by Lucile Hervet . Published: 19 February 2013

Since the beginning of January 2013, ALICE is on the starting blocks. For three weeks the experiment came into a new collision’s program: proton-lead. “The LHC design was not optimized for this kind of asymmetric collisions. LHC was mainly aiming to collisions of the same particle species” according to Federico Ronchetti, Nuclear Physicist at the ALICE experiment. A new challenge for the LHC and ALICE experiment before the long shut down.

A new challenge for ALICE and the LHC

The main objective of p-Pb collisions was to better understand the properties of the strong interaction, which binds quarks to from the larger object such as protons and neutrons. P-Pb data will allow the experiences that are interested in the study of plasma of quarks and gluons as ALICE esperiment, to compare the effects caused by cold nuclear matter effects related to the presence of plasma of quarks and gluons products in Pb-Pb collisions collected in 2010 and 2011. So far the results obtained in Pb-Pb collisions have only been compared with those obtained in p-p collision. The measures in p-Pb collisions are particularly expected. However, reported by Ronchetti “p-Pb collisions are also interesting for the study of the particle showers initiated by cosmic rays which are mainly high energy protons from outer space. For cosmic rays, the energy of the incoming proton is not known: you can only measure the shower. This shower is similar to what we study in pPb collisions, except we know the energies of the protons.”



Federico Ronchetti


An incredible adventure

Three weeks of hard work for the so-called “P2 team”, lead by the Run Coordinator Gilda Scioli. Despite of rush time and the lack of sleep of the team, it’s with a smile and a great satisfaction that they celebrated on Wednesday 13 February the end of the run. “It was hard but it was really a beautiful experience. It’s a pleasure for me to work here and I think that it’s only with the help of the team and their support we could arrived to this successful period” said Scioli. To arrive to this success, physicists had to set up the experiment to ensure that detectors responded to extremes conditions. Indeed usually ALICE runs at a lower luminosity than the other experiments. Things are complicated by the fact that the two rings (one for each beam) are inserted into a single magnet. So that the pulses of the particles are necessarily equal for both beams, the Lead nuclei, and the protons.


Gilda Scioli - Image credit: Mike Struik


In this respect, the machine operators did an excellent job. The recording of data produced by the detectors took place in these three weeks of heavy ion collisions. “We had to try to take the luminosity and all the interaction that the accelerator could give us” added Ronchetti. No second has been lost during the period “you have to give the maximum in a short time and you can’t fail” confessed Scioli.

“ALICE will certainly come up with great results thanks to those people” insisted Scioli. Just finished the program that there is already talk about the lead-lead collisions in 2015. The adventure continues …



ALICE team at P2; waiting for the first proton-lead run.