Probing new physics via the B(s)0→μ(+)μ- effective lifetime

Abstract

We have recently seen new upper bounds for B(s)(0)→μ(+)μ(-), a key decay to search for physics beyond the standard model. Furthermore a nonvanishing decay width difference ΔΓ(s) of the B(s) system has been measured. We show that ΔΓ(s) affects the extraction of the B(s)(0)→μ(+)μ(-) branching ratio and the resulting constraints on the new physics parameter space and give formulas for including this effect. Moreover, we point out that ΔΓ(s) provides a new observable, the effective B(s)(0)→μ(+)μ(-) lifetime τ(μ(+)μ(-)), which offers a theoretically clean probe for new physics searches that is complementary to the branching ratio. Should the B(s)(0)→μ(+)μ(-) branching ratio agree with the standard model, the measurement of τ(μ(+)μ(-)), which appears feasible at upgrades of the Large Hadron Collider experiments, may still reveal large new physics effects.