T. K. Hemmick

Proton and pion production relative to the reaction plane in Au + Au collisions at 11A GeV/c

Results are presented of an analysis of proton and charged pion azimuthal distributions measured with respect to the reaction plane in Au + Au collisions at a beam momentum of about 11A GeV/c. The azimuthal anisotropy is studied as a function of particle rapidity and transverse momentum for different centralities of the collisions. The triple differential (in rapidity, transverse momentum, and azimuthal angle) distributions are reconstructed. A comparison of the results with a previous analysis of charged-particle and transverse energy flow as well as with model predictions are presented. {copyright} {ital 1997} {ital The American Physical Society}

Proton and pion production in Au+Au collisions at 10.8A GeV/c

We present proton and pion tranverse momentum spectra and rapidity distributions for Au+Au collisions at 10.8A GeV/c. The proton spectra exhibit collective transverse flow effects. Evidence of the influence of the Coulomb interaction from the fireball is found in the pion transverse momentum spectra. The data are compared with the predictions of the RQMD event generator.

PHENIX central arm particle ID detectors

Abstract The Ring-Imaging Cherenkov (RICH) and the Time-of-Flight (ToF) systems provide identification of charged particles for the PHENIX central arm. The RICH is located between the inner and outer tracking units and is one of the primary devices for identifying electrons among the very large number of charged pions. The ToF is used to identify hadrons and is located between the most outer pad chamber (PC3) and the electromagnetic calorimeter. A Time Zero (T0) counter that enhances charged particle measurements in p–p collisions is described. Details of the construction and performance of both the RICH, ToF and T0 are given along with typical results from the first PHENIX data taking run.

Measurement of pion enhancement at low transverse momentum and of the Δ resonance abundance in Si-nucleus collisions at AGS energy

Abstract We present measurements of pion transverse momentum ( p t ) spectra in central Si-nucleus collisions in the rapidity range 2.0 y p t down to and including p t = 0. The data exhibit an enhanced pion yield at low p t compared to what is expected for a purely thermal spectral shape. This enhancement is used to determine the Δ resonance abundance at freeze-out. The results are consistent with a direct measurement of the Δ resonance yield by reconstruction of proton-pion pairs and imply a temperature of the system at freeze-out close to 140 MeV.We present measurements of the pion transverse momentum (p_t) spectra in central Si-nucleus collisions in the rapidity range 2.0<y<5.0 for p_t down to and including p_t=0. The data exhibit an enhanced pion yield at low p_t compared to what is expected for a purely thermal spectral shape. This enhancement is used to determine the Delta-resonance abundance at freeze-out. The results are consistent with a direct measurement of the Delta-resonance yield by reconstruction of proton-pion pairs and imply a temperature of the system at freeze-out close to 140 MeV.

Production of Photons and Dileptons in the Glasma

Abstract We study the production of photons and dileptons during the pre-equilibrium Glasma stage in heavy ion collisions and discuss the implications in light of the PHENIX data. We find that the measured distributions of such electromagnetic emissions, while having some features not well understood if hypothesized to entirely arise from a thermalized Quark–Gluon Plasma, have some qualitative features that might be described after including effects from a thermalizing Glasma. The shape and centrality dependence of the transverse momentum spectra of the so-called “thermal photons” are well described. The mass and transverse momentum dependence of intermediate mass dileptons also agree with our estimates. The low transverse momenta from which the excessive dileptons (in low to intermediate mass region) arise is suggestive of emissions from a Bose condensate. We also predict the centrality dependence of dilepton production. Uncertainties in the current approach and improvements in the future are discussed.

Two pion correlations in Au + Au collisions at 10.8-GeV/c per nucleon

Two-particle correlation functions for positive and negative pions have been measured in Au+Au collisions at 10.8GeV/{ital c} per nucleon. The data were analyzed using one- and three-dimensional correlation functions. From the results of the three-dimensional fit the phase space density of pions was calculated. It is consistent with local thermal equilibrium. {copyright} {ital 1997} {ital The American Physical Society}

A Study of Gain Stability and Charging Effects in GEM Foils

A study has been carried out to investigate the gain stability and charging effects in Gas Electron Multipliers (GEMs). It was found that the gain of a GEM typically rises after the initial application of high voltage across the foil, but the degree and rate of rise can depend on a variety of different factors. These factors include the geometry of the foil (inner and outer hole diameter), the rate of ionizing radiation applied to the foil, the amount of water content of the operating gas, and possibly various other factors related to the manufacturing process. We have studied GEMs produced by several different manufacturers and compared their gain behavior as a function of time, after applying and removing the high voltage, gain as a function of rate, and the degree of initial charge up as a function of water content in the gas. While GEMs from all manufacturers exhibited an initial charge up to some degree, there was a large variation in this effect between different foils. The ratio of inner to outer hole diameter and the amount of water content in the gas seem to be two principle factors affecting the degree and rate of the initial charge up effect observed in certain foils.

Construction and expected performance of the hadron blind detector for the PHENIX experiment at RHIC

A new hadron blind detector (HBD) for electron identification in high density hadron environment has been installed in the PHENIX experiment at RHIC in the fall of 2006. The HBD will identify low momentum electron-positron pairs to reduce the combinatorial background in the e + e - mass spectrum, mainly in the region below 1 GeV/c 2 . The HBD is a windowless proximity-focusing Cherenkov detector with a radiator length of 50 cm, a CsI photocathode and three layers of gas electron multipliers (GEM). Pure CF 4 is used as a radiator and a detector gas. This proceeding describes the construction details and the expected performance of the HBD.

Evidence for expansion of a hot fireball from two-pion correlations for Si + Pb collisions at AGS energy

Abstract The two-pion correlation function has been measured for charged pions produced in central 14.6 A GeV/ c Si + Pb collisions at the AGS. Data for like-sign pions show a clear quantum interference effect as expected for identical bosons. The experimental correlation function agrees well with that obtained for events generated by a cascade code (RQMD). The present data are consistent with a time-averaged rms freeze-out radius of 8.3 fm and a mean duration of pion emission of 9 fm/ c . The system has expanded considerably before freeze-out.

Directed flow of light nuclei in Au + Au collisions at 10.8A GeV/c

Directed flow of deuterons, tritons,