A measurement of the CP asymmetry in B0 > K*0 mu+ mu decays is presented, based on 1.0fb1 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.
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, shortdashed), and the background (grey, longdashed). 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. 
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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] HiDef png [115 KiB] Thumbnail [106 KiB] *.C file 

Animated gif made out of all figures. 
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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. 
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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] HiDef png [90 KiB] Thumbnail [42 KiB] tex code 
Created on 11 July 2020.