Laura Ingalls Huntley Office of Science, SULI Program Franklin & Marshall College Stanford Linear Accelerator Center Menlo Park, California 16 August 2006

Consists of 19 layers of steel and particle detectors. Shapes magnetic field as well as provides identification for muons and neutral hadrons. Resistive Plate Chambers (RPCs) were initially installed, but their efficiency has decreased more rapidly than expected. Limited Streamer Tube (LST) installation began in the summer of 2004 and will conclude this fall.

Designed by Iarocci in Is a widely used and understood techonology. Contain a gas mixture of 3% argon, 8% isobutane, and 89% carbon dioxide by volume. Gas is bought from an outside source and mixed on-site. Isobutane has contained impurities in the past that caused LST efficiency to decrease from ~ 90% to ~ 60%. We have been working on a small LST system to test the gas for contaminants.

Consists of two 50.5 cm x 15.4 cm x 2.0 cm LSTs stacked one on top of the other. Cosmic muons are used instead of particles produced by an electron-positron collision. We are using a pre-mixed gas until test module is installed in gas shack. Impure gas was simulated by dropping the voltage in the LSTs below the optimum range (~ 5500 V).

High Voltage (HV) is inputted through four pins into the eight wires in each LST through an HV connector box... Signals from the LSTs travel through capacitor to front-end electronics in the NIM bin.

Counter 1 shows the total number of detections made by the inner two channels of the top LST. Counter 2 shows the number of coincidental detections made by both LSTs. The coincidence rate and the percent coincidence are measured.

Test for basic performance show that our LSTs and electronics are functioning reliably. They show about 1.2 muon detections per square cm per minute, which agrees with literature values for a horizontal detector at sea level. They also show singles rate curves that have an edge at 5300 V and plateau at 5500 V. The coincidence rate has the advantage of not relying on the measurements made by a single LST (false detections due to x-rays, etc.). However, it requires the operator to manually time 5 minutes worth of counts. We have not measured it accurately as of yet. The percent coincidence has the advantage of being very simple to perform, although it also requires at least 5 minutes of counts before it can be considered sufficiently reliable. We have measured the percent coincidence to be approximately 47%. Both tests will most likely be used once the system is installed in the gas shack. Installation will begin once BaBar has gone offline.