Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

The Shape of Strangeness: Transverse Spherocity and Underlying Event studies of φ and its relation to Ξ in √s = 13 TeV pp collisions

Nassirpour, Adrian LU orcid (2022)
Abstract
Through ultrarelativistic particle collisions at the LHC, it is possible to deconfine quarks and gluons. This deconfinement gives rise to a strongly interacting medium, referred to as the Quark-Gluon Plasma (QGP). One of the earliest proposed and observed signatures of the QGP was the enhanced production of strange hadrons since the medium can thermally produce strange quarks. However, recent studies in small systems, such as proton–proton (pp) and proton-lead (pPb) collisions, have exhibited similar features. These findings are
quite puzzling, as the formation of a QGP in these small collision systems challenges current theoretical frameworks.
In this Thesis, I present two different studies on the production of φ mesons, in... (More)
Through ultrarelativistic particle collisions at the LHC, it is possible to deconfine quarks and gluons. This deconfinement gives rise to a strongly interacting medium, referred to as the Quark-Gluon Plasma (QGP). One of the earliest proposed and observed signatures of the QGP was the enhanced production of strange hadrons since the medium can thermally produce strange quarks. However, recent studies in small systems, such as proton–proton (pp) and proton-lead (pPb) collisions, have exhibited similar features. These findings are
quite puzzling, as the formation of a QGP in these small collision systems challenges current theoretical frameworks.
In this Thesis, I present two different studies on the production of φ mesons, in relation to Ξ baryons, in pp collisions at √s = 13 TeV, measured with the ALICE apparatus. Both of these studies aim to investigate the origin of strange hadron enhancement in high-multiplicity pp collisions. First, I report measurements of φ production as a function of the event-shape observable Unweighted Transverse Spherocity, SOpT=1. With SOpT=1 , it is possible to categorize events by their azimuthal topology. I utilize SOpT=1 to contrast particle production in collisions
dominated by many soft initial interactions, with collisions dominated by a single hard scattering. I find that strangeness enhancement is prominent in soft, isotropic topologies, whereas events with di-jet topologies showcase a clear suppression of strange particles.

The second study presents the production of φ mesons and Ξ hadrons as a function of the Relative Transverse Activity RT . With RT , one can control the size of the Underlying Event (UE). By varying RT, it is therefore possible to study the interplay between particle production from hard fragmentation in jets, and soft particles produced by the UE. The reported results suggest that strange particle production is mainly a feature of the UE. When put together, the two studies suggest that high-multiplicity pp collisions are in general dominated by soft physics, which is also responsible for the strangeness enhancement, while
high-multiplicity events dominated by hard physics are rare outliers. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Research Scientist (Chargé de Recherche) Nguyen, Matthew, Laboratoire Leprince-Ringuet / Ecolyte Polytechnique, France
organization
publishing date
type
Thesis
publication status
published
subject
keywords
LHC, ALICE, Quark-Gluon Plasma, small systems, pp collisions, underlying event, event-shape engineering, transverse activity, strangeness enhancement, resonance production, Fysicumarkivet A:2022:Nassirpour
pages
269 pages
publisher
Lund University (Media-Tryck)
defense location
Rydbergsalen, Fysiska Institutionen, Professorsgatan 1, Lund. Join via Zoom: https://lu-se.zoom.us/j/64084844253
defense date
2022-12-09 13:15:00
ISBN
978-91-8039-453-6
978-91-8039-454-3
language
English
LU publication?
yes
id
247766fe-9c0a-4f87-8d03-799297f908ed
date added to LUP
2022-11-15 12:14:22
date last changed
2024-02-02 09:43:04
@phdthesis{247766fe-9c0a-4f87-8d03-799297f908ed,
  abstract     = {{Through ultrarelativistic particle collisions at the LHC, it is possible to deconfine quarks and gluons. This deconfinement gives rise to a strongly interacting medium, referred to as the Quark-Gluon Plasma (QGP). One of the earliest proposed and observed signatures of the QGP was the enhanced production of strange hadrons since the medium can thermally produce strange quarks. However, recent studies in small systems, such as proton–proton (pp) and proton-lead (pPb) collisions, have exhibited similar features. These findings are<br/>quite puzzling, as the formation of a QGP in these small collision systems challenges current theoretical frameworks.<br/>In this Thesis, I present two different studies on the production of φ mesons, in relation to Ξ baryons, in pp collisions at √s = 13 TeV, measured with the ALICE apparatus. Both of these studies aim to investigate the origin of strange hadron enhancement in high-multiplicity pp collisions. First, I report measurements of φ production as a function of the event-shape observable Unweighted Transverse Spherocity, <i>S</i><sub>O</sub><i><sup>p</sup></i><sup>T</sup><i><sup>=1</sup></i>. With <i>S</i><sub>O</sub><i><sup>p</sup></i><sup>T=1 </sup>, it is possible to categorize events by their azimuthal topology. I utilize <i>S</i><sub>O</sub><i><sup>p</sup></i><sup>T=1</sup> to contrast particle production in collisions<br/>dominated by many soft initial interactions, with collisions dominated by a single hard scattering. I find that strangeness enhancement is prominent in soft, isotropic topologies, whereas events with di-jet topologies showcase a clear suppression of strange particles.<br/><br/>The second study presents the production of φ mesons and Ξ hadrons as a function of the Relative Transverse Activity <i>R</i><sub>T</sub> . With <i>R</i><sub>T</sub> , one can control the size of the Underlying Event (UE). By varying <i>R</i><sub>T</sub>, it is therefore possible to study the interplay between particle production from hard fragmentation in jets, and soft particles produced by the UE. The reported results suggest that strange particle production is mainly a feature of the UE. When put together, the two studies suggest that high-multiplicity pp collisions are in general dominated by soft physics, which is also responsible for the strangeness enhancement, while<br/>high-multiplicity events dominated by hard physics are rare outliers.}},
  author       = {{Nassirpour, Adrian}},
  isbn         = {{978-91-8039-453-6}},
  keywords     = {{LHC; ALICE; Quark-Gluon Plasma; small systems; pp collisions; underlying event; event-shape engineering; transverse activity; strangeness enhancement; resonance production; Fysicumarkivet A:2022:Nassirpour}},
  language     = {{eng}},
  publisher    = {{Lund University (Media-Tryck)}},
  school       = {{Lund University}},
  title        = {{The Shape of Strangeness: Transverse Spherocity and Underlying Event studies of φ and its relation to Ξ in √s = 13 TeV pp collisions}},
  url          = {{https://lup.lub.lu.se/search/files/128534177/Adrian_Doctoral_Thesis_Final.pdf}},
  year         = {{2022}},
}