38,141 research outputs found
Critical view of the claimed pentaquark
We use a theoretical model of the reaction
adapted to the experiment done at LEPS where a peak was observed and associated
to the pentaquark. The study shows that the method used in
the experiment to associate momenta to the undetected proton and neutron,
together with the chosen cuts, necessarily creates an artificial broad peak in
the assumed invariant mass in the region of the claimed
. It is shown that the LEPS fit to the data, used to make the
claim of the , grossly distorts the background. An
alternative fit, assuming a background plus a fluctuation, returns a background
practically equal to the theoretical one and a fluctuation identical to the one
seen in the experimental spectrum of 2 significance.Comment: Conference Proceedin
Study of the reaction and an alternative explanation for the " pentaquark" peak
We present a calculation of the reaction with the
aim of seeing if the experimental peak observed in the invariant mass
around 1526 MeV, from where evidence for the existence of the has
been claimed, can be obtained without this resonance as a consequence of the
particular dynamics of the process and the cuts applied in the experimental set
up. We find that a combination of facts leads indeed to a peak around 1530 MeV
for the invariant mass of without the need to invoke any new resonance
around this energy. This, together with statistical fluctuations that we prove
to be large with the statistics of the experiment, is likely to produce the
narrower peak observed there.Comment: published versio
An analysis of the Lattice QCD spectra for and
In this talk I present the results obtained using effective field theories in
a finite volume from a reanalysis of lattice data on the systems,
where bound states of and are found and associated with the states
and , respectively. We confirm the presence of
such states on the lattice data and determine the weight of the channel in
the wave function of and that of in the wave function
of . Our results indicate a large meson-meson component in both
cases.Comment: Conference Proceedings, Hadron 2017, Salamanca, Spai
The control of space manipulators subject to spacecraft attitude control saturation limits
The motions of robotic manipulators mounted on spacecraft can disturb the spacecraft's positions and attitude. These disturbances can surpass the ability of the system's attitude control reaction jets to control them, for the disturbances increase as manipulator speeds increase. If the manipulator moves too quickly the resulting disturbances can exceed the saturation levels of the reaction jets, causing excessive spacecraft motions. A method for planning space manipulator's motions is presented, so that tasks can be performed as quickly as possible without saturating the system's attitude control jets
Three body resonances in two meson-one baryon systems
We report four 's and three 's, in the 1500 - 1800 MeV
region, as two meson - one baryon S-wave resonances. We solve Faddeev
equations in the coupled channel approach. The invariant mass of one of the
meson-baryon pairs and that of the three particles have been varied and peaks
in the squared three body -matrix have been found very close to the existing
= -1, low lying baryon resonances. The input two-body
-matrices for meson-meson and meson-baryon interaction have been calculated
by solving the Bethe-Salpeter equation with the potentials obtained in the
chiral unitary approach.Comment: corrected version, new channels evaluated, new references adde
Monte Carlo simulations of the halo white dwarf population
The interpretation of microlensing results towards the Large Magellanic Cloud
(LMC) still remains controversial. Whereas white dwarfs have been proposed to
explain these results and, hence, to contribute significantly to the mass
budget of our Galaxy, there are as well several constraints on the role played
by white dwarfs. In this paper we analyze self-consistently and simultaneously
four different results, namely, the local halo white dwarf luminosity function,
the microlensing results reported by the MACHO team towards the LMC, the
results of Hubble Deep Field (HDF) and the results of the EROS experiment, for
several initial mass functions and halo ages. We find that the proposed
log-normal initial mass functions do not contribute to solve the problem posed
by the observed microlensing events and, moreover, they overproduce white
dwarfs when compared to the results of the HDF and of the EROS survey. We also
find that the contribution of hydrogen-rich white dwarfs to the dynamical mass
of the halo of the Galaxy cannot be more than .Comment: 17 pages, 10 figures; accepted for publication in Astronomy and
Astrophysic
- …