R. M. Davidson

Form-factors and photoproduction amplitudes

We examine the use of phenomenological form factors in tree level amplitudes for meson photoproduction. Two common recipes are shown to be fundamentally incorrect. An alternate form consistent with gauge invariance and crossing symmetry is proposed.

Effect of form-factors in fits to photoproduction data

We compare the effects of several form factor recipes in fits to pseudoscalar meson photoproduction data. The specific examples of pion and kaon photoproduction are used to illustrate how different choices can alter the results of such analyses.

MAINZ MEASUREMENT OF THE E2/M1 RATIO IN THE N-DELTA TRANSITION. AUTHORS' REPLY

A Comment on the Letter by R. Beck {ital et al.}, Phys.Rev.Lett.{bold 78}, 606 (1997). The authors of the Letter offer a Reply. {copyright} {ital 1997} {ital The American Physical Society}

Watson's theorem and resonant pion photoproduction amplitude in the delta channel

Abstract The CGLN and BL theories of the pion photoproduction on nucleons, used in nuclear calculations, are examined regarding their predictions of the resonant M1+ and E1+ multipoles. The nonunitary BL approach violates Watsons theorem, and predicts these multipoles poorly. In the static limit, the CGLN multipoles satisfy Watsons theorem and are in fine agreement with data. The unitarized BL multipoles agree with those from the Olsson theory and data.

Exploring the reaction mechanism of eta prime photoproduction

Abstract We examine theoretical implications of studying the differential cross-section and some key polarization observables in the η′ photoproduction reaction off protons, from its threshold to about 2 GeV of cm energy, the region of the so-called “missing baryon resonances”. We compare implications of different models all of which generate the observed peak in the total η′ photproduction cross section, but have very different differential cross section and polarization profields. Their measurements are thus crucial in distinguishing these reaction mechanisms, of interest to understanding QCD in its nonperturbative domain.

Are nucleons and deltas deformed

We investigate the extraction and modelling of the electromagnetic multipoles in the transition N↔Δ(1232). We show that the extracted E2 multipole amplitude indicates that nucleons and deltas are not spherical. We study these deformations in various models and discuss possible experiments to test these theoretical inferences.

Role of theD13(1520)resonance inηelectroproduction

We investigate the electroproduction of eta mesons below a center of momentum energy of 1.6 GeV, with particular emphasis on the roles of the N*(1535) and N*(1520) resonances. Using the effective Lagrangian approach, we show that the transverse helicity amplitude of the N*(1535) can be extracted with good accuracy from the new eta electroproduction data, under reasonable assumptions for the strength of the longitudinal helicity amplitude. In addition, although the differential cross section is found to to have a small sensitivity to the N*(1520) resonance, it is shown that a recently completed double polarization experiment is very sensitive to this resonance.

Questions on the Quark Model: Panel Discussion

In atomic, nuclear, and particle physics, one often deals with complicated potentials where the analytic solution to the bound state wave functions is not known. One general approach to this problem is to diagonalize the Hamiltonian in a finite, i.e., truncated, model space. While this method is generally very good in determining the low-lying energy levels, it is not without problems. For example, an operator that is known to commute with the Hamiltonian may not, in the model space, actually commute with the Hamiltonian. To deal with this problem, one tries to find effective operators in the model space that do satisfy the properties of the operators in the untruncated space.

The Role of the D(13)(1520) resonance in eta electroproduction

We investigate the electroproduction of eta mesons below a center of momentum energy of 1.6 GeV, with particular emphasis on the roles of the N*(1535) and N*(1520) resonances. Using the effective Lagrangian approach, we show that the transverse helicity amplitude of the N*(1535) can be extracted with good accuracy from the new eta electroproduction data, under reasonable assumptions for the strength of the longitudinal helicity amplitude. In addition, although the differential cross section is found to to have a small sensitivity to the N*(1520) resonance, it is shown that a recently completed double polarization experiment is very sensitive to this resonance.

Thep(γ→,π0) reaction in the Δ(1232) region

A Comment on the Letter by G. Blanpied [ital et] [ital al]. Phys. Rev. Lett. 69, 1880 (1992).