Robert Orr

Electron signals in the Forward Calorimeter prototype for ATLAS

A pre-production prototype of the Forward Calorimeter (FCal) for the ATLAS detector presently under construction at the Large Hadron Collider (LHC) at CERN, Geneva, Switzerland, was exposed to electrons in the momentum range from 20 to 200 GeV/c in a test beam experiment at CERN in 1998. The measured performance, including a signal linearity within about ±1% and a high energy limit in the relative energy resolution of about 4%, meets the expectations for this kind of calorimeter, and exceeds the physics requirements for successful application in ATLAS.

Results for electrons from the 1995 ATLAS forward calorimeter prototype testbeam

The performance of the ATLAS electromagnetic liquid argon/brass forward calorimeter with its new readout geometry consisting of tube/rod electrodes with cylindrical shell gaps, has been evaluated with a full depth prototype in a testbeam experiment with electrons in 1995. The results for signal linearity of better than 1% and a constant term in the relative energy resolution of 3% meet and even exceed the original performance requirements very well. Space resolution in the order of 0.5 mm in the high energy limit, and an insignificant signal dependency on the electron impact angle have been found in addition.

Construction and initial beam tests of the ATLAS tungsten forward calorimeter

Due to the severe radiation environment, the ATLAS experiment has chosen a compact tungsten/liquid argon forward hadronic calorimeter. The electrode design is unique and consists of hexagonally packed, tubular, thin gap electrodes running parallel to the beam direction. We describe the design criteria, the novel construction methods based on sintered tungsten components, and initial high energy beam tests at CERN.

ATLAS LIQUID ARGON HADRONIC CALORIMETERS

The ATLAS experiment is a general purpose detector designed to exploit the full potential of the Large Hadron Collider at both low and high luminosity running. Central to the ATLAS physics program is what one can term discovery physics. In defining the calorimeter design goals this discovery physics has been a major consideration. An important design touchstone was the ability to discover a standard model Higgs over a wide mass range. This is shown in Fig.1. At low masses the energy resolution for photons, and fine electromagnetic spatial resolution, are at a premium in order to distinguish photons from 0 π and to reconstruct the channel H γγ → against a large background; this sets the design goals for the electromagnetic calorimeter system. In the intermediate mass region the decay channel H l l l l + − + − → again mandates high quality electromagnetic calorimetry over a wide rapidity range. In the high mass region up to 1 TeV, the ability to identify jets and to reconstruct jet invariant masses is a major design consideration. Many “discovery” topics, such as supersymmetery, depend on the detection of missing energy and require hermetic hadronic calorimetry. These are only the major design goals, and clearly more optimization than can be covered here has gone on in the design of ATLAS, see [1]. A summary of the calorimeter design goals, and the chosen technologies is given in Fig. 2. At this meeting the construction and testing of the electromagnetic calorimeters was covered in separate contributions, see [2], [3]. Here we restrict ourselves to a discussion of the Forward Calorimeter, the assembly of the end cap calorimeters, and plans for combined test beams.

OVERVIEW OF THE ATLAS LIQUID ARGON CALORIMETER SYSTEM

The Large Hadron Collider (LHC) at CERN is designed to have an energy and luminosity sufficient to experimentally elucidate the mechanism of electroweak symmetry breaking, and to generally investigate the centre-of-mass energy regime up to 1 TeV constituent collision energy. Given the available machine technology the LHC has been designed to achieve a proton-proton centre-ofmass energy of 14 TeV at a luminosity of 1034cm−2s−1. While these machine parameters bring the opportunity for new and exciting discovery physics, they make stringent requirements on the design of the detector elements.