On hadron deformation: a model independent extraction of EMR from pion photoproduction data

Abstract

The multipole content of pion photoproduction at the ${\Delta }^{+}(1232)$ 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 $-2.5\pm 0.4_{stat+syst}$, 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 hadronic structure. They are in good agreement with phenomenological models which explicitly incorporate pionic degrees of freedom and with lattice QCD calculations.

14 pages, 9 figures, 2 tables

References in corpus (8)

• Unitary Isobar Model - MAID2007
• Electromagnetic excitation of the Delta(1232)-resonance
• Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
• D-state effects in the electromagnetic N-Delta transition
• Nucleon to Delta transition form factors with $N_F=2+1$ domain wall fermions
• A novel analysis method for excited states in lattice QCD - the nucleon case
• Ovrview: The Shape of Hadrons
• Multipole Extraction: A novel, model independent method

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