Upsilon particles come in three distinct "states" which depend on how tightly the quarks and antiquarks that make them are bound. In the lead collision program last autumn, upsilons were produced in a super-hot quark-gluon plasma. Less-bound states were often torn apart by the high energy, reducing the number detected in CMS. Physicists recently presented this phenomenon of upsilon "melting." The image shows a cacaphony of signals from particles produced in a lead-lead collision plus two distinct muon tracks (red lines). The sum of the energies of these muons (near 10 GeV) tags them as coming from an upsilon candidate. Learn more.
Credit: Copyright CERN on behalf of the CMS Collaboration.