### Speaker

Dr
Matthew Wingate
(University of Cambridge)

### Description

The width difference $\Delta \Gamma_s$ is one of three observables,
along with the mass splitting $\Delta M_s$ and the semileptonic CP
asymmetry $a^s_{\mathrm{SL}}$, whose measurements completely constrain
the physics of $B_s-\bar{B}_s$ oscillations. One of the
dominant uncertainties in theoretical calculations of the width
difference is due to not knowing matrix elements of dimension-7
operators beyond the vacuum saturation approximation. In particular,
progress requires a first-principles calculation of the matrix element of
$R_2$, a $\Delta B = 2$ operator with a derivative acting on the
strange quark field. We discuss our methodology and present
preliminary results of a calculation of $\langle B_s | R_2 |
\bar{B}_s\rangle$ using nonrelativistic $b$ quarks and highly-improved
staggered $s$ quarks on the MILC Collaboration's $n_f = 2+1+1$
configurations.

### Primary author

Dr
Matthew Wingate
(University of Cambridge)

### Co-authors

Prof.
Christine Davies
(University of Glasgow)
Dr
Christopher Monahan
(Rutgers University)
Prof.
G. Peter Lepage
(Cornell University)
Prof.
Junko Shigemitsu
(Ohio State University)