Search results for "form factor [N(1535)]"
showing 10 items of 205 documents
ElectromagneticN→N*(1535)transition in the relativistic constituent-quark model
1990
We study a light-cone model of the nucleon and the ${S}_{11}(1535)$ resonance which provides a relativistic generalization of the constituent-quark model in the nonperturbative low-${Q}^{2}$ regime. The two parameters of the model, namely, the size parameter $\ensuremath{\alpha}$ and the constituent-quark mass ${m}_{q}\ensuremath{\approx}300$ MeV, are fixed by the axial form factor. We find good agreement for the electromagnetic form factors of the nucleon up to ${Q}^{2}\ensuremath{\approx}1\ensuremath{-}2$ Ge${\mathrm{V}}^{2}$. All static properties of the nucleon, except for the neutron charge radius, are reproduced within 10%. In addition, we show that the electromagnetic current of the …
Pion electroproduction, partially conserved axial-vector current, chiral Ward identities, and the axial form factor revisited
2003
We reinvestigate Adler's partially conserved axial-vector current relation in the presence of an external electromagnetic field within the framework of QCD coupled to external fields. We discuss pion electroproduction within a tree-level approximation to chiral perturbation theory and explicitly verify a chiral Ward identity referred to as the Adler-Gilman relation. We critically examine soft-momentum techniques and point out how inadmissable approximations may lead to results incompatible with chiral symmetry. As a result we confirm that threshold pion electroproduction is indeed a tool to obtain information on the axial form factor of the nucleon.
Coherent elastic neutrino-nucleus scattering on 40Ar from first principles
2019
Coherent elastic neutrino scattering on the 40Ar nucleus is computed with coupled-cluster theory based on nuclear Hamiltonians inspired by effective field theories of quantum chromodynamics. Our approach is validated by calculating the charge form factor and comparing it to data from electron scattering. We make predictions for the weak form factor, the neutron radius, and the neutron skin, and estimate systematic uncertainties. The neutron-skin thickness of 40Ar40 is consistent with results from density functional theory. Precision measurements from coherent elastic neutrino-nucleus scattering could potentially be used to extract these observables and help to constrain nuclear models.
Measurement of the hadronic form factor inD0→K−e+νedecays
2007
We present a preliminary measurement of the q2 dependence of the D0 --> K- e+ nu_e decay rate. This rate is proportional to the hadronic form factor squared, specified by a single parameter. This is either the mass in the simple pole ansatz m_pole = (1.854 +- 0.016 +- 0.020) GeV/c2 or the scale in the modified pole ansatz alpha_pole = 0.43 +- 0.03 +- 0.04. The first error refers to the statistical, the second to the systematic uncertainty.
Vanishing chiral couplings in the large-Nc resonance theory
2007
5 pages, 2 figures.-- PACS nrs.: 12.39.Fe; 11.15.Pg; 12.38.-t.-- ISI Article Identifier: 000247625300022.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0611375
Quantum loops in the Resonance Chiral Theory: improving the vector form factor
2006
Quantum loops in the Resonance Chiral Theory are needed to improve the implementation of non-perturbative QCD. Furthermore, the one-loop computations can predict chiral low-energy couplings at next-to-leading order, a very appealing task. We present a first calculation of the vector form factor of the pion at subleading order in the 1/N_C expansion. From the analysis of the result at large energies we justify the requirement of considering short-distance constraints from form factors with resonances in the final state. The long-distance limit of our results allows to get a next-to-leading order estimate of \ell_6.
The vector form factor at the next-to-leading order in 1/N(C): chiral couplings L9(mu) and C88(mu) - C90(mu)
2010
24 páginas, 3 figuras, 2 tablas.-- arXiv:1011.5771v1.
Origin of the Large Perturbative Corrections to Higgs Production at Hadron Colliders
2008
The very large K-factor for Higgs-boson production at hadron colliders is shown to result from enhanced perturbative corrections of the form (C_A\pi\alpha_s)^n, which arise in the analytic continuation of the gluon form factor to time-like momentum transfer. These terms are resummed to all orders in perturbation theory using the renormalization group. After the resummation, the K-factor for the production of a light Higgs boson at the LHC is reduced to a value close to 1.3.
Isovector and isoscalar meson cloud contributions to the nucleon electromagnetic form factors
1998
We have calculated the nucleon form factors ${G}_{E,M}^{(p,n)}{(q}^{2})$ in the linear \ensuremath{\sigma} model to one-meson-loop order plus (two-loop) $\ensuremath{\gamma}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$ anomaly. The previously derived $\ensuremath{\gamma}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$ anomaly generally reduces the nucleon radii and produces a shift of the magnetic moments of order 0.1 ${\ensuremath{\mu}}_{N}$ or less. We present analytical results for ${G}_{E,M}^{p,n}(0)$ which display explicitly their dependence on hadron masses and coupling constants. Analytical results for the radii are also given and the chiral singularities they contain $(\mathrm{…
Next-to-next-to-leading order prediction for the photon-to-pion transition form factor
2003
We evaluate the next-to-next-to-leading order corrections to the hard-scattering amplitude of the photon-to-pion transition form factor. Our approach is based on the predictive power of the conformal operator product expansion, which is valid for a vanishing $\beta$-function in the so-called conformal scheme. The Wilson--coefficients appearing in the non-forward kinematics are then entirely determined from those of the polarized deep-inelastic scattering known to next-to-next-to-leading accuracy. We propose different schemes to include explicitly also the conformal symmetry breaking term proportional to the $\beta$-function, and discuss numerical predictions calculated in different kinemati…