Search results for "Momentum transfer"
showing 10 items of 134 documents
Semileptonic D(s) -meson decays in the light of recent data
2018
Inspired by recent improved measurements of charm semileptonic decays at BESIII, we study a large set of $D({D}_{s})$-meson semileptonic decays where the hadron in the final state is one of ${D}^{0}$, $\ensuremath{\rho}$, $\ensuremath{\omega}$, ${\ensuremath{\eta}}^{(\ensuremath{'})}$ in the case of ${D}^{+}$ decays, and ${D}^{0}$, $\ensuremath{\phi}$, ${K}^{0}$, ${K}^{*}(892{)}^{0}$, ${\ensuremath{\eta}}^{(\ensuremath{'})}$ in the case of ${D}_{s}^{+}$ decays. The required hadronic form factors are computed in the full kinematical range of momentum transfer by employing the covariant confined quark model developed by us. A detailed comparison of the form factors with those from other appro…
The γγ Physics Program at BESIII
2018
A key motivation for the two-photon physics program of the BESIII collaboration is the need of high precision data on electromagnetic transition form factors as input to the calculations of the contribution of hadronic Light-by-light scattering to the anomalous magnetic moment of the muon. The data collected with the BESIII detector allow to study the momentum dependence of the form factors at small momentum transfers, which is of special relevance for αμ. In this presentation the ongoing measurements of the transition form factors of π0,η and η' mesons, as well as pion pairs, are discussed, and the potential for first double-tagged measurements at BESIII are pointed out.
Measurement of transition form factors in two-photon collisions at BESIII
2019
The two-photon physics program of the BESIII Collaboration is mainly motivated by the need of new measurements of transition form factors as input for the Standard Model calculations of $ \mathop a\nolimits_\mu ^{HLbL} $, the hadronic light-by-light scattering contribution to the anomalous magentic moment of the muon. The large data sets acquired at BESIII allow to study the transition form factors of pseudoscalar mesons in the relevant region of momentum transfer for $ \mathop a\nolimits_\mu ^{HLbL} $. In this presentation the status of the respective measurements for π0,η and η’ mesons are discussed, and prospects for studies of multi-meson systems as well as of doubly-virtual transition …
Lepton Universality Test in the Photoproduction ofe−e+Versusμ−μ+Pairs on a Proton Target
2015
In view of the significantly different proton charge radius extracted from muonic hydrogen Lamb shift measurements as compared to electronic hydrogen spectroscopy or electron-scattering experiments, we study in this Letter the photoproduction of a lepton pair on a proton target in the limit of very small momentum transfer as a way to provide a test of the lepton universality when extracting the proton charge form factor. By detecting the recoiling proton in the γp→l^{-}l^{+}p reaction, we show that a measurement of a ratio of e^{-}e^{+}+μ^{-}μ^{+} over e^{-}e^{+} cross sections with an absolute precision of 7×10^{-4} would allow for a test to distinguish, at the 3σ level, between the two di…
How to perform QCD analysis of DIS in Analytic Perturbation Theory
2015
We apply (Fractional) Analytic Perturbation Theory (FAPT) to the QCD analysis of the nonsinglet nucleon structure function $F_2(x,Q^2)$ in deep inelastic scattering up to the next leading order and compare the results with ones obtained within the standard perturbation QCD. Based on a popular parameterization of the corresponding parton distribution we perform the analysis within the Jacobi Polynomial formalism and under the control of the numerical inverse Mellin transform. To reveal the main features of the FAPT two-loop approach, we consider a wide range of momentum transfer from high $Q^2\sim 100 {\rm GeV}^2$ to low $Q^2\sim 0.3 {\rm GeV}^2$ where the approach still works.
B-meson to light-meson transition form factors
2007
We report a comprehensive set of results for B-meson heavy-to-light transition form factors calculated using a truncation of, and expression for, the transition amplitudes in which all elements are motivated by the study of Dyson-Schwinger equations in QCD. In this relativistic approach, which realizes confinement and dynamical chiral symmetry breaking, all physical values of momentum transfer in the transition form factors are simultaneously accessible. Our results can be useful in the analysis and correlation of the large body of data being accumulated at extant facilities, and thereby in probing the standard model and beyond.
Chiral extrapolation and finite-volume dependence of the hyperon vector couplings
2014
The hyperon vector form factors at zero momentum transfer, $f_1(0)$, play an important role in a precise determination of the Cabibbo-Kobayashi-Maskawa matrix element $V_{us}$. Recent studies based on lattice chromodynamics (LQCD) simulations and covariant baryon chiral perturbation theory yield contradicting results. In this work, we study chiral extrapolation of and finite-volume corrections to the latest $n_f=2+1$ LQCD simulations. Our results show that finite-volume corrections are relatively small and can be safely ignored at the present LQCD setup of $m_\pi L=4.6$ but chiral extrapolation needs to be performed more carefully. Nevertheless, the discrepancy remains and further studies a…
Nucleon electromagnetic form factors in two-flavor QCD
2015
We present results for the nucleon electromagnetic form factors, including the momentum transfer dependence and derived quantities (charge radii and magnetic moment). The analysis is performed using O(a) improved Wilson fermions in Nf=2 QCD measured on the CLS ensembles. Particular focus is placed on a systematic evaluation of the influence of excited states in three-point correlation functions, which lead to a biased evaluation, if not accounted for correctly. We argue that the use of summed operator insertions and fit ans\"atze including excited states allow us to suppress and control this effect. We employ a novel method to perform joint chiral and continuum extrapolations, by fitting th…
Measurement of theγγ*→π0transition form factor
2009
We study the reaction e+e- --> e+e-pi0 and measure the gamma gamma* --> pi0 transition form factor in the momentum transfer range from 4 to 40 GeV^2. The analysis is based on 442 fb^-1 of integrated luminosity collected at PEP-II with the BABAR detector at e+e- center-of-mass energies near 10.6 GeV.
Description of the spacelike and timelike proton form factors at large momentum transfer in the QCD factorization approach
2012
Abstract We propose QCD factorization approach for description of the soft spectator scattering contribution. It is expected that such contribution is very important for description of the many exclusive processes at moderate values of Q 2 . Assuming the dominance of this mechanism we provide qualitative consideration of the proton form factors in the spacelike and timelike regions. Using the same approach we also provide estimates of the cross sections for the processes γ γ → p p and p p → γ γ at large energy and momentum transfer.