11,908 research outputs found
Time dependent Bs mixing from lepton-kaon correlations with the ALEPH detector
Searches for oscillations were made using data taken with the ALEPH detector in the years 1991--1994. Inclusive methods use leptons to tag the state at decay and to reconstruct the decay time. The state at production time is tagged either with a second lepton in the opposite hemisphere or a jet-charge algorithm. Also kaons from the fragmentation process were used to determine the initial state. Exclusive methods use or -lepton events to reconstruct the at decay time. The initial state is inferred using leptons, jet charge or fragmentation kaons. No oscillations are observed and lower limits for the mass difference are obtained. A combined limit will be presented taking the correlations between the different analyses into account
Heavily Irradiated N-in-p Thin Planar Pixel Sensors with and without Active Edges
We present the results of the characterization of silicon pixel modules
employing n-in-p planar sensors with an active thickness of 150
m, produced at MPP/HLL, and 100-200 m thin active
edge sensor devices, produced at VTT in Finland. These thin sensors are
designed as candidates for the ATLAS pixel detector upgrade to be operated at
the HL-LHC, as they ensure radiation hardness at high fluences. They are
interconnected to the ATLAS FE-I3 and FE-I4 read-out chips. Moreover, the
n-in-p technology only requires a single side processing and thereby it is a
cost-effective alternative to the n-in-n pixel technology presently employed in
the LHC experiments. High precision beam test measurements of the hit
efficiency have been performed on these devices both at the CERN SpS and at
DESY, Hamburg. We studied the behavior of these sensors at different bias
voltages and different beam incident angles up to the maximum one expected for
the new Insertable B-Layer of ATLAS and for HL-LHC detectors. Results obtained
with 150 m thin sensors, assembled with the new ATLAS FE-I4 chip
and irradiated up to a fluence of
410, show that they are
excellent candidates for larger radii of the silicon pixel tracker in the
upgrade of the ATLAS detector at HL-LHC. In addition, the active edge
technology of the VTT devices maximizes the active area of the sensor and
reduces the material budget to suit the requirements for the innermost layers.
The edge pixel performance of VTT modules has been investigated at beam test
experiments and the analysis after irradiation up to a fluence of
510 has been performed
using radioactive sources in the laboratory.Comment: Proceedings for iWoRiD 2013 conference, submitted to JINS
Production and Characterisation of SLID Interconnected n-in-p Pixel Modules with 75 Micrometer Thin Silicon Sensors
The performance of pixel modules built from 75 micrometer thin silicon
sensors and ATLAS read-out chips employing the Solid Liquid InterDiffusion
(SLID) interconnection technology is presented. This technology, developed by
the Fraunhofer EMFT, is a possible alternative to the standard bump-bonding. It
allows for stacking of different interconnected chip and sensor layers without
destroying the already formed bonds. In combination with Inter-Chip-Vias (ICVs)
this paves the way for vertical integration. Both technologies are combined in
a pixel module concept which is the basis for the modules discussed in this
paper.
Mechanical and electrical parameters of pixel modules employing both SLID
interconnections and sensors of 75 micrometer thickness are covered. The
mechanical features discussed include the interconnection efficiency, alignment
precision and mechanical strength. The electrical properties comprise the
leakage currents, tuning characteristics, charge collection, cluster sizes and
hit efficiencies. Targeting at a usage at the high luminosity upgrade of the
LHC accelerator called HL-LHC, the results were obtained before and after
irradiation up to fluences of
(1 MeV neutrons).Comment: 16 pages, 22 figure
Thin n-in-p pixel sensors and the SLID-ICV vertical integration technology for the ATLAS upgrade at the HL-LHC
The R&D activity presented is focused on the development of new modules for
the upgrade of the ATLAS pixel system at the High Luminosity LHC (HL-LHC). The
performance after irradiation of n-in-p pixel sensors of different active
thicknesses is studied, together with an investigation of a novel
interconnection technique offered by the Fraunhofer Institute EMFT in Munich,
the Solid-Liquid-InterDiffusion (SLID), which is an alternative to the standard
solder bump-bonding. The pixel modules are based on thin n-in-p sensors, with
an active thickness of 75 um or 150 um, produced at the MPI Semiconductor
Laboratory (MPI HLL) and on 100 um thick sensors with active edges, fabricated
at VTT, Finland. Hit efficiencies are derived from beam test data for thin
devices irradiated up to a fluence of 4e15 neq/cm^2. For the active edge
devices, the charge collection properties of the edge pixels before irradiation
is discussed in detail, with respect to the inner ones, using measurements with
radioactive sources. Beyond the active edge sensors, an additional ingredient
needed to design four side buttable modules is the possibility of moving the
wire bonding area from the chip surface facing the sensor to the backside,
avoiding the implementation of the cantilever extruding beyond the sensor area.
The feasibility of this process is under investigation with the FE-I3 SLID
modules, where Inter Chip Vias are etched, employing an EMFT technology, with a
cross section of 3 um x 10 um, at the positions of the original wire bonding
pads.Comment: Proceedings for Pixel 2012 Conference, submitted to NIM A, 6 page
Energetics of positron states trapped at vacancies in solids
We report a computational first-principles study of positron trapping at
vacancy defects in metals and semiconductors. The main emphasis is on the
energetics of the trapping process including the interplay between the positron
state and the defect's ionic structure and on the ensuing annihilation
characteristics of the trapped state. For vacancies in covalent semiconductors
the ion relaxation is a crucial part of the positron trapping process enabling
the localization of the positron state. However, positron trapping does not
strongly affect the characteristic features of the electronic structure, e.g.,
the ionization levels change only moderately. Also in the case of metal
vacancies the positron-induced ion relaxation has a noticeable effect on the
calculated positron lifetime and momentum distribution of annihilating
electron-positron pairs.Comment: Submitted to Physical Review B on 17 April 2007. Revised version
submitted on 6 July 200
Spacetime Encodings II - Pictures of Integrability
I visually explore the features of geodesic orbits in arbitrary stationary
axisymmetric vacuum (SAV) spacetimes that are constructed from a complex Ernst
potential. Some of the geometric features of integrable and chaotic orbits are
highlighted. The geodesic problem for these SAV spacetimes is rewritten as a
two degree of freedom problem and the connection between current ideas in
dynamical systems and the study of two manifolds sought. The relationship
between the Hamilton-Jacobi equations, canonical transformations, constants of
motion and Killing tensors are commented on. Wherever possible I illustrate the
concepts by means of examples from general relativity. This investigation is
designed to build the readers' intuition about how integrability arises, and to
summarize some of the known facts about two degree of freedom systems. Evidence
is given, in the form of orbit-crossing structure, that geodesics in SAV
spacetimes might admit, a fourth constant of motion that is quartic in momentum
(by contrast with Kerr spacetime, where Carter's fourth constant is quadratic).Comment: 11 pages, 10 figure
Grover's Quantum Search Algorithm and Diophantine Approximation
In a fundamental paper [Phys. Rev. Lett. 78, 325 (1997)] Grover showed how a
quantum computer can find a single marked object in a database of size N by
using only O(N^{1/2}) queries of the oracle that identifies the object. His
result was generalized to the case of finding one object in a subset of marked
elements. We consider the following computational problem: A subset of marked
elements is given whose number of elements is either M or K, M<K, our task is
to determine which is the case. We show how to solve this problem with a high
probability of success using only iterations of Grover's basic step (and no
other algorithm). Let m be the required number of iterations; we prove that
under certain restrictions on the sizes of M and K the estimation m <
(2N^{1/2})/(K^{1/2}-M^{1/2}) obtains. This bound sharpens previous results and
is known to be optimal up to a constant factor. Our method involves
simultaneous Diophantine approximations, so that Grover's algorithm is
conceptualized as an orbit of an ergodic automorphism of the torus. We comment
on situations where the algorithm may be slow, and note the similarity between
these cases and the problem of small divisors in classical mechanics.Comment: 8 pages, revtex, Title change
Effects of noise on hysteresis and resonance width in graphene and nanotubes resonators
We investigate the role that noise plays in the hysteretic dynamics of a
suspended nanotube or a graphene sheet subject to an oscillating force. We find
that not only the size but also the position of the hysteresis region in these
systems can be controlled by noise. We also find that nano-resonators act as
noise rectifiers: by increasing the noise in the setup, the resonance width of
the characteristic peak in these systems is reduced and, as a result, the
quality factor is increased.Comment: 15 pages, 6 figures. Sent to PRB (in revision
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