In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow v2reflects fluctuations in the shape of the initial state of the system. This allows to select events with the same centrality but different initial geometry. This selection technique, Event Shape Engineering, has been used in the analysis of charge-dependent two- and three-particle correlations in PbâPb collisions at sNN=2.76 TeV. The two-particle correlator ãcosâ¡(ÏÎ±âÏÎ²)ã calculated for different combinations of charges Î± and Î² is almost independent of v2(for a given centrality), while the three-particle correlator ãcosâ¡(ÏÎ±+ÏÎ²â2Î¨2)ã scales almost linearly both with the event v2and charged-particle pseudorapidity density. The charge dependence of the three-particle correlator is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity violating effect of the strong interaction. However, its measured dependence on v2points to a large non-CME contribution to the correlator. Comparing the results with Monte Carlo calculations including a magnetic field due to the spectators, the upper limit of the CME signal contribution to the three-particle correlator in the 10â50% centrality interval is found to be 26â33% at 95% confidence level.
|Titolo:||Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in PbâPb collisions at sNN=2.76 TeV|
|Data di pubblicazione:||2018|
|Appare nelle tipologie:||1.1 Articolo in rivista|