34,272 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
Characterizing the nature of Fossil Groups with XMM
We present an X-ray follow-up, based on XMM plus Chandra, of six Fossil Group
(FG) candidates identified in our previous work using SDSS and RASS data. Four
candidates (out of six) exhibit extended X-ray emission, confirming them as
true FGs. For the other two groups, the RASS emission has its origin as either
an optically dull/X-ray bright AGN, or the blending of distinct X-ray sources.
Using SDSS-DR7 data, we confirm, for all groups, the presence of an r-band
magnitude gap between the seed elliptical and the second-rank galaxy. However,
the gap value depends, up to 0.5mag, on how one estimates the seed galaxy total
flux, which is greatly underestimated when using SDSS (relative to Sersic)
magnitudes. This implies that many FGs may be actually missed when using SDSS
data, a fact that should be carefully taken into account when comparing the
observed number densities of FGs to the expectations from cosmological
simulations. The similarity in the properties of seed--FG and non-fossil
ellipticals, found in our previous study, extends to the sample of X-ray
confirmed FGs, indicating that bright ellipticals in FGs do not represent a
distinct population of galaxies. For one system, we also find that the velocity
distribution of faint galaxies is bimodal, possibly showing that the system
formed through the merging of two groups. This undermines the idea that all
selected FGs form a population of true fossils.Comment: 9 pages, 3 figures. Submitted 01/12/2011 to MNRAS, referee report
received 21/02/2012, accepted 22/02/201
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