ILC NewsLine - 14 September 2006

An event-display of the CALICE summer test-beam. A pion of 30 GeV is entering the calorimeter on the left, crossing first the electromagnetic calorimeter and then interacting in the hadronic calorimeter.

This summer, in the H6 zone of CERN, the CALICE (Calorimeter for Linear Collider Experiment) collaboration carried out test-beams which will continue until the end of October. Three prototypes were installed in a test-beam together with trigger and acquisition systems: a highly segmented electromagnetic silicon tungsten (ECAL), a hadronic scintillator tile-silicon photomultiplier (HCAL) calorimeters and a tail catcher, made of scintillator strip-silicon photomultipliers. All together they represent about ten thousand read-out channels. "By now, approximately 20 million interactions have been recorded," said Jean Claude Brient, spokesperson of the CALICE collaboration, "and we expect 30 million of them by the end of the test."

The CALICE calorimeters were exposed to electrons from 6 to 45 GeV and pions from 6 to 80 GeV. At first sight, these energies may appear much smaller than the 500 GeV centre of mass energy at the ILC. But in fact, it will be crucial to be able to reconstruct particles in this range of low energies. The W, Z and Higgs bosons mainly decay in jets composed of numerous particles whose energy is therefore low. At the ILC, physicists will precisely know the initial state of the particles in collisions which makes it possible to analyse every event. CALICE detectors are ultra-granular in order to identify each particle of every ILC event.

Combined tests of ECAL together with HCAL are essential to evaluate the performances of particle reconstruction in the calorimeter. The test-beam data analysis should lead to important progress in the comprehension and the design of ultra-granular calorimeters. The simulation of hadronic interactions is not easy, especially at low energies. The real conditions of a test-beam exposure let scientists find strong constraints on the models in the "GEANT4" simulation program they use. On the technical side, it can also help in the design of an ultra-segmented calorimeter. For example, electronic backgrounds produced by collective effect on the multiple channels can be estimated.

The CALICE ECAL (foreground), HCAL (behind) and Tail Catcher (blue and orange device behind the HCAL) before being exposed to the beams. In the future, electronics devices should be more and more integrated into the detectors so that the read-out and digitisation of a signal could be done as early as possible.

In August, all 30 layers of the ECAL detector were installed into the beam, half equipped with electronic devices. For the HCAL, one of the two options for the CALICE hadronic calorimeter was tested (read more about this option in the 30th March 2006 issue of NewsLine) with about every second of active layers instrumented. The CALICE collaborators will continue equipping their detectors till the end of the test. In October, most layers of this HCAL should be ready for data taking.

The international CALICE collaboration, consisting of 200 people from 38 institutes in America, Asia and Europe, is also developing and constructing other calorimeter prototypes. These include a scintillator strip ECAL and a gaseous HCAL equipped with resistive plate chambers, gas electron multipliers or Micromegas. Another test-beam is expected to start in early 2008 to expose these new prototypes. In parallel, a second generation of silicon-tungsten ECAL and a new tile HCAL will be designed and built, allowing the testing of new technologies for the ILC detector. The collaboration's purpose is to work on calorimeter R&D independent of the detector concepts. "The CALICE collaboration is a good opportunity to help new ideas and concepts on calorimetry come true," said Brient.