R. Igarashi

Nuclear compton scattering from pion threshold to the delta

Abstract The first measurements of elastic photon scattering on complex nuclei from 150 MeV to the Δ(1232) (Eγ = 300 MeV) are compared with theoretical calculations. Data on 4He at the Δ peak are in agreement with a Δh calculation, but substantial disagreement occurs at lower energies that is at least partly due to the approximate treatment of non-resonant parts of the elementary nucleon amplitude. An impulse approximation calculation which includes meson exchange provides an adequate description of the data at 187 MeV on 4He. Improved data on the proton at 20–30° and 120–140° at a range of energies are in agreement with a recent dispersion relation calculation. Data taken on 12C are still too preliminary to report, due to the difficulty of eliminating inelastic contributions.

Measurement of the H-1 (gamma, pi0) cross-section near threshold

The cross section for the reaction {sup 1}H({gamma},{pi}{sup 0}) has been measured using tagged photons in the threshold region (144.7{endash}169.3 MeV). The total cross section, augmented by angular distribution information, is used to deduce the {ital S}-wave multipole {ital E}{sub 0+}. Extrapolation to threshold yields {ital E}{sub 0+}=({minus}1.32{plus_minus}0.05{plus_minus}0.06){times}10{sup {minus}3}/{ital m}{sub {pi}}, in disagreement with earlier estimates. Suppression of {ital E}{sub 0+} near the {pi}{sup +} threshold is confirmed, in approximate agreement with recent calculations. {copyright} {ital 1996 The American Physical Society.}

Near threshold ({gamma},{pi}{sup 0}) reactions for {sup 4}He and {sup 12}C

The total cross section and angular distributions for the reaction {sup 4}He({gamma},{pi}{sup 0}) from a cryogenic liquid helium target have been measured within 25 MeV of threshold using tagged photons and a large acceptance {pi}{sup 0} spectrometer at the Saskatchewan Accelerator Laboratory. The reduced isovector amplitude p{sub 3}{sup (+)} has been determined from the total cross-section measurement using a distorted-wave impulse approximation analysis. Refinements from earlier analytical methods, specifically an improved background event rejection scheme and a corrective tagged photon energy calibration analysis, have also yielded an improved estimate on the p{sub 3}{sup (+)} amplitude for the {sup 12}C({gamma},{pi}{sup 0}) reaction explored previously.

Measurement of theH1(γ, π0)cross section near threshold

The cross section for the reaction {sup 1}H({gamma},{pi}{sup 0}) has been measured using tagged photons in the threshold region (144.7{endash}169.3 MeV). The total cross section, augmented by angular distribution information, is used to deduce the {ital S}-wave multipole {ital E}{sub 0+}. Extrapolation to threshold yields {ital E}{sub 0+}=({minus}1.32{plus_minus}0.05{plus_minus}0.06){times}10{sup {minus}3}/{ital m}{sub {pi}}, in disagreement with earlier estimates. Suppression of {ital E}{sub 0+} near the {pi}{sup +} threshold is confirmed, in approximate agreement with recent calculations. {copyright} {ital 1996 The American Physical Society.}

Measurement of the {sup 1}H({gamma},{pi}{sup 0}) cross section near threshold

The cross section for the reaction {sup 1}H({gamma},{pi}{sup 0}) has been measured using tagged photons in the threshold region (144.7{endash}169.3 MeV). The total cross section, augmented by angular distribution information, is used to deduce the {ital S}-wave multipole {ital E}{sub 0+}. Extrapolation to threshold yields {ital E}{sub 0+}=({minus}1.32{plus_minus}0.05{plus_minus}0.06){times}10{sup {minus}3}/{ital m}{sub {pi}}, in disagreement with earlier estimates. Suppression of {ital E}{sub 0+} near the {pi}{sup +} threshold is confirmed, in approximate agreement with recent calculations. {copyright} {ital 1996 The American Physical Society.}