7,800 research outputs found
Polarization effects in double open-charm production at LHCb
Double open-charm production is one of the most promising channels to
disentangle single from double parton scattering (DPS) and study different
properties of DPS. Several studies of the DPS contributions have been made. A
missing ingredient so far has been the study of polarization effects, arising
from spin correlations between the two partons inside an unpolarized proton. We
investigate the impact polarization has on the double open-charm cross section.
We show that the longitudinally polarized gluons can give significant
contributions to the cross section, but for most of the considered kinematic
region only have a moderate effect on the shape. We compare our findings to the
LHCb data in the D0D0 final state, identify observables where polarization does
have an impact on the distribution of the final state particles, and suggest
measurements which could lead to first experimental indications of, or limits
on, polarization in DPS.Comment: 16 pages, 13 figure
Removing beam asymmetry bias in precision CMB temperature and polarisation experiments
Asymmetric beams can create significant bias in estimates of the power
spectra from CMB experiments. With the temperature power spectrum many orders
of magnitude stronger than the B-mode power spectrum any systematic error that
couples the two must be carefully controlled and/or removed. Here, we derive
unbiased estimators for the CMB temperature and polarisation power spectra
taking into account general beams and general scan strategies. A simple
consequence of asymmetric beams is that, even with an ideal scan strategy where
every sky pixel is seen at every orientation, there will be residual coupling
from temperature power to B-mode power if the orientation of the beam asymmetry
is not aligned with the orientation of the co-polarisation. We test our
correction algorithm on simulations of two temperature-only experiments and
demonstrate that it is unbiased. The simulated experiments use realistic scan
strategies, noise levels and highly asymmetric beams. We also develop a
map-making algorithm that is capable of removing beam asymmetry bias at the map
level. We demonstrate its implementation using simulations and show that it is
capable of accurately correcting both temperature and polarisation maps for all
of the effects of beam asymmetry including the effects of temperature to
polarisation leakage.Comment: 18 pages, 9 figure
Timelike and spacelike hadron form factors, Fock state components and light-front dynamics
A unified description of spacelike and timelike hadron form factors within a
light-front model was successfully applied to the pion. The model is extended
to the nucleon to study the role of pair production and of
nonvalence components in the nucleon form factors. Preliminary results in the
spacelike range are presented.Comment: 4 pages, espcrc1.sty. proceedings of FB XVIII (August 2006, Brazil),
to be published in Nucl. Phys.
Electromagnetic Hadron Form Factors and Higher Fock Components
Investigation of the spacelike and timelike electromagnetic form factors of
hadrons, within a relativistic microscopical model characterized by a small set
of hypothesis, could shed light on the components of hadron states beyond the
valence one. Our relativistic approach has been successfully applied first to
the pion and then the extension to the nucleon has been undertaken. The pion
case is shortly reviewed as an illustrative example for introducing the main
ingredients of our approach, and preliminary results for the nucleon in the
spacelike range are evaluated.Comment: 8 pages, 6 figs, espcrc1.sty included. Proceedings of Fifth
International Conference on Perspectives In Hadronic Physics, ICTP, May
22-26, 200
Removing beam asymmetry bias in precision CMB temperature and polarisation experiments
Asymmetric beams can create significant bias in estimates of the power
spectra from CMB experiments. With the temperature power spectrum many orders
of magnitude stronger than the B-mode power spectrum any systematic error that
couples the two must be carefully controlled and/or removed. Here, we derive
unbiased estimators for the CMB temperature and polarisation power spectra
taking into account general beams and general scan strategies. A simple
consequence of asymmetric beams is that, even with an ideal scan strategy where
every sky pixel is seen at every orientation, there will be residual coupling
from temperature power to B-mode power if the orientation of the beam asymmetry
is not aligned with the orientation of the co-polarisation. We test our
correction algorithm on simulations of two temperature-only experiments and
demonstrate that it is unbiased. The simulated experiments use realistic scan
strategies, noise levels and highly asymmetric beams. We also develop a
map-making algorithm that is capable of removing beam asymmetry bias at the map
level. We demonstrate its implementation using simulations and show that it is
capable of accurately correcting both temperature and polarisation maps for all
of the effects of beam asymmetry including the effects of temperature to
polarisation leakage.Comment: 18 pages, 9 figure
Electromagnetic form factors of the nucleon in spacelike and timelike regions
An approach for a unified description of the nucleon electromagnetic form
factors in spacelike and timelike regions is presented. The main ingredients of
our model are: a Mandelstam formula for the matrix elements of the nucleon
electromagnetic current; a 3-dimensional reduction of the problem on the
Light-Front performed within the so-called {\tt Propagator Pole Approximation}
({\bf PPA}), which consists in disregarding the analytical structure of the
Bethe-Salpeter amplitudes and of the quark-photon vertex function in the
integration over the minus components of the quark momenta; a dressed
photon vertex in the channel, where the photon is described by its
spin-1, hadronic component.Comment: 8 pages, 9 figs., macro added. Proceedings of the XI Conf. on
Problems in Theoretical Nuclear Physics, Cortona, Oct. 11-14, 200
An HI census of Loose Groups of Galaxies
We present results from our Parkes Multibeam HI survey of 3 loose groups of
galaxies that are analogous to the Local Group. This is a survey of groups
containing only spiral galaxies with mean separations of a few hundred kpc, and
total areas of approximately 1 sq. Mpc; groups similar to our own Local Group.
We present a census of the HI-rich objects in these groups down to an M(HI),
1-sigma sensitivity ~7x10^5 M(sun), as well as the detailed properties of these
detections from follow-up Compact Array observations. We found 7 new HI-rich
members in the 3 groups, all of which have stellar counterparts and are,
therefore, typical dwarf galaxies. The ratio of low-mass to high-mass gas-rich
galaxies in these groups is less than in the Local Group meaning that the
``missing satellite'' problem is not unique. No high-velocity cloud analogs
were found in any of the groups. If HVCs in these groups are the same as in the
Local Group, this implies that HVCs must be located within ~300-400 kpc of the
Milky Way.Comment: 6 pages, to appear in the ASP proceedings of IAU Symposium 217,
"Recycling intergalactic and interstellar matter", eds. Pierre-Alain Duc,
Jonathan Braine, Elias Brink
Identification alone versus intraoperative neuromonitoring of the recurrent laryngeal nerve during thyroid surgery: experience of 2034 consecutive patients
Background: The aim of this study was to evaluate the ability of intraoperative neuromonitoring in reducing the
postoperative recurrent laryngeal nerve palsy rate by a comparison between patients submitted to thyroidectomy
with intraoperative neuromonitoring and with routine identification alone.
Methods: Between June 2007 and December 2012, 2034 consecutive patients underwent thyroidectomy by a
single surgical team. We compared patients who have had neuromonitoring and patients who have undergone
surgery with nerve visualization alone. Patients in which neuromonitoring was not utilized (Group A) were 993,
patients in which was utilized (group B) were 1041.
Results: In group A 28 recurrent laryngeal nerve injuries were observed (2.82%), 21 (2.11%) transient and 7 (0.7%)
permanent. In group B 23 recurrent laryngeal nerve injuries were observed (2.21%), in 17 cases (1.63%) transient
and in 6 (0.58%) permanent. Differences were not statistically significative.
Conclusions: Visual nerve identification remains the gold standard of recurrent laryngeal nerve management in
thyroid surgery. Neuromonitoring helps to identify the nerve, in particular in difficult cases, but it did not decrease
nerve injuries compared with visualization alone. Future studies are warranted to evaluate the benefit of intraoperative
neuromonitoring in thyroidectomy, especially in conditions in which the recurrent nerve is at high risk of injury.
Keywords: Neuromonitoring, Recurrent laryngeal nerve, Thyroidectom
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