Measurement of the isospin asymmetry in $B \to K^{(*)}\mu^+ \mu^-$ decays

Information

LHCb-PAPER-2012-011
CERN-PH-EP-2012-129
arXiv:1205.3422 [PDF]

(Submitted on 15 May 2012)
JHEP 07 (2012) 133
Inspire 1114752

Tools

Abstract

The isospin asymmetries of $B \to K^{(*)}\mu^+\mu^-$ decays and the partial branching fractions of $B^0 \to K^0\mu^+\mu^-$ and $B^+ \to K^{*+}\mu^+\mu^-$ are measured as a function of the di-muon mass squared $q^2$ using an integrated luminosity of 1.0 fb$^{-1}$ collected with the LHCb detector. The $B \to K\mu^+\mu^-$ isospin asymmetry integrated over $q^2$ is negative, deviating from zero with over 4 $\sigma$ significance. The $B \to K^{*}\mu^+\mu^-$ decay measurements are consistent with the Standard Model prediction of negligible isospin asymmetry. The observation of the decay $B^0 \to K^0_{\rm\scriptscriptstyle S}\mu^+\mu^-$ is reported with 5.7 $\sigma$ significance. Assuming that the branching fraction of $B^0 \to K^0\mu^+\mu^-$ is twice that of $B^0 \to K^0_{\rm\scriptscriptstyle S}\mu^+\mu^-$, the branching fractions of $B^0 \to K^0\mu^+\mu^-$ and $B \to K^{*+}\mu^+\mu^-$ are found to be ($0.31^{+0.07}_{-0.06}) \times 10^{-6}$ and ($1.16\pm0.19) \times 10^{-6}$, respectively.

Figures and captions

Mass of the di-muon versus the mass of the $ B ^+ \rightarrow K ^+ \mu ^+ \mu ^- $ candidates. Only the di-muon mass region close to the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and $\psi {(2S)}$ masses is shown. The lines show the boundaries of the regions which are removed. Regions (a)--(c) are explained in the text.	bvsjps[..].pdf [48 KiB] HiDef png [719 KiB] Thumbnail [402 KiB] *.C file
Mass distributions and fits of the signal channels integrated over the full $ q^{2}$ region. For the $ K ^0_{\rm\scriptscriptstyle S}$ channels, the plots are shown separately for the L and D $ K ^0_{\rm\scriptscriptstyle S}$ reconstruction categories, (a,b) and (c,d) respectively. The signal component is shown by the dashed line, the partially reconstructed component in 2(a) and 2(c) is shown by the dotted line while the solid line shows the entire fit model.	ksmumu_LL.pdf [19 KiB] HiDef png [236 KiB] Thumbnail [186 KiB] *.C file
	bukst_LL.pdf [18 KiB] HiDef png [202 KiB] Thumbnail [172 KiB] *.C file
	ksmumu_DD.pdf [21 KiB] HiDef png [252 KiB] Thumbnail [206 KiB] *.C file
	bukst_DD.pdf [19 KiB] HiDef png [236 KiB] Thumbnail [197 KiB] *.C file
	kmumu.pdf [21 KiB] HiDef png [234 KiB] Thumbnail [192 KiB] *.C file
	kstmumu.pdf [21 KiB] HiDef png [227 KiB] Thumbnail [182 KiB] *.C file
Efficiency of the $ K ^0_{\rm\scriptscriptstyle S}$ channels with respect to the $ K ^+$ channels for (left) $ B \rightarrow K \mu ^+ \mu ^- $ and (right) $ B \rightarrow K^{*} \mu ^+ \mu ^- $ , calculated using the simulation. The efficiencies are shown for both L and D $ K ^0_{\rm\scriptscriptstyle S}$ reconstruction categories and include the visible branching fraction of $ K ^0 \rightarrow K ^0_{\rm\scriptscriptstyle S} \rightarrow \pi ^+ \pi ^- $. The error bars are not visible as they are smaller than the marker size.	kmumu_eff.pdf [13 KiB] HiDef png [137 KiB] Thumbnail [117 KiB] *.C file
	kstmum[..].pdf [13 KiB] HiDef png [135 KiB] Thumbnail [114 KiB] *.C file
Differential branching fractions of (left) $ B ^0 \rightarrow K ^0 \mu ^+ \mu ^- $ and (right) $ B ^+ \rightarrow K^{*+} \mu ^+ \mu ^- $ . The theoretical SM predictions are taken from Refs. [23,24].	ksmumu_BF.pdf [18 KiB] HiDef png [138 KiB] Thumbnail [132 KiB] *.C file
	bukst_BF.pdf [18 KiB] HiDef png [151 KiB] Thumbnail [144 KiB] *.C file
Isospin asymmetry of (left) $ B \rightarrow K \mu ^+ \mu ^- $ and (right) $ B \rightarrow K^{} \mu ^+ \mu ^- $ . For $ B \rightarrow K^{} \mu ^+ \mu ^- $ the theoretical SM prediction, which is very close to zero, is shown for $ q^{2}$ below 8.68 $ {\mathrm{ Ge V /}c^2}$ , from Ref. [25].	kmumu_AI.pdf [14 KiB] HiDef png [68 KiB] Thumbnail [40 KiB] *.C file
	kstmumu_AI.pdf [16 KiB] HiDef png [123 KiB] Thumbnail [126 KiB] *.C file
Animated gif made out of all figures.	PAPER-2012-011.gif Thumbnail

Tables and captions

Signal yields of the $ B \rightarrow K^{()} \mu ^+ \mu ^- $ decays. The upper bound of the highest $ q^{2}$ bin, $ q^{2} _{\mathrm{max}}$, is 19.3 $ {\mathrm{ Ge V^2 /}c^4}$ and 23.0 $ {\mathrm{ Ge V^2 /}c^4}$ for $ B \rightarrow K^{} \mu ^+ \mu ^- $ and $ B \rightarrow K \mu ^+ \mu ^- $ , respectively.	Table_1.pdf [53 KiB] HiDef png [77 KiB] Thumbnail [38 KiB] tex code
Partial branching fractions of $ B ^0 \rightarrow K ^0 \mu ^+ \mu ^- $ and isospin asymmetries of $ B \rightarrow K \mu ^+ \mu ^- $ decays. The significance of the deviation of $ A_{\rm I}$ from zero is shown in the last column. The errors include the statistical and systematic uncertainties.	Table_2.pdf [53 KiB] HiDef png [63 KiB] Thumbnail [30 KiB] tex code
Partial branching fractions of $ B ^+ \rightarrow K^{+} \mu ^+ \mu ^- $ and isospin asymmetries of $ B \rightarrow K^{} \mu ^+ \mu ^- $ decays. The significance of the deviation of $ A_{\rm I}$ from zero is shown in the last column. The errors include the statistical and systematic uncertainties.	Table_3.pdf [53 KiB] HiDef png [62 KiB] Thumbnail [30 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [440 KiB]
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