CERN Accelerating science

Thesis
Report number	CERN-THESIS-2014-461
Title	Cross section of bottom electrons in proton-proton collisions in the ALICE experiment
Author(s)	Aronsson, Tomas Robert Prem-Raj (Yale U.)
Publication	999.
Thesis note	PhD : Yale U. : 2014
Thesis supervisor(s)	Harris, John ; Caines, Helen
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ALICE
Abstract	High-energy heavy-ion collisions at the LHC allow for the study of the properties of the quark-gluon plasma (QGP). Heavy quarks, charm and bottom, produced in the initial hard-scattering processes of the collision are excellent probes of the QGP. When heavy quarks traverse the QGP they are expected to lose energy and such energy loss is predicted to be smaller than for gluons and light quarks. On the other hand, recent experimental data indicate larger energy loss than expected. Heavy- flavor production can be studied using electrons from semi-leptonic decays of hadrons containing charm and bottom quarks. The separation of electrons from these two sources (charm and bottom) is of crucial importance to address the expected mass dependence of energy loss. The ALICE EMCal detector possesses outstanding particle identification for electrons at high pT , and this detector is used to identify electrons with high purity. A two-track algorithm to select secondary vertices involving these electrons and surrounding charged tracks was developed and implemented, so called b-tagging; exploiting the tracking precision provided by the Inner Tracking System the electron and surrounding tracks are used to select displaced decay vertices that are likely to originate from B-hadron decay. Bottom electron production in the transverse momentum range 7-13 GeV/c in 7 TeV pp collisions is measured. The invariant cross section for bottom-decay electrons is calculated and compared to fixed ordered next- to-leading-log (FONLL) pQCD predictions. This will serve as a reference for studies of bottom suppression in PbPb collisions.

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