(Test, calibrate, and prepare a BGO photon detector system)

The traveler spent the year at CERN primarily to test, calibrate, and prepare a BGO photon detector system for use in the August 1990 run of WA80 with sulfur beams and for use in future planned runs with an expanded BGO detector. The BGO was used in test-beam runs in December 1989 and April--May 1990 and in the August data-taking run. The Midrapidity Calorimeters (MIRAC) were also prepared in a new geometry for the August run with a new transverse energy trigger. The traveler also continued to refine and carry out simulations of photon detector systems in present and future planned photon detection experiments. The traveler participated in several WA80 collaboration meetings, which were held at CERN throughout the period of stay. Invited talks were presented at the Workshop on High Resolution Electromagnetic Calorimetry in Stockholm, Sweden, November 9--11, 1989, and at the International Workshop on Software Engineering, Artificial Intelligence, and Expert Systems for High-Energy and Nuclear Physics at Lyon, France, March 19--24, 1990. The traveler participated in an experiment to measure particle--particle correlations at 30-MeV/nucleon incident energies at the SARA facility in Grenoble from November 11--24, 1989

Transverse Spin at PHENIX: Results and Prospects

The Relativistic Heavy Ion Collider (RHIC), as the world's first and only polarized proton collider, offers a unique environment in which to study the spin structure of the proton. In order to study the proton's transverse spin structure, the PHENIX experiment at RHIC took data with transversely polarized beams in 2001-02 and 2005, and it has plans for further running with transverse polarization in 2006 and beyond. Results from early running as well as prospective measurements for the future will be discussed.Comment: 6 pages, 2 figures, presented at Transversity 2005, Como, Ital

Azimuthal Correlations in the Target Fragmentation Region of High Energy Nuclear Collisions

Results on the target mass dependence of proton and pion pseudorapidity distributions and of their azimuthal correlations in the target rapidity range $-1.73 \le \eta \le 1.32$ are presented. The data have been taken with the Plastic-Ball detector set-up for 4.9 GeV p + Au collisions at the Berkeley BEVALAC and for 200 $A\cdot$GeV/$c$ p-, O-, and S-induced reactions on different nuclei at the CERN-SPS. The yield of protons at backward rapidities is found to be proportional to the target mass. Although protons show a typical ``back-to-back'' correlations, a ``side-by-side'' correlation is observed for positive pions, which increases both with target mass and with impact parameter of a collision. The data can consistently be described by assuming strong rescattering phenomena including pion absorption effects in the entire excited target nucleus.Comment: 7 pages, figures included, complete postscript available at ftp://qgp.uni-muenster.de/pub/paper/azi-correlations.ps submitted to Phys. Lett.

Dynamical approach to spectator fragmentation in Au+Au reactions at 35 MeV/A

The characteristics of fragment emission in peripheral $^{197}$Au+$^{197}$Au collisions 35 MeV/A are studied using the two clusterization approaches within framework of \emph{quantum molecular dynamics} model. Our model calculations using \emph{minimum spanning tree} (MST) algorithm and advanced clusterization method namely \emph{simulated annealing clusterization algorithm} (SACA) showed that fragment structure can be realized at an earlier time when spectators contribute significantly toward the fragment production even at such a low incident energy. Comparison of model predictions with experimental data reveals that SACA method can nicely reproduce the fragment charge yields and mean charge of the heaviest fragment. This reflects suitability of SACA method over conventional clusterization techniques to investigate spectator matter fragmentation in low energy domain.Comment: 6 pages, 5 figures, accepte

Event Reconstruction in the PHENIX Central Arm Spectrometers

The central arm spectrometers for the PHENIX experiment at the Relativistic Heavy Ion Collider have been designed for the optimization of particle identification in relativistic heavy ion collisions. The spectrometers present a challenging environment for event reconstruction due to a very high track multiplicity in a complicated, focusing, magnetic field. In order to meet this challenge, nine distinct detector types are integrated for charged particle tracking, momentum reconstruction, and particle identification. The techniques which have been developed for the task of event reconstruction are described.Comment: Accepted for publication in Nucl. Instrum. A. 34 pages, 23 figure

Central Pb+Pb Collisions at 158 A GeV/c Studied by Pion-Pion Interferometry

Two-particle correlations have been measured for identified negative pions from central 158 AGeV Pb+Pb collisions and fitted radii of about 7 fm in all dimensions have been obtained. A multi-dimensional study of the radii as a function of kT is presented, including a full correction for the resolution effects of the apparatus. The cross term Rout-long of the standard fit in the Longitudinally CoMoving System (LCMS) and the vl parameter of the generalised Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a boost invariant expansion. The shapes of the correlation functions in Qinv and Qspace have been analyzed in detail. They are not Gaussian but better represented by exponentials. As a consequence, fitting Gaussians to these correlation functions may produce different radii depending on the acceptance of the experimental setup used for the measurement.Comment: 13 pages including 10 figure

Event-by-Event Fluctuations in Particle Multiplicities and Transverse Energy Produced in 158.A GeV Pb+Pb collisions

Event-by-event fluctuations in the multiplicities of charged particles and photons, and the total transverse energy in 158$\cdot A$ GeV Pb+Pb collisions are studied for a wide range of centralities. For narrow centrality bins the multiplicity and transverse energy distributions are found to be near perfect Gaussians. The effect of detector acceptance on the multiplicity fluctuations has been studied and demonstrated to follow statistical considerations. The centrality dependence of the charged particle multiplicity fluctuations in the measured data has been found to agree reasonably well with those obtained from a participant model. However for photons the multiplicity fluctuations has been found to be lower compared to those obtained from a participant model. The multiplicity and transverse energy fluctuations have also been compared to those obtained from the VENUS event generator.Comment: To appear in Physical Review C; changes : more detailed discussion on errors and few figures modifie

Pion Freeze-Out Time in Pb+Pb Collisions at 158 A GeV/c Studied via pi-/pi+ and K-/K+ Ratios

The effect of the final state Coulomb interaction on particles produced in Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment through the study of the pi-/pi+ and K-/K+ ratios measured as a function of transverse mass. While the ratio for kaons shows no significant transverse mass dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with an enhancement that increases with centrality. A silicon pad detector located near the target is used to estimate the contribution of hyperon decays to the pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in which the Coulomb interaction has been incorporated allows to place constraints on the time of the pion freeze-out.Comment: 9 pages, 12 figure

Proximity effect at superconducting Sn-Bi2Se3 interface

We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions down to 250 mK and in different magnetic fields. A number of conductance anomalies were observed below the superconducting transition temperature of Sn, including a small gap different from that of Sn, and a zero-bias conductance peak growing up at lower temperatures. We discussed the possible origins of the smaller gap and the zero-bias conductance peak. These phenomena support that a proximity-effect-induced chiral superconducting phase is formed at the interface between the superconducting Sn and the strong spin-orbit coupling material Bi2Se3.Comment: 7 pages, 8 figure

Inclusive cross section and double helicity asymmetry for \pi^0 production in p+p collisions at sqrt(s)=200 GeV: Implications for the polarized gluon distribution in the proton

The PHENIX experiment presents results from the RHIC 2005 run with polarized proton collisions at sqrt(s)=200 GeV, for inclusive \pi^0 production at mid-rapidity. Unpolarized cross section results are given for transverse momenta p_T=0.5 to 20 GeV/c, extending the range of published data to both lower and higher p_T. The cross section is described well for p_T < 1 GeV/c by an exponential in p_T, and, for p_T > 2 GeV/c, by perturbative QCD. Double helicity asymmetries A_LL are presented based on a factor of five improvement in uncertainties as compared to previously published results, due to both an improved beam polarization of 50%, and to higher integrated luminosity. These measurements are sensitive to the gluon polarization in the proton, and exclude maximal values for the gluon polarization.Comment: 375 authors, 7 pages, 3 figures. Submitted to Phys. Rev. D, Rapid Communications. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm