First results from the MuLan and MuCap experiments

Journal Article · Thu Feb 21 04:00:00 EST 2008 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2898992· OSTI ID:21055371

Banks, T I ^[1]

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1. Department of Physics, University of California, Berkeley, CA 94720 (United States)

MuLan and MuCap are ongoing experiments at the Paul Scherrer Institut, Switzerland, that use the muon lifetime to determine fundamental weak interaction parameters. The goal of MuLan is a 1 ppm measurement of the positive muon lifetime {tau}{sub {mu}{sup +}} to determine the Fermi constant G{sub F} to 0.5 ppm. The goal of MuCap is to make a 1% determination of the rate {lambda}{sub S} of the process of nuclear muon capture by the proton, {mu}p{yields}n{nu}, by measuring the {mu}{sup -} disappearance rate in hydrogen gas to 10 ppm and subtracting the world average for the {mu}{sup +} decay rate. A 1% determination of the capture rate {lambda}{sub S} is of interest because it would enable a 7% determination of g{sub P}, the induced pseudoscalar coupling of the nucleon. In 2007, both experiments published first results based upon data collected by each in 2004. MuLan reported an 11 ppm {mu}{sup +} lifetime measurement, {tau}{sub {mu}{sup +}} = 2.197 013(24) {mu}s, resulting in a new, 9.6 ppm world average, {tau}{sub {mu}{sup +}} = 2.197 019(21) {mu}s, which determines the Fermi constant, G{sub F} = 1.166 371(6)x10{sup -5} GeV{sup -2}, to 5 ppm. MuCap reported a 3% measurement of the muon capture rate from the hyperfine singlet ground state of the {mu}p atom, {lambda}{sub S} = 725.0{+-}17.4 s{sup -1}, from which a 15% value for the pseudoscalar coupling, g{sub P}(q{sup 2} = -0.88m{sub {mu}}{sup 2}) = 7.3{+-}1.1, was extracted.

• OSTI ID: 21055371
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 981; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CAPTURE
COUPLING
FERMI INTERACTIONS
GROUND STATES
HYDROGEN
LIFETIME
MUON-PROTON INTERACTIONS
MUONIC ATOMS
MUONS MINUS
MUONS PLUS
PARTICLE DECAY
PROTONS