共查询到20条相似文献,搜索用时 31 毫秒
1.
O. Benhar S. Fantoni G.I. Lykasov 《The European Physical Journal A - Hadrons and Nuclei》2000,7(3):415-419
The production of backward pions in lepton-nucleus collisions is analyzed. We show that a large yield of high momentum backward
pions can be explained by the Regge asymptotic of the distribution of nucleons carrying a large momentum fraction in the nuclear
target. The calculated spectra of pions emitted in the ν+ Ne →μ+π−+ X and ν+2H →μ+π−+ X reactions are in satisfactory agreement with the available experimental data.
Received: 22 July 1999 / Revised version: 22 November 1999 相似文献
2.
L. Käubler H. Schnare R. Schwengner P. von Brentano F. Dönau J. Eberth J. Enders A. Fitzler C. Fransen M. Grinberg E. Grosse R.-D. Herzberg H. Kaiser P. von Neumann-Cosel N. Pietralla H. Prade A. Richter S. Skoda Ch. Stoyanov H.-G. Thomas H. Tiesler D. Weisshaar I. Wiedenhöver 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):15-18
A nuclear resonance fluorescence experiment on 88Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with
a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742
MeV in 88Sr, in contrast to the previous interpretation as a 1− two-phonon (2+
1⊗ 3−
1) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1+ state at 3.486 MeV may be considered as the 1+
1 one-phonon state and the very strong 1+
1→ 0+
1 deexcitation as proton spin-flip 2p1/2→ 2p3/2 transition.
Received: 3 November 1999 相似文献
3.
Z. Rudy W. Cassing L. Jarczyk B. Kamys P. Kulessa 《The European Physical Journal A - Hadrons and Nuclei》2002,15(3):303-314
The production of K+-mesons in proton-nucleus collisions from 1.0 to 2.5GeV is analyzed with respect to one-step nucleon-nucleon ( NN → NYK
+) and two-step Δ-nucleon ( ΔN → K
+
YN) or pion-nucleon ( πN → K
+
Y) production channels on the basis of a coupled-channel transport approach (CBUU) including the kaon final-state interactions.
The influence of momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are studied as well as
the importance of K+ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental K+ spectra taken at LBL Berkeley, SATURNE, CELSIUS, GSI and COSY-Jülich. It is found that the momentum-dependent baryon potentials
affect the excitation function of the K+ cross-section; at low bombarding energies of ∼ 1.0GeV the attractive baryon potentials in the final state lead to a relative
enhancement of the kaon yield, whereas the net repulsive potential at bombarding energies ∼ 2GeV causes a decrease of the
K+ cross-section. Furthermore, it is pointed out that especially the K+ spectra at low momenta (or kinetic energy T
K) allow to determine the in-medium K+ potential almost model independently due to a relative shift of the K+ spectra in kinetic energy that arises from the acceleration of the kaons when propagating out of the nuclear medium to free
space, i.e. converting the potential energy to the kinetic energy of the free kaon.
Received: 28 January 2002 / Accepted: 3 June 2002 / Published online: 19 November 2002
RID="a"
ID="a"e-mail: Wolfgang.Cassing@theo.physik.uni-giessen.de
Communicated by P. Schuck 相似文献
4.
M.H. Thoma S. Leupold U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):219-223
Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the
dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π+-π− annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the
quark-gluon plasma.
Received: 8 September 1999 / Revised version: 22 October 1999 相似文献
5.
6.
S. Heinz E. Berdermann F. Heine O. Joeres P. Kienle I. Koenig W. Koenig C. Kozhuharov U. Leinberger M. Rhein A. Schröter H. Tsertos 《The European Physical Journal A - Hadrons and Nuclei》1998,1(1):27-37
We present the results of a Doppler-shift correction to the measured e+e−–sum-energy spectra obtained from e+e−–coincidence measurements in 238U +206Pb and 238U +181Ta collisions at beam energies close to the Coulomb barrier, using an improved experimental setup at the double-Orange spectrometer
of GSI. Internal-Pair-Conversion (IPC) e+e− pairs from discrete nuclear transitions of a moving emitter have been observed following Coulomb excitation of the 1.844
MeV (E1) transition in 206Pb and neutron transfer to the 1.770 MeV (M1) transition in 207Pb. In the collision system 238U +181Ta, IPC transitions were observed from the Ta-like as well as from the U-like nuclei. In all systems the Doppler-shift corrected
e+e−–sum-energy spectra show weak lines at the energies expected from the corresponding γ–ray spectra with cross sections being
consistent with the measured excitation cross sections of the γ lines and the theoretically predicted IPC coefficients. No
other than IPC e+e−–sum-energy lines were found in the measured spectra. The transfer cross sections show a strong dependence on the distance
of closest approach (Rmin), thus signaling also a strong dependence on the bombarding energy close to the Coulomb barrier.
Received: 22 July 1997 / Revised version: 15 October 1997 相似文献
7.
V.D. Efros H. Oberhummer A. Pushkin I.J. Thompson 《The European Physical Journal A - Hadrons and Nuclei》1998,1(4):447-453
A semi–microscopic model for the low–energy photodisintegration of the 9Be nucleus is constructed, and the experimental data are analyzed with its help. The older radioactive isotope data are supported
by this analysis. The theoretical photodisintegration cross section is derived. The astrophysical rates for the reaction α+α+n→9Be+γ and the reverse photodisintegration of 9Be are calculated. The new reaction rate for α+α+n→9Be+γ is compared with previous estimations.
Received: 19 January 1998 相似文献
8.
T.R. Saitoh N. Hashimoto G. Sletten R.A. Bark S. Törmänen M. Bergström K. Furuno K. Furutaka G.B. Hagemann T. Hayakawa T. Komatsubara A. Maj S. Mitarai M. Oshima J. Sampson T. Shizuma P.G. Varmette 《The European Physical Journal A - Hadrons and Nuclei》1998,3(3):197-199
High-spin states in 181Ta have been studied via the 176Yb(11B,α2n) reaction at 52 MeV using the PEX array and at 57 MeV using the NORDBALL array, with α-particle detection. The previously
known, Kπ=(7/2)+ ground state band and Kπ=(9/2)− band have been extended to spins (29/2)+ and (31/2)−, respectively. Two new one-quasiparticle bands, the Kπ=(5/2)+ band built on the known (5/2)+ isomer and a Kπ=((1/2)−) band have been observed. Two other rotational bands with three-quasiparticle structure, Kπ=(15/2)− and ((19/2)+ with π(7/2)[404]ν2(1/2)[510](9/2)[624] and π(9/2)[514]ν2(1/2)[510](9/2)[624] configurations, respectively, have been newly observed. The half-life of the Kπ=((19/2)+) bandhead which decays to the head of the (15/2)− band has been measured to be 140(36) ns. However, transitions from the ((19/2)+) state to the (15/2)− band have not been observed.
Received: 26 August 1998 相似文献
9.
E.Ya. Paryev 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):127-137
The inclusive K+ meson production in photon–induced reactions in the near threshold and subthreshold energy regimes is analyzed with respect
to the one–step (γN→K
+
Y, Y=Λ,Σ) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account
the struck target nucleon removal energy and internal momentum distribution (nucleon spectral function), extracted from recent
quasielastic electron scattering experiments and from many–body calculations with realistic models of the NN interaction.
Simple parametrizations for the total and differential cross sections of the K+ production in photon–nucleon collisions are presented. Comparison of the model calculations of the K+ differential cross sections for the reaction γ+C12 in the threshold region with the existing experimental data is given, that displays the contributions to the K+ production at considered incident energies coming from the use of the single–particle part as well as high momentum and high
removal energy part of the nucleon spectral function. Detailed predictions for the K+ total and differential cross sections from γH2, γC12 and γPb208 reactions at subthreshold and near threshold energies are provided. The influence of the uncertainties in the elementary
K+ production cross sections on the K+ yield is explored.
Received: 12 April 1999 / Revised version: 11 September 1999 相似文献
10.
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
11.
J. Hüfner Y.B. He B.Z. Kopeliovich 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):239-244
Prompt gluons are an additional source for charmonium suppression in nuclear collisions, in particular for nucleus-nucleus
collisions. These gluons are radiated as bremsstrahlung in N-N collisions and interact inelastically with the charmonium states
while the nuclei still overlap. The spectra and mean number <n
g> of the prompt gluons are calculated perturbatively and the inelastic cross section σabs
Ψg is estimated. The integrated cross sections σ(A B →J/ψX) for p-A and A-B collisions and the dependence on transverse energy for S-U and Pb-Pb can be described quantitatively with
some adjustment of one parameter <n
g>σabs
Ψg.
Received: 20 August 1999 相似文献
12.
M.V. Polyakov A. Sibirtsev K. Tsushima W. Cassing K. Goeke 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):115-118
The possibility for an observation of a narrow penta-quark Z+-baryon in NN reactions is discussed. It is shown that the pp↦nΣ+
K
+ reaction at excess energies around 100 MeV above threshold provides optimal conditions for Z+-baryon detection by an analysis of the nK+ invariant mass spectrum, if the Z+ mass is located around 1.5 GeV involving a rather narrow width.
Received: 24 May 2000 / Accepted: 3 August 2000 相似文献
13.
The sensitivities of the one-spin and two-spin polarization observables for p+ˉp→P0+V0, with P0=π0, η,η′ and V0=ρ,ω,φ, based on the triplet enhancement hypothesis for strangeness production in pˉp collisions are analyzed. The analysis
is carried out under special kinematical conditions where the P0 meson production angle in the CMS is equal to π/2, for which C-invariance of strong interactions reduces the number of independent
amplitudes to three.
Received: 17 September 1997 相似文献
14.
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
15.
H. Weigel 《The European Physical Journal A - Hadrons and Nuclei》1998,2(4):391-402
Abstact: Within an extended Skyrme soliton model for baryons the interplay between the collective radial motion and the SU(3)–flavor–rotations
is investigated. The coupling between these modes is mediated by flavor symmetry breaking. Collective coordinates which describe
the corresponding large amplitude fluctuations are introduced and treated canonically. When diagonalizing the resulting Hamiltonian
flavor symmetry breaking is fully taken into consideration. As eigenstates not only the low–lying (1/2)+ and (3/2)+ baryons but also their radial excitations are obtained and compared to the empirical data. In particular the relevance of
radial excitations for the penta–quark baryon Z
+ (Y=2, I=0, J
π=(1/2)+) is discussed. In this approach its mass is predicted to be 1.58 GeV. Furthermore the widths for various hadronic decays
are estimated which, for example, yields Γ(Z
+→NK) ∼ 100 MeV for the only permissible decay process of the Z
+.
Received: 20 April 1998 / Revised version: 29 May 1998 相似文献
16.
S. Yamada A. Taniguchi K. Okano K. Aoki 《The European Physical Journal A - Hadrons and Nuclei》2000,7(3):327-334
The β-decay of 146La was studied using the on-line isotope separator KUR-ISOL. Gamma-gamma angular correlation measurements were performed with
a 4-Ge detectors system. Spin assignments of three levels were made: 3+ for the 1576.5 keV level, 4+ for the 1627.1 keV level and 5+ for the 1810.2 keV level. The mixing ratios (E2/M1) were deduced to be δ183.2= 0.25 ± 0.08, δ638.9= 0.33 ± 0.05, δ959.0= 1.19+0.16
−0.14, δ1015.9= 5.4+3.1
−1.5 and δ1318.1= 6.5+1.7
−1.1. These were compared to the calculated values obtained in three cases involving different Majorana force parameter values.
The band structure of 146Ce is discussed based on the results of calculation using the IBM-2 theory.
Received: 20 September 1999 / Revised version: 8 February 2000 相似文献
17.
Ch. Miehé Ph. Dessagne Ch. Pujol G. Walter B. Jonson M. Lindroos 《The European Physical Journal A - Hadrons and Nuclei》1999,5(2):143-150
The β+– electron capture decay of 73Kr, produced at the ISOLDE CERN facility, has been studied by β-delayed proton and gamma emission. The established decay scheme
involves 15 up to now unreported gamma emitting levels in 73Br. The total proton branching ratio has been measured to be 0.0025 ± 0.0003. From this work, a spin and parity 3/2− is assigned to the 73Kr ground state, on the basis of the allowed β branch to the 73Br Jπ= 1/2− ground state and the feeding of the 5/2+ level located at 286 keV in 73Br.
Received: 17 September 1998 / Revised version: 25 January 1999 相似文献
18.
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
19.
J.G. Messchendorp A. Sibirtsev W. Cassing V. Metag S. Schadmand 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):95-103
Simulations based on a coupled-channel transport model have been performed to analyze the feasibility to study the in-medium
ω mass exploiting the process γ + A→π0γ + X for C, Ca and Nb nuclei. The distortions due to final-state interactions of the π0 and background contributions from the reaction γ + A→π0π0 + X are found to be small in the mass range of interest ( 0.6 < M
π0γ < 0.8 GeV). Furthermore, the effect of the detector resolution on the π0γ mass determination is discussed.
Received: 5 December 2000 / Accepted: 18 May 2001 相似文献
20.
W. Cassing Ye.S. Golubeva L.A. Kondratyuk 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):279-285
We study the possibility to measure the elastic ΦN (Φ≡J/ψ,ψ(2S), ψ(3770), χ2c) scattering cross section in the reaction ˉp+d→Φ+n
sp and the elastic D(ˉD)N scattering cross section in the reaction ˉp+d→D
−
D
0
p
sp. Our studies indicate that the elastic scattering cross sections can be determined for Φ momenta about 4–6 GeV/c and D/ˉD momenta 2–5 GeV/c by selecting events with p
t≥ 0.4 GeV/c for Φ's and p
t(p
sp) ≥ 0.5 GeV/c for D/ˉD-meson production.
Received: 8 November 1999 相似文献