Precision Lepton Physics: a Window to New Physics

07 - 30 April 2026

Claudia Hagedorn, Alberto Lusiani, Angela Papa, Joseph D. Price, Alejandro Ibarra

Charged leptons have been key to the current understanding of physics at the shortest length scales and are the focus of precise tests of the Standard Model. In the coming years several experiments with increased sensitivity in charged lepton physics are expected to deliver exciting results. This workshop will offer the possibility for theoretical and experimental physicists to discuss the status and prospects of this field of research.

 

Among the key scientific objectives will be: the study of EFT interpretations for different types of leptonic observables, the identification of which experiments best probe the parameter space of different BSM theories, proposals for the optimal use of existing data, the investigation of new BSM searches at existing and upcoming experiments which go beyond their main physics goals, and proposals for new types of symmetries beyond known flavour and CP symmetries.

 

The workshop has three main topics:
muon precision physics (weeks 1+2), charged lepton flavour violation (weeks 2+3) and tau lepton precision physics (weeks 3+4).

weeks 1+2: muon precision physics

 

  • Status and prospects of the Fermilab muon AMM measurement and the J-PARC experiment 
  • Theory overview of prediction of AMM of the muon in the SM
  • Status of and prospects for measurement of EDM of the muon at different facilities
  • Muon lifetime and its implications
  • Muonium 
  • Searches for muonium-antimuonium oscillations

 

weeks 2+3: charged lepton flavour violation

 

  • Theory overview of cLFV
  • Experimental searches for cLFV in muonic processes
  • Status and prospects of searches for cLFV processes involving tau leptons
  • Searches for cLFV in Z and Higgs boson decays as well as hadron decays
  • Recent developments of EFT techniques and corresponding computer tools
  • Predictions of cLFV in different SM extensions
  • Comparison of reach for cLFV at high-intensity experiments and high-energy colliders
  • Flavour symmetries in the lepton sector and their consequences 
  • Role of CP in the lepton sector

 

weeks 3+4: tau lepton precision physics

 

  • Tests of the SM with tau lepton precision physics, in particular tests of LFU 
  • Status of the evidence of LFU violation in semi-leptonic B-meson decays
  • Determination of Vus and tests of the unitarity of the CKM matrix with tau lepton decays 
  • Determination of alpha_s from tau spectral functions 
  • Measurements and prospects for tau lepton physics at Belle II 
  • Prospects of future Super Charm-Tau Factories, FCC, and CEPC 
  • Status and prospects of measuring the AMM and EDM of the tau lepton