Search results for "gold"
showing 10 items of 1320 documents
Extraction of K --> pi pi matrix elements with Wilson fermions
2001
We present the status of a lattice calculation for the K-->pipi matrix elements of the (delta S=1) effective weak Hamiltonian, directly with two pion in the final state. We study the energy shift of two pion in a finite volume both in the I=0 and I=2 channels. We explain a method to avoid the Goldstone pole contamination in the computation of renormalization constants for (delta I=3/2) operators. Finally we show some preliminary results for the matrix elements of (delta I=1/2) operators. Our quenched simulation is done at beta=6.0, with Wilson fermions, on a (24^3 X 64) lattice.
Isotope shifts of neutron-deficient gold isotopes with 193?A?190
1985
The isotope shift between197Au (stable) and the radioactive Au isotopes190Au,191Au,192Au and193Au were determined by resonance fluorescence spectroscopy in the 6s2S1/2–6p2P1/2.λ=267.6nm line. The unstable Au isotopes were produced at the ISOLDE mass separator at CERN. The nuclei were investigated semi on-line in a resonance vessel, heated to 1,400°C. The results areδν190,197=−11.12(39) GHz,δν191,197=−9.67(12) GHz,δν192,197=−8.32(15) GHz,δν193,197=−6.29(11) GHz, corresponding to a change of the mean-square charge radius byδ〈r2〉190,197 =0.261(12) fm2,δ〈r2〉191,197=0.227(5) fm2,δ〈r2〉192,197=0.195(5) fm2,δ〈r2〉193,197 =0.148(4) fm2.
Universal Bounds for SU(3) Low Energy Constants
2008
In this paper bounds for L_1, L_2 and L_3 are obtained in Chiral Perturbation Theory with three flavours. At the same time we test the compatibility of this theory with axiomatic principles. Following a recent paper we use dispersion relations to write positivity conditions that translate into bounds for the chiral low energy constants. As a first approach we consider the exact SU(3)_V limit and notice that if a common mass of the order of that of the kaon is adopted for the octet of pseudo-Goldstone bosons the bounds have very large O(p^6) corrections. Once the positivity conditions are adapted to account for different masses, we correct the previous bounds for a physical kaon mass and fin…
SINGLE PHOTON DECAYS OF THE $Z^0$ AND SUSY WITH SPONTANEOUSLY BROKEN R-PARITY
1995
Spontaneous violation of R parity can induce rare single photon decays of the $Z^0$ involving the emission of (nearly) massless pseudoscalar Goldstone bosons, majorons, as well as massive CP even or CP odd spin zero bosons that arise in the electroweak breaking sector of these models. We show that the majoron emitting decays can have a sizeable branching ratio of $10^{-5}$ or so, without conflicting any experimental observation from neutrino physics or particle searches. These decays may lead to interesting structures for the single photon spectrum involving either mono chromatic photons as well as continuous spectra that grow with energy. They would easily account for an excess of single p…
Limits on associated production of visibly and invisibly decaying Higgs bosons from Z decays
1994
Many extensions of the standard electroweak model Higgs sector suggest that the main Higgs decay channel is "invisible", for example, $h \to J J$ where $J$ denotes the majoron, a weakly interacting pseudoscalar Goldstone boson associated to the spontaneous violation of lepton number. In many of these models the Higgs boson may also be produced in association to a massive pseudoscalar boson (HA), in addition to the standard Bjorken mechanism (HZ). We describe a general strategy to determine limits from LEP data on the masses and couplings of such Higgs bosons, using the existing data on acoplanar dijet events as well as data on four and six $b$ jet event topologies. For the sake of illustrat…
Majoron emission in muon and tau decays revisited
2009
9 pages, 4 figures.-- ISI article identifier:000264762400078.-- ArXiv pre-print avaible at: http://arxiv.org/abs/0902.0525
Search for the sgoldstino at √s = 189 to 202 GeV.
2000
A search for the supersymmetric partner of the goldstino, the sgoldstino S, at LEP2 is presented. The production Sgamma followed by S decay into two gluons or into two photons was studied at 189 - 202 GeV LEP centre-of-mass energies. No evidence for the S production was found and limits on the S mass corresponding to different theory parameters are given.
The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Nucleon
2004
The Gerasimov-Drell-Hearn sum rule is one of several dispersive sum rules that connect the Compton scattering amplitudes to the inclusive photoproduction cross sections of the target under investigation. Being based on such universal principles as causality, unitarity, and gauge invariance, these sum rules provide a unique testing ground to study the internal degrees of freedom that hold the system together. The present article reviews these sum rules for the spin-dependent cross sections of the nucleon by presenting an overview of recent experiments and theoretical approaches. The generalization from real to virtual photons provides a microscope of variable resolution: At small virtuality …
An ultraviolet completion for the Scotogenic model
2021
The Scotogenic model is an economical scenario that generates neutrino masses at the 1-loop level and includes a dark matter candidate. This is achieved by means of an ad-hoc $\mathbb{Z}_2$ symmetry, which forbids the tree-level generation of neutrino masses and stabilizes the lightest $\mathbb{Z}_2$-odd state. Neutrino masses are also suppressed by a quartic coupling, usually denoted by $\lambda_5$. While the smallness of this parameter is natural, it is not explained in the context of the Scotogenic model. We construct an ultraviolet completion of the Scotogenic model that provides a natural explanation for the smallness of the $\lambda_5$ parameter and induces the $\mathbb{Z}_2$ parity a…
Fitting Simpson's neutrino into the standard model
1985
Abstract I show how to accomodate the 17 keV state recently reported by Simpson as one of the neutrinos of the standard model. Experimental constraints can only be satisfied if the μ and τ neutrino combine to a very good approximation to form a Dirac neutrino of 17 keV leaving a light ν e . Neutrino oscillations will provide the most stringent test of the model. The cosmological bounds are also satisfied in a natural way in models with Goldstone bosons. Explicit examples are given in the framework of majoron-type models. Constraints on the lepton symmetry breaking scale which follow from astrophysics, cosmology and laboratory experiments are discussed.