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  • 2020TeePhD

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A Gluon Transverse Momentum Dependent Parton Distribution Function Analysis Using a J/Ψ + γ Final State at √s = 13 TeV with ATLAS

Research output: ThesisDoctoral Thesis

Publication date21/01/2021
Number of pages215
Awarding Institution
Award date21/01/2021
  • Lancaster University
<mark>Original language</mark>English


This thesis describes a study into Transverse-Momentum-Dependent (TMD) distributions of gluons inside a proton, through a J/ψ meson plus γ final state. The analysis was performed using 2.57 fb−1 of data collected by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV in 2015. A measurement of the continuum J/ψ+γ cross section is carried out, in order to give access to the TMD function fg1(k2T), which describes the distribution of unpolarised gluons in an unpolarised proton. Assuming a Gaussian shape of the TMD distribution, with dependence on the intrinsic transverse momentum of a gluon, kT, a measurement of the mean transverse momentum was achieved at three different invariant mass ranges, Q, of the J/ψ−γ system. The invariant mass ranges, and measured values of ⟨k2T⟩−−−−√ are summarised as follows: for 15 ≤Q< 22 GeV, the mean gluon transverse momentum was found to be ⟨k2T⟩−−−−√ = 1.99 ± 0.25 GeV. For the second invariant mass range considered 22 ≤Q< 31 GeV giving ⟨k2T⟩−−−−√ = 3.63 ± 0.41 GeV. For the last (upper) invariant mass range considered 31 ≤Q< 44 GeV, it was found that 4.08 ± 0.74 GeV. It is shown that between the lowest and highest invariant mass ranges considered, the intrinsic mean transverse momentum of gluons inside an unpolarised proton increases by a factor of 2. The second measurement was an attempt to measure the contribution of the TMD function h⊥g1(k2T), which describes the distribution of linearly polarised gluons inside an unpolarised proton. By measuring the induced angular azimuthal modulations expected from interacting polarised gluons no statistically significant modulation was found with the dataset used.