Strangeness enhancement in singly-strange Hadron Production in p-Pb Collisions with the ALICE experiment

Jevons, Oliver ORCID: 0000-0003-3448-3293 (2022). Strangeness enhancement in singly-strange Hadron Production in p-Pb Collisions with the ALICE experiment. University of Birmingham. Ph.D.

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At conditions of extremely high temperature and energy density, a strongly-interacting state of matter can be formed, known as the Quark Gluon Plasma (QGP). Such QGPs are formed experimentally in heavy-ion collisions, such as those between lead ions (Pb-Pb) carried out at the LHC. Due to the extremely short lifetimes of such states, any produced QGP is not directly observable. Instead, studies are performed on a number of signatures, which indicate the presence of a QGP and its properties. Historically, smaller systems, such as those formed in proton-proton (pp) and proton-lead (p-Pb) collisions, were not thought to be capable of forming a QGP. However, recent ALICE results have shown QGP-like behaviour in pp and p-Pb collisions; as such, these smaller systems are the topic of further study.

One of the observables used to indicate the presence of a QGP is the enhanced production of strange hadrons, relative to their non-strange counterparts. This enhancement is more easily seen in species with a higher strangeness content, such as the multi-strange \(\Xi^{\pm}\) and \(\Omega^{\pm}\) baryons, however, it is also present for singly strange species such as the \(\Lambda\) baryon and \(K^0\) meson. These species can be studied using the high precision tracking and momentum determination available using the ALICE detector, potentially providing further evidence for strangeness enhancement in small systems.

This thesis presents the study of the production of singly strange species (the \(K^0_S\) and \(\Lambda\), also referred to as V0's) as a function of final state multiplicity in p-Pb collisions at a centre-of-mass energy-per-nucleon of 8.16 TeV. The process by which transverse momentum, \(p_T\), spectra are generated and corrected is described, and the spectra, with their errors, are presented. For both species, the spectra display a shift to higher \(p_T\) as the multiplicity increases, which suggests the presence of radial flow.

In order to investigate strangeness enhancement in the events studied in this analysis, the \(p_T\)-integrated yields of both \(K^0_S\) and \(\Lambda\) are compared with measured yields of charged pions in the same collision system. The hadron-to-pion ratios increase as a function of final state multiplicity, suggesting QGP-like behaviour in small systems. A comparison between the results presented in this thesis and those measured in other collision systems and energies is shown. The hadron-to-pion ratios follow a continuous increase, from the low multiplicities present in pp collisions, to the high multiplicities observed in Pb-Pb collisions, suggesting that strangeness enhancement is an effect which is independent of the initial collision energy or system size.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Physics & Astronomy
Funders: Science and Technology Facilities Council
Subjects: Q Science > QC Physics

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