Abstract
Azimuthal correlations of charged particles in xenon-xenon collisions at a center-of-mass energy per nucleon pair of $ \sqrt{s_{_\mathrm{NN}}} =$ 5.44 TeV are studied. The data were collected by the CMS experiment at the LHC with a total integrated luminosity of 3.42 $\mu$b$^{-1}$. The collective motion of the system formed in the collision is parameterized by a Fourier expansion of the azimuthal particle density distribution. The azimuthal anisotropy coefficients $v_{2}$, $v_{3}$, and $v_{4}$ are obtained by the scalar-product, two-particle correlation, and multiparticle correlation methods. Within a hydrodynamic picture, these methods have different sensitivities to non-collective and fluctuation effects. The dependence of the Fourier coefficients on the size of the colliding system is explored by comparing the xenon-xenon results with equivalent lead-lead data. Model calculations that include initial-state fluctuation effects are also compared to the experimental results. The observed angular correlations provide new constraints on the hydrodynamic description of heavy ion collisions.
Highlights
At sufficiently high temperatures or densities, lattice quantum chromodynamics predicts a transition from ordinary hadronic matter to a state of deconfined quarks and gluons, the so-called quark gluon plasma (QGP)
QGP state can be reached through relativistic heavy ion collisions, where the collective behavior of the created medium manifests itself in azimuthal correlations among the emitted particles
Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections
Summary
At sufficiently high temperatures or densities, lattice quantum chromodynamics predicts a transition from ordinary hadronic matter to a state of deconfined quarks and gluons, the so-called quark gluon plasma (QGP) (see, e.g., Ref. [1]). The. QGP state can be reached through relativistic heavy ion collisions, where the collective behavior of the created medium manifests itself in azimuthal correlations among the emitted particles. Collective behavior similar to that observed in collisions of heavy nuclei has been found in high-multiplicity events produced in the proton-lead (pPb) system, and in proton-proton (pp) collisions [11,12,13,14] The results from these small systems raise the question as to how the size of the colliding system affects the onset of QGP formation. The second- and third-order Fourier coefficients are referred to as “elliptic” (v2) and “triangular” (v3) flow, respectively The former reflects the lenticular shape of the collision overlap region, as well as initial-state fluctuations in the positions of nucleons at the moment of impact [18]. The results presented here provide new information on the initial-state geometry and its fluctuations, as well as the system size dependence of the medium properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
