Results from the STAR TPC system test

A system test of various components of the Solenoidal Tracker at RHIC (STAR) detector, operating in concern, has recently come on-line. Communication between a major sub-detector, a sector of the Time Projection Chamber (TPC), and the trigger, data acquisition and slow controls systems has been established, enabling data from cosmic ray muons to be collected. First results from an analysis of the TPC data are presented. These include measurements of system noise, electronic parameters such as amplifier gains and pedestal values, and tracking resolution for cosmic ray muons and laser induced ionization tracks. A discussion on the experience gained in integrating the different components for the system test is also given

A Readout System for the STAR Time Projection Chamber

We describe the readout electronics for the STAR Time Projection Chamber. The system is made up of 136,608 channels of waveform digitizer, each sampling 512 time samples at 6-12 Mega-samples per second. The noise level is about 1000 electrons, and the dynamic range is 800:1, allowing for good energy loss ($dE/dx$) measurement for particles with energy losses up to 40 times minimum ionizing. The system is functioning well, with more than 99% of the channels working within specifications.Comment: 22 pages + 8 separate figures; 2 figures are .jpg photos to appear in Nuclear Instruments and Method

Dielectron Cross Section Measurements in Nucleus-Nucleus Reactions at 1.0 A GeV

We present measured dielectron production cross sections for Ca+Ca, C+C, He+Ca, and d+Ca reactions at 1.0 A GeV. Statistical uncertainties and systematic effects are smaller than in previous DLS nucleus-nucleus data. For pair mass < 0.35 GeV/c2 : 1) the Ca+Ca cross section is larger than the previous DLS measurement and current model results, 2) the mass spectra suggest large contributions from pi0 and eta Dalitz decays, and 3) dsigma/dM is proportional to ApAt. For M > 0.5 GeV/c2 the Ca+Ca to C+C cross section ratio is significantly larger than the ratio of ApAt values.Comment: Submitted to Physical Review Letters. Further analysis information will be posted on our web pages -- http://macdls.lbl.gov Figure 1 has been redrawn to make more legible. Text modified to support redrawn figur

The STAR Time Projection Chamber: A Unique Tool for Studying High Multiplicity Events at RHIC

The STAR Time Projection Chamber (TPC) is used to record collisions at the Relativistic Heavy Ion Collider (RHIC). The TPC is the central element in a suite of detectors that surrounds the interaction vertex. The TPC provides complete coverage around the beam-line, and provides complete tracking for charged particles within +- 1.8 units of pseudo-rapidity of the center-of-mass frame. Charged particles with momenta greater than 100 MeV/c are recorded. Multiplicities in excess of 3,000 tracks per event are routinely reconstructed in the software. The TPC measures 4 m in diameter by 4.2 m long, making it the largest TPC in the world.Comment: 28 pages, 11 figure

Inclusive Dielectron Cross Sections in p+p and p+d Interactions at Beam Energies from 1.04 to 4.88 GeV

Measurements of dielectron production in p+p and p+d collisions with beam kinetic energies from 1.04 to 4.88 GeV are presented. The differential cross section is presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the mass spectra and their evolution with beam energy provide information about the relative importance of the various dielectron production mechanisms in this energy regime. The p+d to p+p ratio of the dielectron yield is also presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the transverse momentum and rapidity spectra from the p+d and p+p systems are found to be similar to one another for each of the beam energies studied. The beam energy dependence of the integrated cross sections is also presented.Comment: 15 pages and 16 figure

Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at sqrt(s_nn) = 130 GeV

The minimum bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons (h-) in Au+Au interactions at sqrt(s_nn) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dNh-/deta|_{eta = 0} = 280 +- 1(stat)+- 20(syst), an increase per participant of 38% relative to ppbar collisions at the same energy. The mean transverse momentum is 0.508 +- 0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h- yield per participant is a strong function of pt. The pseudorapidity distribution is almost constant within |eta|<1.Comment: 6 pages, 3 figure

Water-loss (intracellular) dehydration assessed using urinary tests, how well do they work? Diagnostic accuracy in older people

Background: Water-loss dehydration (hypertonic, hyperosmotic or intra-cellular dehydration) is due to insufficient fluid intake and distinct from hypovolemia due to excess fluid losses. It is associated with poor health outcomes such as disability and mortality in older people. Urine specific gravity (USG), color and urine osmolality have been widely advocated for screening for dehydration in older adults. Objective: To assess the diagnostic accuracy of urinary measures to screen for water-loss dehydration in older people.Design: This was a diagnostic accuracy study of people aged ≥65years taking part in the Dehydration Recognition In our Elders (DRIE, living in long-term care) or Dietary Strategies for Healthy Ageing in Europe (NU-AGE, living in the community) studies. The reference standard was serum osmolality, index tests included USG, urine color, osmolality, cloudiness, additional dipstick measures, ability to provide a urine sample, and volume of a random urine sample. Minimum useful diagnostic accuracy was set at sensitivity and specificity ≥70% or receiver operating characteristics plot area under the curve ≥0.70. Results: DRIE participants (67% women, mean age 86 years, n=162) had more limited cognitive and functional abilities than NU-AGE participants (64% women, mean age 70 years, n=151). 19% of DRIE and 22% of NU-AGE participants were dehydrated (serum osmolality >300mOsm/kg). Neither USG nor any other potential urinary tests were usefully diagnostic for water-loss dehydration. Conclusions: Although USG, urine color and urinary osmolality have been widely advocated for screening for dehydration in older adults, we show in the largest study to date that their diagnostic accuracy is too low to be useful and these measures should not be used to indicate hydration status in older people (either alone or as part of a wider tranche of tests). There is a need to develop simple, inexpensive and non-invasive tools for the assessment of dehydration in older people

Pion Interferometry of sNN=130\sqrt{s_{NN}} = 130 GeV Au+Au Collisions at RHIC

Two-pion correlation functions in Au+Au collisions at $\sqrt{s_{NN}} = 130$ GeV have been measured by the STAR (Solenoidal Tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The HBT parameters display a weak energy dependence over a broad range in $\sqrt{s_{NN}}$.Comment: 6 pages, 3 figures; accepted to Phys Rev Lett; data tables available at STAR web site http://www.star.bnl.gov/ Click on "Publications" in menu ba

Identified Particle Elliptic Flow in Au+Au Collisions at sNN=130\sqrt{s_{_{NN}}}=130 GeV}

We report first results on elliptic flow of identified particles at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV using the STAR TPC at RHIC. The elliptic flow as a function of transverse momentum and centrality differs significantly for particles of different masses. This dependence can be accounted for in hydrodynamic models, indicating that the system created shows a behavior consistent with collective hydrodynamical flow. The fit to the data with a simple model gives information on the temperature and flow velocities at freeze-out.Comment: REVTeX style include