R-hadron Searches and Charged Pion Spectra at High Transverse Momentum in Proton-Proton Collisions at the LHC using the ALICE Detector

Abstract: With the start-up of the Large Hadron Collider (LHC), a new energy regime has opened up. The Standard Model (SM) can be ``rediscovered'' and new theories can be tested. ALICE, the dedicated heavy-ion experiment at LHC, will also record proton-proton (pp) collisions. Even though the main goal of the ALICE proton program is to provide the baseline measurements for interpreting the heavy-ion data, the new heavy stable charged particles ($m>100$~GeV/c$^2$) predicted by some theoretical models, such as R-hadrons in Supersymmetry, are good candidates of ALICE searches for signals beyond the SM. Gluino R-hadron is chosen as an example of a candidate in this thesis, and cross sections and kinematic properties are obtained from PYTHIA simulations for various gluino masses (100-500 GeV/c$^2$). Detailed detector response simulations of the most important signatures for R-hadron identification in the ALICE central barrel are performed for 100 GeV/c$^2$ R-hadron mass. No evidence of particles that pass the R-hadron selection criteria in the Inner Tracking System, Time Projection Chamber (TPC), and the Time-of-Flight detectors can be observed in around 27.5 million pp events at $sqrt{s}=7$ TeV (the maximum energy available for the first two years of the LHC operation). First steps towards identified charged particle spectra at intermediate and high transverse momentum ($p_T$) using the TPC specific ionization energy loss are also taken here. The first charged pion spectra at high $p_T$ in inelastic pp collisions at $sqrt{s}=900$ GeV and $sqrt{s}=7$ TeV by the ALICE experiment at the LHC are presented in this thesis.

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