13-19 May 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

Transverse and longitudinal event-by-event flow fluctuations of $v_1 - v_4$ in 2.76 and 5.02 TeV Pb+Pb collisions with the ATLAS detector

15 May 2018, 15:00
20m
Sala Perla, 1st Floor (Palazzo del Casinò)

Sala Perla, 1st Floor

Palazzo del Casinò

Parallel Talk Correlations and fluctuations Correlations and fluctuations

Speaker

Mingliang Zhou (Stony brook Universty (US))

Description

Multi-particle flow correlations in Pb+Pb collisions provide unique insight into the nature of event-by-event fluctuations of the initial eccentricity as well as final state dynamics in the transverse and longitudinal directions. This talk presents a detailed study of transverse flow fluctuations using 4 and 6-particle cumulants $v_n\{4\}$ and $v_n\{6\}$ for $n=1, 2, 3$, and 4. This includes several new results: the first measurement of a negative dipolar flow $v_{1}\{4\}$; a high-precision measurement of $v_{4}\{4\}$, changing sign around 20-25$\%$ centrality; observation of an intriguing sign-change pattern of $v_2\{4\}$ and $v_2\{6\}$ in ultra-central collisions; a detailed study of the cumulant ratio $v_n\{4\}/v_n\{6\}$ which shows significant deviation of $v_2$ and $v_3$ from both Bessel-Gaussian and elliptic-power distributions. The three-subevent cumulant method is used to show that these results are unlikely to be due to non-flow effects. The talk also presents a detailed study of the longitudinal dynamics of harmonic flow using various correlators involving two, four or six particles. The flow decorrelations for $v_n$ ($n=2, 3$, and 4), as well as their center-of-mass energy dependence are studied over broad range of pseudorapidity ($|\eta|<2.5$) and transverse momentum (0.5<$p_\mathrm{T}$<5 GeV). The decorrelation signals are decomposed into contributions from the forward-backward twist and asymmetry in the flow angle and magnitude, respectively. Furthermore, the decorrelation between $v_n$ and $v_m$ in different $\eta$ is measured to disentangle the longitudinal dependence of the initial-state linear effects and final-state non-linear mode-mixing effects. These results provide a wealth of differential information on event-by-event fluctuations of harmonic flow in both transverse and longitudinal directions, and they can be used to improve event-by-event 3+1D hydrodynamic models.

Content type Experiment
Centralised submission by Collaboration Presenter name already specified
Collaboration ATLAS

Primary author

Barbara Krystyna Wosiek (Institute of Nuclear Physics Polish Academy of Sciences (PL))

Presentation Materials