K+->pi(+)nu(nu)over-bar: a rising star on the stage of flavour physics

摘要

Motivated by the new experimental information reported by the BNL-E787 Collaboration, we analyse the present impact and the future prospects opened by the measurement of B(K+ --> pi(+)nu(ν) over bar). Although still affected by a large error, the BNL-E787 result favours values of B(K+ --> pi(+)nu(ν) over bar )substantially larger than what expected within the Standard Model. As a result, this data already provide non-trivial constraints on the unitarity triangle, when interpreted within the Standard Model framework. We stress the importance of the clean relation between B(K+ --> pi(+)nu(ν) over bar), sin2beta and DeltaM(Bd)/DeltaM(Bs) that in the next few years could provide one of the deepest probes of the Standard Model in the sector of quark-flavour dynamics. A speculative discussion about possible non-standard interpretations of a large B(K+ --> pi(+)nu(ν) over bar) is also presented. Two main scenarios naturally emerge: those with direct new-physics contributions to the s --> dnu(ν) over bar amplitude and those with direct new-physics effects only in B-d-(B-d) over bar mixing. Realistic models originating these two scenarios and possible future strategies to clearly identify them are briefly discussed. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 34]