Last modified 11 years ago Last modified on 2008-10-16 14:56:24


ALICE, A Large Ion Collider Experiment


Jyväskylä university is participating in ALICE experiment in LHC (Large Hadron Collider). ALICE experiment is dedicated to heavy ion studies, but it is capable to measure also during proton-proton collisions in LHC. Collaboration behind ALICE project consist from 86 institutes in 29 different countries and totaling to 1000 members from all over globe. We, Jyväskylä University, are the only Finnish institute in this collaboration. Like all other experiments in LHC the ALICE consist of multiple detectors as shown in image.

JYFL hardware efforts are directed to following detectors: T0, SSD/ITS and EMCal, which as a late addition is missing from the cut-out image (It would be placed on the spot which is cut out) shall be briefly described here.

EMCal, Electro Magnetic Calorimeter

Full EMCal ALICE EMCal is Electromagnetic Calorimeter with large acceptance (110 degrees azimuthal, from -0,7 to 0,7 on pseudorapidity). Official documentation of the design is to be found here. EMCal was not present at original plan for ALICE, so it is missing in some of the designs visible at net. Its main functionality in ALICE is study of jet quenching and to act as L0/L1 trigger (ALICE trigger scheme is found here). EMCal project is co-operation with multiple institutes from USA and Europe, Jyväskylä University was a late comer on the project so it is not mentioned on the Technical Design Report of the EMCal. From TDR you can also find most of the information related to the whole EMCal.

The design of EMCal is based a module of 2X2 = 4 towers of Pb-scintillators, which are then grouped into 12X1 strip modules. 24 strip modules laid side to side are then grouped into super modules of totaling 288 modules and thus 1152 towers. These super modules have a span of Δη = 0,7 and ΔΦ=20°. There are also 2 half sized super modules with half length strip modules.


super module

The half sized super modules have span of Δη = 0,7 and ΔΦ=10°. As you can see from the Figure 2.1, the structure of EMCal is such that two super modules are laid head to head, so spanning the rapidity coverage from -0,7 to 0,7 and then with small gaps (3 cm) on azimuthal arc.

phi 110
eta [-0.7,0.7]

TRU, Trigger Region Unit

The electronics of EMCal are basically updated version of PHOS electronics. The Trigger Region Unit is second board in the trigger chain and first unit to send a Trigger signal from EMCal (L0 trigger). First unit in trigger chain are Front End Electronics boards (FEE), which sends actual data signal to Data Acquisition system and analog sums of modules (2x2 towers) to TRUs for trigger decision. Current plans for EMCal trigger are very similar to the PHOS, but the more powerfull Virtex 5 FPGA in EMCal version gives further opportunities for development. The L1 trigger is mainly handled by STU (Summary Trigger Unit) developed in Grenoble.

Each TRU is getting 4 X 24 Fast OR analog sums (8X48 towers) from FEE boards and on current trigger scheme L0 is 4X4 towers sliding sums (overlapping 4X4 windows for whole area).

TRU towers

The resulting sums are then compared to the programmable threshold levels for trigger decisions.

Jyväskylä University is responsible for producing these TRUs for EMCal and on the code development for them.