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The Silicon Tungsten ECAL

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A few of the several million events recorded by the SiW physics prototype in test beam at the Fermilab MTEST beamline in 2008. The beam enters from the bottom left corner of these images.

viewer_mu.png viewer_e.png viewer_e_gamma.png viewer_mu_pi.png viewer_pi.png viewer_pi2.png


Particle colliders are used to investigate the nature of particles and their interactions at high energies.

The Linear Collider is designed collide electrons and positrons at energies of up to 1 TeV. One or more detectors will be used to record what occurred in these collisions. Each detector is made up of several sub-detectors, designed to measure different properties of the various types of particles.

Quarks are often produced in high energy collisions, so it is important to accurately estimate their energy. This is complicated by the fact that they cannot exist as solitary particles, but always combine with one or more quarks or anti-quarks. At high energy, each quark gives rise to a narrow "jet" containing of order 10 particles.

To accurately measure this jet can be complicated, since it usually contains several types of particle, which each interact in a different way with the different sub-detectors. A new technique, called Particle Flow, has been developed to measure jets' energy in an optimal way. It attempts to individually measure the energy of each particle in the jet, rather than measuring the total jet energy at once. This allows the specific properties of each particle to be taken into account when combining the measurements of each sub-detector.

To see each particle individually requires a detector with very high resolution, or high "granularity", so that nearby particles can be cleanly resolved.

We are developing one of the sub-detectors which will make up the detector. It's main aim is to measure the energy, position and angle of photons, electrons and positrons, and to separate them from other types of particles (which will be measured by other sub-detectors). Photons, electrons and positrons interact largely through the electromagnetic interaction, so this sub-detector is known as an Electromagnetic Calorimeter (or ECAL for short).


The ECAL must be able to measure the energy, position and angle of photons and electrons with good precision, and must be able to resolve them from nearby particles.

It must also be integrated into a larger-scale detector, consisting of several different systems. To ensure that the detector as a whole has good performance, the ECAL must be relatively thin, should have as few insensitive areas as possible, and should not generate too much heat (to prevent the need for bulky cooling systems).

General conceptual design

To satisfy these requirements, the SiW ECAL is designed as a tungsten-silicon based sampling calorimeter. The tungsten absorber plates reduce the size of EM showers in the device, due to its small Moliere radius and short radiation length. This helps to avoid overlapping of showers produced by nearby particles.

Silicon detectors have been chosen to measure the progression of the EM shower within the ECAL. Silicon detectors have the advantage that they are thin (limiting the effective Moliere radius of the ECAL), and relatively easily segmented into small active regions, giving the high granularity required. They are also easy to operate, and quite insensitive with respect to environmental conditions.

The total thickness of the ECAL will be around 27 radiation lengths (corresponding to 20cm), giving adequate containment even of high energy EM particles. Around 30 layers of silicon will be used, giving a sufficient energy resolution. The sampling fraction in the earlier layers will be higher than in latter layers, enhancing the efficiency for the identification of low energy (~100 MeV) photons.

In a final detector, the ECAL will consist of around 3000m2 of silicon sensors, and will have a total mass of about 100 T (mostly in tungsten). It will have a "barrel" section (an octagonal tube with an inner radius of ~2m and a thickness of ~20cm), closed by two octagonal "endcaps". The ECAL will be hung from the front face of the hadronic calorimeter (HCAL). The region between the ECAL and the interaction point will be instrumented with various "tracking" detectors which sense the passage of charged particles.

Present and past activities

Physics prototype

A small prototype SiW ECAL was constructed to test the feasibility of such a SiW ECAL. It has a transverse size of 18x18 cm2, and 30 layers of silicon detectors. The silicon detectors were segmented with a granularity of 1x1 cm2, giving a total of around readout 10,000 channels.

This prototype was exposed to test beams during the years 2006-2008, at the physics laboratories at DESY, CERN and FNAL. It behaved as expected from computer simulations, and validated the general principles of such a detector.

Technological prototype

At present (2010) a second prototype is being constructed, which aims to address the issues connected with the production of a full-scale ECAL, and its integration into a full detector. This includes:

  • the mechanical structure (made of carbon fibre composite) needed to support the tungsten and silicon elements
  • the development of reasonably priced silicon sensors with improved characteristics
  • a new generation of very low power front-end electronics chips (which will treat the electronics signals from the silicon within the ECAL volume)
  • cooling systems to extract generated heat
  • a data acquisition system to read, save and analyse the collected data
This prototype will be tested in particle beams in the coming years (2011-)

Some pictures of the detector construction

3DProtoH_small.png physProtoPhoto_small.jpg slabPhoto_small.png demonstrator_small.jpg themaltest_small.jpg

The team

Laboratoire Leprince-Ringuet (LLR)
  • Daniel Jeans
  • Remi Cornat
  • Marc Anduze
  • Mickael Frotin
  • Jean-Claude Brient
  • Henri Videau
  • Suhail Amjad

Laboratoire de l Accélérateur Linéaire (LAL)
  • Roman Poeschl
  • Julien Bonis
  • Patrick Cornebise
  • Phillipe Doublet

  • Christophe de la Taille
  • Stephane Callier

Laboratoire de Physique Subatomique et de Cosmologie de Grenoble (LPSC)
  • Jean-Yves Hostachy
  • Denis Grondin
  • Julien Giraud
  • Kaloyan Krastev

Institute of Physics, Prague
  • Vaclav Vrba
  • Petr Sicho
  • Jaroslav Cvach

Pictures and schematics

3Dview.png 3Dview.eps3

3DDeadAreas.png 3DDeadAreas.eps3

Slab.png Slab.eps3

ProtoAnglePict.png ProtoAnglePict.eps3

ProtoAngleSchema.png ProtoAngleSchema.eps3

Links (mostly outdated)

EUDET SiW web pages.

See also the original Calice SiW ECAL web pages.

Topic attachments
I Attachment History Action Size Date Who Comment
Unknown file formateps3 3DProtoH.eps3 r1 manage 671.6 K 2008-07-15 - 14:18 AnnemarieMagnan  
PNGpng 3DProtoH.png r1 manage 731.7 K 2008-07-15 - 14:18 AnnemarieMagnan  
PNGpng 3DProtoH_small.png r1 manage 46.2 K 2010-06-17 - 11:31 UnknownUser view of the physics prototype design
Unknown file formateps3 DeadAreas.eps3 r1 manage 326.0 K 2008-07-15 - 14:20 AnnemarieMagnan  
PNGpng DeadAreas.png r1 manage 398.3 K 2008-07-15 - 14:20 AnnemarieMagnan  
Unknown file formateps3 ProtoAnglePict.eps3 r1 manage 322.0 K 2008-07-15 - 14:28 AnnemarieMagnan  
PNGpng ProtoAnglePict.png r1 manage 373.9 K 2008-07-15 - 14:21 AnnemarieMagnan  
Unknown file formateps3 ProtoAngleSchema.eps3 r1 manage 421.9 K 2008-07-15 - 14:29 AnnemarieMagnan  
PNGpng ProtoAngleSchema.png r1 manage 470.7 K 2008-07-15 - 14:29 AnnemarieMagnan  
Unknown file formateps3 Slab.eps3 r1 manage 98.3 K 2008-07-15 - 14:20 AnnemarieMagnan  
PNGpng Slab.png r1 manage 121.5 K 2008-07-15 - 14:20 AnnemarieMagnan  
JPEGjpg demonstrator_small.jpg r1 manage 6.2 K 2010-06-17 - 11:37 UnknownUser mechanical demonstrator
JPEGjpg physProtoPhoto_small.jpg r1 manage 6.0 K 2010-06-17 - 11:33 UnknownUser physics prototype: mechanical structure
PNGpng slabPhoto_small.png r1 manage 59.4 K 2010-06-17 - 11:35 UnknownUser physics prototype detector slab
JPEGjpg themaltest_small.jpg r1 manage 53.5 K 2010-06-17 - 11:42 UnknownUser cooling system tests
PNGpng viewer_e.png r1 manage 7.6 K 2010-06-17 - 10:57 UnknownUser electron in the ECAL
PNGpng viewer_e_gamma.png r1 manage 12.0 K 2010-06-17 - 10:57 UnknownUser electron and nearby photon in the ECAL
PNGpng viewer_mu.png r1 manage 3.0 K 2010-06-17 - 10:57 UnknownUser muon in the ECAL
PNGpng viewer_mu_pi.png r1 manage 7.4 K 2010-06-17 - 10:58 UnknownUser charged pion and nearby muon in the ECAL
PNGpng viewer_pi.png r1 manage 7.8 K 2010-06-17 - 10:58 UnknownUser pion interaction in the ECAL
PNGpng viewer_pi2.png r1 manage 6.6 K 2010-06-17 - 10:59 UnknownUser another pion interaction in the ECAL
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Topic revision: r5 - 2010-06-17 - unknown
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