arXiv subjects

J. A. Wilson

Publications and source records attributed to J. A. Wilson.

9 recordsLinked to original sources

arXiv2011

Design and performance of a CMOS study sensor for a binary readout electromagnetic calorimeter

We present a study of a CMOS test sensor which has been designed, fabricated and characterised to investigate the parameters required for a binary readout electromagnetic calorimeter. The sensors were fabricated with several enhancements in addition to standard CMOS processing. Detailed simulations and experimental results of the performance of the sensor are presented. The sensor and pixels are shown to behave in accordance with expectations and the processing enhancements are found to be essential to achieve the performance required.

physics.ins-det↗

arXiv2010

Study of the interactions of pions in the CALICE silicon-tungsten calorimeter prototype

A prototype silicon-tungsten electromagnetic calorimeter for an ILC detector was tested in 2007 at the CERN SPS test beam. Data were collected with electron and hadron beams in the energy range 8 to 80 GeV. The analysis described here focuses on the interactions of pions in the calorimeter. One of the main objectives of the CALICE program is to validate the Monte Carlo tools available for the design of a full-sized detector. The interactions of pions in the Si-W calorimeter are therefore confronted with the predictions of various physical models implemented in the GEANT4 simulation framework.

physics.ins-det↗

arXiv2010

Construction and Commissioning of the CALICE Analog Hadron Calorimeter Prototype

An analog hadron calorimeter (AHCAL) prototype of 5.3 nuclear interaction lengths thickness has been constructed by members of the CALICE Collaboration. The AHCAL prototype consists of a 38-layer sandwich structure of steel plates and highly-segmented scintillator tiles that are read out by wavelength-shifting fibers coupled to SiPMs. The signal is amplified and shaped with a custom-designed ASIC. A calibration/monitoring system based on LED light was developed to monitor the SiPM gain and to measure the full SiPM response curve in order to correct for non-linearity. Ultimately, the physics goals are the study of hadron shower shapes and testing the concept of particle flow. The technical goal consists of measuring the performance and reliability of 7608 SiPMs. The AHCAL was commissioned in test beams at DESY and CERN. The entire prototype was completed in 2007 and recorded hadron showers, electron showers and muons at different energies and incident angles in test beams at CERN and Fermilab.

physics.ins-det↗

arXiv2009

A digital ECAL based on MAPS

Progress is reported on the development and testing of Monolithic Active Pixel Sensors (MAPS) for a Si-W ECAL for the ILC. Using laser and source setups, a first version of the sensor has been characterised through measurements of the absolute gain calibration, noise and pedestal. The pixel-to-pixel gain spread is 10%. Charge diffusion has been measured and found to be compatible with simulation results. The charge collected by a single pixel varies from 50% to 20% depending on where it is generated. After adding detector effects to the Geant4 simulation of an ILC-like ECAL, using the measured parameters, the energy resolution is found to be 35% higher than the ideal resolution, but is still lower than the resolution obtained for an equivalent analogue ECAL.

physics.ins-det↗

arXiv2008

Design and Electronics Commissioning of the Physics Prototype of a Si-W Electromagnetic Calorimeter for the International Linear Collider

The CALICE collaboration is studying the design of high performance electromagnetic and hadronic calorimeters for future International Linear Collider detectors. For the electromagnetic calorimeter, the current baseline choice is a high granularity sampling calorimeter with tungsten as absorber and silicon detectors as sensitive material. A ``physics prototype'' has been constructed, consisting of thirty sensitive layers. Each layer has an active area of 18x18 cm2 and a pad size of 1x1 cm2. The absorber thickness totals 24 radiation lengths. It has been exposed in 2006 and 2007 to electron and hadron beams at the DESY and CERN beam test facilities, using a wide range of beam energies and incidence angles. In this paper, the prototype and the data acquisition chain are described and a summary of the data taken in the 2006 beam tests is presented. The methods used to subtract the pedestals and calibrate the detector are detailed. The signal-over-noise ratio has been measured at 7.63 +/- 0.01. Some electronics features have been observed; these lead to coherent noise and crosstalk between pads, and also crosstalk between sensitive and passive areas. The performance achieved in terms of uniformity and stability is presented.

physics.ins-det↗

arXiv2008

Monolithic Active Pixel Sensors (MAPS) in a quadruple well technology for nearly 100% fill factor and full CMOS pixels

In this paper we present a novel, quadruple well process developed in a modern 0.18mu CMOS technology called INMAPS. On top of the standard process, we have added a deep P implant that can be used to form a deep P-well and provide screening of N-wells from the P-doped epitaxial layer. This prevents the collection of radiation-induced charge by unrelated N-wells, typically ones where PMOS transistors are integrated. The design of a sensor specifically tailored to a particle physics experiment is presented, where each 50mu pixel has over 150 PMOS and NMOS transistors. The sensor has been fabricated in the INMAPS process and first experimental evidence of the effectiveness of this process on charge collection is presented, showing a significant improvement in efficiency.

physics.ins-det↗

arXiv2007

A MAPS-based Digital Electromagnetic Calorimeter for the ILC

A novel design for a silicon-tungsten electromagnetic calorimeter is described, based on Monolithic Active Pixel Sensors (MAPS). A test sensor with a pixel size of 50x50 um2 has been fabricated in July 2007. The simulation of the physical sensor is done using a detailed three-dimensional charge spread algorithm. Physics studies of the sensor are done including a digitisation algorithm taking into account the charge sharing, charge collection efficiency, noise, and dead areas. The influence of the charge sharing effect is found to be important and hence needs to be measured precisely.

physics.ins-det↗

arXiv2006

Examination of the claim by Loram and Tallon that the energy-resolved STM results, in their apparent inhomogeneity, misrepresent the true bulk behaviour of the HTSC cuprates

An attempt is made at reconciling the results of the prime experiments on the high temperature superconducting cuprates from Loram et al. and Davis et al. relating to electronic specific heat and to energy-resolved scanning tunnelling microscopy (STM), respectively, over the question of electronic inhomogeneity. I see the latter, at the appropriate level, as being essential to the evolution of HTSC in these materials, and try to bring into alignment the above key works, not only with each other, but with a wealth of related work. This is undertaken around a negative-U scenario long advocated by the author.

cond-mat.supr-con↗

arXiv2006

Unconventional resistivity at the border of metallic antiferromagnetism in NiS2

We report low-temperature and high-pressure measurements of the electrical resistivity ρ(T) of the antiferromagnetic compound NiS_2 in its high-pressure metallic state. The form of ρ(T) suggests that metallic antiferromagnetism in NiS_2 is quenched at a critical pressure p_c=76+-5 kbar. Near p_c the temperature variation of ρ(T) is similar to that observed in NiS_{2-x}Se_x near the critical composition x=1 where the Neel temperature vanishes at ambient pressure. In both cases ρ(T) varies approximately as T^{1.5} over a wide range below 100 K. However, on closer analysis the resistivity exponent in NiS_2 exhibits an undulating variation with temperature not seen in NiSSe (x=1). This difference in behaviour may be due to the effects of spin-fluctuation scattering of charge carriers on cold and hot spots of the Fermi surface in the presence of quenched disorder, which is higher in NiSSe than in stoichiometric NiS_2.

cond-mat.str-el↗