# Observation of $C P$ violation in $B^\pm \to D K^\pm$ decays

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## Abstract

An analysis of B+ to DK+ and B+ to Dpi+ decays is presented where the D meson is reconstructed in the two-body final states: K+pi-, K+K-, pi+pi- and pi+K-. Using 1.0 fb-1 of LHCb data, measurements of several observables are made including the first observation of the suppressed mode B+ to DK+, D to pi+K-. CP violation in B+ to DK+ decays is observed with 5.8 sigma significance.

## Figures and captions

 Invariant mass distributions of selected $B ^\pm \rightarrow [ K ^\pm \pi^{\mp}]_Dh^{\pm}$ candidates. The left plots are $B ^-$ candidates, $B ^+$ are on the right. In the top plots, the bachelor track passes the ${\rm DLL}_{K\pi}>4$ cut and the $B$ candidates are reconstructed assigning this track the kaon mass. The remaining events are placed in the sample displayed on the bottom row and are reconstructed with a pion mass hypothesis. The dark (red) curve represents the $B \rightarrow D K ^\pm$ events, the light (green) curve is $B \rightarrow D\pi ^\pm$. The shaded contribution are partially reconstructed events and the total PDF includes the combinatorial component. Fig1.eps [63 KiB] HiDef png [298 KiB] Thumbnail [166 KiB] *.C file Invariant mass distributions of selected $B ^\pm \rightarrow [ K ^+ K ^- ]_Dh^{\pm}$ candidates. See the caption of Fig. 1 for a full description. The contribution from $\Lambda_b\rightarrow \Lambda_c^{\pm} h^{\mp}$ decays is indicated by the dashed line. Fig2.eps [66 KiB] HiDef png [353 KiB] Thumbnail [198 KiB] *.C file Invariant mass distributions of selected $B ^\pm \rightarrow [\pi ^+ \pi ^- ]_Dh^{\pm}$ candidates. See the caption of Fig. 1 for a full description. Fig3.eps [59 KiB] HiDef png [302 KiB] Thumbnail [182 KiB] *.C file Invariant mass distributions of selected $B ^\pm \rightarrow [\pi ^\pm K^{\mp}]_Dh^{\pm}$ candidates. See the caption of Fig. 1 for a full description. The dashed line here represents the partially reconstructed, but Cabibbo favoured, $B ^0_ s \rightarrow \overline{ D }{} ^0 K ^- \pi ^+$ and $\overline{ B }{} ^0_ s \rightarrow D ^0 K ^+ \pi ^-$ decays where the pions are lost. The pollution from favoured mode cross feed is drawn, but is too small to be seen. Fig4.eps [59 KiB] HiDef png [368 KiB] Thumbnail [229 KiB] *.C file Animated gif made out of all figures. PAPER-2012-001.gif Thumbnail

## Tables and captions

 Corrected event yields. Table_1.pdf [41 KiB] HiDef png [98 KiB] Thumbnail [49 KiB] tex code Systematic uncertainties on the observables. PID refers to the fixed efficiency of the ${\rm DLL}_{K\pi}$ cut on the bachelor track. PDFs refers to the variations of the fixed shapes in the fit. "Sim" refers to the use of simulation to estimate relative efficiencies of the signal modes which includes the branching fraction estimates of the $\Lambda_b^0$ background. $A_{\rm instr.}$ quantifies the uncertainty on the production, interaction and detection asymmetries. Table_2.pdf [51 KiB] HiDef png [160 KiB] Thumbnail [75 KiB] tex code

Created on 18 October 2019.