Measurement of the $B^{\pm }$ production asymmetry and the $CP$ asymmetry in $B^{\pm }\to J\mathrm{/}\psi K^{\pm }$ decays

The $B^{\pm }$ meson production asymmetry in $pp$ collisions is measured using $B^{+}\to {\bar{D}}^0{\pi }^{+}$ decays. The data were recorded by the LHCb experiment during Run 1 of the LHC at centre-of-mass energies of $\sqrt{s}=$ 7 and 8 TeV. The production asymmetries, integrated over transverse momenta in the range $2 < p_{\rm T} < 30$GeV\mathrm{/}$c$,andrapiditiesintherange$2.1 < y < 4.5$, are measured to be \begin{align*} $\mathcal{A}${\rm prod}(B^+,\sqrt{s}=7~{\rm TeV}) &= (-0.41 \pm 0.49 \pm 0.10) \times 10^{-2},\ $\mathcal{A}${\rm prod}(B^+,\sqrt{s}=8~{\rm TeV}) &= (-0.53 \pm 0.31 \pm 0.10) \times 10^{-2}, \end{align*} where the first uncertainties are statistical and the second are systematic. These production asymmetries are used to correct the raw asymmetries of $B^{+}\to J\mathrm{/}\psi K^{+}$ decays, thus allowing a measurement of the $CP$ asymmetry, \begin{equation*} $\mathcal{A}$_{CP} = (0.09 \pm 0.27 \pm 0.07) \times 10^{-2}. \end{equation*}