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

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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]
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Diagrams.pdf

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]
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Data_Sim_massFit_Bc2D0pi_Bc2D0K.pdf

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).

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CLS_r_bc_dpi.pdf
CLS_r_[..].pdf [10 KiB]
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CLS_r_bc_dk.pdf

Animated gif made out of all figures.

 PAPER-2016-058.gif
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thumbnail_PAPER-2016-058.gif

Supplementary Material [file]

Supplementary material full pdf

 supple[..].pdf [110 KiB]
 supplementary.pdf

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.

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Fig1.pdf
Fig2.pdf [29 KiB]
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Fig2.pdf

Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.