Flow analysis from multiparticle azimuthal correlations

Abstract

We present a new method for analyzing directed and elliptic flow in heavy ion collisions. Unlike standard methods, it separates the contribution of flow to azimuthal correlations from contributions due to other effects. The separation relies on a cumulant expansion of multiparticle azimuthal correlations, and includes corrections for detector inefficiencies. This new method allows the measurement of the flow of identified particles in narrow phase-space regions, and can be used in every regime, from intermediate to ultrarelativistic energies.25.75.Ld 25.75.Gz

Anisotropic flow from Lee–Yang zeros: a practical guide

“…Further details regarding the choice of weights can be found in Ref. [6]. With unit weights, and neglecting for simplicity multiplicity fluctuations, V n = Mv n , where v n is an average of the Fourier coefficient (1) over the phase space covered by the detector.…”

“…In particular, elliptic flow v 2 is recognized as a sensitive probe of thermalization at RHIC [2]. While anisotropic flow is by definition a collective effect that involves many particles, it has mostly been analyzed using methods based either on a study of twoparticle correlations [3][4][5] or on the cumulants of correlations between a few (in practice, up to 8) particles [6]. We recently proposed a new method of analysis [7,8] that remedies this limitation, and extracts flow from the correlation between a large number of particles instead of only a few.…”

Probe for the strong parity violation effects at RHIC with three particle correlations

“…and represents the difference in correlations projected onto the reaction plane and "out-of-plane" direction [8,9]. The approximate sign in the last equality reflects the fact that particles α and β might be correlated not only via common correlation to the reaction plane -then the average does not factorize into product of averages.…”

“…Note that in the rapidity region symmetric with respect to the mid-rapidity, the average directed flow equals to zero. In practice one estimates the (second order) reaction plane with the third particle [7,8,9] assuming that the particle c is correlated with particles α and β only via common correlation to the reaction plane: cos(φ a + φ β − 2φ c ) = cos(φ a + φ β − 2Ψ RP ) v 2,c . GeV.…”

CMS Physics Technical Design Report: Addendum on High Density QCD with Heavy Ions

“…It was thus proposed to measure flow with multi-particle azimuthal correlations by performing a cumulant expansion where the collective source of correlations can be disentangled from other sources [189,190]. The main advantage of the higher order cumulant analysis lies in the fact that, if the flow is larger than the non-flow correlations, the contribution of the latter to v 2 , extracted from higher order correlators, is suppressed by powers of the particle multiplicity in the event, N 0 .…”