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

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Abstract

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] HiDef png [187 KiB] Thumbnail [188 KiB] *.C file figs_P[..].pdf [18 KiB] HiDef png [200 KiB] Thumbnail [208 KiB] *.C file 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] HiDef png [226 KiB] Thumbnail [159 KiB] *.C file Animated gif made out of all figures. PAPER-2012-035.gif Thumbnail

Tables and captions

 Summary of systematic uncertainties on the $C P$ parameters. Table_1.pdf [51 KiB] HiDef png [100 KiB] Thumbnail [48 KiB] tex code

Created on 18 January 2020.