Huijun Ge

Type

Text

Type

Dissertation

Advisor

Hobbs, John | Jacak, Barbara | Kharzeev, Dmitri | Drees, Axel. | Bathe, Stefan.

Date

2017-08-01

Keywords

Physics

Department

Department of Physics.

Language

en_US

Source

This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree

Identifier

http://hdl.handle.net/11401/78131

Publisher

The Graduate School, Stony Brook University: Stony Brook, NY.

Format

application/pdf

Abstract

Hot and dense matter called quark-gluon plasma (QGP) has been created in high energy heavy ion collisions in the relativistic heavy ion collider (RHIC). Jets are observed to be suppressed in heavy ion collisions compared to those in p+p baseline - a phenomenon known as "jet quenching". This arises from the fact that partons from initial hard scatterings lose energy when traversing through and interacting with the medium. Extensive effort has been made in understanding the energy loss mechanism. Direct photon-hadron correlations are a golden channel to study parton energy loss in QGP. Photons do not interact strongly with the medium and exit unperturbed. High momentum photons are produced back-to-back with partons at leading order in the initial hard scatterings via predominantly QCD Compton scatterings. Their measured momentum will approximately balance those of the opposing partons before any medium modification. Consequently, using high-momentum direct photons as triggers is a most direct measure of the initial parton energy. Compared to di-hadron correlations or reconstructed jets, this measurement has no bias toward the medium surface. The modification of the fragmentation function for the away-side jet can be measured by comparing the integrated $\gamma_{dir}-h$ yields in heavy ion collisions to those in p+p. We analyzed Au+Au data taken by PHENIX in 2011 and combined with the results from 2007 and 2010. The per-trigger-yield of associated hadrons in Au+Au collisions is measured and we observe a suppression compared to p+p for higher momentum fraction ($z_T$) hadrons. A yield enhancement is found at low $z_T$ (high $\xi$). Comparison with theory shows that jet induced medium response is likely to be responsible for the enhanced production of these lower momentum particles. | 188 pages

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