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Proton-proton collisions at the Large Hadron Collider's ALICE Experiment: diffraction and high multiplicity

Matthews, Zoe Louise (2011)
Ph.D. thesis, University of Birmingham.

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Diffraction in pp collisions contributes approximately 30 % of the inelastic cross section. Its influence on the pseudorapidity density is not well constrained at high energy. A method to estimate the contributing fractions of diffractive events to the inelastic cross section has been developed, and the fractions are measured in the ALICE detector at 900 GeV (7 TeV) to be f\(_D\)=0.278\(\pm\)0.055 (f\(_D\)=0.28\(\pm\)0.054) respectively. These results are compatible with recent ATLAS and ALICE measurements. Bjorken’s energy density relation suggests that, in high multiplicity pp collisions at the LHC, an environment comparable to A-A collisions at RHIC could be produced. Such events are of great interest to the ALICE Collaboration. Constraints on the running conditions have been established for obtaining a high multiplicity pp data sample using the ALICE detector’s multiplicity trigger. A model independent method to separate a multiplicity distribution from ‘pile-up’ contributions has been developed, and used in connection with other findings to establish a suitable threshold for a multiplicity trigger. It has been demonstrated data obtained under these conditions for 3 months can be used to conduct early strangeness analyses with multiplicities of over 5 times the mean. These findings have resulted in over 16 million high multiplicity events being obtained to date.

Type of Work:Ph.D. thesis.
Supervisor(s):Evans, David
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:Particle Physics Group, School of Physics and Astronomy
Subjects:QC Physics
T Technology (General)
Institution:University of Birmingham
ID Code:3055
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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