Search results for " form factor"
showing 10 items of 59 documents
Breakdown of the expansion of finite-size corrections to the hydrogen Lamb shift in moments of charge distribution
2015
We quantify a limitation in the usual accounting of the finite-size effects, where the leading $[(Z\alpha)^4]$ and subleading $[(Z\alpha)^5]$ contributions to the Lamb shift are given by the mean-square radius and the third Zemach moment of the charge distribution. In the presence of any non-smooth behaviour of the nuclear form factor at scales comparable to the inverse Bohr radius, the expansion of the Lamb shift in the moments breaks down. This is relevant for some of the explanations of the "proton size puzzle". We find, for instance, that the de R\'ujula toy model of the proton form factor does not resolve the puzzle as claimed, despite the large value of the third Zemach moment. Withou…
The role of the neutron electric form factor ind(e, e? N)N including polarization observables
1988
The influence of the neutron electric form factor on various observables in two-body break-up of deuterons by electrons such as differential cross section, beam, target and beam-target asymmetries and outgoing nucleon polarization as well is investigated for different kinematic regions. The electron-deuteron vector asymmetryAedV and the outgoing nucleon polarization component P′x(n) are the most promising observables in and off the quasi-free region for a determination ofGEn. Also the single polarization observablesAdT and Py0(p) and the double polarization observable P′z(n) show significant influences fromGEn.
Determination of the neutron electric form factor in the D(e,e′n)p reaction and the influence of nuclear binding
1999
The electric form factor of the neutron GE,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q2= 0.15 (GeV/c)2 in a measurement of the recoil polarisation ratio Px/Pz in the quasifree reaction D(e,e′n)p. At this Q2 the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively by a model of Arenhovel et al.. After the corresponding corrections a value of GE,n(0.15 (GeV/c)2) = 0.0481±0.0065stat±0.0053syst is obtained.
The RMS charge radius of the proton and Zemach moments
2010
On the basis of recent precise measurements of the electric form factor of the proton, the Zemach moments, needed as input parameters for the determination of the proton rms radius from the measurement of the Lamb shift in muonic hydrogen, are calculated. It turns out that the new moments give an uncertainty as large as the presently stated error of the recent Lamb shift measurement of Pohl et al.. De Rujula's idea of a large Zemach moment in order to reconcile the five standard deviation discrepancy between the muonic Lamb shift determination and the result of electronic experiments is shown to be in clear contradiction with experiment. Alternative explanations are touched upon.
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 …
Tau anomalous magnetic moment form factor at Super B/Flavor factories
2008
The proposed high-luminosity B/Flavor factories offer new opportunities for the improved determination of the fundamental physical parameters of standard heavy leptons. Compared to the electron or the muon case, the magnetic properties of the $\tau$ lepton are largely unexplored. We show that the electromagnetic properties of the $\tau$, and in particular its magnetic form factor, may be measured competitively in these facilities, using unpolarized or polarized electron beams. Various observables of the $\tau$'s produced on top of the $\Upsilon$ resonances, such as cross-section and normal polarization for unpolarized electrons or longitudinal and transverse asymmetries for polarized beams,…
Nucleon polarization in exclusive deuteron electrodisintegration with polarized electrons and a polarized target
1995
Nucleon polarization in exclusive electrodisintegration of the deuteron using a polarized beam and an oriented target is systematically investigated in a nonrelativistic framework but with lowest order relativistic contributions to the one-body current including the kinematic part of the wave function boost. The structure functions and the asymmetries corresponding to the various nucleon polarization components are studied with respect to their sensitivity to the potential model, to subnuclear degrees of freedom, and to relativistic effects in different kinematical regions. Furthermore, a few new observables are found which are very sensitive to the neutron electric form factor ${\mathit{G}…
Measurement of thee+e−→pp¯cross section in the energy range from 3.0 to 6.5 GeV
2013
The e^+e^−→pp cross section and the proton magnetic form factor have been measured in the center-of-mass energy range from 3.0 to 6.5 GeV using the initial-state radiation technique with an undetected photon. This is the first measurement of the form factor at energies higher than 4.5 GeV. The analysis is based on 469 fb^(−1) of integrated luminosity collected with the BABAR detector at the PEP-II collider at e+e− center-of-mass energies near 10.6 GeV. The branching fractions for the decays J/ψ→pp and ψ(2S)→pp have also been measured.
First measurement of the polarisation transfer on the proton in the reactions $$H(\vec e,e'\vec p)$$ and $$D(\vec e,e'\vec p)$$
1995
The measurement of the polarisation transfer to the proton in the reactions\(H(\vec e,e'\vec p)\) and\(D(\vec e,e'\vec p)\) performed with longitudinally polarised electrons in quasi-free kinematics is presented. The coincidence measurement was executed atQ2≈8fm−2 using the 855 MeV, c.w. beam of the Mainz Microtron MAMI. The recoil polarisation was determined by means of a carbon analyser. The experiment shows that the binding of the nucleon does not modify the polarisationPx of the recoil proton within an error ofΔPx/Px≈10%. The measured polarisation agrees with recent theoretical predictions. Implications for the measurement of the electric form factor of the neutron using the\(D(\vec e,e…
Parity Violating Electron Scattering at the MAMI Facility in Mainz
2005
We report here on a new measurement of the parity violating (PV) asymmetry in the scattering of polarized electrons on unpolarized protons performed with the setup of the A4-collaboration at the MAMI accelerator facility in Mainz. This experiment is the first to use counting techniques in a parity violation experiment. The kinematics of the experiment is complementary to the earlier measurements of the SAMPLE collaboration at the MIT Bates accelerator and the HAPPEX collaboration at Jefferson Lab. After discussing the experimental context of the experiments, the setup at MAMI and preliminary results are presented.