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تسجيل مستخدم جديدNeutral Weak Form Factors of Proton and Neutron
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تأليف
Raza Sabbir Sufian
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We determine the nucleon neutral weak electromagnetic form factors $G^{Z,p(n)}_{E,M}$ by combining results from light-front holographic QCD and lattice QCD calculations. We deduce nucleon electromagnetic form factors from light-front holographic QCD which provides a good parametrization of the experimental data of the nucleon electromagnetic form factors in the entire momentum transfer range and isolate the strange quark electromagnetic form factors $G^{s}_{E,M}$ using lattice QCD. From these calculations, we obtain precise estimates of the neutral weak form factors in the momentum transfer range of $0,text{GeV}^2leq Q^2 leq 0.5 ,text{GeV}^2 $. From the lattice QCD calculation, we present $Q^2$-dependence of the strange quark form factors. We also deduce the neutral weak Dirac and Pauli form factors $F_{1,2}^{Z,p(n)}$ of the proton and the neutron.
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The electromagnetic form factors of the proton and the neutron are computed within lattice QCD using simulations with quarks masses fixed to their physical values. Both connected and disconnected contributions are computed. We analyze two new ensembl
es of $N_f = 2$ and $N_f = 2 + 1 + 1$ twisted mass clover-improved fermions and determine the proton and neutron form factors, the electric and magnetic radii, and the magnetic moments. We use several values of the sink-source time separation in the range of 1.0 fm to 1.6 fm to ensure ground state identification. Disconnected contributions are calculated to an unprecedented accuracy at the physical point. Although they constitute a small correction, they are non-negligible and contribute up to 15% for the case of the neutron electric charge radius.
Nucleon form factors play an especially important role in studying the dynamics of nucleons and explicit structure of the wave functions at arbitrary nucleon velocity. The purpose of the paper is to explain theoretically all four nucleon form factors
measured experimentally in the cross section measurements (by the Rosenbluth method), yielding almost equal normalized form factors $G^p_E,G^p_M,G^n_M$, as well as in the polarization transfer experiments, where a strongly decreasing proton electric form factor has been discovered. It is shown, using relativistic hyperspherical formalism, that the nucleon wave functions in the lowest approximation provide almost equal normalized form factors as seen in the Rosenbluth cross sections, but in the higher components they contain a large admixture of the quark orbital momenta, which strongly decreases $G^p_E$ and this effect is possibly detected in the polarization transfer method (not seen in the classical cross section experiments). Moreover, the same admixture of the higher components explains the small positive form factor $G^n_E$. The resulting form factors, $G^p_M(Q),G^p_E(Q),G^n_M(Q)$ are calculated up to $Q^2approx 10$ GeV$^2$, using the standard and the Lorentz contracted wave functions and shown to be in reasonable agreement with experimental data.
The electromagnetic form factors of the proton are obtained using a particular realization of QCD in the large $N_c$ limit (${QCD}_{infty}$), which sums up the infinite number of zero-width resonances to yield an Eulers Beta function (Dual-${QCD}_{in
fty}$). The form factors $F_1(q^2)$ and $F_2(q^2)$, as well as $G_M(q^2)$ agree very well with reanalyzed space-like data in the whole range of momentum transfer. In addition, the predicted ratio $mu_p G_E/G_M$ is in good agreement with recent polarization transfer measurements at Jefferson Lab.
We present a determination of the neutral current weak axial charge $G^Z_A(0)=-0.654(3)_{rm stat}(5)_{rm sys}$ using the strange quark axial charge $G^s_A(0)$ calculated with lattice QCD. We then perform a phenomenological analysis, where we combine
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