First Evidence for the Decay $B^0_s \to \mu^+\mu^-$

Information

LHCb-PAPER-2012-043
CERN-PH-EP-2012-335
arXiv:1211.2674 [PDF]

(Submitted on 12 Nov 2012)
Phys. Rev. Lett. 110 (2013) 021801
Inspire 1202279

Tools

Abstract

A search for the rare decays Bs->mu+mu- and B0->mu+mu- is performed using data collected in 2011 and 2012 with the LHCb experiment at the Large Hadron Collider. The data samples comprise 1.1 fb^-1 of proton-proton collisions at sqrt{s} = 8 TeV and 1.0 fb^-1 at sqrt{s}=7 TeV. We observe an excess of Bs -> mu+ mu- candidates with respect to the background expectation. The probability that the background could produce such an excess or larger is 5.3 x 10^-4 corresponding to a signal significance of 3.5 standard deviations. A maximum-likelihood fit gives a branching fraction of BR(Bs -> mu+ mu-) = (3.2^{+1.5}_{-1.2}) x 10^-9, where the statistical uncertainty is 95 of the total uncertainty. This result is in agreement with the Standard Model expectation. The observed number of B0 -> mu+ mu- candidates is consistent with the background expectation, giving an upper limit of BR(B0 -> mu+ mu-) < 9.4 x 10^-10 at 95 confidence level.

Figures and captions

$\textrm{CL}_{\textrm{s}}$ as a function of the assumed $ B^0\to\mu^+\mu^-$ branching fraction for the combined 2011+2012 dataset. The dashed gray curve is the median of the expected $\textrm{CL}_{\textrm{s}}$ distribution if background and SM signal were observed. The shaded yellow area covers, for each branching fraction value, 34 % of the expected $\textrm{CL}_{\textrm{s}}$ distribution on each side of its median. The solid red curve is the observed $\textrm{CL}_{\textrm{s}}$ .	Fig1.pdf [14 KiB] HiDef png [192 KiB] Thumbnail [150 KiB]
Invariant mass distribution of the selected $ B^0_s \to\mu^+\mu^-$ candidates (black dots) with ${\rm BDT}>0.7$ in the combined 2011+2012 dataset. The result of the fit is overlaid (blue solid line) and the different components detailed: $ B^0_s \to\mu^+\mu^-$ (red long dashed), $ B^0\to\mu^+\mu^-$ (green medium dashed), $ B^0_{(s)}\to h^+{h}^{\prime -}$ (pink dotted), $ B^0\to \pi^- \mu^+ \nu_\mu$ (black short dashed) and $ B^{0(+)} \to \pi^{0(+)} \mu^+ \mu^-$ (light blue dot dashed), and the combinatorial background (blue medium dashed).	Fig2.pdf [49 KiB] HiDef png [227 KiB] Thumbnail [180 KiB]
Animated gif made out of all figures.	PAPER-2012-043.gif Thumbnail

Tables and captions

Expected and observed limits on the $ B^0\to\mu^+\mu^-$ branching fractions for the 2012 and for the combined 2011+2012 datasets.	Table_1.pdf [45 KiB] HiDef png [68 KiB] Thumbnail [33 KiB] tex code
Expected combinatorial background, $ B^0_{(s)}\to h^+{h}^{\prime -}$ peaking background, cross-feed, and signal events assuming the SM prediction, together with the number of observed candidates in the $ B^0_s \to\mu^+\mu^-$ and $ B^0\to\mu^+\mu^-$ mass signal regions, in bins of BDT for the 2011 (top) and for the 2012 (bottom) data samples. The quoted errors include statistical and systematic uncertainties.	Table_2.pdf [56 KiB] HiDef png [186 KiB] Thumbnail [74 KiB] tex code

Supplementary Material [file]

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2012-043. The files are: Bsmm2012_additional.pdf: synthetic description of the Bsmm analysis, containing also all the blessed plots with the needed caption. All figures availables in various formats (.pdf, .png, .eps) when available; the numbering refers to the one used in the Bsmm2012_supporting.pdf file. Two more figures (.pdf only) with cartoon for a Bsmm and a combinatorial background events	Bsmm20[..].pdf [9 MiB] HiDef png [122 KiB] Thumbnail [53 KiB] *C file
	Bsmm_b[..].pdf [19 KiB] HiDef png [238 KiB] Thumbnail [147 KiB] *C file
	Bsmm_s[..].pdf [18 KiB] HiDef png [180 KiB] Thumbnail [109 KiB] *C file
	Fig1.pdf [14 KiB] HiDef png [112 KiB] Thumbnail [115 KiB] *C file
	Fig10a.pdf [4 MiB] HiDef png [406 KiB] Thumbnail [212 KiB] *C file
	Fig10a_W.pdf [1 MiB] HiDef png [417 KiB] Thumbnail [279 KiB] *C file
	Fig10b.pdf [4 MiB] HiDef png [415 KiB] Thumbnail [215 KiB] *C file
	Fig10b_W.pdf [853 KiB] HiDef png [430 KiB] Thumbnail [289 KiB] *C file
	Fig10c.pdf [47 KiB] HiDef png [86 KiB] Thumbnail [112 KiB] *C file
	Fig11.pdf [15 KiB] HiDef png [115 KiB] Thumbnail [101 KiB] *C file
	Fig11a.pdf [14 KiB] HiDef png [225 KiB] Thumbnail [165 KiB] *C file
	Fig11b.pdf [14 KiB] HiDef png [192 KiB] Thumbnail [150 KiB] *C file
	Fig12a.pdf [53 KiB] HiDef png [429 KiB] Thumbnail [317 KiB] *C file
	Fig12b.pdf [47 KiB] HiDef png [377 KiB] Thumbnail [279 KiB] *C file
	Fig12c.pdf [47 KiB] HiDef png [86 KiB] Thumbnail [112 KiB] *C file
	Fig12d.pdf [50 KiB] HiDef png [117 KiB] Thumbnail [140 KiB] *C file
	Fig13.pdf [15 KiB] HiDef png [115 KiB] Thumbnail [101 KiB] *C file
	Fig14.pdf [31 KiB] HiDef png [170 KiB] Thumbnail [113 KiB] *C file
	Fig14a.pdf [49 KiB] HiDef png [231 KiB] Thumbnail [187 KiB] *C file
	Fig14b.pdf [49 KiB] HiDef png [227 KiB] Thumbnail [180 KiB] *C file
	Fig14c.pdf [49 KiB] HiDef png [236 KiB] Thumbnail [189 KiB] *C file
	Fig14d.pdf [50 KiB] HiDef png [117 KiB] Thumbnail [140 KiB] *C file
	Fig16.pdf [31 KiB] HiDef png [170 KiB] Thumbnail [113 KiB] *C file
	Fig1a.pdf [10 KiB] HiDef png [157 KiB] Thumbnail [153 KiB] *C file
	Fig1b.pdf [10 KiB] HiDef png [166 KiB] Thumbnail [160 KiB] *C file
	Fig1c.pdf [10 KiB] HiDef png [136 KiB] Thumbnail [138 KiB] *C file
	Fig1d.pdf [10 KiB] HiDef png [148 KiB] Thumbnail [148 KiB] *C file
	Fig2.pdf [14 KiB] HiDef png [112 KiB] Thumbnail [115 KiB] *C file
	Fig2a.pdf [25 KiB] HiDef png [272 KiB] Thumbnail [203 KiB] *C file
	Fig2b.pdf [25 KiB] HiDef png [277 KiB] Thumbnail [202 KiB] *C file
	Fig2c.pdf [25 KiB] HiDef png [275 KiB] Thumbnail [192 KiB] *C file
	Fig3a.pdf [25 KiB] HiDef png [272 KiB] Thumbnail [203 KiB] *C file
	Fig3b.pdf [25 KiB] HiDef png [277 KiB] Thumbnail [202 KiB] *C file
	Fig3c.pdf [25 KiB] HiDef png [275 KiB] Thumbnail [192 KiB] *C file
	Fig4.pdf [27 KiB] HiDef png [160 KiB] Thumbnail [102 KiB] *C file
	Fig4a.pdf [28 KiB] HiDef png [306 KiB] Thumbnail [231 KiB] *C file
	Fig4b.pdf [30 KiB] HiDef png [266 KiB] Thumbnail [196 KiB] *C file
	Fig5.pdf [27 KiB] HiDef png [160 KiB] Thumbnail [102 KiB] *C file
	Fig5a.pdf [45 KiB] HiDef png [451 KiB] Thumbnail [318 KiB] *C file
	Fig5b.pdf [47 KiB] HiDef png [62 KiB] Thumbnail [88 KiB] *C file
	Fig6.pdf [49 KiB] HiDef png [518 KiB] Thumbnail [360 KiB] *C file
	Fig6a.pdf [14 KiB] HiDef png [140 KiB] Thumbnail [133 KiB] *C file
	Fig6b.pdf [15 KiB] HiDef png [147 KiB] Thumbnail [139 KiB] *C file
	Fig7a.pdf [45 KiB] HiDef png [451 KiB] Thumbnail [318 KiB] *C file
	Fig7b.pdf [47 KiB] HiDef png [62 KiB] Thumbnail [88 KiB] *C file
	Fig8.pdf [49 KiB] HiDef png [518 KiB] Thumbnail [360 KiB] *C file
	Fig8a.pdf [4 MiB] HiDef png [406 KiB] Thumbnail [212 KiB] *C file
	Fig8a_W.pdf [1 MiB] HiDef png [417 KiB] Thumbnail [279 KiB] *C file
	Fig8b.pdf [4 MiB] HiDef png [416 KiB] Thumbnail [212 KiB] *C file
	Fig8b_W.pdf [853 KiB] HiDef png [430 KiB] Thumbnail [290 KiB] *C file
	Fig9a.pdf [26 KiB] HiDef png [159 KiB] Thumbnail [142 KiB] *C file
	Fig9b.pdf [23 KiB] HiDef png [210 KiB] Thumbnail [169 KiB] *C file