ALICE - A Large Ion Collider Experiment

Welcome to ALICE, a journey to the beginning of the Universe

The proton-lead run

Two of the first proton-lead collision events seen by ALICE during the 2013 proton-lead run (20.1.2013). More images of proton-lead collisons can be seen here.

At the beginning of 2013, just before the LHC shutdown, the ALICE experiment will get another opportunity to collect exciting data with the asymmetric proton-lead collisions. These data are crucial for
understanding the complexity of the lead-lead interaction in many levels
and are a necessary supplement for the baseline proton-proton data.

In fact, the data from the p-Pb collisions will represent an ultimate benchmark for the already published results from Pb-Pb collisions. It will definitely allow to decouple the cold nuclear matter effects and thus will shed light to our quest for the quark-gluon plasma.

The data collected now are part of a short pilot-run, few hours of data taking, that allow the machine to optimize the setup of the injection and collision of the proton and lead beams and the experiments to be ready to collect the physics message that they carry.

The ALICE experiment is investigating the bulk properties of the quark-gluon plasma, which preceded the phase transition to the well known
nucleons (protons and neutrons) some microseconds after the Big Bang.

The way we assess these properties is through a detailed comparison of collisions of single nucleons (proton on proton) with those of heavy lead nuclei (208 nucleons each). In proton-proton collisions no significant volume of the quark-gluon plasma is formed. Essentially all particles formed in this collision fragment into the vacuum. On the contrary, in Pb-Pb collisions large volumes of the plasma are formed and a significant fraction of the particles emerging from the collision move through that plasma. The comparison of observables from the different
collision systems thus allows us to draw conclusions on the properties of the plasma.

The missing link in this game is: what happens if particles formed in a collision of single nucleons traverse cold matter, i.e. a nucleus made of protons and neutrons rather than a plasma of quarks and gluons.
This is what we look at, when we study proton-lead collisions.

On 13 September 2012 a pilot proton-lead run took place. This was to see, whether the LHC can produce these asymmetric collisions. It can and it worked like a charm. With the data collected ALICE has published results already.

Find out more about the proton-lead run here.

Watch interviews of ALICE members and accelerator experts about the proton-lead run:

Paolo Giubellino, Federico Antinori, Andreas Morsch, Urs Wiedemann, Werner Riegler, John Jowett, Reyes Allemany Fernandez on proton-lead collisions.

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ALICE is the acronym for A Large Ion Collider Experiment, one of the largest experiments in the world devoted to research in the physics of matter at an infinitely small scale. Hosted at CERN, the European Laboratory for Nuclear Research, this project involves an international collaboration of more than 1200 physicists, engineers and technicians, including around 200 graduate students, from 132 physics institutes in 36 countries across the world. The ALICE Experiment is going in search of answers to fundamental questions, using the extraordinary tools provided by the LHC:

• What happens to matter when it is heated to 100,000 times the temperature at the centre of the Sun ?

• Why do protons and neutrons weigh 100 times more than the quarks they are made of ?

• Can the quarks inside the protons and neutrons be freed ?

This website aims both at introducing non-initiates to the field of physics covered by ALICE and at providing regular information on the evolution of the experiment, with detailed reports of its results and analysis. It also offers an insight into the scientific community gathered around this project and highlights its contributions to the advancement of our understanding of the universe. So, no matter what your involvement with physics, you are invited to tumble down the rabbit hole into the wonderland of ALICE.

Photo of the Alice Detector in early 2008.

Aerial view of the ALICE site in the territory of Sergy, (France, Ain), 2 km from CERN and the Swiss border (access from St-Genis-Pouilly, Point 2 LHC).