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Title: Exploring the gamma* p --> Delta(1232) Transition at Low Q2 Using CLAS

Abstract

Precision measurements of the p(e, e[prime] p)pi0 reaction were performed using the CEBAF Large Acceptance Spectrometer (CLAS) in the range of photon invariant momentum transfer Q2 = 0.16 – 0.36 GeV2. Fits to the data using both a Unitary Isobar Model and the Sato-Lee dynamical model are used to estimate the `dressed' and `bare' electromagnetic couplings for the magnetic and quadrupole gamma* p --> Delta(1232) transition form factors.

Authors:
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
910567
Report Number(s):
JLAB-PHY-07-683; DOE/OR/23177-0106
Journal ID: ISSN 0094-243X; APCPCS; TRN: US0704258
DOE Contract Number:
AC05-06OR23177
Resource Type:
Conference
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 904; Conference: Workshop on the Shape of Hadrons, 27-29 Apr 2006, Athens, Greece
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCURACY; FORM FACTORS; HADRONS; ISOBAR MODEL; MOMENTUM TRANSFER; PHOTONS; QUADRUPOLES; SHAPE; SPECTROMETERS

Citation Formats

L. C. Smith. Exploring the gamma* p --> Delta(1232) Transition at Low Q2 Using CLAS. United States: N. p., 2007. Web. doi:10.1063/1.2734307.
L. C. Smith. Exploring the gamma* p --> Delta(1232) Transition at Low Q2 Using CLAS. United States. doi:10.1063/1.2734307.
L. C. Smith. Sun . "Exploring the gamma* p --> Delta(1232) Transition at Low Q2 Using CLAS". United States. doi:10.1063/1.2734307. https://www.osti.gov/servlets/purl/910567.
@article{osti_910567,
title = {Exploring the gamma* p --> Delta(1232) Transition at Low Q2 Using CLAS},
author = {L. C. Smith},
abstractNote = {Precision measurements of the p(e, e[prime] p)pi0 reaction were performed using the CEBAF Large Acceptance Spectrometer (CLAS) in the range of photon invariant momentum transfer Q2 = 0.16 – 0.36 GeV2. Fits to the data using both a Unitary Isobar Model and the Sato-Lee dynamical model are used to estimate the `dressed' and `bare' electromagnetic couplings for the magnetic and quadrupole gamma* p --> Delta(1232) transition form factors.},
doi = {10.1063/1.2734307},
journal = {AIP Conference Proceedings},
number = ,
volume = 904,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}

Conference:
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  • Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q{sup 2} dependence of the magnetic (M{sub 1+}), electric (E{sub 1+}), and scalar (S{sub 1+}) multipoles in the {gamma}*p {yields} {Delta}{sup +}(1232) {yields} p{pi}{sup 0} transition. New precision measurements of the ratios E{sub 1+}/M{sub 1+} and S{sub 1+}/M{sub 1+} are reported here over the range Q{sup 2} = 0.4-1.8 GeV{sup 2}. Results are best described by recent unitary models in which the pion cloudmore » plays a dominant role.« less
  • We report a new measurement of the exclusive electroproduction reaction gamma* p --> pi0 p to explore the evolution from soft non-perturbative physics to hard processes via the Q2 dependence of the magnetic (M1+), electric (E1+) and scalar (S1+) multipoles in the N --> Delta transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c2, 4pi center-of-mass solid angle, and Q2 from 3 to 6 GeV2/c2, the highest yet achieved. It is found that the magnetic form factor G M * decreases with Q2 more steeply than the proton magnetic form factor, the ratio E1+/M1+ ismore » small and negative, indicating strong helicity non-conservation, and the ratio S1+/M1+ is negative, while its magnitude increases with Q2.« less
  • A sample of the available experimental data on (..gamma..,p) and (..pi..,p) reactions in complex nuclei is presented, together with a few recent results on the (..gamma..,np) and (..pi../sup +/,pp) processes. The data are seen to provide information on photon and pion interaction mechanisms in the ..delta.. (1232) resonance region.
  • The Generalized Parton Distributions (GPDs) parameterize the non-pertubative content of the nucleon. They appear in the amplitude of hard exclusive processes such as DVCS on the proton (ep → epγ). They correlate the spatial and momentum structure of the nucleon in terms of partonic degrees of freedom. The introduction of transition GPDs extended the GPD formalism to more general final states. These GPDs can be used for instance to describe processes where the recoil nucleon is excited into a nucleon resonance. In this paper we focus on the N-Δ transition. The simplest process to access N-Δ transition GPDs is themore » ΔVCS (ep → eΔ+γ). First experimental beam spin asymmetry results associated to this process and obtained from CLAS data are presented. The Δ+ decaying into Nπ pair, the analysis focused on the ep → eNπγ reactions in the Δ+ region.« less
  • Single pion electroproduction in the resonance region has been studied as a means of exploring the physics underlying the structure of the nucleon. Recent experiments using CLAS at Jefferson Lab/Hall B have measured unpolarized cross sections and beam spin asymmetries over a large kinematic range. The high statistical accuracy of this data set provides important information on the Delta(1232) and the Roper.