Search results for "positron"

showing 10 items of 1346 documents

Positron implantation profiles in layered samples

2009

The paper presents theoretical and experimental studies of the positron implantation profiles in layered samples. The Monte Carlo simulations performed using the GEANT4 toolkit reveal accumulation of positrons in the denser layer embedded between two less dense layers. That effect is significant not only for low energy positrons at slow monoenergetic positron beams but also for high energy positrons which are emitted from radioactive nuclei in conventional experiments. Measurements of the positron implantation profile into the samples which consist of silver and aluminium foils of different thickness show profile features which correspond well with those simulated by the GEANT4 toolkit for …

PhysicsNuclear and High Energy PhysicsHigh energyAstrophysics::High Energy Astrophysical PhenomenaPositron Lifetime SpectroscopyPhysics::Medical PhysicsMonte Carlo methodchemistry.chemical_elementLow energyPositronchemistryAluminiumPhysics::Accelerator PhysicsHigh Energy Physics::ExperimentAtomic physicsInstrumentationLayer (electronics)Positron annihilationNuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
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Electro-produced slow positrons

1989

During the last 6 years it has been demonstrated that electro-produced intense beams of slow positrons are possible. High energy electrons from an accelerator generate bremsstrahlung in a thick conversion target of high element number Z. The photons produce electronpositron pairs and a small fraction of the positrons may be moderated to thermal energies. A review is given of the existing slow positron beam lines using this technique. At accelerator energies of 100 MeV total conversion efficiencies of several slow positrons per 106 primary electrons have been obtained, resulting in average intensities of several 109 slow positrons per second or more than 105 slow positrons in pulses having a…

PhysicsNuclear and High Energy PhysicsHigh energyPhotonBremsstrahlungElectronCondensed Matter PhysicsAtomic and Molecular Physics and OpticsIntensity (physics)Nuclear physicsPositronThermalPhysics::Accelerator PhysicsPhysical and Theoretical ChemistryAtomic physicsOrder of magnitudeHyperfine Interactions
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Measurement of the branching fraction for D0 → K-π+

1997

The branching fraction for D-0 --> K(-)pi(+) is measured with the statistics collected by ALEPH from 1991 to 1994. The method is based on the comparison between the rate for the reconstructed D*+ --> (D) pi(+), D-0 --> K(-)pi(+) decay chain and the rate for inclusive soft pion production at low transverse momentum with respect to the nearest jet. The result is B(D-0 --> K(-)pi(+)) = (3.90 +/- 0.09 +/- 0.12)% (C) 1997 Published by Elsevier Science B.V. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Sanchez, Federico/F-5809-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012

PhysicsNuclear and High Energy PhysicsJet (fluid)010308 nuclear & particles physicsBranching fractionElectron–positron annihilationPhysics01 natural sciencesNuclear physicsALEPH ExperimentPion0103 physical sciencesTransverse momentumDecay chain010306 general physicsALEPH experiment
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Event shapes and jet rates in electron-positron annihilation at NNLO

2009

This article gives the perturbative NNLO results for the most commonly used event shape variables associated to three-jet events in electron-positron annihilation: Thrust, heavy jet mass, wide jet broadening, total jet broadening, C parameter and the Durham three-to-two jet transition variable. In addition the NNLO results for the jet rates corresponding to the Durham, Geneva, Jade-E0 and Cambridge jet algorithms are presented.

PhysicsNuclear and High Energy PhysicsJet (fluid)Particle physicsHigh Energy Physics - PhenomenologyHigh Energy Physics - Phenomenology (hep-ph)AnnihilationElectron–positron annihilationAstrophysics::High Energy Astrophysical PhenomenaFOS: Physical sciencesThrustHigh Energy Physics::ExperimentEvent (particle physics)
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Factorization and resummation for jet broadening

2011

Jet broadening is an event-shape variable probing the transverse momenta of particles inside jets. It has been measured precisely in e+e- annihilations and is used to extract the strong coupling constant. The factorization of the associated cross section at small values of the broadening is afflicted by a collinear anomaly. Based on an analysis of this anomaly, we present the first all-order expressions for jet-broadening distributions, which are free of large perturbative logarithms in the two-jet limit. Our formulae reproduce known results at next-to-leading logarithmic order but also extend to higher orders.

PhysicsNuclear and High Energy PhysicsJet (fluid)Particle physicsLogarithm010308 nuclear & particles physicsElectron–positron annihilationFOS: Physical sciences01 natural sciencessymbols.namesakeHigh Energy Physics - PhenomenologyHigh Energy Physics - Phenomenology (hep-ph)FactorizationQuantum electrodynamics0103 physical sciencesWeierstrass factorization theoremEffective field theorysymbolsAnomaly (physics)Resummation010306 general physicsPHYSICS LETTERS B
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Electron and positron cooling of highly charged ions in a cooler Penning trap

2004

Abstract Electron cooling is a well-established technique to increase the phase space density of particle beams in storage rings. In this paper, we discuss the feasibility of electron and positron cooling of ions in a Penning trap. We calculate the cooling times for the cases of trapped bare ions with nuclear charge Z =1 (protons), Z =36 (krypton) and Z =92 (uranium) with the Spitzer formula. Our calculations show that for typical experimental conditions the time for cooling from initial energies of 10 keV per charge down to rest is in the order of a second. We investigate the dependence of the cooling time on the number of ions and electrons, and their charge and mass.

PhysicsNuclear and High Energy PhysicsKryptonchemistry.chemical_elementElectronPenning trapEffective nuclear chargelaw.inventionIonPositronchemistrylawLaser coolingPhysics::Atomic PhysicsAtomic physicsInstrumentationElectron coolingNuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
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Measurement of time dependentCPasymmetry parameters inB0meson decays toωKS0,η′K0, andπ0KS0

2009

We present measurements of the time-dependent CP-violation parameters S and C in the decays B-0 -> omega K-S(0), B-0 -> eta'K-0, reconstructed as eta'K-S(0) and eta'K-L(0), and B-0 -> pi K-0(S)0. The data sample corresponds to the full BABAR dataset of 467 x 10(6) B (B) over bar pairs produced at the PEP-II asymmetric-energy e(+)e(-) collider at the Stanford Linear Accelerator Center. The results are S-omega KS0 = 0.55(-0.29)(+0.26) +/- 0.02, C-omega KS0 = 0.52(-0.20)(+0.22) +/- 0.03, S-eta'K0 = 0.57 +/- 0.08 +/- 0.02, C-eta'K0 = 0.08 +/- 0.06 +/- 0.02, S-pi 0KS0 = 0.55 +/- 0.20 +/- 0.03, and C-pi 0KS0 = 0.13 +/- 0.13 +/- 0.03, where the first errors are statistical and the second systemati…

PhysicsNuclear and High Energy PhysicsMeson010308 nuclear & particles physicsBETA (programming language)Electron–positron annihilationAnalytical chemistryCenter (category theory)01 natural sciencesOmegaParticle decayPair production0103 physical sciencesCP violationAtomic physics010306 general physicscomputercomputer.programming_languagePhysical Review D
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Precision measurements of B(D+→μ+νμ), the pseudoscalar decay constant fD+, and the quark mixing matrix element |Vcd|

2014

We report a measurement of the branching fraction B(D+ -> mu(+)nu(mu)) = [3.71 +/- 0.19(stat) +/- 0.06(sys)] x 10(-4) based on 2.92 fb(-1) of data accumulated at root s = 3.773 GeV with the BESIII detector at the BEPCII collider. This measurement, in conjunction with the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cd vertical bar determined from a global Standard Model fit, implies a value for the weak decay constant f(D+) = (203.2 +/- 5.3 +/- 1.8) MeV. Additionally, using this branching fraction measurement together with a lattice QCD prediction for f(D+), we find vertical bar V-cd vertical bar 0.2210 +/- 0.0058 +/- 0.0047. In either case, these are the most precise results for…

PhysicsNuclear and High Energy PhysicsMeson010308 nuclear & particles physicsBranching fractionCabibbo–Kobayashi–Maskawa matrixElectron–positron annihilationLattice QCD01 natural sciencesStandard ModelNuclear physicsPseudoscalar0103 physical sciencesExponential decay010306 general physics
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Search for the decay of aB0orB¯0meson toK¯*0K0orK*0K¯0

2006

We present a search for the decay of a B0 or B0bar meson to a K*0bar K0 or K*0 K0bar final state, using a sample of approximately 232 million BBbar events collected with the BABAR detector at the PEP-II asymmetric energy e+e- collider at SLAC. The measured branching fraction is B(B0 --> K*0bar K0) + B(B0 --> K*0 K0bar) = (0.2+0.9-0.8+0.1-0.3)x 10-6. We obtain the following upper limit for the branching fraction at 90% confidence level: B(B0 --> K*0bar K0) + B(B0 --> K*0 K0bar) phi K0 from sin(2beta).

PhysicsNuclear and High Energy PhysicsMeson010308 nuclear & particles physicsBranching fractionElectron–positron annihilation01 natural sciencesParticle identificationStandard Modellaw.inventionNuclear physicsParticle decaylaw0103 physical sciences010306 general physicsColliderPhysical Review D
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Branching fraction measurements of chargedBdecays toK*+K+K−,K*+π+K−,K*+K+π−andK*+π+π−final states

2006

Branching fraction and asymmetry measurements of charmless B+-> K(*+)h(1)(+)h(2)(-) (where h(1,2)=K, pi) decays are presented, using a data sample of 232x10(6) Upsilon(4S)-> B (B) over bar decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy B factory. Using a maximum likelihood fit, the following branching fraction results were obtained: B(B+-> K*+K+K-)=(36.2 +/- 3.3 +/- 3.6)x10(-6) and B(B+-> K*+pi(+)pi(-))=(75.3 +/- 6.0 +/- 8.1)x10(-6). Upper limits were set for B(B+-> K*+pi K-+(-)) K*+K+pi(-)) K*+K+K- and B+-> K*+pi(+)pi(-) were measured to be A(K)(*)KK=0.11 +/- 0.08 +/- 0.03 and A(K)(*)pi pi=0.07 +/- 0.07 +/- 0.04, respectively. The first error quoted on branch…

PhysicsNuclear and High Energy PhysicsMeson010308 nuclear & particles physicsBranching fractionElectron–positron annihilationAnalytical chemistry01 natural sciencesB-factoryParticle decay0103 physical sciencesPiCP violationB mesonAtomic physics010306 general physicsPhysical Review D
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