Strangeness Vector and Axial-Vector Form Factors of the Nucleon

Abstract

Abstract.A revised global fit of electroweak ep and νp elastic scattering data has been performed, with the goal of determining the strange quark contribution to the vector and axial-vector form factors of the nucleon in the momentum-transfer range 0 < Q 2 < 1 GeV 2 . The two vector (electric and magnetic) form factors G s E (Q 2 ) and G s M (Q 2 ) are strongly constrained by ep elastic scattering data, while the major source of information on the axial-vector form factor G s A (Q 2 ) is νp scattering data. Combining the two kinds of data into a single global fit makes possible additional precision in the determination of these form factors, and provides a unique way to determine the strange quark contribution to the nucleon spin, ∆S , independently of leptonic deep-inelastic scattering. The fit makes use of data from the BNL-E734, SAMPLE, HAPPEx, G0, and PVA4 experiments; we will also compare the result of the fit with recent data from MiniBooNE, and anticipate how this fit can be improved when new data from MicroBooNE become available. OverviewThe strange quark contribution to the elastic form factors of the nucleon has been the subject of intense experimental scrutiny for several decades. Experiments involving elastic scattering of neutrinos and anti-neutrinos (BNL E734 [1]), and electrons (SAMPLE [2], HAPPEx [3][4][5][6][7], G0 [8,9], and PVA4 [10][11][12]) from nucleons and nuclei have explored the strange quark presence in the nucleon by exploiting the electromagnetic and weak interactions in a variety of ways. These special data permit a simultaneous determination [13] of the strange quark contribution to the electric (G s E (Q 2 )), magnetic (G s M (Q 2 )), and axial (G s A (Q 2 )) form factors of the nucleon, which respectively allow us to understand how the strange quark contributes to the distribution of charge, current, and spin inside the nucleon. A global fit of these data has been performed, which sets strong limits on the size and Q 2 -dependence of G s E (Q 2 ) and G s M (Q 2 ), and points out the need for additional neutrino scattering data at low Q 2 to complete a measurement of G s A (Q 2 ). Strangeness Form FactorsSince the strange and anti-strange quarks have opposite electric charges, then they contribute to the strangeness electric form factor G s E with opposite sign; therefore, if the s ands distributions in the a

Improving Dark Matter Searches by Measuring the Nucleon Axial Form Factor: Perspectives from MicroBooNE

“…The combination of form factors −G u A + G d A is well determined from charged current neutrino reactions and elastic and deep inelastic electron and muon scattering experiments, as well as neutron decay experiments [5]. The last form factor, G s A , approaches the value of the strange quark spin, Δs, as the momentum transfer squared, Q 2 , goes to zero, Eq.…”

“…Folding the simulated MicroBooNE result into the fit, the uncertainty on the form factor G s A is improved by an order of magnitude [5] [6]. A comparison of the form factors before and after inclusion of the MicroBooNE simulation is shown in Fig.…”

“…Same as Fig. 3, but on the right, the lines include with MicroBooNE projected data folded into the fit [5][6].…”

Coherent μ−e conversion at next-to-leading order

“…T ) where ρ s is the strangeness radius and µ s is the strange magnetic moment [54]. Thus, keeping terms only through NLO the matrix element is given by…”

Strange nucleon form factors and isoscalar charges with $N_f=2+1$ $\mathcal{O}(a)$-improved Wilson fermions

“…In order to control the effects of proton structure in the scattering experiments, knowledge of nucleon form factors is required. Among others, the strange form factors G s E (Q 2 ), G s M (Q 2 ) and G s A (Q 2 ) need to be known precisely, which is a challenging task in experiments [4]. Here, we extract these form factors from a first-principles Lattice QCD study, based on our previous work [5].…”