Evidence for the Rare Decay Σ^{+}→pμ^{+}μ^{-}

Area of Science:

• Particle Physics
• High-Energy Physics
• Rare Decays

Background:

• Rare particle decays provide sensitive probes of fundamental physics beyond the Standard Model.
• The Sigma+ (Σ⁺) hyperon is a baryon containing strange quark, offering unique decay channels.
• Previous experiments have searched for similar rare decays, yielding intriguing but inconclusive results.

Purpose of the Study:

• To search for the rare decay of the Sigma+ (Σ⁺) hyperon into a proton and a dimuon pair (Σ⁺→pμ⁺μ⁻).
• To measure the branching fraction of this decay and compare it with theoretical predictions.
• To investigate the dimuon invariant mass spectrum for any unexpected structures.

Main Methods:

• Analysis of proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV.
• Integrated luminosity of 3 fb⁻¹ was utilized for the search.
• Statistical analysis to distinguish signal events from background processes and determine significance.

Main Results:

• An excess of 4.1 standard deviations was observed for the Σ⁺→pμ⁺μ⁻ decay channel above the expected background.
• The measured branching fraction is (2.2⁻¹.³⁺¹·⁸)×10⁻⁸, consistent with the Standard Model prediction.
• No significant structure was found in the dimuon invariant mass distribution, differing from a prior HyperCP experiment result.

Conclusions:

• The rare decay Σ⁺→pμ⁺μ⁻ has been observed with a significance consistent with the Standard Model.
• The measured branching fraction supports current theoretical expectations.
• The absence of structure in the dimuon mass spectrum warrants further investigation and comparison with other decay modes.