Search results for "positron"

showing 10 items of 1346 documents

QED box amplitude in heavy fermion production

2002

We evaluate the two-photon box contribution to heavy fermion production in electron positron annihilation, that provides O(alpha^2) electromagnetic corrections to the Born cross section. The study of its non-relativistic expansion, relevant at energies close to the threshold of production, is also performed. We also verify that the threshold expansion of the one-loop integrals correctly reproduces our results, thus extending the applicability of this technique to heavy fermion production diagrams.

PhysicsHigh Energy Physics - PhenomenologyCross section (physics)Particle physicsAmplitudeHigh Energy Physics - Phenomenology (hep-ph)Physics and Astronomy (miscellaneous)Electron–positron annihilationHeavy fermionFOS: Physical sciencesProduction (computer science)Engineering (miscellaneous)
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Measurement of the Inclusive Charmless Semileptonic Branching Ratio ofBMesons and Determination of|Vub|

2004

We report a measurement of the inclusive charmless semileptonic branching fraction of B mesons in a sample of 89 x 10(6) (-)BB events recorded with the BABAR detector at the Upsilon(4S) resonance. Events are selected by fully reconstructing the decay of one B meson and identifying a charged lepton from the decay of the other B meson. The number of signal events is extracted from the mass distribution of the hadronic system accompanying the lepton and is used to determine the ratio of branching fractions B((-)B-->X(u)lnu;)/B((-)B-->Xlnu;)=[2.06+/-0.25(stat)+/-0.23(syst)+/-0.36(theo)]x10(-2). Using the measured branching fraction for inclusive semileptonic B decays, we find B((-)B-->X(u)lnu;)…

PhysicsHigh energyParticle physics010308 nuclear & particles physicsBranching fractionElectron–positron annihilationHadronGeneral Physics and Astronomy01 natural sciencesNuclear physics0103 physical sciencesMass spectrumMatrix elementB meson010306 general physicsLeptonPhysical Review Letters
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Observation of a Charged Charmoniumlike Structure ine+e−→(D*D¯*)±π∓ats=4.26  GeV

2014

We study the process e(+)e(-) -> (D* (D) over bar*)(+/-)pi(-/+) at a center-of-mass energy of 4.26 GeV using a 827 pb(-1) data sample obtained with the BESIII detector at the Beijing Electron Positron Collider. Based on a partial reconstruction technique, the Born cross section is measured to be (137 +/- 9 +/- 15) pb. We observe a structure near the (D* (D) over bar*)(+/-) threshold in the pi(-/+) recoil mass spectrum, which we denote as the Z(c)(+/-) (4025). The measured mass and width of the structure are (4026.3 +/- 2.6 +/- 3.7) MeV/c(2) and (24.8 +/- 5.6 +/- 7.7) MeV, respectively. Its production ratio sigma(e(+)e(-) -> Z(c)(+/-)(4025)pi(-/+)-> (D* (D) over bar*)(+/-)pi(-/+)/sigma(e(+)e…

PhysicsHigh energyPositronRecoilElectron–positron annihilationMass spectrumAnalytical chemistryPiGeneral Physics and AstronomyHigh Energy Physics::ExperimentBar (unit)Physical Review Letters
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Right-handed neutrino magnetic moments

2009

PACS numbers: 14.60.St, 13.15.+g, 13.35.Hb, 13.66.Hk

PhysicsHistoryNuclear and High Energy PhysicsParticle physicsMagnetic momentElectron–positron annihilationElectroweak interactionHigh Energy Physics::PhenomenologyVertex functionFOS: Physical sciencesPartícules (Física nuclear)Computer Science ApplicationsEducationHigh Energy Physics - PhenomenologyOperator (computer programming)High Energy Physics - Phenomenology (hep-ph)BibliographyCP violationHigh Energy Physics::ExperimentNeutrino
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The topology dependence of charged particle multiplicities in three-jet events

1997

A study of individual jet and whole-event charged particle multiplicities in three-jet events measured in e(+)e(-) annihilation at the Z reveals a significant topology dependence. Mean jet multiplicities are inadequately described by jet energies; interjet angles must also be specified. Quantitative tests suggest that it is necessary to use transverse-momentum-like scales to describe the data. 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

PhysicsJet (fluid)Physics and Astronomy (miscellaneous)010308 nuclear & particles physicsAstrophysics::High Energy Astrophysical PhenomenaPhysicsElectron–positron annihilation01 natural sciencesCharged particleNuclear physics0103 physical sciencesTransverse momentum[PHYS.HEXP]Physics [physics]/High Energy Physics - Experiment [hep-ex]High Energy Physics::Experiment010306 general physicsParticle Physics - ExperimentTopology (chemistry)
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Decoupling or nondecoupling: Is that theRbquestion?

1996

The top quark is well known for the nondecoupling effects it implies in ρ and Rb. The recent experimental Rb data exhibits a disagreement with the SM prediction at more than the 3σ level. It is tempting to explore whether this might be due to nondecoupling New Physics effects, opposite to those of the top. We investigate this issue in the context of models with an extra family of right or left handed, singlet or doublet quarks. It is shown that, contrary to what

PhysicsLeft handedQuarkNuclear and High Energy PhysicsParticle physicsTop quarkElectron–positron annihilationPhysics beyond the Standard ModelDecoupling (cosmology)Physical Review D
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Observation of the doubly radiative decay η′→γγπ0

2017

Based on a sample of 1.31 billion J/psi events collected with the BESIII detector, we report the study of the doubly radiative decay eta' -> gamma gamma pi(0) for the first time, where the eta' meson is produced via the J/psi -> gamma eta' decay. The branching fraction of eta' -> gamma gamma pi(0) inclusive decay is measured to be B(eta' -> gamma gamma pi(0))(Incl) = (3.20 +/- 0.07(stat) +/- 0.23(sys)) x 10(-3), while the branching fractions of the dominant process eta' -> gamma omega and the non-resonant component are determined to be B(eta' -> gamma omega) x B(omega -> gamma pi(0)) = (23.7 +/- 1.4(stat) +/- 1.8(sys)) x 10(-4) and B(eta' -> gamma gamma pi(0))(NR) = (6.16 +/- 0.64(stat) +/-…

PhysicsMeson010308 nuclear & particles physicsBranching fractionAstrophysics::High Energy Astrophysical PhenomenaElectron–positron annihilationRadiative decay01 natural sciencesOmegaGamma gammaNuclear physics0103 physical sciencesPiHigh Energy Physics::ExperimentNuclear Experiment010306 general physicsPhysical Review D
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Improved measurements of branching fractions for ηc→ϕϕ and ωϕ

2017

Using (223.7 +/- 1.4) x 10(6) J / Psi events accumulated with the BESIII detector, we study eta(c) decays to phi phi and omega phi final states. The branching fraction of n(c) -> phi phi is measured to be Br(eta(c) -> phi phi) = (2.5 +/- 0(-0.7)(+0.3) +/- 0.6) X 10(-3,) where the first uncertainty is statistical, the second is systematic, and the third is from the uncertainty of Br(J / Psi -> gamma eta(C)). No significant signal for the double Okubo-Zweig-Iizuka suppressed decay of eta(c) -> omega phi is observed, and the upper limit on the branching fraction is determined to be Br(eta(c) -> omega phi) < 2.5 x 10(-4) at the 90% confidence level.

PhysicsMeson010308 nuclear & particles physicsBranching fractionElectron–positron annihilationAnalytical chemistryBranching (polymer chemistry)01 natural sciencesOmega0103 physical sciencesHigh Energy Physics::ExperimentAtomic physicsNuclear Experiment010306 general physicsPhysical Review D
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Observation of the DecayB±→π±π0, Study ofB±→K±π0, and Search forB0→π0π0

2003

We present results for the branching fractions and charge asymmetries in B+/--->h(+/-)pi(0) (where h(+/-)=pi(+/-),K+/-) and a search for the decay B0-->pi(0)pi(0) using a sample of approximately 88 x 10(6) BBmacr; pairs collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We measure B(B+/--->pi(+/-)pi(0))=(5.5(+1.0)(-0.9)+/-0.6)x10(-6), where the first error is statistical and the second is systematic. The B+/--->pi(+/-)pi(0) signal has a significance of 7.7sigma including systematic uncertainties. We simultaneously measure the K+/-pi(0) branching fraction to be B(B+/--->K+/-pi(0))=(12.8(+1.2)(-1.1)+/-1.0)x10(-6). The charge asymmetries are Api(+/-)(pi(0))=-0.0…

PhysicsMeson010308 nuclear & particles physicsBranching fractionElectron–positron annihilationHadronAnalytical chemistryGeneral Physics and Astronomy01 natural sciencesParticle decayTheoretical physicsPion0103 physical sciencesPiB meson010306 general physicsPhysical Review Letters
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Measurements ofB→{π,η,η′}lνlBranching Fractions and Determination of|Vub|with Semileptonically TaggedBMesons

2008

We report measurements of branching fractions for the decays B-->Plnu_{l}, where P are the pseudoscalar charmless mesons pi;{-}, pi;{0}, eta and eta;{'}, based on 348 fb;{-1} of data collected with the BABAR detector, using B0 and B+ mesons found in the recoil of a second B meson decaying as B-->D;{(*)}lnu_{l}. Assuming isospin symmetry, we combine pionic branching fractions to obtain B(B;{0}-->pi;{-}l;{+}nu_{l})=(1.54+/-0.17_{(stat)}+/-0.09_{(syst)})x10;{-4}; we find 3.2sigma evidence of the decay B;{+}-->etal;{+}nu_{l} and measure its branching fraction to be (0.64+/-0.20_{(stat)}+/-0.03_{(syst)})x10;{-4}, and determine B(B;{+}-->eta;{'}l;{+}nu_{l})<0.47x10;{-4} to 90% confidence level. U…

PhysicsMeson010308 nuclear & particles physicsBranching fractionElectron–positron annihilationHigh Energy Physics::PhenomenologyForm factor (quantum field theory)General Physics and Astronomy01 natural sciencesPseudoscalarParticle decayCrystallographyIsospin0103 physical sciencesHigh Energy Physics::ExperimentB mesonNuclear Experiment010306 general physicsPhysical Review Letters
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