Octet baryon electromagnetic form factors in nuclear medium

Peña

2017

Phys. Rev. D

The covariant spectator quark model, tested before in a variety of electromagnetic baryon excitations, is applied here to the γ * N → N * (1520) reaction in the timelike regime. The transition form factors are first parametrized in the spacelike region in terms of a valence quark core model together with a parametrization of the meson cloud contribution. The form factor behavior in the timelike region is then predicted, as well as the N * (1520) → γN decay width and the N * (1520) Dalitz decay, N * (1520) → e + e − N . Our results may help in the interpretation of dielectron production from elementary pp collisions and from the new generation of HADES results using a pion beam. In the q 2 = 0-1 GeV 2 range we conclude that the QED approximation (a q 2 independent form factor model) underestimates the electromagnetic coupling of the N * (1520) from 1 up to 2 orders of magnitude. We conclude also that the N * (1520) and ∆(1232) Dalitz decay widths are comparable.

Section: Methodsmentioning

confidence: 99%

“…(The radial wave functions are described later). Its behavior in that region was tested by taking it to the lattice QCD regime [34,35], and also to the nuclear medium [38], both implemented with success.…”

Section: A Quark Form Factorsmentioning

confidence: 99%

γN→N(1520) form factors in the timelike regime

Peña

2017

Phys. Rev. D

“…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:…”

Section: Methodsmentioning

confidence: 99%

“…The covariant spectator quark model was first developed for the study of the electromagnetic properties of nucleon [98][99][100], and subsequently extended for the studies of the electromagnetic properties of several resonances, and electromagnetic transitions between baryon states [105,113,114], including the octet and decuplet baryons [106,107,[109][110][111][112].…”

Section: Covariant Spectator Quark Modelmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Tsushima

2016

Phys. Rev. D

We study the weak interaction axial form factors of the octet baryons, within the covariant spectator quark model, focusing on the dependence of four-momentum transfer squared, Q 2 . In our model the axial form factors GA(Q 2 ) (axial-vector form factor) and GP (Q 2 ) (induced pseudoscalar form factor), are calculated based on the constituent quark axial form factors and the octet baryon wave functions. The quark axial current is parametrized by the two constituent quark form factors, the axial-vector form factor g q A (Q 2 ), and the induced pseudoscalar form factor g q P (Q 2 ). The baryon wave functions are composed of a dominant S-state and a P -state mixture for the relative angular momentum of the quarks. First, we study in detail the nucleon case. We assume that the quark axial-vector form factor g q A (Q 2 ) has the same function form as that of the quark electromagnetic isovector form factor. The remaining parameters of the model, the P -state mixture and the Q 2 -dependence of g q P (Q 2 ), are determined by a fit to the nucleon axial form factor data obtained by lattice QCD simulations with large pion masses. In this lattice QCD regime the meson cloud effects are small, and the physics associated with the valence quarks can be better calibrated. Once the valence quark model is calibrated, we extend the model to the physical regime, and use the low Q 2 experimental data to estimate the meson cloud contributions for GA(Q 2 ) and GP (Q 2 ). Using the calibrated quark axial form factors, and the generalization of the nucleon wave function for the other octet baryon members, we make predictions for all the possible weak interaction axial form factors GA(Q 2 ) and GP (Q 2 ) of the octet baryons. The results are compared with the corresponding experimental data for GA(0), and with the estimates of baryon-meson models based on SU (6) symmetry.

A Relativistic Model for the Electromagnetic Structure of Baryons from the 3rd Resonance Region

2016

Few-Body Syst

We present some predictions for the γ * N → N * transition amplitudes, where N is the nucleon, and N * is a nucleon excitation from the third resonance region. First we estimate the transition amplitudes associated with the second radial excitation of the nucleon, interpreted as the N (1710) state, using the covariant spectator quark model. After that, we combine some results from the covariant spectator quark model with the framework of the single quark transition model, to make predictions for the γ *