3,809 research outputs found
Positronium signature in organic liquid scintillators for neutrino experiments
Electron anti-neutrinos are commonly detected in liquid scintillator
experiments via inverse beta decay, by looking at the coincidence between the
reaction products, neutron and positron. Prior to positron annihilation, an
electron-positron pair may form an orthopositronium (o-Ps) state, with a mean
life of a few ns. Even if the o-Ps decay is speeded up by spin flip or pick off
effects, it may introduce distortions in the photon emission time distribution,
crucial for position reconstruction and pulse shape discrimination algorithms
in anti-neutrino experiments. Reversing the problem, the o-Ps induced time
distortion represents a new signature for tagging anti-neutrinos in liquid
scintillator.
In this paper, we report the results of measurements of the o-Ps formation
probability and lifetime, for the most used solvents for organic liquid
scintillators in neutrino physics (pseudocumene, linear alkyl benzene,
phenylxylylethane, and dodecane). We characterize also a mixture of
pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength
shifter.
In the second part of the paper, we demonstrate that the o-Ps induced
distortion of the scintillation photon emission time distributions represent an
optimal signature for tagging positrons on an event by event basis, potentially
enhancing the anti-neutrino detection.Comment: 6 pages, 9 figure
The Timing Counter of the MEG experiment: calibration and performance
The MEG detector is designed to test Lepton Flavor Violation in the
decay down to a Branching Ratio of a few
. The decay topology consists in the coincident emission of a
monochromatic photon in direction opposite to a monochromatic positron. A
precise measurement of the relative time is crucial to suppress
the background. The Timing Counter (TC) is designed to precisely measure the
time of arrival of the and to provide information to the trigger system.
It consists of two sectors up and down stream the decay target, each consisting
of two layers. The outer one made of scintillating bars and the inner one of
scintillating fibers. Their design criteria and performances are described.Comment: Presented at the 12th Topical Seminar on Innovative Particle and
Radiation Detectors (IPRD10) 7 - 10 June 2010, Siena. Accepted by Nuclear
Physics B (Proceedings Supplements) (2011)tal
Design and test of an extremely high resolution Timing Counter for the MEG II experiment: preliminary results
The design and tests of Timing Counter elements for the upgrade of the MEG
experiment, MEG II,is presented. The detector is based on several small plates
of scintillator with a Silicon PhotoMultipliers dual-side readout. The
optimisation of the single counter elements (SiPMs, scintillators, geometry) is
described. Moreover, the results obtained with a first prototype tested at the
Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati (LNF) are
presented.Comment: 10 pages, 7 figures. Presented at the 13th Topical Seminar on
Innovative Particle and Radiation Detectors (IPRD13) 7-10 October 2013 Siena,
Ital
Impact of Drag Reduction Control on Energy Box of a Fully Developed Turbulent Channel Flow
We introduce the Constant Power Input (CPI) concept to clarify how a drag reduction control a ects energy budget of a fully developed turbulent channel ows. The entire kinetic energy is decomposed into the mean and uctuating components, and the total dissipation is accordingly divided into the dissipation of the mean led and the turbulent dissipation. The CPI condition is essential in the present study, since it strictly restricts the amount of power applied to the ow system. This allows us to identify how each ow control strategy changes the energy ows between each component and the viscous dissipation. Ultimately, if we succeed in suppressing all turbulence, the turbulent dissipation should vanish and the power applied to the ow system should be dissipated only by the dissipation of the mean velocity, which should have a parabolic pro le. Our fundamental question in the present study is whether there exists unique relationship between the changes in the turbulent dissipation and the resultant drag reduction e ect. In order to provide the de nite an- swer to this question, we introduce triple decomposition of the velocity eld, and validate our approach by considering two di erent ow control strategies
Detection of sub-shot-noise spatial correlation in high-gain parametric down-conversion
Using a 1GW-1ps pump laser pulse in high gain parametric down-conversion
allows us to detect sub-shot-noise spatial quantum correlation with up to one
hundred photoelectrons per mode, by means of a high efficiency CCD. The
statistics is performed in single-shot over independent spatial replica of the
system. The paper highlights the evidence of quantum correlation between
symmetrical signal and idler spatial areas in the far field, in the high gain
regime. In accordance with the predictions of numerical calculations the
observed transition from the quantum to the classical regime is interpreted as
a consequence of the narrowing of the down-converted beams in the very high
gain regime.Comment: 4,2 pages, 4 figure
Acceleration with Self-Injection for an All-Optical Radiation Source at LNF
We discuss a new compact gamma-ray source aiming at high spectral density, up
to two orders of magnitude higher than currently available bremsstrahlung
sources, and conceptually similar to Compton Sources based on conventional
linear accelerators. This new source exploits electron bunches from
laser-driven electron acceleration in the so-called self-injection scheme and
uses a counter-propagating laser pulse to obtain X and gamma-ray emission via
Thomson/Compton scattering. The proposed experimental configuration inherently
provides a unique test-bed for studies of fundamental open issues of
electrodynamics. In view of this, a preliminary discussion of recent results on
self-injection with the FLAME laser is also given.Comment: 8 pages, 10 figures, 44 references - Channeling 2012 conferenc
Polarization quantum properties in type-II Optical Parametric Oscillator below threshold
We study the far field spatial distribution of the quantum fluctuations in
the transverse profile of the output light beam generated by a type II Optical
Parametric Oscillator below threshold, including the effects of transverse
walk-off. We study how quadrature field correlations depend on the
polarization. We find spatial EPR entanglement in quadrature-polarization
components: For the far field points not affected by walk-off there is almost
complete noise suppression in the proper quadratures difference of any
orthogonal polarization components. We show the entanglement of the state of
symmetric intense, or macroscopic, spatial light modes. We also investigate
nonclassical polarization properties in terms of the Stokes operators. We find
perfect correlations in all Stokes parameters measured in opposite far field
points in the direction orthogonal to the walk-off, while locally the field is
unpolarized and we find no polarization squeezing.Comment: 16 pages, 18 figure
Spatial correlations in hexagons generated via a Kerr nonlinearity
We consider the hexagonal pattern forming in the cross-section of an optical
beam produced by a Kerr cavity, and we study the quantum correlations
characterizing this structure. By using arguments related to the symmetry
broken by the pattern formation, we identify a complete scenario of six-mode
entanglement. Five independent phase quadratures combinations, connecting the
hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of
a non-linear quantum calculation technique, quantum correlations among the mode
photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure
Multimode Squeezing Properties of a Confocal Opo: Beyond the Thin Crystal Approximation
Up to now, transverse quantum effects (usually labelled as "quantum imaging"
effects) which are generated by nonlinear devices inserted in resonant optical
cavities have been calculated using the "thin crystal approximation", i.e.
taking into account the effect of diffraction only inside the empty part of the
cavity, and neglecting its effect in the nonlinear propagation inside the
nonlinear crystal. We introduce in the present paper a theoretical method which
is not restricted by this approximation. It allows us in particular to treat
configurations closer to the actual experimental ones, where the crystal length
is comparable to the Rayleigh length of the cavity mode. We use this method in
the case of the confocal OPO, where the thin crystal approximation predicts
perfect squeezing on any area of the transverse plane, whatever its size and
shape. We find that there exists in this case a "coherence length" which gives
the minimum size of a detector on which perfect squeezing can be observed, and
which gives therefore a limit to the improvement of optical resolution that can
be obtained using such devices.Comment: soumis le 04.03.2005 a PR
- …