M. Khandaker

Coherent π0 photo-production on 4He at intermediate energies with polarized photons

Abstract The reaction 4 He ( γ ,π 0 ) 4 He has been studied with the LEGS tagged, polarized gamma-ray beam. Data are presented at laboratory angles of 31°, 45°, 72.5°, 90°, 110° and 130° for incoming photon energies of 206, 219, 232, 245, 259, 274, 289, 306 and 322 MeV. The unpolarized cross sections are compared with the Δ-hole theoretical model results available in literature. The measured photon beam asymmetry is −1 as expected from conservation of angular momentum and parity.

The E2/M1 ratio in Δ photoproduction

Abstract New high-precision measurements of p( γ , π) and p( γ , γ) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. Compton scattering has provided two important new constraints on the photo-pion amplitude. The E2/M1 mixing ratio for the N → Δ transition extracted from this analysis is EMR = -3.0% ± 0.3 (stat + sys) ± 0.2 (model).

Polarized Photon Scattering from 4He

We have measured, for the first time, the differential cross section of and the parameter of asymmetry for the reactions 4He ( \(\vec{\gamma }\), γ)4He with linearly polarized photon. The LEGS polarized and tagged gamma-ray beam of Brookhaven National Laboratory has been used in the energy region 180–310 MeV. Data are colleted for five laboratory angles 30°, 45°, 72.5°, 110° and 130°.

Measurements of the spin structure of the nucleon using SPHICE: A strongly polarized hydrogen and deuterium ice target

Frozen‐spin HD polarized targets operating between 0.4 and 4K, used with cold‐transfer (4K) techniques, provide great configurational flexibility. Their long depolarization times under target usage conditions assure reasonable match between polarization production and usage times, for weakly ionizing beam fluxes, and the very long relaxation times at fields above 7T (∼1 yr.) provide an economical storage mode and ‘‘off‐the‐shelf’’ availability.

Measurement of γd→pnπ0 at large nucleon momenta

Coincident protons and neutrons from the reaction γ→d→pnπ0 were measured at a photon energy of 290 MeV. Cross sections and beam asymmetries were extracted for nucleon momenta above the quasifree region for the first time. The measured cross sections are compared with the results of a cascade Monte Carlo calculation.Coincident protons and neutrons from the reaction [rvec ]gg[ital d][r arrow][ital pn][pi][sup 0] were measured at a photon energy of 290 MeV. Cross sections and beam asymmetries were extracted for nucleon momenta above the quasifree region for the first time. The measured cross sections are compared with the results of a cascade Monte Carlo calculation.

The E2/M1 Mixing Ratio in the Excitation of the Δ from Polarized Photo-Reactions

In constituent quark models, a tensor interaction, mixing quark spins with their relative motion, is introduced to reproduce the observed baryon spectrum. This has a consequence completely analogous to the nuclear tensor force between the n and p in deuterium. A D state component is mixed into what would otherwise be a purely S-wave object. The D-wave component breaks spherical symmetry, resulting in a non-vanishing matrix element for the nucleon and a static quadrupole moment and deformation for its first excited state, the Δ resonance, at ∽325 MeV. The magnitude and sign of this D-state component are quite sensitive to the internal structure of the proton and have been of great interest in recent years [1].