-
G. Agakishiev,
A. Balanda,
D. Belver,
A. V. Belyaev,
J. C. Berger-Chen,
A. Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas,
S. Chernenko, [......],
M. Traxler,
R. Trebacz,
H. Tsertos,
T. Vasiliev,
V. Wagner,
M. Weber,
C. Wendisch,
J. Wüstenfel,
S. Yurevich,
Y. V. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the Lambda(1405) resonance produced in the reaction
p+p->Sigma^{pm}+pi^{mp}+K+p at 3.5 GeV kinetic beam energy measured with HADES
at GSI. The two charged decay channels Lambda(1405) -> Sigma^{\pm}+pi^{\mp}
have been reconstructed for the first time in p+p collisions. The efficiency
and acceptance-corrected spectral shapes show a peak position clearly below
1400 MeV/c^2. We find a total production cross section of
sigma_{Lambda(1405)}=9.2 +- 0.9 +- 0.7 +3.3-1.0 mub. The analysis of its polar
angle distribution suggests that the Lambda(1405) is produced isotropically in
the p-p center of mass system.
08/2012;
-
G. Agakishiev,
A. Balanda,
D. Belver,
A. Belyaev,
J. C. Berger-Chen,
A. Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas,
S. Chernenko, [......],
M. Traxler,
R. Trebacz,
H. Tsertos,
T. Vasiliev,
V. Wagner,
M. Weber,
C. Wendisch,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: We present data on dielectron emission in proton induced reactions on a Nb
target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The
data represent the first high statistics measurement of proton-induced
dielectron radiation from cold nuclear matter in a kinematic regime, where
strong medium effects are expected. Combined with the good mass resolution of
2%, it is the first measurement sensitive to changes of the spectral functions
of vector mesons, as predicted by models for hadrons at rest or small relative
momenta. Comparing the e+e invariant mass spectra to elementary p+p data, we
observe for e+e momenta Pee < 0.8 GeV/c a strong modification of the shape of
the spectrum, which we attribute to an additional rho-like contribution and a
decrease of omega yield. These opposite trends are tentatively interpreted as a
strong coupling of the rho meson to baryonic resonances and an absorption of
the omega meson, which are two aspects of in-medium modification of vector
mesons.
05/2012;
-
The HADES Collaboration,
G. Agakishiev,
A. Balanda,
B. Bannier,
R. Bassini,
D. Belver,
A. V. Belyaev,
A. Blanco,
M. Böhmer,
J. L. Boyard, [......],
V. Wagner,
M. Weber,
C. Wendisch,
M. Wisniowski,
T. Wojcik,
J. Wüstenfeld,
S. Yurevich,
Y. V. Zanevsky,
P. Zhou,
P. Zumbruch
[show abstract]
[hide abstract]
ABSTRACT: Results on pp, π+π+, and π−π− intensity interferometry are reported for collisions of Ar+KCl at 1.76A GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The experimental correlation
functions as a function of the relative momentum are compared to model calculations allowing the determination of the space-time
extent of the corresponding emission sources. The ππ source radii are found significantly larger than the pp emission radius.
The present radii do well complement the beam-energy dependences of Gaussian source radii of the collision system of size
A + A ≃ 40 + 40 . The pp source radius at fixed beam energy is found to increase linearly with the cube root of the number of participants.
From this trend, a lower limit of the pp correlation radius is deduced.
European Physical Journal A 04/2012; 47(5):1-8. · 2.19 Impact Factor
-
N. V. Rabin,
D. A. Vasil'ev,
S. V. Vladimirov,
A. G. Nekhaev,
V. T. Smolyankin,
V. I. Ushakov,
P. N. Shishov,
H. Bokemeyer,
W. Koenig,
W. Kuhn, [......],
I. Iori,
A. Kugler,
T. Marek,
R. Pleskac,
A. Taranenko,
A. Tikhonov, P. Tlusty,
M. Benovic,
S. Hlavac,
I. Turzo
[show abstract]
[hide abstract]
ABSTRACT: The HADES spectrometer and a time-of-flight detector based on long-sized (50–250 cm) scintillation counters are described.
The detector is designed for identification of electrons, pions, and protons with momenta of 0.1–1.5 GeV/c at a flight distance of 220–250 cm. The operating conditions are analyzed, and the requirements to the detector and counter
design are formulated. The design of the counters and their arrangement in the spectrometer are considered. The results of
experimental studies of such characteristics of long counters as the light attenuation length in a scintillator and temporal
and spatial resolutions, dependeing on the location of the point of the particle’s hit on the counter, are presented. Analysis
of the data has shown that the main factor determining the spatial resolution of long counters is the quality of the polishing
of the side faces of the scintillators, which determines the effective (averaged over the scintillator side surfaces) coefficient
of total internal reflectionR. It is shown that, forR>-0.99, it is quite possible to achieve temporal and spatial resolutions of 100 ns and 2–3 cm, respectively, for scintillators
with a length of up to 250 cm and a cross section of 1–20 cm2. Foreign and Russian photomultipliers were used in the counters.
Instruments and Experimental Techniques 04/2012; 43(4):435-452. · 0.36 Impact Factor
-
The HADES Collaboration,
S. Spataro,
G. Agakishiev,
C. Agodi,
A. Balanda,
G. Bellia,
D. Belver,
A. Belyaev,
A. Blanco,
M. Böhmer, [......],
I. Veretenkin,
V. Wagner,
H. Wen,
M. Wisniowski,
T. Wojcik,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky,
P. Zhou,
P. Zumbruch
[show abstract]
[hide abstract]
ABSTRACT: The HADES spectrometer at GSI (Darmstadt) is investigating the e
+
e
- pair production in p+p, p+A and A+A collisions. In this contribution we would like to highlight the physics motivations and the experiments performed so far,
focusing mainly on the first results coming from 12C + 12C collisions at 1 and 2AGeV, and on preliminary results from p+p/d+p collisions at 1.25AGeV.
European Physical Journal A 04/2012; 38(2):163-166. · 2.19 Impact Factor
-
The HADES Collaboration,
G. Agakishiev,
A. Balanda,
B. Bannier,
R. Bassini,
D. Belver,
A. Belyaev,
A. Blanco,
M. Böhmer,
J. L. Boyard, [......],
V. Wagner,
M. Weber,
C. Wendisch,
M. Wisniowski,
T. Wojcik,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky,
P. Zhou,
P. Zumbruch
[show abstract]
[hide abstract]
ABSTRACT: We present transverse momentum spectra, rapidity distribution and multiplicity of L \Lambda -hyperons measured with the HADES spectrometer in the reaction Ar(1.76AGeV) + KCl . The yield of X- \Xi^{{-}}_{} is calculated from our previously reported X- \Xi^{{-}}_{}/(L \Lambda + S0 \Sigma^{{0}}_{}) ratio and compared to other strange particle multiplicities. Employing a strangeness balance equation the multiplicities
of the yet unmeasured S± \Sigma^{{\pm}}_{} -hyperons can be estimated. Finally a statistical hadronization model is used to fit the yields of p- \pi^{-}_{} , K+, K
0
s , K-, f \phi , L \Lambda and X- \Xi^{-}_{} . The resulting chemical freeze-out temperature of T = (76±2) MeV is compared to the measured slope parameters obtained from fits to the transverse mass distributions of the
different particles.
European Physical Journal A 04/2012; 47(2):1-9. · 2.19 Impact Factor
-
The HADES Collaboration,
G. Agakichiev,
C. Agodi,
H. Alvarez-Pol,
E. Atkin,
E. Badura,
A. Balanda,
A. Bassi,
R. Bassini,
G. Bellia, [......],
M. Wisniowski,
T. Wojcik,
J. Wüstenfeld,
S. Yurevich,
Y. V. Zanevsky,
K. Zeitelhack,
A. Zentek,
P. Zhou,
D. Zovinec,
P. Zumbruch
[show abstract]
[hide abstract]
ABSTRACT: HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion-induced collisions.
Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting
of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger
array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events
containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and
dense hadronic matter. The detector system is characterized by an 85% azimuthal coverage over a polar angle interval from
18° to 85° , a single electron efficiency of 50% and a vector meson mass resolution of 2.5%. Identification of pions, kaons and protons
is achieved combining time-of-flight and energy loss measurements over a large momentum range ( 0.1 < p < 1.0 GeV/c . This paper describes the main features and the performance of the detector system.
European Physical Journal A 04/2012; 41(2):243-277. · 2.19 Impact Factor
-
G. Agakishiev,
H. Alvarez-Pol,
A. Balanda,
R. Bassini,
M. Böhmer,
H. Bokemeye,
J. L. Boyard,
P. Cabanelas,
S. Chernenko,
T. Christ, [......],
M. Traxler,
R. Trebacz,
H. Tsertos,
V. Wagner,
M. Wisniowski,
T. Wojcik,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky,
P. Zumbruch
[show abstract]
[hide abstract]
ABSTRACT: Data on inclusive dielectron production are presented for the reaction p+p at
2.2 GeV measured with the High Acceptance DiElectron Spectrometer (HADES). Our
results supplement data obtained earlier in this bombarding energy regime by
DLS and HADES. The comparison with the 2.09 GeV DLS data is discussed. The
reconstructed e+e- distributions are confronted with simulated pair cocktails,
revealing an excess yield at invariant masses around 0.5 GeV/c2. Inclusive
cross sections of neutral pion and eta production are obtained.
03/2012;
-
HADES Collaboration,
G. Agakishiev,
H. Alvarez-Pol,
A. Balanda,
R. Bassini,
M. Böhmer,
H. Bokemeyer,
J. L. Boyard,
P. Cabanelas,
S. Chernenko, [......],
M. Traxler,
R. Trebacz,
H. Tsertos,
V. Wagner,
M. Wisniowski,
T. Wojcik,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky,
P. Zumbruch
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of exclusive \pi^{+,0} and \eta\ production in pp
reactions at 1.25 GeV and 2.2 GeV beam kinetic energy in hadron and dielectron
channels. In the case of \pi^+ and \pi^0, high-statistics invariant-mass and
angular distributions are obtained within the HADES acceptance as well as
acceptance corrected distributions, which are compared to a resonance model.
The sensitivity of the data to the yield and production angular distribution of
\Delta(1232) and higher lying baryon resonances is shown, and an improved
parameterization is proposed. The extracted cross sections are of special
interest in the case of pp \to pp \eta, since controversial data exist at 2.0
GeV; we find \sigma =0.142 \pm 0.022 mb. Using the dielectron channels, the
\pi^0 and \eta\ Dalitz decay signals are reconstructed with yields fully
consistent with the hadronic channels. The electron invariant masses and
acceptance corrected helicity angle distributions are found in good agreement
with model predictions.
03/2012;
-
G. Agakishiev,
A. Balanda,
D. Belver,
A. Belyaev,
J. C. Berger-Chen,
A. Blanco,
M. Boehmer,
J. L. Boyard,
P. Cabanelas,
E. Castro, [......], P. Tlusty,
M. Traxler,
R. Trebacz,
H. Tsertos,
V. Wagner,
M. Weber,
C. Wendisch,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: We study the production of Sigma^+-pi^+-pK^+ particle quartets in p+p
reactions at 3.5 GeV kinetic beam energy. The data were taken with the HADES
experiment at GSI. This report evaluates the contribution of resonances like
Lambda(1405$, Sigma(1385)^0, Lambda(1520), Delta(1232), N^* and K^*0 to the
Sigma^+- pi^-+ p K+ final state. The resulting simulation model is compared to
the experimental data in several angular distributions and it shows itself as
suitable to evaluate the acceptance corrections properly.
02/2012;
-
G. Agakishiev,
A. Balanda,
D. Belver,
A. V. Belyaev,
A. Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas,
E. Castro,
J. C. Chen, [......], P. Tlusty,
M. Traxler,
R. Trebacz,
H. Tsertos,
V. Wagner,
M. Weber,
C. Wendisch,
J. Wüstenfeld,
S. Yurevich,
Y. V. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: The aim of the present analysis is to determine the relative production cross
sections of the $\Lambda$(1405) and $\Sigma(1385)^{0}$ resonances in p+p
collisions at E$_{kin}$=3.5 GeV measured with HADES. Upper and lower limits
have been determined for the ratio
$\sigma_{(\Sigma(1385)^{0}+p+K^{+})}/\sigma_{(\Lambda(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$.
The knowledge of this ratio is an essential input for the analysis of the decay
$\Lambda(1405)\rightarrow\Sigma^{\pm}\pi^{\mp}$, where an unambiguous
separation of the $\Lambda$(1405) and $\Sigma(1385)^{0}$ signals is not
possible.
02/2012;
-
G. Agakishiev,
A. Balanda,
D. Belver,
A. Belyaev,
A Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas,
E Castro,
J C Chen, [......], P. Tlusty,
M. Traxler,
R. Trebacz,
H. Tsertos,
V. Wagner,
M Weber,
C. Wendisch,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: We present the inclusive invariant-mass, transverse momentum and rapidity
distributions of dielectrons (e$^{+}$e$^{-}$ pairs) in p+p interactions at 3.5
GeV beam kinetic energy. In the vector-meson mass region, a distinct peak
corresponding to direct $\omega$ decays is reconstructed with 2% mass
resolution. The data is compared to predictions from three model calculations.
Due to the large acceptance of the HADES apparatus for $e^{+}e^{-}$ invariant
masses above 0.2 GeV/$c^{2}$ and for transverse pair momenta p$_{t}$ $ <$ 1
GeV/$c$, acceptance corrections are to a large extent model independent. This
allows us to extract from dielectron data for the first time at this energy the
inclusive production cross sections for light vector mesons. Inclusive
production cross sections for $\pi^o$ and $\eta$ mesons are also reported. The
obtained results will serve as an important reference for the study of vector
meson production in proton-nucleus and heavy-ion collisions. Furthermore, using
this data, an improved value for the upper bound of the branching ratio for
direct $\eta$ decays into the electron-positron channel is obtained.
12/2011;
-
G. Agakishiev,
A. Balanda,
D. Belver,
A. V. Belyaev,
A Blanco,
M. Boehmer,
J. L. Boyard,
P. Cabanelas,
E Castro,
J C Chen, [......], P. Tlusty,
M. Traxler,
R. Trebacz,
H. Tsertos,
V. Wagner,
M Weber,
C. Wendisch,
J. Wuestenfeld,
S. Yurevich,
Y. V. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: We present results of an exclusive measurement of the first excited state of
the Sigma hyperon, Sigma(1385)^+, produced in p+p -> Sigma^+ + K^+ + n at 3.5
GeV beam energy. The extracted data allow to study in detail the invariant mass
distribution of the Sigma(1385)^+. The mass distribution is well described by a
relativistic Breit-Wigner function with a maximum at m_0 = 1383.2 +- 0.9
MeV/c^2 and a width of 40.2 +- 2.1 MeV/c^2. The exclusive production
cross-section comes out to be 22.27 +- 0.89 +- 1.56 +3.07 -2.10 mu b. Angular
distributions of the Sigma(1385)^+ in different reference frames are found to
be compatible with the hypothesis that 33 % of Sigma(1385)^+ result from the
decay of an intermediate Delta^{++} resonance.
09/2011;
-
W. Czyzycki,
E. Epple,
L. Fabbietti,
M. Golubeva,
F. Guber,
A. Ivashkin,
M. Kajetanowicz,
A. Krasa,
F. Krizek,
A. Kugler,
K. Lapidus,
E. Lisowski,
J. Pietraszko,
A. Reshetin,
P. Salabura,
Y. Sobolev,
J. Stanislav, P. Tlusty,
T. Torrieri,
M. Traxler
[show abstract]
[hide abstract]
ABSTRACT: We propose to build the Electromagnetic calorimeter for the HADES di-lepton
spectrometer. It will enable to measure the data on neutral meson production
from nucleus-nucleus collisions, which are essential for interpretation of
dilepton data, but are unknown in the energy range of planned experiments (2-10
GeV per nucleon). The calorimeter will improve the electron-hadron separation,
and will be used for detection of photons from strange resonances in elementary
and HI reactions.
Detailed description of the detector layout, the support structure, the
electronic readout and its performance studied via Monte Carlo simulations and
series of dedicated test experiments is presented.
The device will cover the total area of about 8 m^2 at polar angles between
12 and 45 degrees with almost full azimuthal coverage. The photon and electron
energy resolution achieved in test experiments amounts to 5-6%/sqrt(E[GeV])
which is sufficient for the eta meson reconstruction with S/B ratio of 0.4% in
Ni+Ni collisions at 8 AGeV. A purity of the identified leptons after the hadron
rejection, resulting from simulations based on the test measurements, is better
than 80% at momenta above 500 MeV/c, where time-of-flight cannot be used.
09/2011;
-
Michael Weber,
G Agakishiev,
D Belver,
A Belyaev,
A Blanco,
M Böhmer,
P Cabanelas,
S Chernenko,
A Dybczak,
E Epple, [......], P Tlusty,
M Traxler,
R Trebacz,
H Tsertos,
T Vasiliev,
V Wagner,
M Weber,
J Wüstenfeld,
S Yurevich,
Y Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: We report on recent data of e+e− pair emission in proton nucleus collisions at energies above the light vector meson production thresholds. Invariant mass distributions for the p+Nb system at Ekin = 3.5 GeV are compared to data from elementary p+p reactions at the same beam energy. We observe a constant π0/ω yield ratio for both systems but an excess in the mass region above the π0 mass. Furthermore we present here the normalization procedure that was applied to p+Nb collisions by measuring the production of negative pions in the HADES acceptance.
Journal of Physics Conference Series 09/2011; 316(1):012007.
-
G. Agakishiev,
A. Balanda,
D. Belver,
A. Belyaev,
A Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas,
E Castro,
S. Chernenko, [......],
M. Traxler,
R. Trebacz,
H. Tsertos,
V. Wagner,
M Weber,
C. Wendisch,
M. Wisniowski,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: We present results on dielectron production in Ar+KCl collisions at 1.76A
GeV. For the first time $\omega$ mesons could be reconstructed in a heavy-ion
reaction at a bombarding energy which is well below the production threshold in
free nucleon-nucleon collisions. The omega multiplicity has been extracted and
compared to the yields of other particles, in particular of the phi meson. At
intermediate e+e- invariant masses, we find a strong enhancement of the pair
yield over a reference spectrum from elementary nucleon-nucleon reactions
suggesting the onset of non-trivial effects of the nuclear medium.
Transverse-mass spectra and angular distributions have been reconstructed in
three invariant mass bins. In the former unexpectedly large slopes are found
for high-mass pairs. The latter, in particular the helicity-angle
distributions, are largely consistent with expectations for a pair cocktail
dominated at intermediate masses by delta Dalitz decays.
03/2011;
-
The HADES Collaboration,
A. K. Kurilkin,
G. Agakishiev,
A. Balanda,
D. Belver,
A. Belyaev,
A Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas, [......], P. Tlusty,
M. Traxler,
R. Trebacz,
H. Tsertos,
T. Vasiliev,
V. Wagner,
M Weber,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: The preliminary results on charged pion production in np collisions at an
incident beam energy of 1.25 GeV measured with HADES are presented. The np
reactions were isolated in dp collisions at 1.25 GeV/u using the Forward Wall
hodoscope, which allowed to register spectator protons. The results for np ->
pppi-, np -> nppi+pi- and np -> dpi+pi- channels are compared with OPE
calculations. A reasonable agreement between experimental results and the
predictions of the OPE+OBE model is observed.
02/2011;
-
HADES Collaboration,
P. K. Kurilkin,
G. Agakishiev,
A. Balanda,
D. Belver,
A. Belyaev,
A Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas, [......], P. Tlusty,
M. Traxler,
R. Trebacz,
H. Tsertos,
T. Vasiliev,
V. Wagner,
M Weber,
J. Wüstenfeld,
S. Yurevich,
Y. Zanevsky
[show abstract]
[hide abstract]
ABSTRACT: First results of the differential cross section in dp elastic scattering at
1.25 GeV/u measured with the HADES over a large angular range are reported. The
obtained data corresponds to large transverse momenta, where a high sensitivity
to the two-nucleon and three-nucleon short-range correlations is expected.
02/2011;
-
G. Agakishiev,
A. Balanda,
B. Bannier,
R. Bassini,
D. Belver,
A. Belyaev,
A Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas, [......],
M Weber,
C. Wendisch,
M. Wisniowski,
T. Wojcik,
J. Wuestenfeld,
S. Yurevich,
Y. Zanevsky,
P Zhou,
P. Zumbruch,
HADES Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We present transverse momentum spectra, rapidity distribution and
multiplicity of Lambda-hyperons measured with the HADES spectrometer in the
reaction Ar(1.76A GeV)+KCl. The yield of Xi- is calculated from our previously
reported Xi-/(Lambda+Sigma0) ratio and compared to other strange particle
multiplicities. Employing a strangeness balance equation the multiplicities of
the yet unmeasured charged Sigma hyperons can be estimated. Finally a
statistical hadronization model is used to fit the yields of pi-, K+, K0s, K-,
phi, Lambda and Xi-. The resulting chemical freeze-out temperature of T=(76+-2)
MeV is compared to the measured slope parameters obtained from fits to the
transverse mass distributions of the particles.
10/2010;
-
G. Agakishiev,
A. Balanda,
B. Bannier,
R. Bassini,
D. Belver,
A. V. Belyaev,
A Blanco,
M. Böhmer,
J. L. Boyard,
P. Cabanelas, [......],
H. Tsertos,
V. Wagner,
M Weber,
M. Wisniowski,
T. Wojcik,
J. Wüstenfel,
S. Yurevich,
Y. V. Zanevsky,
P Zhou,
P. Zumbruch
[show abstract]
[hide abstract]
ABSTRACT: We present the transverse momentum spectra and rapidity distributions of $\pi^{-}$ and K$^0_S$ in Ar+KCl reactions at a beam kinetic energy of 1.756 A GeV measured with the spectrometer HADES. The reconstructed K$^0_S$ sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental $\pi^{-}$ and K$^0_S$ distributions to predictions by the IQMD model. The model calculations show that K$^0_S$ at low tranverse momenta constitute a particularly well suited tool to investigate the kaon in-medium potential. Our K$^0_S$ data suggest a strong repulsive in-medium K$^0$ potential of about 40 MeV strength. Comment: 10 pages, 10 figures, accepted by Phys. Rev. C
04/2010;
