Upper limit of the muon-neutrino mass and charged-pion mass from momentum analysis of a surface muon beam
- Paul-Scherrer-Institut, CH-5232 Villigen-PSI (Switzerland)
We have determined the momentum {ital p}{sub {mu}{sup +}} of muons from the decay {pi}{sup +}{r_arrow}{mu}{sup +}{nu}{sub {mu}} at rest, by analyzing a surface muon beam in a magnetic spectrometer equipped with a silicon microstrip detector. The result {ital p}{sub {mu}{sup +}}=(29.79200{plus_minus}0.00011) MeV/{ital c} leads to a squared muon-neutrino mass of {ital m}{sub {nu}{sub {mu}}}{sup 2}=({minus}0.016{plus_minus}0.023) MeV{sup 2}, which corresponds to a {open_quote}{open_quote}laboratory{close_quote}{close_quote} upper limit of 0.17 MeV (C.L.=0.9) for the muon-neutrino mass. The cosmological upper limit of the neutrino mass (65 eV), the muon mass, and the new value of {ital p}{sub {mu}{sup +}} yield the pion mass {ital m}{sub {pi}{sup +}}=(139.57022{plus_minus}0.00014) MeV. Alternatively, if one does not use the cosmological upper limit of {ital m}{sub {nu}{sub {mu}}}, then a combined fit including the new {ital p}{sub {mu}{sup +}} value, and the {ital m}{sub {mu}{sup +}} and {ital m}{sub {pi}{sup {minus}}} values from other experiments and the {ital CPT} theorem ({ital m}{sub {pi}{sup +}}={ital m}{sub {pi}{sup {minus}}}) leads to {ital m}{sub {pi}}{sup {plus_minus}}=(139.57037{plus_minus}0.00021) MeV. As a side result, the mean kinetic energy of the pions stopped in the production target, made of isotropic graphite, immediately before their decay is found to be {ital T}{sub {pi}{sup +}}=(0.425{plus_minus}0.016) eV. This is consistent with the hypothesis that the pions are trapped in the potential well of a spherical harmonic oscillator, {ital V}({ital r})={ital V}{sub 0}+1/2{ital k}{sub {ital sr}}{sup 2}, with {ital k}{sub {ital s}}=(1.144{plus_minus}0.088){times}10{sup 17} eV/cm{sup 2}. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 284558
- Journal Information:
- Physical Review, D, Vol. 53, Issue 11; Other Information: PBD: Jun 1996
- Country of Publication:
- United States
- Language:
- English
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