Study of the Transverse-Momentum-Dependent structure of the nucleon in Semi-Inclusive DIS

Abstract

The aim of this Thesis is to contribute to the understanding of the nucleon structure through the study of two observables accessible in Semi-Inclusive Deep Inelastic Scattering (SIDIS) of high energy leptons off unpolarized protons: the transverse-momentum distributions and the amplitudes of the modulations in the azimuthal angle of the final state hadrons, the latter referred to as "azimuthal asymmetries". They give relevant information on the transverse momentum of the partons inside the nucleon and on the Boer-Mulders TMD PDF. This Thesis summarizes the work done in this direction during my PhD, which consisted in a complete analysis of part of the data collected in 2016 in COMPASS, a fixed target experiment at the CERN SPS using 160 GeV/$c$ ${\mu }^{+}$ and ${\mu }^{-}$ beams and a liquid hydrogen target. The data quality and the detector stability have been investigated, as well as the stability and the consistency of the reconstructed data. A significant effort has been put in the validation of the Monte Carlo simulations, necessary for the evaluation of the acceptance of the spectrometer and to estimate the contamination to the SIDIS sample by the hadrons produced in the decay of diffractively produced vector mesons (particularly ${\rho }^0$ and $\varphi$). This diffractive process had also to be studied in detail and implemented in dedicated Monte Carlo simulations, reducing the systematic uncertainties affecting previous measurements. Other systematic effects have also been investigated, and the corresponding systematic uncertainties evaluated. A deep inspection of the various kinematic dependences has been performed. A phenomenological analysis of the new results is also presented, with a comparison of the current COMPASS findings with the previous ones obtained on a deuteron target.

arXiv commentPhD thesis, University of Trieste, XXXIII cycle, academic year 2019-2020. Supervisor: Prof. Anna Martin

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