Heavy-ion Group

ALICE

ALICE (A Large Ion Colliding Experiment) is one of the 4 large experiments inside CERN. Experiments using CERN's LHC accelerator are all results of international joint efforts, and as such Hungarian researchers are also a part of them. ALICE's main objective is to study a phase of matter least known yet, called quark-gluon plasma (QGP). To create such matter, an extremely high amount of energy must be concentrated in a given volume, therefore ALICE is mainly interested in heavy-ion (mostly lead-lead) collisions.

DAQ - Data Acquisition

Theoretical challanges are accompanied by technical ones caused by the recording and analysis of the immense amount of data generated by the collisions. The raw data coming out of the detectors are on the order of TB/s, which is a speed crying out for filtering. This filtering of data is done with FPGAs, but during the scheduled maintenance and upgrade of the LHC, multiple new detectors will be installed, and the existing ones will also recieve upgrade. These upgrades call out for the present filtering (triggering) architecture to be upgraded, as it will not be able to keep up with the increased data bandwidth. As a solution, GPU-based triggerig is actively being investigated as an alternative.

Simulations

Predicting and reproducing experimental data are the tests of all QGP theories. We only accept certain theories so long as the numerical data (acquired through simulations) are in aggreement with our measured data (acquired through experimenting), and they possess a minimal degree of predictive power. It is equally problematic to simulate QGP events, as it is recreating them inside the accelerator. The former is mostly caused by the computational intensity of a single collision (event), aggravated by the amount of data required to describe such an event. Most of the time in the simulation chain is spent inside the GÉANT module, responsible for calculating the physical interaction of particles. A parallelised version of this module is also actively being developed.

The group participates in the development of Hijing++, which is the high-energy variant of the PYTHIA package used by most CERN experiments, with a heavy focus on integration with the existing PYTHIA framework, as well as making use of modern C++ concstructs to enable maximum CPU parallel performance.

Read more