Master thesis defense by Martin Spangenberg – University of Copenhagen

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Master thesis defense by Martin Spangenberg

Calorimeter calibration and search for R-hadrons at √s = 7 TeV with the ATLAS experiment

Abstract:
Supersymmetric models predict a wide range of new states, both elementary and composite. In the case of Split Supersymmetry a class of stable massive particles called R-hadrons can arise consisting of a supersymmetric gluino or squark strongly bound to light Standard Model quarks. The discovery (or exclusion) of such states would be of fundamental significance.

This thesis focuses on a search for gluino-based R-hadrons exploiting the capabilities of the Inner Detector and calorimeters in ATLAS. Particle discrimination is performed using particle speeds (beta) obtained from calorimeter time measurements, as well as dE/dx-based beta-gamma measurements and the mass estimates derived from these. Particular effort is put into the calibration of calorimeter timing and correction of the resulting beta measurements and their errors.

Utilising the 4.7 fb^-1 ATLAS data from 2011 the search yields a 95% CLs lower gluino mass limit of 981 GeV.

A preliminary study is done on the potential of discrimination of R-hadrons altering their charge during passage through the detector. Results are illuminating, but need further development to be a viable option in a future search.