1,519 research outputs found

### 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

### Inclusive omega photoproduction off nuclei

We investigate inclusive omega photoproduction off complex nuclei,
concentrating on the feasibility to examine a possible in-medium change of the
omega meson properties by observing the pi^0 gamma invariant mass spectrum. The
simulations are performed by means of a BUU transport model including a full
coupled-channel treatment of the final state interactions. In-medium changes of
the omega spectral density are found to yield a moderate modification of the
observables as compared to the situation in free space. Also the effects of a
momentum dependence of the strong omega potential are discussed.Comment: 19 pages, 12 figures, minor corrections, accepted for publication in
EPJ

### Investigation of heavy-heavy pseudoscalar mesons in thermal QCD Sum Rules

We investigate the mass and decay constant of the heavy-heavy pseudoscalar,
$B_c$, $\eta_c$ and $\eta_b$ 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 $T\cong 100 ~MeV$, 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 $B_c$, $\eta_c$ and $\eta_b$
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

### Factorization and Non-Factorization of In-Medium Four-Quark Condensates

It is well-established for the vacuum case that in the limit of a large
number of colors N_c the four-quark condensates factorize into products of the
two-quark condensate. It is shown that in the combined large-N_c and
linear-density approximation four-quark condensates do not factorize in a
medium of pions (finite temperature system) but do factorize in a medium of
nucleons (nuclear system).Comment: 4 page

### Recent topics of mesic atoms and mesic nuclei -- $\phi$ mesic nuclei exist ?--

We study $\phi$-meson production in nuclei to investigate the in-medium
modification of the $\phi$-meson spectral function at finite density. We
consider (${\bar p},\phi$), ($\gamma,p$) and ($\pi^-,n$) reactions to produce a
$\phi$-meson inside the nucleus and evaluate the effects of the medium
modifications to reaction cross sections. The structures of the bound states,
$\phi$-mesic nuclei, are also studied. For strong absorptive interaction cases,
we need to know the spectrum shape in a wide energy region to deduce the
properties of $\phi$.Comment: Talk given at EXA08, Vienna, September 2008. To be published in the
Proceedings, Hyperfine Interactions. 6 pages, 6 figure

### What does the rho-meson do? In-medium mass shift scenarios versus hadronic model calculations

The NA60 experiment has studied low-mass muon pair production in In-In
collisions at $158 {\rm AGeV}$ with unprecedented precision. With these results
there is hope that the in-medium modifications of the vector meson spectral
function can be constrained more thoroughly than before. We investigate in
particular what can be learned about collisional broadening by a hot and dense
medium and what constrains the experimental results put on in-medium mass shift
scenarios. The data show a clear indication of considerable in-medium
broadening effects but disfavor mass shift scenarios where the $\rho$-meson
mass scales with the square root of the chiral condensate. Scaling scenarios
which predict at finite density a dropping of the $\rho$-meson mass that is
stronger than that of the quark condensate are clearly ruled out since they are
also accompanied by a sharpening of the spectral function.Comment: Proceeding contribution, Talk given by J. Ruppert at Workshop for
Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus
Collisions (Hot Quarks 2006), Villasimius, Sardinia, Italy, 15-20 May 2006.
To appear in EPJ

### Quark Matter '99 --- Theoretical Summary: What Next?

I review the three broad areas where major progress has been reported: The
phase structure of strongly interacting matter, the properties of matter at the
instant when it freezes out into individual hadrons in the final stage of the
expansion of the hot fireball, and the status of the main signatures of the
formation of a quark-gluon plasma. In the final section I present some thoughts
about what should be done next, both in the experiemntal and the theoretical
arena.Comment: 10 pages, 1 figure, summary talk at Quark Matter '99, Torino, Italy,
somewhat modified, final versio

### Masses and couplings of vector mesons from the pion electromagnetic, weak, and \pi\gamma transition form factors

We analyse the pion electromagnetic, charged-current, and $\pi\gamma$
transition form factors at timelike momentum transfers $q$, $q^2=s\le 1.4$
GeV$^2$, using a dispersion approach. We discuss in detail the propagator
matrix of the photon-vector-meson system and define certain reduced amplitudes,
or vertex functions, describing the coupling of this system to final states. We
then apply the derived analytic expressions to the analysis of the recent
$e^+e^-\to \pi^+\pi^-$, $\tau^-\to \pi^-\pi^0\nu_\tau$, and $e^+e^-\to
\pi^0\gamma$ data. We find the reduced amplitudes for the coupling of the
photon and vector mesons to two pseudoscalars to be constant, independent of
$s$, in the range considered, indicating a "freezing" of the amplitudes for
$s\le 1$ GeV. The fit to the form factor data leads to the following values of
the Breit-Wigner resonance masses m_{\rho^-}=775.3\pm 0.8 MeV,
m_{\rho^0}=773.7\pm 0.6 MeV and m_\omega=782.43\pm 0.05 MeV, where the errors
are only statistical.Comment: revtex, 23 page

### 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 $\phi$ meson production in the interaction of 2.83 GeV
protons with nuclei. In particular, the A-dependences of the absolute and
relative $\phi$ meson yields are investigated within the different scenarios
for its in-medium width as well as for the cross section ratio $\sigma_{pn \to
pn{\phi}}/{\sigma_{pp \to pp{\phi}}}$. 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 $\phi$ 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 $\sigma_{pn \to pn{\phi}}/{\sigma_{pp \to
pp{\phi}}}$ has a weak effect on the A-dependence of the relative $\phi$ 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

### In-medium Properties of Hadrons -- Observables

We first briefly review the theoretical basis for calculations of changes of
hadronic properties in dense nuclear matter. These changes have usually been
investigated by means of relativistic heavy-ion reactions. Here we discuss that
observable consequences of such changes can also be seen in more elementary
reactions on nuclei. Particular emphasis is put on a discussion of actual
observables in photonuclear reactions; we discuss in detail $\eta$- and
vector-meson production. We show that photoproduction of $\eta$'s can yield
essential information on in-medium properties of the $S_{11}(1535)$ resonance
while the $\phi$ meson properties will probably not be accessible through the
$K^+K^-$ decay channel. However, for $\omega$ mesons the $\pi^0\gamma$ decay
channel, due to its reduced final state interaction, looks more promising in
this respect. Completely free of final state interactions is dilepton
production in the few GeV range. We show that the sensitivity of this decay
channel to changes of hadronic properties in medium in photonuclear reactions
on nuclei is as large as in ultrarelativistic heavy ion collisions. Finally we
discuss that hadron production in nuclei at 10 -- 20 GeV photon energies can
give important information on the hadronization process.Comment: Invited Lecture by U. Mosel at Erice International School on Nuclear
Physics 200

- …