Parton Energy Loss Effect Research Articles

Measurements of the azimuthal anisotropy of prompt and nonprompt charmonia in PbPb collisions at sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV

The second-order (v2) and third-order (v3) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/ψ, as well as prompt ψ(2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb−1 recorded with the CMS detector. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay channel. The v2 and v3 coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measured v2 values for prompt J/ψ mesons are found to be larger than those for nonprompt J/ψ mesons. The prompt J/ψ v2 values at high pT are found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/ψ meson v3 and prompt ψ(2S) v2 and v3 values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.

Atomic mass, Bjorken variable, and scale dependence of quark transport coefficient in Drell-Yan process for proton incident on nucleus* *Supported in part by the National Natural Science Foundation of China (11975090, 11575052).

By means of the nuclear parton distributions determined without the fixed-target Drell-Yan experimental data and the analytic expression of quenching weight based on the BDMPS formalism, next-to-leading order analyses were performed on the Drell-Yan differential cross section ratios from the Fermilab E906 and E866 collaborations. It was found that the results calculated only with the nuclear effects of the parton distribution were not in agreement with the E866 and E906 experimental data. The incoming parton energy loss effect cannot be ignored in the nuclear Drell-Yan reactions. The predicted results indicate that, with the quark transport coefficient as a constant, the suppression due to the target nuclear geometry effect is approximately% for the quark transport coefficient. It was shown that we should consider the target nuclear geometry effect in studying the Drell-Yan reaction on nuclear targets. On the basis of the Bjorken variable and scale dependence of the quark transport coefficient, the atomic mass dependence was incorporated. The quark transport coefficient was determined as a function of the atomic mass, Bjorken variable, and scale by the global fit of the experimental data. The determined constant factor of the quark transport coefficient is GeV/fm. It was found that the atomic mass dependence has a significant impact on the constant factor in the quark transport coefficient in cold nuclear matter.

Impact of parton energy loss and nPDFs on J/ψ production in proton-nucleus collisions

The impact of parton energy loss and nuclear parton distribution functions (nPDFs) on J/ψ production in proton-nucleus collisions are investigated by means of the E866, LHC and RHIC experimental data. By the recent EPPS21 nPDFs, a leading order phenomenological analysis of J/ψ production cross-section ratios is performed for E866 experimental data with considering the parton energy loss effect following Landau-Pomeranchuk-Migdal (LPM) regime. The gluon transport coefficient qˆg extracted from the E866 data in 0.20<xF<0.65 region is qˆg=0.35±0.01 GeV2/fm with χ2/ndf=1.01, which indicates that the significantly better-constrained gluon distributions provided by EPPS21 contribute to accurately determining the gluon energy loss. It is founded that for E866 data in 0.20<xF<0.65 the depletion induced by cc¯ energy loss is the largest, gluon energy loss is the second, and quark energy loss is the smallest. In addition, it can be seen that for LHC and RHIC experiment the role of nPDFs and gluon energy loss on J/ψ production are both significant, which indicates that operating more precise measurements at LHC and RHIC in the future can facilitate significantly better-constrained gluon energy loss and nPDFs.

Drell-Yan nuclear modification due to nuclear effects of nPDFs and initial-state parton energy loss * *Supported partially by National Natural Science Foundation of China (11405043), Natural Science Foundation of Hebei Province (A2018209269) and Science and Technology Foundation of Hebei Education Department (ZD2020104)

By globally analyzing nuclear Drell-Yan data including all incident energies, the nuclear effects of nuclear parton distribution functions (nPDFs) and initial-state parton energy loss are investigated. Based on the Landau-Pomeranchuk-Migdal (LPM) regime, the calculations are carried out by means of analytic parametrizations of quenching weights derived from the Baier-Dokshitzer-Mueller-Peign -Schiff (BDMPS) formalism and using the new EPPS16 nPDFs. It is found that the results are in good agreement with the data and the role of the energy loss effect in the suppression of Drell-Yan ratios is prominent, especially for low-mass Drell-Yan measurements. The nuclear effects of nPDFs become more obvious with increasing nuclear mass number A, the same as the energy loss effect. By a global fit, the transport coefficient extracted is GeV2/fm. In addition, to avoid diminishing the QCD NLO correction to the data form of Drell-Yan ratios, separate calculations of the Compton differential cross section ratios at 120 GeV are performed, which provides a feasible way to better distinguish the gluon energy loss in Compton scattering. It is found that the role of the initial-state gluon energy loss in the suppression of Compton scattering ratios is not very important and disappears with the increase of .

The study of the incoming parton energy loss effect on the NLO nuclear Drell–Yan ratios

At a next-to-leading order (NLO) calculation, the initial-state energy loss of the quark is investigated by means of the Drell–Yan experimental data including the new E906 measurements. Furthermore, the incoming gluon energy loss effect embedded in the Compton scattering subprocess of the nuclear Drell–Yan process is also examined. The NLO computations for Drell–Yan ratios are carried out with the SW quenching weights (provided by Salgado and Wiedemann to evaluate the probability distribution that quark (gluon) loses the energy), as well as the nuclear parton distributions (obtained by only fitting the existing experimental data on nuclear structure functions). It is found that the obtained calculations that consider the incoming quark energy loss agree well with the experimental data particularly for E906 data. In addition, the incoming gluon energy loss embodied in the primary NLO Compton scattering subprocess is not obvious, which may be due to the form of the Drell–Yan differential cross section ratio as a function of the quark momentum fraction () minimizes the influence of the QCD NLO correction.

Multiple scattering and parton energy loss in nuclei

When a fast parton propagates in nuclear medium it may suffer multiple scattering with other partons, which leads to two effects: transverse momentum broadening and jet quenching. In this article, we review the theoretical development of the transverse momentum broadening in the nuclear medium based on the pQCD factorization of higher twist processes, and discuss the implementation of the parton energy loss within higher twist expansion framework in the calculation of the leading hadron productions in relativistic heavy ion collisions at the RHIC and the LHC. We introduce the techniques of next-to-leading order (NLO) calculation for twist-4 process, and verify, for the first time, the universality of nuclear medium property, and we also identify the QCD evolution equation for the nuclear medium. We apply the high twist factorization formalism to calculate the hadron production at backward rapidity in proton-nucleus collisions at RHIC and the LHC, and find that the nuclear enhancement phenomena observed in experiments can be explained as incoherent double scattering. We further investigate parton energy loss effect in the framework of higher twist expansion on the leading hadron production in heavy ion collisions up to the accuracy of NLO pQCD, and calculate the yields and the nuclear modification factors of $\pi^0$, $\eta$, $\rho^0$, $\phi$, $K^0_{\rm~S}$ and $\omega$, and discuss the ratios of the identified hadron yields. By comparing our theoretical results with the latest experimental data on the leading hardon spectra in heavy ion collisions, we also extrapolate the jet transport coefficient. It is found the identified hadron yields in A+A collisions depend on three factors: the initial hard jet spectrum and the energy loss mechanism as well as parton fragmentation functions to the hadron in vacuum.

Initial-state energy loss in cold QCD matter and the Drell-Yan process

The effects of parton energy loss in nuclear matter on the Drell-Yan process in pA and πA collisions at fixed-target energies are investigated. Calculations are based on the Baier-Dokshitzer-Mueller-Peigné-Schiff (BDMPS) framework embedded in a next-to-leading order calculation, using the transport coefficient extracted from J/ψ measurements. Model calculations prove in good agreement with preliminary measurements by the E906 experiment, despite a slightly different magnitude, supporting a consistent picture between Drell-Yan and J/ψ data. Predictions for the COMPASS future measurements in πA collisions at sqrt{s}=18.9 GeV are also performed. At higher collision energy ( sqrt{s}=38.7 GeV), Drell-Yan measurements are only slightly affected by energy loss effects. On the contrary, the E906 results turn out in clear disagreement with nuclear PDF effects alone. The comparison of E772, E866, and E906 measurements indicates for the first time a clear violation of QCD factorization in Drell-Yan production in pA collisions.

The study of gluon energy loss in cold nuclear matter from J/ψ production**Supported by National Natural Science Foundation of China (11405043) and Natural Science Foundation of Hebei Province (A2018209269)

The energy loss effects of the incident quark, gluon, and the color octet on J/ψ suppression in p-A collisions are studied by means of the experimental data at E866, RHIC, and LHC energy. We extracted the transport coefficient for gluon energy loss from the E866 experimental data in the middle xF region (0.20 < xF > 0.65) based on the Salgado-Wiedemann (SW) quenching weights and the recent EPPS16 nuclear parton distribution functions together with nCTEQ15. It was determined that the difference between the values of the transport coefficient for light quark, gluon, and heavy quark in cold nuclear matter is very small. The theoretical results modified by the parton energy loss effects are consistent with the experimental data for E866 and RHIC energy, and the gluon energy loss plays a remarkable role on J/ψ suppression in a broad variable range. Because the corrections of the nuclear parton distribution functions in the J/ψ channel are significant at LHC energy level, the nuclear modification due to the parton energy loss is minimal. It is worth noting that we use the color evaporation model (CEM) at leading order to compute the p-p baseline, and the conclusion in this paper is CEM model dependent.

Nuclear suppression of the phi meson yields with large p_T at the RHIC and the LHC

We calculate phi meson transverse momentum spectra in mathrm{p}+mathrm{p} collisions as well as their nuclear suppressions in central mathrm{A}+mathrm{A} collisions both at the RHIC and the LHC in LO and NLO with the QCD-improved parton model. We have included the parton energy loss effect in a hot/dense QCD medium with the effectively medium-modified phi fragmentation functions in the higher-twist approach of jet quenching. The nuclear modification factors of the phi meson in central mathrm{Au}+mathrm{Au} collisions at the RHIC and central mathrm{Pb}+mathrm{Pb} collisions at the LHC are provided, and nice agreement of our numerical results at NLO with the ALICE measurement is observed. Predictions of the yield ratios of neutral mesons such as phi /pi ^0, phi /eta and phi /rho ^0 at large p_T in relativistic heavy-ion collisions are also presented for the first time.

Two-particle correlations with identified triggers in p -Pb collisions at sNN=5.02 TeV using a multiphase transport model

We report calculations regarding recent measurements of near-side jetlike yields obtained from the angular correlations with pions and protons as trigger particles and unindentified charged hadrons as associated at intermediate transverse momentum (${p}_{T}$). Events generated from the string melting version of a multiphase transport model (AMPT) and HIJING are analyzed to calculate the near-side jetlike yields associated with pion and proton triggers in $p$-Pb collisions at 5.02 TeV. Multiplicity dependence of the near-side jetlike yield is studied by subtracting the so-called long-range correlations. In $A\ensuremath{-}A$ collisions, at intermediate ${p}_{T}$, jetlike yield associated with baryon trigger shows a gradual suppression from peripheral to central events following an initial rise. This suppression was interpreted as a combined effect of parton energy loss due to jet-quenching and particle production via quark recombination generating anomalous baryon to meson enhancement at intermediate ${p}_{T}$. Similar enhancement was also observed in small collision systems like $p$-Pb at CERN Large Hadron Collider (LHC) energy. In absence of any significant jet-medium interplay in small systems, trigger species dependence of the associated jetlike yield may be attributed dominantly to the dynamics of quark coalescence and/or radial flow. The multiplicity evolution of the trigger species dependence of jetlike yields, obtained from AMPT, found to be completely different from the same when extracted from a hydrodynamical model, EPOS. With the data available at LHC, these results may be tested to achieve further insight on the underlying dynamics in small collision systems, and the mechanism of hadronization at intermediate ${p}_{T}$ as well.

Medium-induced flavor conversion and kaon spectra in electron-ion collisions

Multiple scattering and induced parton splitting lead to a medium modification of the QCD evolution for jet fragmentation functions and the final hadron spectra. Medium-induced parton splittings not only lead to energy loss of leading partons and suppression of leading hadron spectra, but also modify the flavor composition of a jet due to induced flavor conversion via gluon emission, quark pair production and annihilation. Through a numerical study of the medium-modified QCD evolution, leading $K^-$ strange meson spectra are found to be particularly sensitive to the induced flavor conversion in semi-inclusive deeply inelastic scatterings (SIDIS) off a large nucleus. The induced flavor conversion can lead to increased number of gluons and sea quarks in a jet and, as a consequence, enhance the leading $K^-$ spectra to counter the effect of parton energy loss in SIDIS with large momentum fractions $x_B$ where the struck quarks are mostly valence quarks of the nucleus.

Quarkonium suppression in heavy-ion collisions from coherent energy loss in cold nuclear matter

The effect of parton energy loss in cold nuclear matter on the suppression of quarkonia (J/ψ, ϒ) in heavy-ion collisions is investigated, by extrapolating a model based on coherent radiative energy loss recently shown to describe successfully J/ψ and ϒ suppression in proton-nucleus collisions. Model predictions in heavy-ion collisions at RHIC (Au-Au, Cu-Cu, and Cu-Au) and LHC (Pb-Pb) show a sizable suppression arising from the sole effect of energy loss in cold matter. This effect should thus be considered in order to get a reliable baseline for cold nuclear matter effects in quarkonium suppression in heavy-ion collisions, in view of disentangling hot from cold nuclear effects.

J/ψ suppression in p–A collisions from parton energy loss in cold nuclear matter

Abstract The effects of parton energy loss in cold nuclear matter on J / ψ suppression in p–A collisions are studied. Results obtained in d–Au collisions at RHIC are compared to PHENIX data, and predictions in p–Pb collisions at the LHC are made.

Centrality and p ⊥ dependence of J/ψ suppression in proton-nucleus collisions from parton energy loss

Abstract The effects of parton energy loss and p ⊥-broadening in cold nuclear matter on the p ⊥ and centrality dependence, at various rapidities, of J/ψ suppression in p-A collisions are investigated. Calculations are systematically compared to E866 and PHENIX measurements. The very good agreement between the data and the theoretical expectations further supports p ⊥-broadening and the associated medium-induced parton energy loss as dominant effects in J/ψ suppression in high-energy p-A collisions. Predictions for J/ψ (and $ \varUpsilon $ ) suppression in p-Pb collisions at the LHC are given.

Jet probes of QCD matter: Single jets and dijets in heavy-ion collisions

Modifications of jets in the existence of a hot and dense QCD medium have recently attracted a lot of attentions. In this talk, we demonstrate how jet-medium interactions change the behavior of jets by offering examples of inclusive jet and dijet productions at $ {\cal O}(\alpha_s^3)$ in heavy ion collisions including initial-state cold nuclear effects and especially the final-state parton energy loss effect. The suppression of inclusive jet spectrum varying with jet radii and a flatter dijet momentum imbalance as compared to those in hadron-hadron collisions are observed in high-energy nuclear collisions.

Heavy-quarkonium suppression in p-A collisions from parton energy loss in cold QCD matter

Abstract The effects of parton energy loss in cold nuclear matter on heavy-quarkonium suppression in p-A collisions are studied. It is shown from first principles that at large quarkonium energy E and small production angle in the nucleus rest frame, the medium-induced energy loss scales as E. Using this result, a phenomenological model depending on a single free parameter is able to reproduce J/ψ and Υ suppression data in a broad x F -range and at various center-of-mass energies. These results strongly support energy loss as the dominant effect in heavy-quarkonium suppression in p-A collisions. Predictions for J/ψ and Υ suppression in p-Pb collisions at the LHC are made. It is argued that parton energy loss scaling as E should generally apply to hadron production in p-A collisions, such as light hadron or open charm production.

Monte Carlo approach for hadron azimuthal correlations in high energy proton and nuclear collisions

We use a Monte Carlo approach to study hadron azimuthal angular correlations in high energy proton-proton and central nucleus-nucleus collisions at the BNL Relativistic Heavy Ion Collider (RHIC) energies at mid-rapidity. We build a hadron event generator that incorporates the production of $2\to 2$ and $2\to 3$ parton processes and their evolution into hadron states. For nucleus-nucleus collisions we include the effect of parton energy loss in the Quark-Gluon Plasma using a modified fragmentation function approach. In the presence of the medium, for the case when three partons are produced in the hard scattering, we analyze the Monte Carlo sample in parton and hadron momentum bins to reconstruct the angular correlations. We characterize this sample by the number of partons that are able to hadronize by fragmentation within the selected bins. In the nuclear environment the model allows hadronization by fragmentation only for partons with momentum above a threshold $p_T^{{\tiny{thresh}}}=2.4$ GeV. We argue that one should treat properly the effect of those partons with momentum below the threshold, since their interaction with the medium may lead to showers of low momentum hadrons along the direction of motion of the original partons as the medium becomes diluted.

Cold nuclear matter effects on dijet productions in relativistic heavy-ion reactions at LHC

We investigate the cold nuclear matter (CNM) effects on dijet productions in high-energy nuclear collisions at LHC with the next-to-leading order perturbative QCD. The nuclear modifications for dijet angular distributions, dijet invariant mass spectra, dijet transverse momentum spectra and dijet momentum imbalance due to CNM effects are calculated by incorporating EPS, EKS, HKN and DS parametrization sets of parton distributions in nucleus. It is found that dijet angular distributions and dijet momentum imbalance are insensitive to the initial-state CNM effects and thus provide optimal tools to study the final-state hot QGP effects such as jet quenching. On the other hand, the invariant mass spectra and the transverse momentum spectra of dijet are generally enhanced in a wide region of the invariant mass or transverse momentum due to CNM effects with a feature opposite to the expected suppression because of the final-state parton energy loss effect in the QGP. The difference of EPS, EKS, HKN and DS parametrization sets of nuclear parton distribution functions is appreciable for dijet invariant mass spectra and transverse momentum spectra at p+Pb collisions, and becomes more pronounced for those at Pb+Pb reactions.

Quenching of hadron and photon spectra in heavy-ion collisions from RHIC to LHC

The generic features of parton energy loss effects on the quenching of single hadron spectra in heavy-ion collisions are discussed, paying attention to the expected differences from RHIC to LHC. The need for precise baseline measurements in p–Pb collisions at the LHC is also emphasized. Finally, I briefly mention the production of prompt photons in heavy-ion collisions as well as some open questions.

Parton energy loss and modified beam quark distribution functions in Drell–Yan process in collisions

Within the framework of generalized collinear factorization in perturbative QCD (pQCD), we study the effect of initial multiple parton scattering and induced parton energy loss in Drell-Yan (DY) process in proton-nucleus collisions. We express the contribution from multiple parton scattering and induced gluon radiation to the DY dilepton spectra in terms of nuclear modified effective beam quark distribution functions. The modification depends on the quark transport parameter in nuclear medium. This is similar to the final-state multiple parton scattering in deeply inelastic scattering (DIS) off large nuclei and leads to the suppression of the Drell-Yan cross section in $p+A$ relative to $p+p$ collisions. With the value of quark transport parameter determined from the nuclear modification of single-inclusive DIS hadron spectra as measured by the HERMES experiment, we calculate DY spectra in $p+A$ collisions and find the nuclear suppression due to beam parton energy loss negligible at the Fermilab energy $E_{\rm lab}$=800 GeV in the kinematic region as covered by the E866 experiment. Most of the observed nuclear suppression of DY spectra in E866 experiment can be described well by parton shadowing in target nuclei as given by the EPS08 parameterization. The effect of beam parton energy loss, however, becomes significant for DY lepton pairs with large beam parton momentum fraction $x^{\prime}$ or small target parton momentum fraction $x$. We also predict the DY cross section in $p+A$ collisions at lower beam proton energy $E_{\rm lab}$=120 GeV and show significant suppression due to initial state parton energy loss at moderately large $x^{\prime}$ where the effect of parton shadowing is very small.