Evaluation of the E2/M1 ratio in the N → Δ(1232) transition from the (γ)over-right-arrow(p)over-right-arrow → pπ0 reaction

(A2 Collaboration at MAMI) Mornacchi, E; Pedroni, P; Afzal, F; Wunderlich, Y; Abt, S; Achenbach, P; Annand, JRM; Arends, HJ; Bashkanov, M; Biroth, M; Beck, R; Borisov, N; Braghieri, A; Briscoe, WJ; Cividini, F; Collicott, C; Denig, A; Dolzhikov, AS; Downie, E; Fegan, S; Fix, A; Ghosal, D; Gorodnov, I; Gradl, W; Gurevich, GG; Heijkenskjöld, L; Hornidge, D; Huber, GM; Kashevarov, VL; Kay, SJD; Korolija, Milorad; Lazarev, A; Livingston, K; Lutterer, S; MacGregor, IJD; Manley, DM; Martel, PP; Miskimen, R; Mocanu, M; Mullen, C; Neganov, A; Neiser, A; Oberle, M; Ostrick, M; Otte, PB; Paudyal, D; Powell, A; Rostomyan, T; Sokhoyan, V; Spieker, K; Steffen, O; Strakovsky, II; Thiel, M; Thomas, A; Usov, YA; Wagner, S; Watts, DP; Werthmueller, D; Wettig, J; Witthauer, L; Wolfes, M; Zachariou, N (2024) Evaluation of the E2/M1 ratio in the N → Δ(1232) transition from the (γ)over-right-arrow(p)over-right-arrow → pπ0 reaction. Physical Review C, 109 (5).

PDF - Submitted Version - article Available under License Creative Commons Attribution. Download (1MB)

Abstract

A new data set for the helicity-dependent differential cross section of the single-meson photoproduction reaction gamma p -> p pi(0) was obtained for the photon energy interval 150-400 MeV. The experiment was performed at the A2 tagged photon facility of the Mainz Microtron MAMI using a circularly polarized photon beam and a longitudinally polarized proton target. The reaction products were detected with the large-acceptance Crystal Ball and TAPS calorimeters covering 97% of the full solid angle. These new results, obtained with a fine energy and polar angle binning, greatly increase both the existing quantity and quality of the data available for this observable. A moment analysis, based on a finite expansion in Legendre polynomials, was applied to these data by using a bootstrap-based fitting method to correctly account for their systematic uncertainties. From the resulting decomposition of the differential cross sections, the E2/M1 ratio for the N -> Delta(1232) transition was determined to be [-2.38 +/- 0.16(stat.+sys.) +/- 0.10 (model)]%. Combining this value with previous results also allowed us to evaluate the most precise available estimate of the E2/M1 ratio to be used for all further reference and model comparisons.

Item Type:	Article
Uncontrolled Keywords:	single pi(0) photoproduction; helicity dependence; polarization; photon; spectrometer; extraction; shape
Subjects:	NATURAL SCIENCES > Physics NATURAL SCIENCES > Physics > Physics of Elementary Particles and Fields
Divisions:	Division of Experimental Physics
Depositing User:	Ema Buhin Šaler
Date Deposited:	14 Apr 2026 10:11
URI:	http://fulir.irb.hr/id/eprint/11692
DOI:	10.1103/PhysRevC.109.055201

Actions (login required)

View Item