Upper limit of the muon-neutrino mass and charged-pion mass from momentum analysis of a surface muon beam

Abstract

We have determined the momentum p ϩ of muons from the decay ϩ → ϩ at rest, by analyzing a surface muon beam in a magnetic spectrometer equipped with a silicon microstrip detector. The result p ϩϭ (29.792 00Ϯ0.000 11) MeV/c leads to a squared muon-neutrino mass of m 2 ϭ(Ϫ0.016Ϯ0.023)MeV 2 , which corresponds to a ''laboratory'' upper limit of 0.17 MeV ͑C.L.ϭ0.9͒ for the muon-neutrino mass.The cosmological upper limit of the neutrino mass ͑65 eV͒, the muon mass, and the new value of p ϩ yield the pion mass m ϩϭ (139.570 22Ϯ0.000 14) MeV. Alternatively, if one does not use the cosmological upper limit of m , then a combined fit including the new p ϩ value, and the m ϩ and m Ϫ values from other experiments and the CPT theorem (m ϩϭ m Ϫ) leads to m Ϯϭ (139.570 37Ϯ0.000 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 T ϩϭ (0.425Ϯ0.016) eV. This is consistent with the hypothesis that the pions are trapped in the potential well of a spherical harmonic oscillator, V(r)ϭV 0 ϩ 1 2 k s r 2 , with k s ϭ(1.144Ϯ0.088)ϫ10 17 eV/cm 2 .

Attempt at laser spectroscopy of pionic helium atoms at PSI

“…The π − mass has been previously determined to a fractional precision of 10 −5 − 10 −6 in two ways, i): the x-ray transition energies of some π − atoms were compared with relativistic boundstate calculations [18,19], or ii): the recoil momentum [20] of the µ + which emerged from a stationary π + undergoing decay was precisely measured. Depending on the atomic cascade models used in the analysis of the x-ray transition energies, the π − mass values varied by ∼ 10 −5 [18].…”

Tachyonic field theory and neutrino mass running

“…Otherwise, it seems that the high-energy OPERA data [5] (in the GeV range) cannot be reconciled with the low-energy experimental results (in the keV range) of Refs. [6][7][8][9][10][11][12]. Of course, this statement holds provided the OPERA data are not subject to a hitherto undiscovered systematic error.…”

“…which is at least six orders of magnitude larger than the neutrino masses at low energy [6][7][8][9][10][11][12]. Likewise, assuming the dispersion relation (3) implies that…”

“…One of the prime candidates for a genuinely superluminal particle is the neutrino, which has never been observed at rest. A number of experimental groups have measured negative mass squares for the electron neutrino from tritium beta decay endpoints [6][7][8][9] with mean values in the interval −147 eV 2 < 2 ν < 0 for the electron neutrino mass square, at an energy of the order of E ν ≈ 18 keV. While some recent measurements indicate values consistent with a vanishing neutrino mass [10][11][12] at even lower energies, the mean value of the experimental data for 2 ν (electron neutrino) still is negative and of the order of a few negative eV 2 (for an excellent overview, see The Ultimate Neutrino Page 1 ).…”

Measurement of the charged pion mass using a low-density target of light atoms

“…1 following years the pion mass has been re-measured several times using X-ray spectroscopy of pionic atoms with continuously improved accuracy [10][11][12][13][14][15][16]. In parallel, additional results for the charged pion mass were obtained from the measurement of the muon momentum in the decay π + → μ + ν μ [17][18][19].…”