S. Mioduszewski

High pt measurements from PHENIX.

Abstract We present recent high transverse momentum measurements by the PHENIX experiment for Au+Au and p+p collisions at S N N = 200 GeV at the Relativistic Heavy Ion Collider (RHIC). We show particle spectra for neutral pions and charged hadrons, define and show the nuclear modification factor, and discuss particle composition. By means of the nuclear modification factor, we observe a suppression factor of 5–6 for neutral pions and 3–4 for charged hadrons in central collisions at high pT. We find that the ratio of π0 to (h+ + h−)/2 remains nearly constant at ∼ 0.5 for pT = 2 − 9GeV/c. Finally we present strong evidence for the observation of jets in Au+Au collisions.

Azimuthal Angle Correlations for Rapidity Separated Hadron Pairs in d+Au Collisions at {radical}(s{sub NN})=200 GeV

Deuteron-gold (d+Au) collisions at the Relativistic Heavy Ion Collider provide ideal platforms for testing QCD theories in dense nuclear matter at high energy. In particular, models suggesting strong saturation effects for partons carrying small nucleon momentum fraction (x) predict modifications to jet production at forward rapidity (deuteron-going direction) in d+Au collisions. We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at midrapidity in d+Au and p+p collisions at root s(NN)=200 GeV. Jet structures observed in the correlations are quantified in terms of the conditional yield and angular width of away-side partners. The kinematic region studied here samples partons in the gold nucleus with x similar to 0.1 to similar to 0.01. Within this range, we find no x dependence of the jet structure in d+Au collisions.

Inclusive soft pion production from 12.3-Gev/c and 17.5-GeV/c protons on Be, Cu and Au

Differential cross-sections are presented for the inclusive production of charged pions in the momentum range 0.1 to 1.2 GeV/c in interactions of 12.3 and 17.5 GeV/c protons with Be, Cu, and Au targets. The measurements were made by Experiment 910 at the Alternating Gradient Synchrotron in Brookhaven National Laboratory. The cross-sections are presented as a function of pion total momentum and production polar angle

Measuring centrality with slow protons in proton-nucleus collisions at 18 GeV/c

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Calibration and performance of the STAR Muon Telescope Detector using cosmic rays

with respect to the beam.

PHENIX on-line and off-line computing

Experiment E910 has measured slow protons and deuterons from collisions of 18 GeV/c protons with Be, Cu, and Au targets at the BNL AGS. These correspond to the {open_quotes}grey tracks{close_quotes} first observed in emulsion experiments. We report on their momentum and angular distributions and investigate their use in measuring the centrality of a collision, as defined by the mean number of projectile-nucleon interactions. The relation between the measured N{sub grey} and the mean number of interactions {bar {nu}}(N{sub grey}) is studied using several simple models, one newly proposed, as well as the RQMD event generator. RQMD is shown to reproduce the N{sub grey} distribution, and exhibits a dependence of N{sub grey} on centrality that is similar to the behavior of the simple models. We find a strong linear dependence of {ovr N{sub grey}} on {nu}, with a constant of proportionality that varies with target. For the Au target, we report a relative systematic error for extracting {bar {nu}}(N{sub grey}) that lies between 10 and 20h{percent} over all N{sub grey}. {copyright} {ital 1999} {ital The American Physical Society}

Antiproton Production in p+A Collisions at 12.3 and 17.5 GeV/c

We report the timing and spatial resolution from the Muon Telescope Detector (MTD) installed in the STAR experiment at RHIC. Cosmic ray muons traversing the STAR detector have an average transverse momentum of 6 GeV/c. Due to their very small multiple scattering, these cosmic muons provide an ideal tool to calibrate the detectors and measure their timing and spatial resolution. The values obtained were ∼100 ps and ∼1-2 cm, respectively. These values are comparable to those obtained from cosmic-ray bench tests and test beams.

Strangeness enhancement in p–A collisions: Consequences for the interpretation of strangeness production in A–A collisions

Data handling in PHENIX is carried out by the On-Line Computing System (ONCS) and Off-Line Computing System (Off-Line). ONCS provides the overall control and monitoring of the front-end electronics, trigger and data acquisition system and detector ancillary systems. It configures and initializes the on-line system, monitors and controls the data flow, coordinates calibration processes, interlocks the data acquisition process with the slow control subsystems and performs a number of other functions. ONCS uses CORBA software to monitor and control the hardware. Off-Line provides all aspects of data handling not directly connected to the collection of data and monitoring, such as event simulation and reconstruction, data analysis and information management. The impact of the unprecedented data volumes on the design is presented, along with a detailed discussion of the tasks and methods of simulating, obtaining and monitoring the data.

Single Electrons from Heavy-Flavor Decays in p+p Collisions at {radical}(s)=200 GeV

Inclusive and semi-inclusive measurements are presented for antiproton (

Measurement of Identified {pi}{sup 0} and Inclusive Photon Second-Harmonic Parameter v{sub 2} and Implications for Direct Photon Production in {radical}(s{sub NN})=200 GeV Au+Au

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