Speaker
Description
The fundamental theory of strong nuclear force, quantum chromodynamics, predicts the existence of an extreme state of matter dubbed quark--gluon plasma (QGP) under extreme values of temperature and/or baryon density, which are attainable in ultra-relativistic heavy-ion collisions at Large Hadron Collider. Properties of QGP can be inferred via its hydrodynamic response to the anisotropies in the initial state geometry. This phenomenon is known as collective anisotropic flow, and its measurements were crucial in establishing the perfect liquid paradigm about QGP properties.
The most precise anisotropic flow measurements to date are based on the formalism of multivariate cumulants. This approach introduced the flow-specific observables in the field, $v_n\{k\}$, in terms of which most experimental results and theoretical predictions have been reported in flow analyses in the past two decades. However, it was realized recently that the usage of multivariate cumulants in flow analyses is flawed. The non-trivial properties of cumulants are preserved only for the stochastic observables for which the cumulant expansion has been performed directly, and if there are no underlying symmetries due to which some terms in the cumulant expansion are identically zero. Both of these assumptions are violated in the derivation of observables $v_n\{k\}$, which produces non-negligible systematic biases particularly in collisions with a small number of produced particles.
In this work, we attempt for the first time to reconcile the strict mathematical formalism of multivariate cumulants, with the usage of cumulants in anisotropic flow analyses. As a consequence, the outcome of this study will produce the next generation techniques and observables for flow analyses in high-energy nuclear collisions.
