Search results for "Elementary Particle"
showing 10 items of 659 documents
Asimetría de carga en la colisión de Leptones Positivos y Negativos con Núcleos : Efecto del intercambio de dos Fotones
1984
Test of Lorentz invariance with spin precession of ultracold neutrons
2009
A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and $^{199}$Hg atoms is reported. %57 No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field $b_{\bot} < 2 \times 10^{-20} {\rm eV}$ (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron $|g_n| < 0.3 $eV/$c^2$ m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit $|g_n| < 3 \times …
Antiproton-proton annihilation at rest in H2 gas into π+ π− π0
1990
Antiproton-proton annihilation at rest into π+ π− π0 has been studied by stopping antiprotons from LEAR in a H2 gas target at normal temperature and pressure. The reaction is observed in coincidence withL X-rays which are emitted in the cascade of\(\bar pp\) atoms. The X-rays populate one of the angular momentumL=1 states of a\(\bar pp\) atom which then annihilates. A spinparity analysis of the π+ π− π0 Dalitz plot gives contributions from the threeP states from which annihilation into three pions is allowed. The most striking features of the Dalitz plot are production of charged and neutral ϱ(770) and off2(1270) mesons. Production of ϱ(770) mesons proceeds via the isoscalar part of the1P1 …
New determination of the electron's mass.
2001
A new independent value for the electron's mass in units of the atomic mass unit is presented, ${m}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.0005485799092(4)\mathrm{u}$. The value is obtained from our recent measurement of the $g$ factor of the electron in ${}^{12}{\mathrm{C}}^{5+}$ in combination with the most recent quantum electrodynamical (QED) predictions. In the QED corrections, terms of order ${\ensuremath{\alpha}}^{2}$ were included by a perturbation expansion in $Z\ensuremath{\alpha}$. Our total precision is three times better than that of the accepted value for the electron's mass.
Search for Muon Neutrino and Antineutrino Disappearance in MiniBooNE
2009
The MiniBooNE Collaboration reports a search for nu(mu) and nu(mu) disappearance in the Delta m(2) region of 0.5-40 eV(2). These measurements are important for constraining models with extra types of neutrinos, extra dimensions, and CPT violation. Fits to the shape of the nu(mu) and nu(mu) energy spectra reveal no evidence for disappearance at the 90% confidence level (C.L.) in either mode. The test of nu(mu) disappearance probes a region below Delta m(2)=40 eV(2) never explored before.
GHOSTLY BEACONS OF NEW PHYSICS
2013
The article discusses the elementary particle of the neutrino, with information on research regarding its fundamental properties and how it differs from other particles. Topics include the connection between neutrinos and their antiparticles, the observation of the particles' activity during nuclear beta decay and their interactions, and the possible implications that an asymmetric relationship between neutrinos and their antimatter would suggest regarding the composition of the universe with a majority of matter.
Majorons and supernova cooling
1990
We consider the role of Majoron emission in supernova cooling and its implications for the neutrino mass and lifetime in generic single Majoron models. It is found that, for ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ with mass $m$, if the lifetime for the decay ${\ensuremath{\nu}}_{\ensuremath{\tau}}\ensuremath{\rightarrow}\mathrm{Majoron}+{\ensuremath{\nu}}_{e,\ensuremath{\mu}}$ is shorter than ${10}^{\ensuremath{-}7}$ (m/MeV) sec, then Majorons are so strongly trapped by the inverse process that the resulting Majoron luminosity is small enough not to destabilize the observed ${\ensuremath{\nu}}_{e}$ pulse from SN 1987A. For ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ with a longer lifetime, th…
Neutrino Pair Synchrotron Radiation from Relativistic Electrons in Strong Magnetic Fields
1995
The emissivity for the neutrino pair synchrotron radiation in strong magnetic fields has been calculated both analytically and numerically for high densities and moderate temperatures, as can be found in neutron stars. Under these conditions, the electrons are relativistic and degenerate. We give here our results in terms of an universal function of a single variable. For two different regimes of the electron gas we present a simplified calculation and compare our results to those of Kaminker et al. Agreement is found for the classical region, where many Landau levels contribute to the emissivity , but some differences arise in the quantum regime. One finds that the emissivity for neutrino …
New calculations of grossβ-decay properties for astrophysical applications: Speeding-up the classicalrprocess
2003
Recent compilations of experimental gross $\ensuremath{\beta}$-decay properties, i.e., half-lives ${(T}_{1/2})$ and neutron-emission probabilities ${(P}_{\mathrm{n}}),$ are compared to improved global macroscopic-microscopic model predictions. The model combines calculations within the quasiparticle (QP) random-phase approximation for the Gamow-Teller (GT) part with an empirical spreading of the QP strength and the gross theory for the first-forbidden part of ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay. Nuclear masses are either taken from the 1995 data compilation of Audi et al., when available, otherwise from the finite-range droplet model. Especially for spherical and neutron-(sub-)mag…
Pairing-excitation versus intruder states inNi68andZr90
2010
A discussion on the nature of the 0{sup +} states in {sup 68}Ni (Z=28, N=40) is presented and a comparison is made with its valence counterpart {sup 90}Zr (Z=40, N=50). Evidence is given for a 0{sup +} proton-intruder state at only {approx}2.2-MeV excitation energy in {sup 68}Ni, while the analogous neutron-intruder states in {sup 90}Zr reside at 4126 and 5441 keV. The application of a shell-model description of 0{sup +} intruder states reveals that many pair-scattered neutrons across N=40 have to be involved to explain the low excitation energy of the proton-intruder configuration in {sup 68}Ni.