Cross section for γn→π0n measured at the Mainz A2 experiment

W J Briscoe,M Hadžimehmedović,M Biroth,I Gorodnov,F Cividini,I Supek,M Korolija,M Wolfes,C Sfienti,D P Watts,A Denig,V E Tarasov,R Miskimen,D M Manley,R Beck,M Bashkanov,B Oussena,I I Strakovsky,A Mushkarenkov,K Bantawa,S Lutterer,A Käser,A Thomas,P P Martel,A Neiser,L Heijkenskjöld,J Wettig,N Zachariou,F Afzal,B Krusche,S Fegan,M Unverzagt,A Braghieri,K Livingston,V Sokhoyan,A E Kudryavtsev,J Stahov,E Mornacchi,D Werthmüller,H J Arends,P Aguar-Bartolomé,M Ostrick,M Thiel,T Rostomyan,J R M Annand,P B Otte,S Abt,R L Workman,G M Huber,S Costanza,P Pedroni,I J D Macgregor,D Ghosal,D Hornidge,S A Bulychjov,D G Middleton,V L Kashevarov,N K Walford,W Gradl,K Spieker,S Gardner,A Thiel,M I Ferretti Bondy,Yu A Usov,P Drexler,C Mullen,Z Ahmed,O Steffen,D I Glazier,C S Akondi,E J Downie,R Macrae,S Kay,G Ron,C Collicott,J C Mcgeorge,D Paudyal,L Tiator,R Omerović,P Achenbach,H Osmanović,Alfred Švarc ,A B Neganov ,A J Sarty ,D Gurevich ,N S Borisov ,S Prakhov ,A B Lazarev ,M Martemianov ,A Powell ,S.r Wagner ,Michael Günther ,V Kulikov

doi:10.1103/physrevc.100.065205

Abstract

The $\gamma n \to \pi^0 n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290-813 MeV (W = 1.195-1.553 GeV) and the pion c.m. polar production angles, ranging from 18 deg to 162 deg, making use of model-dependent nuclear corrections to extract pi0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883-MeV electron beam of the Mainz Microtron MAMI was used for the 0-meson production. Our accumulation of 3.6 x 10^6 $\gamma n \to \pi^0 n$ events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared to predictions of previous SAID, MAID, and BnGa partial-wave analyses and to the latest SAID fit MA19 that included our data. Selected photon decay amplitudes $N^* \to \gamma n$ at the resonance poles are determined for the first time.

Highlights

The N ∗ and ∆∗ families of nucleon resonances have many well-established members [1], several of which overlap, having very similar masses and widths but different JP spin-parity values
The neutron detection efficiency is defined directly from data by the method proposed in Ref. [36]; εBackg is the background extraction efficiency, which included the empty target correction and the correction for random photons in the beam; εPID is the correction factor for the particle identification detector (PID) inefficiency, this value was estimated on the experimental data from Crystal Ball (CB) and multi-wire proportional chambers (MWPC) and required to select a neutral decay channel; εFSI is the final-state interaction (FSI)-effect correction to get the γn → π0n cross section from the deuteron measurements, εFSI = R(E, θ)−1
Since our results for the γn → π0n differential cross sections consist of 492 experimental points, they are not tabulated in this publication but are available in the SAID database [5] along with their uncertainties and the energy binning

Summary

Introduction

The N ∗ and ∆∗ families of nucleon resonances have many well-established members [1], several of which overlap, having very similar masses and widths but different JP spin-parity values.

Methods

Results

Conclusion