-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
M. Wilfert,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The gluon polarisation in the nucleon was measured using open charm
production by scattering 160 GeV/c polarised muons off longitudinally polarised
protons or deuterons. The data were taken by the COMPASS collaboration between
2002 and 2007. A detailed account is given of the analysis method that includes
the application of neural networks. Several decay channels of D^0 mesons are
investigated. Longitudinal spin asymmetries of the D meson production
cross-sections are extracted in bins of D^0 transverse momentum and energy. At
leading order QCD accuracy the average gluon polarisation is determined as
(Delta g/G)^LO=-0.06 +/- 0.21 (stat.) +/- 0.08 (syst.) at the scale <mu^2> ~13
(GeV/c)^2 and an average gluon momentum fraction ~ 0.11. For the first time,
the average gluon polarisation is also obtained at next-to-leading order QCD
accuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at the
scale <mu^2> ~ 13 (\GeV/c)^2 and ~ 0.20.
11/2012;
-
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
A. A. Antonov,
A. Austregesilo,
B. Badelek,
F. Balestra, [......],
M. Wilfert,
R. Windmolders,
W. Wislicki,
H. Wollny,
K. Zaremba,
M. Zavertyaev,
E. Zemlyanichkina,
M. Ziembicki,
N. Zhuravlev,
A. Zvyagin
[show abstract]
[hide abstract]
ABSTRACT: The production of D* and D mesons in inelastic scattering of 160 GeV/c muons
off a ^6LiD target has been investigated with the COMPASS spectrometer at CERN
for 0.003 (GeV/c)^2 < Q^2 < 10 (GeV/c)^2 and 3x10^-5< x_Bj < 0.1. The study is
based on 8100 events where a D^0 or anti D^0 is detected subsequently to a D*+
or D*- decay, and on 34000 events, where only a D^0 or anti D^0 is detected.
Kinematic distributions of D*, D and K*_2 are given as a function of their
energy E, transverse momentum p_T, energy fraction z, and of the virtual photon
variables nu, Q^2 and x_Bj. Semi-inclusive differential D* production
cross-sections are compared with theoretical predictions for D* production via
photon-gluon fusion into open charm. The total observed production
cross-section for D*+/- mesons with laboratory energies between 22 and 86 GeV
is 1.9 nb. Significant cross-section asymmetries are observed between D*+ and
D*- production for nu<40 GeV and z>0.6.
European Physical Journal C 11/2012; 72(12). · 3.63 Impact Factor
-
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
-
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;
-
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;
-
[show abstract]
[hide abstract]
ABSTRACT: Evidence is reported for two nucleon resonances with spin-parity $J^P=1/2^-$
and $J^P=3/2^-$ at a mass just below 1.9\,GeV. The evidence is derived from a
coupled-channel analysis of a large number of pion and photo-produced
reactions. The two resonances are nearly degenerate in mass with two resonances
of the same spin but positive parity. Such parity doublets are predicted in
models claiming restoration of chiral symmetry in high-mass excitations of the
nucleon. Further examples of spin parity doublets are found in addition.
Alternatively, the spin doublet can be interpreted as member of the 56-plet
expected in the third excitation band of the nucleon. Implications for the
problem of the {\it missing resonances} are discussed.
11/2011;
-
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;
-
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;
-
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
