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[show abstract]
[hide abstract]
ABSTRACT: Differential cross sections for the process gn-->pi-p have been extracted
from MAMI-B measurements of gd-->pi-pp, accounting for final-state interaction
effects, using a diagrammatic technique taking into account the NN and piN
final-state interaction amplitudes. Results are compared to previous
measurements of the inverse process, pi-p--> ng, and recent multipole analyses.
08/2012;
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I. I. Strakovsky,
W. Chen,
H. Gao,
W. J. Briscoe,
D. Dutta,
A. E. Kudryavtsev,
M. Mirazite,
M. Paris,
P. Rossi,
S. Stepanyan, V. E. Tarasov,
R. L. Workman
[show abstract]
[hide abstract]
ABSTRACT: We report a new extraction of nucleon resonance couplings using pi-
photoproduction cross sections on the neutron. The world database for the
process gn-->pi-p above 1 GeV has quadrupled with the addition of new
differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS)
at Jefferson Lab in Hall B. Differential cross sections from CLAS have been
improved with a new final-state interaction determination using a diagrammatic
technique taking into account the SAID phenomenological NN and piN final-state
interaction amplitudes. Resonance couplings have been extracted and compared to
previous determinations. With the addition of these new cross sections,
significant changes are seen in the high-energy behavior of the SAID cross
sections and amplitudes.
08/2012;
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The CLAS Collaboration,
Y. Ilieva,
B. L. Berman,
A. E. Kudryavtsev,
I. I. Strakovsky, V. E. Tarasov,
M. Amarian,
P. Ambrozewicz,
M. Anghinolfi,
G. Asryan, [......],
L. B. Weinstein,
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
L. Zana,
J. Zhang,
B. Zhao,
Z. Zhao
[show abstract]
[hide abstract]
ABSTRACT: High-quality cross sections for the reaction γd → π0
d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the η-meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near
E
γ = 700 MeV. Our model analysis shows that it can be explained by η excitation in the intermediate state. The effect is the result of the contribution of the N(1535)S
11-resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the
excitation of an intermediate η-meson dominates.
European Physical Journal A 04/2012; 43(3):261-267. · 2.19 Impact Factor
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W. Chen,
H. Gao,
W. J. Briscoe,
D. Dutta,
A. E. Kudryavtsev,
M. Mirazita,
M. Paris,
P. Rossi,
S. Stepanyan,
I. I. Strakovsky, V. E. Tarasov,
R. L. Workman
[show abstract]
[hide abstract]
ABSTRACT: We report a new extraction of nucleon resonance couplings using pi-
photoproduction cross sections on the neutron. The world database for the
process gamma n --> pi- p above 1 GeV has quadrupled with the addition of new
differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS)
at Jefferson Lab in Hall B. Differential cross sections from CLAS have been
improved with a new final-state interaction determination using a diagramatic
technique taking into account the NN and piN final-state interaction
amplitudes. Resonance couplings have been extracted and compared to previous
determinations. With the addition of these new cross sections, significant
changes are seen in the high-energy behavior of the SAID cross sections and
amplitudes.
03/2012;
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[show abstract]
[hide abstract]
ABSTRACT: The {\bar p}p-annihilation reactions {\bar p}p-->eta eta eta and {\bar p}p-->
eta K{\bar K} at rest are considered in the tree approximation in the framework
of SU(3) chiral effective theory at leading order. The calculated branchings
are compared with the data. The results for neutral (eta eta eta, K^0{\bar
K^0}eta) and charged (K^+ K^- eta) channels are essentially different.
02/2012;
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[show abstract]
[hide abstract]
ABSTRACT: The incoherent pion photoproduction reaction γd → π−pp is considered theoretically in a wide energy region Eth≤Eγ≤2700 MeV. The model applied contains the impulse approximation as well as the NN and πN final-state-interaction (FSI) amplitudes. The aim of the paper is to study a reliable way for getting the information on elementary γn → π−p reaction cross sections beyond the impulse approximation for γd → π−pp. For the elementary γN → πN, N N → N N, and πN → πN amplitudes, the results of The George Washington University (GW) Data Analysis Center (DAC) are used. There are no additional theoretical constraints. The calculated cross sections dσ /dΩ(γd → π−pp) are compared with existing data. The procedure used to extract information on the differential cross section dσ /dΩ(γn → π−p) on the neutron from the deuteron data using the FSI correction factor R is discussed. The calculations for R versus π−p center-of-mass (CM) angle θ1 of the outgoing pion are performed at different photon-beam energies with kinematic cuts for a “quasifree” process γn → π−p. The results show a sizable FSI effect R≠1 from the S-wave part of pp-FSI at small angles close to θ1∼0: this region narrows as the photon energy increases. At larger angles, the effect is small (|R − 1|≪1) and agrees with estimations of FSI in the Glauber approach.
Phys. Rev. C. 09/2011; 84(3).
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[show abstract]
[hide abstract]
ABSTRACT: The incoherent pion photoproduction reaction gd-->pi-pp is considered
theoretically in a wide energy region Eth =< Eg =< 2700 MeV. The model applied
contains the impulse approximation as well as the NN- and piN-FSI amplitudes.
The aim of the paper is to study a reliable way for getting the information on
elementary gn-->pi-p reaction cross section beyond the impulse approximation
for gd-->pi-pp. For the elementary gN-->piN, NN-->NN, and piN-->piN amplitudes,
the results of the GW DAC are used. There are no additional theoretical
constraints. The calculated cross section dSigma/dOmega(gd->pi-pp) are compared
with existing data. The procedure used to extract information on the
differential cross section dSigma/dOmega(gn-->pi-p) on the neutron from the
deuteron data using the FSI correction factor R is discussed. The calculations
for R versus pi-p CM angle \theta_1 of the outgoing pion are performed at
different photon-beam energies with kinematical cuts for "quasi-free" process
gn-->pi-p. The results show a sizeable FSI effect R \neq 1 from S-wave part of
pp-FSI at small angles close to \theta_1 ~ 0: this region narrows as the photon
energy increases. At larger angles, the effect is small (|R-1|<<1) and agrees
with estimations of FSI in the Glauber approach.
05/2011;
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[show abstract]
[hide abstract]
ABSTRACT: The Kd reactions are considered in the impulse approximation with NN final-state interactions (NN FSI) taken into account. The realistic parameters for the KN phase shifts are used. The "quasi-elastic" energy region, in which the elementary KN interaction is predominantly elastic, is considered. The theoretical predictions are compared with the data on the K^+d->K^+pn, K^+d->K^0pp, K^+d->K^+d and K^+d total cross sections. The NN FSI effect in the reaction K^+d->K^+pn has been found to be large. The predictions for the Kd cross sections are also given for slow kaons, produced from phi(1020) decays, as the functions of the isoscalar KN scattering length a_0. These predictions can be used to extract the value of a_0 from the data.
08/2007;
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[show abstract]
[hide abstract]
ABSTRACT: High-quality cross sections for the reaction gamma+d->pi^0+d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the eta-meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near E_gamma=700 MeV. Our model analysis shows that it can be explained by eta excitation in the intermediate state. The effect is the result of the contribution of the N(1535)S_11 resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the excitation of an intermediate eta meson dominates. Comment: slightly modified title, additional paragraph and a table (Table 2) added on p. 5; to be submitted to EPJA, 6 pages, 3 figures
03/2007;
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Article:
a
P. V. Fedorets,
M. Büscher,
V. P. Chernyshev,
S. N. Dymov,
V. Yu. Grishina,
C. Hanhart,
M. Hartmann,
V. Hejny,
V. Kleber,
H. R. Koch, [......],
P. Kulessa,
S. I. Merzliakov,
S. M. Mikirtychiants,
M. E. Nekipelov,
H. Ohm,
R. Schleichert,
H. Ströher, V. E. Tarasov,
K. -H. Watzlawik,
I. Zychor
[show abstract]
[hide abstract]
ABSTRACT: The reaction pp → dπ
+
η has been measured at a beam energy of T
p
= 2.65 GeV (p
p
= 3.46 GeV/c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected dπ
+ pairs exhibits a peak around the η mass on top of a strong background of multipion pp → dπ
+(nπ) events. The differential cross section d
4
σ/dΩd
dΩ
π
+
dp
d
dp
π
+ for the reaction pp → dπ
+
η has been determined model independently for two regions of phase space. Employing a dynamical model for the a
0
+
production allows one then to deduce a total cross section of σ(pp → da
0
+
→ dπ
+
η) = 1.1 ± 0.3stat ± 0.7syst µb for the production of π
+
η via the scalar a
0
+
(980) resonance and σ(pp → dπ
+
η) = 3.5 ± 0.3stat ± 1.0syst µb for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction
pp ® dK+ [`(K)]0pp \to dK^ + \bar K^0
, the ratio of the total cross sections is
s(pp ® d(K+ [`(K)]0 )L = 0 )/s(pp ® da0+ ® dp+ h) = 0.029 ±0.008stat ±0.009syst\sigma (pp \to d(K^ + \bar K^0 )_{L = 0} )/\sigma (pp \to da_0^ + \to d\pi ^ + \eta ) = 0.029 \pm 0.008_{stat} \pm 0.009_{syst}
, which is in agreement with branching ratios in the literature.
Physics of Atomic Nuclei 01/2006; 69(2):306-313. · 0.57 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We consider the reaction γd→π0d in a wide energy range around and above the η-meson photoproduction threshold at backward c.m. angles of the outgoing pions. Our theoretical analysis is motivated by the recent measurements of the CLAS Collaboration at Jefferson Lab, where this kinematical region of the reaction has been thoroughly studied for the first time and an enhancement in the energy dependence of the differential cross section in the region of Eγ~600-800 MeV has been observed. Our preliminary and qualitative analysis, based on single- and double-scattering diagrams, shows that the observed structure can be explained by the contribution of the double-scattering diagram with intermediate production of the η meson. The effect, to a considerable extent, is due to the contribution of the N(1535) resonance to the amplitudes of subprocesses on the nucleons.
Phys. Rev. C. 03/2005; 71(3).
-
P. Fedorets,
M. Buescher,
V. P. Chernyshev,
S. Dymov,
V. Yu. Grishina,
C. Hanhart,
M Hartmann,
V. Hejny,
V. Kleber,
H. R. Koch, [......],
P. Kulessa,
S. Merzliakov,
S. Mikirtychiants,
M. Nekipelov,
H. Ohm,
R. Schleichert,
H. Stroeher, V. E. Tarasov,
K.-H. Watzlawik,
I. Zychor
[show abstract]
[hide abstract]
ABSTRACT: The reaction pp -> dpi+eta has been measured at a beam energy of T=2.65 GeV (p=3.46 GeV/c) using the ANKE spectrometer at COSY-Juelich. The missing mass distribution of the detected dpi+ pairs exhibits a peak around the eta mass on top of a strong background of multi-pion pp -> dpi+(n(pi)) events. The differential cross section d^4(sigma)/d(Omega_d)d(Omega_pi+)d(p_d)d(p_pi+) for the reaction pp -> dpi+eta has been determined model independently for two regions of phase space. Employing a dynamical model for the a0+ production allows one then to deduce a total cross section of sigma(pp -> da0+ -> dpi+eta)=(1.1 +/- 0.3_(stat) +/- 0.7_(syst)) microbarn for the production of pi+eta via the scalar a0+(980) resonance and sigma(pp -> dpi+eta) = (3.5 +/- 0.3_(stat) +/- 1.0_(syst)) microbarn for the non-resonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction pp -> dK+(bar(K0)), the ratio of the total cross sections is sigma(pp -> d(K+(bar(K0)))_(L=0))/sigma(pp -> da0+ -> dpi+eta) = 0.029 +/- 0.008_(stat) +/- 0.009_(syst), which is in agreement with branching ratios in the literature.
02/2005;
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[show abstract]
[hide abstract]
ABSTRACT: We consider the reaction g+d -> pi+d in a wide energy range around and above the eta-meson photoproduction threshold at backward CM angles of the outgoing pion. Our theoretical analysis is essentially motivated by the recent measurements of the CLAS Collaboration at Jefferson Lab, where this kinematical region of the reaction has been thoroughly studied for the first time and a cusps in the energy dependence of the differential cross section in the region of Eg = 600-800 MeV has been observed. Our preliminary and qualitative analysis, based on single- and double-scattering diagrams, shows that the observed structure can be explained by the contribution of the double-scattering diagram with intermediate production of the eta meson. The effect, to a considerable extent, is formed due to the contribution of N(1535) resonance to the amplitudes of subprocesses on the nucleons.
09/2004;
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[show abstract]
[hide abstract]
ABSTRACT: The reactions pp → dπ
+
η and pn → dπ
0
η are of special interest for investigating the a
0(980) (J
P=0+) resonance in the process NN → da
0 → dπη. We study some aspects of those reactions within a general formalism and also in a concrete phenomenological model. In particular,
it is shown that the presence of nonresonant (i.e., without excitation of the a
0 resonance) contributions to these reactions yields nonvanishing values for specific polarization observables, i.e., to effects
like those generated by a
0
0
-f
0 mixing. An experimental determination of these observables for the reaction
[(p)\vec]p ® dp+ h\vec pp \to d\pi ^ + \eta
would provide concrete information on the magnitude of those nonresonant contributions to πη production. We also discuss the possibility of extracting information about a
0
0
-f
0 mixing from the reaction
[(p)\vec]n ® dp0 h\vec pn \to d\pi ^0 \eta
with a polarized proton beam.
Physics of Atomic Nuclei 09/2003; 66(10):1946-1952. · 0.57 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The reactions pp\to d\pi^+\eta and pn\to d\pi^0\eta are of special interest for investigating the a_0(980) (J^P=0^+) resonance in the process NN \to da_0 \to d\pi\eta. We study some aspects of those reactions within a general formalism and also in a concrete phenomenological model. In particular, it is shown that the presence of nonresonant (i.e. without excitation of the a_0 resonance) contributions to these reactions yields nonvanishing values for specific polarization observables, i.e. to effects like those generated by a_0-f_0 mixing. An experimental determination of these observables for the reaction pp\to d\pi^+\eta would provide concrete information on the magnitude of those nonresonant contributions to \pi\eta production. We discuss also the possibility of extracting information about a_0-f_0 mixing from the reaction pn \to d\pi^0\eta with polarized proton beam.
05/2003;
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[show abstract]
[hide abstract]
ABSTRACT: We discuss rescattering corrections to the impulse approximation for the processes $\pi^- d\to\pi^- d$ and $\gamma d\to\pi^0 d$. It is shown that the rescattering effects (RE) give non-negligible contribution to the real part of these amplitudes. At the same time the contributions from the imaginary parts of impulse and rescattering corrections drastically cancel each other. This cancellation means that the processes $\pi^- d\to \pi^0 nn$ and $\gamma d\to \pi^+ nn / \pi^- pp$ are strongly suppressed near threshold as required by the Pauli principle.
02/2003;
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[show abstract]
[hide abstract]
ABSTRACT: Some aspects of a00-f0 mixing effects in the reaction p⃗n⃗da00 with perpendicular polarized proton beam are discussed. An angular-asymmetry parameter A is defined to study those effects. It is shown that, for energies close to the production threshold, the angular-asymmetry parameter A(θ,φ) is proportional to the a00-f0 mixing amplitude for arbitrary polar and azimuthal angles θ and φ of the outgoing a0 meson. This statement is also valid for arbitrary energies, but then only at polar angles θ=0° and θ=90°. The mass dependence of the differential cross section dσ/dmπ0η in the reaction pn⃗dπ0η in the presence of a00-f0 mixing is also discussed.
Phys. Rev. C. 07/2002; 66(1).
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[show abstract]
[hide abstract]
ABSTRACT: Some aspects of a0-f0 mixing effects in the reaction ${\vec p} n\to da^0_0$ with perpendicular polarized proton beam are discussed. An angular--asymmetry parameter $A$ is defined to study those effects. It is shown that, for energies close to the production threshold, the angular--asymmetry parameter $A(\theta, \phi)$ is proportional to the a0-f0 mixing amplitude for arbitrary polar and azimuthal angles $\theta$ and $\phi$ of the outgoing $a_0$ meson. This statement is also valid for arbitrary energies, but then only at polar angles $\theta=0^0$ and $\theta=90^0$. The mass dependence of the differential cross section $d\sigma/dm_{\pi^0\eta}$ in the reaction $pn\to d\pi^0\eta$ in the presence of \mix mixing is also discussed.
04/2002;
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[show abstract]
[hide abstract]
ABSTRACT: The differential spectra in the reaction $pp\to K^+\bar K^0 d$ for different reasonable versions of the production amplitude are discussed at the initial proton energy $T_p=2.645$ GeV.
11/2001;
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[show abstract]
[hide abstract]
ABSTRACT: We discuss the experimental and theoretical status of charge-symmetry violation (CSV) in the elastic scattering of pi+ and pi- on 3H and 3He. Analysis of the experimental data for the ratios r1, r2, and R at Tpi = 142, 180, 220, and 256 MeV provides evidence for the presence of CSV. We describe pion scattering from the three-nucleon system in terms of single- and double-scattering amplitudes. External and internal Coulomb interactions as well as the Delta-mass splitting are taken into account as sources of CSV. Reasonable agreement between our theoretical calculations and the experimental data is obtained for Tpi = 180, 220, and 256 MeV. For these energies, it is found that the Delta-mass splitting and the internal Coulomb interaction are the most important contributions for CSV in the three-nucleon system. The CSV effects are rather sensitive to the choice of pion-nuclear scattering mechanisms, but at the same time, our theoretical predictions are much less sensitive to the choice of the nuclear wave function. It is found, however, that data for r2 and R at Tpi = 142 MeV do not agree with the predictions of our model, which may indicate that there are additional mechanisms for CSV which are important only at lower energies.
10/2001;
