We report on a polarization measurement of inclusive J /ψ mesons in the di-electron decay channel at mid-rapidity at 2 < p T < 6 GeV/c in p + p collisions at √ s = 200 GeV. Data were taken with the STAR detector at RHIC. The J /ψ polarization measurement should help to distinguish between different models of the J /ψ production mechanism since they predict different p T dependences of the J /ψ polarization. In this analysis, J /ψ polarization is studied in the helicity frame. The polarization parameter λ θ measured at RHIC becomes smaller towards high p T , indicating more longitudinal J /ψ polarization as p T increases.The result is compared with predictions of presently available models.
We report new STAR measurements of the single-spin asymmetries AL for W + and W − bosons produced in polarized proton-proton collisions at √ s = 510 GeV as a function of the decay-positron and decay-electron pseudorapidity. The data were obtained in 2013 and correspond to an integrated luminosity of 250 pb −1 . The results are combined with previous results obtained with 86 pb −1 . A comparison with theoretical expectations based on polarized lepton-nucleon deep-inelastic scattering and prior polarized proton-proton data suggests a difference between the ū and d quark helicity distributions for 0.05 < x < 0.25. In addition, we report new results for the double-spin asymmetries ALL for W ± , as well as AL for Z/γ * production and subsequent decay into electron-positron pairs.
We study quantum corrections at the one loop level in open superstring tachyon condensation using the boundary string field theory (BSFT) method. We find that the tachyon field action has the same form as at the disc level, but with a renormalized effective coupling λ ′ = g ren s e −T 2 /4 (g ren s is the renormalized dimensionless closed string coupling, e −T 2 /4 is the tachyonic field expectation value) and with an effective string tension. This result is in agreement with that based on general analysis of loop effects.April, 2001 * kviswana@sfu.ca † yyangc@sfu.ca
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