Search for the lepton flavour violating decay $\tau^-\to \mu^-\mu^+\mu^-$

Information

LHCb-PAPER-2014-052
CERN-PH-EP-2014-236
arXiv:1409.8548 [PDF]

(Submitted on 30 Sep 2014)
JHEP 02 (2015) 121
Inspire 1319484

Tools

Abstract

A search for the lepton flavour violating decay $\tau^-\to \mu^-\mu^+\mu^-$ is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of $1.0\mathrm{ fb}^{-1}$ of proton-proton collisions at a centre-of-mass energy of $7\mathrm{ Te V}$ and $2.0\mathrm{ fb}^{-1}$ at $8\mathrm{ Te V}$. No evidence is found for a signal, and a limit is set at $90\%$ confidence level on the branching fraction, $\mathcal{B}(\tau^-\to \mu^-\mu^+\mu^-) < 4.6 \times 10^{-8}$.

Figures and captions

Distribution of (a) $D_s^-$ flight distance and (b) $ {\rm \mathcal{M}_{3body}}$ response for $ D_s^-\rightarrow \phi \left(\mu^+\mu^-\right) \pi^-$ candidates at 8 $\mathrm{ Te V}$ . The dashed (red) lines indicate the data and the solid (black) lines indicate the simulation. The data is background-subtracted using the sPlot technique [29].	dataMC_FD.pdf [14 KiB] HiDef png [148 KiB] Thumbnail [146 KiB] *.C file
	dataMC.pdf [14 KiB] HiDef png [149 KiB] Thumbnail [148 KiB] *.C file
Distribution of (a) $ {\rm \mathcal{M}_{3body}}$ and (b) $ {\rm \mathcal{M}_{PID}}$ response for 7 $\mathrm{ Te V}$ data and (c) $ {\rm \mathcal{M}_{3body}}$ and (d) $ {\rm \mathcal{M}_{PID}}$ response for 8 $\mathrm{ Te V}$ data. The binnings correspond to those used in the extraction of the final results. The short-dashed (red) lines show the response of the data sidebands, whilst the long-dashed (blue) and solid (black) lines show the response of simulated signal events before and after calibration. In all cases the first bin is excluded from the analysis.	m3body[..].pdf [13 KiB] HiDef png [152 KiB] Thumbnail [144 KiB] *.C file
	mPID_2[..].pdf [13 KiB] HiDef png [147 KiB] Thumbnail [142 KiB] *.C file
	m3body[..].pdf [14 KiB] HiDef png [149 KiB] Thumbnail [145 KiB] *.C file
	mPID_2[..].pdf [14 KiB] HiDef png [148 KiB] Thumbnail [144 KiB] *.C file
Invariant mass distribution of $\phi(\mu^+\mu^-)\pi^-$ candidates in 8 $\mathrm{ Te V}$ data. The solid (blue) line shows the overall fit, the long-dashed (green) and short-dashed (red) lines show the two Gaussian components of the $D^-_s$ signal and the dot-dashed (black) line shows the combinatorial background contribution.	Ds_dat[..].pdf [26 KiB] HiDef png [225 KiB] Thumbnail [188 KiB] *.C file
Invariant mass distributions and fits to the mass sidebands in (a) 7 $\mathrm{ Te V}$ and (b) 8 $\mathrm{ Te V}$ data for $\mu^+\mu^-\mu^-$ candidates in the bins of $ {\rm \mathcal{M}_{3body}}$ and $ {\rm \mathcal{M}_{PID}}$ response that contain the highest signal probabilities.	Bkg2011.pdf [17 KiB] HiDef png [150 KiB] Thumbnail [134 KiB] *.C file
	Bkg2012.pdf [17 KiB] HiDef png [143 KiB] Thumbnail [122 KiB] *.C file
Distribution of $\textrm{CL}_{\textrm{s}}$ values as a function of the assumed branching fraction for $\tau^-\rightarrow \mu^-\mu^+\mu^-$ , under the hypothesis to observe background events only. The dashed line indicates the expected limit and the solid line the observed one. The light (yellow) and dark (green) bands cover the regions of 68% and 95% confidence for the expected limit.	bananaB.pdf [21 KiB] HiDef png [170 KiB] Thumbnail [135 KiB] *.C file
Animated gif made out of all figures.	PAPER-2014-052.gif Thumbnail

Tables and captions

Terms entering into the normalisation factors, $\alpha$, and their combined statistical and systematic uncertainties.	Table_1.pdf [60 KiB] HiDef png [59 KiB] Thumbnail [27 KiB] tex code
Expected background candidate yields in the 7 $\mathrm{ Te V}$ data set, with their uncertainties, and observed candidate yields within the $\tau^-$ signal window in the different bins of classifier response. The classifier responses range from $0$ (most background-like) to $+1$ (most signal-like). The first bin in each classifier response is excluded from the analysis.	Table_2.pdf [30 KiB] HiDef png [206 KiB] Thumbnail [100 KiB] tex code
Expected background candidate yields in the 8 $\mathrm{ Te V}$ data set, with their uncertainties, and observed candidate yields within the $\tau^-$ signal window in the different bins of classifier response. The classifier responses range from $0$ (most background-like) to $+1$ (most signal-like). The first bin in each classifier response is excluded from the analysis.	Table_3.pdf [30 KiB] HiDef png [226 KiB] Thumbnail [112 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [272 KiB]
This zip file contains supplementary material for the publication LHCb-PAPER-2014-052. The files included are: Supplementary.pdf: The appendix from the paper, including the figures with captions and some brief explanation. pdf, eps, png, C: The figures	Fig1.pdf [26 KiB] HiDef png [212 KiB] Thumbnail [176 KiB] *C file
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