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Evidence for the rare decay $\Sigma^+ \to p \mu^+ \mu^-$

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Abstract

A search for the rare decay $\Sigma^+ \to p \mu^+ \mu^-$ is performed using $pp$ collision data recorded by the LHCb experiment at centre-of-mass energies $\sqrt{s} = 7$ and $8$ TeV, corresponding to an integrated luminosity of $3 fb^{-1}$. An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured $\Sigma^+ \to p \mu^+ \mu^-$ branching fraction is $(2.2\,^{+\,1.8}_{-\,1.3})\times 10^{-8}$, where statistical and systematic uncertainties are included, which is consistent with the Standard Model prediction.

Figures and captions

Distribution of the corrected mass $m_{\Sigma}^{\text{corr}}$, defined as in the text, for $\Sigma^+ \rightarrow p \pi^0$ candidates superimposed with the fit to data.

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Invariant mass distribution of $\Sigma^+ \rightarrow p \mu^+ \mu^-$ candidates in data.

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Background-subtracted distribution of the dimuon invariant mass for $\Sigma^+ \rightarrow p \mu^+ \mu^-$ candidates, superimposed with the distribution from the simulated phase-space (PS) model. Uncertainties on data points are calculated as the square root of the sum of squared weights.

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Tables and captions

Relative systematic uncertainties associated with the normalisation.

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Supplementary Material [file]

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2017-049. The files are: Supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in variuous formats

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