Physics and Astronomy
Journal or Book Title
Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark–gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons 1–4 . In this state, matter behaves as a nearly inviscid fluid 5 that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton–proton (p+p) and proton–nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton–gold (p+Au), deuteron–gold (d+Au) and helium–gold ( 3 He+Au) collisions at a nucleon–nucleon centre-of-mass energy sNN = 200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide the best simultaneous description of these measurements.
Aidala, C.; Apadula, Nicole J.; Hill, John C.; Hotvedt, Nels J.; Lajoie, John G.; Lebedev, Alexandre; Lee, S. H.; Ogilvie, Craig; Patel, Milap R.; Perry, Joshua; Rinn, Timothy T.; Rosati, Marzia; Runchey, Jonathan C.; Sen, Abhisek; Shimomura, M.; Timilsina, Arbin; et al.; and PHENIX Collaboration, "Creation of quark–gluon plasma droplets with three distinct geometries" (2019). Physics and Astronomy Publications. 498.