Abstract

Precision measurements of τ lepton properties, its mass, lifetime, and leptonic branching fractions, provide interesting tests of lepton universality.

At Z-pole energies, the τ lifetime is determined via measurement of the 2.2 mm average flight distance. A lifetime measurement matching the 1e−5 statistical precision would then correspond to a flight-distance measurement to a few tens of nanometers accuracy. Approaching as far as possible towards this limit imposes formidable requirements on the accuracy of the construction and the alignment of the vertex detector. With a 10–15 mm beam pipe radius, the first vertex detector layer will be very close to the beam line and an impact parameter resolution of about 3 μm looks feasible.

• The corresponding Snowmass LOI

Bibliography

• Measurement of the τ-lepton lifetime at Belle - the most precise measurememnt to date
• Local Alignment of the BABAR Silicon Vertex Tracking Detector, D.N. Brown et al, NIM A 603 (2009) 467–484
• Review of tau lifetime measurements, S. Wasserbaech, Nucl.Phys.Proc.Suppl. 76 (1999) 107
• Some LEP papers :
  • A Precise Measurement of the Tau Lifetime, DELPHI (2004)
  • A Precise measurement of the tau lepton lifetime, ALEPH (1992), and an update from 1997