Darmstadt 2016 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 70: Instrumentation XX

HK 70.5: Talk

Friday, March 18, 2016, 15:15–15:30, S1/01 A3

Investigation of the energy spectra of a hybrid GEM-MicroMegas detector — •Matthias Liebtrau, Viktor Ratza, Markus Ball, and Bernhard Ketzer for the ALICE collaboration — Helmholtz-Institut für Strahlen- und Kernphysik, Bonn University

In the context of the upgrade of the LHC during the second long shutdown the interaction rate of the ALICE experiment will be increased up to 50 kHz for Pb-Pb collisions. As a consequence, a continuous operation of the Time Projection Chamber will be required. To handle the expected increase of space charge distortions the currently installed multi wire proportional counter (MWPC) charge amplification system has to be replaced. Micropattern gaseous detectors (MPGDs) offer a way to suppress the backdrift of ions to the drift volume to a tolerable level. At the same time, however, a good energy resolution of the detector has to be maintained. As an alternative to the 4-GEM baseline solution, a hybrid detector consisting of 2 GEMs and a Micromegas stage has been investigated.

Both ion backflow and energy resolution were studied systematically with a small (10 × 10) cm² detector. An ion backflow as low as 0.6% was achieved. A background under the photopeak, if not taken into account in the fit model, was found to systematically bias the energy resolution towards larger values. Methods to suppress the background as well as to fully include it in the fit model were developed. The results show that the hybrid detector fulfills the requirements concerning ion backflow and energy resolution.