Test of lepton universality using $B^{+}\rightarrow K^{+}\ell^{+}\ell^{-}$ decays

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LHCb-PAPER-2014-024
PH-EP-2014-140
arXiv:1406.6482 [PDF]

(Submitted on 25 Jun 2014)
Phys. Rev. Lett. 113 (2014) 151601
Inspire 1303108

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Abstract

A measurement of the ratio of the branching fractions of the $B^{+}\rightarrow K^{+}\mu^{+}\mu^{-}$ and $B^{+}\rightarrow K^{+}e^{+}e^{-}$ decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded with the LHCb experiment at center-of-mass energies of 7 and 8 $\mathrm{\,Te V}$. The value of the ratio of branching fractions for the dilepton invariant mass squared range $1<q^{2}<6\mathrm{\,Ge V^2\!/}c^4$ is measured to be $0.745^{+0.090}_{-0.074}\mathrm{\,(stat)}\,\pm0.036\mathrm{\,(syst)}$. This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the SM prediction within $2.6$ standard deviations.

Figures and captions

Dilepton invariant mass squared, $ q^2$ , as a function of the $ K ^+ \ell^+ \ell^- $ invariant mass, $m( K ^+ \ell^+ \ell^- )$, for selected (a) $ B ^+ \!\rightarrow K ^+ \mu ^+\mu ^- $ and (b) $ B ^+ \!\rightarrow K ^+ e ^+ e ^- $ candidates. The radiative tail of the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and $\psi {(2S)}$ mesons is most pronounced in the electron mode due to the larger bremsstrahlung and because the energy resolution of the ECAL is lower compared to the momentum resolution of the tracking system.	Fig1a.pdf [65 KiB] HiDef png [1 MiB] Thumbnail [208 KiB] *.C file
	Fig1b.pdf [53 KiB] HiDef png [1 MiB] Thumbnail [174 KiB] *.C file
Mass distributions with fit projections overlaid of selected $ B ^+ \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\rightarrow e ^+ e ^- ) K ^+ $ candidates triggered in the hardware trigger by (a) one of the two electrons, (b) by the $ K ^+$ and (c) by other particles in the event. Mass distributions with fit projections overlaid of selected $ B ^+ \!\rightarrow K ^+ e ^+ e ^- $ candidates in the same categories, triggered by (d) one of the two electrons, (e) the $ K ^+$ and (f) by other particles in the event. The total fit model is shown in black, the combinatorial background component is indicated by the dark shaded region and the background from partially reconstructed $ b $ -hadron decays by the light shaded region.	Fig2a.pdf [17 KiB] HiDef png [146 KiB] Thumbnail [59 KiB] *.C file
	Fig2b.pdf [17 KiB] HiDef png [156 KiB] Thumbnail [63 KiB] *.C file
	Fig2c.pdf [17 KiB] HiDef png [151 KiB] Thumbnail [61 KiB] *.C file
	Fig2d.pdf [17 KiB] HiDef png [177 KiB] Thumbnail [74 KiB] *.C file
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	Fig2f.pdf [17 KiB] HiDef png [171 KiB] Thumbnail [70 KiB] *.C file
Animated gif made out of all figures.	PAPER-2014-024.gif Thumbnail

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [136 KiB]
	Fig1-S.pdf [13 KiB] HiDef png [92 KiB] Thumbnail [39 KiB] *C file
	Fig2-S.pdf [48 KiB] HiDef png [181 KiB] Thumbnail [54 KiB] *C file
	Fig3a-S.pdf [19 KiB] HiDef png [146 KiB] Thumbnail [58 KiB] *C file
	Fig3b-S.pdf [19 KiB] HiDef png [159 KiB] Thumbnail [61 KiB] *C file