Heavy Flavor Mesons Research Articles

Open Heavy Flavor Production at Forward Angles in PHENIX

The measurement of the nuclear modification factor ($R_{\rm AA}$) for heavy-flavor production in heavy-ion collisions tests predictions for cold- and hot-nuclear-matter effects. Heavy-flavor production in \pp\ collisions tests pQCD calculations and serves as a reference for understanding heavy-flavor production in heavy-ion collisions. Using the PHENIX muon-arm spectrometers, the transverse momentum spectra of inclusive muon candidates are measured for \pp\ and $\cucu$ collisions at $\snn = 200$\,GeV. After subtracting backgrounds, we obtain the measured invariant yields of negative muons from the decay of heavy flavor mesons. For \pp\ collisions, we measure the charm-production cross section integrated over $\pt$ and in the rapidity range $1.4<y<1.9$ to be $d\sigma_{c\bar{c}}/dy = 0.139\pm 0.029\ {\rm (stat)\,}^{+0.051}_{-0.058}\ {\rm (syst)}$ mb. This result is compared to a recent FONLL calculation and to a PHENIX measurement at mid-rapidity. For $\cucu$ collisions, we measure the $R_{\rm AA}$ for heavy-flavor muons in three centrality bins for $1<\pt<4$ GeV/$c$, with suppression observed for central collisions. We compare our measurement for central collisions to a recent theoretical prediction.

Heavy flavor suppression: Role of hadronic matter

The role of hadronic matter in the suppression of open heavy-flavored mesons is studied. The heavy-quark suppression factors are calculated and contrasted with the experimental data obtained from nuclear collisions at the Relativistic Heavy Ion Collider (RHIC) and LHC experiments. It is found that the suppression in the hadronic phase at RHIC energy is around 20%--25% whereas at the LHC it is around 10%--12% for the $D$ meson. In the case of $B$ mesons the hadronic suppression is around 10%--12% and 5%--6% at RHIC and LHC energies, respectively. The present study suggests that the suppression of heavy flavor in the hadronic phase is significant at the RHIC. However, the effect of hadronic suppression at the LHC is marginal; this makes the characterization of quark-gluon plasma at the LHC less complicated.

Heavy quark energy loss and thermalization in hot and dense nuclear matter

We study heavy quark energy loss and thermalization in hot and dense nuclear medium. The diffusion of heavy quarks is calculated via a Langevin equation, both for a static medium as well as for a quark-gluon plasma (QGP) medium generated by a (3+1)-dimensional hydrodynamic model. We investigate how the initial configuration of the QGP and its properties affect the final state spectra and elliptic flow of heavy flavor mesons and non-photonic electrons. It is observed that both the geometric anisotropy of the initial profile and the flow profile of the hydrodynamic medium play important roles in the heavy quark energy loss process and the development of elliptic flow. Within our definition of the thermalization criterion and for reasonable values of the diffusion constant, we observe thermalization times that are longer than the lifetime of the QGP phase.

Heavy flavor and vector boson associated production

The mechanism of production of heavy-flavoured mesons, containing b or c quarks, in association with vector bosons, W or Z/γ⁎, in the Standard Model is only partially understood. The study of events with one or two well-identified and isolated leptons accompanied by b-jets or secondary vertices is therefore crucial to refine the theoretical calculations in perturbative QCD, as well as validate associated Monte Carlo techniques. The deep understanding of these processes is furthermore required by Higgs and BSM analyses with similar final states. Using the LHC proton-proton collision data collected in 2010 and 2011 at a centre of mass energy of 7 TeV by the CMS detector, preliminary measurements of the Z/γ⁎+b(b) cross sections and angular correlations are presented. Finally, the study of the W+c production rate with respect to the W charge and W+light jets rates allows to probe the strange quark content of the proton. These results are also presented.

MSSM PREDICTIONS ON LEPTON FLAVOR VIOLATION DECAYS OF VECTOR MESONS

In the minimal supersymmetric extension of the Standard Model (MSSM) the interactions between the SUSY particles and the Standard Model (SM) particles can contribute to the lepton flavor violation (LFV) decays of vector mesons at loop level. Taking the constraint on the lightest Higgs mass around 126 GeV, we study these decays by a scan over the parameter space which gives the predictions on μ-e conversion and τ→μγ satisfying the experimental bounds. The branching ratios of the vector mesons decays into eμ are strongly suppressed. However, the branching ratios of the heavy flavor mesons decays into τμ can reach the experimental sensitivity in near future. Therefore, the experimental signals of these decays may serve as a probe of the MSSM.

Cold-Nuclear-Matter Effects on Heavy-Quark Production ind+AuCollisions atsNN=200 GeV

The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d+Au and p+p collisions at sqrt(s_NN)=200 GeV at the Relativistic Heavy Ion Collider, in the transverse-momentum range 0.85 < pT < 8.5 GeV/c. In central d+Au collisions, the nuclear modification factor R_dA at 1.5 < pT < 5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p+p collisions, and shows that the mass-dependent Cronin enhancement observed at RHIC extends to the heavy-D-meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the pi0 and heavy-flavor-electron nuclear modification factor R_AA.

Nuclear-modification factor for open-heavy-flavor production at forward rapidity in Cu+Cu collisions atsNN=200GeV

Background: Heavy-flavor production in p+p collisions tests perturbative-quantum-chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from p+p results, quantified with the nuclear-modification factor (R_AA), provides information on both cold- and hot-nuclear-matter effects. Purpose: Determine transverse-momentum, pt, spectra and the corresponding R_AA for muons from heavy-flavor mesons decay in p+p and Cu+Cu collisions at sqrt(s_NN)=200 GeV and y=1.65. Method: Results are obtained using the semi-leptonic decay of heavy-flavor mesons into negative muons. The PHENIX muon-arm spectrometers measure the p_T spectra of inclusive muon candidates. Backgrounds, primarily due to light hadrons, are determined with a Monte-Carlo calculation using a set of input hadron distributions tuned to match measured-hadron distributions in the same detector and statistically subtracted. Results: The charm-production cross section in p+p collisions at sqrt{s}=200 GeV, integrated over pt and in the rapidity range 1.4<y<1.9 is found to be dsigma_ccbar/dy = 0.139 +/- 0.029 (stat) ^{+0.051}_{-0.058} (syst) mb. This result is consistent with calculations and with expectations based on the corresponding midrapidity charm-production cross section measured earlier by PHENIX. The R_AA for heavy-flavor muons in Cu+Cu collisions is measured in three centrality intervals for 1<pt<4 GeV/c. Suppression relative to binary-collision scaling (R_AA<1) increases with centrality. Conclusions: Within experimental and theoretical uncertainties, the measured heavy-flavor yield in p+p collisions is consistent with state-of-the-art pQCD calculations. Suppression in central Cu+Cu collisions suggests the presence of significant cold-nuclear-matter effects and final-state energy loss.

Properties of heavy flavoured mesons using NRQCD formalism

The mass spectrum of the cc̄ meson is reviewed in non-relativistic phenomenological quark anti-quark potential of the type , with v varying from 0.5 to 2. The spin hyperfine and spin-orbit interactions are employed to obtain the masses of the pseudoscalar and vector mesons. The decay constants with QCD corrections are computed in this model. The di-gamma and di-leptonic decays of cc̄ meson are investigated using some of the known potential models by incorporating radiative corrections up to the lowest order, bound state effects and contribution from quark/antiquark propagator. The decay rates of cc̄ meson are studied in the NRQCD formalism, and also with the relativistic corrections of order v4. These decay widths are also computed using the pNRQCD for comparison.

Heavy-quark diffusion and hadronization in quark-gluon plasma

We calculate diffusion and hadronization of heavy quarks in high-energy heavy-ion collisions, implementing the notion of a strongly coupled quark-gluon plasma in both micro- and macroscopic components. The diffusion process is simulated using relativistic Fokker-Planck dynamics for elastic scattering in a hydrodynamic background. The heavy-quark transport coefficients in the medium are obtained from nonperturbative $T$-matrix interactions which build up resonant correlations close to the transition temperature. The latter also form the basis for hadronization of heavy quarks into heavy-flavor mesons via recombination with light quarks from the medium. The pertinent resonance recombination satisfies energy conservation and provides an equilibrium mapping between quark and meson distributions. The recombination probability is derived from the resonant heavy-quark scattering rate. Recombination is found to dominate at low transverse momentum (${p}_{T}$) and to yield to fragmentation at high ${p}_{T}$. Our approach emphasizes the role of resonance correlations in the diffusion and hadronization processes. Calculations of the nuclear modification factor and elliptic flow of $D$ and $B$ mesons and their decay electrons in Au-Au collisions at the Relativistic Heavy Ion Collider indicate the importance of a realistic medium flow in a quantitative interpretation of heavy-flavor data.

Quark recombination and heavy quark diffusion in hot nuclear matter

We discuss resonance recombination for quarks and show that it is compatible with quark and hadron distributions in local thermal equilibrium. We then calculate realistic heavy quark phase space distributions in heavy ion collisions using Langevin simulations with non-perturbative T-matrix interactions in hydrodynamic backgrounds. We hadronize the heavy quarks on the critical hypersurface given by hydrodynamics after constructing a criterion for the relative recombination and fragmentation contributions. We discuss the influence of recombination and flow on the resulting heavy meson and single electron RAA and elliptic flow. We will also comment on the effect of diffusion of open heavy flavor mesons in the hadronic phase.

Heavy-quark production inp+pand energy loss and flow of heavy quarks in Au + Au collisions atsNN=200GeV

Transverse momentum (p^e_T) spectra of electrons from semileptonic weak decays of heavy flavor mesons in the range of 0.3 < p^e_T < 9.0 GeV/c have been measured at mid-rapidity (|eta| < 0.35) by the PHENIX experiment at the Relativistic Heavy Ion Collider in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The nuclear modification factor R_AA with respect to p+p collisions indicates substantial energy loss of heavy quarks in the produced medium. In addition, the azimuthal anisotropy parameter v_2 has been measured for 0.3 < p^e_T < 5.0 GeV/c in Au+Au collisions. Comparisons of R_AA and v_2 are made to various model calculations.

Measurement of semi electronic decay of heavy flavor mesons in d+Au collision at RHIC using PHENIX detector

Abstract The PHENIX detector at RHIC has measured single electron spectra from heavy flavor decays in p+p and Au+Au collisions at s N N = 200 GeV . A strong suppression is observed compared to the binary scaling of p+p collisions for high p T single electrons in Au+Au collisions providing evidence for strong medium effects. The motivation for measuring the single electron spectra from the decay of heavy flavor mesons in d+Au collisions from the 2008 RHIC run (Run8) is to determine parton distribution modifications, the Cronin effect and possible energy loss present in cold nuclear matter. These phenomena can mask hot nuclear matter effects and therefore must be understood in order to interpret the Au+Au results. The analysis is still in progress, but the latest results and technical details are being shown in the current paper.

PRODUCTIONS OF HEAVY FLAVORED MESONS IN RELATIVISTIC HEAVY ION COLLISIONS IN THE RECOMBINATION MODEL

We find the distributions of shower partons initiated by heavy quarks c and b by studying the fragmentation functions in the framework of the recombination model. The transverse momentum spectra of heavy flavored mesons are predicted with these distributions. We find that the contribution from the recombination of thermal-shower partons is an important part in the total spectrum for the mesons. We predict the heavy flavored meson productions for different centralities with the heavy quark fugacities fitted by the experimental data of J/ψ transverse momentum spectra in Au+Au collisions.

Azimuthal correlations of electrons from heavy-flavor decay with hadrons inp+pand Au+Au collisions atsNN=200GeV

Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary scaled p+p collisions. These measurements indicate that charm and bottom quarks interact with the hot-dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whether the modification of the away-side-jet shape seen in hadron-hadron correlations is present when the trigger particle is from heavy-meson decay and whether the overall level of away-side jet suppression is consistent. We statistically subtract correlations of electrons arising from background sources from the inclusive electron-hadron correlations and obtain two-particle azimuthal correlations at sqrt(s_NN)=$200 GeV between electrons from heavy-flavor decay with charged hadrons in p+p and also first results in Au+Au collisions. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to p+p collisions.

Erratum: Transverse Momentum and Centrality Dependence of High-pTNonphotonic Electron Suppression inAu+AuCollisions atsNN=200 GeV[Phys. Rev. Lett.98, 192301 (2007)

The STAR collaboration at RHIC reports measurements of the inclusive yield of non-photonic electrons, which arise dominantly from semi-leptonic decays of heavy flavor mesons, over a broad range of transverse momenta ($1.2 < \pt < 10$ \gevc) in \pp, \dAu, and \AuAu collisions at \sqrtsNN = 200 GeV. The non-photonic electron yield exhibits unexpectedly large suppression in central \AuAu collisions at high \pt, suggesting substantial heavy quark energy loss at RHIC. The centrality and \pt dependences of the suppression provide constraints on theoretical models of suppression.

HEAVY-FLAVOR MESON PRODUCTION AT RHIC

Collisions of heavy atomic nuclei at very high beam energies allow to create and study hot QCD matter under laboratory-controlled conditions. Measurements at the SPS and RHIC facilities have yielded compelling evidence for the formation of this novel state of matter, the so-called Quark-Gluon Plasma (QGP). Due to their large mass, heavy quarks (charm and bottom) are believed to be predominantly produced in the initial state of the collision so that they probe the entire lifetime of the QGP. Thus, the investigation of heavy-flavor meson production in nucleus-nucleus collisions provides profound insight into the QGP properties. In this paper we review recent results from the RHIC facility on heavy-flavor meson production and their interaction with the QCD matter on the partonic level.

Measurement of the Bottom Quark Contribution to Nonphotonic Electron Production inp+pCollisions ats=200 GeV

The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p + p collisions at √s=200 GeV has been measured using azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of pT≥5 GeV/c. These measurements constrain the nuclear modification factor for electrons from B and D meson decays. The result indicates that B meson production in heavy ion collisions is also suppressed at high pT.

Two-photon, two-gluon and radiative decays of heavy flavoured mesons

Here we present the two-photon and two-gluon decay widths of the S-wave ( η Q ∈ c , b ) and P-wave ( χ Q ∈ c , b J ) charmonium and bottonium states and the radiative transition decay widths of c c ¯ , b b ¯ and c b ¯ systems based on Coulomb plus power form of the inter-quark potential ( CPP ν ) with exponent ν. The Schrödinger equation is solved numerically for different choices of the exponent ν. We employ the masses of different states and their radial wave functions obtained from the study to compute the two-photon and two-gluon decay widths and the E1 and M1 radiative transitions. It is found that the quarkonia mass spectra and the E1 transition can be described by the same interquark model potential of the CPP ν with ν = 1.0 for c c ¯ and ν = 0.7 for b b ¯ systems, while the M1 transition (at which the spin of the system changes) and the decay rates in the annihilation channel of quarkonia are better estimated by a shallow potential with ν < 1.0 .

TrackInCaloTools: A package for measuring muon energy loss and calorimetric isolation in ATLAS

Muons in the ATLAS detector are reconstructed by combining the information from the two tracking devices: the Inner Detector and the Muon Spectrometer (MS), located in the outermost part of the experiment. Until they reach the MS, muons traverse typically 100 radiation lengths (X0) of material, most part instrumented by the electromagnetic and hadronic calorimeters. The proper account for multiple scattering and energy loss effects is essential for the reconstruction and the use of the calorimeter measurement can improve the transverse momentum resolution, specially in case of high energy deposits. On the other hand, the calorimeter activity around a muon, or conversely its isolation, is one of the most powerful features to distinguish W and Z decays from semi-leptonic decays of heavy flavour mesons (containing b and c quarks). The principle of the software package that performs these tasks, called TrackInCaloTools is presented together with the expected performance in physics analyses.

Open Heavy Flavor Production at Forward Rapidity in [formula omitted] Cu+Cu Collisions

The first measurement of the nuclear modification factor, R A A , for single muons produced in Cu+Cu collisions at s N N = 200 GeV is presented, which is the first measurement of the nuclear modification factor for open heavy flavor production made at forward angles in heavy ion collisions. Single muons are used to tag heavy flavor quark production via semi-leptonic decay of open heavy flavor mesons. With its muon arms, PHENIX has a unique ability to measure single muons at forward rapidity ( 1.2 < | η | < 2.2 ) .