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Lowest order Feynman diagrams contributing to electron-nucleon scattering. The electroweak currents of the nucleon are indicated by the shaded disks.
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The measurement of parity violation in the helicity dependence of electron-nucleon scattering provides unique information about the basic quark structure of the nucleons. This review presents the general formalism of parity-violating electron scattering, with emphasis on elastic electron-nucleon scattering. The physics issues addressed by such expe...
Contexts in source publication
Context 1
... observables in electroweak electron-nucleon scattering, the overall electromag- netic and neutral weak currents (as indicated in Figure 1), may be related to the currents of the elementary quarks in the nucleon. Assuming the quarks are point- like Dirac particles, the form of such currents is ...
Context 2
... are important contributions to electroweak electron-nucleon scattering beyond those appearing in Fig. 1. Examples of some of these processes are shown in Fig. 2. These can be considered radiative corrections to the ordinary weak Z 0 Fig. 2. Examples of higher order diagrams that contribute to electroweak electron-nucleon scat- ...
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Citations
... When this happens, |t| is of moderate size, M H = M nucleon and we retain both form factors. F 1 and F 2 take on different values depending if they are for the neutron or proton. Their values are given [81,82] by solving the system of equations ...
We consider generic neutrino dipole portals between left-handed neutrinos, photons, and right-handed heavy neutral leptons (HNL) with Dirac masses. The dominance of this portal significantly alters the conventional phenomenology of HNLs. We derive a comprehensive set of constraints on the dipole portal to HNLs by utilizing data from LEP, LHC, MiniBooNE, LSND as well as observations of Supernova 1987A and consistency of the standard Big Bang Nucleosynthesis. We calculate projected sensitivities from the proposed high-intensity SHiP beam dump experiment, and the ongoing experiments at the Short-Baseline Neutrino facility at Fermilab. Dipole mediated Primakoff neutrino upscattering and Dalitz-like meson decays are found to be the main production mechanisms in most of the parametric regime under consideration. Proposed explanations of LSND and MiniBooNE anomalies based on HNLs with dipole-induced decays are found to be severely constrained, or to be tested in the future experiments.
... [19][20][21][22], a detailed convincing understanding about the sign and magnitude of strange EM form factors is still lacking. A detailed critical review of these theoretical efforts can be found in [23]. ...
We report a lattice QCD calculation of the strange quark contribution to the proton's magnetic moment and charge radius. This analysis presents the first direct determination of strange electromagnetic form factors including the physical pion mass with chiral fermions. We perform a model-independent extraction of the strange magnetic moment and the strange charge radius from the electromagnetic form factors in the momentum transfer range of $0.051 \,\text{GeV}^2 \lesssim Q^2 \lesssim 1.31 \,\text{GeV}^2 $. The finite lattice spacing and finite volume corrections are included in a global fitting with $17$ valence quark masses on three lattices with different lattice spacings, different volumes, and three sea quark masses including one at the physical pion mass. We obtain the strange magnetic moment $G^s_M(0) = - 0.073(17)(08)\, \mu_N$. The 4-sigma precision in statistics is achieved partly due to the low-mode averaging of the quark loop and low-mode substitution of the nucleon source to improve the statistics of the nucleon propagator. We also obtain the strange charge radius \mbox{$\langle r_s^2\rangle_E = -0.0046 (21)(10)\,$ $\text{fm}^2$}.
... One example is the measurement of a neutron electric dipole moment [41]. Another is the parity violating scattering experiments which aim at measuring the weak charge of the proton or its strangeness form factor [42]. If parity is not a good quantum number, two additional form factors are necessary to parametrize the matrix elements of the vector current on a spin 1/2 bound state, ...
A few chosen nucleon properties are described from a lattice QCD perspective:
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form factors in the nucleon, including the vector strangeness contribution, as
well as parity breaking effects like the anapole and electric dipole moment;
and finally the axial and tensor charges of the nucleon. The status of the
lattice calculations is presented and their potential impact on phenomenology
is discussed.
... Most of theoretical calculations at that time predicted a negative value for G s M . In particular, the KΛ meson cloud model gave negative G s M [22]. If the strange quark contribution to the magnetic form factor were indeed large and positive, then, as it was shown in [23], the |uud¯ ss > component of the nucleon would have had the ¯ s quark in the ground S-wave state and the uuds system in the P-wave. ...
A review of experimental results for the measurement of the strange quark distributions in the nucleon, is given. Contributions
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... We see that the investigation of the elastic NC neutrino-nucleon scattering gives the opportunity to explore the nucleon strangeness [18, 19] (mainly the axial strange part). The strangeness of the nucleon is also investigated in the elastic ep scattering [9, 20]. The extraction of this contribution is sensitive to the accuracy of the EM form-factors. ...
The electromagnetic nucleon form-factors data are studied with artificial feed forward neural networks. As a result the unbiased
model-independent form-factor parametrizations are evaluated together with uncertainties. The Bayesian approach for the neural
networks is adapted for χ
2 error-like function and applied to the data analysis. The sequence of the feed forward neural networks with one hidden layer
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determine the best form factor parametrization.
KeywordsLepton-Nucleon Scattering
... Ce résultat est néanmoins affecté de nombreuses sources d'erreurs mal maîtrisées, comme l'incertitude sur les données πN , l'extrapolation au point non physique de "Cheng-Daschen", ou l'incertitude sur les ordres supérieurs dans les corrections chiralesà apporter aux relations de masse des baryons etc. . . [BH01]. Des calculs en QCD sur réseau ontété menés mais ne parviennent pas non plusà un concensus [Liu06], ce qui illustre la complexité analytique liéeà la description du nucléon. ...
... L'étude de la structure des nucléons, et en particulier de la contribution du quarkétrange aux propriétésélectromagnétiques de ces derniers, se place dans le cadre non perturbatif de QCD, ce qui en fait toute la complexité.De nombreux modèles, plus ou moins basés sur les propriétés intrinsèques de QCD, ontété développés pour prédire la contribution du quarkétrange. Une revue détaillée d'une grande partie de ces modèles est effectuée par les auteurs de la référence[BH01]. Ce chapitre a pour objectif de présenter quelques uns de ces modèles afin de donner un aperçu de leur diversité. ...
The complexity of the nucleon structure makes its understanding one of the most challenging problem in hadronic physics. Over the past 20 years, a vast experimental program was developped to measure the strange quark contribution to the properties of nucleons, such as their mass, spin or momentum, in order to investigate the contribution of the sea. We report here on the results of the G0 experiment which measured the strange quark contribution to the electromagnetic form factors of nucleons. The experiment measures parity violating asymmetries of polarized electrons scattered from proton and deuteron targets at both forward and backward scattering angles. In this work, we focus on the data analysis of the backward experiment which corresponds to four datasets on hydrogen and deuterium targets at Q2=0.23 and 0.63 (GeV/c)2. The formalism which leads to the nucleon electric and magnetic form factors and the presentation of the G0 apparatus are first discussed. The second part is dedicated to the data analysis which leads to the asymmetry and particularly focuses on the correction of all effects related to the electronics because they are a major contribution to the global systematics. The backward and forward angle measurements together are finally combined to determine the strange quark form factors which are then compared to the world data.
... In recent years, there has been a vigorous experimental effort to determine the strange contribution to the nucleon's elastic electroweak form factors. In particular, a number of experiments have sought to measure the strange electric and magnetic form factors via parity-violating electron scattering [1], notably SAMPLE, A4, HAPPEX, and G0. Recent combined analyses [2, 3] find values for G s E (Q 2 ) and G s M (Q 2 ) that are small and consistent with zero in the range of momenta so far explored. ...
We discuss the calculation of disconnected diagrams needed for determining the strange quark content of the nucleon on the lattice. We present results for the strange scalar form factor and the related parameter f_Ts, which enters into the cross-section for the scattering of dark matter off nuclei in supersymmetric extensions of the standard model. In addition, we present results for the strange contribution to the nucleon's axial and electromagnetic form factors. The calculations were performed with two dynamical flavors of Wilson fermions on a 24^3 x 64 anisotropic lattice with a_s = 3a_t = 0.11 fm and M_pi ~ 400 MeV.
... In het vorige hoofdstuk werden vormfactoren ingevoerd om de elektrozwakke stromen te beschrijven. Na enig rekenwerk vindt men een uitdrukking voor de asymmetrie in functie van deze vormfactoren [92]: ...
Measurement of the helicity dependent elastic electron–proton scattering cross section provides a key means of investigating parity violation within the proton. However, such measurements exhibit potential instrumental effects associated with the detection of polarized recoiled protons. In particular, spin–orbit interactions within a massive detector induce a systematic spatial shift in the detector signal. In this study, we determine the size of this shift using the Geant4 simulation toolkit. For a typical hadron calorimeter, we found a polarization dependent shift on the order of 0.01-0.1 mm, multiple orders of magnitude smaller than the typical spatial resolution seen in hadronic calorimeters. Additionally, we provide the custom modifications required of the Geant4 source code to implement the quasi-elastic scattering of polarized protons incident on nuclei in the detector. The modifications are readily extendable to generic matter sources, and can be used for the study of additional spin dependent observables in Geant4.
A brief review on some recent progresses in our understanding of multi-quark components in baryons is presented. The multi-quark components in baryons seem to be mainly in colored quark cluster configurations rather than in "meson cloud" configurations or in the form of a sea of quark-antiquark pairs. The colored quark cluster multi-quark picture gives a natural explanation of empirical indications for a positive strangeness magnetic moment μs of the proton and the longstanding mass-reverse problem of S11(1535) and P11(1440) N* resonances. A model-prediction for the μs of the proton is given.
