Search results for "form factor"
showing 10 items of 261 documents
Search for CP violation in the decay Z → τ+τ−
1995
Data collected by ALEPH in the years 1990, 1991 and 1992 have been used to update a previous search for CP violation in the decay of the Z into tau(+)tau(-). The measurement of the weak dipole form factor of the tau lepton has been performed by studying correlations between the tau leptons. No signal of CP violation was found. The weak dipole form factor is found to be ($) over tilde d(tau) = (+0.15 +/- 0.58(stat) +/- 0.38(sys)) 10(-17)e . cm, obtained with 19628 identified tau(+)tau(-) events. This gives an upper limit on the weak dipole form factor of j\($) over tilde d(tau)\ < 1.5 . 10(-17)e . cm at the 95% confidence level.
Analytic results for planar three-loop integrals for massive form factors
2016
We use the method of differential equations to analytically evaluate all planar three-loop Feynman integrals relevant for form factor calculations involving massive particles. Our results for ninety master integrals at general $q^2$ are expressed in terms of multiple polylogarithms, and results for fiftyone master integrals at the threshold $q^2=4m^2$ are expressed in terms of multiple polylogarithms of argument one, with indices equal to zero or to a sixth root of unity.
Search for newπ0-like particles produced in association with aτ-lepton pair
2014
We report on a search in e^+e^− annihilations for new π^0-like particles produced in association with a τ-lepton pair. These objects, with a similar mass and similar decay modes to π^0 mesons, could provide an explanation for the non-asymptotic behavior of the pion-photon transition form factor observed by the BABAR Collaboration. No significant signal is observed, and limits on the production cross section at the level of 73 fb or 370 fb, depending on the model parameters, are determined at 90% confidence level. These upper limits lie below the cross section values needed to explain the BABAR form factor data.
Hadronic contribution to the lepton anomalous magnetic moment and pion form factor in lattice QCD
2012
Abstract The Mainz lattice QCD group is currently carrying out simulations of lattice QCD with the aim of making predictions for a wide range of phenomenologically relevant Standard Model properties. Here we present progress in understanding and controlling systematic effects in the computation of the pion vector form factor and the leading hadronic contribution to the lepton anomalous magnetic moment.
Tau spin correlations and the anomalous magnetic moment
2009
We show that the precise determination of the Tau magnetic properties is possible in the next generation accelerators, specially at B/Flavour factories. We define spin correlation observables suitable to extract the real part of the magnetic form factor that, for the first time, will allow to test the standard model-QED predictions. In particular, the predicted QED-dependence with both the momentum transfer and the lepton mass can be precisely measured. Until now, the most stringent bounds on the $\tau$ magnetic moment $a_\tau$ come from LEP data with strong assumptions on the physics involved on the observed process. In this paper, we find three different combinations of spin correlations …
The scalar pion form factor in two-flavor lattice QCD
2013
We calculate the scalar form factor of the pion using two dynamical flavors of non-perturbatively $\mathcal{O}(a)$-improved Wilson fermions, including both the connected and the disconnected contribution to the relevant correlation functions. We employ the calculation of all-to-all propagators using stochastic sources and a generalized hopping parameter expansion. From the form factor data at vanishing momentum transfer, $Q^2=0$, and two non-vanishing $Q^2$ we obtain an estimate for the scalar radius $\left^\pi_{_{\rm S}}$ of the pion at one value of the lattice spacing and for five different pion masses. Using Chiral Perturbation Theory at next-to-leading order, we find $\left^\pi_{_{\rm S…
Vector form factor of the pion from unitarity and analyticity: a model-independent approach
2001
7 páginas, 2 figuras, 3 tablas.-- PACS number(s): 13.35.Dx, 12.39.Fe, 13.40.Gp, 13.65.1i
Measurements of the Hadronic Cross Section and of Meson Transition Form Factors at BESIII for an improved Standard Model Prediction of (g−2)μ
2015
Abstract The BESIII experiment at the Beijing tau-charm factory BEPCII recently has embarked on a series of form factor measurements with the goal to improve the hadronic vacuum polarization as well as the hadronic light-by-light contributions to ( g − 2 ) μ . The status of the flagship measurements and preliminary results are presented.
Plausible explanation for theΔ5/2+(2000)puzzle
2011
From a Faddeev calculation for the $\ensuremath{\pi}$-$(\ensuremath{\Delta}\ensuremath{\rho}){}_{{N}_{5/{2}^{\ensuremath{-}}}(1675)}$ system we show the plausible existence of three dynamically generated $I({J}^{P})=3/2(5/{2}^{+})$ baryon states below 2.3 GeV, whereas only two resonances, ${\ensuremath{\Delta}}_{5/{2}^{+}}(1905)(****)$ and ${\ensuremath{\Delta}}_{5/{2}^{+}}(2000)(**),$ are cataloged in the Particle Data Book Review. Our results give theoretical support to data analyses extracting two distinctive resonances, ${\ensuremath{\Delta}}_{5/{2}^{+}}(~$1740) and ${\ensuremath{\Delta}}_{5/{2}^{+}}(~$2200), from which the mass of ${\ensuremath{\Delta}}_{5/{2}^{+}}(2000)(**)$ is estima…
Search for anomalous quarticWWγγcouplings in dielectron and missing energy final states inpp¯collisions ats=1.96 TeV
2013
We present a search for anomalous components of the quartic gauge boson coupling WW gamma gamma in events with an electron, a positron and missing transverse energy. The analyzed data correspond to 9.7 fb(-1) of integrated luminosity collected by the D0 detector in p (p) over bar collisions at root s 1.96 TeV. The presence of anomalous quartic gauge couplings would manifest itself as an excess of boosted WW events. No such excess is found in the data, and we set the most stringent limits to date on the anomalous coupling parameters a(0)(W) and a(C)(W). When a form factor with Lambda(cutoff) = 0.5 TeV is used, the observed upper limits at 95% C. L. are vertical bar a(0)(W)/Lambda(2)vertical …