HINDA: Development of a Detector Array for Compton Scattering using Polarized Beams and Targets

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The photonuclear physics group at James Madison University (JMU) is engaged in a program of Compton scattering at the High Intensity Gamma Source (HI S) facility at the Duke Free Electron Laser Laboratory (DFELL) laboratory at Duke University, operated by the Triangle Universities Nuclear Laboratory (TUNL). The proposed research uses photon-induced reactions to investigate the properties of the nucleon and nucleon resonances. The dominant component of this program is the use of beam and target polarization observables in photonuclear reactions. The program of Compton scattering at HI S will be carried out by a collaboration of 32 physicists from 14 institutions. To carry out this photon scattering program, a large acceptance, highresolution -ray spectrometer, HINDA, consisting of eight large NaI detectors surrounded by segmented NaI anti-coincidence shields is being constructed. Along with the large NaI detectors in-hand at TUNL, we are requesting funding to purchase eight NaI shields and electronics. The HI S facility opens a new window to the study of fundamental quantities related to the structure of the nucleon through Compton scattering from both polarized and unpolarized nucleons and nuclear targets. These studies allow the extraction of electromagnetic polarizabilities of the neutron with unprecedentedaccuracy, and will provide data for the first time on currently unknown quantities such as spin polarizabilities of the nucleon. These polarizabilities characterize the response of the nucleon to the electric and magnetic fields of the photon. Furthermore, Compton scattering from helium isotopes will allow for a precision determination of the polarizabilities of the 3He and 4He nuclei. These studies will also allow for precision tests of effective field theories, lattice quantum chromodynamics calculations and predictions of the standard model of nuclear physics. The NaI anti-coincidence shields will be shipped to JMU for assembly, initial testing and calibration by JMU undergraduates. After construction of the detector development lab and student training during the summer of 2006, the assembly and calibration of all eight shields will be completed during the academic 2006-2007 year. This is well within the scope of a project for undergraduates and should not be stronglyaffected by class schedules during the academic year since most of the time is spent collecting data.This schedule complements the expected completion of the HI S upgrade by the end of 2006 and the arrival of the UVa polarized target at TUNL in early 2007. With the target installed during the spring, HINDA will be installed in the summer of 2007. The detectors in the HINDA array will be supported by a detector stand designed to allow great flexibility in their disposition around the target. TUNL has recently hired a mechanical engineer who will design this support system. JMU students will contribute to the assembly of the system at HI S during the summer of 2007.Undergraduate involvement in this project at JMU will be of enourmous benefit to our students. Byconfiguring the electronics and data acquisition system, and then characterizing individual detector performance, these undergraduate students will gain valuable experimental skills. Once trained on-campus, the students will participate in installation of the HINDA array and associated experimental hardware at HI S. Following this, they will assist in data acquisition during the summer breaks. Advanced students will also assist with data analyzes in the later stages of the program.