Eur. Phys. J. A (2013) 49: 136
https://doi.org/10.1140/epja/i2013-13136-2

Regular Article - Experimental Physics

Measurements of the γ*p → Δ reaction at low Q²

¹ Department of Physics, Temple University, 19122, Philadelphia, Pennsylvania, USA
² Department of Physics, Laboratory for Nuclear Science and Bates Linear Accelerator Center, Massachusetts Institute of Technology, 02139, Cambridge, Massachusetts, USA
³ Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, D-55099, Mainz, Germany
⁴ Radiation Laboratory, 351-0198, Saitama, Japan
⁵ Institute of Accelerating Systems and Applications and Department of Physics, University of Athens, Athens, Greece
⁶ Department of Physics, University of Zagreb, HR-10002, Zagreb, Croatia
⁷ Department of Physics and Astronomy, University of Kentucky, 40206, Lexington, Kentucky, USA
⁸ Institute Jožef Stefan, University of Ljubljana, SI-1000, Ljubljana, Slovenia

^* e-mail: sparveri@temple.edu

Received: 2 July 2013
Revised: 27 September 2013
Accepted: 5 October 2013
Published online: 31 October 2013

Abstract

We report new p(e, e′p)π° measurements in the Δ ⁺(1232) resonance at the low momentum transfer region utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The mesonic cloud dynamics are predicted to be dominant and appreciably changing in this region while the momentum transfer is sufficiently low to be able to test chiral effective field theory calculations. The results disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations with pion cloud effects, chiral effective field theory and lattice calculations. The reported measurements suggest that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements.