LHC pauses proton collisions to focus on heavy nuclei

Ars Technica : As is becoming tradition at CERN’s Large Hadron Collider (LHC) at this time of year, the proton–proton collisions that were used to find the Higgs particle have been put on hiatus so heavy-ion collisions can be studied. On 25 November, the LHC began firing lead nuclei against each other and immediately achieved record levels of collision energy. The resulting quark–gluon plasma provides glimpses into the nature of the strong force, which binds quarks into hadrons and governs hadron interactions. In previous years when the LHC has switched to heavy-ion collisions, the data have served to verify work previously done at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory in New York. This year’s collisions will extend that work and perhaps reveal more evidence about recently discovered pentaquarks or other theoretical and unexpected particles.