187 research outputs found
Observation of ÏK -atoms with DIRAC-II
We present evidence for the first observation of electromagnetically bound Ï Â± K âââ-pairs (ÏK-atoms) with the DIRAC-II experiment at the CERN-PS. The ÏK-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the dissociated Ï Â± and K âââ-mesons analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173±54 ÏK-atoms. The mean life of ÏK-atoms is related to the s-wave ÏK-scattering lengths. From these first data we derive a lower limit for the mean life of 1.5fs at 84% confidence leve
Scintillation efficiency of liquid argon in low energy neutron-argon scattering
Experiments searching for weak interacting massive particles with noble gases
such as liquid argon require very low detection thresholds for nuclear recoils.
A determination of the scintillation efficiency is crucial to quantify the
response of the detector at low energy. We report the results obtained with a
small liquid argon cell using a monoenergetic neutron beam produced by a
deuterium-deuterium fusion source. The light yield relative to electrons was
measured for six argon recoil energies between 11 and 120 keV at zero electric
drift field.Comment: 21 pages, 19 figures, 4 table
Extraction of electric field in heavily irradiated silicon pixel sensors
A new method for the extraction of the electric field in the bulk of heavily
irradiated silicon pixel sensors is presented. It is based on the measurement
of the Lorentz deflection and mobility of electrons as a function of depth. The
measurements were made at the CERN H2 beam line, with the beam at a shallow
angle with respect to the pixel sensor surface. The extracted electric field is
used to simulate the charge collection and the Lorentz deflection in the pixel
sensor. The simulated charge collection and the Lorentz deflection is in good
agreement with the measurements both for non-irradiated and irradiated up to
1E15 neq/cm2 sensors.Comment: 6 pages, 11 figures, presented at the 13th International Workshop on
Vertex Detectors for High Energy Physics, September 13-18, 2004,
Menaggio-Como, Italy. Submitted to Nucl. Instr. Meth.
Simulation of Heavily Irradiated Silicon Pixel Detectors
We show that doubly peaked electric fields are necessary to describe
grazing-angle charge collection measurements of irradiated silicon pixel
sensors. A model of irradiated silicon based upon two defect levels with
opposite charge states and the trapping of charge carriers can be tuned to
produce a good description of the measured charge collection profiles in the
fluence range from 0.5x10^{14} Neq/cm^2 to 5.9x10^{14} Neq/cm^2. The model
correctly predicts the variation in the profiles as the temperature is changed
from -10C to -25C. The measured charge collection profiles are inconsistent
with the linearly-varying electric fields predicted by the usual description
based upon a uniform effective doping density. This observation calls into
question the practice of using effective doping densities to characterize
irradiated silicon. The model is now being used to calibrate pixel hit
reconstruction algorithms for CMS.Comment: Invited talk at International Symposium on the Development of
Detectors for Particle, AstroParticle and Synchrtron Radiation Experiments,
Stanford Ca (SNIC06) 8 pages, LaTeX, 11 eps figure
A double junction model of irradiated silicon pixel sensors for LHC
In this paper we discuss the measurement of charge collection in irradiated
silicon pixel sensors and the comparison with a detailed simulation. The
simulation implements a model of radiation damage by including two defect
levels with opposite charge states and trapping of charge carriers. The
modeling proves that a doubly peaked electric field generated by the two defect
levels is necessary to describe the data and excludes a description based on
acceptor defects uniformly distributed across the sensor bulk. In addition, the
dependence of trap concentrations upon fluence is established by comparing the
measured and simulated profiles at several fluences and bias voltages.Comment: Talk presented at the 10th European Symposium on Semiconductor
Detectors, June 12-16 2005, Wildbad Kreuth, Germany. 9 pages, 4 figure
Observation, modeling, and temperature dependence of doubly peaked electric fields in irradiated silicon pixel sensors
We show that doubly peaked electric fields are necessary to describe
grazing-angle charge collection measurements of irradiated silicon pixel
sensors. A model of irradiated silicon based upon two defect levels with
opposite charge states and the trapping of charge carriers can be tuned to
produce a good description of the measured charge collection profiles in the
fluence range from 0.5x10^{14} Neq/cm^2 to 5.9x10^{14} Neq/cm^2. The model
correctly predicts the variation in the profiles as the temperature is changed
from -10C to -25C. The measured charge collection profiles are inconsistent
with the linearly-varying electric fields predicted by the usual description
based upon a uniform effective doping density. This observation calls into
question the practice of using effective doping densities to characterize
irradiated silicon.Comment: 8 pages, LaTeX document, 10 figures. Presented at Pixel 2005
Workshop, Bonn, Sept 2005. Small cosmetic revisions in response to referee
comments and to fix broken reference link
Study of nuclear recoils in liquid argon with monoenergetic neutrons
For the development of liquid argon dark matter detectors we assembled a
setup in the laboratory to scatter neutrons on a small liquid argon target. The
neutrons are produced mono-energetically (E_kin=2.45 MeV) by nuclear fusion in
a deuterium plasma and are collimated onto a 3" liquid argon cell operating in
single-phase mode (zero electric field). Organic liquid scintillators are used
to tag scattered neutrons and to provide a time-of-flight measurement. The
setup is designed to study light pulse shapes and scintillation yields from
nuclear and electronic recoils as well as from {\alpha}-particles at working
points relevant to dark matter searches. Liquid argon offers the possibility to
scrutinise scintillation yields in noble liquids with respect to the
populations of the two fundamental excimer states. Here we present experimental
methods and first results from recent data towards such studies.Comment: 9 pages, 8 figures, proceedings of TAUP 2011, to be published in
Journal of Physics: Conference Series (JCPS
A New Approach to Background Subtraction in Low-Energy Neutrino Experiments
We discuss a new method to extract neutrino signals in low energy
experiments. In this scheme the symmetric nature of most backgrounds allows for
direct cancellation from data. The application of this technique to the Palo
Verde reactor neutrino oscillation experiment allowed us to reduce the
measurement errors on the anti-neutrino flux from % to %. We
expect this method to substantially improve the data quality in future low
background experiments such as KamLAND and LENS.Comment: 7 pages, 2 figure
Predicting Neutron Production from Cosmic-ray Muons
Fast neutrons from cosmic-ray muons are an important background to
underground low energy experiments. The estimate of such background is often
hampered by the difficulty of measuring and calculating neutron production with
sufficient accuracy. Indeed substantial disagreement exists between the
different analytical calculations performed so far, while data reported by
different experiments is not always consistent. We discuss a new unified
approach to estimate the neutron yield, the energy spectrum, the multiplicity
and the angular distribution from cosmic muons using the Monte Carlo simulation
package FLUKA and show that it gives a good description of most of the existing
measurements once the appropriate corrections have been applied.Comment: 8 pages, 7 figure
Precise Measurements of Atmospheric Muon Fluxes with the BESS Spectrometer
The vertical absolute fluxes of atmospheric muons and muon charge ratio have
been measured precisely at different geomagnetic locations by using the BESS
spectrometer. The observations had been performed at sea level (30 m above sea
level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada.
The vertical cutoff rigidities in Tsukuba (36.2 N, 140.1 E) and in Lynn Lake
(56.5 N, 101.0 W) are 11.4 GV and 0.4 GV, respectively. We have obtained
vertical fluxes of positive and negative muons in a momentum range from 0.6 to
20 GeV/c with systematic errors less than 3 % in both measurements. By
comparing the data collected at two different geomagnetic latitudes, we have
seen an effect of cutoff rigidity. The dependence on the atmospheric pressure
and temperature, and the solar modulation effect have been also clearly
observed. We also clearly observed the decrease of charge ratio of muons at low
momentum side with at higher cutoff rigidity region.Comment: 35 pages, 9 figures. Submitted to Astroparticle Physic
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