G. S. Mutchler

The time-of-flight system for CLAS

The time-of-flight system for the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility is described. The system, covering an area of 206-square-meters, is composed of scintillation counters 5.08 cm thick, 15 and 22 cm wide, and lengths which vary from 32 cm at the most forward angle to 450 cm at larger angles. All of the components of the system have been designed to optimize the time resolution. Event timing, achieved by leading-edge discrimination with time-walk correction, has been measured with cosmic rays, a laser pulser, and known particle interactions. The intrinsic time resolution varies from about 80 ps for the short counters to 160 ps for the longer counters. Reconstruction of interacting particles during the first period of operation yields an average time resolution for electrons of 163 ps.

The STAR trigger

Abstract We describe the trigger system that we designed and implemented for the STAR detector at RHIC. This is a 10 MHz pipelined system based on fast detector output that controls the event selection for the much slower tracking detectors. Results from the first run are presented and new detectors for the 2001 run are discussed.

Λ production by 11.6 A GeV/c Au beam on Au target

Abstract We present the first measurement at AGS energies of the rapidity and transverse mass distributions for Λ production with Au beam on Au target. The measurements cover the rapidity region of 2.0–3.2 and transverse momenta of 0.0–1.4 GeV/c. The results are compared with the predictions of two models.

Measurement of the transverse spin dependence of the pp total cross section in the 1–3 GeV/c region☆

Abstract The pp total cross section difference between pure transverse spin states was measured in the laboratory momentum range 1–3 GeV/ c . Significant differences were found and these differences show striking energy dependence. This structure is in disagreement with the predictions of simple exchange models.

The (d, n) reaction on 1p shell nuclei at Ed = 11.8 MeV

Abstract The absolute differential cross sections have been measured for (d, n) reactions on 10, 11 B and 12, 13 C at an incident deuteron energy of 11.8 MeV. The measured angular distributions were compared with distorted-wave Born approximation (DWBA) calculations using average 1p shell parameters. These calculations successfully reproduce the general shape of the angular distributions, but fail to predict the magnitude of the cross sections at back angles. Absolute spectroscopic factors have been extracted and compared with theoretical predictions and previous experimental measurements. A definite J -dependence in the structure of the angular distributions is observed but is not reproduced by the DWBA calculations. The deduced spectroscopic factors are also compared with the results from (τ, d) reactions to look for a possible T -dependence.

Lambda production by 11.6-A/GeV/c Au beam on Au target

Abstract We present the first measurement at AGS energies of the rapidity and transverse mass distributions for Λ production with Au beam on Au target. The measurements cover the rapidity region of 2.0–3.2 and transverse momenta of 0.0–1.4 GeV/c. The results are compared with the predictions of two models.

Spin-parity analysis of the ƒ1(1285)π− system in the reaction π−p → ƒ1(1285)π−p at 18 GeV / c

Abstract We have carried out a study of the reaction π − p → ƒ 1 (1285) π − p at 18 GeV / c , with ƒ 1 (1285) → K + K 0 π − This reaction is almost entirely mediated by the natural-parity exchange, presumably ƒ 2 (1270) or ϱ exchange. We find evidence for two possible resonances - a JPC = 1++ state at 1.7 GeV / c2 and a broad JPC = 1−+ structure at 1.6–2.2 GeV/c2.

Measurement of the spin parameters A and Ann in pp elastic scattering in the 1–3 GeV/c region☆

Abstract We have measured the asymmetry parameter A and the spin correlation parameter A nn in pp elastic scattering, using the Argonne ZGS polarized proton beam and a polarized proton target. Angular distributions of A and A nn for | t | ≳ 0.2 (GeV/ c ) 2 were obtained at eight momenta between 1.10 and 2 if 2.75 GeV/ c . We find significant structure in both the energy and t -dependence of A nn at these energies. At p lab ≈ 1.34 GeV/ c A nn reaches a very large value of about 0.8–0.9 near θ cm = 90°.

Rapidity distributions of Ks0's and Λ's produced by 14.6×A GeV/cSi beams on Si and Pb targets

Abstract We present the first measurement at AGS energies of rapidity distributions of K s 0 and Λ production with silicon beams on silicon and lead targets. The measurements cover the rapidity region of 2.0 y K s 0 s and 1.4 y Λ s.

In-beam tests of proximity mesh dynode tubes for the STAR TOF subsystem

Abstract The performance of Bicron BC404, BC408 and BC420 scintillators coupled to a Hamamatsu R3432 proximity mesh dynode photomultiplier tube was studied using pion beams from the TRIUMF cyclotron and the Brookhaven National Laboratory AGS accelerator. A system resolution of better than 100 ps seems feasible. This will satisfy the requirement for charged particle identification in the STAR detector at RHIC.