Heavy-flavour Hadron Decays Research Articles

Measurements of heavy-flavour decay leptons in pp, p-Pb, and Pb-Pb collisions with ALICE

We present measurements of electrons and muons originating from the semi-leptonic decays of heavy-flavour hadrons at central and forward rapidities with ALICE in pp ( = 2.76 and 7 TeV), p-Pb ( = 5.02 TeV), and Pb-Pb ( = 2.76 TeV) collisions. The measured pT-differential production cross sections in pp collisions, the nuclear modification factors in p-Pb and Pb-Pb, and the v2 measurements in Pb-Pb collision are disgusted. In addition, the angular correlation distribution between heavy-flavour decay electrons and charged particles, measured in p-Pb collisions, is shown. The results are compared to their corresponding theoretical predictions.

Heavy flavor production in STAR

We report on the recent STAR results on heavy flavor production in Au+Au collisions at = 200, 62.4 and 39 GeV. We present the nuclear modification factor and elliptic flow of open charm mesons and electrons from semileptonic decays of heavy flavor hadrons. We also report on new measurements of energy dependence of J/ψ production. STAR data are compared to theoretical model calculations and physics implications are discussed.

Measurement of electrons from heavy-flavour decays in Pb-Pb collisions at = 2.76 TeV with ALICE

The measurement of heavy-flavour (charm and beauty) production in ultra-relativistic heavy-ion collisions provides an important contribution to the study of the properties of the hot and dense medium created in such collisions. One approach to measure heavy-flavour production is via electrons from semi-leptonic decays of heavy-flavour hadrons. In this contribution we present the nuclear modification factor (RAA) and the azimuthal anisotropy (v2) of heavy-flavour decay electrons in Pb-Pb collisions at = 2.76 TeV, which are sensitive to the interaction of c and b quarks with the medium. We also present, for the first time, the azimuthal angular correlations of heavy-flavour decay electrons and charged hadrons, Δϕ(HFE,h), in Pb-Pb collisions and the corresponding near-side yield ratio (IAA).

Heavy-flavour decay lepton measurements in pp, p–Pb, and Pb–Pb collisions with ALICE at the LHC

We present the measurements of electrons and muons from the semi-leptonic decays of heavy-flavour hadrons measured in the central and forward rapidity regions with ALICE in pp ( s = 2.76 TeV and 7 TeV), Pb–Pb ( s NN = 2.76 TeV ), and p–Pb ( s NN = 5.02 TeV ) collisions at the LHC. The p T -differential production cross section in pp collisions, the elliptic flow in Pb–Pb collisions, and the nuclear modification factor in Pb–Pb and p–Pb collisions are shown. The results are compared to theoretical predictions.

Measurements of jet quenching and heavy flavor production with the ATLAS detector

Measurements of jet suppression in PbPb collisions by the ATLAS Collaboration are reported. The production of inclusive jet yields as a function of jet pt, collision centrality and jet size parameter R are measured and presented through the central-to-peripheral ratio, Rcp. Jets are found to be suppressed in central collisions relative to peripheral collisions by approximately a factor of two. The suppression is found to show almost no variation with jet pt, and the Rcp is found to increase slighly with increasing R. Measurements of heavy quark energy loss are also presented using muons from semi-leptonic decays of heavy flavor hadrons. The maximal suppression is observed to be Rcp ~ 0.5 and shows no significant depedence on the muon pt.

Heavy-flavour production in ALICE at the LHC

ALICE at the LHC is the experiment dedicated to study the physics of nucleus-nucleus collisions. The apparatus is well suited for the measurement of heavy-quark hadron production, making use of the high spatial resolution provided by the tracking detectors and the excellent particle identification, which are distinctive of the ALICE apparatus. Results from proton–proton collisions at s=2.76 and 7 TeV, and from Pb–Pb collisions at sNN=2.76 TeV are presented. The measurements in pp collisions provide an important test of perturbative QCD predictions. The precise vertex reconstruction together with the electron identification, allows the separation of the charm and the beauty components. Furthermore, the pp results are essential as a reference for the measurements in heavy-ion collisions. Nuclear modification factors were measured for D mesons, for electrons and for muons from heavy-flavour hadron decays. The elliptic flow of D mesons is also discussed. These measurements are important because they will provide information on the Quark–Gluon Plasma produced in heavy-ion collisions, via the energy loss of the heavy partons in the strongly interacting medium, and hints on the medium thermalization.

Components of the dilepton continuum in Pb+Pb collisions atsNN=2.76TeV

The dilepton invariant mass spectrum measured in heavy-ion collisions includes contributions from important quark-gluon plasma (QGP) probes such as thermal radiation and the quarkonium ($J/\ensuremath{\psi}$, ${\ensuremath{\psi}}^{\ensuremath{'}}$, and $\ensuremath{\Upsilon}$) states. Dileptons coming from hard $q\overline{q}$ scattering, the Drell-Yan process, contribute in all mass regions. In heavy-ion colliders, such as the Large Hadron Collider (LHC), semileptonic decays of heavy flavor hadrons provide a substantial contribution to the dilepton continuum. Because the dilepton continuum can provide quantitative information on heavy quark yields and their medium modifications, it is important to identify which dilepton sources populate different parts of the continuum. In the present study, we calculate $c\overline{c}$ and $b\overline{b}$ production and determine their contributions to the dilepton continuum in Pb+Pb collisions at $\sqrt{{s}_{{}_{NN}}}=2.76$ TeV with and without including heavy quark energy loss. We also calculate the rates for Drell-Yan and thermal dilepton production. The contributions to the continuum from these dilepton sources are studied in the kinematic ranges relevant for the LHC detectors. The relatively high ${p}_{T}$ cutoff for single leptons excludes most dileptons produced by the thermal medium. Heavy flavors are the dominant source of dilepton production in all the kinematic regimes except at forward rapidities where Drell-Yan dileptons become dominant for masses greater than 10 GeV/${c}^{2}$.

Investigation of charm and beauty production via semileptonic decays of heavy-flavour hadrons in pp at 7 TeV and Pb–Pb at 2.76 TeV with ALICE

Electron spectra measured with ALICE at mid-rapidity are used to study the production of hadrons carrying a charm or a beauty quark. The production cross section of electrons from heavy-flavour hadron decays is measured in pp collisions at = 7 TeV. Electrons from the beauty decays are identified via the displacement from the interaction vertex. From the electron spectra measured in Pb–Pb collisions, we determine the nuclear modification factor, which is sensitive to the heavy-quark energy loss in a hot strongly interacting medium.

Inclusive electron spectrum from heavy-flavour decays in proton-proton collisions at [formula omitted] measured with ALICE at LHC

We present the status of the analysis on heavy-flavour production in proton-proton collisions at s = 7 TeV via a measurement of their semileptonic decay spectrum at mid-rapidity. An important goal of QCD studies at the LHC is a precise understanding of the heavy-quark production cross section at the high energy frontier in terms of the pQCD framework. Furthermore, heavy quarks are an excellent probe of the hot matter produced in high energy nucleus-nucleus collisions. Establishing precision measurements in proton-proton collisions is a very important baseline for the interpretation of their behaviour in the Quark Gluon Plasma. We present first measurements of the inclusive spectrum of single electrons, using the excellent particle identification capabilities of the ALICE experiment. The subtraction of a cocktail describing photonic and other background sources, as well as an analysis of impact parameter distributions relative to the interaction vertex, are ongoing and will allow the isolation of electrons from heavy-flavour hadron decays.

Search for anomalous semileptonic decay of heavy flavor hadrons produced in association with aWboson at CDF II

We present a search for anomalous semileptonic decays of heavy flavor hadrons produced in association with a $W$ boson, in proton-antiproton collisions at sqrt{s}=1.96 TeV. We use 162 pb-1 of data collected with the CDF II detector at the Fermilab Tevatron Collider. We select events with one W boson and at least one jet with an identified secondary vertex. In the jets with a secondary vertex we look for a semileptonic decay to a muon. We compare the number of jets with both a secondary vertex and a semileptonic decay, and the kinematic properties of these jets, with the standard model expectation of W plus heavy flavor production and decay. No discrepancy is seen between the observation and the expectation, and we set limits on the production cross section of a B-like hadron with an anomalously high semileptonic branching ratio.

Lifetimes of heavy-flavour hadrons—whence and whither?

A theoretical treatment for the weak decays of heavy-flavour hadrons has been developed that is genuinely based on QCD. Its methodology as it applies to total lifetimes and the underlying theoretical issues are sketched. Predictions are compared with present data. One discrepancy emerges: the beauty baryon lifetime appears to be significantly shorter than expected. The ramifications of those findings are analyzed in detail.

Sum rules for heavy flavor transitions in the small velocity limit.

We show how sum rules for the weak decays of heavy flavor hadrons can be derived as the moments of spectral distributions in the small velocity limit. Our derivation of the sum rules is based on the operator product expansion. This systematic approach allows us to determine corrections to these sum rules, to obtain new sum rules, and it provides us with a transparent physical interpretation; it also opens a new perspective on the notion of the heavy quark mass. Applying these sum rules we derive a lower bound on the deviation of the exclusive form factor ${\mathit{F}}_{\mathit{B}\ensuremath{\rightarrow}\mathit{D}}^{\mathrm{*}}$ from unity at zero recoil; likewise we give a field-theoretical derivation of a previously formulated inequality between the expectation value for the kinetic energy operator of the heavy quark and for the chromomagnetic operator. We analyze how the known results on nonperturbative corrections must be understood when one takes into account the normalization point dependence of the low scale parameters. The relation between the field-theoretic derivation of the sum rules and the quantum-mechanical approach is elucidated.

Weak annihilation and the end-point spectrum in semileptonic B decays

A general relationship is formulated between the contributions of ‘Weak Annihilation’ (WA) to inclusive semileptonic decays of heavy flavour hadrons and the matrix elements of four-fermion operators. We argue that non-perturbative contributions from low-energy hadronic final states provide the dominant impact of WA on the semileptonic b → u width of B − mesons. In that case WA affects the lepton spectrum mainly in its end-point region - i.e. beyond the kinematical boundary for b → c transitions - and we expect the latter to look quite different in B − than in B d decays. At present we are unable to make a truly quantitative prediction; yet a detailed experimental comparison of the B − and the B d lepton spectra will enable us to determine the size of the relevant matrix elements and to check directly to what extent the factorization approximation works here. Using universal analyticity properties of the decay amplitude we analyse WA in the perturbative regime and rederive our earlier results about the absence of a power enhancement due to gluon emission in a more general way. We also address the problem of the invariant mass of hadrons in the final state in semileptonic B decays and identify non-trivial cancellations in 〈 M hadr 2〉.

Nonperturbative corrections to inclusive beauty and charm decays. QCD versus phenomenological models

We present a self-consistent method for treating nonperturbative effects in inclusive nonleptonic and semileptonic decays of heavy flavour hadrons. These effects give rise to powerlike corrections ∝ 1 m Q n with n ⩾ 2. The leading correction to the semileptonic branching ratio occurs for n = 2. It is expressed in terms of the vector-pseudoscalar mass splitting: δ BR sl BR sl ≅ BR nl · 6 [ (M v 2−M p 2) m Q 2 ](c + 2−c − 2) 2N c and yields a reduction of BR sl. This nonperturbative correction contributes to the nonleptonic width with a sign opposite to that of the perturbative terms that are non-leading in 1 N c . In beauty decays the former reduces the latter by 20% whereas in charm decays they more or less cancel. This leads to a reduction of BR sl by no more than 10% in beauty decays and by a factor of roughly two in charm decays. Phenomenological models of heavy flavour decays are unable to mimic these leading corrections by a specific choice of quark masses or by invoking Fermi motion.