New strategy for Bs branching ratio measurements and the search for new physics in Bs0 → μ+ μ-

The LHCb experiment at CERN's Large Hadron Collider will soon allow us to enter a new era in the exploration of Bs decays. A particularly promising channel for the search of new physics'' is B-s(0) -> mu(+) mu(-). The systematic key uncertainty affecting the measurement of this- and in fact all Bs- decay branching ratios-is the ratio of fragmentation functions f(d)/f(s). As the currently available methods for determining f(d)/f(s) are not sufficient to meet the high precision at LHCb, we propose a new strategy using B-s(0) -> D-s(+)pi(-) and B-d(0) -> D+K-. It allows us to obtain a lower experimental bound on BR(B-s(0) -> mu(+) mu(-)) which offers a powerful probe for new physics. In order to go beyond this bound and to determine fd/fs with a theoretical precision matching the experimental one it is sufficient to know the SU(3)-breaking correction to a form- factor ratio from nonperturbative methods at the level of 20%. Thanks to our strategy, we can detect new physics in B-s(0) -> mu(+) mu(-) at LHCb with 5 sigma for a branching ratio as small as twice the standard model value, which represents an improvement of the new- physics reach by about a factor of 2 with respect to the current LHCb expectation.