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First evidence of direct $C P$ violation in charmless two-body decays of $B^0_s$ mesons

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Abstract

Using a data sample corresponding to an integrated luminosity of 0.35 $\mathrm{fb}^{-1}$ collected by LHCb in 2011, we report the first evidence of CP violation in the decays of $B^0_s$ mesons to $K^\pm \pi^\mp$ pairs, $A_{CP}(B^0_s \rightarrow K \pi)=0.27 \pm 0.08 \mathrm{(stat)} \pm 0.02 \mathrm{(syst)}$, with a significance of 3.3$\sigma$. Furthermore, we report the first observation of CP violation in $B^0$ decays at a hadron collider, $A_{CP}(B^0 \rightarrow K\pi)=-0.088 \pm 0.011 \mathrm{(stat)} \pm 0.008 \mathrm{(syst)}$, with a significance exceeding 6$\sigma$.

Figures and captions

Invariant $K\pi$ mass spectra obtained using the event selection adopted for the best sensitivity on (a, b) $A_{C P}(B^0 \rightarrow K\pi)$ and (c, d) $A_{C P}(B^0_s \rightarrow K\pi)$. Plots (a) and (c) represent the $K^+\pi^-$ invariant mass whereas plots (b) and (d) represent the $K^-\pi^+$ invariant mass. The results of the unbinned maximum likelihood fits are overlaid. The main components contributing to the fit model are also shown.

 ckpi_b[..].pdf [138 KiB]
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ckpi_bd2kpi.pdf
cpik_b[..].pdf [170 KiB]
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cpik_bd2kpi.pdf
ckpi_b[..].pdf [136 KiB]
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ckpi_bs2pik.pdf
cpik_b[..].pdf [135 KiB]
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cpik_bs2pik.pdf

Distributions of the invariant mass or invariant mass difference of (a) $D^{0}\rightarrow K^{-}\pi^{+}$, (b) $D^{*+}\rightarrow D^{0}(K^{-}\pi^{+})\pi^{+}$, (c) $D^{*+}\rightarrow D^{0}(K^{-}K^{+})\pi^{+}$ and (d) $B^{0}\rightarrow J/\psi(\mu^+\mu^-) K^{*0}(K^+\pi^-)$. The results of the maximum likelihood fits are overlaid.

 d02kpi.pdf [125 KiB]
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d02kpi.pdf
dstard[..].pdf [122 KiB]
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dstard02kpi.pdf
dstarD02kk.pdf [127 KiB]
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dstarD02kk.pdf
B02jps[..].pdf [121 KiB]
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B02jpsiKstar.pdf

Animated gif made out of all figures.

 PAPER-2011-029.gif
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Tables and captions

Summary of selection criteria adopted for the measurement of $A_{C P}(B^0 \rightarrow K\pi)$ and $A_{C P}(B^0_s \rightarrow K \pi)$.

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Summary of systematic uncertainties on $A_{C P}(B^0 \rightarrow K \pi)$ and $A_{C P}(B^0_s \rightarrow K\pi)$. The categories (a), (b) and (c) defined in the text are also indicated. The total systematic uncertainties given in the last row are obtained by summing the individual contributions in quadrature.

 Table_2.pdf [48 KiB]
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Created on 27 April 2024.