Extracting theΩ−electric quadrupole moment from lattice QCD data

Abstract

The Ω − has an extremely long lifetime, and is the most stable of the baryons with spin 3/2. Therefore the Ω − magnetic moment is very accurately known. Nevertheless, its electric quadrupole moment was never measured, although estimates exist in different formalisms. In principle, lattice QCD simulations provide at present the most appropriate way to estimate the Ω − form factors, as function of the square of the transferred four-momentum, Q 2 , since it describes baryon systems at the physical mass for the strange quark. However, lattice QCD form factors, and in particular GE2, are determined at finite Q 2 only, and the extraction of the electric quadrupole moment,, involves an extrapolation of the numerical lattice results. In this work we reproduce the lattice QCD data with a covariant spectator quark model for Ω − which includes a mixture of S and two D states for the relative quark-diquark motion. Once the model is calibrated, it is used to determine Q Ω − . Our prediction is Q Ω − = (0.96 ± 0.02) × 10 −2 efm 2 [GE2(0) = 0.680 ± 0.012].

Axial form factors of the octet baryons in a covariant quark model

“…In this case we have a more clean parametrization (free of meson cloud effects) for the valence quark effects. The same method was used previously and successfully in the studies of the electromagnetic proprieties of the nucleon, the Roper, the γ * N → ∆ reaction, as well as in the studies of the octet and decuplet baryon properties [102][103][104][106][107][108][109]. The methodology used in the present study can be summarized as follows:…”

“…The model has successfully been applied in studies of the electromagnetic structure of nucleon [98][99][100], several nucleon resonances [1,[101][102][103][104][105] and other baryons [106][107][108][109][110][111][112][113][114]. The covariant spectator quark model is based on the assumption that the constituent quarks have their own internal structure, which can be parametrized by individual quark (electromagnetic) form factors.…”

Semirelativistic approximation to the γ*N→N(1520) and γ*NRamalho1 2017Phys. Rev. DSelf Cite182120View full textAdd to dashboardCite

“…The wave functions of the nucleon, N (1520) and N (1535) are discussed in Refs. [8,9,22].The covariant spectator quark model was already applied to the nucleon [22,23,[36][37][38], several nucleon resonances [8-10, 25, 27], ∆ resonances [10,34,35,[39][40][41][42], and other transitions between baryon states [24,30,[43][44][45].When the baryon wave functions are represented in terms of the single quark and quark-pair states, one can write the transition current in a relativistic impulse approximation as [22][23][24] where j µ q is the quark current operator and Γ labels the scalar diquark and vectorial diquark (projections Λ = 0, ±) polarizations. The factor 3 takes account of the contributions of all the quark-pairs by symmetry.…”

γ*N→N*(1520) form factors in the timelike regime

“…This model is based on the covariant spectator theory (CST) [19]. In a relatively successful and unifying way, our approach pictures a large variety of baryons as a superposition of a core of three valence quarks and meson cloud components [6][7][8][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. After a series of applications of the model to the electromagnetic excitation of baryons in the spacelike regime, we analyzed also the impact of the ∆(1232) resonance in the timelike reactions [6,7].…”