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PRECISE MEASUREMENTS OF TRANSVERSE SPIN-DEPENDENT AZIMUTHAL CORRELATIONS OF CHARGED PION PAIRS IN TRANSVERSELY POLARISED PROTON-PROTON COLLISIONS AT CENTER-OF-MASS ENERGY = 510 GIGA ELECTRON VOLT AT STAR
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Thesis/Dissertation
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2024-05
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Physics
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http://dx.doi.org/10.34944/dspace/10265
Abstract
At leading twist, the spin structure of the nucleon is described by three fundamental parton distribution functions (PDFs): unpolarized PDFs (f_1 (x)), helicity PDFs (g_1 (x)), and transversity PDFs (h_1^q (x)). Unlike f_1 (x) and g_1 (x), h_1^q (x) is a chiral-odd function that must couple with another chiral-odd function to manifest in experimentally observable chiral-even physical quantities such as cross-sections or asymmetries. Due to its chiral-odd nature, h_1^q (x) remains inaccessible in inclusive deep inelastic scattering (DIS) experiments, where f_1 (x) and g_1 (x) garner a larger amount of experimental data to constrain them, hence making h_1^q (x) one of the least constrained fundamental PDFs.
In the Standard Model, only a few channels exist where h_1^q (x) couples with another chiral-odd function. The production of di-hadron in the final state from transversely polarized pp collisions represents one of the theoretically cleanest channels, where h_1^q (x) couples with another chiral-odd distribution function known as the interference fragmentation function (IFF, H_1^∢ (z,M_h^2)) and gives experimentally observable di-hadron azimuthal correlation asymmetry (A_UT^sin(φ_RS ) ). This thesis work presents the most precise measurement, to date, of the di-pion A_UT^sin(φ_RS ) in the mid-pseudorapidity region (-1 <η<1) using STAR 2017 transversely polarized pp data at a center-of-mass energy (√s) of 500 GeV. In 2017, STAR collected a dataset of 350 pb^(-1), approximately 15 times larger than the previous STAR 2011 dataset. Consequently, this new dataset improves the statistical precision of A_UT^sin(φ_RS ) by a factor of 4, which will contribute significantly to constraining the h_1^q (x) in the global analyses.¬
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