Measurement Of Nuclear Modification Factor Research Articles

Measurement of inclusive electrons from open heavy-flavor hadron decays in p+p collisions at s=200 GeV with the STAR detector

We report a new measurement of the production cross section for inclusive electrons from open heavy-flavor hadron decays as a function of transverse momentum ($p_{\rm T}$) at mid-rapidity ($|y|<$ 0.7) in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV. The result is presented for 2.5 $<p_{\rm T}<$ 10 GeV/$c$ with an improved precision above 6 GeV/$c$ with respect to the previous measurements, providing more constraints on perturbative QCD calculations. Moreover, this measurement also provides a high-precision reference for measurements of nuclear modification factors for inclusive electrons from open-charm and -bottom hadron decays in heavy-ion collisions.

Measurements of electrons from heavy-flavor hadron decays in 27, 54.4, and 200 GeV Au+Au collisions in STAR

In these proceedings, we present the measurements of nuclear modification factors for electrons from open charm (c→e) and bottom hadron decays (b→e) at mid-rapidity region in Au+Au collisions at √SNN = 200 GeV. The significance of the difference in nuclear modification factors between b→e and c→e is ≥ 3σ. We also present the measurements of the elliptic flow (v2) of inclusive heavy-flavor hadron decayed electrons (HFE) in Au+Au collisions at √SNN = 27 and 54.4 GeV. The results show non-zero HFE v2 in 54.4 GeV Au+Au collisions and a hint of smaller HFE v2 in 27 GeV Au+Au collisions than those at 54.4 and 200 GeV.

Measurement of nuclear modification factors of ϒ(1S), ϒ(2S), and ϒ(3S) mesons in PbPb collisions at [formula omitted] TeV

The cross sections for ϒ(1S), ϒ(2S), and ϒ(3S) production in lead–lead (PbPb) and proton–proton (pp) collisions at sNN=5.02 TeV have been measured using the CMS detector at the LHC. The nuclear modification factors, RAA, derived from the PbPb-to-pp ratio of yields for each state, are studied as functions of meson rapidity and transverse momentum, as well as PbPb collision centrality. The yields of all three states are found to be significantly suppressed, and compatible with a sequential ordering of the suppression, RAA(ϒ(1S))>RAA(ϒ(2S))>RAA(ϒ(3S)). The suppression of ϒ(1S) is larger than that seen at sNN=2.76TeV, although the two are compatible within uncertainties. The upper limit on the RAA of ϒ(3S) integrated over pT, rapidity and centrality is 0.096 at 95% confidence level, which is the strongest suppression observed for a quarkonium state in heavy ion collisions to date.

Nuclear modification factors of light mesons in Cu+Au collisions

Strongly interacting quark-gluon plasma (sQGP) is a state of nuclear matter at extremely high values of temperature with quarks and gluons as degrees of freedom. Jet-quenching is one of the evidences for sQGP formation in relativistic heavy ion collisions (A+A) and is manifested by suppression of particle yields at high transverse momentum relative to yields of the same particles measured at elementary proton-proton collisions at the same collision energy. Systematic experimental research of jet-quenching is provided by the measurement of nuclear modification factors of light mesons (π0, η, , ω etc.) in different A+A systems. Asymmetric system of Cu+Au collisions at GeV is characterised by similar energy density but different collision geometry when compared to symmetric systems (Au+Au or Cu+Cu). This paper presents measurements of π0 and η mesons nuclear modification factors in Cu+Au collisions. Results are compared with ones measured in Au+Au and Cu+Cu collisions at the same collision energy.

Measurement of the D-meson nuclear modification factor and elliptic flow in Pb–Pb collisions at √SNN = 5.02 TeV with ALICE at the LHC

Heavy-flavour hadrons are recognised as a powerful probe for the characterisation of the deconfined medium created in heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of D0, D+, D*+ and [see formula in PDF] mesons in Pb–Pb collisions at [see formula in PDF] = 5.02 TeV. The measurement of the nuclear modification factor (RAA) provides a strong evidence of the in-medium parton energy loss. The comparison between the [see formula in PDF] and the non-strange D-meson RAA can help to study the hadronisation mechanism of the charm quark in the QGP. In mid-central collisions, the measurement of the D-meson elliptic flow v2 at low transverse momentum (pT) gives insight into the participation of the charm quark into the collective motion of the system, while at high pT it constrains the path-length dependence of the energy loss. The [see formula in PDF] v2, measured for the first time at the LHC, is found to be compatible to that of non-strange D mesons and positive with a significance of about 2.6 σ. The coupling of the charm quark to the light quarks in the underlying medium is further investigated for the first time with the application of the Event-Shape Engineering (ESE) technique to D-meson elliptic flow.

Open Bottom Production in Au+Au Collisions at s NN = 200 GeV with the STAR Experiment

In these proceedings, we present measurements of open bottom hadron production through multiple decay channels in Au+Au collisions at [Formula: see text] = 200 GeV by the STAR experiment. Namely, measurements of nuclear modification factors for electrons, [Formula: see text], and [Formula: see text] from open bottom hadron decays are shown. The decay products are topologically identified utilizing the Heavy Flavor Tracker, a silicon vertex detector installed at STAR during the period of 2014 - 2016. It enables precise reconstruction of displaced decay vertices. The results show large suppression for non-prompt [Formula: see text] and non-prompt [Formula: see text] at high transverse momenta, and indicate less suppression for electrons from bottom hadron decays than for those from charm hadron decays at [Formula: see text] significance level.

B meson nuclear modification factor in Pb–Pb at 5.02 TeV with CMS

The study of beauty production in heavy-ion collisions is considered to be one of the key measurement to address the flavour-dependence of in-medium energy loss in PbPb collisions. The Compact Muon Solenoid (CMS) experiment has excellent capabilities for measuring b-quark production thanks to the excellent performances of its muon and tracker system. In this talk, the measurement of nuclear modification factor of fully reconstructed B mesons for the first time in pp and PbPb collisions at 5.02 TeV as a function of transverse momentum will be presented.

Measurement of inclusive jet spectra in pp, p–Pb, and Pb–Pb collisions with the ALICE detector

Highly energetic jets are sensitive probes of the kinematic properties and the topology of high energy hadron collisions. Jets are collimated sprays of charged and neutral particles, which are produced in fragmentation of hard scattered partons from an early stage of the collision. In ALICE, jets have been measured in pp, p–Pb, and Pb–Pb collisions at several collision energies. While analyses of Pb–Pb events unveil properties of the hot and dense medium formed in heavy-ion collisions, pp and p–Pb collisions can shed light on hadronization and cold nuclear matter effects in jet production. Additionally, pp and p–Pb collisions serve as a baseline for disentangling hot and cold nuclear matter effects. A possible modification of the initial state is tested in p–Pb analyses. For the extraction of a jet signal, the exact evaluation of the background from the underlying event is an especially important ingredient. Due to the different nature of underlying events, each collision system requires a different analysis technique for removing the effect of the background on the jet sample. The focus of this publication is on the ALICE measurements of nuclear modification factors connecting p–Pb and Pb–Pb events to pp collisions. Furthermore, the radial jet structure is explored by comparing jet spectra reconstructed with different resolution parameters.

Nuclear Modification Factor of D0 Meson in Au + Au Collisions at [formula omitted

Heavy-flavor quarks are dominantly produced in initial hard scattering processes and experience the whole evolution of the system in heavy-ion collisions at RHIC energies. Thus they are suggested to be an excellent probe to the medium properties through their interaction with the medium. In this proceedings, we report our first measurement of D0 production via topological reconstruction using STAR's recently installed Heavy Flavor Tracker (HFT). We also report our new measurement of Nuclear Modification Factor (RAA) of D0 mesons in central Au+Au collisions at sNN=200 GeV as a function of transverse momentum (pT). New results confirm the strong suppression at high pT with a much improved precision, and show that the RAA at high pT are comparable with light hadrons (π) and with D meson measurements at the LHC. Furthermore, several theoretical calculations are compared to our data, and with charm diffusion coefficient 2πTDS∼2-12 can reproduce both the D0RAA and v2 data in Au+Au collisions at RHIC.

Recent Developments in Open Heavy Flavor Experiments

Heavy quark program has been one of the focused programs at RHIC and LHC to study detail properties of strongly-coupled Quark-Gluon Plasma (sQGP). I will review recent experimental achievements on open heavy flavor production in heavy ion collisions, including measurements of nuclear modification factors, elliptic flow and heavy quark triggered correlations. By comparing with most sophisticated theoretical models, I will comment on physics implications on current understanding of sQGP medium properties. In the end, I will discuss future plans of utilizing heavy flavor quarks to probe emergent QCD properties in heavy ion collisions at both RHIC and LHC.

ATLAS results on heavy flavour production and its relation to quark matter

We present measurements of J/ψ and ψ (2S) production in proton-lead collisions at a centre of mass energy per nucleon-nucleon interaction of √sNN = 5.02 TeV and in proton- proton collisions at √s = 2.76 TeV, with integrated luminosities of 28.1 nb-1 and 4.0 pb-1, respectively. Both measurements are based on data recorded by the ATLAS detector in 2013 and are performed in the dimuon decay channel. Prompt components of J/ψ and ψ(2S) are separated from the nonprompt components resulting from b-hadron decays through an analysis of the distance between the J/ψ and ψ(2S) decay vertexes and the event primary vertex. The measurements of nuclear modification factors and self-normalized yields for the J/ψ and ψ(2S) are performed in the following ranges: 8.5 < pTµµ < 30 GeV in transverse momentum, -1.5 <y*µµ 1.5 in centre-of-mass rapidity and 0 — 90% in centrality. The differential cross section for production of nonprompt J/ψ is compared to a FONLL calculation which does not include nuclear effects for the ranges of 8 < pTµµ < 30 GeV in transverse momentum, and for |y*| µµ < 1.94 in centre-of-mass rapidity. Forward-backward production ratios are presented and compared to theoretical predictions.

Jet Measurements in Heavy-ion Collisions with CMS

The production of a strongly interacting medium in heavy-ion collisions is identified through suppression of high transverse momentum jets leading to an effect known as jet quenching. Detailed measurements of nuclear modification factors and energy flow of the aforementioned quenched jets are performed with the CMS detector. These new results extend previous measurements to large angles with respect to the quenched jets and increase reach in the transverse momentum range. High statistics pp, pPb and PbPb data taken in 2011-13 are used in the following analysis. A new data-driven method to estimate the underlying event contribution from the forward calorimeter energy distribution is employed which takes into account possible event by event flow modulation. The flavor dependence of energy loss of jets is studied by tagging heavy flavor b-jets in these systems.

Measurements of b-jet nuclear modification factors in pPb and PbPb collisions with CMS

We present measurements of the nuclear modification factors RAA and RpA(PYTHIA) of b jets in lead-lead and proton-lead collisions, respectively, using the CMS detector. Jets from b-quark fragmentations are found by exploiting the long lifetime of the b-quark through tagging methods using distributions of the secondary vertex displacement. From these, b-jet cross-sections are calculated and compared to the pp cross-section from the 2.76 TeV pp data collected in 2013 and to a PYTHIA simulation at 5.02 TeV, where these center-of-mass energies correspond to those of the PbPb and pPb data. We observe significant suppression for b jets in PbPb, and a RpA(PYTHIA) value consistent with unity for b jets in pPb. Results from both collision species show remarkable correspondence with inclusive-jet suppression measurements, indicating that mass-dependent energy-loss effects are negligible at pT values greater than around 50 GeV/c. We use 150 inverse {\mu}b of lead-lead data and 35 inverse nb of proton-lead data collected at the LHC.

ALICE measurements in p–Pb collisions: Charged particle multiplicity, centrality determination and implications for binary scaling

Measurements of particle production in proton-nucleus collisions provide a reference to disentangle final state effects, i.e. signatures of the formation of a deconfined hot medium, from initial state effects, already present in cold nuclear matter. Since many initial state effects are expected to vary as a function of the number of collisions suffered by the incoming proton, it is crucial to estimate the centrality of the collision. In p-Pb collisions categorization of events into different centrality classes using a particle multiplicity distribution is complicated by the low particle multiplicities and the large multiplicity fluctuations. We present ALICE measurements of particle production in p-Pb collisions at sqrt(sNN) = 5.02$ TeV, including the pseudo-rapidity and transverse momentum dependence, we discuss the event classification in centrality classes and its implications for the measurements of nuclear modification factors.

Nuclear modification of vector boson production in proton–lead collisions at the LHC

In anticipating the upcoming proton–lead run at the LHC in the near future, we present predictions for the nuclear modification factor of transverse momentum spectrum of Z0 production and transverse momentum broadening of vector boson (J/ψ, ϒ, W/Z0) production in proton–lead collisions at s=5 TeV, respectively. We find that the measurement of nuclear modification factor of Z0 production provides a clean and unambiguous test of the nuclear anti-shadowing proposed in the recent EPS09. In addition, the dramatic difference in transverse momentum broadening between the heavy quarkonium and W/Z0 production could be a signature prediction of QCD parton multiple scattering, and it provides valuable information on color neutralization of a produced heavy quark pair when it transmutes into a physical quarkonium.

Inclusive Open Charm Production in pp and Pb-Pb collisions with the ALICE Detector

ALICE is the dedicated heavy-ion experiment at the LHC. Its main physics goal is to study the properties of strongly-interacting matter at conditions of high energy density (>10 GeV/fm3) and high temperature (> 0.5 GeV) expected to be reached in central PbPb collisions. Charm and beauty quarks are powerful tools to investigate this high density and strongly interacting state of matter since they are produced in initial hard scatterings that are therefore generated early in the system evolution and probe its hottest, densest stage. The measurement of the charm production cross sections in pp collisions provides an interesting insight into QCD processes and is crucial as a reference for heavy ion studies. We present open charm cross section measurements in pp collisions at = 7 TeV and =2.76 TeV in the central rapidity region. In addition, the first measurement of nuclear modification factor of D-meson in Pb–Pb collisions at = 2.76 TeV is shown.

Nuclear modification factors from the CMS experiment

We report the measurements of nuclear modification factors of the Z bosons, isolated photons and charged particles in = 2.76 TeV Pb–Pb collisions with the Compact Muon Solenoid detector. The nuclear modification factors are constructed by dividing the Pb–Pb pT spectra, normalized to the number of binary collisions, by the pp references. No modifications are observed in the isolated photon and Z boson production with respect to the pp references, while a large suppression is observed in the charged particles.

Nuclear modification factor in an anisotropic quark-gluon plasma

We calculate the nuclear modification factor (${R}_{AA}$) of light hadrons by taking into account the initial state momentum anisotropy of the quark-gluon plasma (QGP) expected to be formed in relativistic heavy ion collisions. Such an anisotropy can result from the initial rapid longitudinal expansion of the matter. A phenomenological model for the space-time evolution of the anisotropic QGP is used to obtain the time dependence of the anisotropy parameter $\ensuremath{\xi}$ and the hard momentum scale, ${p}_{\mathrm{hard}}$. The result is then compared with the PHENIX experimental data to constrain the isotropization time scale, ${\ensuremath{\tau}}_{\mathrm{iso}}$ for fixed initial conditions (FIC). It is shown that the extracted value of ${\ensuremath{\tau}}_{\mathrm{iso}}$ lies in the range $0.5\ensuremath{\leqslant}{\ensuremath{\tau}}_{\mathrm{iso}}\ensuremath{\leqslant}1.5$. However, using a fixed final multiplicity (FFM) condition does not lead to any firm conclusion about the extraction of the isotropization time. The present calculation is also extended to contrast with the recent measurement of nuclear modification factor by the ALICE collaboration at $\sqrt{s}=2.76$ TeV. It is argued that in the present approach, the extraction of ${\ensuremath{\tau}}_{\mathrm{iso}}$ at this energy is uncertain and, therefore, refinement of the model is necessary. The sensitivity of the results on the initial conditions has been discussed. We also present the nuclear modification factor at Large Hadron Collider (LHC) energies with $\sqrt{s}=5.5$ TeV.

Recent Results from PHENIX Experiment at RHIC: Exploring the QCD Medium

We review some important results from the PHENIX experiment at RHIC. They were obtained in a unique environment for studying QCD bulk matter at temperatures and densities that sur- pass the limits where hadrons exist as individual entities, so raising to prominence the quark- gluon degrees of freedom. We present measurements of nuclear modification factors for neutral pions, light favors (strange hadrons), direct-photons and non-photonic electrons from decays of particles carrying charm or beauty quarks. We interpret the large suppression of hadron produc- tion at high transverse momenta as resulting from a large energy loss by the precursor parton on its path through the dense matter, primarily driven by gluon radiation. This dense QCD matter responds to energy loss in a pattern consistent with that expected from a hydrodynamic fluid. Further, its elliptic flow measurements suggest that the hadronization of bulk partonic matter exhibits collectivity with effective partonic degrees of freedom. The results are shown as a function of transverse momentum, centrality in different collision systems and energies.

Measurement of nuclear-modification factors for π 0, η, and ϕ mesons and protons in heavy-ion interactions in the PHENIX experiment

Light hadrons provide a convenient tool for studying the properties of hot and dense media formed in central collisions of relativistic heavy nuclei. The results obtained in the PHENIX experiment at the relativistic heavy-ion collider (RHIC, Brookhaven National Laboratory, USA) by measuring nuclearmodification factors for light hadrons in various colliding systems (pp, dAu, CuCu, and AuAu) at the c.m. energies of √sNN = 62.4 and 200 GeV are presented.