Strange magnetic form factor of the nucleon in a chiral effective model at next to leading order

Abstract

The strange magnetic form factor of the nucleon is studied in the heavy baryon chiral effective approach at next to leading order. The one loop contributions from kaon and intermediate octet and decuplet hyperons are included, using finite-range-regularization to deal with the ultra-violet divergences. Drawing on an established connection between quenched and full QCD, this model makes it possible to predict the strange magnetic form factor under the hypothesis that for a dipole regulator mass Λ around 0.8 GeV, strangeness in the core is negligible. The strange magnetic form factor is found to be small and negative over a range of momentum transfer, while the strange magnetic moment is consistent with the best lattice QCD determinations.

Constraining nucleon strangeness

“…Aside from precise measurements of the Sachs form factors, great interest attaches also to the parameters µ s and ρ s defined in Eq. (19), which have in fact already been constrained to some extent by previous analyses [23,24], though the uncertainties of fits to elastic data remain fairly large. These fits generically proceed by ascribing a simple Q 2 dependence to the vector and axial form factors, and leaving ρ s and µ s , as well as vector and axial masses as free parameters to be constrained by data.…”

“…(23) responsible for the widest spread in the elastic observables µ s and ρ s introduced in Eq. (19). Then, if we take the Gaussian calculation constrained to satisfy the combination of extrema [xS + = 0.040, xS − = 0.005] (G1) and [xS + = 0.040, xS − = −0.001] (G2) as distinct models, we obtain the family of parameter values listed in Table I after running scans over the input parameter ranges just described with a 50-point sampling of 1 ≤ N s ≤ 100.…”

“…[5] for a recent review) to detect the signatures for nucleon strangeness in PV elastic measurements at SAMPLE [6], HAPPEX I -III [7][8][9], Mainz [10,11], and G0 [12,13], and remains a relevant consideration in experimental searches for BSM physics [14] and phenomena such as partonic charge symmetry breaking [15,16]. On the other hand, a number of theoretical studies, e.g., [17][18][19][20][21], have proceeded in tandem with these experimental developments, including several global analyses of the elastic data [22][23][24].…”

Strange-quark asymmetry in the proton in chiral effective theory

“…which implies that for the q −q difference the moments vanish, x n−1 q−q = 0, for all even n. Indeed, the matching equation (14) can be written in terms of the moments as…”

“…Recognition that the spatial distributions of strange quarks and antiquarks could be different further motivated searches for strange contributions to the nucleon's electroweak form factors [3][4][5][6][7][8]. Dedicated programs of strange form factor measurements through parityviolating electron scattering at Jefferson Lab and other facilities [9][10][11] subsequently yielded very precise determinations of both the strange electric and magnetic form factors of the nucleon [12], enabling rigorous comparisons with lattice QCD and chiral effective theory [13,14], as well as fundamental tests of the Standard Model [15].…”