Measuring Semileptonic Asymmetries in LHCb

TL;DR

This paper reports the most precise measurements to date of semileptonic asymmetries in neutral B mesons from LHCb, testing the Standard Model and discussing future improvements with full dataset analysis.

Contribution

LHCb presents new measurements of $a_{sl}^d$ and $a_{sl}^s$ with improved precision, including plans for analysis with the full dataset and enhanced systematic control.

Findings

Measured $a_{sl}^s$ as (-0.06 ± 0.50 (stat) ± 0.36 (syst))%.

Measured $a_{sl}^d$ as (-0.02 ± 0.19 (stat) ± 0.30 (syst))%.

Most precise parameters $a_{sl}^s$ and $a_{sl}^d$ to date.

Abstract

The $C\!P$-violating flavour-specific asymmetry in neutral $b$ mesons provides a method for testing the Standard Model. The measurements from the D0 experiment yield values of this asymmetry that disagree with the Standard Model at a level of 3.6 $\sigma$. This contribution discusses the latest LHCb measurements in this sector both from $B^0$ mesons ($a_{\mathrm{sl}}^d$) and $B^0_s$ mesons ($a_{\mathrm{sl}}^s$). Using their 2011 dataset, corresponding to an integrated luminosity of 1.0 $\mathrm{fb}^{-1}$ obtained in 2011, LHCb measured a value of $a_{\mathrm{sl}}^s = (-0.06 \pm 0.50_{\text{stat}} \pm 0.36_{\text{syst}}) \%$. Combining the 2011 and 2012 datasets, with an integrated luminosity of 3 $\mathrm{fb}^{-1}$, LHCb measured $a_{\mathrm{sl}}^d = (-0.02 \pm 0.19_{\text{stat}} \pm 0.30_{\text{syst}}) \%$. These are the most precise measurements of the parameters $a_{\mathrm{sl}}^s$ and $a_{\mathrm{sl}}^d$ to date. Plans for an updated result for $a_{\mathrm{sl}}^s$ using the full 3 $\mathrm{fb}^{-1}$ dataset are discussed. This will include new methods to determine detection asymmetries which are the dominating systematic uncertainty of the 2011 measurement.