https://doi.org/10.1140/epja/i2014-14173-y
Regular Article - Experimental Physics
Helicity dependence of the γ 3He → πX reactions in the Δ(1232) resonance region
1
Sezione di Pavia, INFN, I-27100, Pavia, Italy
2
Dipartimento di Fisica, Università di Pavia, I-27100, Pavia, Italy
3
Sezione di Catania, INFN, I-95123, Catania, Italy
4
Dipartimento di Fisica e Scienze della Terra, Università di Messina, I-98166, Messina, Italy
5
Institut für Kernphysik, Universität Mainz, D-55099, Mainz, Germany
6
SUPA School of Physics & Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK
7
Helmholtz-Institut für Strahlen und Kernphysik, University of Bonn, D-53115, Bonn, Germany
8
Petersburg Nuclear Physics Institute, RU-188300, Gatchina, Russia
9
II Physikalisches Institut, University of Giessen, D-35392, Giessen, Germany
10
The George Washington University, 20052-0001, Washington, DC, USA
11
Institute for Nuclear Research, RU-125047, Moscow, Russia
12
Dalhousie University, B3H 4R2, Halifax, NS, Canada
13
Saint Mary’s University, B3H 3C3, Halifax, NS, Canada
14
Tomsk Polytechnic University, Tomsk, Russia
15
SUPA School of Physics & Astronomy, University of Edinburgh, EH9 3JZ, Edinburgh, UK
16
Institut für Physik, Universität Mainz, D-55099, Mainz, Germany
17
Mount Allison University, E4L-1E6, Sackville, NB, Canada
18
Institut für Physik, University of Basel, CH-4056, Basel, Switzerland
19
University of Regina, S4S-0A2, Regina, SK, Canada
20
Lebedev Physical Institute, RU-119991, Moscow, Russia
21
Rudjer Boskovic Institute, HR-10000, Zagreb, Croatia
22
Kent State University, 44242-0001, Kent, Ohio, USA
23
University of California, 90095-1547, Los Angeles, California, USA
* e-mail: pedroni@pv.infn.it
Received:
5
September
2013
Revised:
24
October
2014
Accepted:
10
November
2014
Published online:
24
November
2014
The helicity dependences of the differential cross sections for the semi-inclusive γ 3He → π0 X and γ 3He → π± X reactions have been measured for the first time in the energy region 200 < E γ 450 MeV. The experiment was performed at the tagged photon beam facility of the MAMI accelerator in Mainz using a longitudinally polarised high-pressure 3He gas target. Hadronic products were measured with the large-acceptance Crystal Ball detector complemented with additional devices for charged-particle tracking and identification. Unpolarised differential cross sections and their helicity dependence are compared with theoretical calculations using the Fix-Arenhövel model. The effect of the intermediate excitation of the Δ(1232) resonance can be clearly seen from this comparison, especially for the polarised case, where nuclear effects are relatively small. The model provides a better theoretical description of the unpolarised charged pion photoproduction data than the neutral pion channel. It does significantly better in describing the helicity-dependent data in both channels. These comparisons provide new information on the mechanisms involved in pion photoproduction on 3He and suggest that a polarised 3He target can provide valuable information on the corresponding polarised quasi-free neutron reactions.
© SIF, Springer-Verlag Berlin Heidelberg, 2014