2018 Impact factor 2.481
Hadrons and Nuclei
Eur. Phys. J. A 16, 259-273 (2003)
DOI: 10.1140/epja/i2002-10093-9

Quasi-free Compton scattering and the polarizabilities of the neutron

K. Kossert1, M. Camen1, F. Wissmann1, J. Ahrens2, J.R.M. Annand3, H.-J. Arends2, R. Beck2, G. Caselotti2, P. Grabmayr4, O. Jahn2, P. Jennewein2, M.I. Levchuk5, A.I. L'vov6, J.C. McGeorge3, A. Natter4, V. Olmos de León2, V.A. Petrun'kin6, G. Rosner3, M. Schumacher1, B. Seitz1, F. Smend1, A. Thomas2, W. Weihofen1 and F. Zapadtka1

1  II. Physikalisches Institut, Universität Göttingen, D-37073 Göttingen, Germany
2  Institut für Kernphysik, Universität Mainz, D-55099 Mainz, Germany
3  Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
4  Physikalisches Institut, Universität Tübingen, D-72076 Tübingen, Germany
5  B.I. Stepanov Institute of Physics, Belarussian Academy of Sciences, 220072 Minsk, Belarus
6  P.N. Lebedev Physical Institute, 117924 Moscow, Russia

schumacher@physik2.uni-goettingen.de

(Received: 21 August 2002 / Revised version: 14 October 2002 / Published online: 11 February 2003)

Abstract
Differential cross-sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been measured using the Glasgow/Mainz photon tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48 cm $\O$ $\times$ 64 cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV at $\theta^{\rm LAB}_\gamma = 136.2^\circ$. Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron detection efficiency of the SENECA detector was measured via the reaction $p(\gamma,\pi^+ n)$. The "free" proton Compton scattering cross-sections extracted from the bound proton data are in reasonable agreement with those for the free proton which gives confidence in the method to extract the differential cross-section for free scattering from quasi-free data. Differential cross-sections on the free neutron have been extracted and the difference of the electromagnetic polarizabilities of the neutron has been determined to be $\alpha_n - \beta_n = 9.8 \pm 3.6 \text{(stat)}
\, {}^{+2.1}_{-1.1} \text{(syst)} \pm 2.2 \text{(model)}$ in units of $10^{-4}{\rm fm}^3$. In combination with the polarizability sum $\alpha_n + \beta_n = 15.2 \pm 0.5$ deduced from photoabsorption data, the neutron electric and magnetic polarizabilities, $\alpha_n
= 12.5 \pm 1.8 \text{(stat)} \, {}^{+1.1}_{-0.6} \text{(syst)} \pm 1.1
\text{(model)}$ and $\beta_n = 2.7 \mp 1.8 \text{(stat)}
\, {}^{+0.6}_{-1.1} \text{(syst)} \mp 1.1 \text{(model)}$ are obtained. The backward spin polarizability of the neutron was determined to be $\gamma^{(n)}_\pi= (58.6 \pm 4.0) \times 10^{-4}{\rm fm}^4$.

PACS
13.60.Fz - Elastic and Compton scattering.
14.20.Dh - Protons and neutrons.
25.20.Dc - Photon absorption and scattering.

© Società Italiana di Fisica, Springer-Verlag 2003