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Acharya, S.,Adam, J.,Adamová,, D.,Adolfsson, J.,Aggarwal, M.M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahmad, N.,Ahn, S.U.,Aiola, S.,Akindinov, A.,Al-Turany, M.,Alam, S.N.,Albuqu North-Holland Pub. Co 2018 Physics letters. Section B Vol.777 No.-
<P><B>Abstract</B></P> <P>In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow <SUB> v 2 </SUB> reflects 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 Pb–Pb collisions at <SUB> s NN </SUB> = 2.76 TeV. The two-particle correlator 〈 cos ( <SUB> φ α </SUB> − <SUB> φ β </SUB> ) 〉 , calculated for different combinations of charges <I>α</I> and <I>β</I>, is almost independent of <SUB> v 2 </SUB> (for a given centrality), while the three-particle correlator 〈 cos ( <SUB> φ α </SUB> + <SUB> φ β </SUB> − 2 <SUB> Ψ 2 </SUB> ) 〉 scales almost linearly both with the event <SUB> v 2 </SUB> and 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 <SUB> v 2 </SUB> points 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 10–50% centrality interval is found to be 26–33% at 95% confidence level.</P>
Neutral pion and η meson production at midrapidity in Pb-Pb collisions at sNN=2.76 TeV
Acharya, S.,Acosta, F. T.-.,Adamová,, D.,Adolfsson, J.,Aggarwal, M. M.,Aglieri Rinella, G.,Agnello, M.,Agrawal, N.,Ahammed, Z.,Ahn, S. U.,Aiola, S.,Akindinov, A.,Al-Turany, M.,Alam, S. N.,Albuqu American Physical Society 2018 Physical review. C Vol.98 No.4
<P>Neutral pion and eta meson production in the transverse momentum range 1 < p(T) < 20 GeV/c have been measured at midrapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semicentral Pb-Pb collisions at root S-NN = 2.76 TeV. These results were obtained using the photon conversion method as well as the Photon Spectrometer (PHOS) and Electromagnetic Calorimeter detectors. The results extend the upper p(T) reach of the previous ALICE pi(0) measurements from 12 to 20 GeV/c and present the first measurement of eta meson production in heavy-ion collisions at the LHC. The eta/pi(0) ratio is similar for the two centralities and reaches at high p(T) a plateau value of 0.457 +/- 0.013(stat) +/- 0.018(syst) A suppression of similar magnitude for pi(0) and eta meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of Next to Leading Order (NLO) pQCD predictions and hydrodynamic models. The measurements show a stronger suppression than observed at lower center-of-mass energies in the p T range 6 < p(T) < 10 GeV/c. For p(T) < 3 GeV/c, hadronization models describe the pi(0) results while for the eta some tension is observed.</P>