Search results for "positron"

showing 10 items of 1346 documents

Observation ofe+e−→ηJ/ψat center-of-mass energys=4.009  GeV

2012

Using a 478 pb(-1) data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider storage ring at a center-of-mass energy of root s = 4.009 GeV, the production of e(+)e(-) -> eta J/psi is observed for the first time with a statistical significance of greater than 10 sigma. The Born cross section is measured to be (32.1 +/- 2.8 +/- 1.3) pb, where the first error is statistical and the second systematic. Assuming the eta J/psi signal is from a hadronic transition of the psi(4040), the fractional transition rate is determined to be B(psi(4040) -> eta J/psi) = (5.2 +/- 0.5 +/- 0.2 +/- 0.5) x 10(-3), where the first, second, and third errors are statistical, s…

Nuclear physicsPhysicsNuclear and High Energy PhysicsPositronAnnihilationlawElectron–positron annihilationHadronHigh Energy Physics::ExperimentCenter of massColliderEnergy (signal processing)law.inventionPhysical Review D
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Measurement of the B0→D*−π+π−π+ branching fraction

2016

Using a sample of (470.9 +- 2.8) x 10^6 BB-bar pairs, we measure the decay branching fraction B(B^0 -> D^*- pi^+ pi^- pi^+) = (7.26 +- 0.11 +- 0.31) x 10^-3, where the first uncertainty is statistical and the second is systematic. Our measurement will be helpful in studies of lepton universality by measuring B(B^0 -> D^*- tau^+ nu_tau) using tau^+ -> pi^+ pi^- pi^+ nu-bar_tau decays, normalized to B(B^0 -> D^*- pi^+ pi^- pi^+.

Nuclear physicsPhysicsParticle physics010308 nuclear & particles physicsBranching fractionElectron–positron annihilation0103 physical sciences010306 general physics01 natural sciencesLeptonUniversality (dynamical systems)
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The Influence of Magnetic Field on Annihilation of Positrons in Corroded Steel St-20

2006

Nuclear physicsPhysicsPositronAnnihilationCondensed matter physicsGeneral Physics and AstronomyMagnetic fieldActa Physica Polonica A
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Positron-Electron Angular Correlations in Heavy Ion Collisions

1987

Recent measurements of positrons in coincidence with electrons emitted in U+Th collisions near the Coulomb barrier show sharp line structures in the sum and difference energy spectra of the two leptons (ref. 1). A possible method to clarify the origin of these lines is to study the angular correlation of the leptons. In this short contribution we want to report on a positron-electron coincidence test measurement performed with the TORI spectrometer. This apparatus offers the possibility to measure positrons in coincidence with electrons emitted into the same and opposite hemisphere as well.

Nuclear physicsPhysicsPositronSpectrometerAstrophysics::High Energy Astrophysical PhenomenaCollision cascadeCoulomb barrierHigh Energy Physics::ExperimentElectronCoincidenceSpectral lineLepton
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Observation of the Semileptonic Decay D0→a0(980)−e+νe and Evidence for D+→a0(980)0e+νe

2018

Using an e(+)e(-) collision data sample of 2.93 fb(-1) collected at a center-of-mass energy of 3.773 GeV by the BESIII detector at BEPCII, we report the observation of D-0 -> a(0)(980)(-)e(+)nu( ...

Nuclear physicsPhysicsSemileptonic decay010308 nuclear & particles physicsElectron–positron annihilation0103 physical sciencesDetectorGeneral Physics and Astronomy010306 general physics01 natural sciencesEnergy (signal processing)Physical Review Letters
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The Distribution of Slowing-Down Times of Positrons Emitted from <sup>22</sup>Na and <sup>68</sup>Ge\<sup>68</sup&gt…

2010

The results of the Monte Carlo simulation, using GEANT4 codes, of the slowing-down time prior to the thermalization in metals for positrons emitted from the 22Na and 68Ge\68Ga sources are presented. Due to the energy spectrum and probabilistic processes accompanying positrons traversing a medium the slowing-down time exhibits a distribution which has a long tail. Nevertheless, the average value of the time is ranged from 0.4 ps to 8 ps depending on the density of the medium as it is for the 22Na positrons. For positrons emitted from the 68Ga nucleus the average value of the slowing-down time increases and it is ranged from 1 ps to 20 ps.

Nuclear physicsPhysicsThermalisationPositronDistribution (mathematics)IsotopeMechanics of MaterialsMechanical EngineeringMonte Carlo methodEnergy spectrumGeneral Materials ScienceAtomic physicsCondensed Matter PhysicsMaterials Science Forum
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REVIEW OF R MEASUREMENTS

2013

We review the status of R measurements in the energy range below 12 GeV, where recently a major progress has been achieved recently. These measurements are phenomenologically motivated by their impact on precision QCD and on electroweak parameters. We also report on improved results which can be expected in near future from presently running or upcoming facilities.

Nuclear physicsQuantum chromodynamicsPhysicsNuclear and High Energy PhysicsParticle physicsElectron–positron annihilationElectroweak interactionGeneral Physics and AstronomyHigh Energy Physics::ExperimentAstronomy and AstrophysicsModern Physics Letters A
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Next-to-next-to-leading order corrections to three-jet observables in electron-positron annihilation.

2008

I report on a numerical program, which can be used to calculate any infrared safe three-jet observable in electron-positron annihilation to next-to-next-to-leading order in the strong coupling constant ${\ensuremath{\alpha}}_{s}$. The results are compared to a recent calculation by another group. Numerical differences in three color factors are discussed and explained.

Nuclear physicsQuantum chromodynamicsPhysicsRenormalizationParticle physicsColor modelAnnihilationElectron–positron annihilationGeneral Physics and AstronomyOrder (ring theory)ObservableJet (particle physics)Physical review letters
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Surface Physics With Slow Positrons

1983

Recent progress in slow beam studies of positron-surface interactions is reviewed. The key physical phenomena are introduced, and the present knowledge of the parameters involved is reviewed. The potential of the slow positron technique for surface science is discussed.

Nuclear physicsSurface (mathematics)PhysicsSurface sciencePositronPhysical phenomenaPhysics::Accelerator PhysicsAtomic physicsCondensed Matter PhysicsMathematical PhysicsAtomic and Molecular Physics and OpticsBeam (structure)Physica Scripta
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Estimates of the Nuclear Time Delay in Dissipative U + U and U + Cm Collisions Derived from the Shape of Positron andδ-Ray Spectra

1983

Positron and delta-ray spectra have been measured in coincidence with quasielastic scattered particles and fission fragments from the bombardment of Pd, U, and Cm targets with U beams of energies between 5.9 and 8.4 MeV/u. For collisions leading to a fission reaction, the atomic positron and delta-ray spectra fall off more steeply at high energies than expected from calculations based on pure Rutherford trajectories. A quantitative analysis of this effect is in accord with a nuclear contact time of about 10/sup -21/ s.

Nuclear reactionElastic scatteringPhysicsAntiparticleFissionAstrophysics::High Energy Astrophysical PhenomenaNuclear TheoryGeneral Physics and AstronomyNuclear physicssymbols.namesakePositronNuclear fissionAntimattersymbolsPhysics::Accelerator PhysicsRutherford scatteringAtomic physicsNuclear ExperimentPhysical Review Letters
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