Heavy Flavor Production Research Articles

Reweighted nuclear PDFs using heavy-flavor production data at the LHC

We present the reweighting of two sets of nuclear parton distribution functions (PDFs), nCTEQ15 and EPPS16, using a selection of experimental data on heavy-flavor meson [${D}^{0}$, $J/\ensuremath{\psi}$, $B\ensuremath{\rightarrow}J/\ensuremath{\psi}$ and $\mathrm{\ensuremath{\Upsilon}}(1S)$] production in proton-lead collisions at the LHC which were not used in the original determination of these nuclear PDFs. The reweighted PDFs exhibit significantly smaller uncertainties thanks to these new heavy-flavor constraints. We present a comparison with another selection of data from the LHC and relativistic heavy ion collider (RHIC) which were not included in our reweighting procedure. The comparison is overall very good and serves as a validation of these reweighted nuclear PDF sets, which we dub $\mathrm{nCTEQ}{15}_{\mathrm{rwHF}}$ and $\mathrm{EPPS}{16}_{\mathrm{rwHF}}$. This indicates that the LHC and forward RHIC heavy-flavor data can be described within the standard collinear factorization framework with the same (universal) small-$x$ gluon distribution. We discuss how we believe such reweighted PDFs should be used as well as the limitations of our procedure.

Recent highlights on open heavy-flavour production from ALICE

This work presents the latest highlights of open heavy-flavour measurements by the ALICE Collaboration in pp, p–Pb, and Pb–Pb collisions from Run 2 of the LHC. The nuclear modification and flow measurements of charm and beauty particles in Pb–Pb collisions are shown, as well as the latest measurements of non-prompt strange and non-strange D mesons, the multiplicity dependence of Λ+c baryon production, and measurements of heavier charmed baryon states including Ξc and Σ0,++c baryons.

Inclusive heavy-flavour production at central and forward rapidity in Xe–Xe collisions at [formula omitted] TeV

The first measurements of the production of muons and electrons from heavy-flavour hadron decays in Xe–Xe collisions at sNN=5.44 TeV, using the ALICE detector at the LHC, are reported. The measurement of the nuclear modification factor RAA is performed as a function of transverse momentum pT in several centrality classes at forward rapidity (2.5<y<4) and midrapidity (|y|<0.8) for muons and electrons from heavy-flavour hadron decays, respectively. A suppression by a factor up to about 2.5 compared to the binary-scaled pp reference is observed in central collisions at both central and forward rapidities. The RAA of muons from heavy-flavour hadron decays is compared to previous measurements in Pb–Pb collisions at sNN=5.02 TeV. When the nuclear modification factors are compared in the centrality classes 0–10% for Xe–Xe collisions and 10–20% for Pb–Pb collisions, which have similar charged-particle multiplicity density, a similar suppression, with RAA∼0.4 in the pT interval 4<pT<8 GeV/c, is observed. The comparison of the measured RAA values in the two collision systems brings new insights on the properties of the quark-gluon plasma by investigating the system-size and geometry dependence of medium-induced parton energy loss. The results of muons and electrons from heavy-flavour hadron decays provide new constraints to model calculations.

NNLO QCD predictions for W+c-jet production at the LHC

We study the production of a W boson in association with a c-jet at the LHC. We calculate, for the first time, the complete set of NNLO QCD corrections to the dominant CKM-diagonal contribution to this process. Both signatures, pp → μ+νμjc and pp → {mu}^{-}{overline{nu}}_{mu }{mathrm{j}}_c are considered. We present predictions for fiducial cross sections and differential distributions for each one of the two signatures as well as for their ratio. The theoretical predictions are compared with ATLAS measurements at 7 TeV. The results of this work are essential for the precision description of associated heavy flavor production at hadron colliders and for the determination of the strange-quark content of the proton from LHC data in NNLO QCD.

Rapidity dependence of heavy-flavour production in heavy-ion collisions within a full 3+1 transport approach: quenching, elliptic and directed flow

We extend our POWLANG transport setup for the modelling of heavy-flavour production in heavy-ion collisions to the case of full 3+1 simulations, dropping the approximation of longitudinal boost-invariance of the background medium. This enables us to provide predictions for observables for which the rapidity dependence is essential in order to obtain a non-vanishing signal, like the directed flow v1, and to get reliable results also for kinematic distributions of heavy-flavour particles at forward rapidity. We compare our predictions with experimental data obtained in Au-Au and Pb-Pb collisions at RHIC and at the LHC.

Heavy meson tomography of cold nuclear matter at the electron-ion collider

An important part of the physics program of the future electron-ion collider is to understand the nature of hadronization and the transport of energy and matter in large nuclei. Open heavy flavor production in deep inelastic scattering provides a new tool to address these critical questions. We present the first calculation of D-mesons and B-meson cross sections in electron-nucleus collisions at the EIC by including both next-to-leading order QCD corrections and cold nuclear matter effects. Our formalism employs generalized DGLAP evolution to include the contribution of in-medium parton showers, and is based on methods developed in soft-collinear effective theory with Glauber gluons that describe inclusive hadron production in reactions with nucleons and nuclei. The comprehensive study summarized here allows us to identify the optimal observables, center-of-mass energies, and kinematic regions most sensitive to the physics of energy loss and hadronization at the EIC.

Coupled Boltzmann transport equations of heavy quarks and quarkonia in quark-gluon plasma

We develop a framework of coupled transport equations for open heavy flavor and quarkonium states, in order to describe their transport inside the quark-gluon plasma. Our framework is capable of studying simultaneously both open and hidden heavy flavor observables in heavy-ion collision experiments and can account for both, uncorrelated and correlated recombination. Our recombination implementation depends on real-time open heavy quark and antiquark distributions. We carry out consistency tests to show how the interplay among open heavy flavor transport, quarkonium dissociation and recombination drives the system to equilibrium. We then apply our framework to study bottomonium production in heavy-ion collisions. We include ϒ(1S), ϒ(2S), ϒ(3S), χb(1P) and χb(2P) in the framework and take feed-down contributions during the hadronic gas stage into account. Cold nuclear matter effects are included by using nuclear parton distribution functions for the initial primordial heavy flavor production. A calibrated 2 + 1 dimensional viscous hydrodynamics is used to describe the bulk QCD medium. We calculate both the nuclear modification factor RAA of all bottomonia states and the azimuthal angular anisotropy coefficient v2 of the ϒ(1S) state and find that our results agree reasonably with experimental measurements. Our calculations indicate that correlated cross-talk recombination is an important production mechanism of bottomonium in current heavy-ion experiments. The importance of correlated recombination can be tested experimentally by measuring the ratio of RAA(χb(1P)) and RAA(ϒ(2S)).

Highlights from the ATLAS experiment

The ATLAS experiment at the LHC has undertaken an extensive program to probe and characterize the hot and dense quark-gluon plasma created in relativistic heavy ion collisions and, in general, to study non-perturbative and collective properties of the strong interaction. In this report we summarize the most recent results on the collectivity in pp, p+Pb and nucleus-nucleus collisions, results on jets, quarkonia, heavy flavor and electroweak boson production, measured in Pb+Pb and p+Pb collisions. This report covers also new results on electromagnetic processes studied in ultra-peripheral collisions.

Heavy-flavour jet production and correlations with ALICE

This contribution focuses on the latest studies of heavy-flavour jets performed with the ALICE detector. The measurements of the jet momentum fraction carried by the D meson in pp collisions at s=5.02TeV and13TeV will be presented. The comparison to POWHEG+PYTHIA will be shown. Moreover, the first measurement at the LHC of the jet-momentum fraction carried by the Λ+c baryon in pp collisions at s=13TeV will be reported. Production of heavy-flavour jets in pp collisions at s=5.02TeV will be also addressed with charged jets tagged by heavy-flavour hadron decay electrons and beauty-hadron decay vertices. The nuclear modification factor of heavy-flavour tagged jets in p–Pb collisions at sNN=5.02TeV will be presented.

Latest results on [formula omitted] and D production in pp and Pb-Pb collisions at [formula omitted] with ALICE at the LHC

The measurement of heavy-flavour production is a powerful tool to study the medium formed in high-energy heavy-ion collisions. Produced in hard scattering processes on a timescale shorter than the formation time of the Quark Gluon Plasma (QGP), they experience the whole evolution of the medium interacting with its constituents. The measurement of charm-hadron production allows testing the mechanisms of in-medium parton energy loss. Moreover, the study of charm-baryon production in heavy-ion collisions, and in particular the baryon-to-meson ratio, provides unique information on hadronisation mechanisms, constraining the role of coalescence. In this contribution, the ALICE results on open charmed meson and baryon production in large and small systems will be presented with a focus on the recent measurements of Λc+/D0 and Ds+/D0 ratios in central and peripheral Pb–Pb collisions and on the new results obtained for the same ratios in proton-proton collisions as a function of the charged particle multiplicity. The prospects for the Ξc0 analysis will also be discussed.

ATLAS results on quarkonia and heavy flavor production

The associated production a vector boson with [Formula: see text] is a key observable for understanding of the quarkonium production mechanisms, including the separation of single and double parton scattering components. Measurements from the ATLAS detector at LHC on quarkonium production, including associated production of a [Formula: see text] and [Formula: see text] are presented. A study of the hidden-charm states [Formula: see text] is also provided.

Heavy-flavour production in proton–proton collisions with the ALICE experiment

The production of heavy-flavour hadrons in high-energy hadronic collisions is a unique source of information on various aspects of quantum chromodynamics (QCD). Production of heavy-flavour hadrons in proton-proton collisions allows the test of perturbative QCD models, while the comparison of mesons and baryons with heavy-flavour quarks can differentiate between fragmentation scenarios. Multiplicity-dependent measurements allow for the understanding of semi-hard vacuum QCD effects, as well as to study the coalescence mechanisms of heavy-flavour quarks with light and strange quarks. Recent results from the ALICE experiment in proton-proton collisions on the production of D mesons and leptons from the decay of heavy-flavour hadrons, as well as charmed baryons, are presented in this contribution. Furthermore, the multiplicity dependence of self-normalised heavy-flavour electron yields, as well as that of strange to non-strange D-meson and charmed baryon-to-meson ratios are also shown.

PHENIX heavy flavor highlights

Heavy flavor production is a sensitive probe of the initial gluon density in the nucleon and is modified by the entire evolution of the hot quark and gluon medium created in high-energy nucleus–nucleus collisions. Besides, it is a process that can be calculated by perturbative QCD because of their large mass. The PHENIX experiment at RHIC studied the heavy flavor productions for a broad momentum and rapidity ranges using single leptons from the semileptonic decay of charm and bottom hadrons, and dileptons from [Formula: see text] decays in [Formula: see text], [Formula: see text]A, and Au[Formula: see text]Au collisions at [Formula: see text][Formula: see text]200[Formula: see text]GeV. In these proceedings, the recent experimental results in [Formula: see text], Au[Formula: see text]Au, and the small collision systems are presented and the heavy flavor productions and their modifications are discussed.

Heavy flavor jets in ALICE

Heavy-flavor quarks are considered to be effective probes of the Quark–Gluon Plasma (QGP) produced in ultra-relativistic heavy-ion collisions. Since quarks have a large mass, their production takes place mostly in initial hard processes, and it is calculable using perturbative QCD. Thus, heavy flavor quarks can be considered as ideal early-generated penetrating probes of the created medium and utilized to investigate mass-dependent properties of in-medium parton energy loss. Moreover, the measurement of heavy-flavor jet production in pp, besides being a natural reference for Pb–Pb studies, allows testing pQCD calculations and models of charm fragmentation in vacuum. In addition, similar measurements in p–Pb collisions allow assessing the importance of cold nuclear matter effects. The ALICE experiment at the LHC has excellent particle tracking capabilities, that allow for a precise jet reconstruction and for the identification of [Formula: see text]-meson and beauty hadron decay vertices, displaced hundreds of micrometers from the primary interaction vertex. In this proceedings, we will report the latest heavy-flavor jet measurements performed in p–Pb and pp collisions.

An experimental review of open heavy flavor and quarkonium production at RHIC

Open heavy flavor and quarkonium are unique probes of the hot-dense medium produced in heavy-ion collisions. Their production in p+p collisions also provide important test of QCD. In this paper, we review the selected results on open heavy flavor and quarkonium in p+p and heavy-ion collisions achieved at RHIC. Physics implications are also discussed.

Summary of charm results from ALICE

An overview of the most recent charm measurements from the ALICE Collaboration is presented in this document. The study of heavy-flavour production is important to understand the properties of the hot and dense medium formed in ultra-relativistic heavyion collisions. In this document the journey of charm in the medium, from the production to the hadronisation into hadrons, is described. Both open charm and quarkonium measurements are presented, starting from D-meson and J/ψ production cross sections in pp collisions and their comparison with theoretical calculations. Recent measurements of relative abundances of different particle species are discussed, in particular the Ds/D0 and ratios, that are sensitive to the hadronisation mechanisms and to the strangeness and to the baryon-to-meson enhancement. The energy loss mechanisms and the collective motion in the medium are investigated through the D-meson and J/ψ nuclear modification factor and the elliptic flow measurements. Further investigations on possible medium-like effects observed in high-multiplicity pp and p-Pb collisions are also addressed.

Far-forward neutrinos at the Large Hadron Collider

We present a new calculation of the energy distribution of high-energy neutrinos from the decay of charm and bottom hadrons produced at the Large Hadron Collider (LHC). In the kinematical region of very forward rapidities, heavy-flavor production and decay is a source of tau neutrinos that leads to thousands of charged-current tau neutrino events in a 1 m long, 1 m radius lead neutrino detector at a distance of 480 m from the interaction region. In our computation, next-to-leading order QCD radiative corrections are accounted for in the production cross-sections. Non-perturbative intrinsic-kT effects are approximated by a simple phenomenological model introducing a Gaussian kT -smearing of the parton distribution functions, which might also mimic perturbative effects due to multiple initial-state soft-gluon emissions. The transition from partonic to hadronic states is described by phenomenological fragmentation functions. To study the effect of various input parameters, theoretical predictions for {D}_s^{pm } production are compared with LHCb data on double-differential cross-sections in transverse momentum and rapidity. The uncertain- ties related to the choice of the input parameter values, ultimately affecting the predictions of the tau neutrino event distributions, are discussed. We consider a 3+1 neutrino mixing scenario to illustrate the potential for a neutrino experiment to constrain the 3+1 parameter space using tau neutrinos and antineutrinos. We find large theoretical uncertainties in the predictions of the neutrino fluxes in the far-forward region. Untangling the effects of tau neutrino oscillations into sterile neutrinos and distinguishing a 3+1 scenario from the standard scenario with three active neutrino flavours, will be challenging due to the large theoretical uncertainties from QCD.

A Study of the Properties of the QCD Phase Diagram in High-Energy Nuclear Collisions

With the aim of understanding the phase structure of nuclear matter created in high-energy nuclear collisions at finite baryon density, a beam energy scan program has been carried out at Relativistic Heavy Ion Collider (RHIC). In this mini-review, most recent experimental results on collectivity, criticality and heavy flavor productions will be discussed. The goal here is to establish the connection between current available data and future heavy-ion collision experiments in a high baryon density region.

Improved constraints on parton distributions using LHCb, ALICE and HERA heavy-flavour measurements and implications for the predictions for prompt atmospheric-neutrino fluxes

The impact of measurements of heavy-flavour production in deep inelastic ep scattering and in pp collisions on parton distribution functions is studied in a QCD analysis at next-to-leading order. Recent combined results of inclusive and heavy-flavour produc- tion cross sections in deep inelastic scattering at HERA are investigated together with heavy-flavour production measurements at the LHC. Differential cross sections of charm- and beauty-hadron production measured by the LHCb collaboration at the centre-of-mass energies of 5, 7 and 13 TeV as well as the recent measurements of the ALICE experiment at the centre-of-mass energies of 5 and 7 TeV are explored. These data impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions x of the proton momentum, down to x ≈ 10−6. The impact of the resulting parton distribution function in the predictions for the prompt atmospheric-neutrino fluxes is studied.

Improvement of heavy flavor production in a multiphase transport model updated with modern nuclear parton distribution functions

Recently we have updated a multi-phase transport (AMPT) model with modern parton distribution functions of nuclei (nPDFs). Here we study open charm production in the updated AMPT model and compare to the experimental data from $pp$ and $AA$ collisions over a wide range of collision energies. Besides the update of nPDFs, we have removed the transverse momentum cutoff on initial heavy quark productions and also included the resultant heavy flavor cross section into the total minijet cross section in the initial condition as described by the HIJING model. We show that the AMPT model with these updates provides a much better description of the yields and transverse momentum spectra of various open charm hadrons in comparison with the experimental data. This lays the foundation for further heavy flavor studies within the transport model approach.