D. Banfi

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.

Cell response equalisation of the ATLAS electromagnetic calorimeter without the direct knowledge of the ionisation signals

The ATLAS liquid Argon electromagnetic calorimeter provides multiply-sampled digitised signals with a frequency of 40 MHz. The signal amplitude is reconstructed from the samples using a digital filtering technique; the computation of the digital filter weights requires the precise knowledge of the shape of the signal emerging from the front-end electronics. Each read-out channel can be calibrated by means of electronic pulsers that mimic the ionisation signal produced by an electromagnetic shower. However, the calibration signal differs from the ionisation one, because the injected current pulses are different in shape (exponential/triangular, respectively) and injection point (at the detector end/inside the detector). In order to perform a correct cell equalisation, the ionisation signal shape must have the correct normalisation with respect to the calibration pulse used to compute the actual electronic gain of each channel, thus taking into account the mentioned differences. This document describes a set of algorithms developed to predict the ionisation signal solely from the information contained in the corresponding calibration pulse. The advantage of this approach is that the proper gain of each channel and the corrections for the electrical properties of each cell can be directly inferred and then embedded in the digital filtering reconstruction, without any direct knowledge of the response of the cell to the shower-induced ionisation current. The performance of the algorithms has been tested on the electron test-beam data taken from an ATLAS liquid Argon electromagnetic calorimeter production module, demonstrating the ability to predict ionisation pulse shapes in agreement with the observed ones to better than 1% (0.2% at the peak). The digital filtering weights have been applied to reconstruct the energy of 245 GeV electrons with an energy resolution of 0.8% and a response uniformity better than 0.4%, which fulfill the ATLAS performance requirements.

HOW TO MAXIMIZE THE HL-LHC PERFORMANCE *

This contribution presents an overview of the parameter space for the HL-LHC [1] upgrade options that would maximize the LHC performance after LS3. The analysis is assuming the baseline HL-LHC upgrade options including among others, 25ns spacing, LIU [2] parameters, large aperture triplet and matching-section magnets, as well as crab cavities. The analysis then focuses on illustrations of the transmission efficiency of the LIU beam parameters from the injection process to stable conditions for physics, the minimization of the luminous region volume while preserving at the same time the separation of multiple vertices, the luminosity control mechanisms to extend the duration of the most efficient data taking conditions together with the associated concerns (machine efficiency, beam instabilities, halo population, cryogenic load, and beam dump frequency) and risks (failure scenarios, and radiation damage). In conclusion the expected integrated luminosity per fill and year is presented.

Construction, assembly and tests of the ATLAS electromagnetic end-cap calorimeters

The construction and the assembly of the two end-caps of the ATLAS liquid argon electromagnetic calorimeter as well as their test and qualification programs are described. The work described here started at the beginning of 2001 and lasted for approximately three years. The results of the qualification tests performed before installation in the LHC ATLAS pit are given. The detectors are now installed in the ATLAS cavern, full of liquid argon and being commissioned. The complete detectors coverage is powered with high voltage and readout.

PICs: what do we gain in beam performance

The beam parameters in the LHC resulting from the Performance Improvement Consolidation (PIC) activities presented in (1)(2) will be briefly recalled and motivated assuming that LINAC4 will be operational as PS-Booster Injector. The corresponding limitations in the LHC are outlined. Based on the above performance an estimate of the LHC yearly integrated luminosity will be provided. The evaluation of the need and extent of the performance and reliability improvement for some of the PIC items might imply additional information: the necessary machine studies and the specific operational experience required during Run 2 will be summarized.