Searching for J/ψ collective flow in 13 TeV pp collisions at CMS

Quark gluon plasma (QGP) is an extremely hot, dense state of matter in which the quarks and gluons, normally confined to colorless hadrons, are temporarily deconfined. The QGP can be formed in high-energy nuclear collisions such as PbPb, and possibly in smaller systems such as pPb collisions. The question of how small a system can form a droplet of QGP is one of much experimental and theoretical interest. One way to probe the QGP is by measuring anisotropic flow, which manifests in long-range correlations between particles as the QGP droplet expands with anisotropic pressure gradients. It is expected that heavier particles will have little or no flow. The CMS collaboration at CERN has measured the flow of open and closed charm mesons and compared the values to those of lighter hadrons. They found the flow of J/ψ mesons to be similar to that of D⁰ mesons in both high multiplicity pPb and PbPb collisions. While the open heavy flavor mesons may acquire flow because they contain light quarks that equilibrate in the medium, for J/ψ to flow the charm quarks needs to flow as well, which is more difficult, especially in small systems. These observations may signal that mechanisms other than QGP formation and pressure gradients are responsible for the azimuthal anisotropy in J/ψ production. To provide insight into this puzzle we aim to measure the J/ψ azimuthal distributions and look for flow in pp collisions using the CMS detector.