Abstract
A search for the rare decay Σ^{+}→pμ^{+}μ^{-} is performed using pp collision data recorded by the LHCb experiment at center-of-mass energies sqrt[s]=7 and 8TeV, 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 Σ^{+}→pμ^{+}μ^{-} branching fraction is (2.2_{-1.3}^{+1.8})×10^{-8}, where statistical and systematic uncertainties are included, which is consistent with the standard model prediction.
Highlights
R m corr Σ [MeV/c 2]Candidates / ( 5 MeV/c2 ) Weighted candidates / ( 2 MeV/c2 ) Σ +→ pμ+μ− LHCb0 1200 mpμ+μ− [MeV/c2][43]
The signal yield is obtained from a fit to the pμþμ− invariant-mass spectrum and is converted into a branching fraction by normalizing to the Σþ → pπ0 control channel
The sample of Σþ → pμþμ− candidates in data after the initial selection is dominated by combinatorial background, part of which is due to misidentified particles
Summary
The signal yield is obtained from a fit to the pμþμ− invariant-mass spectrum and is converted into a branching fraction by normalizing to the Σþ → pπ0 control channel. Given the large production rate of Σþ baryons in pp collisions, the present search can be performed with data selected at one or more trigger stages by other particles in the event.
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