d: a forgotten null test of the standard model

• Published in: Journal of physics. G, Nuclear and particle physics Nuclear and particle physics, 2011-01, Vol.38 (1)
• Main Author: Gershon, Tim
• Format: Article
• Language: English
• ISSN: 0954-3899; 1361-6471
• DOI: 10.1088/0954-3899/38/1/015007

The recent measurement of an anomalous like-sign dimuon asymmetry by the D0 collaboration has prompted theoretical speculation on possible sources of physics beyond the Standard Model that may affect lifetimes and lifetime differences in neutral B meson systems. One observable that deserves closer attention is the width difference in the B 0 d system, ∆Γ d. Since the Standard Model prediction for this quantity is well below 1 %, it serves as a " null test " whereby the measurement of a larger value would cleanly reveal the presence of new physics. Methods to measure ∆Γ d at current and future experiments are reviewed and an attractive new approach is proposed. Recently, the D0 collaboration have measured an anomalous like-sign dimuon asymmetry [ 1, 2 ], which could originate from CP violation effects in either or both of the B 0 d - ¯ B 0 d and B 0 s - ¯ B 0 s systems. Since the Standard Model (SM) predictions for CP violation in mixing in both systems are O(10 −3) or smaller [ 3 ], a significant effect at the percent level would be a clear signal of non-SM contributions. When combined with other constraints on CP violation in B 0 d - ¯ B 0 d [ 4, 5 ] and B 0 s - ¯ B 0 s [ 6 ] mixing, it appears most likely that the effect is not solely due to either neutral meson system alone, but rather that anomalous CP violation effects may be manifest in both [ 1, 2, 7 ]. Despite the many experimental studies of the B 0 d system over the past decade, the possibility of such effects is not ruled out (see for example Ref. [ 8 ] and references therein).