5,416 research outputs found
Meson Mixing and Dilepton Production in Heavy Ion Collisions
We study the possibility of mixing via N-N excitations in dense
nuclear matter. This mixing is found to induce a peak in the dilepton spectra
at an invariant mass equal to that of the . We calculate the cross section
for dilepton production through mixing and we compare its size with that of
annihilation. In-medium masses and mixing angles are also calculated.
Some preliminary results of the mixing effect on the dilepton production rates
at finite temperature are also presented.Comment: To be published in the proceedings of CIPANP 200
Squeezing lepton pairs out of broken symmetries
We discuss two possible signatures of symmetry breaking that can appear in
dilepton spectra, as measured in relativistic heavy ion collisions. The first
involves scalar-vector meson mixing and is related to the breaking of Lorentz
symmetry by a hot medium. The second is related to the breaking of Furry's
theorem by a charged quark-gluon plasma. Those signals will be accessible to
upcoming measurements to be performed at the GSI, RHIC, and the LHC.Comment: 5 pages, 4 figures, talk given at the INPC 2001 (International
Conference on Nuclear Physics), 30 July - 3 August 2001, Berkeley, C
Aspects of meson properties in dense nuclear matter
We investigate the modification of meson spectral densities in dense nuclear
matter at zero temperature. These effects are studied in a fully relativistic
mean field model which goes beyond the linear density approximation and also
includes baryon resonances. In particular, the role of N*(1520) and N*(1720) on
the rho meson spectral density is highlighted. Even though the nucleon-nucleon
loop and the nucleon-resonance loop contribute with the opposite sign, an
overall reduction of rho meson mass is still observed at high density.
Importantly, it is shown that the resonances cause substantial broadening of
the rho meson spectral density in matter and also induces non-trivial momentum
dependence. The spectral density of the a0 meson is also shown. We study the
dispersion relations and collective oscillations induced by the rho meson
propagation in nuclear matter together with the influence of the mixing of rho
with the a0 meson. The relevant expression for the plasma frequency is also
recovered analytically in the appropriate limit.Comment: 19 pages, 17 figure
Simulacija porarizacijskih mjerenja u elektrotvorbi kaona Monte Carlo metodom
Kaon electro-production experiments with polarized electron beam are planed at the Thomas Jefferson National Accelerator Facility (Virginia, USA) in order to complete the information on polarization response functions for the kaon electro-production reactions. The experiment uses the self analyzing property of the Î recoil. The scattered electrons will be detected in coincidence with the kaons and the decay protons. This paper presents the simulation of this experiment which takes into account the spectrometer acceptances, multiple scattering and radiative corrections. The phase space distribution of the decay protons in the Î center-of-mass system are generated in order to extract information on the polarization on the three directions. An experimental test with an unpolarized beam has been performed to estimate the efficiency of the method.U Thomas Jefferson National Accelerator Facility (Virginia, USA) predlaĆŸu se mjerenja elektrotvorbi s polariziranim elektronima radi cjelovitosti podataka o polarizacijskim funkcijama odziva u elektrotvorbi kaona. Mjerenje rabi samoanalizacijsko svojstvo odboja Î Äestice. RasprĆĄeni elektroni opaĆŸat Äe se sudesno s kaonima i protonima. Ovaj rad predstavlja simulaciju tog eksperimenta u kojoj se uzimaju u obzir prihvati spektrometara, viĆĄestruko rasprĆĄenje i radijativne popravke. Izvodi se fazna raspodjela protona u centru mase Î Äestice radi dobivanja podataka o polarizaciji u trima smjerovima. Mjerenjem pomoÄu nepolariziranog snopa ocijenili smo uÄinkovitost metode
Planetary nebulae and stellar kinematics in the flattened elliptical galaxy NGC 1344
We present photometric and kinematic information obtained by measuring 197
planetary nebulae (PNs) discovered in the flattened Fornax elliptical galaxy
NGC 1344 (also known as NGC 1340) with an on-band, off-band, grism + on-band
filter technique. We build the PN luminosity function (PNLF) and use it to
derive a distance modulus m-M=31.4, slightly smaller than, but in good
agreement with, the surface brightness fluctuation distance. The PNLF also
provides an estimate of the specific PN formation rate: 6x10^-12 PNs per year
per solar luminosity. Combining the positional information from the on-band
image with PN positions measured on the grism + on-band image, we can measure
the radial velocities of 195 PNs, some of them distant more than 3 effective
radii from the center of NGC 1344. We complement this data set with stellar
kinematics derived from integrated spectra along the major and minor axes, and
parallel to the major axis of NGC 1344. The line-of-sight velocity dispersion
profile indicates the presence of a dark matter halo around this galaxy.Comment: 45 pages, 18 figures, accepted for publication in Ap
Semiclassical evolution of the spectral curve in the normal random matrix ensemble as Whitham hierarchy
We continue the analysis of the spectral curve of the normal random matrix
ensemble, introduced in an earlier paper. Evolution of the full quantum curve
is given in terms of compatibility equations of independent flows. The
semiclassical limit of these flows is expressed through canonical differential
forms of the spectral curve. We also prove that the semiclassical limit of the
evolution equations is equivalent to Whitham hierarchy.Comment: 14 page
The effects of meson mixing on dilepton spectra
The effect of scalar and vector meson mixing on the dilepton radiation from
hot and dense hadronic matter is estimated in different isospin channels. In
particular, we study the effect of - and mixing and
calculate the corresponding rates. Effects are found to be significant compared
to standard - and - annihilations. While the mixing in
the isoscalar channel mostly gives a contribution in the invariant mass range
between the two-pion threshold and the peak, the isovector channel
mixing induces an additional peak just below that of the .
Experimentally, the dilepton signals from - mixing seem to be more
tractable than those from - mixing.Comment: 10 pages, 9 figure
Signatures of accretion events in the halos of early-type galaxies from comparing PNe and GCs kinematics
We have compared the halo kinematics traced by globular clusters (GCs) and
planetary nebulae (PNe) for two elliptical galaxies in the Fornax and Virgo
clusters NGC 1399 and NGC 4649, and for the merger remnant NGC 5128 (Centaurus
A). We find differences in the rotational properties of the PN, red GC, and
blue GC systems in all these three galaxies. NGC 1399 PNe and GCs show line of
sight velocity distributions in specific regions that are significantly
different, based on Kolmogorov-Smirnov tests. The PN system shows multi-spin
components, with nearly opposite direction of rotation in the inner and the
outer parts. The GCs velocity field is not point-symmetric in the outer regions
of the galaxy, indicating that the system has not reached dynamical equilibrium
yet. In NGC 4649 PNe, red and blue GCs have different rotation axes and
rotational velocities. Finally, in NGC 5128 both PNe and GCs deviate from
equilibrium in the outer regions of the galaxy, and in the inner regions the PN
system is rotationally supported, whereas the GC system is dominated by
velocity dispersion. The observed different kinematic properties, including
deviations from point-symmetry, between PNe and GCs suggest that these systems
are accreted at different times by the host galaxy, and the most recent
accretion took place only few Gyr ago.We discuss two scenarios which may
explain some of these differences: i) tidal stripping of loosely-bound GCs, and
ii) multiple accretion of low luminosity and dwarf galaxies. Because these two
mechanisms affect mostly the GC system, differences with the PNe kinematics can
be expected.Comment: 14 pages, 13 figures, Accepted for publication in MNRAS. This new
version contains an improved analysis, which includes the study of
point-symmetry in the velocity fields and its implications for dynamical
equilibriu
Concentric double hollow grid cathode discharges
A new cathode system, consisting of two concentric spherical hollow grids with two aligned orifices, is investigated by space-resolved Langmuir probe measurements and non-linear dynamics analysis. Negative biases of this spherical hollow grids arrangement lead to the formation of two complex space charge structures in the regions of the orifices. The overall dynamics of the current-voltage characteristic (IâV characteristic) of each discharge is characterized by strong oscillatory behaviour with various waveforms correlated with jumps in the static IâV characteristics. Space-resolved measurements through the two aligned orifices of the two grids show a peak increase of the electron temperature and particle density in the regions of the two space-charge structures. The effects of the biases and Ar pressure on the overall spatial distribution of all plasma parameters are investigated. Two important working points of the concentric double hollow grid cathode discharges are revealed which could make this configuration suitable as an electron source
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