# Observation of $B_{c}^{+} \rightarrow D^{0} K^{+}$ decays

[to restricted-access page]

## Abstract

Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV, the $B_{c}^{+} \rightarrow D^{0} K^{+}$ decay is observed with a statistical significance of 5.1 standard deviations. By normalising to $B^{+} \rightarrow \bar{D}^{0} \pi^{+}$ decays, a measurement of the branching fraction multiplied by the production rates for $B_{c}^{+}$ relative to $B^{+}$ mesons in the LHCb acceptance is obtained, $$R_{D^{0} K} = \frac{f_{c}}{f_{u}}\times\mathcal{B}(B_{c}^{+} \rightarrow D^{0} K^{+}) = (9.3 ^{+2.8}_{-2.5} \pm 0.6) \times 10^{-7} ,$$ where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B_{c}^{+}$ decay of this nature to be observed.

## Figures and captions

 Tree (a), penguin (b), and weak annihilation (c) diagrams for the decays studied. In each case, the meson appearing before the comma denotes the favoured decay. Diagrams.pdf [193 KiB] HiDef png [78 KiB] Thumbnail [50 KiB] *.C file Results of the simultaneous fit to the $D ^0 K ^+$ (top plot) and $D ^0 \pi ^+$ (bottom plot) invariant mass distributions in the $B _ c ^+$ mass region, including the $D ^0 \rightarrow K ^- \pi ^+$ and $D ^0 \rightarrow K ^- \pi ^+ \pi ^- \pi ^+$ final states. Inclusion of the charge conjugate decays is implied. The red solid curve illustrates $B _ c ^+ \rightarrow D ^0 K^+$ decays, the red dashed curve illustrates $B _ c ^+ \rightarrow D ^{*0} K^+$ decays, the green dashed curve represents $B _ c ^+ \rightarrow D ^{*0} \pi^+$ decays, the grey shaded region represents partially reconstructed background decays, the cyan dashed line represents the combinatorial background, and the total PDF is displayed as a blue solid line. The small drop visible in the total $B _ c ^+ \rightarrow D^{(*)0} \pi ^+$ PDF around the $B _ c ^+$ mass arises from the fact that the fit finds a small negative value for the $B _ c ^+ \rightarrow D ^0 \pi ^+$ yield. Data_S[..].pdf [19 KiB] HiDef png [326 KiB] Thumbnail [239 KiB] *.C file CL$_{\text{s}}$ $p$-value distributions for the $R_{ D ^0 h}$ observables. The dashed line represents the expected CL$_{\text{s}}$ values, where the $1\sigma$ and $2\sigma$ contours are indicated by the green (dark) and yellow (light) shaded regions, respectively. Upper limits are determined by the points at which the observed $\text{CL}_{\text{s+b}}$ $p$-values (black points connected by straight lines) fall below 5% (red solid line). Also displayed are the corresponding $\text{CL}_{\text{s}} = \text{CL}_{\text{s+b}} / \text{CL}_{\text{b}}$ values (blue points connected by straight dotted lines). CLS_r_[..].pdf [10 KiB] HiDef png [119 KiB] Thumbnail [86 KiB] *.C file CLS_r_[..].pdf [10 KiB] HiDef png [147 KiB] Thumbnail [108 KiB] *.C file Animated gif made out of all figures. PAPER-2016-058.gif Thumbnail

## Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [110 KiB] Supplementary material for LHCb-PAPER-2016-058 Contains the invariant mass fits to the B- -> (D0 -> K- π+) π- and B- -> (D0 -> K- π+ π- π+) π- modes, in Fig. 1 and Fig. 2, respectively. The normalisation yield used in this paper is taken from the sum of the signal yields measured in both of these fits. Fig1.pdf [29 KiB] HiDef png [561 KiB] Thumbnail [283 KiB] *C file Fig2.pdf [29 KiB] HiDef png [494 KiB] Thumbnail [273 KiB] *C file

Created on 18 October 2019.