ALICE gets its first ‘upgrade’

The ALICE experiment has reached another milestone with the successful installation of the first two modules of the electromagnetic calorimeter.

Preparations for installing the EMCal in the ALICE cavern.

On 17 and 19 March the first two sections of the electromagnetic calorimeter (EMCal) were fitted in the ALICE cavern. The full EMCal, a lead-scintillator sampling calorimeter, will be made up of 12 separate modules plus 2 half modules. Weighing 8 tons each, these modules required a whole new support structure to be built and a sophisticated ‘bridge’ device (pictured) to install them in situ.

Project Leader, Tom Cormier from Wayne State University, notes that: "The EMCal is a late addition to ALICE, arriving in effect as a first upgrade. Indeed full approval with construction funds occurred only in early 2008." Although ALICE has excellent momentum measurement and identification capabilities for charged hadrons it previously lacked the capability to measure the neutral energy component of jets. The new electromagnetic calorimeter provides ALICE with this capability. This is crucial for determining the overall energy of the ‘jets’ of hadrons created when quarks and gluons recombine after having formed the quark-gluon plasma.

Did you know?

During the heavy-ion collisions inside the ALICE detector, the protons and neutrons will ‘melt’, freeing the quarks from their bonds with the gluons. The experiment will probe this strange form of matter, known as Quark-Gluon Plasma (QGP), by looking at how high-energy quarks and gluons lose energy as they fly through this ‘particle soup’. Once out of the QGP these high-energy quarks and gluons quickly reform creating a ‘jet’ of hadrons. By looking at the total energy of these ‘jets’ the ALICE physicists can determine the density and interaction strength of the QGP.