Search results for "positron"
showing 10 items of 1346 documents
Evidence for thehb(1P)meson in the decayΥ(3S)→π0hb(1P)
2011
Using a sample of 122×10^6 Υ(3S) events recorded with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at SLAC, we search for the h_b(1P) spin-singlet partner of the P-wave χ_(bJ)(1P) states in the sequential decay Υ(3S)→π^0h_b(1P), hb(1P)→γη_b(1S). We observe an excess of events above background in the distribution of the recoil mass against the π0 at mass 9902±4(stat)±2(syst) MeV/c^2. The width of the observed signal is consistent with experimental resolution, and its significance is 3.1σ, including systematic uncertainties. We obtain the value (4.3±1.1(stat)±0.9(syst))×10^(-4) for the product branching fraction B(Υ(3S)→π^0h_b)×B(h_b→γη_b).
Branching fractions andCP-violating asymmetries in radiativeBdecays toηKγ
2009
We present measurements of the CP-violation parameters S and C for the radiative decay B^0 → ηK^0_Sγ for B → ηKγ we also measure the branching fractions and for B^+ → ηK^+γ the time-integrated charge asymmetry A_(ch). The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 465 × 10^6 BB pairs produced in e^+e^- annihilation. The results are S = -0.18^(+0.49)_(-0.46) ± 0.12, C = -0.32^(+0.40)_(-0.39) ± 0.07, B(B^0 → ηK^0γ) = (7.1^(+2.1)_(-2.0) ± 0.4) × 10^(-6), B(B^+ → ηK^+γ) = (7.7 ± 1.0 ± 0.4) × 10^(-6), and A_(ch) = (-9.0^(+10.4)_(-9.8) ± 1.4) × 10^(-2). The first error quoted is statistical and the second systematic.
MQPM description of the structure and beta decays of the odd Mo and Tc isotopes
2010
The odd-mass isotopes A=95,97 of molybdenum are of interest for neutrino-physics applications. The microscopic quasiparticle-phonon model (MQPM) is used to calculate energy and decay characteristics of these nuclei and their beta-decay partners (Tc95 and Tc97). A realistic single-particle valence space and two-body interaction are used in the calculations. The computed results are compared with available data. The obtained energy spectra are also compared with earlier calculations. We present the first ever calculations for the rates of allowed and forbidden β+/EC decay transitions in these nuclei. In general our computed numbers agree rather well with the available data.
Observation of the decayψ(3686)→ΛΣ¯±π∓+c.c.
2013
Using a sample of 1:06 X 10(8) psi(3686) events collected with the BESIII detector, we present the first observation of the decays of psi(3686) -> Lambda(Sigma) over bar (+) pi(-) + c.c. and psi(3686) -> Lambda(Sigma) over bar (-) pi(+) + c.c. The branching fractions are measured to be B(psi(3686) -> Lambda(Sigma) over bar (+) pi(-) + c.c.) = (1.40 +/- 0.03 +/- 0.13) X 10(-4) and B(psi(3686) -> Lambda (Sigma) over bar (-) pi(+) + c.c.) = (1.54 +/- 0.04 +/- 0.13) X 10(-4) where the first errors are statistical and the second ones systematic.
Normal and transverse single tau polarization at the Z-peak
1994
Abstract We study normal (to the collision plane) and transverse (within the collision plane) single-τ polarization in τ pairs produced in e + e − unpolarized collisions at the Z -resonance. The transverse polarization component is sensitive to the anomalous weak-magnetic moment, whereas the normal polarization component is sensitive to a CP-violating weak-electric dipole moment. We show how these components of the single τ polarization are accessible from the angular distribution of its decay products. We define a CP violating asymmetry of the τ decay products which, with 10 7 Z ′s produced, provides a sensitivity of 2.3 × 10 −18 e ·cm for the weak-electric dipole moment.
New approach for numerical solution of configuration-space Faddeev equations
1996
A new computational scheme for solving the bound state configuration-space Faddeev equations is applied. The scheme is based on the spline-approximation and the adiabatic limit of Faddeev equations. An ordering of variables being in agreement with the limit was chosen. As a result the matrix of the eigenvalue problem has a sparse block structure. Calculations of the bound states of µpp, µdd, µtt mesic molecules and ¯pdd, ¯ptt antiprotonic ones, were performed. To check the method, calculations of the binding energies for such systems as the positronium ion Ps−,3H and3He were carried out. The results are compared with the best results of other authors.
Relativistic approach to positronium levels in a strong magnetic field
2001
We have investigated the bound states of an electron and positron in superstrong magnetic fields typical for neutron stars. The complete relativistic problem of positronium in a strong magnetic field has not been succesfully solved up to now. In particular, we have studied the positronium when it moves relativistically across the magnetic field. A number of problems which deal with the pulsar magnetosphere, as well as the evolution of protoneutron stars, could be considered as a field for application.
Constraints on anomalous QGC's in $e^{+}e^{-}$ interactions from 183 to 209 GeV
2004
The acoplanar photon pairs produced in the reaction e+ e- --> nu nubar gamma gamma are analysed in the 700 inverse nanobarns of data collected by the ALEPH detector at centre-of-mass energies between 183 and 209 GeV. No deviation from the Standard Model predictions is seen in any of the distributions examined. The resulting 95% C.L. limits set on the anomalous QGC's, az_0, az_c, aw_0 and aw_c, are -0.012 GeV**-2 < az_0/Lambda**2 < +0.019 GeV**-2, -0.041 GeV**-2 < az_c/Lambda**2 < +0.044 GeV**-2, -0.060 GeV**-2 < aw_0/Lambda**2 < +0.055 GeV**-2, -0.099 GeV**-2 < aw_c/Lambda**2 < +0.093 GeV**-2, where Lambda is the energy scale of the new Physics responsible for the anomalous couplings.
Measurement of triple gauge-boson couplings at 172 GeV
1998
The triple gauge-boson couplings, αWΦ, αW and αBΦ, have been measured using 34 semileptonically and 54 hadronically decaying W+W- candidate events. The events were selected in the data recorded during 1996 with the ALEPH detector at 172 GeV, corresponding to an integrated luminosity of 10.65 pb-1. The triple gauge-boson couplings have been measured using optimal observables constructed from kinematic information of W+W- events. The results are in agreement with the Standard Model expectation.
Set of sum rules for anomalous gauge boson couplings
1999
The dependence of the differential cross-section for on-shell W-pair production on the anomalous trilinear gauge couplings invariant under C and P is examined. It is shown that the contributions of the anomalous magnetic moments of the W boson due to the photon and the Z can be individually projected out by means of two appropriately constructed polynomials. The remaining four anomalous couplings are shown to satisfy a set of model-independent sum rules. Specific models which predict special relations among the anomalous couplings are then studied; in particular, the composite model of Brodsky and Hiller, and the linear and non-linear effective Lagrangian approaches. The relations predicted…