22,423 research outputs found
Tetraquark Production in Double Parton Scattering
We develop a model to study tetraquark production in hadronic collisions. We
focus on double parton scattering and formulate a version of the color
evaporation model for the production of the and of the
tetraquark, a state composed by the quarks. We find that
the production cross section grows rapidly with the collision energy
and make predictions for the forthcoming higher energy data of the LHC.Comment: 13 pages, 3 figures. Corrections in the text and reference
Morphology of low-redshift compact galaxy clusters I. Shapes and radial profiles
The morphology of clusters of galaxies may be described with a set of
parameters which contain information about the formation and evolutionary
history of these systems. In this paper we present a preliminary study of the
morphological parameters of a sample of 28 compact Abell clusters extracted
from DPOSS data. The morphology of galaxy clusters is parameterized by their
apparent ellipticity, position angle of the major axis, centre coordinates,
core radius and beta-model power law index. Our procedure provides estimates of
these parameters by simultaneously fitting them all, overcoming some of the
difficulties induced by sparse data and low number statistics typical of this
kind of analysis. The cluster parameters were fitted in a 3 x 3 h^-2 sqMpc
region, measuring the background in a 2 <R< 2.5 h^-1Mpc annulus. We also
explore the correlations between shape and profile parameters and other cluster
properties. One third of this compact cluster sample has core radii smaller
than 50 h^-1 kpc, i.e. near the limit that our data allow us to resolve,
possibly consistent with cusped models. The remaining clusters span a broad
range of core radii up to 750 h^-1 kpc. More than 80 per cent of this sample
has ellipticity higher than 0.2. The alignment between the cluster and the
major axis of the dominant galaxy is confirmed, while no correlation is
observed with other bright cluster members. No significant correlation is found
between cluster richness and ellipticity. Instead, cluster richness is found to
correlate, albeit with large scatter, with the cluster core radius.[abridged]Comment: 23 pages, 17 figures, accepted for publication in MNRAS. Full paper
including full resolution figures 2 and 9 at
http://www.eso.org/~vstrazzu/P/ME1030fv.pd
An automatic procedure to extract galaxy clusters from CRoNaRio catalogs
We present preliminary results of a simple peak finding algorithm applied to
catalogues of galaxies, extracted from the Second Palomar Sky Survey in the
framework of the CRoNaRio project. All previously known Abell and Zwicky
clusters in a test region of 5x5 sq. deg. are recovered and new candidate
clusters are also detected. This algorithm represents an alternative way of
searching for galaxy clusters with respect to that implemented and tested at
Caltech on the same type of data (Gal et al. 1998).Comment: in the proceeding of the XLIII SAIt national conference Mem. Soc.
Astr. It., in pres
Controlling entanglement by direct quantum feedback
We discuss the generation of entanglement between electronic states of two
atoms in a cavity using direct quantum feedback schemes. We compare the effects
of different control Hamiltonians and detection processes in the performance of
entanglement production and show that the quantum-jump-based feedback proposed
by us in Phys. Rev. A {\bf 76} 010301(R) (2007) can protect highly entangled
states against decoherence. We provide analytical results that explain the
robustness of jump feedback, and also analyse the perspectives of experimental
implementation by scrutinising the effects of imperfections and approximations
in our model.Comment: 10 pages, 8 figures. To appear in PR
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