26,235 research outputs found
QCD description of backward vector meson hard electroproduction
We consider backward vector meson exclusive electroproduction off nucleons in
the framework of collinear QCD factorization. Nucleon to vector meson
transition distribution amplitudes arise as building blocks for the
corresponding factorized amplitudes. In the near-backward kinematics, the
suggested factorization mechanism results in the dominance of the transverse
cross section of vector meson production () and in the
characteristic -scaling behavior of the cross section. We evaluate
nucleon to vector meson TDAs in the cross-channel nucleon exchange model and
present estimates of the differential cross section for backward ,
and meson production off protons. The resulting cross sections
are shown to be measurable in the forthcoming JLab@12 GeV experiments.Comment: 37 pages, 8 figures, 1 tabl
Nucleon-to-pion transition distribution amplitudes and backward electroproduction of pions
Baryon to meson transition distribution amplitudes (TDAs), non-diagonal
matrix elements of the nonlocal three quark operator between a nucleon and a
meson state, extend the concept of generalized parton distributions. These
non-perturbative objects which encode the information on three quark
correlations inside the nucleon may be accessed experimentally in backward
meson electroproduction reactions. We suggest a general framework for modelling
nucleon to pion (pi N) TDAs employing the spectral representation for pi N TDAs
in terms of quadruple distributions. The factorized Ansatz for quadruple
distributions with input from the soft-pion theorem for pi N TDAs is proposed.
It is to be complemented with a D-term like contribution from the nucleon
exchange in the cross channel.
We present our estimates of the unpolarized cross section and of the
transverse target single spin asymmetry for backward pion electroproduction
within the QCD collinear factorization approach in which the non-perturbative
part of the amplitude involves pi N TDAs. The cross section is sizable enough
to be studied in high luminosity experiments such as J-lab@12GeV and EIC.Comment: proceedings of QNP 2012, Sixth International Conference on Quarks and
Nuclear Physics, April 16-20, 2012, Ecole Polytechnique, Palaiseau, Franc
Schroedinger Cat States of a Nanomechanical Resonator
We present a scheme of generating large-amplitude Schr\"{o}dinger cat states
and entanglement in a coupled system of nanomechanical resonator and single
Cooper pair box (SCPB), without being limited by the magnitude of the coupling.
It is shown that the entanglement between the resonator and the SCPB can be
detected by a spectroscopic method.Comment: 1 figur
Crossed channel analysis of quark and gluon generalized parton distributions with helicity flip
Quark and gluon helicity flip generalized parton distributions (GPDs) address
the transversity quark and gluon structure of the nucleon. In order to
construct a theoretically consistent parametrization of these hadronic matrix
elements, we work out the set of combinations of those GPDs suitable for the
partial wave (PW) expansion in the cross-channel. This universal
result will help to build up a flexible parametrization of these important
hadronic non-perturbative quantities, using for instance the approaches based
on the conformal PW expansion of GPDs such as the Mellin-Barnes integral or the
dual parametrization techniques.Comment: 34 pages, 1 figure, 4 table
Exploring the nucleon structure through GPDs and TDAs in hard exclusive processes
Generalized Parton Distributions (GPDs) offer a new way to access the quark
and gluon nucleon structure. We review recent progress in this domain,
emphasizing the need to supplement the experimental study of deeply virtual
Compton scattering by its crossed version, timelike Compton scattering. We also
describe the extension of the GPD concept to three quark operators and the
relevance of their nucleon to meson matrix elements, namely the transition
distribution amplitudes (TDAs) which factorize in backward meson
electroproduction and related processes. We discuss the main properties of the
TDAs. \Comment: 8 pages; to be published in the proceedings of the conference "PHOTON
2011, International Conference on the Structure and the Interactions of the
Photon ", Spa, Belgium, 22-27 Mai 201
Toward modelization of quark and gluon transversity generalized parton distributions
Quark and gluon helicity flip generalized parton distributions (GPDs) encode
the information on the nucleon structure in the transversity sector. In order
to build a theoretically consistent phenomenological parametrization for these
hadronic matrix element within the framework of the dual parametrization of
GPDs (or with the equivalent approach of the SO(3) partial waves (PW) expansion
with the Mellin-Barnes integral techniques) we establish the set of
combinations of parton helicity flip GPDs suitable for the expansion in the
cross channel SO(3) PWs.Comment: 6 pages, DIS 2014, XXII. International Workshop on Deep-Inelastic
Scattering and Related Subjects, 28 April - 2 May 2014, Warsaw, Polan
Feedback local optimality principle applied to rocket vertical landing VTVL
Vertical landing is becoming popular in the last fifteen years, a technology known under the acronym VTVL, Vertical Takeoff and Vertical Landing [1,2]. The interest in such landing technology is dictated by possible cost reductions [3,4], that impose spaceship’s recycling. The rockets are not generally de- signed to perform landing operations, rather their design is aimed at takeoff operations, guaranteeing a very high forward acceleration to gain the velocity needed to escape the gravitational force. In this paper a new control method based on Feedback Local Optimality Principle, named FLOP is applied to the rocket landing problem. The FLOP belongs to a special class of optimal controllers, developed by the mechatronic and vehicle dynamics lab of Sapienza, named Variational Feedback Controllers - VFC, that are part of an ongoing research and are recently applied in different field: nonlinear system [5], marine and terrestrial autonomous vehicles [6,7,8], multi agents interactions and vibration control [9, 10]. The paper is devoted to show the robustness of the nonlinear controlled system, comparing the performances with the LQR, one of the most acknowledged methods in optimal control
New results in exclusive hard reactions
Generalized Parton Distributions offer a new way to access the quark and
gluon nucleon structure. We review recent progress in this domain, emphasizing
the need to supplement the experimental study of DVCS by its crossed version,
timelike Compton scattering (TCS), where data at high energy should appear
thanks to the study of ultraperipheral collisions at the LHC. This will open
the access to very low skewness quark and gluon GPDs. Our leading order
estimates show that the factorization scale dependence of the amplitudes is
quite high. This fact demands the understanding of higher order contributions
with the hope that they will stabilize this scale dependence. The magnitudes of
the NLO coefficient functions are not small and neither is the difference of
the coefficient functions appearing respectively in the DVCS and TCS
amplitudes. The conclusion is that extracting the universal GPDs from both TCS
and DVCS reactions requires much care. We also describe the extension of the
GPD concept to three quark operators and the relevance of their nucleon to
meson matrix elements, namely the transition distribution amplitudes (TDAs)
which factorize in hard exclusive pion electroproduction off a nucleon in the
backward region and baryon-antibaryon annihilation into a pion and a lepton
pair. We discuss the main properties of the TDAs.Comment: 4 pages, to be published in the proceedings of the 2011 Europhysics
Conference on High Energy Physics-HEP 2011, July 21-27, 2011, Grenoble,
Rhone-Alpes, Franc
Multiphoton Coincidence Spectroscopy
We extend the analysis of photon coincidence spectroscopy beyond bichromatic
excitation and two-photon coincidence detection to include multichromatic
excitation and multiphoton coincidence detection. Trichromatic excitation and
three-photon coincidence spectroscopy are studied in detail, and we identify an
observable signature of a triple resonance in an atom-cavity system.Comment: 6 page, REVTeXs, 6 Postscript figures. The abstract appeared in the
Proceedings of ACOLS9
An adaptive dwell time scheduling model for phased array radar based on three-way decision
Real-time resource allocation is crucial for phased array radars to undertake multi-task with limited resources such as in the situation of multi-target tracking, in which targets need to be prioritized so that resources can be allocated accordingly and effectively. In this paper, a three-way decision-based model is proposed for adaptive scheduling of phased radar dwell time. Using the model, the threat posed by a target is measured by an evaluation function, and therefore, a target is assigned to one of the three possible decision regions, i.e., positive region, negative region, and boundary region. A different region has a various priority in terms of resource demand, and as such, a different radar resource allocation decision is applied to each region to satisfy different tracking accuracy of multi-target. In addition, the dwell time scheduling model can be further optimized by implementing a strategy for determining a proper threshold of three-way decision making to optimize the thresholds adaptively in real-time. The advantages and the performance of the proposed model has been verified by experimental simulations with comparison to the traditional two-way decision model and the three-way decision model without threshold optimization. The experiential results have demonstrated that the performance of the proposed model has a certain advantage in detecting high threat targets.
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