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Title: Sum rule measurements of the spin-dependent compton amplitude (nucleon spin structure at Q{sup 2} = 0)

Abstract

Energy weighted integrals of the difference in helicity-dependent photo-production cross sections ({sigma}{sub {1/2}} - {sigma}{sub 3/2}) provide information on the nucleon`s Spin-dependent Polarizability ({gamma}), and on the spin-dependent part of the asymptotic forward Compton amplitude through the Drell-Hearn-Gerasimov (DHG) sum rule. (The latter forms the Q{sup 2}=0 limit of recent spin-asymmetry experiments in deep-inelastic lepton-scattering.) There are no direct measurements of {sigma}{sub {1/2}} or {sigma}{sub 3/2}, for either the proton or the neutron. Estimates from current {pi}-photo-production multipole analyses, particularly for the proton-neutron difference, are in good agreement with relativistic-l-loop Chiral calculations ({chi}PT) for {gamma} but predict large deviations from the DHG sum rule. Either (a) both the 2-loop corrections to the Spin-Polarizability are large and the existing multipoles are wrong, or (b) modifications to the Drell-Hearn-Gerasimov sum rule are required to fully describe the isospin structure of the nucleon. The helicity-dependent photo-reaction amplitudes, for both the proton and the neutron, will be measured at LEGS from pion-threshold to 470 MeV. In these double-polarization experiments, circularly polarized photons from LEGS will be used with SPHICE, a new frozen-spin target consisting of {rvec H} {center_dot} {rvec D} in the solid phase. Reaction channels will be identified in SASY, a large detectormore » array covering about 80% of 4{pi}. A high degree of symmetry in both target and detector will be used to minimize systematic uncertainties.« less

Authors:
;  [1]; ;  [2];  [3]; ; ;  [4];  [5];  [6]
  1. Laboratori Nationali di Frascati-INFN, Rome (Italy)
  2. Univ. of Virginia, Charlottesville, VA (United States)
  3. Virginia Polytechnic Institute and State Univ., Blacksburg, VA (United States)
  4. IN2P3, Orsay (France)
  5. Brookhaven National Lab., Upton, NY (United States)
  6. Syracuse Univ., NY (United States); and others
Publication Date:
Research Org.:
Brookhaven National Lab., Upton, NY (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10105911
Report Number(s):
BNL-61005
ON: DE95003947; TRN: 95:000634
DOE Contract Number:  
AC02-76CH00016
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: [1995]
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; HYDROGEN 1 TARGET; PHOTONUCLEAR REACTIONS; DEUTERIUM TARGET; COMPTON EFFECT; POLARIZED TARGETS; SUM RULES; POLARIZABILITY; 663410; 663510; PHOTONUCLEAR REACTIONS AND PHOTON SCATTERING; A = 1-5

Citation Formats

Babusci, D, Giordano, G, Baghaei, H, Cichocki, A, Blecher, M, Breuer, M, Commeaux, C, Didelez, J P, Caracappa, A, and Fan, Q. Sum rule measurements of the spin-dependent compton amplitude (nucleon spin structure at Q{sup 2} = 0). United States: N. p., 1995. Web. doi:10.2172/10105911.
Babusci, D, Giordano, G, Baghaei, H, Cichocki, A, Blecher, M, Breuer, M, Commeaux, C, Didelez, J P, Caracappa, A, & Fan, Q. Sum rule measurements of the spin-dependent compton amplitude (nucleon spin structure at Q{sup 2} = 0). United States. https://doi.org/10.2172/10105911
Babusci, D, Giordano, G, Baghaei, H, Cichocki, A, Blecher, M, Breuer, M, Commeaux, C, Didelez, J P, Caracappa, A, and Fan, Q. 1995. "Sum rule measurements of the spin-dependent compton amplitude (nucleon spin structure at Q{sup 2} = 0)". United States. https://doi.org/10.2172/10105911. https://www.osti.gov/servlets/purl/10105911.
@article{osti_10105911,
title = {Sum rule measurements of the spin-dependent compton amplitude (nucleon spin structure at Q{sup 2} = 0)},
author = {Babusci, D and Giordano, G and Baghaei, H and Cichocki, A and Blecher, M and Breuer, M and Commeaux, C and Didelez, J P and Caracappa, A and Fan, Q},
abstractNote = {Energy weighted integrals of the difference in helicity-dependent photo-production cross sections ({sigma}{sub {1/2}} - {sigma}{sub 3/2}) provide information on the nucleon`s Spin-dependent Polarizability ({gamma}), and on the spin-dependent part of the asymptotic forward Compton amplitude through the Drell-Hearn-Gerasimov (DHG) sum rule. (The latter forms the Q{sup 2}=0 limit of recent spin-asymmetry experiments in deep-inelastic lepton-scattering.) There are no direct measurements of {sigma}{sub {1/2}} or {sigma}{sub 3/2}, for either the proton or the neutron. Estimates from current {pi}-photo-production multipole analyses, particularly for the proton-neutron difference, are in good agreement with relativistic-l-loop Chiral calculations ({chi}PT) for {gamma} but predict large deviations from the DHG sum rule. Either (a) both the 2-loop corrections to the Spin-Polarizability are large and the existing multipoles are wrong, or (b) modifications to the Drell-Hearn-Gerasimov sum rule are required to fully describe the isospin structure of the nucleon. The helicity-dependent photo-reaction amplitudes, for both the proton and the neutron, will be measured at LEGS from pion-threshold to 470 MeV. In these double-polarization experiments, circularly polarized photons from LEGS will be used with SPHICE, a new frozen-spin target consisting of {rvec H} {center_dot} {rvec D} in the solid phase. Reaction channels will be identified in SASY, a large detector array covering about 80% of 4{pi}. A high degree of symmetry in both target and detector will be used to minimize systematic uncertainties.},
doi = {10.2172/10105911},
url = {https://www.osti.gov/biblio/10105911}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1995},
month = {12}
}