CP violation at a linear collider with transverse polarization

Abstract

We show how transverse beam polarization at e⁺e⁻ colliders can provide a novel means to search for CP violation by observing the distribution of a single final-state particle without measuring its spin. We suggest an azimuthal asymmetry which singles out interference terms between standard model contribution and new-physics scalar or tensor effective interactions in the limit in which the electron mass is neglected. Such terms are inaccessible with unpolarized or longitudinally polarized beams. The asymmetry is sensitive to CP violation when the transverse polarizations of the electron and positron are in opposite senses. The sensitivity of planned future linear colliders to new-physics CP violation in e⁺e⁻→tt̅ is estimated in a model-independent parametrization. It would be possible to put a bound of ~7TeV on the new-physics scale Λ at the 90% C.L. for √s=500GeV and ∫dtL=500fb⁻¹, with transverse polarizations of 80% and 60% for the electron and positron beams, respectively.