APS » PROLA » Phys. Rev. D » Volume 53 » Issue 11

Phys. Rev. D 53, 6065 - 6077 (1996)

Upper limit of the muon-neutrino mass and charged-pion mass from momentum analysis of a surface muon beam
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K. Assamagan4 *, Ch. Brönnimann1,2, M. Daum1, H. Forrer1,3 †, R. Frosch1, P. Gheno1, R. Horisberger1, M. Janousch1,2 ‡, P. -R. Kettle1, Th. Spirig1,2 §, and C. Wigger1,2
1Paul-Scherrer-Institut, CH-5232 Villigen-PSI, Switzerland
2Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
3Institut für Teilchenphysik, Eidgenössische Technische Hochschule, CH-5232 Villigen-PSI, Switzerland
4Institute of Nuclear and Particle Physics, University of Virginia, Charlottesville, Virginia 22901

Received 15 December 1995

We have determined the momentum pμ+ of muons from the decay π+→μ+νμ at rest, by analyzing a surface muon beam in a magnetic spectrometer equipped with a silicon microstrip detector. The result pμ+=(29.792 00±0.000 11) MeV/c leads to a squared muon-neutrino mass of mνμ2=(-0.016±0.023) MeV2, which corresponds to a "laboratory" 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 pμ+ yield the pion mass mπ+=(139.570 22±0.000 14) MeV. Alternatively, if one does not use the cosmological upper limit of mνμ, then a combined fit including the new pμ+ value, and the mμ+ and mπ- values from other experiments and the CPT theorem (mπ+=mπ-) leads to mπ±=(139.570 37±0.000 21) 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 Tπ+―=(0.425±0.016) eV. This is consistent with the hypothesis that the pions are trapped in the potential well of a spherical harmonic oscillator, V(r)=V0+1 / 2ksr2, with ks=(1.144±0.088)×1017 eV/cm2.


©1996 The American Physical Society

URL: http://link.aps.org/abstract/PRD/v53/p6065
DOI: 10.1103/PhysRevD.53.6065
PACS: 14.60.Pq, 14.40.Aq, 14.60.Ef

* Present address: Department of Physics, Hampton University, Hampton, Virginia 23668.
† Present address: Seminar für Angewandte Mathematik, Eidgenössische Technische Hochschule, Rämistrasse 101, CH-8092 Zürich, Switzerland.
‡ Present address: Institut für Teilchenphysik, Eidgenössische Technische Hochschule, CH-5232 Villigen-PSI, Switzerland.
§ Present address: Paul-Scherrer-Institut Zürich, Badenerstrasse 569, CH-8048 Zürich, Switzerland.

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