Maurice Goodrick, Takuma Goto, Bart Hommels, Mark Thomson, David Ward, Wenbiao Yan

The International Linear Collider

The International Linear Collider (ILC) is intended to be an electron-positron linear collider producing collisions in the energy range 0.5-1 TeV. The ILC is widely acknowledged to be one of the highest priorities for the future of Particle Physics. Several fully developed proposals for such a machine, have been put forward in recent years (e.g. TESLA at DESY). All regions of the world have now combined behind a common technology choice, based on the superconducting r.f. accelerating cavities of TESLA, and are carrying out a full technical design.

CALICE - Calorimetry for an ILC detector

The Cambridge group is a member of the CALICE collaboration, along with five other UK university groups and RAL. CALICE is an umbrella for several R&D projects investigating high resolution calorimetry for a linear collider. The activities are focussed on a series of beam tests being performed in 2006-8 in which a series of prototype calorimeter modules are being exposed to a variety of hadron and electron beams. The prototypes are all directed towards the construction of calorimeters with high granularity.

The prototype electromagnetic calorimeter will be a silicon-tungsten sampling calorimeter, with readout through 1x1cm2 silicon pads. The 18x18x18cm3 prototype has approximately 104 readout channels. A first beam test of a one-third instrumented prototype at DESY in February 2005 was highly successful. Further tests will follow in 2006-7 at DESY and CERN and in 2008 at Fermilab.

The hadronic calorimeter prototype will initially be of the iron-scintillator sampling type, with dimensions 1x1x1m3 and sampling using 3x3cm2 tiles in the shower core. Later, the scintillator will be replaced by RPCs and GEMs with digital readout in pads of size 1x1cm2. The electromagnetic and hadronic calorimeters were tested together in CERN in 2006-7, and in Fermilab from 2008.

As well as yielding information about various detector technologies, the beam tests will play a crucial role in validating the Monte Carlo simulation programs which will be used to optimise the design of a full detector. In particular, simulations of hadronic shower processes in calorimeters are notoriously problematic, and good data are essential before credible simulation results can be delivered.

Physics at the ILC

The ILC will complement the LHC program very effectively. Whatever new discoveries may be made at LHC (the Higgs boson, supersymmetry etc), an electron-positron collider will be able to study the new physics with much smaller backgrounds and hence much greater precision. This will be crucial in establishing any theory beyond the present standard model.

Many of the physics processes to be studied at such a machine require the measurement of the momenta of quarks, which will be detected as jets. The accurate measurement of the energy of a jet requires combining the measurements of different types of particles in different parts of the detector (tracking detectors and calorimeters). Experience from LEP tells us that good spatial resolution in the calorimetry is a crucial ingredient in combining all the information optimally. It is clear that an integrated approach to the detector design will be needed to achieve the best performance.

Cambridge in CALICE

  • The Cambridge group has been playing a leading role in the simulation effort in the UK. This has involved technical studies, comparing the simulation of key physics processes in various Monte Carlo packages, which has now led into comparisons with test beam data. The latest version of GEANT4 has been found to give satisfactory agreement with the electron beam data, while older versions were not acceptable.
  • We are also providing monitoring software for use in the test beam runs.
  • We are carrying out studies of algorithms for jet reconstruction, and their implications for detector design. The problem of pattern recognition in highly granular calorimeters is a challenging one, and the quality of jet reconstruction largely relies on being able to separate the energy depositions from different particles and associate them with charged particles as appropriate. Three algorithms have been developed at Cambridge for this purpose.
  • Global detector design studies are being carried out worldwide, in the context of three conceptual detector designs. Cambridge is involved with one of these: ILD .
  • We are carrying out longer term electronics R&D for the electromagnetic calorimeter. The physics needs require that the calorimeter be very compact. Signals from tens of millions of silicon sensors have to be read out in minimal space, with minimal power dissipation. This forms the basis for a challenging R&D project.
The prototype ECAL on top of the first few layers of the HCAL, being tested with cosmic rays at DESY. A high energy jet in the tracker and calorimeter. Each particle is coded with a different colour.

More information

International Linear Collider

TESLA Home Page

CALICE home page


Linear Collider work in the UK (LCUK)