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Search for $D^{*}(2007)^0\to\mu^+\mu^-$ in $B^-\to\pi^-\mu^+\mu^-$ decays

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Abstract

The very rare $D^{*}(2007)^0\to\mu^+\mu^-$ decay is searched for by analysing $B^-\to\pi^-\mu^+\mu^-$ decays. The analysis uses a sample of beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. The signal signature corresponds to simultaneous peaks in the $\mu^+\mu^-$ and $\pi^-\mu^+\mu^-$ invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at ${\cal B}(D^{*}(2007)^0\to\mu^+\mu^-) < 2.6\times 10^{-8}$ at $90\%$ confidence level. This is the first limit on the branching fraction of $D^{*}(2007)^0\to\mu^+\mu^-$ decays and the most stringent limit on $D^{*}(2007)^0$ decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.

Figures and captions

Reconstructed (left) $\mu ^+\mu ^- $ and (right) $\pi ^- \mu ^+\mu ^- $ invariant-mass distributions for the selected $ B ^- \rightarrow D ^{*0} (\mu ^+\mu ^- ) \pi ^- $ candidates, with results of the fit superimposed.

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Two-dimensional distribution of $\mu ^+\mu ^- $ invariant mass versus $\pi ^- \mu ^+\mu ^- $ invariant mass for the selected $ B ^- \rightarrow D ^{*0} (\mu ^+\mu ^- ) \pi ^- $ candidates. The red box corresponds to a range of about $\pm3\sigma$ around the expected signal peak position in each dimension.

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Reconstructed (left) $\mu ^+\mu ^- $ and (right) $ K ^- \mu ^+\mu ^- $ invariant-mass distributions for the selected $ B ^- \rightarrow { J \mskip -3mu/\mskip -2mu\psi } (\mu ^+\mu ^- ) K ^- $ candidates, with results of the fits superimposed. The contributions from misidentified $ B ^- \rightarrow { J \mskip -3mu/\mskip -2mu\psi } (\mu ^+\mu ^- )\pi ^- $ decays and combinatorial background are negligible and thus barely visible.

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Confidence belts generated using pseudoexperiments according to the Feldman--Cousins prescription [60]. The vertical black line shows the result of the fit to data.

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Animated gif made out of all figures.

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Tables and captions

Yields obtained from the fit to data described in the text, with statistical uncertainties only.

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Input parameters used in the estimation of the $ D ^{*0} \rightarrow \mu ^+\mu ^- $ branching fraction. The uncertainties correspond to the statistical and systematic uncertainties added in quadrature.

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Created on 27 April 2024.