Laura Ingalls HuntleyOffice of Science, SULI Program

Franklin & Marshall CollegeStanford Linear Accelerator Center

Menlo Park, California16 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 1978. 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.