Radiative Pion Capture in Nuclei

Abstract

The process of radiative pion capture has in recent years been shown to be a good probe of nuclear structure. The experiments and theoretical results which support this statement are reviewed. High-re solution data on the photon spectra from nuclei ranging in mass l£A<209 are shown. We discuss the observation of giant resonances in T z = +1 nuclei, the quasi-free capture process, and transitions to individual bound nu clear states. The observed transition rates in lp-shell nuclei are compared with recent shell model calculations based on an impulse-approximation Hamiltonian whose ampli tudes are not adjustable constants, but are obtained from the fundamental process on the nucleon, IT" + p -* n + y. The agreement is good within the limits set by the uncertainties of pionic x-ray data. Some features of radiative TT capture on very light nuclei-A=2, 3 and 4-are reviewed. Finally, we discuss the ir" + Li (l"'")-»'Y+°He(0 \) transition where the PCAC hypothesis and soft-pion limit have been applied. The ls-state radiative cap ture rate evaluated with these assumptions is found to agree with impulae approximation calculations and is within reasonable agreement with the recent data when corrections for 2p capture are made.

The sample experiment and weak nucleon structure

“…First, negatively charged pions are also produced along with their decay muons, but these muons are likely radiatively captured in the target before decay. The approximately 100 MeV photon released in the radiative capture process [115] can shower and create a smallČerenkov signal. Finally, the largest source of rate from pion production in a deuterium target is coherent π 0 production.…”

Double radiative pion capture on hydrogen and deuterium and the nucleon's pion cloud

“…For 12 C, we derived values for R(2γ/1γ) of (7.2±1.3)×10 −4 from Mazzucato et al and (8.4±1.3)× 10 −4 from Deutsch et al when normalized using the branching ratio for single radiative capture from Bistirlich et al [45]. For 9 Be, we obtained a value for R(2γ/1γ) of (4.8±1.3)×10 −4 when normalized using the mean branching ratio for single radiative capture from the neighboring 7 Li-10 B nuclei [46]. Clearlyas summarized in Table VII -the values of R(2γ/1γ) on light nuclei are much larger than the corresponding ratios for hydrogen (7.68±0.69±0.79)×10 −5 and deuterium (5.44 ± 0.34 0.46 (stat.)…”

Radiative pion capture in 2H, 3He and 3H

“…We take it in the form of the one-body Kroll-Rudermann operator j KR [25] and start with the nonrelativistic formula from Ref. [2]:…”