https://doi.org/10.1140/epja/i2018-12549-7
Regular Article - Experimental Physics
On hadron deformation: A model independent extraction of EMR from pion photoproduction data
1
The Cyprus Institute, K. Kavafi 20, 2121, Nicosia, Cyprus
2
National and Kapodistrian University of Athens, Physics Department, 15771, Athens, Greece
* e-mail: cnp@cyi.ac.cy
Received:
14
March
2018
Accepted:
8
June
2018
Published online:
11
July
2018
The multipole content of pion photoproduction at the 
(1232) resonance has been extracted from a data set dominated by recent Mainz Microtron (MAMI) precision measurements. The analysis has been carried out in the Athens Model Independent Analysis Scheme (AMIAS), thus eliminating any model bias. The benchmark quantity for nucleon deformation, EMR = E2/M1 = E
1+
3/2/M
1+
3/2, was determined to be -2.5±0.4stat+syst, thus reconfirming in a model independent way that the conjecture of baryon deformation is valid. The derived multipole amplitudes provide stringent constraints on QCD simulations and QCD inspired models striving to describe the hadronic structure. They are in good agreement with phenomenological models which explicitly incorporate pionic degrees of freedom and with lattice QCD calculations.
© SIF, Springer-Verlag GmbH Germany, part of Springer Nature, 2018
