ACU Student Abstracts

Below are several sample abstracts of recent ACU participants in CEU.

Single and Dimuon Track Reconstruction in the PHENIX South Muon Arm
Travis Hunter (Abilene Christian University), PHENIX Collaboration

The south muon arm of the PHENIX experiment at RHIC was completed and operational for the Au Au and p p runs fo 2001.  The south muon arm will be augmented by another muon detector system, the north arm, which will be completed in the fall of this year. In both muon arm assemblies there are two different detectors, one for determining particle momentum and the other for particle identification.  Analysis of these first data from the south muon arm during the 2001 runs has utilized software to iteratively reconstruct the muon tracks and momenta through these two detectors during these first Au Au and p p runs.  It is also possible to generate simulated events for analysis using a program called PISA (PHENIX Integrated Simulation Application).  By defining within PISA what particles one wants to create and where they should go, one can run the data analysis software on the generated events to test its functionality.  Using PISA to track single muons through the detector, one can use these data to test the reconstruction performance of the muon tracking software.  The muon arms are also designed to measure Φ, J/Ψ, Ψ', and Υ production in Au Au and p p collisions.  These can also be generated using PISA and analysed for software reconstruction performance of dimuon events in the muon arms.  J/Ψ is the focus of analysis of dimuon events for the first year of running.

Nuclear Cross Section of the π- p → π0 n Interaction
Chad Bircher (Abilene Christian University), Crystal Ball Collaboration

The Crystal Ball Collaboration is measuring differential scattering cross sections for the π- p → π0 n interaction using the Crystal Ball multi-photon spectrometer. The experiment used a beam of negatively charged pions incident on a liquid hydrogen target at the Alternating Gradient Synchrocyclotron at Brookhaven National Laboratory. The energies and directions of gamma rays that arise from π0 → γγ decay are detected by the Crystal Ball and analyzed. The reaction can be identified from the reconstruction of the invariant mass and missing mass and the energy and scattering angle of the π0 can be deduced. An important part of the analysis is the determination of the properties of the beam, such as the electron and muon contaminations and the central momentum. Based on the known masses of pions, muons, and electrons, and the time taken for these particles to travel between detectors it was possible to determine the fraction of different particles in the beam and to provide a consistency check on the beam momentum.

Low energy pion-nucleon charge exchange measurements
Melissa Travis (Abilene Christian University)

One of the goals of E913 is to explore pion-nucleon charge exchange scattering by making measurements of absolute differential crossections at 140-322 MeV/c (π-p→π0n). These data that will be presented were taken using the Crystal Ball multi-photon spectrometer at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory. The Crystal Ball is almost a 4π detector; its large acceptance, high energy resolution, and spacial segmentation make it uniquely capable to detect the neutral mesons produced in this reaction, which decay into multiple gamma rays. Several important open questions concerning strong-interaction physics at intermediate energies require a much more complete baryon spectroscopy. The measurements from E913 will ultimately impact investigations of isospin invariance in the πN system, the isospin-odd s-wave scattering length, the πN σ term, the πNN coupling constant, the mass splitting of the P_33(1232) resonance, and the up-down quark mass difference.

Momentum calibration of pion beams for the Crystal Ball
Michael Joy (Abilene Christian University), Crystal Ball Collaboration

An independent determination of the pion beam momentum for E913 (π- p → π0 n) at Brookhaven National Laboratory will be presented. The technique utilizes the good energy and spatial resolution of the Crystal Ball detector. Analysis and calibration of the data goes as follows:

1.  The invariant mass of the π0 is calculated from the individual γ energies in the detector and the opening angle of the γ's from π0 decay from data and through Monte Carlo simulation.

2.  A multiplicative factor is adjusted to align the invariant mass with the known value of the π0 (134.97 MeV/c^2).

3.  Missing mass is obtained using our analyzer for both the real and Monte Carlo simulation data. The difference between the missing mass from both data sets is then plotted.

A linear fitted line on this plot allows us to find our “real momenta”. We then have a calibration of the assumed nominal momentum to reflect the real momentum at target center. Comparisons of this “real momenta” with time of flight analysis and with beam line simulations that account for momentum loss in the scintillators, air and liquid hydrogen target will be presented.

Installation of the North Muon Tracking Detector for PHENIX
James Drachenberg (Abilene Christian University), PHENIX Collaboration

In preparation for run three of the PHENIX experiment at RHIC, installation of the north muon arm completes the muon tracking system, enabling PHENIX with unique muon tracking capabilities. The north muon arm offers a more precise mass resolution of ~190 MeV/c2, compared to the south muon arm mass resolution of ~240 MeV/c2. This will help to resolve the mass of muon pairs coming from different resonances, for example, the Υ. With the installation of the north muon arm, PHENIX can now track muons in both forward regions. The north arm is larger than the south arm, so the installation allows for non-asymmetric runs such as proton-on-deuterium or proton-on-gold collisions. The north arm is also critical for the detection of open heavy flavor (D → μX, B → J/Ψ→ μ μ-).