Driftgeschwindigkeits- und Signalverstaerkungsmessungen in Gasen fuer das aeussere Spurkammersystem des HERA-B Detektors

Abstract

This work is concerned with measurements of drift velocity, gas gain and energy resolution of gas mixtures made up of the components argon, CF_4 and a quencher, methane, propane or CO_2. This is done within the context of the outer tracking system of the HERA-B detector. Special interest lies in finding fast enough mixtures that fulfill the requirements of HERA-B. Furthermore, the impact of ethanol and methylal is studied, as these additives are expected to have a favourable effect on the critical aging properties of the tracking chambers. The mixtures with highest drift velocities of more than 12 cm/#mu#s at moderate field strengths are those with methane or propane as quencher and at least 15% CF_4. CO_2 is clearly slower. Ethanol reduces the drift velocity significantly, methylal less. The size of the reduction depends on the quencher that is used. The gas gain decreases at a given wire voltage with increasing fraction of CF_4 and increases upon addition of ethanol or methylal. Propane as a quencher leads to higher gain than methane or CO_2. The energy resolution is systematically deteriorating with increasing fraction of CF_4. This can be explained with the large probability for electron attachment in CF_4 that reaches 80% already at lower CF_4 fractions. The measured variation of the resolution with the gas gain is qualitatively different for different mixtures. With respect to their drift velocity, all tested Ar:CF_4:CH_4 and Ar:CF_4:C_3H_8 mixtures, even with a few percent methylal, and Ar:CF_4:CO_2 mixtures without additive and only a small fraction of CO_2 are suited for the tracking system. (orig.)33 refs.SIGLEAvailable from TIB Hannover: RR 8919(1998-023) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman