PROBING THE LOW-X GLUON HELICITY DISTRIBUTION WITH DIJET DOUBLE SPIN ASYMMETRIES IN POLARIZED PROTON COLLISIONS AT √S = 510 GEV

Author

Suvarna Ramachandran, University of KentuckyFollow

Date Available

10-22-2018

Year of Publication

2018

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Arts and Sciences

Department/School/Program

Physics and Astronomy

Advisor

Dr. Renee H. Fatemi

Abstract

The proton is a complex subatomic particle consisting of quarks and gluons, and one of the key questions in nuclear physics is how the spin of the proton is distributed amongst its constituents. Polarized deep inelastic scattering experiments with leptons and protons estimate that the quark spin contribution is approximately 30%. The limited kinematic reach of these experiments, combined with the fact that they are only indirectly sensitive to the electrically neutral gluon, means they can provide very little information about the gluon contribution to the spin of the proton. In contrast, hadronic probes, such as polarized proton collisions provide direct access to the gluon helicity distribution.

The production of jets in polarized proton collisions at STAR is dominated by quark-gluon and gluon-gluon scattering processes. The dijet longitudinal double spin asymmetry (A_LL) is sensitive to the polarized parton distributions and may be used to extract information about the gluon contribution to the spin of the proton. Previous STAR jet measurements at √s = 200 GeV show evidence of polarized gluons for gluon momentum fractions above 0.05. The measurement of dijet A_LL at √s = 510 GeV will extend the current constraints on the gluon helicity distribution to low momentum fractions and allow for the reconstruction of the partonic kinematics. Information about the initial state momentum provides unique constraints on the functional form of the gluon helicity distribution, thus reducing the uncertainty on extrapolations to poorly constrained regions. This thesis will present the first measurement of the dijet A_LL at √s = 510 GeV, from polarized proton data taken during the 2012 RHIC run.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2018.416

Recommended Citation

Ramachandran, Suvarna, "PROBING THE LOW-X GLUON HELICITY DISTRIBUTION WITH DIJET DOUBLE SPIN ASYMMETRIES IN POLARIZED PROTON COLLISIONS AT √S = 510 GEV" (2018). Theses and Dissertations--Physics and Astronomy. 58.
https://uknowledge.uky.edu/physastron_etds/58