42 research outputs found
In-Medium properties of the omega meson in photon induced nuclear reactions
We discuss the possibility to study the in-medium changes of the properties
of the omega meson in reactions on ordinary nuclei with elementary
electromagnetic probes. We present a tree-level calculation of the elementary
gamma p -> omega p process which is extended to describe also the
photoproduction of medium-modified omega mesons in nuclear matter. Using a
semi-classical transport approach we obtain results for e+e- and pi0 gamma
photoproduction off heavy nuclei in the invariant mass range of the rho and
omega mesons. Both reactions are also studied experimentally and are presently
being analyzed at accelerator facilities in Bonn and at Jefferson Lab. We show
that the in-medium signals expected can be as large as those obtained in
heavy-ion reactions.Comment: 8 pages, 7 figures, Contribution to the "Workshop on In-Medium Hadron
Physics", Giessen, Germany, 11-13 November 200
The spectral function of the omega meson in nuclear matter from a coupled-channel resonance model
We calculate the spectral function of the omega meson in nuclear matter at
zero temperature by means of the low-density theorem. The omega N forward
scattering amplitude is calculated within a unitary coupled-channel effective
Lagrangian model that has been applied successfully to the combined analysis of
pion- and photon-induced reactions. While the peak of the omega spectral
distribution is shifted only slightly, we find a considerable broadening of the
omega meson due to resonance-hole excitations. For omega mesons at rest with
respect to the surrounding nuclear medium, we find an additional width of about
60 MeV at saturation density.Comment: 26 pages, 10 figures, added short discussio
Study of in-medium meson properties in Ap, pA and AA collisions
We propose to investigate the in-medium properties of vector mesons
at the normal nuclear density in Ap(pA) collisions and at higher density in AA
collisions at the ITEP accelerator facility TWAC. Using of the inverse Ap
kinematics will permit us to study the meson production in a wide
momentum interval included the not yet explored range of small meson momenta
relative to the projectile nuclei where the mass modification effect in nuclear
matter is expected to be the strongest. Momentum dependence of the in-medium
meson width will be studied in the traditional pA kinematics. We
intend to use the electromagnetic calorimeter for reconstruction of the
meson invariant mass by detecting photons from the decay. The model calculations and simulations with
RQMD generator show feasibility of the proposed experiment. Available now
intensity of the ion beams provides a possibility to collect large statistics
and make decisive conclusion about the meson properties at density of
normal nuclei. At the second stage of the investigation the meson
properties will be studied in AA collisions at higher density. Interpretation
of these measurements will be based on the results obtained in Ap(pA)
interactions. Further investigation of the in-medium properties of light
unflavored and charmed mesons can be performed at ITEP and at GSI(FAIR) where
higher ion energies will be accessible in near future.Comment: 26 pages, 10 figures, 2 table
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 - and
vector-meson production. We show that photoproduction of 's can yield
essential information on in-medium properties of the resonance
while the meson properties will probably not be accessible through the
decay channel. However, for mesons the 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
In-Medium Properties of Hadrons - Observables II
In this review we discuss the observable consequences of in-medium changes of
hadronic properties in reactions with elementary probes, and in particular
photons, on nuclei. After an outline of the theoretical method used we focus on
a discussion of actual observables in photonuclear reactions; we discuss in
detail - and vector-meson production. We show that the
photoproduction data can be well described by final state interactions of the
pions produced whereas the semi-charged channel exhibits a major
discrepancy with theory. For production on nuclei in the TAPS/CB@ELSA
experiment we analyse the decay channel, and illustrate the
strength of the method by simulating experimental acceptance problems.
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 and make predictions for the
on-going G7 experiment at JLAB. Finally we discuss that hadron production in
nuclei at 10 -- 20 GeV photon energies can give important information on the
hadronization process, and in particular on the time-scales involved. We show
here detailed calculations for the low-energy (12 GeV) run at HERMES and
predictions for planned experiments at JLAB.Comment: Invited Talk by U. Mosel, Proceedings of the Int. School on Nuclear
Physics, 26th Course, "Lepton scattering and the structure of hadrons and
nuclei", Erice (Sicily), September 16th-24th, 2004, short piece of text adde
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
Hadrons in Nuclei -- from High (200 GeV) to Low (1 GeV) energies
The study of the interaction of hadrons, produced by elementary probes in a
nucleus, with the surrounding nuclear medium can give insight into two
important questions. First, at high energies, the production process, the
time-scales connected with it and the prehadronic interactions can be studied
by using the nuclear radius as a length-scale. We do this here by analyzing
data from the EMC and HERMES experiements on nuclear attenuation. Second, at
low energies the spectral function, and thus the selfenergy of the produced
hadron, can be studied. Specifically, we analyze the CBELSA/TAPS data on
production in nuclei and discuss the importance of understanding
in-medium effects both on the primary production cross section and the final
state branching ratio. In both of these studies an excellent control of the
final state interactions is essential.Comment: Lecture given by U. Mosel at International School of Nuclear Physics:
29th Course: Quarks in Hadrons and Nuclei, Erice, Sicily, Italy, 16-24 Sep
200
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