One unresolved question in hadronic physics is the origin of large transverse single-spin asymmetries, AN, observed in hadron production from high-energy polarized-proton collisions. Collinear perturbative Quantum Chromodynamics (pQCD) predicts that AN should scale with the quark mass, however, experiments have since reported large AN for inclusive hadron production. Recent measurements from RHIC experiments show examples of these asymmetries at forward angles in a kinematic region where pQCD cross-section calculations reasonably agree with measured cross-sections. Disentangling dynamical contributions to AN from hadro-production requires moving beyond inclusive measurements. One possibility is to investigate asymmetries in two-particle correlations due to Interference Fragmentation Functions (IFF) and the Sivers effect. In 2008, RHIC dedicated a portion of the run to transversely polarized proton collisions at sqrt(s) = 200 GeV. STAR was equipped with a Foward Meson Spectrometer (FMS) and a Forward Time Projection Chamber (FTPC), overlapping in the pseudorapidity range of 2.5 < eta &lt; 4. By analyzing neutral pions with the FMS correlated with charged particles from the FTPC, correlation asymmetries can be measured at kinematics where large inclusive asymmetries have been measured. Correlations are measured for pi^0's with 2 &lt; pT, pi^0 &lt; 5 GeV/c and associated charged particles in two ranges of transverse momentum: 1 &lt; pT, ch &lt; 2 GeV/c and 0.5 &lt; pT, ch &lt; 1 GeV/c. IFF and Sivers asymmetries manifest themselves through the correlation of two particles from the same jet. These events are selected through a cut on the pair radius, delta R. Gain non-uniformities and electronics failures have resulted in large holes in trigger acceptance and associated particle acceptance, respectively. This non-uniform acceptance allows the Sivers and IFF effects to mix and distort the raw asymmetries. Techniques are developed to measure this leak-through by means of unpolarized yields and event weighting. They result in small corrections to the asymmetries. IFF and Sivers asymmetries both for xF > 0 and for xF &lt; 0 are reported for forward-angle pi^0-charged particle correlations from polarized-proton collisions at sqrt(s) = 200 GeV. Asymmetries are shown corrected for full underlying-event and pileup backgrounds, as well as corrected only for pile-up contributions. It appears the asymmetries are less sensitive to delta R when corrected for the full underlying-event background. Unfortunately, statistics limitations preclude a firm conclusion.

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.¬ / Physics

Submitted by Wagner Maciel Castilho (castilho.w@gmail.com) on 2017-12-05T10:53:57Z No. of bitstreams: 1 TeseWagner.pdf: 4189219 bytes, checksum: dbc77f46b31b8872c5aafe68d8a5b7d0 (MD5) / Approved for entry into archive by Pamella Benevides Gonçalves null (pamella@feg.unesp.br) on 2017-12-05T12:38:21Z (GMT) No. of bitstreams: 1 catilho_wm_dr_guara.pdf: 4189219 bytes, checksum: dbc77f46b31b8872c5aafe68d8a5b7d0 (MD5) / Made available in DSpace on 2017-12-05T12:38:21Z (GMT). No. of bitstreams: 1 catilho_wm_dr_guara.pdf: 4189219 bytes, checksum: dbc77f46b31b8872c5aafe68d8a5b7d0 (MD5) Previous issue date: 2017-11-10 / Os fenômenos físicos envolvidos em colisões relativísticas de íons pesados foram estudados utilizando o código hidrodinâmico NeXSPheRIO, com condições iniciais flutuantes evento a evento, caracterizado por tubos de fluxo longitudinais de altas energias. Foram realizadas análises para o espectro de hádrons em função dos momentos transversais pelos cálculos das distribuições de partículas em sete janelas de centralidade de colisão, de acordo com dados publicados pela Colaboração STAR. A coletividade da matéria nuclear formada durante as colisões foi investigada em termos de correlações azimutais entre hádrons. Verificou-se que as estruturas da correlação dependem do momento transversal e da centralidade. Tais estruturas são atribuídas à interação entre um fundo dependente da centralidade e as flutuações de evento a evento na multiplicidade. Como resultado, as correlações observadas são apresentadas por um duplo pico na região do away-side que mudam continuamente para um pico único sob certas circunstâncias. Em termos do modelo do tubo periférico, o fundo é dominado pelo fluxo elíptico que aumenta com a descentralização. Pelos cálculos numéricos, a anisotropia do sistema é estudada quanto aos coeficientes de fluxo harmônico até a quarta ordem, de acordo com os dados da colaboração PHENIX. A anisotropia do fundo contribui para as correlações entre hádrons e pôde ser avaliada pelo método ZYAM. Após sua subtração na produção do sinal de correlação próprio, a estrutura de correlação resultante é uma função da centralidade, plano de evento e do momento transverso de acordo com os dados das colaborações PHENIX e STAR. Mostrou-se que a estrutura do duplo pico no away-side muda continuamente para um pico único com a redução na centralidade. Além disso, em relação à dependência do plano de eventos, a estrutura de duplo pico no away-side evolui para um pico único à medida que o ângulo azimutal das partículas gatilho se move do plano para o da direção fora do plano de eventos. Também foi mostrado que a estrutura resultante do away-side pode ser sensível ao esquema detalhado pelo método ZYAM, particularmente, a subtração do terceiro coeficiente harmônico. Por último, mas não menos importante, a magnitude da correlação diminuiu com o aumento do momento transversal das partículas associadas. Nossas análises apresentaram um acordo razoável com os dados experimentais publicados pela colaboração PHENIX e STAR do RHIC / The physical phenomena involved in relativistic heavy-ion collisions were studied using a hydrodynamic code, NeXSPheRIO, with event-by-event fluctuating initial conditions featured by high-energy longitudinal flux tubes. Analyses were carried out for hadron spectrum as a function of the transverse momentum by the calculations of particle distributions in seven collision centrality windows, according to the data published by the STAR Collaboration. Also, the collectivity of the nuclear matter formed during the collisions was investigated in terms of dihadron azimuthal correlations. The correlation structures were found to be dependent on the transverse momentum and centrality. They are attributed to the interplay between the centrality dependent background and the eventby-event multiplicity fluctuations. As a result, the observed correlations are featured by a double-peak in the away-side region that continuously change to a single peak under certain circumstances. In terms of the peripheral tube model, the background is dominated by the elliptic flow which increases with decreasing centrality. By numerical calculations, the anisotropy of the system is studied regarding the harmonic flow coefficients up to fourth order, in accordance with the existing RHIC data. The background anisotropy contributes to the dihadron correlations, and can be evaluated by the ZYAM method. After it is subtracted from the proper correlation yields, the resultant correlation structure is a function of centrality, event plane and transverse moment, in accordance with the data from the PHENIX and STAR Collaborations. It was shown that the double-peak structure in the away-side continually changes to a single peak as centrality decreases. In addition, concerning the event plane dependence, the double-peak structure in the away-side evolves into a single peak as the azimuthal angle of the trigger particles moves from the in-plane to the out-of-plane direction. It was also shown that the resultant away-side structure can be sensitive to the detailed schemes of the ZYAM method, particularly, to the subtraction of the third harmonic coefficient. Last but not least, the magnitude of the correlation was found to decrease with increasing transverse moment of the associated particles. Our analyses manifestly presented a reasonable agreement with the experimental data published by the PHENIX and STAR Collaborations