Mechanisms in the <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>C</mi></mrow><mprescripts></mprescripts><mrow></mrow><mrow><mn>12</mn></mrow><mrow></mrow><mrow></mrow></mmultiscripts></mrow><mo>(</mo><mi>γ</mi><mo>,</mo><mi mathvariant="italic">pn</mi><mo>)</mo></math></span> and <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>(</mo><mi>γ</mi><mo>,</mo><mi mathvariant="italic">pp</mi><mo>)</mo></math></span> Reactions

I. J. D. MacGregor; T. T-H. Yau; J. Ahrens; J. R. M. Annand; R. Beck; D. Branford; P. Grabmayr; S. J. Hall; P. D. Harty; T. Hehl; J. D. Kellie; T. Lamparter; M. Liang; J. A. MacKenzie; S. McAllister; J. C. McGeorge; R. O. Owens; J. Ryckebusch; M. Sauer; R. Schneider; D. P. Watts

doi:10.1103/PhysRevLett.80.245

Mechanisms in the ${}^{12}C (γ, pn)$ and $(γ, pp)$ Reactions

I. J. D. MacGregor, T. T-H. Yau, J. Ahrens, J. R. M. Annand, R. Beck, D. Branford, P. Grabmayr, S. J. Hall, P. D. Harty, T. Hehl, J. D. Kellie, T. Lamparter, M. Liang, J. A. MacKenzie, S. McAllister, J. C. McGeorge, R. O. Owens, J. Ryckebusch, M. Sauer, R. Schneider, and D. P. Watts

Phys. Rev. Lett. 80, 245 – Published 12 January 1998

Abstract

$^{12} C (γ, p n)$ and $(γ, p p)$ cross sections have been measured in kinematics which emphasize direct $2 N$ knockout for $E_{γ} = 120 - 400 MeV$ and $θ_{p} = 23 ° - 152 °$ . The cross sections for both reactions peak strongly in the $Δ$ -resonance region. Theoretical calculations that account for the medium dependence of the $Δ$ propagator predict a similar photon energy dependence to the data and describe the general trends of the measured $(γ, p p) / (γ, p n)$ ratio. Both cross sections show strong angular dependence, and the large differences between the two channels indicate different microscopic reaction mechanisms.

Received 3 September 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.245

Authors & Affiliations

I. J. D. MacGregor¹, T. T-H. Yau^1,*, J. Ahrens⁴, J. R. M. Annand¹, R. Beck⁴, D. Branford², P. Grabmayr³, S. J. Hall¹, P. D. Harty^1,†, T. Hehl³, J. D. Kellie¹, T. Lamparter³, M. Liang^2,‡, J. A. MacKenzie², S. McAllister¹, J. C. McGeorge¹, R. O. Owens¹, J. Ryckebusch⁵, M. Sauer³, R. Schneider³, and D. P. Watts¹

¹Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom
²Department of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
³Physikalisches Institut, Universität Tübingen, D-72076 Tübingen, Germany
⁴Institut für Kernphysik, Universität Mainz, D-55099 Mainz, Germany
⁵Department of Subatomic and Radiation Sciences, University of Gent, Proeftuinstraat 86, B-9000 Gent, Belgium

^*Present address: Chase Research, Basingstoke, U.K.
^†Present address: Physics Department, University of Auckland, Auckland, New Zealand.
^‡Present address: Thomas Jefferson Lab, Newport News, VA 23606.