CP Violation In Single Top Production And Decay Via p p-bar -> t b-bar +X -> W^+ b b-bar +X Within The MSSM: A Possible Application For Measuring \arg(A_t) At Hadron Colliders

摘要

CP-nonconserving effects in the reaction p p-bar -> t b-bar +X -> W^+ b b-bar+X, driven by the supersymmetric CP-odd phase of the stop trilinear softbreaking term, \arg(A_t), are studied. We discuss the CP-nonconserving effectsin both production and the associated decay amplitudes of the top. We findthat, within a plausible low energy scenario of the MSSM and keeping theneutron electric dipole moment below its current limit, a CP-violatingcross-section asymmetry as large as 2-3% can arise if some of the parameterslie in a favorable range. A partial rate asymmetry originating only in the topdecay t -> W^+ b is found to be, in general, below the 0.1% level which issomewhat smaller than previous claims. For a low \tan\beta of order one thedecay asymmetry can reach at the most ~0.3%. This (few) percent level overallCP-violating signal in p p-bar -> t b-bar +X -> W^+ b b-bar +X might be withinthe reach of the future 2(4) TeV pp-bar Tevatron collider that may be able toproduce ~10000(~30000) such tb-bar events with an integrated luminosity of 30fb^{-1}. In particular, it may be used to place an upper bound on \arg(A_t) ifindeed \arg(\mu) -> 0, as implied from the present experimental limit on theneutron electric dipole moment. The partial rate asymmetry in the top decay(~few \times 10^{-3}) may also be within the reach of the LHC with ~10^7 pairsof tt-bar produced, provided detector systematics are sufficiently small. Wealso show that if the GUT-scale universality of the soft breaking trilinear $A$terms is relaxed, then the phases associated with \arg A_u and \arg A_d cantake values up to ~few \times 10^{-1} even with squarks and gluino masses ofseveral hundred GeV's without contradicting the experimental limit on theneutron electric dipole moment.