Heavy Flavor Quarks Research Articles

Dynamics of heavy flavor quarks in high energy nuclear collisions

A general overview on the role of heavy quarks as probes of the medium formed in high energy nuclear collisions is presented. Experimental data compared to model calculations at low and moderate pT are exploited to extract information on the transport coefficients of the medium, on possible modifications of heavy flavor hadronization in a hot environment and to provide quantitative answers to the issue of kinetic (and chemical, at conceivable future experimental facilities) thermalization of charm. Finally, the role of heavy flavor at high pT as a tool to study the mass and color-charge dependence the jet quenching is also analyzed.

Study of heavy-flavor quarks produced in association with top-quark pairs ats=7 TeVusing the ATLAS detector

Using a sample of dilepton top-quark pair (ttbar) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, ttbar+b+X or ttbar+c+X, collectively referred to as ttbar+HF. The dataset used corresponds to an integrated luminosity of 4.7 fb-1 of proton--proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The presence of additional HF quarks in the ttbar sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b-quarks from the ttbar decays and the third to additional HF production. The dominant background to ttbar+HF in this sample is ttbar+jet events in which a light-flavor jet is misidentified as a heavy-flavor jet. To determine the heavy- and light-flavor content of the additional b-tagged jets, a fit to the vertex mass distribution of b-tagged jets in the sample is performed. The result of the fit shows that 79 +/- 14 (stat.) +/- 22 (syst.) of the 105 selected extra b-tagged jets originate from HF quarks, three standard deviations away from the hypothesis of zero ttbar+HF production. The result for extra HF production is quoted as a ratio (R_HF) of the cross section for ttbar+HF production to the cross section for ttbar production with at least one additional jet. Both cross sections are measured in a fiducial kinematic region within the ATLAS acceptance. R_HF is measured to be [6.2 +/- 1.1 (stat.) +/- 1.8 (syst.)]% for jets with pT>25 GeV and |eta|<2.5, in agreement with the expectations from Monte Carlo generators.

Molecular states with two heavy quarks

Within the one-boson-exchange (OBE) potential model, we perform a coupled-channel study of the possible deuteron-like molecular states with two heavy flavor quarks. In our study, we take into account the S-D mixing and the coupled-channel effect in the flavor space. Interestingly, we predict some molecular states which are suggested to be searched for in the further experiments.

Meson decays in an extended Nambu—Jona-Lasinio model with heavy quark flavors

In a previous work, we proposed an extended Nambu-Jona-Lasinio (NJL) model including heavy quark flavors. In this work, we will calculate strong and radiative decays of vector mesons in this extended NJL model, including light ρ, ω, K*, Φ and heavy D*, Ds*, B*, Bs*.

Coupled-channel analysis of the possibleD(*)D(*),B¯(*)B¯(*)andD(*)B¯(*)molecular states

We perform a coupled-channel study of the possible deuteron-like molecules with two heavy flavor quarks, including the systems of $D^{(*)}D^{(*)}$ with double charm, $\bar{B}^{(*)}\bar{B}^{(*)}$ with double bottom and $D^{(*)}\bar{B}^{(*)}$ with both charm and bottom, within the one-boson-exchange model. In our study, we take into account the S-D mixing which plays an important role in the formation of the loosely bound deuteron, and particularly, the coupled-channel effect in the flavor space. According to our calculation, the states $D^{(*)}D^{(*)}[I(J^P)=0(1^+)]$ and $(D^{(*)}D^{(*)})_s[J^P=1^+]$ with double charm, the states $\bar{B}^{(*)}\bar{B}^{(*)}[I(J^P)=0(1^+),0(2^+),1(0^+),1(1^+),1(2^+)]$, $(\bar{B}^{(*)}\bar{B}^{(*)})_s[J^P=0^+,1^+,2^+]$ and $(\bar{B}^{(*)}\bar{B}^{(*)})_{ss}[J^P=0^+,1^+,2^+]$ with double bottom, and the states $D^{(*)}\bar{B}^{(*)}[I(J^P)=0(0^+),0(1^+)]$ and $(D^{(*)}\bar{B}^{(*)})_s[J^P=0^+,1^+]$ with both charm and bottom are good molecule candidates. However, the existence of the states $D^{(*)}D^{(*)}[I(J^P)=0(2^+)]$ with double charm and $D^{(*)}\bar{B}^{(*)}[I(J^P)=1(1^+)]$ with both charm and bottom is ruled out.

Study of Charmed and Bottom Baryons in a Variational Approach and Chiral Interactions

Models have been widely used to study charmed and bottom baryons. In this work using the confining, one gluon exchange and Goldstone boson exchange terms as inter-quark interactions, we study the heavy flavour baryon spectrum in the framework of the constituent quark model. We use a variational method to solve the non-relativistic three-body problem for baryons in the hypercentral approach. The masses of heavy baryons containing one, two, and three heavy flavour quarks are found to be in accordance with the existing experimental values or with other theoretical predictions. The magnetic moments of single heavy baryons with J^p=3/2^+ are also obtained.

Intrinsic strangeness and charm of the nucleon using improved staggered fermions

We calculate the intrinsic strangeness of the nucleon, <N|ss|N> - <0|ss|0>, using the MILC library of improved staggered gauge configurations using the Asqtad and HISQ actions. Additionally, we present a preliminary calculation of the intrinsic charm of the nucleon using the HISQ action with dynamical charm. The calculation is done with a method which incorporates features of both commonly-used methods, the direct evaluation of the three-point function and the application of the Feynman- Hellman theorem. We present an improvement on this method that further reduces the statistical error, and check the result from this hybrid method against the other two methods and find that they are consistent. The values for <N|ss|N> and <N|cc|N> found here, together with perturbative results for heavy quarks, show that dark matter scattering through Higgs-like exchange receives roughly equal contributions from all heavy quark flavors.

Consequences of heavy-quark symmetries for hadronic molecules

Among the newly observed structures in the heavy-quarkonium mass region, some have been proposed to be hadronic molecules. We investigate the consequences of heavy-quark flavor symmetry on these heavy meson hadronic molecules. The symmetry allows us to predict new hadronic molecules on one hand, and test the hadronic molecular assumption of the observed structures on the other hand. We explore the consequences of the flavor symmetry assuming the $X(3872)$ and ${Z}_{b}(10\text{ }610)$ as an isoscalar $D{\overline{D}}^{*}$ and isovector $B{\overline{B}}^{*}$ hadronic molecule, respectively. A series of hadronic molecules composed of heavy mesons are predicted. In particular, there is an isoscalar ${1}^{++}$ $B{\overline{B}}^{*}$ bound state with a mass about 10 580 MeV which may be searched for in the $\ensuremath{\Upsilon}(1S,2S){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ mass distribution; the isovector charmonium partners of the ${Z}_{b}(10\text{ }610)$ and the ${Z}_{b}(10\text{ }650)$ are also predicted, which probably corresponds to the very recently observed ${Z}_{c}(3900)$ and ${Z}_{c}(4025)$ resonances by the BESIII Collaboration.

Heavy-quark binary scattering in the quark-gluon plasma

I argue that the strong quenching and the sizable anisotropy of heavy quark flavors observed in heavy-ion collisions has a substantial component from binary scattering processes in the quark-gluon plasma. To arrive at this conclusion, I illustrate essential requirements for a more accurate theoretical description by considering first the average collisional energy loss of heavy quarks in a thermal background. On this basis, I describe a consistent transport approach, formulating the in-medium evolution of heavy quarks as a stochastic Markov process, which has been implemented for applications in heavy-ion phenomenology.

Measurement of muon tagged open heavy flavor production in Pb + Pb collisions at 2.76 TeV with ATLAS

Abstract Heavy flavor quarks are an important probe with which to study the hot, dense medium produced in heavy ion collisions. Charm and bottom quarks are produced at a relatively early stage of the collision and are predicted to have a smaller gluon radiation due to the dead cone effect. Semi-leptonic heavy flavor decays can be identified by the presence of a muon and separated from the light meson background using a template fitting method. In this talk, the R CP for heavy flavor muons in Pb + Pb collisions at s N N = 2.76 TeV with the ATLAS detector at the LHC is presented as a function of muon transverse momentum.

Testing the operator product expansion Wilson coefficient forA2from lattice QCD with a dynamical charm

Gluon and ghost propagators data, obtained in Landau gauge from lattice simulations with two light and two heavy dynamical quark flavours ($N_f$=2+1+1), are described here with a running formula including a four-loop perturbative expression and a nonperturbative OPE correction dominated by the local operator $A^2$. The Wilson coefficients and their variation as a function of the coupling constant are extracted from the numerical data and compared with the theoretical expressions that, after being properly renormalized, are known at ${\cal O}(\alpha^4)$. As also $\Lambda_{\msbar}$ is rather well known for $N_f$=2+1+1, this allows for a precise consistency test of the OPE approach in the joint description of different observables.

Heavy Flavor Results from STAR

Heavy flavor quarks are considered to be unique probes of the medium created in high energy heavy ion collisions. These proceedings report selected STAR results from various measurements of heavy flavor production, including J/ψ suppression and collectivity, Υ suppression, ratio of bottom-decay electrons to charm-decay electrons, D meson spectra and charm cross section.

Measurement of heavy-flavor production in Pb—Pb collisions at the LHC with ALICE

A Large Ion Collider Experiment (ALICE) at the Large Hadron Collider (LHC) has been built in order to study the Quark-Gluon Plasma (QGP) created in high-energy nuclear collisions. As heavy-flavor quarks are produced at the early stage of the collision, they serve as sensitive probes for the QGP. The ALICE detector with its capabilities such as particle identification, secondary vertexing and tracking in a high multiplicity environment can address, among other measurements, the heavy-flavor sector in heavy-ion collisions.We present latest results on the measurement of the nuclear modification factor of open heavy-flavors as well as on the measurement of open heavy-flavor azimuthal anisotropy v2 in Pb-Pb collisions at TeV.Open charmed hadrons are reconstructed in the hadronic decay channels D° K−−π+, D+ K−−π+π+, and D*+ D0π+ applying a secondary decay-vertex topology. Complementary measurements are performed by detecting electrons (muons) from semi-leptonic decays of open heavy-flavor hadrons in the central (forward) rapidity region.

Track reconstruction and b-jet identification for the ATLAS trigger system

A sophisticated trigger system, capable of real-time track reconstruction, is used in the ATLAS experiment to select interesting events in the proton-proton collisions at the Large Hadron Collider at CERN. A set of b-jet triggers was activated in ATLAS for the entire 2011 data-taking campaign and successfully selected events enriched in jets arising from heavy-flavour quarks. Such triggers were demonstrated to be crucial for the selection of events with no lepton signature and a large jet multiplicity. An overview of the track reconstruction and online b-jet selection with performance estimates from data is presented in these proceedings.

Ground State Heavy Mesons Spectrum in Cornell Potential

This paper studies the meson masses containing heavy flavour quark (anti-quark) with light flavour combination. The considered potential is Coulomb as well as linear confining terms. Also, an improved form of the hyperfine interaction is introduced. The ground state masses (J=0 and J=1) of heavy mesons and magnetic moments of heavy mesons with J=1 using the effective mass of the confined quarks are computed. The obtained results are very close to the ones obtained in experiments or in other works. Key words: Confining potential, hyperfine interaction, Heavy mesons.

PROJECTION OF A MEASUREMENT OF THE NONPHOTONIC ELECTRON v2 IN Au + Au COLLISIONS AT STAR

We present a method of measuring the elliptic flow (v2) of nonphotonic electrons from heavy flavor quark decays using the STAR detector at RHIC in Au + Au collisions at [Formula: see text]. Inclusive electrons are identified in the pT range 0.5–4 GeV /c at mid-rapidity -1 &lt; η &lt; 0 by the STAR time projection chamber (TPC) and time-of-flight detector. Photonic e+e- pairs with characteristic low invariant mass are reconstructed in the TPC and their v2 is measured using the standard event plane method by subtracting the combinatorial background in the dN/dΔϕ distributions in each pT bin. The nonphotonic electron v2 and its propagated error can be derived from the inclusive and photonic electron v2. We estimate the necessary statistics and errors of nonphotonic electron v2 for a more recent RHIC run.

CONSTRAINTS ON B→π, K TRANSITION FORM-FACTORS FROM EXCLUSIVE SEMILEPTONIC D-MESON DECAYS

According to the heavy-quark flavor symmetry, the B→π, K transition form-factors could be related to the corresponding ones of D-meson decays near the zero recoil point. With the recent precisely measured exclusive semileptonic decays D →πℓν and D→K ℓν, we perform a phenomenological study of B →π, K transition form-factors based on this symmetry. Using BK, BZ and Series Expansion parametrizations of the form-factor slope, we extrapolate B →π, K transition form-factors from [Formula: see text] to q2 = 0. It is found that, although being consistent with each other within error bars, the central values of our results for B →π, K form-factors at q2 = 0, [Formula: see text], are smaller than predictions of the QCD light-cone sum rules, but are in good agreements with the ones extracted from hadronic B-meson decays within the SCET framework. Moreover, smaller form-factors are also favored by the QCD factorization approach for hadronic B-meson decays.

Heavy flavour kinetic equilibration in the confined phase

By making use of a non-perturbative definition of a momentum diffusion coefficient as well as Heavy Meson Chiral Perturbation Theory, we investigate the Brownian motion and kinetic equilibration of heavy quark flavours deep in the confined phase. It appears that the momentum diffusion coefficient can be expressed in terms of known low-energy constants; it increases rapidly at temperatures above 50 MeV, behaving as ~ T^7/F_pi^4 for m_pi / pi << T << F_pi, where m_pi and F_pi are the pion mass and decay constant, respectively. The early increase may suggest a broad peak in kappa/T^3 around the QCD crossover. For a more detailed understanding the computation could be generalized in a number of ways.

Variable flavor number parton distributions and weak gauge and Higgs boson production at hadron colliders at next-to-next-to-leading order of QCD

Based on our recent next-to-next-to-leading order (NNLO) dynamical parton distributions as obtained in the 'fixed flavor number scheme', we generate radiatively parton distributions in the 'variable flavor number scheme' where the heavy-quark flavors (c,b,t) also become massless partons within the nucleon. Only within this latter factorization scheme are NNLO calculations feasible at present, since the required partonic subprocesses are only available in the approximation of massless initial-state partons. The NNLO predictions for gauge boson production are typically larger (by more than 1{sigma}) than the next-to-leading order (NLO) ones, and rates at LHC energies can be predicted with an accuracy of about 5%, whereas at Tevatron they are more than 2{sigma} above the NLO ones. The NNLO predictions for standard model Higgs-boson production via the dominant gluon fusion process have a total (parton distribution function and scale) uncertainty of about 10% at LHC which almost doubles at the lower Tevatron energies; they are typically about 20% larger than the ones at NLO but the total uncertainty bands overlap.

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 ) .