P. Delpierre

ExperimentalJ/ψ hadronic production from 150 to 280 GeV/c

A detailed study ofJ/ψ hadronic production has been performed in a high statistics experiment (more than 1.5 106J/ψ observed in their dimuon decay mode). Data have been taken with incident π±,K±,p±, on hydrogen and platinum targets, at 150, 200 and 280 GeV/c. We find from the observed nuclear dependance of the cross sections, that about 18% of theJ/ψ are produced diffractively. Using known structure functions of the quarks in the nucleon and in the pion, we derive estimations for the gluon structure functions.

The ATLAS Silicon Pixel Sensors

Prototype sensors for the ATLAS silicon pixel detector have been developed. The design of the sensors is guided by the need to operate them in the severe LHC radiation environment at up to several hundred volts while maintaining a good signal-to-noise ratio, small cell size, and minimal multiple scattering. The ability to be operated under full bias for electrical characterization prior to attachment of the readout integrated circuit electronics is also desired.

First results of XPAD3, a new photon counting chip for X-ray CT-scanner with energy discrimination

XVAD3 is a single photon counting chip based on hybrid pixel counters, with low noise, high dynamics and high speed readout. Its features have been improved to provide an high counting rate capability, a very low threshold, an energy discrimination and a fast image readout. The chip is designed in 0.25 mum IBM technology, and contains 9600 pixels (130 mum times 130 mum) distributed into 80 columns of 120 elements each. An innovative architecture has been designed in order to prevent the digital circuits from disturbing the very sensitive analogue cells. XPAD3 was realized into two versions. The XPAD3-S version accepts positive input charges and offers an energy range from 4 keV to 40 keV with a single threshold. The XPAD3-C version accepts negative input charge and has an energy range from 6 keV to 60 keV with a windowed energy selection set by two independent thresholds. This last feature will be quite useful for experimentations where high contrast resolution is needed. The XPAD3 circuits can be bump-bonded with Si, CdTe or GaAs sensors to match detection efficiency with increasing photon energy. The aim of this development is to combine several XPAD3 circuits to build an 7.5 cm x 12 cm sensitive area for the development of a small animal micro-CT scanner, PIXSCAN and synchrotron X-ray scattering experiments. First prototypes of single chip detectors bump- bonded with a Si sensor and double chip detectors bump-bonded with a CdTe sensor have been produced and tested and preliminary results are presented.

Detective quantum efficiency, modulation transfer function and energy resolution comparison between CdTe and silicon sensors bump-bonded to XPAD3S

XPAD3S is a single-photon-counting chip developed in collaboration by SOLEIL Synchrotron, the Institut Louis Néel and the Centre de Physique de Particules de Marseille. The circuit, designed in the 0.25 microm IBM technology, contains 9600 square pixels with 130 microm side giving a total size of 1 cm x 1.5 cm. The main features of each pixel are: single threshold adjustable from 4.5 keV up to 35 keV, 2 ms frame rate, 10(7) photons s(-1) mm(-2) maximum local count rate, and a 12-bit internal counter with overflow allowing a full 27-bit dynamic range to be reached. The XPAD3S was hybridized using the flip-chip technology with both a 500 microm silicon sensor and a 700 microm CdTe sensor with Schottky contacts. Imaging performances of both detectors were evaluated using X-rays from 6 keV up to 35 keV. The detective quantum efficiency at zero line-pairs mm(-1) for a silicon sensor follows the absorption law whereas for CdTe a strong deficit at low photon energy, produced by an inefficient entrance layer, is measured. The modulation transfer function was evaluated and it was shown that both detectors present an ideal modulation transfer function at 26 keV, limited only by the pixel size. The influence of the Cd and Te K-edges of the CdTe sensor was measured and simulated, establishing that fluorescence photons reduce the contrast transfer at the Nyquist frequency from 60% to 40% which remains acceptable. The energy resolution was evaluated at 6% with silicon using 16 keV X-rays, and 8% with CdTe using 35 keV X-rays. A 7 cm x 12 cm XPAD3 imager, built with eight silicon modules (seven circuits per module) tiled together, was successfully used for X-ray diffraction experiments. A first result recently obtained with a new 2 cm x 3 cm CdTe imager is also presented.

A measurement of Lorentz angle and spatial resolution of radiation hard silicon pixel sensors

Silicon pixel sensors developed by the ATLAS collaboration to meet LHC requirements and to withstand hadronic irradiation to fluences of up to

A counting pixel readout chip for imaging applications

10^{15} n_eq/cm^{2}

Radiation tolerance of single-sided silicon microstrips

have been evaluated using a test beam facility at CERN providing a magnetic field. The Lorentz angle was measured and found to alter from 9.0 deg. before irradiation, when the detectors operated at 150 V bias at B=1.48 T, to 3.1 deg after irradiation and operating at 600 V bias at 1.01 T. In addition to the effect due to magnetic field variation, this change is explained by the variation of the electric field inside the detectors arising from the different bias conditions. The depletion depths of irradiated sensors at various bias voltages were also measured. At 600 V bias 280 micron thick sensors depleted to ~200 micron after irradiation at the design fluence of 1 10^{15} 1 MeV n_eq/cm2 and were almost fully depleted at a fluence of 0.5 * 10^{15} 1 MeV n_eq/cm2. The spatial resolution was measured for angles of incidence between 0 deg and 30 deg. The optimal value was found to be better than 5.3 micron before irradiation and 7.4 micron after irradiation.

PIXEL ANALOG CELLS PROTOTYPES FOR ATLAS IN DMILL TECHNOLOGY

Abstract A pixel readout chip for imaging applications has been designed and tested. It consists of an array of 12 × 63 pixels with an active pixel cell area of 50 μ m × 350 μ m. Every pixel contains a low-noise charge sensitive amplifier, a CMOS comparator including individually adjustable thresholds, and a 15 bit counter realized using a linear feedback shift register. During data accumulation, every pixel independently counts the number of signal hits above threshold. After accumulation all counters in a column are sequentially read out, all columns in parallel. Thresholds can be set globally with the possibility of an individual threshold adjust in every cell. The chip can be operated with threshold settings in every cell well below equivalent noise charges (ENC) of 1000 electrons. The dead time of a pixel after being hit is ∼500 ns. The chip is alive for data accumulation in > 99.9% of the total data acquisition time. For photon counting in biomedical or material science applications, a suitable sensor with high Z material can be bump bonded to the counting chip.

A pixel detector with large dynamic range for high photon counting rates

Abstract The RD20 collaboration is investigating the design and operation of an LHC inner tracking detector based on silicon microstrips. Measurements have been made on prototype detectors after irradiation with electrons, neutrons, photons, and protons for doses up to 5 Mrad and fluences up to 10 15 particles/cm 2 . The annealing of effective doping changes caused by high neutron fluences, one of the major limits to detector lifetime at the LHC, is shown to be strongly inhibited by cooling below room temperature. Detailed results are presented on the critical issue of microstrip capacitance. We have also investigated bulk damage caused by high-energy protons, interstrip isolation after neutron irradiation, and MOS capacitors irradiated with electrons and photons.

The DELPHI pixels

Abstract In this paper, we describe the circuit we propose for pixel applications. In particular, we present the different parts of the analog cell, which includes a charge pre-amplifier using PJFET, bipolar and MOS transistors. The pre-amplifier incorporates a new DC feedback circuit which eases tunability, enhances stability and makes the pre-amplifier less sensitive to leakage current. The first stage is followed by a low offset bipolar-based comparator, in which special attention has been paid to reducing threshold spread. We also present experimental results on cell-to-cell mismatch and time walk, which are crucial parameters for realizing an accurate and reliable pixel detector.