Search results for "Particle physics"

Threshold pion photoproduction in a light-cone quark model

1991

Abstract The instantaneous and seagull graphs are calculated for pion photoproduction in a relativistic light-cone model of the nucleon. In both pseudoscalar and pseudovector coupling we find the ratios A (−) : A (0) : A (+) = 1: ( −1 2 μ):( −9 5 μ) in the nonrelativistic limit. These results correspond to the sum of seagull and Z -graph in the nonrelativistic quark model. In pseudovector coupling also the numerical results for realistic-model parameters are close to those values.

Radiative muon capture on 12C and 16O

1979

Abstract We study exclusive radiative muon capture on 12 C(g.s.) leading to 12 B(g.s.), and on 16 O(g.s.) leading to 16 N(0 − , 120 keV). Our investigation, which is based on impulse approximation, puts special emphasis on elementary particle aspects of radiative capture, such as tests of magnitude and momentum transfer dependence of the induced pseudoscalar, and possible contributions of axial currents of second kind (weak electricity). We calculate several correlation observables which are sensitive to the nucleonic currents but depend very little on the structure of the nuclear initial and final states. In particular, it is shown that in capture on 12 C the polarization and alignment of …

Photoproduction of delta and Roper resonances in the cloudy bag model.

1988

The photoproduction of delta and Roper resonances has been calculated within the framework of the cloudy bag model. Two alternative formulations, the original pseudoscalar surface coupling and the pseudovector volume coupling of pions, have been used, and the results are compared. The helicity amplitudes are in fair agreement with experimental data, the prediction for the small ${E}_{1+}$/${M}_{1+}$ ratio for delta production is -1.8% for a bag radius of 1 fm and pseudovector coupling.

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.

QCD formulation of the tau decay and determination of Lambda (MS)

1988

Abstract We present a simple formulation of the inclusive and exclusive semi-hadronic decays of the tau lepton using QCD-duality finite energy sum rules (FESRs). We find that the tau decay is a good laboratory for measuring the QCD scaleΛ. Within the present experimental accuracy, we obtain Λ M S ¯ ⋍ 100–200 MeV to four loops. This prediction can be sensibly improved once the experimental situation has been clarified.

Leptons and QCD

2015

Three important QCD-related aspects of the τ and μ dynamics are reviewed: the determination of the strong coupling from the hadronic tau decay width, leading to the updated value αs(mτ2)=0.331±0.013; the measurement of |Vus| through the Cabibbo-suppressed decays of the τ, and the Standard Model prediction for the muon anomalous magnetic moment.

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.

Erratum to: Quark mass dependence of the nuclear forces

2003

Heavy quark impact factor and the single bottom production at the LHC

2014

Grigorios Chachamis Instituto de Fisica Corpuscular, Universitat de Valencia – Consejo Superior de Investigaciones Cientificas, Parc Cientific, E-46980 Paterna (Valencia), Spain E-mail: grigorios.chachamis@ific.uv.es Michal Deak∗ Instituto de Fisica Corpuscular, Universitat de Valencia – Consejo Superior de Investigaciones Cientificas, Parc Cientific, E-46980 Paterna (Valencia), Spain E-mail: michal.deak@ific.uv.es

10.7 Weak quark mixing and the CKM matrix

2008