) and partly Supported by China University of Geosciences (Wuhan) (162301182691)

We investigate cold nuclear matter (CNM) effects on the productions of isolated prompt photons and jet in proton-lead collisions at TeV under next-to-leading order perturbative quantum chromodynamics calculations with four parameterizations for nuclear parton distribution functions (nPDFs), i.e., DSSZ, EPPS16, nCTEQ15, and nIMParton. Our theoretical calculations provide good descriptions of the pp baseline in the ATLAS collaboration and make predictions for future experimental results at + collisions. We calculate the dependence of the nuclear modification factor of isolated prompt photons on transverse momentum and pseudo-rapidity at very forward and backward rapidity regions, and we demonstrate that the forward-to-backward yield asymmetries as a function of with different nPDF parameterizations have diverse behaviors. Furthermore, the nuclear modification factor of isolated- jet as a function of jet's pseudo-rapidity at different average transverse momenta has been discussed. This can facilitate a tomographic study of CNM effects with precise locations in a rather wide kinematic region by varying the transverse momenta and rapidities of both isolated photons and jets in p+A collisions.

Jet fragmentation transverse momentum measurements from di-hadron correlations in sqrt{mathrm{s}}=7 TeV pp and sqrt{s_{mathrm{NN}}}=5.02 TeV p\u2013Pb collisions

The transverse structure of jets was studied via jet fragmentation transverse momentum (jT) distributions, obtained using two-particle correlations in proton-proton and proton-lead collisions, measured with the ALICE experiment at the LHC. The highest transverse momentum particle in each event is used as the trigger particle and the region 3 < pTt < 15GeV/c is explored in this study. The measured distributions show a clear narrow Gaussian component and a wide non-Gaussian one. Based on Pythia simulations, the narrow component can be related to non-perturbative hadronization and the wide component to quantum chromodynamical splitting. The width of the narrow component shows a weak dependence on the transverse momentum of the trigger particle, in agreement with the expectation of universality of the hadronization process. On the other hand, the width of the wide component shows a rising trend suggesting increased branching for higher transverse momentum. The results obtained in pp collisions at sqrt{s}=7 TeV and in p–Pb collisions at sqrt{s_{mathrm{NN}}}=5.02 TeV are compatible within uncertainties and hence no significant cold nuclear matter effects are observed. The results are compared to previous measurements from CCOR and PHENIX as well as to Pythia 8 and Herwig 7 simulations.

Measurements of charm, bottom, and Drell-Yan via dimuons in p+p and p+Au collisions at [formula omitted] with PHENIX at RHIC

Dilepton spectra are a classic probe to study ultra-relativistic heavy ion collisions. At RHIC energies, the dimuon continuum is dominated by correlated pairs from semi-leptonic decays of charm and bottom hadrons and the Drell-Yan process. The dimuon spectra contain information on heavy flavor angular correlations, which can constrain the relative contributions from different heavy flavor production mechanisms. Studying heavy flavor correlations in p+Au collisions may provide further insight on cold nuclear matter effects. Measurements of the Drell-Yan cross-section can provide constraints to PDFs, as well as further our understanding in initial state interactions in p+Au collisions.In this talk, we report measurements of μμ pairs from charm, bottom, and Drell-Yan in p+p and p+Au collisions at sNN=200GeV. A further shape analysis is applied to the heavy flavor pair correlations to extract the relative contributions to heavy flavor production mechanisms.

Quarkonium production in nuclear collisions

In these proceedings, an overview of recent quarkonium measurements in nuclear collisions carried out at both RHIC and LHC is presented. In p+p collisions, despite theoretical progresses made in understanding the production mechanisms for quarkonia, a complete picture is still yet to be achieved. In p+A collisions where measurements are done to quantify the cold nuclear matter effects, significant suppression of quarkonium production is observed for low transverse momentum region at both forward- and mid-rapidities. Furthermore, results from A+A collisions show the interplay of dissociation and regeneration contributions for charmonium at different collision energies, while a correspondence between the suppression level and the binding energy is observed for bottomonium family. Comparisons to experimental data provide stringent tests to model calculations, and help constrain the temperature of the deconfined medium created in heavy-ion collisions.

Prompt [formula omitted] baryons and D0 meson production cross-section and nuclear modification in pPb collisions at [formula omitted] with the LHCb detector

Λc+ baryons and D0 mesons are studied in pPb collisions at sNN=5.02TeV. The nuclear modification factor and forward-backward cross-section asymmetry are measured in order to study the cold nuclear matter effects. The prompt Λc+ production cross-section is compared to that of the prompt D0 mesons, providing insights into the hadronisation mechanism of charmed hadrons.

Open heavy-flavour production and elliptic flow in p-Pb collisions at the LHC with ALICE

Measurements of open heavy flavour production in p–A collisions allow the investigation of Cold Nuclear Matter effects. In addition, they are an important tool for a complementary investigation of the long-range correlations found in small systems in the light flavour sector. In this work, production measurements of D mesons at mid-rapidity in p–Pb collisions at sNN=5.02TeV are reported. Production yields are also reported for the heavy-flavour hadron decay electrons at central rapidity at sNN=5.02 and 8.16 TeV. The elliptic flow (v2) of heavy-flavour hadron decay electrons in high-multiplicity p-Pb collisions at sNN=5.02TeV is found to be positive with a significance larger than 5σ.

Results on quarkonia production in Heavy Ion collisions from the ATLAS Experiment

The observed quarkonia states in heavy ion collisions provide a powerful tool to probe the dynamics of the Quark Gluon Plasma. Measurements performed on the ground and excited quarkonia states, as well as their separation into prompt and non-prompt components, reveal the effects of colour screening and colour recombination. In addition, quarkonium production rates and their excited to ground state production ratios in lighter p+Pb collisions are an interesting probe of cold nuclear matter effects. In these proceedings, the latest results of the ATLAS experiment at the LHC on these observables will be presented.

Quark branching in QCD matter to any order in opacity beyond the soft gluon emission limit

Cold nuclear matter effects in reactions with nuclei at a future electron-ion collider (EIC) lead to a modification of semi-inclusive hadron production, jet cross sections, and jet substructure when compared to the vacuum. At leading order in the strong coupling, a jet produced at an EIC is initiated as an energetic quark, and the process of this quark splitting into a quark-gluon system underlies experimental observables. The spectrum of gluons associated with the branching of this quark jet is heavily modified by multiple scattering in a medium, allowing jet cross sections and jet substructure to be used as a probe of the medium's properties. We present a formalism that allows us to compute the gluon spectrum of a quark jet to an arbitrary order in opacity, the average number of scatterings in the medium. This calculation goes beyond the simplifying limit in which the gluon radiation is soft and can be interpreted as energy loss of the quark, and it significantly extends previous work which computes the full gluon spectrum only to first order in opacity. The theoretical framework demonstrated here applies equally well to light parton and heavy quark branching, and is easily generalizable to all in-medium splitting processes.

Properties of Light Mesons in Interactions between Heavy Nuclei in the PHENIX Experiment

Observations of collective effects in (A + A) collisions of heavy nuclei confirm the formation of quark–gluon plasma. The systematic study of collective effects of hot nuclear matter associated with the quark–gluon medium and their separation from the effects of cold nuclear matter associated with nucleon medium is one of the main aims of modern high-energy physics. Such studies are conducted using different systems of colliding nuclei. The results are presented from measuring the nuclear modification factors of neutral pions in Cu + Au, p + Au, d + Au, and 3He + Au collisions at 200 GeV.