共查询到20条相似文献,搜索用时 15 毫秒
1.
D. Ebert M. Nagy M. K. Volkov V. L. Yudichev 《The European Physical Journal A - Hadrons and Nuclei》2000,8(4):567-576
Ground-state scalar isoscalar mesons and a scalar glueball are described in a U(3)×U(3) chiral quark model of the Nambu-Jona-Lasinio (NJL) type with 't Hooft interaction. The latter interaction produces singlet-octet
mixing in the scalar and pseudoscalar sectors. The glueball is introduced into the effective meson Lagrangian as a dilaton
on the base of scale invariance. The mixing of the glueball with scalar isoscalar quarkonia and amplitudes of their decays
into two pseudoscalar mesons are shown to be proportional to current quark masses, vanishing in the chiral limit. Mass spectra
of the scalar mesons and the glueball and their main modes of strong decay are described.
Received: 14 July 2000 / Accepted: 31 July 2000 相似文献
2.
E. Oset J.A. Oller U.-G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2001,12(4):435-446
We perform a study of the final-state interactions of the K
+
and the
d systems in the reactions pp↦dK
+
and pp↦dπ+η. Since the two-meson system couples strongly to the a
0(980) resonance, these reactions are expected to be an additional source of information about the controversial scalar sector.
We also show that these reactions present peculiar features which can shed additional light on the much debated meson-baryon
scalar sector with strangeness -1. We deduce the general structure of the amplitudes close to the dK
+
threshold, allowing for primary K
+
as well as π+η production with the two mesons in relative S- or P-wave. The interactions of the mesons are accounted for by using chiral unitary techniques, which generate dynamically the
a
0(980) resonance, and the
d interaction is also taken into account. General formulae are derived that allow to incorporate the final-state interactions
in these systems for any model of the production mechanism. We illustrate this approach by considering two specific production
mechanisms based on three flavor meson-baryon chiral perturbation theory. It is demonstrated that in this scenario the
d interactions are very important and can change the cross-section by as much as one order of magnitude. The amount of π+ηversus
K
+
production is shown to depend critically on the primary mixture of the two mechanisms, with large interference effects due
to final-state interactions. These effects are also shown to occur in the event distributions of invariant masses which are
drastically modified by the final-state interactions of the two-meson or the
d system.
Received: 28 September 2001 / Accepted: 26 November 2001 相似文献
3.
The KNΛ and KNΣ coupling constants have been calculated in the framework of the Chiral Bag Model(CBM). We find −3.88 ≤g
KNΛ≤−3.67 and 1.15 ≤g
KNΣ≤ 1.24 by taking into account pseudoscalar mesons (π, K) and vector mesons (ρ, ω, K
*) field effects. Particularly, it is shown that vector mesons make significant contributions to the coupling constants g
KNΛ and g
KNΣ. Our values are existing within the experimental limits compared to the phenomenological values extracted from the kaon photoproduction
and kaon-nucleon scattering experiments. Also, form factors are suggested for the πNN, πNΔ, KNΛ and KNΣ couplings.
Received: 17 August 1998 / Revised version: 22 December 1998 相似文献
4.
This paper is a sequel of a previous one (Scalar mesons in a chiral quark model with glueball, Eur. Phys. J. A 8, 567 (2000)) where an attempt to construct an effective U(3)×U(3)-symmetric meson Lagrangian with a scalar glueball was made. The glueball was introduced by using the dilaton model on
the base of scale invariance. The scale invariance breaking because of current quark masses and the scale anomaly of QCD,
reproduced by the dilaton potential, was taken into account. However, in the previous paper, the scale invariance breaking
because of the terms like h
φφ2 and h
σ
, where φ and are the pseudoscalar and scalar isosinglets, was not taken into account. These terms are produced by the part of the 't Hooft
interaction that is connected with gluon anomalies. Allowing for the scale invariance breaking by these terms has a decisive
effect on the quarkonium-glueball mixing and noticeably changes the widths of glueball strong decays. Taking account of this
additional source of the scale invariance breaking and its implications are the subject of the present work. It is also shown
that in the decay of a glueball into four pions, the channel with two ρ-resonances dominates.
Received: 11 January 2001 / Accepted: 25 January 2001 相似文献
5.
N. Kaiser 《The European Physical Journal A - Hadrons and Nuclei》1999,5(1):105-110
We analyze the recent total cross section data for pp→pΛK
+ near threshold measured at COSY. Using an effective range approximation for the on-shell pΛ S-wave final state interaction we extract from these data the combination ?= (2|K
s|2+|K
t|2)−1/2= 0.38 fm4 of the singlet (K
s) and triplet (K
t) threshold transition amplitudes. We present an exploratory calculation of various (tree-level) vector and pseudoscalar meson
exchange diagrams. Pointlike ω-exchange alone and the combined (ρ0,ω,K*+)-exchange can explain the experimental value of ?. The pseudoscalar meson exchanges based on a SU(3) chiral Lagrangian turn
out to be too large. However, when adding π0-exchange in combination with the resonant πN→S
11(1650) →KΛ transition and introducing monopole form factors with a cut-off Λc= 1.5 GeV one is again able to reproduce the experimental value of ?. More exclusive measurements are necessary to reveal
the details of the pp→pΛK
+ production mechanism.
Received: 28 October 1998 / Revised version: 12 January 1999 相似文献
6.
We analyse the baryon mass spectrum in a framework which combines the 1/N
c expansion with chiral perturbation theory. Meson loop contributions involving the full SU(3) octet of pseudoscalar Goldstone
bosons are evaluated, and the influence of explicit chiral and flavor symmetry breaking by non-zero and unequal quark masses
is investigated. We also discuss sigma terms and the strangeness contribution to the nucleon mass.
Received: 29 June 1998 / Revised version: 25 November 1998 相似文献
7.
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
8.
B. Borasoy 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):95-107
The importance of Born terms and resonance exchange for η and η' photoproduction off both the proton and neutron within
U(3) baryon chiral perturbation theory is investigated. Low-lying resonances such as the vector mesons and J
P = 1/2+, 1/2- baryon resonances are included explicitly and their contributions together with the Born terms are calculated. The coupling
constants of the resonances are determined from strong and radiative decays. We obtain reasonable agreement with experimental
data near threshold.
Received: 17 March 2000 / Accepted: 8 September 2000 相似文献
9.
Hungchong Kim 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):121-125
Within the conventional QCD sum rules, we calculate the πNN coupling constant, g
πN, beyond the chiral limit using two-point correlation function with a pion. For this purpose, we consider the Dirac structure,
iγ5, at m
π
2 order in the expansion of the correlator in terms of the pion momentum. For a consistent treatment of the sum rule, we include
the linear terms in quark mass as they constitute the same chiral order as m
π
2. In this sum rule, we obtain g
πN= 13.3 ± 1.2, which is very close to the empirical πNN coupling. This demonstrates that going beyond the chiral limit is crucial in determining the coupling.
Received: 8 July 1999 / Revised version: 20 August 1999 相似文献
10.
Y.C. Shin M.K. Cheoun K.S. Kim T.K. Choi 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):87-93
A role of the axial-vector mesons, such as K1 and a1, on the emitted-photon spectrum in hot hadronic matter is studied through the channels πρ→a
1→πγ and Kρ→K
1→Kγ. Both channels could be dominant over the region lower than E
γ∼ 0.5 GeV, while the role of the K1 meson is diminished in the higher E
γ region. This study is carried out with an SU
L(3) ⊗SU
R(3) effective chiral Lagrangian which includes vector and axial-vector mesons systematically and explains well their hadronic
and radiative decays simultaneously.
Received: 8 August 2001 / Accepted: 4 February 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.
13.
Ye.S. Golubeva W. Cassing L.A. Kondratyuk 《The European Physical Journal A - Hadrons and Nuclei》2002,14(2):255-263
We study the perspectives of resonant and nonresonant charmed-meson production in ˉp + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(3770),Ψ(4040)
and Ψ(4160) on various nuclei, their propagation and decay to D,ˉD, D
*,ˉD*, D
s,ˉDs in the medium and vacuum, respectively. The modifications of the open charm vector mesons in the nuclear medium are found
to be rather moderate or even small such that dilepton spectroscopy will require an invariant mass resolution of a few MeV.
Furthermore, the elastic and inelastic interactions of the open charm mesons in the medium are taken into account, which can
be related to (u, d )-, s- or c-quark exchange with nucleons. It is found that by studying the D/ˉD ratio for low momenta in the laboratory ( ? 2 - 2.2 GeV/c) as a function of the target mass A stringent constraints on the c-quark exchange cross-section can be obtained. On the other hand, the ratios D
-
s/D
+
s as well as D/D
-
s and D/D
+
s at low momenta as a function of A will permit to fix independently the strength of the s-quark exchange reaction in D
-
s
N scattering.
Received: 1 March 2002 / Accepted: 21 March 2002 相似文献
14.
15.
This contribution summarizes the work explained in arXiv:hep-ph/0608290 where we perform a non-perturbative chiral study of
the masses of the lightest pseudoscalar mesons. The pseudoscalar self-energies are calculated by the evaluation of the scalar
self-energy loops with full S-wave meson-meson amplitudes taken from Unitary Chiral Perturbation Theory (UCHPT). These amplitudes, among other features,
contain the lightest nonet of scalar resonances σ, f
0(980), a
0(980) and κ. The self-energy loops are regularized by a proper subtraction of the infinities within a dispersion relation formulation
of the amplitudes. Values for the bare masses of pions and kaons and the η
8 mass are obtained. We then match to the self-energies from standard Chiral Perturbation Theory (CHPT) to O(p
4) and resum higher orders from our calculated scalar self-energies. The dependence of the self-energies on the quark masses
allows a determination of the ratio of the strange-quark mass over the mean of the lightest-quark masses, m
s/
, in terms of the O(p
4) CHPT low-energy constant combinations 2L
r
8 - L
r
5 and 2L
r
6 - L
r
4. In this way, we give a range for the values of these low-energy counterterms and for 3L
7 + L
r
8, once the η-meson mass is invoked. The low-energy constants are further constraint by performing a fit to the recent MILC lattice data
on the pseudoscalar masses, and m
s/
= 25.6±2.5 results. This value is consistent with 24.4±1.5 from CHPT and phenomenology and more marginally with the value
27.4±0.5 obtained from pure perturbative chiral extrapolations of the MILC lattice data to physical values of the lightest-quark
masses. 相似文献
16.
The double differential dilepton spectrum d/(d
2
d
⊥
2) at fixed transverse mass M
⊥ allows a direct access to the vector meson spectral functions. Within a fireball model the sensitivity of d/(d
2
d
⊥
2) against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast
to the integrated invariant-mass spectrum d/d
2, in the spectrum d/(d
2
d
⊥
2) with fixed M
⊥ the ω signal is clearly seen as bump riding on the ρ background even in case of strong in-medium modifications.[3mm]
Received: 16 November 2000 / Accepted: 16 January 2001 相似文献
17.
We calculate the radiative decay widths of the a
0(980) and f
0(980) scalar mesons into ργ and ωγ considering the dynamically generated nature of these scalar resonances within the realm
of the chiral unitary approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the
loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the
photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of
those with a vector meson in the loop are written in terms of the two-meson loop function easily regularizable. We provide
results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark
loops models and some version of vector meson dominance. 相似文献
18.
Shi-Lin Zhu 《The European Physical Journal A - Hadrons and Nuclei》1999,4(3):277-281
The light cone QCD sum rules are derived for the K
*
Kπ coupling g
K
*
Kπ and the ρππ coupling g
ρππ. The contribution from the excited states and the continuum is subtracted cleanly through the double Borel transform with
respect to the two external momenta, p
1
2, p
2
2= (p−q)2. Our result g
K
*
Kπ= (8.7 ± 0.5) and g
ρππ= (11.5 ± 0.8) is in good agreement with the experimental value.
Received: 31 July 1998 / Revised version: 20 November 1998 相似文献
19.
V. Bernard N. Kaiser U.-G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):209-216
We investigate near-threshold neutral pion photoproduction off protons to fourth order in heavy-baryon chiral perturbation
theory in the light of the new data from MAMI. We show that the unitarity cusp at the secondary π+
n threshold is in agreement with expectations from the final-state theorem. We also analyze the fourth-order corrections to
the P-wave low-energy theorems and show that potentially large Δ isobar contributions are cancelled by sizeable pion loop effects.
This solidifies the parameter-free third-order predictions, which are in good agreement with the data.
Received: 25 May 2001 / Accepted: 21 June 2001 相似文献
20.
S. K. Bose 《Fortschritte der Physik》1976,24(10):555-564
We study the pseudoscalar mesons in the framework of broken chiral SU(4) SU(4) symmetry when the symmetry-breaking Hamiltonian, HSB, is taken as –(u0 + cu8 + du15) and the symmetry of the Hamiltonian is realized in Goldstone-Nambu way. An interesting property of two chimeral SU(4) subgroups and the Goldstone nature of some of the pseudoscalar mesons in certain symmetry limits are exploited to obtain some mass relations and the ratio c/d. 相似文献