Measurement of the time-dependent $CP$ asymmetry in $B^0 \to J/\psi K^0_{\rm S}$ decays

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This Letter reports a measurement of the CP violation observables S_J/{\psi}KS0 and C_J/{\psi}KS0 in the decay channel B0 -> J/{\psi} KS0 performed with 1.0/fb of pp collisions at sqrt(s) = 7 TeV collected by the LHCb experiment. The fit to the data yields S_J/{\psi}KS0 = 0.73 +- 0.07 (stat) +- 0.04 (syst) and C_J/{\psi}KS0 = 0.03 +- 0.09 (stat) +- 0.01 (syst). Both values are consistent with the current world averages and within expectations from the Standard Model.

Figures and captions

Invariant mass (left) and decay time (right) distributions of the $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^0_{\rm\scriptscriptstyle S} $ candidates. The solid line shows the projection of the full PDF and the shaded area the projection of the background component.

figs_P[..].pdf [18 KiB]
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figs_P[..].pdf [18 KiB]
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Time-dependent asymmetry $(N_{\overline{ B }{} ^0 }-N_{ B ^0 })/(N_{\overline{ B }{} ^0 }+N_{ B ^0 })$. Here, $N_{ B ^0 }$ ($N_{\overline{ B }{} ^0 }$) is the number of $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^0_{\rm\scriptscriptstyle S} $ decays with a $ B ^0$ ( $\overline{ B }{} ^0$ ) flavour tag. The data points are obtained with the sPlot technique, assigning signal weights to the events based on a fit to the reconstructed mass distributions. The solid curve is the signal projection of the PDF. The green shaded band corresponds to the one standard deviation statistical error.

figs_A[..].pdf [16 KiB]
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Animated gif made out of all figures.


Tables and captions

Summary of systematic uncertainties on the $ C P$ parameters.

Table_1.pdf [51 KiB]
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tex code

Created on 06 March 2021.