Observation of the Very Rare Σ^{+}→pμ^{+}μ^{-} Decay.

Area of Science:

• Particle Physics
• High-Energy Physics
• Hadron Spectroscopy

Background:

• The Standard Model of particle physics describes fundamental particles and forces.
• Baryon decays provide crucial tests for theoretical models.
• Observing rare decays probes physics beyond the Standard Model.

Purpose of the Study:

• To report the first observation of the Sigma+ → pμ+μ- decay.
• To measure the branching fraction and properties of this rare decay.
• To search for new physics phenomena in the dimuon invariant-mass spectrum.

Main Methods:

• Analysis of proton-proton collision data collected by the LHCb detector.
• Utilizing an integrated luminosity of 5.4 fb⁻¹ at a center-of-mass energy of 13 TeV.
• Statistical analysis of 237 observed Σ+ → pμ+μ- decay events.

Main Results:

• First observation of the Σ+ → pμ+μ- decay with high significance.
• Measured branching fraction of (1.08 ± 0.17) × 10⁻⁸.
• No evidence for resonant structures in the dimuon invariant-mass distribution.
• Observed decay is the rarest baryon decay ever recorded.

Conclusions:

• The observed decay is consistent with Standard Model predictions.
• This measurement opens new avenues for studying rare baryon decays.
• Further studies could reveal subtle deviations from the Standard Model.