176 research outputs found
Best-First Width Search for Lifted Classical Planning
Lifted planners are useful to solve tasks that are too hard to ground. Still, computing informative lifted heuristics is difficult: directly adapting ground heuristics to the lifted setting is often too expensive, and extracting heuristics from the lifted representation can be uninformative. A natural alternative for lifted planners is to use width-based search. These algorithms are among the strongest for ground planning, even the variants that do not access the action model. In this work, we adapt best-first width search to the lifted setting and show that this yields state-of-the-art performance for hard-to-ground planning tasks
Self-consistent solution for the polarized vacuum in a no-photon QED model
We study the Bogoliubov-Dirac-Fock model introduced by Chaix and Iracane
({\it J. Phys. B.}, 22, 3791--3814, 1989) which is a mean-field theory deduced
from no-photon QED. The associated functional is bounded from below. In the
presence of an external field, a minimizer, if it exists, is interpreted as the
polarized vacuum and it solves a self-consistent equation.
In a recent paper math-ph/0403005, we proved the convergence of the iterative
fixed-point scheme naturally associated with this equation to a global
minimizer of the BDF functional, under some restrictive conditions on the
external potential, the ultraviolet cut-off and the bare fine
structure constant . In the present work, we improve this result by
showing the existence of the minimizer by a variational method, for any cut-off
and without any constraint on the external field.
We also study the behaviour of the minimizer as goes to infinity
and show that the theory is "nullified" in that limit, as predicted first by
Landau: the vacuum totally kills the external potential. Therefore the limit
case of an infinite cut-off makes no sense both from a physical and
mathematical point of view.
Finally, we perform a charge and density renormalization scheme applying
simultaneously to all orders of the fine structure constant , on a
simplified model where the exchange term is neglected.Comment: Final version, to appear in J. Phys. A: Math. Ge
New Results on Pb-Au Collisions at 40 AGeV from the CERES/NA45 Experiment
In 1999 the CERES/NA45 ran at the CERN SPS with a beam energy of 40
GeV/nucleon. The data set comprises about 8.7 millions Pb-Au events with a
trigger selection corresponding to approximately the most central 30% of the
geometrical cross section. Results on low-mass electron pair analysis are
presented.
The upgrade of the experimental setup with the radial drift TPC has allowed
to enhance hadron physics capabilities of the experiment. New results on hadron
spectra (including Lambda) and flow are presented.Comment: Talk at the International Nuclear Physics Conference INPC2001,
Berkeley, CA, July 29th - August 3rd 200
Low-mass e+e- pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum
We report a measurement of low-mass electron pairs observed in 158
GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of
invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4
(stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As
observed previously in S-Au collisions, the enhancement is most pronounced in
the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong
increase of the enhancement with centrality. In addition, we show that the
enhancement covers a wide range in transverse momentum, but is largest at the
lowest observed pt.Comment: 17 pages, 4 figures, submitted to Phys.Lett.
Flow and non-flow event anisotropies at the SPS
A study of differential elliptic event anisotropies (v_2) of charged
particles and high-pt pions in 158 AGeV/c Pb+Au collisions is presented.
Results from correlations with respect to the event plane and from two-particle
azimuthal correlations are compared. The latter give systematically higher v_2
values at pt>1.2GeV/c providing possibly an evidence of a non-flow semihard
component.Comment: 4 pages, 6 figures, Quark Matter 2002, Nantes, to appear in Nucl.
Phys.
Recent results from Pb-Au collisions at 158 GeV/c per nucleon obtained with the CERES spectrometer
During the 1996 lead run time, CERES has accumulated 42 million events,
corresponding to a factor of 5 more statistics than in 1995 and 2.5 million
events of a special photon-run. We report on the results of the low-mass
ee-pair analysis. Since the most critical item is the poor
signal-to-background ratio we also discuss the understanding of this
background, in absolute terms, with the help of a detailed Monte Carlo
simulation. We show preliminary results of the photon analysis and summarize
the results of the hadron analysis preliminarily reported on already at QM'97Comment: 10 pages, 9 figures, Proceedings of the XIV Int. Conf. on
Nucleus-Nucleus Collisions,Quark Matter 99, Torino, Italy, May 10 - 15, 199
e+e--pair production in Pb-Au collisions at 158 GeV per nucleon
We present the combined results on electron-pair production in 158 GeV/n
{Pb-Au} (= 17.2 GeV) collisions taken at the CERN SPS in 1995 and
1996, and give a detailed account of the data analysis. The enhancement over
the reference of neutral meson decays amounts to a factor of 2.31 for semi-central collisions (28%
) when yields are integrated over 200 MeV/ in
invariant mass. The measured yield, its stronger-than-linear scaling with
, and the dominance of low pair strongly suggest an
interpretation as {\it thermal radiation} from pion annihilation in the
hadronic fireball. The shape of the excess centring at 500
MeV/, however, cannot be described without strong medium modifications of
the meson. The results are put into perspective by comparison to
predictions from Brown-Rho scaling governed by chiral symmetry restoration, and
from the spectral-function many-body treatment in which the approach to the
phase boundary is less explicit.Comment: 39 pages, 40 figures, to appear in Eur.Phys.J.C. (2005
Event-by-event fluctuations of the mean transverse momentum in 40, 80, and 158 A GeV/c Pb-Au collisions
Measurements of event-by-event fluctuations of the mean transverse momentum
in Pb-Au collisions at 40, 80, and 158 A GeV/c are presented. A significant
excess of mean p_T fluctuations at mid-rapidity is observed over the
expectation from statistically independent particle emission. The results are
somewhat smaller than recent measurements at RHIC. A possible non-monotonic
behaviour of the mean p_T fluctuations as function of collision energy, which
may have indicated that the system has passed the critical point of the QCD
phase diagram in the range of mu_B under investigation, has not been observed.
The centrality dependence of mean p_T fluctuations in Pb-Au is consistent with
an extrapolation from pp collisions assuming that the non-statistical
fluctuations scale with multiplicity. The results are compared to calculations
by the RQMD and UrQMD event generators.Comment: 28 pages, 10 figure
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