3,002 research outputs found
Light Hadron Spectroscopy: Theory and Experiment
Rapporteur talk at the Lepton-Photon Conference, Rome, July 2001: reviewing
the evidence and strategies for understanding scalar mesons, glueballs and
hybrids, the gluonic Pomeron and the interplay of heavy flavours and light
hadron dynamics. Dedicated to the memory of Nathan Isgur, long-time
collaborator and friend, whose original ideas in hadron spectroscopy formed the
basis for much of the talk.Comment: to be published in "Lepton Photon 2001 Conference Proceedings" (World
Scientific Publishing), 19 pages with 6 figure
Spin of ground state baryons
We calculate the quark spin contribution to the total angular momentum of
flavor octet and flavor decuplet ground state baryons using a spin-flavor
symmetry based parametrization method of quantum chromodynamics. We find that
third order SU(6) symmetry breaking three-quark operators are necessary to
explain the experimental result Sigma_1=0.32(10). For spin 3/2 decuplet baryons
we predict that the quark spin contribution is Sigma_3=3.93(22), i.e.
considerably larger than their total angular momentum.Comment: 8 page
Epsilon Indi Ba/Bb: the nearest binary brown dwarf
We have carried out high angular resolution near-infrared imaging and
low-resolution (R~1000) spectroscopy of the nearest known brown dwarf, Eps Indi
B, using the ESO VLT NAOS/CONICA adaptive optics system. We find it to be a
close binary (as also noted by Volk et al. 2003) with an angular separation of
0.732 arcsec, corresponding to 2.65AU at the 3.626pc distance of the Eps Indi
system. In our discovery paper (Scholz et al. 2003), we concluded that Eps Indi
B was a ~50Mjup T2.5 dwarf: our revised finding is that the two system
components (Eps Indi Ba and Eps Indi Bb) have spectral types of T1 and T6,
respectively, and estimated masses of 47 and 28Mjup, respectively, assuming an
age of 1.3Gyr. Errors in the masses are +/-10 and +/-7Mjup, respectively,
dominated by the uncertainty in the age determination (0.8-2Gyr range). This
uniquely well-characterised T dwarf binary system should prove important in the
study of low-mass, cool brown dwarfs. The two components are bright and
relatively well-resolved: Eps Indi B is the only T dwarf binary in which
spectra have been obtained for both components. They have a well-established
distance and age. Finally, their orbital motion can be measured on a fairly
short timescale (nominal orbital period 15 yrs), permitting an accurate
determination of the true total system mass, helping to calibrate brown dwarf
evolutionary models.Comment: Accepted for publication by Astronomy & Astrophysics main journal.
This replacement version includes minor changes made following comments by
the referee, along with a reworking of the photometric data and derived
quantities using 2MASS catalogue photometry as the basis, with only a minor
impact on the final result
Open-charm meson spectroscopy
We present a theoretical framework that accounts for the new and
mesons measured in the open-charm sector. These resonances are
properly described if considered as a mixture of conventional wave
quark-antiquark states and four-quark components. The narrowest states are
basically wave quark-antiquark mesons, while the dominantly four-quark
states are shifted above the corresponding two-meson threshold, being broad
resonances. We study the electromagnetic decay widths as basic tools to
scrutiny their nature. The proposed explanation incorporates in a natural way
the most recently discovered mesons in charmonium spectroscopy.Comment: 15 pages, 5 tables. Accepted for publication in Phys. Rev.
A detector for continuous measurement of ultra-cold atoms in real time
We present the first detector capable of recording high-bandwidth real time
atom number density measurements of a Bose Einstein condensate. Based on a
two-color Mach-Zehnder interferometer, our detector has a response time that is
six orders of magnitude faster than current detectors based on CCD cameras
while still operating at the shot-noise limit. With this minimally destructive
system it may be possible to implement feedback to stabilize a Bose-Einstein
condensate or an atom laser.Comment: 3 pages, 3 figures, submitted to optics letter
Pulsed pumping of a Bose-Einstein condensate
In this work, we examine a system for coherent transfer of atoms into a
Bose-Einstein condensate. We utilize two spatially separate Bose-Einstein
condensates in different hyperfine ground states held in the same dc magnetic
trap. By means of a pulsed transfer of atoms, we are able to show a clear
resonance in the timing of the transfer, both in temperature and number, from
which we draw conclusions about the underlying physical process. The results
are discussed in the context of the recently demonstrated pumped atom laser.Comment: 5 pages, 5 figures, published in Physical Review
A lattice determination of moments of unpolarised nucleon structure functions using improved Wilson fermions
Within the framework of quenched lattice QCD and using O(a) improved Wilson
fermions and non-perturbative renormalisation, a high statistics computation of
low moments of the unpolarised nucleon structure functions is given. Particular
attention is paid to the chiral and continuum extrapolations.Comment: LaTeX, 66 pages, 22 figure
Positive Parity Scalar Mesons in the 1-2 GeV Mass Range
Based on the observation that K_0(1430) is lighter than its SU_3 counterpart,
a_0(1450), we examine the possibility that these particles, together with
f_0(1370), f_0(1500) and f_0(1710), fill a tetraquark recurrence of the sub-GeV
0^{++} nonet mixed with a glueball state. We find the picture to be consistent
with the known data about the three f_0 resonances, more than the q-qbar
hypothesis. Conventional spin-orbit coupling suggests the q-qbar, P-wave, nonet
to lie around 1200 MeV. We review possible experimental indications of a scalar
isovector resonance at 1.29 GeV, first observed by OBELIX in p-pbar
annihilation.Comment: 12 pages, 9 figures. Extended version. References added. Results and
conclusions unchange
A Heavenly Example of Scale Free Networks and Self-Organized Criticality
The sun provides an explosive, heavenly example of self-organized
criticality. Sudden bursts of intense radiation emanate from rapid
rearrangements of the magnetic field network in the corona. Avalanches are
triggered by loops of flux that reconnect or snap into lower energy
configurations when they are overly stressed. Our recent analysis of
observational data reveals that the loops (links) and footpoints (nodes), where
they attach on the photosphere, embody a scale free network. The statistics of
the avalanches and of the network structure are unified through a simple
dynamical model where the avalanches and network co-generate each other into a
complex, critical state. This particular example points toward a general
dynamical mechanism for self-generation of complex networks.Comment: Submitted to proceedings for the Latin American Workshop on Nonlinear
Phenomena, Salvador, Brazil (2003
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