Measurement of the $C P$ asymmetry in $B^0 \to K^{*0} \mu^+ \mu^-$ decays

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A measurement of the CP asymmetry in B0 -> K*0 mu+ mu- decays is presented, based on 1.0fb-1 of pp collision data recorded by the LHCb experiment during 2011. The measurement is performed in six bins of invariant mass squared of the mu+ mu- pair, excluding the J/psi and psi(2S) resonance regions. Production and detection asymmetries are removed using the B0 -> J/Psi K*0 decay as a control mode. The integrated CP asymmetry is found to be -0.072 +- 0.040 (stat.) +- 0.005 (syst.), consistent with the Standard Model.

Figures and captions

Mass fits for $ B ^0 \rightarrow K^{*0} \mu^+ \mu^-$ decays used to extract the integrated $ C P$ asymmetry. The curves displayed are the full mass fit (blue, solid), the signal peak (red, short-dashed), and the background (grey, long-dashed). The mass fits on the top row correspond to the (a) $ B ^0$ and (b) $\overline{ B }{} ^0$ decays for one magnet polarity, while the bottom row shows the mass fits for (c) $ B ^0$ and (d) $\overline{ B }{} ^0$ for the reverse polarity.

BdToKs[..].pdf [42 KiB]
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*.C file

Fitted value of $ {\cal A}_{ C P }$ in $ B ^0 \rightarrow K^{*0} \mu^+ \mu^-$ decays in bins of the $\mu ^+\mu ^-$ invariant mass squared ( $ q^2$ ). The red vertical lines mark the charmonium vetoes. The points are plotted at the mean value of $ q^2$ in each bin. The uncertainties on each $ {\cal A}_{ C P }$ value are the statistical and systematic uncertainties added in quadrature. The dashed line corresponds to the $ q^2$ integrated value, and the grey band is the 1$\sigma$ uncertainty on this value.

ACP_Bi[..].pdf [14 KiB]
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*.C file

Animated gif made out of all figures.


Tables and captions

Systematic uncertainties on $ {\cal A}_{ C P }$ , from residual kinematic asymmetries, muon asymmetry, choice of signal model, and the modelling of the mass resolution, for each $ q^2$ bin. The total uncertainty is calculated by adding the individual uncertainties in quadrature.

Table_1.pdf [40 KiB]
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Values of $ {\cal A}_{ C P }$ for $ B ^0 \rightarrow K^{*0} \mu^+ \mu^-$ in the $ q^2$ bins used in the analysis.

Table_2.pdf [46 KiB]
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Created on 06 March 2021.