3,011 research outputs found
The Centrality Dependence of the Parton Bubble Model for high energy heavy ion collisions and fireball surface substructure at RHIC
In an earlier paper we developed a QCD inspired theoretical parton bubble
model (PBM) for RHIC/LHC. The PBM quantitatively agreed with the strong charged
particle pair correlations observed by the STAR collaboration at RHIC in the
highest energy Au + Au central collisions, and also agreed with the Hanbury
Brown and Twiss (HBT) observed small final state source size approximately 2f
radii in the transverse momentum range above 0.8 GeV/c. The model assumed a
substructure of a ring of localized adjoining 2f radius bubbles(gluonic hot
spots) perpendicular to the collider beam direction, centered on the beam, at
mid-rapidity and located on the expanding fireball surface of the Au + Au
collisions. In this paper we extend the model (PBME) to include the changing
development of bubbles with centrality from the most central region where
bubbles are very important to the most peripheral where the bubbles are gone.
Energy density is found to be related to bubble formation and as centrality
decreases the maximum energy density and bubbles shift from symmetry around the
beam axis to the reaction plane region causing a strong correlation of bubble
formation with elliptic flow. We obtained reasonably quantitative agreement
(within a few percent of the total correlations) with a new precision RHIC
experiment which extended the centrality region investigated to the range 0-80%
(most central to most peripheral). The characteristics and behavior of the
bubbles imply they represent a significant substructure formed on the surface
of the fireball at kinetic freezeoutComment: ACCEPTED for publication in Phys. Rev. C. minor referee changes.20
pages, 12 figures, 3 table
Local Variation as a Statistical Hypothesis Test
The goal of image oversegmentation is to divide an image into several pieces,
each of which should ideally be part of an object. One of the simplest and yet
most effective oversegmentation algorithms is known as local variation (LV)
(Felzenszwalb and Huttenlocher 2004). In this work, we study this algorithm and
show that algorithms similar to LV can be devised by applying different
statistical models and decisions, thus providing further theoretical
justification and a well-founded explanation for the unexpected high
performance of the LV approach. Some of these algorithms are based on
statistics of natural images and on a hypothesis testing decision; we denote
these algorithms probabilistic local variation (pLV). The best pLV algorithm,
which relies on censored estimation, presents state-of-the-art results while
keeping the same computational complexity of the LV algorithm
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