共查询到20条相似文献,搜索用时 31 毫秒
1.
U. Siodlaczek P. Achenbach J. Ahrens H.-J. Arends R. Beck R. Bilger H. Clement V. Hejny J.D. Kellie M. Kotulla B. Krusche V. Kuhr R. Leukel J.C. McGeorge V. Metag R. Novotny V. Olmos de León F. Rambo M. Schepkin A. Schmidt H. Ströher G.J. Wagner Th. Walcher J. Weiß F. Wissmann M. Wolf 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):309-311
The reaction γd↦π0
X has been measured with TAPS at MAMI in the energy range E
γ = 140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation
functions of integral and differential total cross-sections show no structures of statistical significance > 2σ. Upper limits
for the production of narrow isoscalar or isovector dibaryons with masses m? 2100 MeV/c2 were deduced. They are in the range 2-5 μb averaged over the 0.8 MeV energy resolution.
Received: 25 October 2000 / Accepted: 24 November 2000 相似文献
2.
B. Tatischeff J. Yonnet M. Boivin M.P. Comets P. Courtat R. Gacougnolle Y. Le Bornec E. Loireleux M. MacCormick F. Reide N. Willis 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):245-267
The reaction pp → pπ+
X was studied at different incident energies around T
p = 2 GeV. Narrow baryonic structures were observed in the missing mass M
X and in the invariant mass M
pπ{+}. The masses of these structures are 1004, 1044, 1094, 1136, 1173, 1249, 1277, and 1384 MeV (and possibly 1339 MeV). Some
of them were also observed at the same masses in the missing-mass spectra of the dp → ppX reaction although with a weaker
signature. Many checks were performed to make sure that these structures were not produced by experimental artifacts. Several
narrow small-amplitude peaks, were also extracted using already published photonucleon cross-sections. The small widths of
all these results, and the stability of the observed structures, regardless of the experiment, were used to conclude that
they are genuine baryons and not merely the consequence of dynamical rescatterings. These baryons cannot be associated with
classical q3 quark configurations. We associate them with two colored-quark cluster configurations.
Received: 3 July 2002 / Accepted: 30 January 2003 / Published online: 5 June 2003 相似文献
3.
S.V. Golovkin A.P. Kozhevnikov V.P. Kubarovsky V.F. Kurshetsov L.G. Landsberg V.V. Molchanov V.A. Mukhin S.V. Petrenko V.A. Senko D.V. Vavilov V.A. Victorov V.Z. Kolganov G.S. Lomkatsi A.F. Nilov V.T. Smolyankin 《The European Physical Journal A - Hadrons and Nuclei》1999,5(4):409-416
New data for the diffractive reaction p+N→ [Σ0
K
+] +N at E
p= 70 GeV were obtained with partially upgraded SPHINX setup. The data are in a good agreement with the results of our previous
study of this reaction. In the mass spectrum M(Σ0
K
+) a structure at the threshold region with a mass ∼1810 MeV and a distinct X(2000) peak with M= 1989 ± 6 MeV and γ= 91 ± 20 MeV are observed. Unusual features of the massive X(2000) state (narrow decay width, anomalously
large branching ratio for the decay channel with strange particle emission) make it a serious candidate for cryptoexotic pentaquark
baryon with hidden strangeness |qqqsˉs>. We also present new results on the narrow threshold structure X(1810) with M= 1807 ± 7 MeV and γ= 62 ± 19 MeV which is produced in the region of very small P
2
T < 0.01 GeV2. The possibility of the Coulomb production mechanism for X(1810) is discussed.
Received: 28 April 1999 相似文献
4.
《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):241-244
The helicity dependence of the γ
p↦pη reaction has been measured for the first time at a center-of-mass angle θ*
η = 70° in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector
system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section
is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.
Received: 19 December 2002 / Accepted: 10 March 2003 / Published online: 20 May 2003 相似文献
5.
P. Bartsch D. Baumann J. Bermuth K. Bohinc R. Böhm D. Bosnar N. Clawiter S. Derber M. Ding M.O. Distler A. Ebbes I. Ewald J.M. Friedrich J. Friedrich P. Jennewein M. Kahrau M. Kohl A. Kozlov K.W. Krygier M. Kuss A. Liesenfeld H. Merkel P. Merle U. Müller R. Neuhausen T. Pospischil M. Potokar D. Rohe G. Rosner H. Schmieden S. Širca A. Wagner T. Walcher M. Weis S. Wolf 《The European Physical Journal A - Hadrons and Nuclei》1999,4(3):209-216
The reaction 12C(e,e'Δ0)11C →12C(e,e'pπ−)11C was investigated at the Mainz Microtron MAMI in a triple coincidence measurement using the three spectrometer setup of the
A1 Collaboration. The good missing mass resolution of σm= 0.27 MeV/c2 allowed to select the events belonging to the ground state of 11C. Cutting on these events the excitation energy spectra of 12CΔ0 show evidence for two peaks of about 4 MeV width (FWHM) at 282 MeV and 296 MeV with a significance of about 4.5 standard
deviations. The peaks are interpreted in a simple weak coupling model as bound Δ0 states in 12CΔ0.
Received: 23 December 1998 相似文献
6.
7.
V. Koptev M. Nekipelov M. Büscher S. Dymov M. Hartmann V. Hejny H.R. Koch N. Lang S. Mikirtichyants H. Ohm A. Petrus Z. Rudy R. Schleichert A. Sibirtsev K. Sistemich H. Ströher K.-H. Watzlawik 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):235-240
Results of a first experiment on (K+p) and (K+d) correlations from proton-carbon (pC) and proton-deuteron (pd) interactions at beam energies above and much below the threshold for elementary kaon production in nucleon-nucleon reactions
( T
NN = 1580 MeV) are discussed. These data, obtained with the ANKE spectrometer at COSY-Jülich, provide first direct evidence
for K+ production via the two-step mechanism and an indication for a cluster mechanism. It is shown that both processes contribute
significantly in pC collisions at 1200 MeV, while they are strongly suppressed at 2300 MeV and also in pd-interactions at 1344 MeV. It is emphasized that the underlying kinematics can be exploited to distinguish between these reaction
mechanisms.
Received: 26 November 2002 / Accepted: 26 March 2003 / Published online: 20 May 2003 相似文献
8.
T. Shizuma K. Furuno K. Hata H. Ishiyama T. Jumatsu M. Kato T. Komatsubara K. Matsuura Y. Sasaki K. Uchiyama T. Hayakawa 《The European Physical Journal A - Hadrons and Nuclei》1998,1(3):245-246
High-spin states in 183Os have been studied by means of in-beam γ-ray spectroscopy. Two isomers with I
π= ((43/2)−) and (43/2)+ have been identified at excitation energies of E
x
= 5.068 and 5.168 MeV. The half-lives are determined as T
1/2= 27 ± 3 and 24 ± 2 ns.
Received: 22 December 1997 相似文献
9.
G. Panaccione G. van der Laan H.A. Dürr J. Vogel N.B. Brookes 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):281-287
We measured high-quality Co 2p magnetic circular dichroism (MCD) spectra in photoemission for > 5 ML Co films grown on Cu(1 1 13) using a “complete” experiment,
where the sample magnetization and the light helicity vector were reversed separately. We show how the four measured spectra,
M±P±, can be used to make new linear combinations, which correspond to the circular dichroism in the angular dependence (CDAD),
magnetic linear dichroism in the angular dependence (MLDAD) and MCD spectra. The integrated signals of the MLDAD and CDAD
can be used to estimate the error caused by the difference in the degrees of magnetization and light polarization, respectively,
in the opposite alignments. The MCD signal integrated over the entire 2p region does not average to zero, as one would have expected from the sum rule for photoemission to a non-interacting continuum
state. There is a strong MCD signal in the entire region between the 2p
3/2 and 2p
1/2 main lines with pronounced satellite structure. The differences between the measured and calculated results for an independent-particle
and an atomic model indicate the presence of interatomic electron correlation effects and configurational mixing.
Received 26 September 2000 相似文献
10.
C.M. Marian F. Schneider M. Kleinschmidt J. Tatchen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):357-367
Electronic spectra of uracil in its diketo (lactam) form and five enol (lactim) tautomeric forms have been investigated by
means of combined density functional and configuration interaction methods. We have simulated the effects of hydrogen bonding
with a protic solvent by recomputing the spectrum of uracil in the presence of two, four, or six water molecules. Geometries
of the electronic ground state and several low-lying excited states have been optimized. Spin-orbit coupling has been determined
for correlated wavefunctions employing a non-empirical spin-orbit mean-field approach. In accord with experiment, we find
the diketo tautomer to be the most stable one. The calculations confirm that the first absorption band arises from the 1( π↦π*) S
0↦S
2 excitation. The experimentally observed vibrational structure in this band originates from a breathing mode of the six ring.
Complexation with water molecules is seen to cause a significant blue shift of n↦π* excitations while leaving π↦π* excitations nearly uninfluenced. Computed radiative lifetimes are presented for the experimentally known weak phosphorescence
from the π↦π* excited T1 state. Among the uracil lactim tautomers, one is particularly interesting from a spectroscopic point of view. In this tautomer,
the π↦π* excitation gives rise to the S1 state.
Received 18 February 2002 / Received in final form 5 June 2002 Published online 13 September 2002 相似文献
11.
M. Koll R. Ricken D. Merten B.C. Metsch H.R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):73-94
We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation.
Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual
interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with
a natural solution of the U
A(1) problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this
paper, we will also discuss our results concerning numerous meson decay properties. For processes like π+/K
+↦e
+υeγ and 0-↦γγ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors
of the K
?3 decay and on the decay constants of the π, K and η mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged π
and K mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data.
Received: 28 August 2000 / Accepted: 12 September 2000 相似文献
12.
R.A. Radhi 《The European Physical Journal A - Hadrons and Nuclei》2003,16(3):387-392
Electron scattering Coulomb form factors for the single-particle quadrupole transitions in p-shell and sd-shell nuclei have been studied. Core polarization effects are included through a microscopic theory that includes excitations
from the core orbits up to higher orbits with 2ω excitations. The modified surface delta interaction is adopted as a residual
interaction. The results are discussed for the ( 1p
1/2
-1↦1p
3/2
-1) proton transition in 15N, ( 1d
5/2↦2s
1/2) neutron transition in 17O and ( 1d
3/2
-1↦2s
1/2
-1) proton transition in 39K. The inclusion of core polarization effects modifies the form factors markedly and describes the experimental data very
well in both the absolute strength and the momentum transfer dependence.
Received: 18 April 2002 / Accepted: 1 July 2002 / Published online: 6 March 2003
RID="a"
ID="a"e-mail: baguniv@uruklink.net
Communicated by A. Molinari 相似文献
13.
V. Olmos de León F. Wissmann P. Achenbach J. Ahrens H.-J. Arends R. Beck P.D. Harty V. Hejny P. Jennewein M. Kotulla B. Krusche V. Kuhr R. Leukel J.C. McGeorge V. Metag R. Novotny A. Polonski F. Rambo A. Schmidt M. Schumacher U. Siodlaczek H. Ströher A. Thomas J. Weiß M. Wolf 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):207-215
Differential cross-sections for Compton scattering from the proton have been measured at the MAMI tagged photon facility using
the TAPS setup. The data cover an angular range of θlab
γ = 59°-155° and photon energies ranging from 55 MeV to 165 MeV. Our results are in good agreement with those from previous experiments,
but yield higher precision. Using dispersion relations the proton polarizabilities have been determined to be = [11.9±0.5stat.±1.3syst.±0.3mod.] . 10-4
fm
3 and = [1.2±0.7stat.±0.3syst.±0.4mod.)] . 10-4
fm
3. These results confirm the Baldin sum rule which was re-evaluated to be + = [13.8±0.4] . 10-4
fm
3. We can also conclude that there is no significant additional asymptotic contribution to the backward spin polarizability
γπ beyond the t-channel π0-exchange.
Received: 9 January 2001 / Accepted: 13 February 2001 相似文献
14.
Ya.I. Azimov 《The European Physical Journal A - Hadrons and Nuclei》2003,16(2):209-219
Isospin-violating mixing of ρ- and ω-mesons is reconsidered in terms of propagators. Its influence on various pairs of (ρ,ω)-decays
to the same final states is demonstrated. Some of them, (ρ,ω)↦π+π- and (ρ,ω)↦πγ, have been earlier discussed in the literature, others (e.g., (ρ,ω)↦ηγ and (ρ,ω)↦e
+
e
-) are new in this context. Changes in partial widths for all the decay pairs are shown to be correlated. The set of present
experimental data, though yet inconclusive, provides some limits for the direct (ρω)-coupling and indirectly supports enhancement
of ρ↦πγ in comparison with ρ±↦π±γ, though not so large as in some previous estimates.
Received: 16 September 2002 / Accepted: 23 September 2002 / Published online: 4 February 2003
RID="a"
ID="a"e-mail: azimov@pa1400.spb.edu
Communicated by V.V. Anisovich 相似文献
15.
A mean-field theory for domain structures in random multiblock copolymer melts is developed. We focus on the finite molecular
weight effects resulting in a competition between macroscopic phase separation and microdomain formation in the system. We
identify an essential parameter N
ε controlling the phase behavior of the system, where N is the number of blocks per chain and ε is the composition asymmetry parameter (= the difference between the mean copolymer
composition and its critical value). The phase diagram involving N
ε and the reduced temperature as variables is obtained. The regions of coexistence of two or more phases are identified. We
show that a superstructure formation on cooling is always pre-empted by a macroscopic phase separation of the macroscopically
homogeneous (disordered) system yielding two homogeneous phases: H
0↦H
1 + H
2. The third (lamellar) phase separates on further cooling. Then hexagonal and body-centred-cubic phases take over if N
ε
1. As the Flory interaction parameter χ increases further, the standard transitions BCC↦HEX↦LAM take place.
Received 13 July 2001 相似文献
16.
Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV
《The European Physical Journal A - Hadrons and Nuclei》1998,3(4):335-349
The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by
defolding the pt spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions
of resonances are obtained from the invariant masses of (p, π±) pairs. With both methods the deduced mass distributions are shifted by an average value of −60 MeV/c2 relative to the mass distribution of the free Δ(1232) resonance, the distributions descent almost exponentially towards mass
values of 2000 MeV/c2. The observed differences between (p, π−) and (p, π+) pairs indicate a contribution of isospin I = 1/2 resonances. The attempt to consistently describe the deduced mass distributions
and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e.
to rather low temperatures and large expansion velocities.
Received: 26 June 1998 / Revised version: 2 September 1998 相似文献
17.
S. Wolf V. Lisin R. Kondratiev A.M. Massone G. Galler J. Ahrens H.-J. Arends R. Beck M. Camen G.P. Capitani P. Grabmayr F. Härter T. Hehl P. Jennewein K. Kossert A.I. L'vov C. Molinari P. Ottonello R.O. Owens J. Peise I. Preobrajenskij S. Proff A. Robbiano M. Sanzone M. Schumacher M. Schmitz F. Wissmann 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):231-252
18.
K. Jessen W. Andrejtscheff M. Bergström P. von Brentano A. Dewald B. Herskind H. Meise C. Schumacher G. Sletten O. Stuch D. Weißhaar I. Wiedenhöver J. Wrzesinski 《The European Physical Journal A - Hadrons and Nuclei》1999,4(1):9-10
A new high-spin isomer in 145Sm was observed by in-beam γ-ray spectroscopy with the reaction 122Sn(27Al,3np) at 127 MeV performed at the Nordball multi-detector array in Roskilde. The excitation energy of the isomer was determined
to be E
x= 11147 keV, and using the generalized centroid-shift method its half-life was found to be T
1/2= (7.4 ± 1.0) ns.
Received: 23 October 1998 相似文献
19.
N. Beverini E. Maccioni F. Sorrentino V. Baraulia M. Coca 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):223-228
We have measured the ratio between the transition probabilities of two forbidden lines in Ca: the intercombination line at
657.3 nm and the E
2 line at 457.5 nm. The value we obtained for this ratio is (54.1±2.4). Combined with the most accurate value available in literature for the lifetime of the
3
P
1
level, our measurement gives a value of (54.4±4.0) s-1 for the
1
S
0
↦
1
D
2
transition probability, significantly more accurate than the previous determinations.
Received 17 June 2002 / Received in final form 9 December 2002 Published online 4 March 2003 相似文献
20.
V.Yu. Grishina L.A. Kondratyuk E.L. Bratkovskaya M. Büscher W. Cassing 《The European Physical Journal A - Hadrons and Nuclei》2000,9(2):277-285
We investigate the reactions πN↦a
0
N and pp↦da
0
+ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different
contributions to the cross-section of the reaction πN↦a
0
N. These results are used to calculate the differential and total cross-sections of the reaction pp↦da
0
+ within the framework of the two-step model in which two nucleons produce an a0-meson via π-meson exchange and fuse to a deuteron. The necessity of new measurements on a0 production and branching fractions (of its decay to the K
and πη channels) is emphasized for clarifying the a0 structure. Detailed predictions for the reaction pp→da
0
+ are presented for the energy regime of the proton synchrotron COSY-Jülich.
Received: 4 August 2000 / Accepted: 17 September 2000 相似文献