A Precise Probe of the Quark-Gluon Plasma

Immediately after the big bang, the Universe was filled with a hot, dense soup of quarks and gluons. Scientists can recreate this quark-gluon plasma (QGP) in particle accelerators by smashing heavy ions together. The collisions also produce partons (quark and gluons) that subsequently produce hadron jets. The energy lost by the partons as they travel through the QGP can be determined from measurements of the jets, revealing properties of the QGP. Now, the CMS Collaboration at the Large Hadron Collider has measured a jet produced in coincidence with so-called Z bosons—the carriers of the weak interaction. These combined Z-boson–jet measurements may characterize the QGP more precisely than conventional measurements probing the jets only.