1,161 research outputs found
Perfect preferential orientation of nitrogen-vacancy defects in a synthetic diamond sample
We show that the orientation of nitrogen-vacancy (NV) defects in diamond can
be efficiently controlled through chemical vapor deposition (CVD) growth on a
(111)-oriented diamond substrate. More precisely, we demonstrate that
spontaneously generated NV defects are oriented with a ~ 97 % probability along
the [111] axis, corresponding to the most appealing orientation among the four
possible crystallographic axes. Such a nearly perfect preferential orientation
is explained by analyzing the diamond growth mechanism on a (111)-oriented
substrate and could be extended to other types of defects. This work is a
significant step towards the design of optimized diamond samples for quantum
information and sensing applications.Comment: 6 pages, 4 figure
Factorization effects in a model of unstable particles
The effects of factorization are considered within the framework of the model
of unstable particles with a smeared mass. It is shown that two-particle cross
section and three-particle decay width can be described by the universal
factorized formulae for an unstable particles of an arbitrary spin in an
intermediate state. The exact factorization is caused by the specific structure
of the model unstable-particle propagators. This result is generalized to
complicated scattering and decay-chain processes with unstable particles in
intermediate states. We analyze applicability of the method and evaluate its
accuracy.Comment: 13 pages, 7 figure
Magnetic imaging with an ensemble of Nitrogen Vacancy centers in diamond
The nitrogen-vacancy (NV) color center in diamond is an atom-like system in
the solid-state which specific spin properties can be efficiently used as a
sensitive magnetic sensor. An external magnetic field induces Zeeman shifts of
the NV center levels which can be measured using Optically Detected Magnetic
Resonance (ODMR). In this work, we exploit the ODMR signal of an ensemble of NV
centers in order to quantitatively map the vectorial structure of a magnetic
field produced by a sample close to the surface of a CVD diamond hosting a thin
layer of NV centers. The reconstruction of the magnetic field is based on a
maximum-likelihood technique which exploits the response of the four intrinsic
orientations of the NV center inside the diamond lattice. The sensitivity
associated to a 1 {\mu}m^2 area of the doped layer, equivalent to a sensor
consisting of approximately 10^4 NV centers, is of the order of 2
{\mu}T/sqrt{Hz}. The spatial resolution of the imaging device is 400 nm,
limited by the numerical aperture of the optical microscope which is used to
collect the photoluminescence of the NV layer. The versatility of the sensor is
illustrated by the accurate reconstruction of the magnetic field created by a
DC current inside a copper wire deposited on the diamond sample.Comment: 11 pages, 5 figures, figure 4 added, results unchange
Anomalously interacting new extra vector bosons and their first LHC constraints
In this review phenomenological consequences of the Standard Model extension
by means of new spin-1 chiral fields with the internal quantum numbers of the
electroweak Higgs doublets are summarized. The prospects for resonance
production and detection of the chiral vector and bosons at
the LHC energies are considered. The boson can be observed as a
Breit-Wigner resonance peak in the invariant dilepton mass distributions in the
same way as the well-known extra gauge bosons. However, the bosons
have unique signatures in transverse momentum, angular and pseudorapidity
distributions of the final leptons, which allow one to distinguish them from
other heavy neutral resonances. In 2010, with 40 pb of the LHC
proton-proton data at the energy 7 TeV, the ATLAS detector was used to search
for narrow resonances in the invariant mass spectrum of and
final states and high-mass charged states decaying to a charged
lepton and a neutrino. No statistically significant excess above the Standard
Model expectation was observed. The exclusion mass limits of 1.15 TeV and
1.35 TeV were obtained for the chiral neutral and charged
bosons, respectively. These are the first direct limits on the and
boson production. For almost all currently considered exotic models the
relevant signal is expected in the central dijet rapidity region. On the
contrary, the chiral bosons do not contribute to this region but produce an
excess of dijet events far away from it. For these bosons the appropriate
kinematic restrictions lead to a dip in the centrality ratio distribution over
the dijet invariant mass instead of a bump expected in the most exotic models.Comment: 24 pages, 34 figure, based on talk given by V.A.Bednyakov at 15th
Lomonosov conference, 22.08.201
Study of the stability of a paramagnetic label linked to mesoporous silica surface in contact with rat mesothelial cells in culture.
Stable radicals detectable by electron paramagnetic resonance (EPR) may be use in the investigation of early events in cell-particle toxicity. Piperidine-N-oxyl derivatives (nitroxides), covalently linked to the surface of a high surface area silica (used as model solid for the technique), served as probes in the investigation of the effects of incubation of silica particles with mesothelial cells. A mesoporous silica (MCM-41), prepared by precipitation from a micellar solution, was the most appropriate silica-based particle for this purpose, as its channels allow direct contact with small molecules but not with macromolecules. The cytotoxicity of this amorphous silica is very low, allowing relatively high particle loading in the cell cultures. Both the high surface area of the sample and the large amount of inorganic material extracted from the cell culture provide enough material to run reasonably intense EPR spectra. Computer-aided analysis of the EPR spectra of silica-bound nitroxides provided information on the sensitivity of the labeled silica monitoring different environments, e.g., to follow the path of particles in a mammalian cell culture. Upon contact of the particles with mesothelial cells, the mean distance among the labels at the silica surface decreased as a consequence of the release of oxidizing and/or radical moieties from the cells
High-Energy QCD Asymptotics of Photon-Photon Collisions
The high-energy behaviour of the total cross section for highly virtual
photons, as predicted by the BFKL equation at next-to-leading order (NLO) in
QCD, is discussed. The NLO BFKL predictions, improved by the BLM optimal scale
setting, are in good agreement with recent OPAL and L3 data at CERN LEP2. NLO
BFKL predictions for future linear colliders are presented.Comment: Latex, 7 pages, 4 figure
The use of cosmic muons in detecting heterogeneities in large volumes
The muon intensity attenuation method to detect heterogeneities in large
matter volumes is analyzed. Approximate analytical expressions to estimate the
collection time and the signal to noise ratio, are proposed and validated by
Monte Carlo simulations. Important parameters, including point spread function
and coordinate reconstruction uncertainty are also estimated using Monte Carlo
simulations.Comment: 8 pages, 11 figures, submetted to NIM
Bosonic Quartic Couplings at LHC
We analyze the potential of the CERN Large Hadron Collider (LHC) to study
anomalous quartic vector-boson interactions Z Z gamma gamma, Z Z Z gamma, W+ W-
gamma gamma, and W+ W- Z gamma through the weak boson fusion processes q q -> q
q gamma gamma and q q -> q q gamma Z(-> l+ l-) with l = electron or muon. After
a careful study of the backgrounds and how to extract them from the data, we
show that the process p p -> j j gamma l+ l- is potentially the most sensitive
to deviations from the Standard Model, improving the sensitivity to anomalous
couplings by up to a factor 10^4 (10^2) with respect to the present direct
(indirect) limits.Comment: 18 pages, 2 figures, revised versio
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