The Atlas Electromagnetic Calorimeter

The barrel calorimeter inside the cryostat vessel



 The electromagnetic calorimeter detects and identifies electrons and photons, and measures their energy.


The technology which is used offers a fast response to detected particles and an excellent stability.

  Contribution by IRFU


-Bruno Mansoulié: co-convenor of the working group in the conceptual phase; Task Leader for the construction of the barrel electromagnetic calorimeter (1997-2003).

Calorimeter Description

In general, a calorimeter is made of metal sheets (absorbers) and a detection medium. Whenever a particle meets the absorber, it interacts with the material and produces a shower of secondary particles which are detected in the detection medium. In the electromagnetic calorimeter the absorbers are made of lead and the detection medium is liquid agon. The space filled with liquid argon is under an intense electric field (2000 V over 2 mm). Particles in the shower produce ionization electrons which drift through the liquid argon driven by the electric field. The signal derived from this electron current is amplified, shaped, digitized and recorded.

The calorimeter is embedded in a cryostat filled with liquid argon at 88 °K.


- "Accordion" structure for fast readout and reduced dead zones.
- Fine granularity, both lateral and longitudinal to the shower direction.
- High performance electronics


Topics and programs

Innovation in detection systems / Detector development
Innovation in detection systems / Signal processing and online data acquisition


The conception, development, construction and testing of the barrel electromagnetic calorimeter was a collaborative effort by the following institutes:

IRFU Saclay
LAL Orsay, LAP Annecy, LPNHE Paris,
CERN Geneva,
BNL New York (Brookhaven)
Italy (Milan)



 Main phases of the project

- Aachen 1990 : R&D proposal to study a liquid argon calorimeter with an "accordion" geometry at the LHC ;
- July 1993 : ATLAS chooses this technology for the electromagnetic calorimeter; IRFU(Dapnia) starts involvement;
- December 1996 : Technical Design Report. Layout decided; sharing of responsibilities agreed upon;
- June 2000 : Start construction of first module at Saclay;

- May 2003 : Last module received at CERN;
- December 2003: Barrel calorimeter inserted into cryostat;
- June-July 2004 : Final validation tests in liquid argon;
- October 2004 : Lowering of barrel calorimeter +  cryostat into the underground Atlas cavern;

- 2006 : Cooldown and filling with liquid argon;
- end 2006: Calorimeter is operational and records cosmic rays;
- December 2007: End of commissioning.

-2013-2019: Phase 1 upgrade; replacement of the analog trigger cards by digital ones to allow for a better spatial granularity and a more performant triggering scheme.

- 2017-2014: Phase 2 upgrade; replacement of all front end electronics (except phase 1 trigger cards).


Module assembly in the clean room


   Fact sheet

The barrel calorimeter is made of two 60 ton "wheels" of 16 modules each (R int = 3m, R ext = 4m, Length = 3.2m).  Each module is an assembly of 64 absorbers and as many electrodes.

110 000 readout channels; radiation hard electronics (40 MHz, 17 bits)


The calorimeter performance was measured in particle beam tests with the actual modules:

- Response homogeneity: 0,6 %  
- Linearity : 0,1% in the range 15 to 180 GeV
- Energy resolution: 10%/sqrt(E[GeV]) & 0,2 %



Scientific output


Energy linearity and resolution of the ATLAS electromagnetic barrel
calorimeter in an electron test-beam.
By ATLAS Electromagnetic Barrel Calorimeter Collaboration (M. Aharrouche et
al.). Aug 2006. 48pp.
Published in Nucl.Instrum.Meth.A568:601-623,2006.
e-Print: physics/0608012 
Construction, assembly and tests of the ATLAS electromagnetic barrel
By ATLAS Electromagnetic Barrel Liquid Argon Calorimeter Group (B. Aubert et
al.). CERN-PH-EP-2005-034, Jul 2005. 77pp.
Published in Nucl.Instrum.Meth.A558:388-418,2006.

Performance of the ATLAS electromagnetic calorimeter end-cap module 0.
By The ATLAS Electromagnetic Liquid Argon Calorimeter Group (B. Aubert et al.).
CERN-EP-2002-104, Nov 2002. 31pp.
Published in Nucl.Instrum.Meth.A500:178-201,2003. 
Performance of the ATLAS electromagnetic calorimeter barrel module 0.
By ATLAS Electromagnetic Liquid Argon Calorimeter Group (B. Aubert et al.).
CERN-EP-2002-087, Nov 2002. 48pp.
Published in Nucl.Instrum.Meth.A500:202-231,2003,
Mechanical aspects of the ATLAS barrel electro-magnetic calorimeter.
B. Mansoulie (DAPNIA, Saclay) . Jun 1996.
Prepared for 6th International Conference on Calorimetry in High-energy Physics
(ICCHEP 96), Rome, Italy, 8-14 Jun 1996.
Published in *Frascati 1996, Calorimetry in high energy physics* 407-416

Hadron energy reconstruction for the ATLAS calorimetry in the framework of
the nonparametrical method.
By ATLAS Collaboration (S. Akhmadalev et al.). Apr 2001. 33pp.
Published in Nucl.Instrum.Meth.A480:508-523,2002.

Measurement of the photon direction in the ATLAS electromagnetic calorimeter
with the help of neural networks.
By ATLAS Liquid Argon Collaboration (B. Mansoulie et al.). Jun 1999.
Prepared for 8th International Conference on Calorimetry in High-Energy Physics
(CALOR 99), Lisbon, Portugal, 13-19 Jun 1999.
Published in *Lisbon 1999, Calorimetry in high energy physics* 736-743

Results from a new combined test of an electromagnetic liquid argon
calorimeter with a hadronic scintillating-tile calorimeter.
By ATLAS Collaboration (S. Akhmadalev et al.). 2000.
Published in Nucl.Instrum.Meth.A449:461-477,2000. 
ATLAS calorimeter performance Technical Design Report.
By ATLAS Collaboration (A. Airapetian et al.). CERN-LHCC-96-40, Dec 1996. 189pp.

Test beam results of a stereo preshower integrated in the liquid argon
accordion calorimeter.
By RD3 Collaboration (R.A. Davis et al.). CERN-PPE-97-133, Aug 1997. 35pp.
Published in Nucl.Instrum.Meth.A411:313-329,1998.

Results from a combined test of an electromagnetic liquid argon calorimeter
with a hadronic scintillating tile calorimeter.
By ATLAS Collaboration (Z. Ajaltouni et al.). CERN-PPE-96-178, Nov 1996. 28pp.
Published in Nucl.Instrum.Meth.A387:333-351,1997.

Performance of a large scale prototype of the ATLAS accordion
electromagnetic calorimeter.
By RD3 Collaboration (D.M. Gingrich et al.). CERN-PPE-95-035, CERN-PPE-95-35,
Mar 1995. 39pp.
Published in Nucl.Instrum.Meth.A364:290-306,1995. 

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