-
A. Thiel,
A. V. Anisovich,
D. Bayadilov, B. Bantes,
R. Beck,
Yu. Beloglazov,
M. Bichow,
S. Böse,
K. -Th. Brinkmann,
Th. Challand, [......],
V. Sokhoyan,
V. Sumachev,
U. Thoma,
H. van Pee,
D. Walther,
Ch. Wendel,
U. Wiedner,
A. Wilson,
A. Winnebeck,
Y. Wunderlich
[show abstract]
[hide abstract]
ABSTRACT: The first measurement is reported of the double-polarization observable G in
photoproduction of neutral pions off protons, covering the photon energy range
from 620 to 1120 MeV and the full solid angle. G describes the correlation
between the photon polarization plane and the scattering plane for protons
polarized along the direction of the incoming photon. The observable is highly
sensitive to contributions from baryon resonances. The new results are compared
to the predictions from SAID, MAID, and BnGa partial wave analyses. In spite of
the long-lasting efforts to understand {\gamma}p -> p{\pi} 0 as the simplest
photoproduction reaction, surprisingly large differences between the new data
and the latest predictions are observed which are traced to different
contributions of the N (1535) with spin-parity J^P = 1/2^- and N (1520) with
J^P = 3/2^- . In the third resonance region, where N (1680) with J^P = 5/2^+
production dominates, the new data are reasonably close to the predictions.
07/2012;
-
The CBELSA/TAPS Collaboration,
I. Jaegle,
T. Mertens,
A. Fix,
F. Huang,
K. Nakayama,
L. Tiator,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes, [......],
S. V. Shende,
V. Sokhoyan,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Quasi-free photoproduction of h¢ \eta{^\prime} -mesons off nucleons bound in the deuteron has been measured with the combined Crystal Barrel - TAPS detector. The experiment
was done at a tagged photon beam of the ELSA electron accelerator in Bonn for incident photon energies from the production
threshold up to 2.5GeV. The h¢ \eta{^\prime} -mesons have been detected in coincidence with recoil protons and recoil neutrons. The quasi-free proton data are in good
agreement with the results for free protons, indicating that nuclear effects have no significant impact. The coincidence with
recoil neutrons provides the first data for the g \gamma
n
® \rightarrow
n
h¢ \eta{^\prime} reaction. In addition, also first estimates for coherent h¢ \eta{^\prime} -production off the deuteron have been obtained. In agreement with model predictions, the total cross-section for this channel
is found to be very small, at most at the level of a few nb. The data are compared to model calculations taking into account
contributions from nucleon resonances and t -channel exchanges.
European Physical Journal A 04/2012; 47(1):1-18. · 2.19 Impact Factor
-
The CBELSA/TAPS Collaboration,
I. Jaegle,
B. Krusche,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. E. Bayadilov,
R. Beck,
Y. A. Beloglazov, [......],
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
C. Wendel,
D. Werthmüller,
L. Witthauer
[show abstract]
[hide abstract]
ABSTRACT: Precise data for quasi-free photoproduction of η-mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for
incident photon energies up to 2.5GeV. The η-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and
re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to η-production off the free proton. No significant effects beyond the folding of the free cross-section with the momentum distribution
of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of
the η-nucleon pairs reconstructed from the final-state four-momenta of the particles. The total cross-section for quasi-free η-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around
1GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant-mass
spectrum of the η-neutron pairs. Position and width of the peak in the invariant-mass spectrum are W ≈ 1665 MeV and FWHM Γ ≈ 25 MeV. The data are compared to the results of different models.
European Physical Journal A 04/2012; 47(8):1-25. · 2.19 Impact Factor
-
The CBELSA/TAPS Collaboration,
M. Nanova,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Y. A. Beloglazov,
R. Castelijns,
V. Crede, [......],
V. Sokhoyan,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
Ch. Weinheimer,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The exclusive reactions γp → K
*0Σ+(1189) and γp → K
0π0Σ+(1189) , leading to the p 4π0 final state, have been measured with a tagged photon beam for incident energies from threshold up to 2.5GeV. The experiment
has been performed at the tagged photon facility of the ELSA accelerator (Bonn). The Crystal Barrel and TAPS detectors were
combined to a photon detector system of almost 4π geometrical acceptance. Differential and total cross-sections are reported.
At energies close to the threshold, a flat angular distribution has been observed for the reaction γp → K
0π0Σ+ suggesting dominant s -channel production. Σ*(1385) and higher-lying hyperon states have been observed. An enhancement in the forward direction in the angular distributions
of the reaction γp → K
*0Σ+ indicates a t -channel exchange contribution to the reaction mechanism. The experimental data are in reasonable agreement with recent theoretical
predictions.
European Physical Journal A 04/2012; 35(3):333-342. · 2.19 Impact Factor
-
R. Ewald,
A. V. Anisovich, B. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Y. A. Beloglazov,
K. -T. Brinkmann,
V Crede,
H. Dutz, [......],
S. Shende,
V. Sokhoyan,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U Thoma,
D. Trnka,
R Varma,
D Walther,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The $\gamma + p \rightarrow K^0 + \Sigma^+$ photoproduction reaction is
investigated in the energy region from threshold to $E_\gamma = 2250$\,MeV. The
differential cross section exhibits increasing forward-peaking with energy, but
only up to the $K^*$ threshold. Beyond, it suddenly returns to a flat
distribution with the forward cross section dropping by a factor of four. In
the total cross section a pronounced structure is observed between the
$K^*\Lambda$ and $K^*\Sigma$ thresholds. It is speculated whether this signals
the turnover of the reaction mechanism from t-channel exchange below the $K^*$
production threshold to an s-channel mechanism associated with the formation of
a dynamically generated $K^*$-hyperon intermediate state.
12/2011;
-
I. Jaegle,
B. Krusche,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. E. Bayadilov,
R. Beck,
Y. A. Beloglazov,
R. Castelijns, [......],
A. Suele,
V. V. Sumachev,
T. Szczepanek,
U Thoma,
D. Trnka,
R Varma,
D Walther,
C. Wendel,
D. Werthmueller,
L. Witthauer
[show abstract]
[hide abstract]
ABSTRACT: Precise data for quasi-free photoproduction of $\eta$ mesons off the deuteron
have been measured at the Bonn ELSA accelerator with the combined Crystal
Barrel/TAPS detector for incident photon energies up to 2.5 GeV. The
$\eta$-mesons have been detected in coincidence with recoil protons and
neutrons. Possible nuclear effects like Fermi motion and re-scattering can be
studied via a comparison of the quasi-free reaction off the bound proton to
$\eta$-production off the free proton. No significant effects beyond the
folding of the free cross section with the momentum distribution of the bound
protons have been found. These Fermi motion effects can be removed by an
analysis using the invariant mass of the $\eta$-nucleon pairs reconstructed
from the final state four-momenta of the particles. The total cross section for
quasi-free $\eta$-photoproduction off the neutron reveals even without
correction for Fermi motion a pronounced bump-like structure around 1 GeV of
incident photon energy, which is not observed for the proton. This structure is
even narrower in the invariant mass spectrum of the $\eta$-neutron pairs.
Position and width of the peak in the invariant mass spectrum are $W\approx
1665$ MeV and FWHM $\Gamma\approx 25$ MeV. The data are compared to the results
of different models.
07/2011;
-
E. Gutz,
V. Sokhoyan,
H. van Pee,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Yu Beloglazov, [......],
A. Suele,
V Sumachev,
T. Szczepanek,
A. Thiel,
U Thoma,
D. Trnka,
R Varma,
D Walther,
Ch. Weinheimer,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The polarization observable I^s, a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction g p -> p pi0 eta are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I^c. The comparably large asymmetries demonstrate a high sensitivity of I^s to the dynamics of the reaction. Fits using Bonn-Gatchina partial wave analysis demonstrate that the new polarization observables carry significant information on the contributing partial waves. Comment: 11 pages, 6 figures, v2 to appear in Phys. Lett. B
12/2009;
-
The CBELSA/TAPS Collaboration,
D. Elsner, B. Bantes,
O. Bartholomy,
D. E. Bayadilov,
R. Beck,
Y. A. Beloglazov,
R. Castelijns,
V. Crede,
A. Ehmanns, [......],
B. Schoch,
S. Shende,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
D. Walther,
C. Weinheimer,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: At the electron accelerator ELSA a linearly polarised tagged photon beam is produced by coherent bremsstrahlung off a diamond
crystal. Orientation and energy range of the linear polarisation can be deliberately chosen by accurate positioning of the
crystal with a goniometer. The degree of polarisation is determined by the form of the scattered electron spectrum. Good agreement
between experiment and expectations on the basis of the experimental conditions is obtained. Polarisation degrees of Pg=40\ensuremath P_{\gamma}=40 % are typically achieved at half of the primary electron energy. The determination of Pg\ensuremath P_{\gamma} is confirmed by measuring the beam asymmetry, S \Sigma , in p0 \pi^{0}_{} photoproduction and by a comparison of the results to independent measurements using laser backscattering.
European Physical Journal A 02/2009; 39(3):373-381. · 2.19 Impact Factor
-
Frank Klein,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Y. A. Beloglazov,
R. Castelijns,
V. Crede, [......],
V. Sokhoyan,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
Ch. Weinheimer,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The photoproduction of ω mesons off protons has been studied at the Bonn ELSA accelerator from threshold to Eγ=1700 MeV. Linearly polarized beams were produced via coherent bremsstrahlung. Large photon asymmetries in excess of 50% were obtained. For the first time the pion asymmetries associated with the ω→π0γ decay were measured and found close to zero. The asymmetries indicate s-channel resonance formation on top of t-channel exchange processes.
Phys. Rev. D. 12/2008; 78(11).
-
T. Mertens,
I. Jaegle,
P. Muehlich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. E. Bayadilov,
R. Beck,
Y. A. Beloglazov,
R. Castelijns, [......],
V. Sokhoyan,
A. Suele,
V. V. Sumachev,
T. Szczepanek,
U Thoma,
D. Trnka,
R Varma,
D Walther,
C. Weinheimer,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Photoproduction of $\eta$ mesons off $^{12}$C, $^{40}$Ca, $^{93}$Nb, and $^{nat}$Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2 GeV. The experiment was performed at the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties of the S$_{11}$(1535) nucleon resonance and the study of the absorption properties of nuclear matter for $\eta$ mesons. Careful consideration was given to contributions from $\eta\pi$ final states and secondary production mechanisms of $\eta$-mesons e.g. from inelastic $\pi N$ reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross section $\sigma_{N\eta}$ for $\eta$ mesons is constant over a wide range of the $\eta$ momentum. The comparison of the excitation functions to data off the deuteron and to calculations in the framework of a BUU-model show no unexplained in-medium modifications of the S$_{11}$(1535).
11/2008;
-
I Jaegle,
T Mertens,
A V Anisovich,
J C S Bacelar, B Bantes,
O Bartholomy,
D Bayadilov,
R Beck,
Y A Beloglazov,
R Castelijns, [......],
V Sokhoyan,
A Süle,
V V Sumachev,
T Szczepanek,
U Thoma,
D Trnka,
R Varma,
D Walther,
Ch Weinheimer,
Ch Wendel
[show abstract]
[hide abstract]
ABSTRACT: Quasifree photoproduction of eta mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasifree n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta production off the neutron shows a pronounced bumplike structure at W=1.68 GeV (E{gamma} approximately 1 GeV), which is absent for the proton.
Physical Review Letters 06/2008; 100(25):252002. · 7.37 Impact Factor
-
I. Jaegle,
T. Mertens,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Y. A. Beloglazov,
R. Castelijns, [......],
V. Sokhoyan,
A. Suele,
V. V. Sumachev,
T. Szczepanek,
U Thoma,
D. Trnka,
R Varma,
D Walther,
C. Weinheimer,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Quasi-free photoproduction of eta-mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta-mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasi-free n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta-production off the neutron shows a pronounced bump-like structure at W=1.68 GeV (E_g ~ 1 GeV), which is absent for the proton.
05/2008;
-
The CBELSA/TAPS Collaboration,
E. Gutz,
V. Sokhoyan,
H. van Pee,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck, [......],
B. Schoch,
S. Shende,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
D. Walther,
Ch. Weinheimer,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: In photoproduction experiments, a large number of final states yielding various resonance contributions are accessible. To
extract resonance parameters via partial-wave analysis not only the measurement of differential cross-sections is necessary,
but also the determination of polarization observables. At the electron accelerator ELSA (Bonn) the coherent bremsstrahlung
method was used to generate a linearly polarized photon beam. Using the CBELSA/TAPS detector setup, the beam asymmetry Σ in
the reaction γp → pπ0η was determined as a function of various masses and angles for photon energies between 970MeV and 1650MeV.
European Physical Journal A 02/2008; 35(3):291-293. · 2.19 Impact Factor
-
The CBELSA/TAPS Collaboration,
T. Mertens,
I. Jaegle,
P. Mühlich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. E. Bayadilov,
R. Beck,
Y. A. Beloglazov, [......],
V. Sokhoyan,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
C. Weinheimer,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The photoproduction of η -mesons off 12C , 40Ca , 93Nb , and
nat
Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2GeV. The experiment was performed at
the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties
of the S
11(1535) nucleon resonance and the study of the absorption properties of nuclear matter for η -mesons. Careful consideration
was given to contributions from ηπ final states and secondary production mechanisms of η -mesons, e.g. from inelastic πN reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross-section
sNh \sigma_{{N\eta}}^{} for η -mesons is constant over a wide range of the η momentum. The comparison of the excitation functions to data off the
deuteron and to calculations in the framework of a BUU model show no unexplained in-medium modifications of the S
11(1535) .
European Physical Journal A 01/2008; 38(2):195-207. · 2.19 Impact Factor
-
The CBELSA/TAPS Collaboration,
R. Castelijns,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
Y. A. Beloglazov,
V. Crede,
H. Dutz, [......],
S. Shende,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
C. Weinheimer,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Hyperon production off the proton in the K
0Σ+ channel has been studied at the tagged-photon beam facility at the ELSA electron accelerator in Bonn. This experiment was
part of a series of neutral meson production experiments on various targets. For this purpose, the Crystal Barrel and TAPS
photon spectrometers have been combined to provide a 4π detector for multi-neutral-particle final states. A high-quality excitation
function, recoil polarizations, and angular distributions from threshold up to 2.3GeV center-of-mass energy were obtained.
The results are compared with predictions of recent coupled-channel calculations within the K -matrix formalism and are interpreted by the partial-wave analysis within the Bonn-Gatchina model.
European Physical Journal A 12/2007; 35(1):39-45. · 2.19 Impact Factor
-
The CBELSA/TAPS Collaboration,
D. Elsner,
A. V. Anisovich,
G. Anton,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. E. Bayadilov,
R. Beck,
Y. A. Beloglazov, [......],
S. Shende,
G. Suft,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
D. Walther,
C. Weinheimer,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The beam asymmetry, Σ , was measured at ELSA in the reaction
g \boldsymbol\gamma
p → ηp using linearly polarised tagged photon beams, produced by coherent bremsstrahlung off a diamond. The crystal was oriented
to provide polarised photons in the energy range E
γ = 800 to 1400MeV with the maximum polarisation of P
γ = 49 % obtained at 1305MeV. Both dominant decay modes of the η into two photons and 3π0 were used to extract the beam asymmetry from the azimuthal modulation of the cross-section. The measurements cover the angular
range Θcm ≃ 50 -150 degrees. Large asymmetries up to 80% are observed, in agreement with a previous measurement. The eta-MAID model
and the Bonn-Gatchina partial wave analysis describe the measurements, but the required partial waves differ significantly.
European Physical Journal A 01/2007; 33(2):147-155. · 2.19 Impact Factor
-
The CBELSA/TAPS Collaboration,
R. Castelijns,
A. V. Anisovich,
J. C. S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
Y. A. Beloglazov,
V Crede,
H. Dutz, [......],
S. Shende,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U Thoma,
D. Trnka,
R Varma,
D Walther,
C. Weinheimer,
C. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Hyperon production off the proton in the K 0Σ+ channel has been studied at the tagged-photon beam facility at the ELSA electron accelerator in Bonn. This experiment was part of a series of neutral meson production experiments on various targets. For this purpose, the Crystal Barrel and TAPS photon spectrometers have been combined to provide a 4π detector for multi-neutral-particle final states. A high-quality excitation function, recoil polarizations, and angular distributions from threshold up to 2.3GeV center-of-mass energy were obtained. The results are compared with predictions of recent coupled-channel calculations within the K-matrix formalism and are interpreted by the partial-wave analysis within the Bonn-Gatchina model.
http://dx.doi.org/10.1140/epja/i2007-10529-8.
-
E. Gutz,
V. Sokhoyan,
H. van Pee,
A.V. Anisovich,
J.C.S. Bacelar, B. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Yu. Beloglazov, [......],
A. Süle,
V. Sumachev,
T. Szczepanek,
A. Thiel,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
Ch. Weinheimer,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The polarization observable Is, a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry Ic. The comparably large asymmetries demonstrate a high sensitivity of Is to the dynamics of the reaction. The sensitivity of these new polarization observables to the contributing partial waves is demonstrated by fits using the Bonn–Gatchina partial wave analysis.
Physics Letters B.
-
B Bantes,
H Dutz,
H Eberhardt,
D Elsner,
R Ewald,
K Fornet-Ponse,
S Goertz,
D Hammann,
J Hannappel,
W Hillert, [......],
G Gervino,
D Glazier,
D Watts,
D Burdeinyi,
V Ganenko,
G Vashchenko,
A S Ignatov,
A M Lapik,
V G Nedorezov,
A A Turinge
