Open Charm Hadrons Research Articles

Observation of double charm production involving open charm in pp collisions at $ \sqrt {s} = {7}\;{\text{TeV}} $

Abstract The production of J/ψ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 355 pb−1 collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured J/ψ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.

Open charm hadron measurement in p+p and Au+Au collisions at = 200 GeV in STAR

We present the measurements of D0 and D* in p+p and D0 in Au+Au collisions via hadronic decays D0 → K−π+, D*+ → D0π+ → K−π+π+ in mid-rapidity |y| < 1 at = 200 GeV, covering pT from 0.2 to 6 GeV/c in p+p and 0.4 to 5 GeV/c in Au+Au, respectively. The charm pair production cross section per nucleon–nucleon collision at mid-rapidity is measured to be 202 ± 56 (stat.) ± 40 (sys.) ± 20 (norm.) μb in p+p and 186 ± 22 (stat.) ± 30 (sys.) ± 18 (norm.) μb in Au+Au minimum bias collisions. The number of binary collisions scaling of charm cross section indicates that charm is produced via initial hard scatterings. No suppression of D0 RAA in Au+Au 0–80% minbias collisions is observed at pT below 3 GeV/c. Blast-wave predictions with light-quark hadron parameters are different from data, which may indicate that D0 decouples earlier from the medium than the light-quark hadrons.

Open charm measurement with HFT at STAR

Thermalization is one of the key questions in understanding the matter created in Au+Au collisions at RHIC. Heavy-flavor quark collectivity could be used to indicate the degree of thermalization of the light-flavor quarks. Heavy quark energy loss could give important information on color charge density of the medium. Direct reconstruction of open charm hadrons is essential for these measurements. The Heavy Flavor Tracker (HFT) is a proposed upgrade of the STAR experiment. Full GEANT simulation of tracking with HFT was performed, showing its excellent capability to reconstruct open charm hadrons in broad p_T range at midrapidity. Estimated errors on measurement of D0 meson v_2 and R_{CP} are presented.

Status of the ALICE experiment and first results on heavy flavour production

The ALICE experiment is the LHC detector mainly dedicated to the study of the Quark Gluon Plasma (QGP) in Pb-Pb collisions. The detector has started the data taking less than one year ago, delivering immediately relevant results. An overview of the first physics results obtained in the first six month of running of the experiment will be summarized, giving special emphasis to heavy flavour measurements. Heavy flavours are ideal probes to explore both the formation and properties of the QGP, since they experience the full collision history and are expected to be copiously produced at LHC, much more than at any other collider. With ALICE we will measure heavy flavours down to small transverse momentum, combining hadronic and leptonic channels, both at central and forward rapidity. In particular, in the central rapidity region, it is possible to exclusively reconstruct open charm mesons and baryons via hadronic decay channels. Furthermore, the good identification of electrons allows to measure the production both of charmonium and open beauty. First results from p-p collisions at 7 TeV will be shown, including the clear signals of open and hidden charm hadrons reconstructed at ALICE. These data provide interesting insight into QCD processes in a new energy regime, are important as a baseline for the Pb-Pb program and demonstrate the potential for heavy flavour cross section measurements with the ALICE detector.

STAR inner tracking upgrade—a performance study

Anisotropic flow measurements have demonstrated development of partonic collectivity in 200 GeV Au+Au collisions at RHIC. To understand the partonic EOS, thermalization must be addressed. Collective motion of heavy-flavor (c, b) quarks can be used to indicate the degree of thermalization of the light-flavor quarks (u, d, s). Measurement of heavy-flavor quark collectivity requires direct reconstruction of heavy-flavor hadrons in the low p T region. Measurement of open charm spectra to high p T can be used to investigate heavy-quark energy loss and medium properties. The Heavy Flavor Tracker (HFT), a proposed upgrade to the STAR experiment at midrapidity, will measure v 2 of open-charm hadrons to very low p T by reconstructing their displaced decay vertices. The innermost part of the HFT is the PIXEL detector (made of two low mass monolithic active pixel sensor layers), which delivers a high precision position measurement close to the collision vertex. The Intermediate Silicon Tracker (IST), a 1-layer strip detector, is essential to improve hit identification in the PIXEL detector when running at full RHIC-II luminosity. Using a full GEANT simulation, open charm measurement capabilities of STAR with the HFT will be shown. Its performance in a broad p T range will be demonstrated on v 2 (p T>0.5 GeV/c) and R CP (p T<10 GeV/c) measurements of D0 meson. Results of reconstruction of ΛC baryon in heavy-ion collisions are presented.

Open charm production at RHIC

Recent experimental measurements on open charm production in proton-proton, proton (deuteron)-nucleus and nucleus-nucleus collisions at RHIC are reviewed. A comparison with theoretical predictions is made. Some unsettled issues in open charm production call for precise measurements on directly reconstructed open charm hadrons.

Open Charm Production at RHIC: Recent Results from STAR

We report recent measurements on the open charm production in d+Au and p+p collisions at \(\sqrt {s_{NN} } = 200\) GeV from the STAR detector at RHIC. The two independent measurements — direct open charm hadron (D0, D* etc.) reconstruction and non-photonic single electron spectrum — provide consistent results. The mid-rapidity charm differential cross section per nucleon-nucleon collision from d+Au collisions at RHIC is \(d\sigma _{c\bar c}^{NN} /dy = 0.30 \pm 0.04(stat.) \pm 0.09(syst.)\) mb, which is higher than predictions from most of the NLO pQCD calculations. Implications for charmonium production in Au+Au collisions will also be discussed.

Statistical hadronization of charmed quarks at SPS and RHIC

Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model. The charmed quark-antiquark pairs are assumed to be created at the initial stage of the reaction in hard parton collisions. The number of these pairs is conserved during the evolution of the system. At the hadronization stage, the charmed (anti)quarks are distributed among open and hidden charm hadrons in accordance with the laws of statistical mechanics. The model is in agreement with the experimental data on J/psi to Drell-Yan ratio in Pb+Pb collisions at SPS. This agreement can be reached only if a rather strong enhancement of the open charm production in central Pb+Pb collisions is assumed. A possible mechanism of the charm enhancement is discussed. At the top RHIC energy, the model predicts an increase of J/psi to Drell-Yan ratio in more central nucleus-nucleus collisions with respect to less central ones.

Statistical J/ψ production and open charm enhancement in Pb + Pb collisions at CERN SPS

Production of open and hidden charm hadrons in heavy-ion collisions is considered within the statistical coalescence model. Charmed quarks and antiquarks are assumed to be created at the initial stage of the reaction and their number is conserved during the evolution of the system. They are distributed among open and hidden charm hadrons at the hadronization stage in accordance with laws of statistical mechanics. The model is in excellent agreement with the experimental data on J/ψ production in lead–lead collisions at CERN SPS and predicts strong enhancement of the open charm multiplicity over the standard extrapolation from nucleon–nucleon to nucleus–nucleus collisions. A possible mechanism of the charm enhancement is proposed.

B Decay Charm Counting Via Topological Vertexing

We present a new and unique measurement of the branching fractions of b hadrons to states with 0, 1 and 2 open charm hadrons, using a sample of 350,000 Z's collected during the SLD/SLC 97-98 run. The analysis takes advantage of the excellent vertexing resolution of the VXD3, a pixel-based CCD vertex detector, which allows the separation of B and cascade D decay vertices. Analysis of the decay length distributions for each of the 1-, 2-, and 3-vertex topologies allows the extraction of the inclusive branching fractions. We measure: BR(b → 0D) =5.6% ± 1.1%(stat.) ± 2.0%(syst.), BR(b → 2D)= 24.6% ± 1.4%(stat.)± 4.0%(syst.) (preliminary), where b and D represent mixtures of open b and open c hadrons.