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Register a new userNucleon charges and form factors using clover and HISQ ensembles
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We present high statistics ($mathcal{O}(2times 10^5)$ measurements) preliminary results on (i) the isovector charges, $g^{u-d}_{A,S,T}$, and form factors, $G^{u-d}_E(Q^2)$, $G^{u-d}_M(Q^2)$, $G^{u-d}_A(Q^2)$, $widetilde G^{u-d}_P(Q^2)$, $G^{u-d}_P(Q^2)$, on six 2+1-flavor Wilson-clover ensembles generated by the JLab/W&M/LANL/MIT collaboration with lattice parameters given in Table 1. Examples of the impact of using different estimates of the excited state spectra are given for the clover-on-clover data, and as discussed in [1], the biggest difference on including the lower energy (close to $Npi$ and $Npipi$) states is in the axial channel. (ii) Flavor diagonal axial, tensor and scalar charges, $g^{u,d,s}_{A,S,T}$, are calculated with the clover-on-HISQ formulation using nine 2+1+1-flavor HISQ ensembles generated by the MILC collaboration [2] with lattice parameters given in Table 2. Once finished, the calculations of $g^{u,d,s}_{A,T}$ will update the results given in Refs.[3,4]. The estimates for $g^{u,d,s}_{S}$ and $sigma_{Npi}$ are new. Overall, a large part of the focus is on understanding the excited state contamination (ESC), and the results discussed provide a partial status report on developing defensible analyses strategies that include contributions of possible low-lying excited states to individual nucleon matrix elements.
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We present high statistics results for the isovector nucleon charges and form factors using seven ensembles of 2+1-flavor Wilson-clover fermions. The axial and pseudoscalar form factors obtained on each ensemble satisfy the PCAC relation once the lowest energy $Npi$ excited state is included in the spectral decomposition of the correlation functions used for extracting the ground state matrix elements. Similarly, we find evidence that the $Npipi $ excited state contributes to the correlation functions with the vector current, consistent with the vector meson dominance model. The resulting form factors are consistent with the Kelly parameterization of the experimental electric and magnetic data. Our final estimates for the isovector charges are $g_{A}^{u-d} = 1.31(06)(05)_{sys}$, $g_{S}^{u-d} = 1.06(10)(06)_{sys}$, and $g_{T}^{u-d} = 0.95(05)(02)_{sys}$, where the first error is the overall analysis uncertainty and the second is an additional combined systematic uncertainty. The form factors yield: (i) the axial charge radius squared, ${langle r_A^2 rangle}^{u-d}=0.428(53)(30)_{sys} {rm fm}^2$, (ii) the induced pseudoscalar charge, $g_P^ast=7.9(7)(9)_{sys}$, (iii) the pion-nucleon coupling $g_{pi {rm NN}} = 12.4(1.2)$, (iv) the electric charge radius squared, ${langle r_E^2 rangle}^{u-d} = 0.85(12)(19)_{sys} {rm fm}^2$, (v) the magnetic charge radius squared, ${langle r_M^2 rangle}^{u-d} = 0.71(19)(23)_{rm sys} {rm fm}^2$, and (vi) the magnetic moment $mu^{u-d} = 4.15(22)(10)_{rm sys}$. All our results are consistent with phenomenological/experimental values but with larger errors. Lastly, we present a Pade parameterization of the axial, electric and magnetic form factors over the range $0.04< Q^2 <1$ GeV${}^2$ for phenomenological studies.
We report updates to an ongoing lattice-QCD calculation of the form factors for the semileptonic decays $B to pi ell u$, $B_s to K ell u$, $B to pi ell^+ ell^-$, and $B to K ell^+ ell^-$. The tree-level decays $B_{(s)} to pi (K) ell u$ enable precise determinations of the CKM matrix element $|V_{ub}|$, while the flavor-changing neutral-current interactions $B to pi (K) ell^+ ell^-$ are sensitive to contributions from new physics. This work uses MILCs (2+1+1)-flavor HISQ ensembles at approximate lattice spacings between $0.057$ and $0.15$ fm, with physical sea-quark masses on four out of the seven ensembles. The valence sector is comprised of a clover $b$ quark (in the Fermilab interpretation) and HISQ light and $s$ quarks. We present preliminary results for the form factors $f_0$, $f_+$, and $f_T$, including studies of systematic errors.
We present results on the nucleon electromagnetic form factors from Lattice QCD at momentum transfer up to about $12$~GeV$^2$. We analyze two gauge ensembles with the Wilson-clover fermion action, a lattice spacing of $aapprox 0.09$~fm and pion masses $m_piapprox 170$~MeV and $m_piapprox 280$~MeV. In our analysis we employ momentum smearing as well as a set of techniques to investigate excited state effects. Good agreement with experiment and phenomenology is found for the ratios $G_E/G_M$ and $F_2/F_1$, whereas discrepancies are observed for the individual form factors $F_1$ and $F_2$. We discuss various systematics that may affect our calculation.
We give an update on our ongoing efforts to compute the nucleons form factors and moments of structure functions using Nf=2 flavours of non-perturbatively improved Clover fermions. We focus on new results obtained on gauge configurations where the pseudo-scalar meson mass is in the range of 170-270 MeV. We will compare our results with various estimates obtained from chiral effective theories since we have some overlap with the quark mass region where results from such theories are believed to be applicable.
We present preliminary results on the electromagnetic form factors and axial charge of the nucleon from ensembles generated by the CLS effort with $N_mathrm{f}=2+1$ flavours of non-perturbatively $mathrm{O}(a)$-improved Wilson fermions and open temporal boundary conditions. Systematic effects due to excited-state contamination are accounted for using both two-state fits and the method of summed operator insertions. This exploratory analysis demonstrates the viability of obtaining precision baryon observables with $N_mathrm{f}=2+1$ flavours of Wilson fermions on fine lattices, aiming towards controlled chiral and continuum limits in the future.
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