Rencontres de Moriond QCD 2012: Probing the nature of heavy-ion collisions

Wednesday began with presentations by experiments worldwide on their investigations into the intriguing nature of the Quark Gluon Plasma (QGP).

The ALICE Collaboration examined further preliminary results from the LHC’s 2010 Pb-Pb run, observing that particles containing strange quarks were more abundant than they are in proton-proton collisions – indicating the presence of QGP. They also presented results from the so-called “soft probes” that allow scientists to look at the collective behaviour of the QGP medium. 

The ATLAS and CMS Collaborations provided a very different approach to the study heavy ion physics: examining particle energy loss in the QGP by looking at the momentum of particle jets leaving the medium. ATLAS reported their results on a variety of studies using jets, charged hadrons and weak bosons produced in heavy-ion collisions during the 2010 run.

Presenting their results from the 2011 run, the CMS Collaboration found that there is energy loss across all values of jet momentum. “Theorists are still working on incorporating this energy loss into current QCD models,” says Yetkin Yilmaz, from Massachusetts Institute of Technology. “In other words, we can’t yet say what this measurement tells us about the fundamental parameters of the QGP medium.”

The afternoon took quite a different turn, with a session devoted to cosmological searches that overlap with the HEP field. This was followed by a common session with the Moriond Cosmology Conference. Presentations emphasised how cosmological studies can complement LHC searches (and vice versa) in a variety of areas, such as the investigation of CP violation in non-weak interactions.

by Katarina Anthony