Showing papers on "Lepton published in 1988"

Bounds on exotic-particle interactions from SN1987A.

Abstract: The observation of a neutrino pulse from the supernova SN 1987A constrains the production of light exotic particles in the protoneutron star. A new bound on the axion decay constant is derived, f(a) of greater than about 10 to the 10th GeV. If right-handed (RH) neutrinos exist, 'RH Fermi constant' is G(RH) of less than about 10 exp-4 G(F), two orders of magnitude below laboratory bounds. The Dirac mass of hv sub m can be constrained below laboratory limits. The Dirac mass of the mu-neutrino can be constrained below laboratory limits.

Observation in the Kamiokande-II detector of the neutrino burst from supernova SN1987A.

Abstract: The properties of the Kamiokande-II detector and the method of measurement are described in detail. The data on the neutrino burst from the supernova SN1987A on 23 February 1987 at 7:35:35 UT\ifmmode\pm\else\textpm\fi{}1 min are presented, with records of earlier and later observation periods in which other neutrino events possibly associated with SN1987A might have occurred. There is no evidence in the data for any excess of neutrino-induced events, either in a burst of a few seconds duration or over a longer time interval, relative to the usual count rate, excepting only the neutrino burst at 7:35:35 UT. The nature of the single, observed neutrino burst coincides remarkably well with the elements of the current model of type-II supernovae and neutron-star formation. This is the first direct observation in neutrino astronomy.

Mixing between ordinary and exotic fermions

Abstract: The results of a comprehensive analysis of the limits on mixings between ordinary fermions and possible heavy fermions with exotic SU(2) x U(1) assignments (e.g., left-handed singlets and/or right-handed doublets) are presented. A general formalism for describing such mixings is given. It is shown that a variety of constraints, including the relation between the W and Z masses and the Fermi constant, charged-current universality, limits on induced right-handed charged currents, and flavor-diagonal neutral currents suffice to limit all directions in parameter space that are not excluded by the absence of flavor-changing neutral currents. Limits on s/sup 2/, the square of the mixing between ordinary and exotic fermions, are quite stringent for the ..nu../sub ..mu..//sub L/, ..mu../sub L//sup -/, u/sub L/, and d/sub L/ (s/sup 2/less than or equal to0.002--0.005) if only one particle is allowed to mix at a time, but are weaker by an order of magnitude if fine-tuned cancellations between different mixings are allowed. Similar statements apply to quark mixings with heavy sequential doublets. Limits on s/sup 2/ for the other light fermions (..nu../sub e//sub L/, e/sub L//sup -/,e/sub R//sup -/,..mu../sub R//sup -/, u/sub R/,d/sub R/) are in the range 0.02--0.06, while those for the s, c, b,more » ..nu../sub tau/, and tau/sup -/ are considerably weaker. Slightly stronger limits are found in specific models (e.g., E/sub 6/). Implications for the masses of the heavy exotic fermions are discussed.« less

Nuclear Structure Effects in Double beta Decay

Abstract: Using the quasiparticle random phase approximation, we calculate the nuclear matrix elements governing two-neutrino and neutrinoless double-beta decay. We show that a consistent treatment, including both particle-hole and particle-particle interactions, helps to resolve the longstanding discrepancy between experimental and calculated two-neutrino decay rates. The particle-particle force, which allows us to bring calculated EC/β+ decay rates in semimagic nuclei into closer agreement with experiment, is in large part responsible for suppressing calculated two-neutrino decay rates that are otherwise too fast. We test the validity of our procedure by comparing quasiparticle random phase approximation results with exact solutions for a solvable model, in which the suppression of two-neutrino decay by the particle-particle interaction is confirmed. We then extend our approach to the neutrinoless decay associated with a finite Majorana neutrino mass and, conceivably, with majoron emission, and demonstrate that the nuclear matrix elements governing these processes are also suppressed. We present predicted half-lives for both two-neutrino and neutrinoless double-beta decay in several candidate nuclei, and discuss the difficulties associated with the calculation of such highly suppressed quantities.

Testing the principle of equivalence with neutrino oscillations.

Abstract: If the equivalence principle is violated, and gravity is not universally coupled to all leptonic flavors, a gravitational field may contribute to neutrino oscillations. The laboratory limits on the oscillation process can thus be interpreted as tests of the equivalence principle in the quantum-relativistic regime, and put severe constraints on a maximal violation of this principle in the case of massless neutrinos coupled to the Earth's gravitational field.

Limit on the magnetic moment of the neutrino from supernova 1987A observations.

Abstract: We consider the possible emission of right-handed neutrinos ..nu../sub R/ from SN1987A by neutrino-magneitc-moment interactions. By imposing a bound on the ..nu../sub R/ luminosity, we get a limit on the neutrino magnetic moment, ..mu../sub v/ nu../sub L/ rotation in the galactic magnetic field, may lead to a stronger bound, ..mu../sub ..nu../<(10/sup -13/--10/sup -12/)..mu../sub B/ under specific assumptions.

Exclusive semi-leptonic decays of bottom mesons in the spectator quark model

Abstract: We calculate the exclusive semileptonic bottom meson decays\(B \to D(D*) + l^ - + \bar v_l \) in the spectator quark model. The helicity structure of the mesonic current transitionsB→D(D*) is matched to the helicity structure of the free quark current transitionsb→c at minimum momentum transferq2=0. The results are continued toq2≠=0 by pole-dominated form factors. Our results are compared to recent calculations that use quark model dynamics at maximum momentum transferq max 2 = (M1 −M2)2. We find agreement atq max 2 . Atq2=0 there are significant differences between the predictions of the two approaches leading to marked differences in the predictions for the shape of the lepton energy spectrum, the shape of theq2-distribution, and the helicity composition of the transition measurable in the angular distributions of the decaysD*→Dπ and\(W_{virtual}^ - \to l^ - + \bar v_l \).

Test of the weak equivalence principle for neutrinos and photons.

Abstract: The observation of a neutrino burst within 3 h of the associated optical burst from supernova 1987A in the Large Magellanic Cloud provides a new test of the weak equivalence principle, by demonstrating that neutrinos and photons follow the same trajectories in the gravitational field of the galaxy. The accuracy of the test depends on the poorly known mass distribution in the outer parts of the galaxy, but is at least 0.5% and probably much better. This result provides direct evidence that the Shapiro geodesic time delay is identical, to this accuracy, for different elementary particles, independent of spin and internal quantum numbers.

Lepton-number violation and massless nonorthogonal neutrinos.

Abstract: Mixing between light and heavy neutrinos can induce lepton-flavor and total-lepton-number violation in the light sector, even if the light neutrino masses are zero or extremely small, because the states actually produced in weak processes are generally nonorthogonal. We develop the formalism for describing such nonorthogonal neutrinos and explore the phenomenological implications for neutrino ``oscillation'' experiments, the solar-neutrino problem, constraints from universality and other charged- and neutral-current experiments, \ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}, and \ensuremath{\Delta}L=\ifmmode\pm\else\textpm\fi{}2 effects in muon decay and neutrinoless double-beta decay.

Structure and single-phase regime of boron carbides.

Abstract: The boron carbides are composed of twelve-atom icosahedral clusters which are linked by direct covalent bonds and through three-atom intericosahedral chains. The boron carbides are known to exist as a single phase with carbon concentrations from about 8 to about 20 at. %. This range of carbon concentrations is made possible by the substitution of boron and carbon atoms for one another within both the icosahedra and intericosahedral chains. The most widely accepted structural model for ${\mathrm{B}}_{4}$C (the boron carbide with nominally 20% carbon) has ${\mathrm{B}}_{11}$C icosahedra with C-B-C intericosahedral chains. Here, the free energy of the boron carbides is studied as a function of carbon concentration by considering the effects of replacing carbon atoms within ${\mathrm{B}}_{4}$C with boron atoms. It is concluded that entropic and energetic considerations both favor the replacement of carbon atoms with boron atoms within the intericosahedral chains, C-B-C\ensuremath{\rightarrow}C-B-B. Once the carbon concentration is so low that the vast majority of the chains are C-B-B chains, near ${\mathrm{B}}_{13}$${\mathrm{C}}_{2}$, subsequent substitutions of carbon atoms with boron atoms occur within the icosahedra, ${\mathrm{B}}_{11}$C\ensuremath{\rightarrow}${\mathrm{B}}_{12}$. Maxima of the free energy occur at the most ordered compositions: ${\mathrm{B}}_{4}$C,${\mathrm{B}}_{13}$${\mathrm{C}}_{2}$,${\mathrm{B}}_{14}$C. This structural model, determined by studying the free energy, agrees with that previously suggested by analysis of electronic and thermal transport data. These considerations also provide an explanation for the wide single-phase regime found for boron carbides. The significant entropies associated with compositional disorder within the boron carbides, the high temperatures at which boron carbides are formed (g2000 K), and the relatively modest energies associated with replacing carbon atoms with boron atoms enable the material's entropy to be usually important in determining its composition. As a result, boron carbides are able to exist in a wide range of compositions.

The width of the Z boson

Abstract: We present a detailed discussion of the electroweak radiative corrections to the partial decay widths of theZ boson into lepton and quark pairs (q≠t) and to the total width for 5 flavors. The results are only very weakly dependent on the Higgs mass. The top mass dependence leads to sizable variations ofΓ z which have to be taken into account for precision experiments at thee + e − colliders LEP and SLC.

Neutrino Heating in Supernovae

Abstract: I argue that standard descriptions of stellar collapse omit the primary mechanism for dissipative neutrino reactions in nuclear matter, nuclear excitation by neutral-current scattering. The nuclear heating rate, due to primarily to muon- and tauon-neutrino excitation of giant resonance states, is on the order of 90 MeV/nucleon sec at a radius of 100 km. I discuss possible effects of both neutral- and charged-current neutrino heating in models of stellar collapse.

Strongly coupled charged scalar in B and T decays.

Abstract: Limits on charged-scalar Yukawa couplings from $\ensuremath{\tau}$ and $B$ decays are discussed. They (and other existing limits) are consistent with "strong" couplings (\ensuremath{\sim}1 for the third generation) even if the lightest scalar mass is in the range $20 \mathrm{GeV}\ensuremath{\lesssim}{M}_{\ensuremath{\varphi}}\ensuremath{\lesssim}100 \mathrm{GeV}$ but saturated in this case. $B(B\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{ u}X)$ and (for ${M}_{\ensuremath{\varphi}}g{m}_{t}$) $B(T\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{ u}X)$ may be then as large as 30% and 70%, respectively. Both for ${M}_{\ensuremath{\varphi}}l{m}_{t}$ and ${M}_{\ensuremath{\varphi}}g{m}_{t}$ the potentially possible top-quark signature in $p\overline{p}$ collisions is $\ensuremath{\tau}+2$ jets final state. The upper limit for $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{ u}\ensuremath{\eta}\ensuremath{\pi}\mathrm{is}\ensuremath{\simeq}0.003%$.

Supersymmetric majoron signatures and solar neutrino oscillations.

Abstract: Spontaneous R-parity breaking in supergravity solves the solar neutrino problem through matter-enhanced neutrino oscillations. The model may be tested in collider experiments and through ``dynamical'' effects associated with the existence of a weakly interacting majoron. Apart from astrophysical effects, majoron emission can produce observable changes in \ensuremath{\mu} and \ensuremath{\tau} decay spectra for parameter values that substantially reduce the solar neutrino flux. A signature of the model is the possible observation of the decay \ensuremath{\mu}\ensuremath{\rightarrow}e+majoron.

Implications of the supernova SN1987A neutrino signals.

Abstract: The neutrino events from the supernova SN1987A observed by the Kamiokande II and Irvine-Michigan-Brookhaven detectors are used to suggest constraints on neutrino physics. In particular, bounds on the value of the electron neutrino magnetic moment ${\mathrm{\ensuremath{\mu}}}_{\mathit{v}\mathit{e}}$\ensuremath{\lesssim}(${10}^{\mathrm{\ensuremath{-}}12}$-${10}^{\mathrm{\ensuremath{-}}13}$)${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$ are suggested.

New bounds on neutrino magnetic moments from stellar collapse

Abstract: Magnetic or electric dipole moments of neutrinos are indicators for possible extensions of the standard weak-interaction model. Certain values were recently proposed to explain the time variation in the detected solar-neutrino flux and an extragalactic background of ionizing radiation. Here we give a detailed analysis of their implications for a stellar collapse. We find two independent new upper bounds of 1.5 x 10/sup -12/..mu../sub B/ and 6 x 10/sup -12/..mu../sub B/ on the dipole moment of electron neutrinos, improving the existing bounds by one to two orders of magnitude and ruling out the proposed solar-neutrino effect. For values approx. >10/sup -13/..mu../sub B/ the coherently enhanced dipole scattering on the large nuclei in a collapsing star would flip the trapped left-handed neutrinos into right-handed ones, which would escape in a highly energetic prebounce ..nu../sub e/ ''collapse burst.'' This also reduces the trapped lepton number of the collapsing star. We calculate the spectra of the emitted neutrinos and the associated lepton-number decrease. From the supernova 1987A up to 100 neutrinos from this additional output should have been detected in the Kamiokande II detector. The absence of such events imposes the upper bound ..mu../sub ..nu..//sub >//sub e//sub =/ //sub e//sub =/<6 x 10/sup -12/..mu../sub B/, providing an independent supplementary bound.« less