Strategy for detecting b polarization effects.
We suggest a strategy for detecting {ital b} polarization effects in {ital e}{sup +}{ital e}{sup {minus}} annihilation on {ital Z} resonance. Using two types of inclusive leptonic samples with different {Lambda}{sub {ital b}} fractions in {ital Z}{r_arrow}{ital b{bar b}} events, the {ital b} polarization effects may be detected without large uncertainties of {ital b} fragmentation and the {Lambda}{sub {ital b}} decay model.
The weak-magnetic moment of heavy quarks
Abstract With initial and final particles on-shell, the anomalous weak-magnetic dipole moments of b and c quarks are electroweak gauge invariant quantities of the effective couplings Zb b and Zc c , respectively, and good candidates to test the Standard Model and/or new physics. Here we present a complete computation of these quantities within the Standard Model. We show that decoupling properties with respect to heavy particles do take place in the weak magnetic moment. The obtained values, a b ( M Z 2 ) = (2.98 − 1.56 i ) × 10 −4 and a c ( M Z 2 ) = (−2.80 + 1.09 i ) × 10 −5 are dominated by one-gluon exchange diagrams. The electroweak corrections are less than 1% of the total magnitude.
Monte carlo simulation of events with Drell-Yan lepton pairs from antiproton-proton collisions
The complete knowledge of the nucleon spin structure at leading twist requires also addressing the transverse spin distribution of quarks, or transversity, which is yet unexplored because of its chiral-odd nature. Transversity can be best extracted from single-spin asymmetries in fully polarized Drell-Yan processes with antiprotons, where valence contributions are involved anyway. Alternatively, in single-polarized Drell-Yan the transversity happens convoluted with another chiral-odd function, which is likely to be responsible for the well known (and yet unexplained) violation of the Lam-Tung sum rule in the corresponding unpolarized cross section. We present Monte Carlo simulations for the unpolarized and single-polarized Drell-Yan pp{sup ({up_arrow}}{sup )}{yields}{mu}{sup +}{mu}{sup -}X at different center-of-mass energies in both configurations where the antiproton beam hits a fixed proton target or it collides on another proton beam. The goal is to estimate the minimum number of events needed to extract the above chiral-odd distributions from future measurements at the high energy storage ring (HESR) at GSI. It is important to study the feasibility of such experiments at HESR in order to demonstrate that interesting spin physics can be explored already using unpolarized antiprotons.