Results on Identified Charged Hadrons from the PHENIX Experiment at RHIC

Recent results on identified hadrons from the PHENIX experiment in Au+Au collisions at mid-rapidity at $\sqrt{s_{NN}}$ = 200 GeV are presented. The centrality dependence of transverse momentum distributions and particle ratios for identified charged hadrons are studied.Comment: 10pp. To appear in the proceedings of The XVI International Conference on Particles and Nuclei (PaNic02), Osaka, Japan, September 30 - October 4, 200

Results on Identified Hadrons from the PHENIX Experiment at RHIC

Recent results on identified hadrons from the PHENIX experiment in Au+Au collisions at mid-rapidity at $\sqrt{s_{NN}}$ = 200 GeV are presented. The centrality dependence of transverse momentum distributions and particle ratios for identified charged hadrons are studied. The transverse flow velocity and freeze-out temperature are extracted from $p_{T}$ spectra within the framework of a hydrodynamic collective flow model. Two-particle HBT correlations for charged pions are measured in different centrality selections for a broad range of transverse momentum of the pair. Results on elliptic flow measurements with respect to the reaction plane for identified particles are also presented.Comment: 10 pages, 10 figures. Talk presented at Quark Matter 2002, Nantes, France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A

Λ c + production in pp collisions at√ s=7 TeV and in p-Pb collisions at√ sNN=5.02 TeV

The pT-differential production cross section of prompt Λ c + charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at s√=7 TeV and in p-Pb collisions at sNN−−−√=5.02 TeV at midrapidity. The Λ c + and Λ¯¯¯¯c¯¯¯ were reconstructed in the hadronic decay modes Λ c +  → pK−π+, Λ c +  → pK S 0 and in the semileptonic channel Λ c +  → e+νeΛ (and charge conjugates). The measured values of the Λ c + /D0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and pT intervals, where the Λ c + production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ c + nuclear modification factor, RpPb, is also presented. The RpPb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium

Search for the onset of baryon anomaly at RHIC-PHENIX

The baryon production mechanism at the intermediate $p_T$ (2 - 5 GeV/$c$) at RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au systems at RHIC may provide us a further insight on the origin of the baryon anomaly and its evolution as a function of $\sqrt{s_{NN}}$. In 2005 RHIC physics program, the PHENIX experiment accumulated the first intensive low beam energy data in Cu+Cu collisions. We present the preliminary results of identified charged hadron spectra in Cu+Cu at $\sqrt{s_{NN}}$ = 22.5 and 62.4 GeV using the PHENIX detector. The centrality and beam energy dependences of (anti)proton to pion ratios and the nuclear modification factors for charged pions and (anti)protons are presented.Comment: 5 pages, 9 figures, proceedings for Hot Quarks 2006 workshop, Villasimius, Sardinia, Italy, May 15 - 20, 2006. Proceedings of the conference will be published in The European Physical Journal

Simple Front End Electronics for Multigap Resistive Plate Chambers

A simple circuit for the presentation of the signals from Multi-gap Resistive Plate Chambers (MRPCs) to standard existing digitization electronics is described. The circuit is based on "off-the-shelf" discrete components. An optimization of the values of specific components is required to match the aspects of the MRPCs for the given application. This simple circuit is an attractive option for the initial signal processing for MRPC prototyping and bench- or beam-testing efforts, as well as for final implementations of small-area Time-of-Flight systems with existing data acquisition systems.Comment: submitted to Nucl. Inst. and Methods, Section

Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX

The intermediate $p_T$ region (2 - 5 GeV/$c$) in central Au+Au collisions at RHIC has a rich physics content. The (anti)proton to pion ratio at the intermediate $p_T$ gives us a powerful tool to investigate the bulk properties of the hot and dense matter created at RHIC and their hadronization processes. We present the preliminary results of identified charged hadron spectra at the lower beam energies at RHIC. The excitation function of (anti)proton to pion ratios from SPS to RHIC are shown. We also discuss the onset of the baryon enhancement at the high energy heavy ion collisions.Comment: 4 pages, 3 figures, Quark Matter 2006 conference proceeding

Influence of hydrodynamics on the interpretation of the high pTp_{T} hadron suppression at RHIC

A hybrid parameterization including contributions of hydrodynamics and of expectations from the spectral shape observed in p+p collisions is introduced. This parameterization can successfully describe identified hadron spectra over a wide range of $p_{T}$ in Au+Au reactions at $\sqrt{s_{NN}}$ = 200 GeV for all centralities. The parameters of the hydrodynamic source compare reasonably well to other attempts to describe the spectra. The description is obtained using one universal suppression factor of the hard scattering component independent of $p_{T}$ and hadron species. For the fit results obtained the observed nuclear modification factor for the different particles converges to a universal suppression behavior for $p_{T} > 6 \mathrm{GeV}/c$.Comment: updated version (only typos), 16 pages, 10 figure

First measurement of 0c production in pp collisions at √s=7TeV

The production of the charm-strange baryon 0cis measured for the first time at the LHC via its semileptonic decay into e+−νein ppcollisions at √s=7TeV with the ALICE detector. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 1 <pT<8GeV/cat mid-rapidity, |y| <0.5. The transverse momentum dependence of the 0cbaryon production relative to the D0meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio

Measurements of e(+)e(-) pairs from open heavy flavor in p plus p and d plus A collisions at root S-NN=200 GeV

We report a measurement of e+e− pairs from semileptonic heavy-flavor decays in p+p collisions at √sNN=200 GeV. The e+e− pair yield from b¯b and c¯c is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and pT. We used three different event generators, pythia, mc@nlo, and powheg, to simulate the e+e− spectra from c¯c and b¯b production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4π, significant differences are observed for the total cross section. These difference are less pronounced for b¯b than for c¯c. The same model dependence was observed in already published d+A data. The p+p data are also directly compared with d+A data in mass and pT, and within the statistical accuracy no nuclear modification is seen

Lévy-stable two-pion Bose-Einstein correlations in √sNN=200 GeV Au+Au collisions

We present a detailed measurement of charged two-pion correlation functions in 0–30% centrality √sNN=200 GeV Au+Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Lévy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter λ, the Lévy index of stability α, and the Lévy length scale parameter R as a function of average transverse mass of the pair mT. We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same Lévy-stable source functions. The λ(mT) measurements indicate a decrease of the strength of the correlations at low mT. The Lévy length scale parameter R(mT) decreases with increasing mT, following a hydrodynamically predicted type of scaling behavior. The values of the Lévy index of stability α are found to be significantly lower than the Gaussian case of α=2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition