by Lucile Hervet. Published: 19 February 2013

Since the beginning of January 2013, ALICE is on the starting blocks. For three weeks the experiment pursued a new programme: proton-lead. “The LHC design was not optimized for this kind of asymmetric collisions. LHC was designed to provide 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 lead-lead collisions is to better understand the properties of the strong interaction, which binds quarks to form larger objects such as protons and neutrons. Proton-Lead data are of special interest for experiments studying the quark-gluon plasma, such as ALICE. They allow to distinguish effects caused by the hot plasma from effects caused by the cold matter that makes up lead nuclei. So far the results obtained in lead-lead collisions have only been compared with those obtained in proton-proton collisions. However, reported Ronchetti, “proton-lead 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”, led by the Run Coordinator Gilda Scioli. Despite of stressful times and 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 that we 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 extreme conditions. Indeed usually ALICE runs at a lower luminosity than the other experiments.

Gilda Scioli - Image credit: Mike Struik

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 interactions 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. The programme has just finished and there is already talk about the lead-lead collisions in 2015. The adventure continues …

First day of the p+Pb run in the ALICE control room.