Direct and mixing-induced CP-violating asymmetries in Bs -> K+K- decays are measured for the first time using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0 fb^{-1}, collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The results are C_{KK} = 0.14 \pm 0.11 \pm 0.03 and S_{KK} = 0.30 \pm 0.12 \pm 0.04, where the first uncertainties are statistical and the second systematic. The corresponding quantities are also determined for B0 -> pi+pi- decays to be C_{pipi} = -0.38 \pm 0.15 \pm 0.02 and S_{pipi} = -0.71 \pm 0.13 \pm 0.02, in good agreement with existing measurements.
Fits to the (a) $\pi^+\pi^-$ and (b) $K^+K^-$ invariant mass spectra, after applying preselection and PID requirements. The components contributing to the fit model are shown. |
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Decay time distributions corresponding to (a, b, c) high- and (d, e, f) low-mass sidebands from the (a and d) $K^\pm\pi^\mp$, (b and e) $\pi^+\pi^-$ and (c and f) $K^+K^-$ mass spectra, with the results of fits superimposed. In the bottom plots, the combinatorial background component (dashed) and the three-body background component (dotted) are shown. |
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Distributions of $K^\pm\pi^\mp$ (a) mass and (b) decay time, with the result of the fit overlaid. The main components contributing to the fit model are also shown. |
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Raw mixing asymmetries for candidates in the $ B ^0 \rightarrow K ^+ \pi ^- $ signal mass region, corresponding to the five tagging categories, with the result of the fit overlaid. |
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Distributions of $K^+K^-$ (a) mass and (b) decay time, with the result of the fit overlaid. The main components contributing to the fit model are also shown. |
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Time-dependent raw asymmetry for candidates in the $ B ^0_ s \rightarrow K ^+ K ^- $ signal mass region with the result of the fit overlaid. In order to enhance the visibility of the oscillation, only candidates belonging to the first two tagging categories are used. The offset $t_0 = 0.6$ $ {\rm ps}$ corresponds to the preselection requirement on the decay time. |
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Distributions of $\pi^+\pi^-$ (a) mass and (b) decay time, with the result of the fit overlaid. The main components contributing to the fit model are also shown. |
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Time-dependent raw asymmetry for candidates in the $ B ^0 \rightarrow \pi ^+ \pi ^- $ signal mass region with the result of the fit overlaid. Tagged candidates belonging to all tagging categories are used. |
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Animated gif made out of all figures. |
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Kinematic requirements applied by the event preselection. |
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Definition of the five tagging categories determined from the optimization algorithm, in terms of ranges of the mistag probability $\eta$. |
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Signal tagging efficiencies, mistag probabilities and associated asymmetries, corresponding to the five tagging categories, as determined from the $K^\pm\pi^\mp$ mass and decay time fit. The uncertainties are statististical only. |
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Systematic uncertainties affecting the $B^0_s \rightarrow K^+K^-$ and $B^0 \rightarrow \pi^+\pi^-$ direct and mixing-induced $ C P$ asymmetry coefficients. The total systematic uncertainties are obtained by summing the individual contributions in quadrature. |
Table_4.pdf [36 KiB] HiDef png [130 KiB] Thumbnail [56 KiB] tex code |
Created on 27 April 2024.