4,461 research outputs found
Fluence Dependence of Charge Collection of irradiated Pixel Sensors
The barrel region of the CMS pixel detector will be equipped with ``n-in-n''
type silicon sensors. They are processed on DOFZ material, use the moderated
p-spray technique and feature a bias grid. The latter leads to a small fraction
of the pixel area to be less sensitive to particles. In order to quantify this
inefficiency prototype pixel sensors irradiated to particle fluences between
and 2.6\times 10^{15} \Neq have been bump bonded to
un-irradiated readout chips and tested using high energy pions at the H2 beam
line of the CERN SPS. The readout chip allows a non zero suppressed analogue
readout and is therefore well suited to measure the charge collection
properties of the sensors.
In this paper we discuss the fluence dependence of the collected signal and
the particle detection efficiency. Further the position dependence of the
efficiency is investigated.Comment: 11 Pages, Presented at the 5th Int. Conf. on Radiation Effects on
Semiconductor Materials Detectors and Devices, October 10-13, 2004 in
Florence, Italy, v3: more typos corrected, minor changes required by the
refere
Improved radiative corrections for (e, e'p) experiments: Beyond the peaking approximation and implications of the soft-photon approximation
Abstract.: Analyzing (e, e'p) experimental data involves corrections for radiative effects which change the interaction kinematics and which have to be carefully considered in order to obtain the desired accuracy. Missing momentum and energy due to bremsstrahlung have so far often been incorporated into the simulations and the experimental analyses using the peaking approximation. It assumes that all bremsstrahlung is emitted in the direction of the radiating particle. In this article we introduce a full angular Monte Carlo simulation method which overcomes this approximation. As a test, the angular distribution of the bremsstrahlung photons is reconstructed from H(e, e'p) data. Its width is found to be underestimated by the peaking approximation and described much better by the approach developed in this work. The impact of the soft-photon approximation on the photon angular distribution is found to be minor as compared to the impact of the peaking approximatio
Tests of silicon sensors for the CMS pixel detector
The tracking system of the CMS experiment, currently under construction at
the Large Hadron Collider (LHC) at CERN (Geneva, Switzerland), will include a
silicon pixel detector providing three spacial measurements in its final
configuration for tracks produced in high energy pp collisions. In this paper
we present the results of test beam measurements performed at CERN on
irradiated silicon pixel sensors. Lorentz angle and charge collection
efficiency were measured for two sensor designs and at various bias voltages.Comment: Talk presented at 6th International Conference on Large Scale
Applications and Radiation Hardness of Semiconductor Detectors, September
29-October 1, 2003, Firenze, Italy. Proceedings will be published in Nuclear
Instr. & Methods in Phys. Research, Section
Improved radiative corrections for (e,e'p) experiments: Beyond the peaking approximation and implications of the soft-photon approximation
Analysing (e,e'p) experimental data involves corrections for radiative
effects which change the interaction kinematics and which have to be carefully
considered in order to obtain the desired accuracy. Missing momentum and energy
due to bremsstrahlung have so far always been calculated using the peaking
approximation which assumes that all bremsstrahlung is emitted in the direction
of the radiating particle. In this article we introduce a full angular Monte
Carlo simulation method which overcomes this approximation. The angular
distribution of the bremsstrahlung photons is reconstructed from H(e,e'p) data.
Its width is found to be underestimated by the peaking approximation and
described much better by the approach developed in this work.Comment: 11 pages, 13 figure
Position Dependence of Charge Collection in Prototype Sensors for the CMS Pixel Detector
This paper reports on the sensor R&D activity for the CMS pixel detector.
Devices featuring several design and technology options have been irradiated up
to a proton fluencec of 1E15 n_eq/cm**2 at the CERN PS. Afterward they were
bump bonded to unirradiated readout chips and tested using high energy pions in
the H2 beam line of the CERN SPS. The readout chip allows a non zero suppressed
full analogue readout and therefore a good characterization of the sensors in
terms of noise and charge collection properties. The position dependence of
signal is presented and the differences between the two sensor options are
discussed.Comment: Contribution to the IEEE-NSS Oct. 2003, Portland, OR, USA, submitted
to IEEE-TNS 7 pages, 8 figures, 1 table. Revised, title change
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.
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
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
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
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