共查询到20条相似文献,搜索用时 406 毫秒
1.
V. Bernard N. Kaiser Ulf-G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》1999,4(3):259-275
We evaluate the threshold matrix–element for the reaction pp→ppπ0 in a fully relativistic Feynman diagrammatic approach. We employ a simple effective range approximation to take care of the
S–wave pp final–state interaction. The experimental value for the threshold amplitude A = (2.7 −i0.3) fm4 can be reproduced by contributions from tree level chiral (long–range) pion exchange and short–range effects related to vector
meson exchanges, with ω-exchange giving the largest individual contribution. Pion loop effects appear to be small. We stress
that the commonly used heavy baryon formalism is not applicable in the NN–system above the pion production threshold due to
the large external momentum, |p|≃ (Mm
π)−1/2, with M and m
π the nucleon and the pion mass, respectively. We furthermore investigate the reaction pp→pnπ+ near threshold within the same approach. We extract from the data the triplet threshold amplitude as B = (2.8 −i1.5) fm4. Its real part can be well understood from (relativistic) tree level meson–exchange diagrams. In addition, we investigate
the process pp→ppη near threshold. We use a simple factorization ansatz for the ppη final–state interaction and extract from the data the modulus of the threshold amplitude, |C|= 1.32 fm4. With g
ηN= 5.3, this value can be reproduced by (relativistic) tree level meson–exchange diagrams and η–rescattering, whose strength
is fixed by the ηN scattering length. We also comment on the recent near threshold data for η′–production.
Received: 27 November 1998 相似文献
2.
It is shown that the (8, 8) model and explicitηπ
0 mixing successfully explain theη→3π decay width whereas the decay width calculated from the mass difference
is about one order less than the experimental value. 相似文献
3.
Final state interaction effects inpp→ pΛK
+ andpd →3Heη reactions are explored near threshold to study the sensitivity of the cross-sections to thepΛ potential and theηN scattering matrix. The final state scattering wave functions between Λ andp andη and3He are described rigorously. The Λ production is described by the exchange of one pion and aK-meson between two protons in the incident channel. Theη production is described by a two-step model, where in the first step a pion is produced. This pion then produces anη by interacting with another nucleon 相似文献
4.
L.V. Fil'kov V.L. Kashevarov 《The European Physical Journal A - Hadrons and Nuclei》1999,5(3):285-292
The Compton scattering on a charged pion and the process γγ→π0π0 are studied using the dispersion relations. Unknown parameters of the S-wave ππ interaction and a sum and a difference of the π0 meson polarizabilities are found from a fit to the experimental data for the γγ→π0π0 process. The found parameters of the ππ interaction are used for the calculation of the cross section of the elastic γπ± scattering. The analysis of the obtained results shows that the experimental data for the elastic γπ± scattering in the energy region up to 1 GeV together with the data for the γγ→π0π0 process could be used both for a determination of the pion polarizability values and for study of the S-wave ππ interaction.
Received: 20 November 1998 / Revised version: 22 January 1999 相似文献
5.
Dong-Sheng Du Xue-Qian Li Zheng-Tao Wei Bing-Song Zou 《The European Physical Journal A - Hadrons and Nuclei》1999,4(1):91-96
We study the final-state interactions in B →π K decays through B → VV →π K processes where the inelastic rescattering occurs
via single pion exchange. The next-to-leading order low-energy effective Hamiltonian and Bauer-Stech-Wirbel (BSW) model are
used to evaluate the weak transition matrix elements and final-state interactions. We found that the final-state interaction
effects in B →ρ K*→π K processes are significant. The Fleischer-Mannel relation for the Cabibbo-Kobayashi-Maskawa (CKM) angle γ can be significantly
modified.
Received: 13 August 1998 相似文献
6.
Bijan K Bagchi 《Pramana》1981,17(5):405-414
We consider the effects ofη−π mixing on the violation of the |ΔI|=1/2 rule in |ΔS|=1 weak transitions. The processes considered are theK→2π,K→3π, Λ, Ξ and Λ hyperon decays. 相似文献
7.
On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive
quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality
of cross sections such as σtot
πp/σtot
pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion
and proton (antiproton) in the impact parameter space of quarks, σπ(r
1⊥, r
2⊥; s) and σp(r
1⊥, r
2⊥, r
3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r
i⊥−r
k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented.
Received: 15 December 1998 相似文献
8.
D. E. Bayadilov Yu. A. Beloglazov A. B. Gridnev N. G. Kozlenko S. P. Kruglov A. A. Kulbardis I. V. Lopatin D. V. Novinsky A. K. Radkov V. V. Sumachev E. A. Filimonov 《The European Physical Journal A - Hadrons and Nuclei》2008,35(3):287-290
The differential cross-sections (DCS) of the η -production reaction π-
p → ηn are measured at momenta of incident π- mesons (700, 710 and 720MeV/c) close to the threshold of this reaction. The experiment is carried out at the pion channel
of the PNPI synchrocyclotron (with the momentum spread of the pion beam equal to 1.5%) using the Neutral Meson Spectrometer
(NMS) designed and created at the Meson Physics Laboratory for detecting two photons from the decay η → 2γ . This spectrometer
consisting of two electromagnetic total absorption calorimeter (24 CsI(Na) crystals in each calorimeter) allowed to obtain
the DCS in the whole angular range from 0° to 180° in the c.m.s. It is shown that at 700MeV/c the DCS angular dependence is isotropic, indicating on the S -wave character of the η -production process while at higher momenta a significant contribution of the D -wave has led to the anisotropic angular dependence having a bowl-like shape. 相似文献
9.
Ji Xiaobin 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):672-675
The report includes the new observation of X(1835) in J/ψ→γη
′
π
+
π
-, the ωφ threshold enhancement in J/ψ→γωφ, the ωω structure in J/ψ→γωω and the broad 1- structure at the low K
+
K
- invariant-mass spectrum in J/ψ→K
+
K
-
π
0. 相似文献
10.
Yun Chang Shin Bong Soo Han Myung Ki Cheoun K.S. Kim Il-Tong Cheon 《The European Physical Journal A - Hadrons and Nuclei》2000,9(2):269-276
A SU(2) effective Lagrangian is extended to a SU
L(3) ⊗SU
R(3) by including the vector and axial vector meson. With this effective Lagrangian, electromagnetic form factors of charged
pion and kaon are calculated in both time- and space-like regions. The pseudoscalar meson loops are taken into account. Good
agreement with experimental data is obtained for those form factors and charged pseudoscalar meson radii. Decay widths of
ρ→ππ and φ→K
+
K
- are also calculated and shown to agree with experimental data very well.
Received: 20 December 1999 / Accepted: 12 October 2000 相似文献
11.
It is pointed out that the coupling characterizing theψ-γ vertex must change substantially between the limits,ψ on mass-shell which occurs inψ→e
+
e
− and photon on mass-shell which is relevant in radiative decays likeψ→ππγ, ψ→ηγ and photoproduction ofψ. This has the consequence that the value ofψN total cross section must be larger than what is inferred from the use of naive vector dominance in photoproduction. 相似文献
12.
V. Dorofeev R. Dzhelyadin A. Ekimov Yu. Gavrilov Yu. Gouz A. Ivashin V. Kabachenko I. Kachaev A. Karyukhin Yu. Khokhlov V. Konstantinov M. Makouski V. Matveev A. Myagkov V. Nikolaenko A. Ostankov B. Polyakov D. Ryabchikov N. Shalanda M. Soldatov A. A. Solodkov A. V. Solodkov O. Solovianov E. Starchenko A. Zaitsev 《The European Physical Journal A - Hadrons and Nuclei》2008,38(2):149-154
The isospin-violating decay f
1(1285) → π+π-π0 has been studied at the VES facility. This study is based on the statistics acquired in π-
Be interactions at 27, 36.6 and 41 GeV/c in the diffractive reaction π-
N → (f
1π-)N . The f
1(1285) → π+π-π0 decay is observed. The preliminary ratio of decay probabilities BR(f
1(1285) → π+π-π0) to BR(f
1(1285) → ηπ+π-).
BR(η → γγ) is ∼ 2% .
Original article based on material presented at HADRON 2007. 相似文献
13.
G.I. Lykasov W. Cassing A. Sibirtsev M.V. Rzjanin 《The European Physical Journal A - Hadrons and Nuclei》1999,6(1):71-81
We calculate the elastic and inelastic ωN→ωN, →πN, →ρN, →ρπN, →ππN, →σN reactions within a boson exchange approximation where the ωρπ coupling constant and form factor are fixed by the reaction
πN→ωN in comparison to the experimental data. We find rather large ωN cross sections at low relative momenta of the ω-meson which
leads to a substantial broadening of the ω-meson width in nuclear matter. The implications of the ωN final state interactions are studied for ω production in 12C +12C, 40Ca +40Ca and 58Ni +58Ni reactions at about 2 · A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative
to a general m
T-scaling (for π0 and η mesons) might be controlled experimentally by the TAPS Collaboration.
Received: 28 April 1999 / Revised version: 7 June 1999 相似文献
14.
Vladimir G. Neudatchin Igor T. Obukhovsky Ludmila L. Sviridova Nikolai P. Yudin 《Central European Journal of Physics》2004,2(3):511-522
The pion momentum distributions (MDs) in four channels of virtual decay p→B+π, B = N, Δ, N
1/2-(1535), N
1/2+(1440) are calculated in two models, the microscopic model of 3
P
0 scalar q−q fluctuation with the pion as a composite q−q-system and the chiral semi-microscopic model of πq interaction with the pion as a structureless Goldstone boson. The results of the above models are similar for the baryon
states B = N, Δ, N
1/2-(1535) but are rather different for the Roper resonance N
1/2+(1440) which corresponds to excitation of two oscillator quanta in the nucleon. The experimental investigation of pion MDs
by means of the reaction of quasi-elastic knockout of pion by an electron of a few GeV energy p(e, e′ π)B may be very suitable for Jefferson Laboratory, Virginia (JLab). 相似文献
15.
16.
A ππ, ˉKK, and ρρ(ωω) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities
for elastic ππ scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the
meson resonance table of the Particle Data Group. As expected, the ππ inelasticity is very strongly related to the opening
of the ˉK channel near 1 GeV, and the opening of ρρ(4π) and ωω(6π) channels in the 1.5 GeV region. The predictions of this model are
compared to the various elastic ππ→ππ amplitudes, that were obtained from analyses of π− p →π−π+n data. The role of the various resonances, in particular the glueball candidate f
0(1500) and the f
J(1710) is investigated.
Received: 19 November 1997 相似文献
17.
The K-matrix approach with effective Lagrangians is used to describe the S and P pion-nucleon partial-wave amplitudes in the energy range E
lab≤ 1 GeV. It is demonstrated, that treating the resonance as K-matrix a pole gives the natural way to separate the resonance and non-resonance parts of the πN amplitude. The model includes all the four-star πN resonances, the non-resonance contributions are calculated from relevant Feynman graphs without any phenomenological form
factors. Different contributions to the inelastic π−
p→ηn amplitude are estimated.
Received: 9 July 1998 相似文献
18.
X.-J. Wang J.-H. Jiang M.-L. Yan 《The European Physical Journal A - Hadrons and Nuclei》2002,14(2):219-224
In terms of effective field theory and mixed-propagator approach, we show that there is a larger hidden effect of isospin
breaking in ρ→πγ decay due to a ω exchange, ρ→ω→πγ. The branching ratio is predicted as B(ρ→πγ) = (11.67±2.0)×10-4, which is much larger than Particle Data Group's datum (6.8±1.7)×10-4 and one of charged mode, B(ρ±→π±γ) = (4.5±0.5)×10-4.
Received: 7 January 2002 / Accepted: 2 April 2002 相似文献
19.
L. Theußl R.F. Wagenbrunn B. Desplanques W. Plessas 《The European Physical Journal A - Hadrons and Nuclei》2001,12(1):91-101
π and η decay modes of light baryon resonances are investigated within a chiral quark model whose hyperfine interaction is
based on Goldstone-boson exchange. For the decay mechanism a modified version of the 3
P
0 model is employed. Our primary aim is to provide a further test of the recently proposed Goldstone-boson exchange constituent
quark model. We compare the predictions for π and η decay widths with experiment and also with results from a traditional
one-gluon exchange constituent quark model. The differences between nonrelativistic and semirelativistic versions of the constituent
quark models are outlined. We also discuss the sensitivity of the results on the parameterization of the meson wave function
entering the 3
P
0 model.
Received: 11 May 2001 / Accepted: 17 September 2001 相似文献
20.
V.V. Anisovich A.V. Sarantsev 《The European Physical Journal A - Hadrons and Nuclei》2003,16(2):229-258
We present the results of the current analysis of the partial wave IJ
PC = 00+ + based on the available data for meson spectra ( ππ, KˉK,ηη,η,ππππ). In the framework of the K-matrix approach, the analytical amplitude has been reconstructed in the mass region 280 MeV < < 1900 MeV. The following scalar-isoscalar states are seen: comparatively narrow resonances f
0(980), f
0(1300), f
0(1500), f
0(1750) and the broad state f0(1200-1600). The positions of the amplitude poles (masses and total widths of the resonances) are determined as well as pole
residues (partial widths to meson channels ππ, KˉK,ηη,η,ππππ). The fitted amplitude gives us the positions of the K-matrix poles (bare states) and the values of bare-state couplings to meson channels thus allowing the quark-antiquark nonet
classification of bare states. On the basis of the obtained partial widths to the channels ππ, KˉK,ηη,η, we estimate the quark/gluonium content of f
0(980), f
0(1300), f
0(1500), f
0(1750), f0(1200-1600). For f
0(980), f
0(1300), f
0(1500) and f
0(1750), their partial widths testify the qˉq origin of these mesons though being unable to provide precise evaluation of the possible admixture of the gluonium component
in these resonances. The ratios of the decay coupling constants for the f0(1200-1600) support the idea about the gluonium nature of this broad state.
Received: 14 May 2002 / Accepted: 20 August 2002 / Published online: 11 February 2003
RID="a"
ID="a"e-mail: anisovic@thd.pnpi.spb.ru
Communicated by A. Sch?fer 相似文献