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We report the most sensitive direct upper limit set on the mass my of the electron antineutrino. Our measurements of the shape of the fi decay spectrum of free molecular tritium yield, under the assumption of no new physics other than that of mass, a central value for mv of -147 ±68 ±41 eV^, which corresponds to an upper limit of 9.3 eV (95% confidence level) on mv. The result is in clear disagreement with a reported value of 26(5) eV.PACS numbers: 23.40.Bw, 14.60.GhThat the mass of the electron neutrino (or antineutrino) could be determined from the shape of p spectra has been known since Fermi's formulation of the theory of p decay. A group at the Institute for Theoretical and Experimental Physics (ITEP) in Moscow have reported [1] from their studies of the tritium p spectrum that the Ve mass lies in the range 17-40 eV, with revolutionary implications for particle physics and cosmology. Not only are massive neutrinos incompatible with the otherwise successful minimal standard model of particle physics, a neutrino mass in that range would be sufficient both to close the Universe gravitationally and to account qualitatively for observational evidence for dark matter. Other experiments [2][3][4], however, do not support the ITEP claim.When tritium decays to ^He, the orbital electrons redistribute themselves over the set of eigenstates of the residual molecule. The resulting energy spread impressed on the outgoing p must be very precisely calculated if serious errors in interpreting the data are to be avoided. Such calculations can be carried out with some confidence for atomic and molecular tritium, in contrast to the multielectron solid sources used heretofore [1][2][3]. Our experiment at the Los Alamos National Laboratory is the first to make use of a gaseous source of T2 to capitalize on the simplicity of the two-electron system. The gaseous source also confers minimal, well understood energy-loss corrections, and freedom from backscatter; together with detailed measurements of the instrumental resolution function, energy-loss, energy efficiency, and other effects, it has made possible a reliable mass measurement at the 10-eV level.In an earlier paper [4] we described our apparatus briefly and reported our initial result, rriy < 27 eV. The source is a tube fed at its midpoint with a steady flow of T2 gas and placed on the axis of a solenoidal magnetic field whose strength decreases monotonically toward the extraction end. Electrons from p decay near the axis are guided to the object point of a toroidal-field magnetic spectrometer of 5-m focal length. The most significant of many improvements [5] made recently are the elimina-tion of electron trapping in the source and replacement of the single-element proportional counter in the spectrometer by an octagonal array of Si microstrip detectors, each with twelve pads. Signals from pads at the same location along the dispersion axis are combined to form twelve simultaneously acquired spectra, each independently calibrated by a ^^Kr'" spectrum similarly formed.Tritium...

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We demonstrate, using two different quark models of hadrons, that there should be isodoublets of dibaryons with strangeness -3 and 7 = 1,2, which are stable with respect to strong decay.

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We consider the possibility that neutrinos are coupled very weakly to an extremely light scalar boson. We first analyze the simple problem of one generation of neutrino and show that, for ranges of parameters that are allowed by existing data, such a system can have serious consequences for the evolution of stars and could impact precision laboratory measurements. We discuss the extension to more generations and show that the general conclusion remains viable. Finally, we note that, should such a scalar field be present, experiments give information about effective masses, not the masses that arise in unified field theories.

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