Measurement of the τ-lepton lifetime at Belle

Area of Science:

• Particle Physics
• High-Energy Physics
• Lepton Physics

Background:

• The tau lepton is a fundamental particle.
• Understanding its properties is crucial for testing the Standard Model of particle physics.
• Precise measurements of tau lepton properties can reveal new physics phenomena.

Purpose of the Study:

• To precisely measure the mean lifetime of the tau lepton.
• To perform the first measurement of the lifetime difference between tau positive and tau negative leptons.
• To set limits on potential differences in tau lepton behavior based on charge.

Main Methods:

• Utilized data from e+e- collisions collected by the Belle detector.
• Focused on the tau+ tau- → 3πν(τ) decay channel.
• Analyzed a large dataset (711 fb⁻¹) collected at the ϒ(4S) resonance and nearby energy points.

Main Results:

• The mean tau lepton lifetime was determined to be τ=(290.17±0.53(stat)±0.33(syst))×10⁻¹⁵ s.
• The first measurement of the lifetime difference between τ+ and τ- was reported.
• An upper limit on the relative lifetime difference was established: |Δτ|/τ<7.0×10⁻³ at 90% confidence level.

Conclusions:

• The measured tau lepton lifetime provides a precise value for this fundamental parameter.
• The absence of a significant lifetime difference between τ+ and τ- places constraints on theories beyond the Standard Model.
• This study contributes to the ongoing effort to precisely test the Standard Model and search for new physics.