P. Perrodo

Energy linearity and resolution of the ATLAS electromagnetic barrel calorimeter in an electron test-beam

A module of the ATLAS electromagnetic barrel liquid argon calorimeter was exposed to the CERN electron test-beam at the H8 beam line upgraded for precision momentum measurement. The available energies of the electron beam ranged from 10 to 245 GeV. The electron beam impinged at one point corresponding to a pseudo-rapidity of eta=0.687 and an azimuthal angle of phi=0.28 in the ATLAS coordinate system. A detailed study of several effects biasing the electron energy measurement allowed an energy reconstruction procedure to be developed that ensures a good linearity and a good resolution. Use is made of detailed Monte Carlo simulations based on Geant which describe the longitudinal and transverse shower profiles as well as the energy distributions. For electron energies between 15 GeV and 180 GeV the deviation of the measured incident electron energy over the beam energy is within 0.1%. The systematic uncertainty of the measurement is about 0.1% at low energies and negligible at high energies. The energy resolution is found to be about 10% sqrt(E) for the sampling term and about 0.2% for the local constant term.

The ATLAS LAr calibration board

In order to calibrate the ATLAS Liquid Argon calorimeters to an accuracy better than 1%, over 16 bits dynamic range, 2 prototype boards with 128 pulse generators have been built using DMILL components. The logic of control is able to enable the required channels, to load the DAC value, to delay and send the calibration command. The DAC voltage is distributed to the 128 channels in order to produce the 2 μA – 200 mA precision current. The voltage to current conversion uses a low-offset opamp and a 0.1% 5Ω resistor. Exhaustive measurements have been performed on this prototype (uniformity, linearity, jitters ...) and will be presented in detail.

Calibration boards for the ATLAS LAr calorimeters

In order to calibrate the ATLAS Liquid Argon (LAr) calorimeters to an accuracy better than 1%, over 16 bit dynamic range, chips have been designed in DMILL technology. The design and performance of a 16 bit DAC, a static low offset operational amplifier and a digital chip to control the calibration boards are presented. A 8 channels board using these chips has also been realised and carefully measured as this module will be replicated 16 times to design the final 128 channels calibration board.

The ATLAS calorimeter calibration board : tests of a first set of boards

The ATLAS Liquid Argon electromagnetic calorimeter needs a very accurate calibration system in order to fulfill its physics requirements. A set of 10 calibration boards has now been produced to test the calorimeter modules in electron beam. These boards contain a programmable sequencer which allows the loading and execution of a complete calibration run (various DAC values, delays and patterns) and provide 128 signals which are injected to the electrodes through high precision resistors. Measurements have demonstrated a good uniformity and a good linearity though small distortions have been identified. Radiation tests with both neutrons and gammas have shown many shortcomings in the pulser and control logic. New developments to address these shortcomings are discussed.