Search for the lepton-number-violating decay Xi(-)-->pmu(-)mu(-).

Area of Science:

• Particle Physics
• Experimental Physics
• Hyperon Decays

Background:

• Lepton number conservation is a fundamental principle in particle physics.
• Rare decays of hyperons provide sensitive probes for new physics beyond the Standard Model.
• Previous searches for Xi(-) to proton and two muons decay (Xi(-)-->pμ⁻μ⁻) lacked sufficient sensitivity.

Purpose of the Study:

• To conduct a sensitive search for the lepton-number-violating decay Xi(-)-->pμ⁻μ⁻.
• To establish a stringent upper limit on the branching fraction of this decay.
• To constrain theories beyond the Standard Model that predict such violations.

Main Methods:

• Utilized a large sample of approximately 10⁹ Xi⁻ hyperons.
• Collected data from 800 GeV/c proton-copper (p-Cu) collisions.
• Performed a sensitive search analysis to identify the Xi(-)-->pμ⁻μ⁻ decay signature.

Main Results:

• Obtained an upper limit for the branching fraction B(Xi(-)-->pμ⁻μ⁻) < 4.0 x 10⁻⁸ at 90% confidence level.
• This result improves the previous best limit by four orders of magnitude.
• No evidence for the decay was observed within the analyzed data.

Conclusions:

• The search significantly constrains the possibility of lepton-number violation in Xi⁻ decays.
• The improved limit challenges theoretical models that predict a larger branching fraction for this decay.
• Further investigations with even larger datasets may be needed to probe even smaller branching fractions.