Abstract
The CMS collaboration measured second-order single-particle anisotropy, ν2, using 2-, 4-, 6- and 8-particle correlations as well as the Lee-Yang Zero method in pPb and PbPb collisions. This result shows that the correlations found in the small and highly asymmetric pPb collision system are long-range and have a many-particle origin. Deeper insight into the nature of these correlations is achieved by studying the factorization breaking effect which appears trough a pT-dependent event plane angle, caused by the initial-state fluctuations. The effect is largest for the most-central PbPb collisions (up to 20%), while it is on the level of few percent for peripheral PbPb and high-multiplicity pPb events. Hydrodynamics models which include a pT-dependent event plane angle semi-quantitatively describe the data and suggest that the effect is mainly determined by the initial-state conditions.
Highlights
The Quark-Gluon Plasma (QGP), formed in the relativistic heavy-ion collisions, undergoes a collective expansion which is called flow
Such different behavior could be explained by the presence of lenticular shape of the overlapping region in PbPb collisions, while in the case of pPb collisions the shape of the overlapping region is determined by the initial-state fluctuations
For lower multiplicity pPb events, for 120< Ntorkf f line
Summary
The Quark-Gluon Plasma (QGP), formed in the relativistic heavy-ion collisions, undergoes a collective expansion which is called flow. Particles are preferentially emitted in the plane with the biggest pressure gradient This plane is called the event plane (EP) and it is characterized via its azimuthal angle Ψn. Performing a projection of the constructed 2D particle correlations onto the Δφ axis, we obtain azimuthal correlations of particle pairs which could be characterized by a Fourier decomposition dN dΔφ The results in this contribution are, obtained by the direct calculations of Fourier coefficients VnΔ as. The background distribution is calculated in the same way as the signal one with the only difference that particles forming a pair are taken from different events with similar multiplicities and within 2 cm wide range of vertex position in the z direction. The rn value greater than one means that there are unremoved non-flow effects
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