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Search for $D^{+}_{(s)} \rightarrow \pi^{+} \mu^{+} \mu^{-}$ and $D^{+}_{(s)} \rightarrow \pi^{-} \mu^{+} \mu^{+}$ decays

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Abstract

A search for non-resonant D+(s) to pi+mu+mu- and D+(s) to pi-mu+mu+ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb-1, at sqrt(s) = 7 TeV recorded by the LHCb experiment in 2011. No signals are observed and the 90% (95%) confidence level (CL) limits on the branching fractions are B(D+ to pi+mu+mu-) < 7.3 (8.3) x 10-8, B(Ds+ to pi+mu+mu-) < 4.1 (4.8) x 10-7, B(D+ to pi-mu+mu+) < 2.2 (2.5) x 10-8, B(Ds+ to pi-mu+mu+) < 1.2 (1.4) x 10-7. These limits are the most stringent to date.

Figures and captions

Feynman diagrams for (a,b) the FCNC decay $ D ^+ \!\rightarrow \pi ^+ \mu ^+\mu ^- $ , (c) the weak annihilation of a $ D ^+ _{( s )}$ meson and (d) a possible LNV $ D ^+ _{( s )}$ meson decay mediated by a Majorana neutrino.

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Invariant mass distributions for $ D ^+ _{( s )} \!\rightarrow \pi ^+ \mu ^+\mu ^- $ candidates in the five $m(\mu ^+\mu ^- )$ bins. Shown are the (a) low- $ m(\mu ^+\mu ^- )$ , (b) $\eta$ , (c) $\rho$ / $\omega$ , (d) $\phi$ (including trigger lines with $ m(\mu ^+\mu ^- ) >1.0 {\mathrm{\,GeV\!/}c^2} $), and (e) high- $ m(\mu ^+\mu ^- )$ regions. The data are shown as points (black) and the total PDF (dark blue line) is overlaid. The components of the fit are also shown: the signal (light green line), the peaking background (solid area) and the non-peaking background (dashed line).

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Invariant mass distributions for $ D ^+ _{( s )} \!\rightarrow \pi ^- \mu ^+ \mu ^+ $ in the four $m(\pi ^- \mu ^+ )$ regions. Shown are (a) bin 1, (b) bin 2, (c) bin 3, and (d) bin 4. The data are shown as black points and the total PDF (dark blue line) is overlaid. The components of the fit are also shown: the signal (light green line), the peaking background (solid area) and the non-peaking background (dashed line).

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Background-subtracted m( $\mu ^+\mu ^-$ ) spectrum of (a) $ D ^+ \!\rightarrow \pi ^+ \mu ^+\mu ^- $ and (b) $ D ^+_ s \!\rightarrow \pi ^+ \mu ^+\mu ^- $ candidates that pass the final selection. The inset shows the $\phi$ contribution, and the main figure shows the $\eta$ and the $\rho$ / $\omega$ contributions. The non-peaking structure of the low and high- $ m(\mu ^+\mu ^- )$ regions is also visible.

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Observed (solid curve) and expected (dashed curve) $\mathrm{CL}_{s}$ values as a function of $\cal B$ ( $ D ^+ \!\rightarrow \pi ^+ \mu ^+\mu ^- $ ). The green (yellow) shaded area contains the $\pm1\sigma$ ($\pm2\sigma$) interval of possible results compatible with the expected value if only background is observed. The upper limits at the 90% (95%) $\mathrm{CL}$ are indicated by the dashed (solid) line.

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Animated gif made out of all figures.

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Tables and captions

Signal yields for the $ D ^+ _{( s )} \!\rightarrow \pi ^+ \mu ^+\mu ^- $ fits. The $\phi$ region yields differ due to the different trigger conditions.

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Signal yields for the $ D ^+ _{( s )} \!\rightarrow \pi ^- \mu ^+ \mu ^+ $ fit. The $\phi$ region from the $ D ^+ _{( s )} \!\rightarrow \pi ^+ \mu ^+\mu ^- $ channel is used for normalisation. The particle '$x$' is a $\pi $ when referring to $ D ^+ _{( s )} \!\rightarrow \pi ^- \mu ^+ \mu ^+ $ data and a $\mu $ for $ D ^+ _{( s )} \!\rightarrow \pi ^+ \mu ^+\mu ^- $ data.

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Relative systematic uncertainties averaged over all bins and decay modes for the control mode branching fraction and efficiency ratio. The number in parentheses refers to the $ D ^+_ s $ decay.

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Total systematic uncertainty in each $ m(\mu ^+\mu ^- )$ and $ m(\pi ^- \mu ^+ )$ bin with the uncertainty on the control mode branching fraction, the efficiency ratio and the statistical uncertainty stemming from the size of the simulated samples added in quadrature. The numbers in parentheses refer to the $ D ^+_ s $ decay.

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Upper limits in each $ m(\mu ^+\mu ^- )$ and $ m(\pi ^- \mu ^+ )$ bin and total branching fractions at the 90% and 95% $\mathrm{CL}$ and p-values for the background-only hypothesis.

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Supplementary Material [file]

Supplementary material full pdf

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supplementary.pdf

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2012-051. The files are: supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in various formats

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Created on 17 December 2018.Citation count from INSPIRE on 18 December 2018.