Centauro and STrange Object Research (CASTOR) - A specialized detector system dedicated to the search for Centauros and Strangelets in the baryon dense, very forward phase space region in central Pb + Pb collisions at the CERN LHC.

Forward Multiplicity Detector (FMD) - The FMD system provides information on the number of charged particles in the forward rapidity range, primary vertex z location, and allowing for the rejection of beam gas events.

Photon Multiplicity Detector (PMD) - Measures the number of photons in the forward region adding information about the event 'shape' and its spin fluctuations.

START - The START detector is designed to give a high quality fast indication of the starting time of an event. This starting time is used by other detectors like the TOF, TPC, ITS, and the TRD.

Transition Radiation Detector (TRD) - Greatly improves the identification of electrons and consequently improves the identification of heavy meson decays. It will also provide an additional input signal to the trigger.

Zero Degree Calorimeter (ZDC) - Detects spectator nucleons, and thereby measures the relative impact parameter, centrality, between the two nuclei.

ALICE Detectors Not Shown

Helen CainesHoward DykeJason HubbellTom Humanic

Mike LisaBjorn Nilsen

Guy PaićEvan Sugarbaker

Ohio State Participants in the ALICE Project

At high energies, where the yield of particles is low and it makes little sense to measure particles on an event-by-event basis, there is a smaller detector (14 square meters) for identifying the mass of the particles. This detector is based on the detection of Cherenkov photons emitted by the particles in a dielectric medium. Hence the detector is called a RICH (Ring Imaging CHernkov) because the pattern of the photons detected by a CsI photocatode is ring like. The two-third prototype successfully tested at CERN in November 1997 is shown. The large area CsI photocathodes are the result of a CERN R&D program.

High-Momentum Particle Identification DetectorA special task of the ALICE experiment is to identify

the mass of the particles emitted. If the low energy particles may be identified by the loss of energy, the higher ones are detected by measuring the time it takes for a particle to reach from the collision point to the detector barrel which is 3.5 meters away. The sensor for the arrival of the particles will be Parallel Plate Counters - 160,000 of them distributed over 150 square meters. Using the tracking information from other detectors, every track firing a sensor is identified. An early prototype is shown.

Time Of Flight

Particle tracking will continue outside the ITS in a large detector called the Time Projection Chamber (TPC). The TPC will be full of gas with an electric field applied across it. When charged particles pass through, they will knock electrons out of atoms in the gas and these will drift in the electric field. By measuring the arrival time of the electrons at the end of the chamber, the TPC will reconstruct the path of the original charged particles in all three spatial dimensions.

Time Projection Chamber

Absorber Dipole Magnet

The ALICE Collaboration is building a dedicated heavy-ion detector to exploit the unique physics potential of nucleus-nucleus interactions at LHC energies. Our aim is to study the physics of strongly interacting matter at extreme energy densities, where the formation of a new phase of matter, the quark-gluon plasma, is expected. The existence of such a phase and its properties are key issues in QCD for the understanding of confinement and of chiral-symmetry restoration. For this purpose, we intend to carry out a comprehensive study of the hadrons, electrons, muons and photons produced in the collision between heavy nuclei.

ALICE - A Large Ion Collider Experiment

The Inner Tracking System (ITS) will be made from six cylindrical layers of silicon detectors. They will surround the collision point and measure the properties of particles emerging from the collision, pin-pointing their positions to a fraction of a millimeter. The ITS will look for particles containing strange and charm quarks by identifying the points at which they decay. Shown is a prototype of one of the silicon detectors used, Silicon Drift Detectors.

Inner Tracking SystemThe photon spectrometer (PHOS) is designed to measure the temperature of the fireball produced by the collisions of the ions by detecting the photons emerging from it. It is made of lead- tungstate crystals like those shown here. When high energy photons strike lead tungstate, they cause it to glow, or scintillate, and this glow can be measured. Lead tungstate is extremely dense, which means that it stops most photons that reach it.

Photon SpectrometerThe tracking chambers of the ALICE muon arm will be made of 'sandwich composite' technology like this. Sandwich composites are highly rigid but use very little material. One job of the muon arm will be to measure J/ particles via their decay into muons. Since these particles can decay into a pair of muons, two muons coming from the same place signal a possible J/ decay.

Muon Chamber

L3 Magnet