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Measurement of the nuclear modification factor for muons from charm and bottom hadrons in Pb+Pb collisions at 5.02 TeV with the ATLAS detector
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Abstract and Figures
Heavy-flavour hadron production provides information about the transport properties and microscopic structure of the quark-gluon plasma created in ultra-relativistic heavy-ion collisions. A measurement of the muons from semileptonic decays of charm and bottom hadrons produced in Pb+Pb and pp collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV with the ATLAS detector at the Large Hadron Collider is presented. The Pb+Pb data were collected in 2015 and 2018 with sampled integrated luminosities of and , respectively, and pp data with a sampled integrated luminosity of were collected in 2017. Muons from heavy-flavour semileptonic decays are separated from the light-flavour hadronic background using the momentum imbalance between the inner detector and muon spectrometer measurements, and muons originating from charm and bottom decays are further separated via the muon track's transverse impact parameter. Differential yields in Pb+Pb collisions and differential cross sections in pp collisions for such muons are measured as a function of muon transverse momentum from 4 GeV to 30 GeV in the absolute pseudorapidity interval . Nuclear modification factors for charm and bottom muons are presented as a function of muon transverse momentum in intervals of Pb+Pb collision centrality. The measured nuclear modification factors quantify a significant suppression of the yields of muons from decays of charm and bottom hadrons, with stronger effects for muons from charm hadron decays.
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A bstract
Heavy flavour production in proton-proton (pp) collisions provides insights into the fundamental properties of Quantum Chromodynamics (QCD). Beauty hadron production measurements are widely performed through indirect approaches based on their inclusive decay modes. A Bayesian unfolding data-driven analysis of the ALICE and LHCb data was performed in this study, which recovers the full kinematic information of the beauty hadrons via different inclusive decay channels. The corresponding beauty hadron production cross sections obtained after the Bayesian unfolding are found to be consistent within their uncertainties. The weighted average open beauty production cross sections are presented as a function of the transverse momentum and rapidity in pp collisions at s = 5 . 02 TeV and s = 13 TeV, respectively. The p T -integrated open beauty production d σ/ d y and the total b b ¯ cross section σ b b ¯ are also reported. The precision of these results significantly improves upon worldwide measurements, providing valuable validation and constraints on mechanisms of heavy flavour production in pp collisions at the LHC energies.
Collective flow, its anisotropies and its event-to-event fluctuations in
relativistic heavy-ion collisions, and the extraction of the specific shear
viscosity of quark-gluon plasma (QGP) from collective flow data collected in
heavy-ion collision experiments at RHIC and LHC are reviewed. Specific emphasis
is placed on the similarities between the Big Bang of our universe and the
Little Bangs created in heavy-ion collisions.
We consider propagation of heavy quarks in QCD matter. Because of large quark mass, the radiative quark energy loss appears to be qualitatively different from that of light quarks at all energies of practical importance. Finite quark mass effects lead to an in-medium enhancement of the heavy-to-light D/π ratio at moderately large (5–10 GeV) transverse momenta. For hot QCD matter a large enhancement is expected, whose magnitude and shape are exponentially sensitive to the density of colour charges in the medium.
The ultrarelativistic heavy-ion programs at the Relativistic Heavy Ion Collider and the Large Hadron Collider have entered an era of quantitative analysis of quantum chromodynamics (QCD) at high temperatures. The remarkable discovery of the strongly coupled quark–gluon plasma (sQGP), as deduced from its hydrodynamic behavior at long wavelengths, calls for probes that can reveal its inner workings. Charm- and bottom-hadron spectra offer unique insights into the transport properties and the microscopic structure of the QCD medium created in these collisions. At low momentum the Brownian motion of heavy quarks in the sQGP gives access to their diffusion constant, at intermediate momentum these quarks give insight into hadronization mechanisms, and at high momentum they are expected to merge into a radiative-energy loss regime. We review recent experimental and theoretical achievements on measuring a variety of heavy-flavor observables, characterizing the different regimes in momentum and extracting pertinent transport coefficients to unravel the structure of the sQGP and its hadronization.
Expected final online publication date for the Annual Review of Nuclear and Particle Science, Volume 69 is October 21, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Several transport models have been employed in recent years to analyze heavy-flavor meson spectra in high-energy heavy-ion collisions. Heavy-quark transport coefficients extracted from these models with their default parameters vary, however, by up to a factor of 5 at high momenta. To investigate the origin of this large theoretical uncertainty, a systematic comparison of heavy-quark transport coefficients is carried out between various transport models. Within a common scheme devised for the nuclear modification factor of charm quarks in a brick medium of a quark-gluon plasma, the systematic uncertainty of the extracted drag coefficient among these models is shown to be reduced to a factor of 2, which can be viewed as the smallest intrinsic systematical error band achievable at present time. This indicates the importance of a realistic hydrodynamic evolution constrained by bulk hadron spectra and of heavy-quark hadronization for understanding the final heavy-flavor hadron spectra and extracting heavy-quark drag coefficient. The transverse transport coefficient is less constrained due to the influence of the underlying mechanism for heavy-quark medium interaction. Additional constraints on transport models such as energy loss fluctuation and transverse-momentum broadening can further reduce theoretical uncertainties in the extracted transport coefficients.
We utilize the parton cascade model to study the evolution of charm quarks propagating through a thermal brick of QCD matter. We determine the energy loss and the transport coefficient \stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q} for charm quarks. The calculations are done at a constant temperature of 350 MeV and the results are compared to analytical calculations of heavy-quark energy loss in order to validate the applicability of using a parton cascade model for the study of heavy-quark dynamics in hot and dense QCD matter.
This review discusses the design and initial operation of the Relativistic Heavy Ion Collider (RHIC), noting the novel features of a heavy ion collider that are distinct from conventional hadron colliders. These features reflect the experimental requirements of operation with a variety of ion species over a wide energy range, including collisions between ions of unequal energies and polarized protons. Other unique aspects of RHIC include intrabeam scattering, interaction-region error compensation, and transition crossing with a slow ramp rate. The RHIC facility has just completed the second physics run after beam commissioning in 2000.
The Large Hadron Collider (LHC) at CERN near Geneva is the world's
newest and most powerful tool for Particle Physics research. It is
designed to collide proton beams with a centre-of-mass energy of 14 TeV
and an unprecedented luminosity of 1034
cm-2 s-1. It can also collide heavy (Pb) ions
with an energy of 2.8 TeV per nucleon and a peak luminosity of
1027 cm-2 s-1. In this paper, the
machine design is described.
Hadrons carrying open heavy flavor, i.e. single charm or bottom quarks, are among the key diagnostic tools available today for the hot and dense state of strongly interacting matter which is produced in collisions of heavy atomic nuclei at ultra-relativistic energies. First systematic heavy-flavor measurements in nucleus–nucleus collisions and the reference proton–proton system at Brookhaven National Laboratory’s (BNL) Relativistic Heavy Ion Collider (RHIC) have led to tantalizing results. These studies are now continued and extended at RHIC and at CERN’s Large Hadron Collider (LHC), where considerably higher collision energies are available. This review focuses on experimental results on open heavy-flavor observables at RHIC and the LHC published until July 2012. Yields of heavy-flavor hadrons and their decay products, their transverse momentum and rapidity distributions, as well as their azimuthal distributions with respect to the reaction plane in heavy-ion collisions are investigated. Various theoretical approaches are confronted with the data and implications for the properties of the hot and dense medium produced in ultra-relativistic heavy-ion collisions are discussed.
This is a review of the theoretical background, experimental techniques, and phenomenology of what is called the "Glauber Model" in relativistic heavy ion physics. This model is used to calculate "geometric" quantities, which are typically expressed as impact parameter (b), number of participating nucleons (N_part) and number of binary nucleon-nucleon collisions (N_coll). A brief history of the original Glauber model is presented, with emphasis on its development into the purely classical, geometric picture that is used for present-day data analyses. Distinctions are made between the "optical limit" and Monte Carlo approaches, which are often used interchangably but have some essential differences in particular contexts. The methods used by the four RHIC experiments are compared and contrasted, although the end results are reassuringly similar for the various geometric observables. Finally, several important RHIC measurements are highlighted that rely on geometric quantities, estimated from Glauber calculations, to draw insight from experimental observables. The status and future of Glauber modeling in the next generation of heavy ion physics studies is briefly discussed.