[Jlab-seminars] Seminar Announcement

[Luci Collins]

*Seminar   
Monday, Oct. 26, 2009
10:00 AM
CEBAF Center F113

Sam Boblit
BNL

*


*"Recent results of double polarization pion photoproduction
measurements with frozen-spin HDice from the LEGS facility at BNL."*


The last round of experiments at the Laser-Electron-Gamma-Source facility at
Brookhaven produced tagged polarized photon beams up to 0.4 GeV and utilized
frozen-Spin HDice targets to measure spin-dependent pion production cross
sections. A quasi-4pi spectrometer was used, first in a calorimeter mode
optimized for neutrals and then incorporating a Time-Projection Chamber and
solenoid to provide pi +/- charge separation. Inclusive results for the
photo-production of charged and neutral pions on the proton have provided
new information on the convergence of the Gerasimov-Drell-Hearn-Hosoda-
Yamamoto (GDH) sum rule. Recent results from Mainz and Bonn exceeded the GDH
prediction for the proton by 22 microbarns. LEGS pi0 data reveal a different
angular dependence from that assumed in Mainz analysis and integrate to a
value 18 microbarns lower, indicating a rapid convergence. Inclusive results
on Deuterium are lower than existing state of the art calculations for the
GDH integrand in Deuterium. Preliminary exclusive results for D(gamma,pi0n)p
allow a separation of coherent and incoherent pi0 production on D and shed
some light on these differences. Restrictive kinematic requirements on these
exclusive pi0 n data will also provide the first spin-data in pi0 production
from an approximately free neutron.










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