Simulations for an experiment to probe the in-medium properties of photoproduced vector mesons
- Univ. of Paris-Sud, Orsay (France)
The g7 experiment has been devised to measure the modifications of the vector meson properties, such as mass or width, inside nuclear medium, based on the ideas presented in the numerous papers published during the fifteen years that preceded its run. It consisted in sending a bremstrahlung photon beam on a target that contained elements with different densities, a liquid deuterium cell, and seven solid foils: carbon, iron, carbon, lead, carbon, titanium, carbon. The goal of the experiment is to examine the inclusive e+e- photoproduction in the incoherent region. The reaction of interest to g7 is γA → VA' → e+e-A' where V could be a ρ an ω or a Ψ meson. The goal of the present thesis was to present the simulation work done prior to the g7 run in the fall of 2002 at Jlab, essential for the choice of the ideal experimental setup and conditions, as well as the test run of June 2002. The simulations needed a particular attention, given the many experimental challenges that awaited the g7 team. First, one had to prove that the resolution of the CLAS detector was sufficient to properly locate the vertices of the events given the multi-segmented target, and the simulations proved that fact. They also provided a rough idea of the systematic errors that one had to expect. Using nuclei bigger than carbon was a first time for CLAS. Given the very small branching ratio for ρ → e+e-, a very intense beam had to be sent on the target containing high-Z material. Thus, a huge background, formed of low energy e+e- pairs, was expected around the target and the region I of the drift chambers and which one had to reduce in an efficient way. The simulations showed that using the mini torus with its current set to 75% of its maximum value would give a reduction of about a factor of 3 in the number of hits in the region I of the drift chambers, compared to the case with no mini torus in, which the test run confirmed. In addition, the branching ratio for ρ → π+π- being five orders of magnitude bigger than the one for ρ → e+e-, a very rigorous way of discriminating the electrons from the pions had to be devised, where the g7 team had again to take up the challenge for the first time in the collaboration. A method of electron/pion discrimination with CLAS has been briefly presented and still needs to be tested on the g7 data.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 824884
- Report Number(s):
- JLAB-PHY-03-37; DOE/ER/40150-2740; TRN: US0402192
- Resource Relation:
- Other Information: TH: Thesis (M.S.); Submitted to the Univ. of South Carolina, Columbia, SC (US); PBD: 1 Apr 2003
- Country of Publication:
- United States
- Language:
- English
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