共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
E.G. Drukarev M.G. Ryskin V.A. Sadovnikova 《The European Physical Journal A - Hadrons and Nuclei》1999,4(2):171-186
We calculate the contribution of pions to the $\bar qq$-expectation value κ(ρ) =<M|ˉq
q|M> in symmetric nuclear matter. We employ exact pion propagator renormalized by nucleon-hole and isobar-hole excitations. Conventional
straightforward calculation leads to the “pion condensation” at unrealistically small values of densities, causing even earlier
restoration of chiral symmetry. This requires a self-consistent approach, consisting in using the models, which include direct
dependence of in-medium mass values on κ(ρ), e.g. the Nambu–Jona-Lasinio–model. We show, that in the self-consistent approach
the ρ-dependence of the condensate is described by a smooth curve. The “pion condensate” point is removed to much higher values
of density. The chiral restoration does not take place at least while ρ < 2.8ρ0 with ρ0 being the saturation value. Validity of our approach is limited by possible accumulation of heavier baryons (delta isobars)
in the ground state of nuclear matter. For the value of effective nucleon mass at the saturation density we found m
*(ρ0) = 0.6m, consistent with nowadays results of other authors.
Received: 8 October 1998 相似文献
3.
D. Blaschke M.K. Volkov V.L. Yudichev 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):103-110
The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It
is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model.
We present two schemes of parametrization of the model where, within the first one, a first-order phase transition from a
phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T
t = 55 MeV occurs, whereas for the second one a second-order phase transition for temperatures below T
t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity,
which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition
at high baryon densities are discussed.
Received: 3 January 2003 / Accepted: 21 February 2003 / Published online: 24 April 2003 相似文献
4.
An extensive and systematic study of the recent η photo-production data up to 1.2 GeV is presented within a chiral constituent
quark model. A model embodying all known nucleonic resonances shows clear need for a yet undiscovered third S11 resonance in the second resonance region, for which we determine the mass (1.729 GeV) and the total width (183 MeV). Furthermore,
we extract the configuration mixing angles, an important property of the quark-quark interaction in the quark model, for the
resonances S
11(1535) and S
11(1650), as well as for the resonances D
13(1520) and D
13(1700). Our results agree well with the quark model predictions. In addition, the partial ηN decay widths and/or the photo-excitation helicity amplitudes for the nucleonic resonances S
11(1535), S
11(1650), P
11(1710), P
13(1720), D
13(1520), D
13(1700), D
15(1675), and F
15(1680) are also obtained in this approach.
Received: 14 February 2001 / Accepted: 22 June 2001 相似文献
5.
Bing An Li 《The European Physical Journal A - Hadrons and Nuclei》2001,10(3):347-353
Based on a phenomenologically successful effective chiral theory of pseudoscalar, vector, and axial-vector mesons, all the
coefficients of the chiral perturbation theory are predicted. There is no new adjustable parameter in these predictions. Up
to O(m
2
q) the formulas of the masses of the pseudoscalar mesons are the same as the ones obtained by ChPT.
Received: 31 August 2000 / Accepted: 16 March 2001 相似文献
6.
We extend a recent chiral approach to nuclear matter of Lutz et al.Phys. Lett. B 474, 7 (2000)) by calculating the underlying (complex-valued) single-particle potential U(p, k
f) + iW(p, k
f). The potential for a nucleon at the bottom of the Fermi sea, U(0, k
f0) = - 20.0 MeV, comes out as much too weakly attractive in this approach. Even more seriously, the total single-particle energy
does not rise monotonically with the nucleon momentum p, implying a negative effective nucleon mass at the Fermi surface. Also, the imaginary single-particle potential, W(0, k
f0) = 51.1 MeV, is too large. More realistic single-particle properties together with a good nuclear-matter equation of state
can be obtained if the short-range contributions of non-pionic origin are treated in mean-field approximation (i.e. if they are not further iterated with 1π-exchange). We also consider the equation of state of pure neutron matter ˉEn(k
n) and the asymmetry energy A(k
f) in that approach. The downward bending of these quantities above nuclear-matter saturation density seems to be a generic
feature of perturbative chiral pion-nucleon dynamics.
Received: 19 December 2002 / Accepted: 11 February 2003 / Published online: 15 April 2003 相似文献
7.
S. Choe 《The European Physical Journal A - Hadrons and Nuclei》1998,3(1):65-73
In the QCD sum rule approach we predict the Λ (1405) mass by choosing the π0Σ0 multiquark interpolating field. It is found that the mass is about 1.419 GeV from Π1 (q
2) sum rule which is more reliable than Πq (q
2) sum rule, where Πq (q
2) and Π1 (q
2) are two invariant functions of the correlator Π (q
2). We also present the sum rules for the K
+
p and the π+Σ+ multiquark states, and compare to those for the π0Σ0 multiquark state. The mass of the Λ (1600) can be also reproduced in our approach.
Received: 11 November 1997 / Revised version: 28 April 1998 相似文献
8.
J. Benlliure P. Armbruster M. Bernas C. Böckstiegel S. Czajkowski C. Donzaud H. Geissel A. Heinz C. Kozhuharov P. Dessagne G. Münzenberg M. Pfützner C. Stéphan K.-H. Schmidt K. Sümmerer W. Schwab L. Tassan-Got B. Voss 《The European Physical Journal A - Hadrons and Nuclei》1998,2(2):193-198
Projectile fragmentation of 238U in a lead target was investigated at a bombarding energy of 750 A MeV. Isotopic production cross sections of about 250 different projectile fragments in the element range Z= 30–53 were measured with the FRagment Separator (FRS). The magnetic selection and the kinematical analysis of the measured
isotopes allowed to disentangle fission and fragmentation residues. The mass loss of these residues indicates a violent collision
where a large amount of energy is dissipated. The position of the fragmentation corridor defined by the measured residues
was used to determine an effective proton-evaporation barrier.
Received: 3 October 1997 / Revised version: 27 February 1998 相似文献
9.
We investigate η- mixing in infrared regularized U(3) chiral perturbation theory by calculating the η and masses up to one-loop order. From this analysis it becomes obvious that even at leading order η--mixing does not obey the usually assumed one-mixing-angle scheme if large N
c counting rules are not employed.
Received: 12 March 2001 / Accepted: 4 July 2001 相似文献
10.
Effective charges are calculated for protons and neutrons in the region of mass 90. It is found that their magnitudes differ
appreciably depending on whether the proton p
1/2 shell is empty or full. The calculated values are compared with values deduced from nuclei with simple configurations, and
from a fit to N=50 data. The empirical values are used in shell-model calculations of quadrupole moments of N=50-58 nuclei.
Received: 16 February 1998 相似文献
11.
We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons,
pions and delta-resonances as explicit degrees of freedom. We point out that the usual power counting applied so far to this
problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified power counting and compare the resulting chiral extrapolation function to
available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result
from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective
field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions
in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here
are consistent with the Padé fit ansatz introduced by the Adelaide group a few years ago.
Received: 23 April 2002 / Accepted: 18 July 2002 / Published online: 17 December 2002
RID="c"
ID="c"e-mail: themmert@physik.tu-muenchen.de
RID="d"
ID="d"e-mail: weise@ect.it
Communicated by A. Sch?fer 相似文献
12.
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
13.
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
14.
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
15.
The lattice QCD studies indicate that the critical temperature T
c ≃ 260-280 MeV of the deconfinement phase transition in quenched QCD is considerably smaller than the lowest-lying glueball
mass m
G ≃ 1500-1700 MeV, i.e., T
c ≪ m
G. As a consequence of this large difference, the thermal excitation of the glueball in the confinement phase is strongly suppressed
by the statistical factor e
-mG/Tc ≃ 0.00207 even near T ≃ T
c. We consider its physical implication, and argue the abnormal feature of the deconfinement phase transition in quenched QCD
from the statistical viewpoint. To appreciate this, we demonstrate a statistical argument of the QCD phase transition using
the recent lattice QCD data. From the phenomenological relation between T
c and the glueball mass, the deconfinement transition is found to take place in quenched QCD before a reasonable amount of
glueballs is thermally excited. In this way, quenched QCD reveals a question “what is the trigger of the deconfinement phase
transition ?”
Received: 18 November 2002 / Accepted: 4 February 2003 / Published online: 29 April 2003 相似文献
16.
Z. Rudy W. Cassing L. Jarczyk B. Kamys P. Kulessa O.W.B. Schult A. Strzałkowski 《The European Physical Journal A - Hadrons and Nuclei》1999,5(2):127-129
It is shown that the mass dependence of the Λ-lifetime in heavy hypernuclei is sensitive to the ratio of neutron-induced
to proton-induced non-mesonic decay rates R
n/R
p. A comparison of the experimental mass dependence of the lifetimes with the calculated ones for different values of R
n/R
p leads to the conclusion that this ratio is larger than 2 on the confidence level of 0.75. This suggests that the phenomenological
ΔI= 1/2 rule might be violated for the nonmesonic decay of the Λ-hyperon.
Received: 31 March 1999 相似文献
17.
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
18.
19.
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
20.
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