-
Y. Maghrbi,
R. Gregor, S. Lugert,
J. Ahrens,
J. R. M. Annand,
H. J. Arends,
R. Beck,
V. Bekrenev,
B. Boillat,
A. Braghieri, [......],
S. Schadmand,
S. Schumann,
D. Sober,
S. Starostin,
I. Supek,
A. Thomas,
M. Unverzagt,
D. P. Watts,
D. Werthmueller,
F. Zehr
[show abstract]
[hide abstract]
ABSTRACT: Photoproduction of $\pi^{0}\pi^{0}$ and $\pi^{0}\pi^{\pm}$ pairs from nuclei
has been measured over a wide mass range ($^2$H, $^{7}$Li, $^{12}$C, $^{40}$Ca,
and $^{\rm nat}$Pb) for photon energies from threshold to 600 MeV. The
experiments were performed at the MAMI accelerator in Mainz, using the Glasgow
photon tagging spectrometer and a 4$\pi$ electromagnetic calorimeter consisting
of the Crystal Ball and TAPS detectors. A shift of the pion-pion invariant mass
spectra for heavy nuclei to small invariant masses has been observed for
$\pi^0$ pairs but also for the mixed-charge pairs. The precise results allow
for the first time a model-independent analysis of the influence of pion
final-state interactions. The corresponding effects are found to be large and
must be carefully considered in the search for possible in-medium modifications
of the $\sigma$-meson. Results from a transport model calculation reproduce the
shape of the invariant-mass distributions for the mixed-charge pairs better
than for the neutral pairs, but also for the latter differences between model
results and experiment are not large, leaving not much room for
$\sigma$-in-medium modification.
04/2013;
-
Y. Maghrbi,
B. Krusche,
J. Ahrens,
J. R. M. Annand,
H. J. Arends,
R. Beck,
V. Bekrenev,
B. Boillat,
A. Braghieri,
D. Branford, [......],
S. Schumann,
D. Sober,
A. Starostin,
I. Supek,
C. M. Tarbert,
A. Thomas,
M. Unverzagt,
D. P. Watts,
D. Werthmueller,
F. Zehr
[show abstract]
[hide abstract]
ABSTRACT: Coherent photoproduction of $\pi^0$-mesons from threshold ($E_{th} \approx$
136 MeV) throughout the $\Delta$-resonance region and of $\eta$-mesons close to
the production threshold ($E_{th} \approx$ 570 MeV for $\eta$) has been
measured for $^7$Li nuclei. The experiment was performed using the
tagged-photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS
detectors combined to give an almost 4$\pi$ solid-angle electromagnetic
calorimeter. The reactions were identified by a combined invariant-mass and
missing-energy analysis. A comparison of the pion data to plane-wave impulse
modelling tests the nuclear mass form factor. So far coherent $\eta$-production
had been only identified for the lightest nuclear systems ($^2$H and $^3$He).
For $^3$He a large enhancement of the cross section above plane-wave
approximations had been reported, indicating the formation of a quasi-bound
state. The present Li-data for $\eta$-production agree with a plane-wave
approximation. Contrary to $^3$He, neither a threshold enhancement of the total
cross section nor a deviation of the angular distributions from the expected
form-factor dependence were observed.
03/2013;
-
A. Nikolaev,
P. Aguar-Bartolomé,
J. Ahrens,
J. R. M. Annand,
H. J. Arends,
R. Beck,
V. Bekrenev,
B. Boillat,
A. Braghieri,
D. Branford, [......],
S. Schumann,
D. Sober,
A. Starostin,
I. Supek,
C. M. Tarbert,
A. Thomas,
M. Unverzagt,
Th. Walcher,
D. P. Watts,
F. Zehr
[show abstract]
[hide abstract]
ABSTRACT: A new precise determination of the {\eta} meson mass is presented. It is
based on a measurement of the threshold for the {\gamma}p -> p{\eta} reaction
using the tagger focal-plane microscope detector at the MAMI-B facility in
Mainz. The tagger microscope has a higher energy resolution than the standard
tagging spectrometer and, hence, allowed an improvement in the accuracy
compared to the previous {\eta} mass measurement at MAMI-B. The result m{\eta}
= (547.851 +- 0.031 stat. +- 0.062 syst.) MeV agrees very well with the precise
values of the NA48, KLOE and CLEO collaborations and deviates by about
5{\sigma} from the smaller, but also very precise value obtained by the GEM
collaboration at COSY.
07/2012;
-
F. Zehr,
B. Krusche,
P. Aguar,
J. Ahrens,
J. R. M. Annand,
H. J. Arends,
R. Beck,
V. Bekrenev,
B. Boillat,
A. Braghieri, [......],
T. Rostomyan,
S. Schumann,
D. Sober,
A. Starostin,
I. Supek,
C. M. Tarbert,
A. Thomas,
M. Unverzagt,
Th. Walcher,
D. P. Watts
[show abstract]
[hide abstract]
ABSTRACT: Precise total cross-sections and invariant-mass distributions have been
measured for photoproduction of pion pairs off the proton producing
$p\pi^0\pi^0$ and $n\pi^+\pi^0$ final states from the threshold region up to
800 MeV incident photon energy. Additionally, beam helicity asymmetries have
been measured in the second resonance region (550 MeV - 820 MeV). The
experiment was performed at the tagged photon beam of the Mainz MAMI
accelerator with the Crystal Ball and TAPS detectors combined to give an almost
4$\pi$ solid-angle electromagnetic calorimeter. The results are much more
precise than any previous measurements and confirm the chiral perturbation
theory predictions for the threshold behavior of these reactions. In the second
resonance region, the invariant-mass distributions of meson-meson and
meson-nucleon pairs are in reasonable agreement with model predictions, but
none of the models reproduce the asymmetries for the mixed-charge channel.
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
-
The CBELSA/TAPS Collaboration,
M. Nanova,
J. Weil,
S. Friedrich,
V. Metag,
U. Mosel,
M. Thiel,
G. Anton,
J. C. S. Bacelar,
O. Bartholomy, [......],
G. Suft,
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 w \omega mesons on LH2 , C and Nb has been measured for incident photon energies from 900 to 1300MeV using the CB/TAPS detector at ELSA. The w \omega lineshape does not show any significant difference between the LH2 and the Nb targets. The experiment was motivated by transport calculations that predicted a sensitivity of the w \omega lineshape to in-medium modifications near the production threshold on a free nucleon of Eglab=1109\ensuremath{E_{\gamma}^{lab}=1109} MeV. A comparison with recent calculations is given.
European Physical Journal A 04/2012; 47(2):1-5. · 2.19 Impact Factor
-
M. Nanova,
V. Metag,
A. Ramos,
E. Oset,
I. Jaegle,
K. Makonyi,
K. Brinkmann,
O. Bartholomy,
D. Bayadilov,
Y. A. Beloglazov, [......],
H. Schmieden,
B. Schoch,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: The photoproduction of \eta'-mesons off different nuclei has been measured
with the CBELSA/TAPS detector system for incident photon energies between 1500
- 2200 MeV. The transparency ratio has been deduced and compared to theoretical
calculations describing the propagation of \eta'-mesons in nuclei. The
comparison indicates a width of the \eta' -meson of the order of \Gamma= 15-25
MeV at \rho =\rho_0 for an average momentum p_{\eta'} = 1050 MeV/c, at which
the \eta'-meson is produced in the nuclear rest frame. The inelastic \eta' N
cross section is estimated to be 3 - 10 mb. Parameterizing the photoproduction
cross section of \eta'-mesons by \sigma(A) = \sigma_0 A^{\alpha}, a value of
\alpha = 0.84\pm0.03 has been deduced.
04/2012;
-
TAPS and Collaborations The Crystal Ball at MAMI,
S. Schumann,
B. Boillat,
E. J. Downie,
P. Aguar-Bartolomé,
J. Ahrens,
J. R. M. Annand,
H. J. Arends,
R. Beck,
V. Bekrenev, [......],
T. Rostomyan,
D. Sober,
A. Starostin,
I. Supek,
C. M. Tarbert,
A. Thomas,
M. Unverzagt,
Th. Walcher,
D. P. Watts,
F. Zehr
[show abstract]
[hide abstract]
ABSTRACT: The reaction γp → pπ
0γ′ has been measured with the Crystal Ball/TAPS detectors using the energy-tagged photon beam at the electron accelerator
facility MAMI-B. Energy and angular differential cross-sections for the emitted photon γ′ and angular differential cross-sections
for the π0 have been determined with high statistics in the energy range of the Δ+ (1232)-resonance. Cross-sections and the ratio of the cross-section to the nonradiative process γp → pπ
0 are compared to theoretical reaction models, having the anomalous magnetic moment κ
Δ
as free parameter. As the shape of the experimental distributions is not reproduced in detail by the model calculations,
currently no extraction of κ
Δ
is feasible.
European Physical Journal A 04/2012; 43(3):269-282. · 2.19 Impact Factor
-
The CBELSA/TAPS Collaboration: V. Crede,
N. Sparks,
A. Wilson,
A. V. Anisovich,
J. C. S. Bacelar,
R. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Y. A. Beloglazov, [......],
S. Shende,
V. Sokhoyan,
A. Suele,
V. V. Sumachev,
T. Szczepanek,
U Thoma,
D. Trnka,
R Varma,
D Walther,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Photoproduction of neutral pions has been studied with the CBELSA/TAPS
detector in the reaction $\gamma p\to p\pi^0$ for photon energies between 0.85
and 2.50 GeV. The $\pi^0$ mesons are observed in their dominant neutral decay
mode: $\pi^0\to\gamma\gamma$. For the first time, the differential cross
sections cover the very forward region, $\theta_{\rm c.m.}<60^\circ$. A
partial-wave analysis of these data within the Bonn-Gatchina framework observes
the high-mass resonances $G_{17}$(2190), $D_{13}$(2080), and $D_{15}$(2070).
07/2011;
-
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;
-
M. Nanova,
V. Metag,
G. Anton,
J. C. S. Bacelar,
O. Bartholomy,
D. Bayadilov,
Y. A. Beloglazov,
R. Bogendörfer,
R. Castelijns,
V. Crede, [......],
G. Suft,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
Ch. Weinheimer,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Data on the photoproduction of ω mesons on nuclei have been reanalyzed in a search for in-medium modifications. The data were taken with the crystal barrel (CB)/two-arm photon spectrometer (TAPS) detector system at the ELectron Stretcher Anlage (ELSA) accelerator facility in Bonn. First results from the analysis of the data set were published by Trnka et al. Phys. Rev. Lett. 94 192303 (2005), claiming a lowering of the ω mass in the nuclear medium by 14% at normal nuclear matter density. The extracted ω line shape was found to be sensitive to the background subtraction. For this reason a reanalysis of the same data set has been initiated, and a new method has been developed to reduce the background and to determine the shape and absolute magnitude of the background directly from the data. Details of the reanalysis and of the background determination are described. The ω signal on the Nb target, extracted in the reanalysis, does not show a deviation from the corresponding line shape on a LH2 target, measured as reference. The earlier claim of an in-medium mass shift is thus not confirmed. The sensitivity of the ω line shape to different in-medium modification scenarios is discussed.
Phys. Rev. C. 09/2010; 82(3).
-
M. Nanova,
J. Weil,
S. Friedrich,
V. Metag,
U. Mosel,
G. Anton,
J. C. S. Bacelar,
O. Bartholomy,
D. Bayadilov,
Y. A. Beloglazov, [......],
G. Suft,
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 $\omega$ mesons on LH_2, C and Nb has been studied for
incident photon energies from 900 to 1300 MeV using the CB/TAPS detector at
ELSA. The $\omega$ line shape does not show any significant difference between
the LH_2 and the Nb targets. The data are compared with results of transport
calculations that predict a sensitivity of the $\omega$ line shape to in-medium
modifications near the production threshold on a free nucleon of
$E_{\gamma}^{lab}$ = 1109 MeV.}
08/2010;
-
The The CBELSA/TAPS Collaboration: M. Nanova,
V. Metag,
G. Anton,
J. C. S. Bacelar,
O. Bartholomy,
D. Bayadilov,
Y. A. Beloglazov,
R. Bogendörfer,
R. Castelijns,
V. Crede, [......],
G. Suft,
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
Ch. Weinheimer,
Ch. Wendel
[show abstract]
[hide abstract]
ABSTRACT: Data on the photoproduction of $\omega$ mesons on nuclei have been
re-analyzed in a search for in-medium modifications. The data were taken with
the Crystal Barrel(CB)/TAPS detector system at the ELSA accelerator facility in
Bonn. First results from the analysis of the data set were published by D.
Trnka et al. in Phys. Rev. Lett 94 (2005) 192303 \cite{david}, claiming a
lowering of the $\omega$ mass in the nuclear medium by 14$%$ at normal nuclear
matter density. The extracted $\omega$ line shape was found to be sensitive to
the background subtraction. For this reason a re-analysis of the same data set
has been initiated and a new method has been developed to reduce the background
and to determine the shape and absolute magnitude of the background directly
from the data. Details of the re-analysis and of the background determination
are described. The $\omega$ signal on the $Nb$ target, extracted in the
re-analysis, does not show a deviation from the corresponding line shape on a
$LH_2$ target, measured as reference. The earlier claim of an in-medium mass
shift is thus not confirmed. The sensitivity of the $\omega$ line shape to
different in-medium modification scenarios is discussed.
05/2010;
-
N. Sparks,
V Crede,
A. V. Anisovich,
J. C. S. Bacelar,
R. 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. Wendel,
A. Wilson
[show abstract]
[hide abstract]
ABSTRACT: Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector for photon energies between 0.92 and 1.68~GeV at the electron accelerator ELSA. The beam asymmetry~$\Sigma$ has been extracted for $115^\circ < \theta_{\rm c.m.} < 155^\circ$ of the $\pi^0$~meson and for $\theta_{\rm c.m.} < 60^\circ$. The new beam asymmetry data improve the world database for photon energies above 1.5~GeV and, by covering the very forward region, extend previously published data for the same reaction by our collaboration. The angular dependence of $\Sigma$ shows overall good agreement with the SAID parameterization. Comment: 11 pages, 10 figures, published in Phys. Rev. C, included LEPS data and MAID 2007 predictions for comparison with our data
03/2010;
-
S. Schumann,
B Boillat,
E. J. Downie,
P. Aguar-Bartolomé,
J. Ahrens,
J. R. M. Annand,
H.J. Arends,
R. Beck,
V. Bekrenev,
A. Braghieri, [......],
T. Rostomyan,
D. Sober,
A. Starostin,
I. Supek,
C. M. Tarbert,
A Thomas,
M. Unverzagt,
Th. Walcher,
D. P. Watts,
F. Zehr
[show abstract]
[hide abstract]
ABSTRACT: The reaction gamma p -> p pi0 gamma' has been measured with the Crystal Ball / TAPS detectors using the energy-tagged photon beam at the electron accelerator facility MAMI-B. Energy and angular differential cross sections for the emitted photon gamma' and angular differential cross sections for the pi0 have been determined with high statistics in the energy range of the Delta+(1232) resonance. Cross sections and the ratio of the cross section to the non-radiative process gamma p -> p pi0 are compared to theoretical reaction models, having the anomalous magnetic moment kappa_Delta+ as free parameter. As the shape of the experimental distributions is not reproduced in detail by the model calculations, currently no extraction of kappa_Delta+ is feasible. Comment: 14 pages, 19 figures
01/2010;
-
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;
-
V. Crede,
A. McVeigh,
A. V. Anisovich,
J. C. S. Bacelar,
R. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Y. A. Beloglazov,
R. Castelijns, [......],
A. Süle,
V. V. Sumachev,
T. Szczepanek,
U. Thoma,
D. Trnka,
R. Varma,
D. Walther,
Ch. Weinheimer,
Ch. Wendel,
A. Wilson
[show abstract]
[hide abstract]
ABSTRACT: Total and differential cross sections for η and η'photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The η mesons are detected in their two neutral decay modes, η→γγ and η→3π0→6γ, and for the first time, cover the full angular range in cos θc.m. of the η meson. These new η photoproduction data are consistent with the earlier CB-ELSA results. The η' mesons are observed in their neutral decay to π0π0η→6γ and also extend the coverage in angular range.
Phys. Rev. C. 11/2009; 80(5).
-
The CBELSA,
TAPS Collaboration: Volker Crede,
A. McVeigh,
A. Anisovich,
J. Bacelar,
R. Bantes,
O. Bartholomy,
D. Bayadilov,
R. Beck,
Y. Beloglazov, [......],
A. Suele,
V Sumachev,
T. Szczepanek,
U Thoma,
D. Trnka,
R Varma,
D Walther,
C. Weinheimer,
C. Wendel,
A. Wilson
[show abstract]
[hide abstract]
ABSTRACT: Total and differential cross sections for $\eta$ and $\eta ^\prime$ photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The $\eta$ mesons are detected in their two neutral decay modes, $\eta\to\gamma\gamma$ and $\eta\to 3\pi^0\to 6\gamma$, and for the first time, cover the full angular range in $\rm cos \theta_{cm}$ of the $\eta$ meson. These new $\eta$ photoproduction data are consistent with the earlier CB-ELSA results. The $\eta ^\prime$ mesons are observed in their neutral decay to $\pi^0\pi^0\eta\to 6\gamma$ and also extend the coverage in angular range. Comment: 13 pages, 21 figures, updated author list, submitted to PRC
09/2009;
