eprintid: 23888
rev_number: 15
eprint_status: archive
userid: 3511
dir: disk0/00/02/38/88
datestamp: 2018-01-04 08:41:52
lastmod: 2018-01-22 10:29:58
status_changed: 2018-01-04 08:41:52
type: doctoralThesis
metadata_visibility: show
creators_name: Bock, Friederike
title: Measurement of Direct Photons and Neutral Mesons in Small Collisions Systems with the ALICE Experiment at the LHC
subjects: ddc-530
divisions: i-130200
adv_faculty: af-13
cterms_swd: neutral mesons
cterms_swd: direct photons
cterms_swd: LHC
cterms_swd: pp collisions
cterms_swd: pPb collisions
cterms_swd: ALICE
abstract: The Quark-Gluon Plasma (QGP), a strongly interacting state of matter in which quarks and gluons are
deconfined, is hypothesized to have existed merely a few micro-seconds after the Big Bang. This state can
be studied experimentally in heavy ion collisions at the current high-energy particle accelerators, like the
Large Hadron Collider (LHC). However, recently the size of the collision system, which is required to create
a QGP has been been put into question and many measurements suggests that this might even be possible in
high multiplicity pp or p–Pb collisions. The research
study of direct carried out in this thesis focuses on the
photons and neutral mesons in pp collisions at √s = 2.76 TeV and p–Pb collisions at √sNN = 5.02 TeV
with the ALICE detector at the LHC. The neutral pion and η meson have been reconstructed in their two
photon decay channels. For that up to four different reconstruction methods have been pursued within this
thesis, out of which two are entirely new within ALICE, exploiting the full photon detection capabilities
of ALICE. Like this the neutral pion spectra could be measured up to transverse momenta of 40 GeV/c
in pp collision and a new level of precision could be reached for identified particle measurements in p–Pb
collisions at √sNN = 5.02 TeV. For pp collisions new high precision inputs for the determination of the
fragmentation functions for neutral pions and η mesons are provided and the current models are compared
to the obtained results. For p–Pb collisions a small suppression can be observed beyond 4 GeV/c with respect
to an interpolated pp reference at the same center-of-mass energy. It is investigated further through the
comparison with various models and results from other identified particles, in order to test whether another
ansatz, taking into account only cold nuclear matter effects, would yield a similar suppression. For the direct
photons three partially independent reconstruction techniques are presented, two of which are entirely new
in ALICE, as well as, their combined results for in minimum bias pp and p–Pb collisions. The combination of
the results yields a significant direct photon excess in p–Pb collisions beyond 6 GeV/c, which is in agreement
with the predicted excess from prompt photons in this collision system. Below these momenta and for pp
collision at √s = 2.76 TeV upper limits on the possible direct photon production can be provided. In this
region a possible thermal photon signal of 2 − 3% cannot be excluded within the current uncertainties.
date: 2017
id_scheme: DOI
id_number: 10.11588/heidok.00023888
ppn_swb: 1658692136
own_urn: urn:nbn:de:bsz:16-heidok-238884
date_accepted: 2017-11-29
advisor: HASH(0x556028c9cd10)
language: eng
bibsort: BOCKFRIEDEMEASUREMEN2017
full_text_status: public
citation:   Bock, Friederike  (2017) Measurement of Direct Photons and Neutral Mesons in Small Collisions Systems with the ALICE Experiment at the LHC.  [Dissertation]     
document_url: https://archiv.ub.uni-heidelberg.de/volltextserver/23888/1/PHDThesis_SubmissionVersion_20171016.pdf