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The contribution from the sea quarks to the proton spin have been poorly constrained mainly because of the limited knowledge we have on the fragmentation function in polarized Semi Inclusive Deep Inelastic Scattering (SIDIS) experments. The parity-violating longitudinal single spin asymmetry A[subscript L] in the production of W bosons in p + p collisions does not involve fragmentation function and is an alternative better way of exploring the polarization of sea quarks in the proton. The measurement will be useful especially in constraining ū and d̄ in the very backward and forward rapidities respectively. However, identifying the muons from the decay of the W is challenging due to a great background of hadronic in flight decays and other muon producing processes such as heavy flavor decays. In the forward and backward hemispheres of PHENIX at RHIC, the muon spectrometers have been recently upgraded in order to provide additional trigger and tracking information to suppress those backgrounds. One of those upgrades is the Forward Vertex (FVTX) detector, a silicon-strip tracker. In 2013, PHENIX accumulated the largest amount of polarized p + p collision data ever collected in the world (~ 240pb−1) at [square root symbol] s = 510 GeV with a beam polarization of 56%. The analysis techniques used to extract the signal from the data and the longitudinal single spin asymmetries A[subscript L] in RHIC 2013 run will be discussed.
Understanding the structure of the proton is an ongoing effort in the particle physics community. Existing in the region of nonperturbative QCD, the various models for proton structure must be informed and constrained by experimental data. In 2009, the STAR experiment at Brookhaven National Lab recorded over 12 pb-1 of data from polarized p+p collisions at 500 GeV center-of-mass energy provided by the RHIC accelerator. This has offered a first look at the spin-dependent production of W+(-) bosons, and hence at the spin-flavor structure of the proton, where the main production mode is through d+u (u+d) annihilation. Using STAR's large Time Projection Chamber and its wide-acceptance electromagnetic calorimeters, it is possible to identify the e+ + v (e- + v) decay mode of the W bosons produced. This thesis presents the first STAR measurement of charge-separated W production, both the pseudorapidity-dependent ratio and the longitudinal single-spin asymmetry. These results show good agreement with theoretical expectations, validating the methods used and paving the way for the analysis of larger datasets that will be available soon. In the near future the range of this measurement will be augmented with the Forward GEM Tracker. A discussion of the design and implementation of this upgrade is also included, along with projections for its impact.
Twenty years of polarized lepton-nucleon scattering experiments have found that the contribution from quark spins (1/2[delta] [sigma]) to the spin of the proton is only ~ 35%. This has lead researchers to look elsewhere, specifically to gluon spin ([delta sigma]) for a large contribution to proton spin. [delta sigma] has been only loosely constrained in polarized DIS and SIDIS experiments. Polarized proton-proton collisions at RHIC provide sensitivity to [delta sigma] through measurements of the longitudinal double-spin asymmetry, ALL. This work presents a measurement of ALL for inclusive 7ro production in polarized proton-proton collisions using the STAR detector and data from RHIC Run 6. 7r0s are abundantly produced at mid-rapidity in proton-proton collisions, making them natural candidates for studies of [delta] [sigma]. Novel techniques for reconstructing 7ros at STAR are discussed, and a measurement of the unpolarized cross section presented. Finally, the measured ALL is compared to perturbative QCD predictions and from this comparison constraints are placed on [delta] [sigma].
We present the Inclusive Jet Longitudinal Double-Spin Asymmetry for polarized protons at \s = 200 GeV. The data were taken on the STAR experiment at RHIC during the 2005 run period and cover a jet transverse momentum range of 5
We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb−1 of data collected at (square root)s = 1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron p{bar p} Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.
Understanding what contributes to the intrinsic angular momentum (spin) of the proton has been a major goal of the nuclear physics community. In the 1980s, it was discovered that quarks contribute 30% to the spin of the proton. This information led to a search to find other contributions to the spin of the proton. At STAR, the double spin asymmetry (ALL) is measured as it is sensitive to the polarized gluon distribution (Dg(x)). The STAR 2009 inclusive jet ALL at sqrt(s) = 200 GeV has been incorporated into two independent global fits. These fits show for the first time a statistically significant non-zero gluon contribution to the spin of the proton in the parton momentum fraction range x > 0.05. Dijet ALL is also measured at STAR. Dijets are advantageous since the parton momentum fraction (x) of the initial partons may be reconstructed to first order from final state measurements. In 2013 STAR collected an estimated 250 pb-1 of data at sqrt(s) = 510 GeV. The higher center of mass energy will allow STAR to probe Dg(x) at x values as low as 0.02. The large statistics will allow a reduction in the uncertainties. Once the data is incorporated into future global fits, it will allow for a more precise determination of Dg(x). The 2013 dijet ALL results will be presented. The results show good agreement with both global fits and previous STAR results dijet measurements.