
G. Blanpied,
M. Blecher,
A. Caracappa,
R. Deininger,
C. Djalali,
G. Giordano,
K. Hicks,
S. Hoblit,
M. Khandaker,
O. C. Kistner, [......],
A. M. Sandorfi,
C. Schaerf,
R. M. Sealock,
H. Ströher,
C. E. Thorn,
S. T. Thornton,
J. Tonnison,
C. S. Whisnant, H. Zhang,
X. Zhao [Show abstract] [Hide abstract]
ABSTRACT: We report new highprecision measurements of p(γ>,γ),
p(γ>,π0) and p(γ>,π+)
cross section and beam asymmetry angular distributions for photon beam
energies in the range from 213 MeV to 333 MeV. The cross sections for
all three channels are locked together with a small common systematic
scale uncertainty of 2%. A large overdetermination of kinematic
parameters was used to achieve the first complete separation of the
Compton scattering and π0production channels. This has
also allowed all detector efficiencies for the p(γ>,γ)
and p(γ>,π0) channels to be measured directly
from the data itself without resorting to simulations. The new Compton
results are approximately 30% higher than previous Bonn data near the
peak of the Δ resonance, resolving a longstanding unitarity
puzzle. However, our p(γ>,π0) and
p(γ>,π+) cross sections are also about 10%
higher than both earlier Bonn data and recent Mainz measurements, while
our p(γ>,π+) cross sections are in good
agreement with results from Tokyo. Our polarization asymmetry data are
of the highest precision yet available and have considerable impact upon
multipole analyses. These new data have been combined with other
polarization ratios in a simultaneous analysis of both Compton
scattering and π production, with Compton scattering providing two
new constraints on the photopion amplitude. This analysis has improved
the accuracy in the E2/M1 mixing ratio for the N>Δ
transition, EMR=[3.07+/0.26(stat+syst)+/0.24(model)](%), and the
corresponding N>Δ transverse helicity amplitudes,
A1/2=[135.7+/1.3(stat+syst)+/3.7(model)](103
GeV1/2) and
A3/2=[266.9+/1.6(stat+syst)+/7.8(model)](103
GeV1/2). From these we deduce an oblate spectroscopic
deformation for the Δ+. The same simultaneous analysis
has been used to extract the proton dipole polarizabilities,
α¯β¯=+[10.39+/1.77(stat+syst)+1.021.87(model)](104
fm3) in agreement with previous low energy measurements, and
α¯+β¯=+[13.25+/0.86(stat+syst)+0.230.58(model)](104
fm3) in agreement with recent evaluations of the Baldin sum
rule. Our simultaneous analysis has also provided the first
determination of the proton spin polarizabilities,
γπ=[27.23+/2.27(stat+syst)+2.242.10(model)](104
fm4),
γ0=[1.55+/0.15(stat+syst)+0.030.03(model)](104
fm4),
γ13=+[3.94+/0.53(stat+syst)+0.200.18(model)](104
fm4), and
γ14=[2.20+/0.27(stat+syst)+0.050.09(model)](104
fm4). The extracted value of the backward spin
polarizability, γπ, is considerably different from
other analyses and this has been instrumental in bringing the value of
α¯β¯ extracted from high energy data into
agreement with low energy experiments. Physical Review C 07/2001; 64(2):25203. · 3.72 Impact Factor

G. Blanpied,
M. Blecher,
A. Caracappa,
R. Deininger,
C. Djalali,
G. Giordano,
K. Hicks,
S. Hoblit,
M. Khandaker,
O. C. Kistner, [......],
A. M. Sandorfi,
C. Schaerf,
R. M. Sealock,
H. Ströher,
C. E. Thorn,
S. T. Thornton,
J. Tonnison,
C. S. Whisnant, H. Zhang,
X. Zhao Physical Review C 07/2001; 64(2). · 3.72 Impact Factor

G. Blanpied,
M. Blecher,
A. Caracappa,
R. Deininger,
C Djalali,
G Giordano,
K Hicks,
S. Hoblit,
M Khandaker,
O. C. Kistner, [......],
A. M. Sandorfi,
C. Schaerf,
R. M. Sealock,
H. Ströher,
C. E. Thorn,
S. T. Thornton,
J. Tonnison,
C S Whisnant, H Zhang,
X Zhao 01/2001;

A.M. Sandorfi,
G. Blanpied,
M. Blecher,
A. Caracappa,
C. Djalali,
G. Giordano,
K. Hicks,
S. Hoblit,
M. Khandaker,
O.C. Kistner, [......],
D. Rebreyend,
C. Schaerf,
R.M. Sealock,
H. Ströher,
C.E. Thorn,
S.T. Thornton,
J. Tonnison,
C.S. Whisnant, H. Zhang,
X. Zhao [Show abstract] [Hide abstract]
ABSTRACT: New highprecision measurements of p(, π) and p(, γ) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. Compton scattering has provided two important new constraints on the photopion amplitude. The E2/M1 mixing ratio for the N → Δ transition extracted from this analysis is EMR = 3.0% ± 0.3 (stat + sys) ± 0.2 (model). Nuclear Physics A. 02/1998; 629(s 1–2):171–179.

G. Blanpied,
M. Blecher,
A. Caracappa,
C. Djalali,
G. Giordano,
K. Hicks,
S. Hoblit,
M. Khandaker,
O. C. Kistner,
A. Kuczewski, [......],
A. M. Sandorfi,
C. Schaerf,
R. M. Sealock,
H. Ströher,
C. E. Thorn,
S. T. Thornton,
J. Tonnison,
C. S. Whisnant, H. Zhang,
X. Zhao [Show abstract] [Hide abstract]
ABSTRACT: New highprecision measurements of p(γ[over →],π) and p(γ[over →],γ) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. Compton scattering has provided two important new constraints on the photopion amplitude. The E2/M1 mixing ratio for the N→Δ transition extracted from this analysis is [3.0±0.3(stat+syst)±0.2 (model)]%. Both data and analysis of this work are in conflict with recent results from Mainz. Physical Review Letters 12/1997; 79(22). · 7.73 Impact Factor

A. Caracappa,
S. Hoblit,
M. Khandaker,
O.C. Kistner,
A. Kuczewski,
M. Lowry,
L. Miceli,
A.M. Sandorfi,
C.E. Thorn,
J. Tonnison, [......],
B. Preedom,
D. Rebreyend,
C.S. Whisnant,
R.M. Sealock,
S.T. Thornton,
M. Blecher,
X. Zhao,
K. Hicks, H. Zhang,
H. Stroeher [Show abstract] [Hide abstract]
ABSTRACT: New highprecision measurements of p({rvec {gamma}},{pi}) and p({rvec {gamma}},{gamma}) cross sections and beam asymmetries have been combined with other polarization ratios in a simultaneous analysis of both reactions. Compton scattering has provided two important new constraints on the photopion amplitude. The E2/M1 mixing ratio for the N{r_arrow}{Delta} transition extracted from this analysis is [{minus}3.0{plus_minus}0.3(stat+syst) {plus_minus}0.2 (model)] {percent} . Both data and analysis of this work are in conflict with recent results from Mainz. {copyright} {ital 1997} {ital The American Physical Society} Physical Review Letters 12/1997; 79(22). · 7.73 Impact Factor

G Blanpied,
M Blecher,
A Caracappa,
C Djalali,
G Giordano,
K Hicks,
S Hoblit,
M Khandaker,
OC Kistner,
G Matone, [......],
D Rebreyend,
AM Sandorfi,
C Schaerf,
RM Sealock,
H Ströher,
CE Thorn,
ST Thornton,
CS Whisnant, H Zhang,
X Zhao [Show abstract] [Hide abstract]
ABSTRACT: New precision measurements of cross sections and polarization asymmetries in the p\(gamma>,gammap\) reaction at 90° c.m. are presented for incident energies between 213 and 333 MeV. A longstanding problem with earlier experiments that appeared to violate unitarity at the peak of the Delta is resolved. Data are compared to theories based on baryon resonance structure and to dispersion relations. Recent calculations using the proton polarizabilities are closest to the data, although inconsistencies are observed near the Delta resonance. Physical Review Letters 03/1996; 76(7):10231026. · 7.73 Impact Factor