F. K. Wohn

Electromagnetic dissociation of Au targets by relativistic Pb projectiles

Abstract Electromagnetic Dissociation (ED) occurs in collisions of relativistic heavy ions involving impact parameters larger than the nuclear interaction radius. In such collisions strong electromagnetic fields acting at the nucleus can produce, for high charges and ultrarelativistic energies, cross sections much larger than the total nuclear interaction cross section. In ED collisions absorption of a virtual photon generally leads to excitation of a nuclear giant resonance. The NA53 experiment studied ED by bombarding Au targets with 158 GeV/nucleon Pb projectiles from the SPS accelerator. Preliminary values of σ ED for the one- and two-neutron removal processes were determined to be 26.4 ± 4.0 and 4.6 ± 0.7 barns, respectively. Theoretical predictions for σ ED were calculated including the effects of both the E1 and E2 giant resonances. The calculations are extended to energies planned for heavy ion collisions at the RHIC and LHC colliders.

The PHENIX Level-1 Trigger system

The PHENIX detector at the Relativistic Heavy Ion Collider (RHIC) will study the dynamics of ultra-relativistic heavy ion collisions and search for exotic states of matter, most notably the quark gluon plasma (QGP). Substantial event selectivity is needed at RHIC to enhance interesting events relative to more common ones and to satisfy the requirements of the data acquisition system. The first on-line screening is achieved by the Level-1 Trigger. The Level-1 Trigger is a beamclock parallel-pipeline system that uses six Local Level-1 (LL1) algorithms pertaining to the six fastest PHENIX subdetectors, followed by a Global Level-1 (GL1) system that processes encoded LL1 reduced-bit data to issue up to 128 triggers. The GLI system is also responsible for organizing the partitioned running of the PHENIX detector. The LL1 algorithms operate on raw data to produce a first estimate of the number of electrons, photons, muons and hadrons as well as the transverse energy, event multiplicity, interaction time and vertex. The latency of the entire system is less than 40 beam crossings. The Level-1 Trigger is implemented using custom-designed 9U VME-P format boards.

Nuclear modification of electron spectra and implications for heavy quark energy loss in Au + Au collisions at root s(NN)=200 GeV

The PHENIX experiment has measured midrapidity ([FORMULA: SEE TEXT]) transverse momentum spectra ([FORMULA: SEE TEXT]) of electrons as a function of centrality in Au+Au collisions at [FORMULA: SEE TEXT]. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi0 and eta mesons, were removed. The resulting nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to nonphotonic electrons in p+p collisions. A significant suppression of electrons at high pT is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.

Measurement of Lambda and Anti-Lambda particles in Au plus Au collisions at root s(NN)=130 GeV

We present results on the measurement of Lambda and Lambda(macro) production in Au+Au collisions at square root of (S (NN) = 130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The Lambda;/Lambda ratios are constant as a function of p(T) and the number of participants. The measured net Lambda density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.We present results on the measurement of Λ and Λ - production in Au+Au collisions at √s NN =130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The Λ - /Λ ratios are constant as a function of p T and the number of participants. The measured net Λ density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.

Centrality dependence of pi(+/-), K-+/-, p, and (p)over-bar production from root(NN)-N-S = 130 GeV Au+Au collisions at RHIC

Identified pi(+/-), K(+/-), p, and (-)p transverse momentum spectra at midrapidity in sqrt[s(NN)] = 130 GeV Au+Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. Within errors, all midrapidity particle yields per participant are found to be increasing with the number of participating nucleons. There is an indication that K(+/-), p, and (-)p yields per participant increase faster than the pi(+/-) yields. In central collisions at high transverse momenta (p(T) > or =2 GeV/c), (-)p and p yields are comparable to the pi(+/-) yields.

Implementation of PHENIX trigger algorithms on massively parallel computers

The event selection requirements of contemporary high energy and nuclear physics experiments are met by the introduction of on‐line trigger algorithms which identify potentially interesting events and reduce the data acquisition rate to levels that are manageable by the electronics. Such algorithms being parallel in nature can be simulated off‐line using massively parallel computers. The PHENIX experiment intends to investigate the possible existence of a new phase of matter called the quark gluon plasma which has been theorized to have existed in very early stages of the evolution of the universe by studying collisions of heavy nuclei at ultra‐relativistic energies. Such interactions can also reveal important information regarding the structure of the nucleus and mandate a thorough investigation of the simpler proton‐nucleus collisions at the same energies. The complexity of PHENIX events and the need to analyze and also simulate them at rates similar to the data collection ones imposes enormous computation demands. This work is a first effort to implement PHENIX trigger algorithms on parallel computers and to study the feasibility of using such machines to run the complex programs necessary for the simulation of the PHENIX detector response. Fine and coarse grain approaches have been studied and evaluated. Depending on the application the performance of a massively parallel computer can be much better or much worse than that of a serial workstation. A comparison between single instruction and multiple instruction computers is also made and possible applications of the single instruction machines to high energy and nuclear physics experiments are outlined.