Jet radius dependence of dijet momentum balance and suppression in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

Romero Hernandez, Anabel Cristina

Permalink

https://hdl.handle.net/2142/127140 Copy

Description

Title

Jet radius dependence of dijet momentum balance and suppression in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

Author(s)

Romero Hernandez, Anabel Cristina

Issue Date

2024-08-26

Director of Research (if dissertation) or Advisor (if thesis)

Sickles, Anne

Doctoral Committee Chair(s)

Noronha-Hostler, Jacquelyn

Committee Member(s)

• Beck, Douglas
• Goldschmidt, Elizabeth

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Relativistic heavy-ion collisions
• jet & heavy flavor physics
• quark-gluon plasma
• Pb+Pb
• dijet asymmetry
• dijet momentum balance
• jet radius dependence
• jet suppression
• jet quenching

Abstract

The quark gluon plasma (QGP) is a high energy, high density state of matter that existed less than a second after the big bang. The QGP is made of elementary particles called partons that interact through the strong force, one of the fundamental forces of nature. The QGP can be created in ultra-relativistic heavy ion collisions in order to study the strong force. This is done by colliding accelerated beams of heavy nuclei and measuring the products of the collisions with a particle detector. In particle collisions, partons can scatter off each other with a large momentum transfer, and when they come out of the collisions, they create collimated sprays of particles that are called jets. In heavy ion collisions, these hard scattered partons make their way through the QGP, interacting with it and losing energy, a phenomenon known as jet quenching. Jets created in heavy ion collisions are modified with respect to jets created in vacuum due to the strong interactions with the QGP. When partons are hard scattered, pairs of jets called dijets are emitted in opposite directions with the same energy. When dijets are created in heavy ion collisions, they lose energy when they interact with the QGP. Traveling different path lengths within the QGP can cause the dijets to become imbalanced in momentum due to the associated energy loss. Thus, dijet measurements of jet quenching are a powerful tool for studying the QGP and the strong force. This thesis describes a measurement of the jet radius dependence of the momentum balance between leading back-to-back dijets in Pb+Pb and pp collisions at a per-nucleon-pair center of mass energy √s_NN = 5.02 TeV. The data was collected by the ATLAS detector at the LHC, with a total integrated luminosity of 1.72 nb^−1 of Pb+Pb collisions collected in 2018, and 255 pb^−1 of pp collisions collected in 2017. Jets were reconstructed using the anti-k t algorithm with jet radius parameters R = 0.2, 0.3, 0.4, 0.5 and 0.6. The dijet momentum balance distributions are constructed for leading jets with transverse momentum p_T from 100 to 562 GeV for R = 0.2, 0.3 and 0.4 jets, and from 158 to 562 GeV for R = 0.5 and 0.6 jets. The absolutely normalized dijet momentum balance distributions are constructed to compare measurements of the dijet yields in Pb+Pb collisions directly to the dijet cross sections in pp collisions. For all jet radii considered here, there is a suppression of more balanced dijets in Pb+Pb collisions compared to pp collisions, while for more imbalanced dijets there is an enhancement. There is a jet radius dependence to the dijet yields, being stronger for more imbalanced dijets than for more balanced dijets. Additionally, jet pair nuclear modification factors are measured. The subleading jet yields are found to be more suppressed than leading jet yields in dijets. A jet radius dependence of the pair nuclear modification factors is observed, with the suppression decreasing with increasing jet radius. These measurements provide new constraints on jet quenching scenarios in the quark-gluon plasma.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127140

Copyright and License Information

Copyright 2024 Anabel Cristina Romero Hernandez

Owning Collections