Results from the GDH experiment at Mainz and Bonn Alessandro Braghieri, INFN Pavia A2 and GDH Collaborations • First measurements in double polarization: physical motivation • Experimental set-up • Results: Gerasimov-Drell-Hearn sum rule and resonance contribution • Comments October 12-15, 2005
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Results from the GDH experiment at Mainz and Bonn Alessandro Braghieri, INFN Pavia A2 and GDH Collaborations First measurements in double polarization:
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Results from the GDH experiment at Mainz and Bonn
Alessandro Braghieri, INFN Pavia
A2 and GDH Collaborations
• First measurements in double polarization: physical motivation• Experimental set-up• Results: Gerasimov-Drell-Hearn sum rule and resonance contribution• Comments
Fundamental check of our knowledge of the N interaction
Important comparison for nucleon models
Valid for any system with (2H, 3He) . “Bridge” between nuclear and particle physics
The same formalism leads to a relation for the so-called forward spin polarizability
03
2/30
)(
4
1
dEE
Connection with the ‘Spin Crisis’ Measurement of the polarized structure function on the nucleon (D.I.S., EMC 1985 …)
114.0),(1
0
2
1 xdQxgp
How the proton spin is shared between partons?
gqqqspin Fraction carried by valence q
EMC QCD npQCD
0!!! 75% 10-50%
Anselmino , Ioffe, Leader, Sov. J. Nucl. Phys. 49:136, 1989
),(2
)( 21
0
12
22 Qxgdx
Q
mQI GDH)(0 22 QIQ
1991, OctHELICITY STRUCTURE OF PION PHOTOPRODUCTIONSpokeperson: D. Sober (CUA),Proposal E91-015 at CEBAF
MEASUREMENT OF POLARIZED STRUCTURE FUNCTIONS IN INELASTIC ELECTRON PROTON SCATTERING USING THE CEBAF LARGE ACCEPTANCE SPECTROMETERSpokepersons: V. Burkert (Jlab), D. Crabb(Virginia U.), Minehart (Virginia U.)Proposal E91-023 at CEBAF
1992, AprPROPOSAL TO MEASURE THE DRELL-HEARN-GERASIMOV SUM RULEApril 1992, proposal at ELSA
1993, AprEXPERIMENTAL CHECK OF THE DRELL-HEARN-GERASIMOV SUM RULESpokeperson: J. Ahrens (Mainz U.)Proposal A2/2-93
2000HELICITY DEPENDENCE OF p --> N BELOW 450-MeV AND CONTRIBUTION TO THE GERASIMOV-DRELL-HEARN SUM RULEBy GDH and A2 Collaborations (J. Ahrens et al.),Published in Phys. Rev. Lett. 84:5950-5954, 2000
1Institute of Experimental Physics, Ruhr-University, Bochum, Germany 2 Physics Institute, University of Bonn, Germany 3 Physics Institute, University of Erlangen-Nuernberg, Erlangen, Germany 4 Nuclear Physics Laboratory, Gent, Belgium 5 CEA Saclay, DSM/DAPNIA/SPhN, Gif-sur-Yvette, France 6 Department of Physics & Astronomy, University of Glasgow, U.K. 7 II.Physics Institute, University of Goettingen, Germany 8 Department of Physics, University of Lund, Sweden 9,10 Institute of Nucl. Physics and Inst. of Physics, University of Mainz, Germany 11 Faculty of Engineering, Miyazaki University, Miyazaki, Japan 12 INR, Academy of Science, Moscow, Russia 13,14 Department of Physics and CIRSE, Nagoya University, Nagoya, Japan 15,16 INFN Sezione di Pavia and Dept. of Nucl. Physics of the University , Pavia, Italy 17 Physics Institute, University of Tuebingen, Germany
• Data taking to check the GDH sum rule was completed• Proton and Deuteron targets have been used• Most of the analysis on the proton finished (inclusive and partial channels)• Analysis on Deuteron in progress• Check of the partial channels on the bound neutron• Check of the methods using the bound proton• Comparison with the results with the (free) proton• Theoretical calculations