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نویسنده
چکیده
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+ → πνν̄). Although still affected by a large error, the BNL–E787 result favours values of B(K+ → πνν̄) 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+ → πνν̄), sin 2β and ∆MBd/∆MBs 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+ → πνν̄) is also presented. Two main scenarios naturally emerge: those with direct new-physics contributions to the s → dνν̄ amplitude and those with direct new-physics effects only in Bd–B̄d mixing. Realistic models originating these two scenarios and possible future strategies to clearly identify them are briefly discussed. † On leave of absence at Theory Division, CERN, CH-1211 Geneva 23, Switzerland. ∗ Work supported in part by TMR, EC–Contract No. ERBFMRX-CT980169 (EURODAΦNE).
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تاریخ انتشار 2002