Measurement of the $B_c^{-}$ meson production fraction and asymmetry in 7 and 13 TeV $pp$ collisions

The production fraction of the $B_c^{-}$ meson with respect to the sum of $B^{-}$ and ${\overline{B}}^0$ mesons is measured in both 7 and 13 TeV center-of-mass (c.m.) energy $pp$ collisions produced by the Large Hadron Collider (LHC), using the LHCb detector. The rate, approximately 3.7 per mille, does not change with energy, but shows a transverse momentum dependence. The $B_c^{-}-B_c^{+}$ production asymmetry is also measured and is consistent with zero within the determined statistical and systematic uncertainties of a few percent.

Figure 1

Distributions of corrected mass $m_{\mathrm{cor}}$ and $m(J/\psi {\mu }^{-})$ for (top) 7 TeV and (bottom) 13 TeV data, where (a) and (c) are data and (b) and (d) simulated signal. The (red) dashed line indicates the $m(J/\psi {\mu }^{-})>4.5\mathrm{GeV}$ requirement.

Figure 2

Fitted $m_{\mathrm{cor}}$ distributions in (a) 7 TeV and (b) 13 TeV samples. The signal and the backgrounds are shown as the dark (orange) and lighter (gray) areas. The dashed (cyan) curves show the $B_c^{-}\to J/\psi {\tau }^{-}{\nu }_{\tau }$ components, while the dotted (blue) curves show the $B_c^{-}\to {\chi }_{c0,1,2}{\mu }^{-}\overline{\nu }$ components. The $B_c^{-}\to \psi (2S){\mu }^{-}\overline{\nu }$ contribution is also in the fit but is too small to be seen. The total fit is shown by the solid (red) curve.

Figure 3

The total efficiency for $B_c^{-}\to J/\psi {\mu }^{-}\overline{\nu }$, as a function of $p_{\mathrm{T}}(B_c^{-})$ in different intervals of $\eta$ in (a) 7 TeV and (b) 13 TeV samples.

Figure 4

Invariant-mass distributions of (a) $K^{-}{\pi }^{+}$ and (b) $K^{-}{\pi }^{+}{\pi }^{+}$ for 7 TeV, and (c) and (d) for 13 TeV collisions. The data are shown by solid points. The (red) dashed lines represent the signal components. The combinatorial backgrounds are shown as the dotted (magenta) line, and the solid (blue) line shows the total fit.

Figure 5

Total efficiencies for the (a) $D^{0}X{\mu }^{-}\overline{\nu }$ and (b) $D^{+}X{\mu }^{-}\overline{\nu }$ signals in 7 TeV and (c) and (d) 13 TeV samples as functions of $p_{\mathrm{T}}$ in $\eta$ intervals.

Figure 6

The $k$-factor corrections as a function of invariant mass of (a) $m(J/\psi {\mu }^{-})$, (b) $m(D^0{\mu }^{-})$, and (c) $m(D^{+}{\mu }^{-})$ for the 13 TeV simulation samples. (The 7 TeV results are almost identical.) The points (magenta) are the average $k$-factor corrections, and the (green) dashed line shows a second-order polynomial fit to the average data.

Figure 7

Ratio of production fractions after the $k$-factor correction as a function of (a) $p_{\mathrm{T}}(H_b)$ and (c) $\eta$ in 7 TeV data and (b) and (d) in 13 TeV data. The smaller error bars show the statistical uncertainties, and the larger ones include the statistical and systematic uncertainties. The horizontal (green) dashed-lines show the average values.

Figure 8

Ratio of the $B_c^{-}$ production fractions at 13–7 TeV as a function of (a) $p_{\mathrm{T}}(H_b)$ and (b) $\eta$. The smaller error bars show the statistical uncertainties, and the larger ones include the statistical and systematic uncertainties added in quadrature.