1,560 research outputs found
Estimates for X(4350) Decays from the Effective Lagrangian Approach
The strong and electromagnetic decays of with quantum numbers and have been studied by using the effective Lagrangian
approach. The coupling constant between and
is determined with the help of the compositeness condition which means that
is a bound state of . Other coupling
constants applied in the calculation are determined phenomenologically. Our
numerical results show that, using the present data within the present model,
the possibility that is a molecule can not
be ruled out.Comment: 15 pages, 4 eps figure
Studying the properties in pA collisions via the decay
Within transport calculations we study the production and decay of
-mesons in reactions at COSY energies including elastic and
inelastic rescattering, the Dalitz decay
as well as rescattering. The resulting invariant mass
distributions indicate that in-medium modifications of the -meson may
be observed experimentally.Comment: 5 pages, espcrc2-style, including 5 ps-figure
Pion transition form factor in the Regge approach and incomplete vector-meson dominance
The concept of incomplete vector-meson dominance and Regge models is applied
to the transition form factor of the pion. First, we argue that variants of the
chiral quark model fulfilling the chiral anomaly may violate the Terazawa-West
unitarity bounds, as these bounds are based on unverified assumptions for the
real parts of the amplitudes, precluding a possible presence of polynomial
terms. A direct consequence is that the transition form factor need not
necessarily vanish at large values of the photon virtuality. Moreover, in the
range of the BaBar experiment, the Terazawa-West bound is an order of magnitude
above the data, thus is of formal rather than practical interest. Then we
demonstrate how the experimental data may be properly explained with incomplete
vector-meson dominance in a simple model with one state, as well as in more
sophisticated Regge models. Generalizations of the simple Regge model along the
lines of Dominguez result in a proper description of the data, where one may
adjust the parameters in such a way that the Terazawa-West bound is satisfied
or violated. We also impose the experimental constraint from the Z -> pi0 gamma
decay. Finally, we point out that the photon momentum asymmetry parameter may
noticeably influence the precision analysis.Comment: 11 pages, 7 figure
The role of the N*(1535) resonance and the pi^- p --> KY amplitudes in the OZI forbidden pi N --> phi N reaction
We study the pi N --> phi N reaction close to the phi N threshold within the
chiral unitary approach, by combining the pi^- p --> K^+ Sigma^-, pi^- p -->
K^0 Sigma^0 and pi^- p --> K^0 Lambda amplitudes with the coupling of the phi
to the K components of the final states of these reactions via quantum loops.
We obtain a good agreement with experiment when the dominant pi^- p --> K^0
Lambda amplitude is constrained with its experimental cross section. We also
evaluate the coupling of the N*(1535) to phi N and find a moderate coupling as
a consequence of partial cancellation of the large KY components of the
N*(1535). We also show that the N*(1535) pole approximation is too small to
reproduce the measured cross section for the pi N --> phi N reaction.Comment: 10 pages, 6 figure
Properties of Hadrons in the Nuclear Medium
This review is devoted to the discussion of hadron properties in the nuclear
medium and its relation to the partial restoration of chiral symmetry. Special
attention is given to disentangle in-medium effects due to conventional
many-body interactions from those due to the change of the chiral condensate.
In particular, we shall discuss medium effects on the Goldstone bosons (pion,
kaon and eta), the vector mesons (rho, omega, phi), and the nucleon. Also, for
each proposed in-medium effect the experimental consequence and results will be
reviewed.Comment: 43 pages, 8 figures, uses epsf-style file. To appear in Ann. Rev.
Nucl. Part. Sci. Vol 4
-Meson Production and Decay in Proton-Nucleus Collisions
We analyze the production of -mesons in reactions including
both the production by proton-nucleon as well as pion-nucleon collisions within
a coupled channel transport approach. The final state interactions of the
-meson with nucleons are evaluated from a resonance model which allows to
extract elastic and inelastic cross sections. We include the latter final state
interactions, the -meson decay into two pions as well as the final
pion-nucleon interactions within the transport approach. We find the invariant
mass distribution of pion pairs to be sensitive to the -meson properties
in the nuclear medium. However, due to the strong final state interactions of
pions only light targets like might be suited to extract a
-signal from the uncorrelated two pion background which carries
information about the in-medium properties of the -meson.Comment: 27 pages, LaTeX, including 13 ps-figures, UGI-97-20, Nucl. Phys. A.,
in pres
Investigation of heavy-heavy pseudoscalar mesons in thermal QCD Sum Rules
We investigate the mass and decay constant of the heavy-heavy pseudoscalar,
, and mesons in the framework of finite temperature QCD
sum rules. The annihilation and scattering parts of spectral density are
calculated in the lowest order of perturbation theory. Taking into account the
additional operators arising at finite temperature, the nonperturbative
corrections are also evaluated. The masses and decay constants remain unchanged
under , but after this point, they start to diminish with
increasing the temperature. At critical or deconfinement temperature, the decay
constants reach approximately to 35% of their values in the vacuum, while the
masses are decreased about 7%, 12% and 2% for , and
states, respectively. The results at zero temperature are in a good consistency
with the existing experimental values as well as predictions of the other
nonperturbative approaches.Comment: 11 Pages, 2 Tables and 6 Figure
Phases of QCD, Thermal Quasiparticles and Dilepton Radiation from a Fireball
We calculate dilepton production rates from a fireball adapted to the
kinematical conditions realized in ultrarelativistic heavy ion collisions over
a broad range of beam energies. The freeze-out state of the fireball is fixed
by hadronic observables. We use this information combined with the initial
geometry of the collision region to follow the space-time evolution of the
fireball. Assuming entropy conservation, its bulk thermodynamic properties can
then be uniquely obtained once the equation of state (EoS) is specified. The
high-temperature (QGP) phase is modelled by a non-perturbative quasiparticle
model that incorporates a phenomenological confinement description, adapted to
lattice QCD results. For the hadronic phase, we interpolate the EoS into the
region where a resonance gas approach seems applicable, keeping track of a
possible overpopulation of the pion phase space. In this way, the fireball
evolution is specified without reference to dilepton data, thus eliminating it
as an adjustable parameter in the rate calculations. Dilepton emission in the
QGP phase is then calculated within the quasiparticle model. In the hadronic
phase, both temperature and finite baryon density effects on the photon
spectral function are incorporated. Existing dilepton data from CERES at 158
and 40 AGeV Pb-Au collisions are well described, and a prediction for the
PHENIX setup at RHIC for sqrt(s) = 200 AGeV is given.Comment: 31 pages, 15 figures, final versio
Absorption of phi mesons in near-threshold proton-nucleus reactions
In the framework of the nuclear spectral function approach for incoherent
primary proton--nucleon and secondary pion--nucleon production processes we
study the inclusive meson production in the interaction of 2.83 GeV
protons with nuclei. In particular, the A-dependences of the absolute and
relative meson yields are investigated within the different scenarios
for its in-medium width as well as for the cross section ratio . Our model calculations take into account
the acceptance window of the ANKE facility used in a recent experiment
performed at COSY. They show that the pion--nucleon production channel
contributes distinctly to the creation in heavy nuclei in the chosen
kinematics and, hence, has to be taken into consideration on close examination
of the dependences of the phi meson yields on the target mass number with the
aim to get information on its width in the medium. They also demonstrate that
the experimentally unknown ratio has a weak effect on the A-dependence of the relative meson
production cross section at incident energy of present interest, whereas it is
found to be appreciably sensitive to the phi in-medium width, which means that
this relative observable can indeed be useful to help determine the above width
from the direct comparison the results of our calculations with the future data
from the respective ANKE-at-COSY experiment.Comment: 16 pages, 9 figure
Regge description of two pseudoscalar meson production in antiproton-proton annihilation
A Regge-inspired model is used to discuss the hard exclusive two-body
hadronic reactions (pbar p ----> pi+ pi-, pi0 pi0, K+ K-, Kbar0 K0) for the
FAIR facility project at GSI with the Panda detector. The comparison between
the differential cross sections predictions and the available data is shown to
determine the values of the few parameters of the model.Comment: 9 pages, 13 figure
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