Jet-like correlations with neutral pion triggers in pp and central Pb-Pb collisions at 2.76 TeV

We present measurements of two-particle correlations with neutral pion trigger particles of transverse momenta 8 < p(T)(trig) < 16 GeV/c and associated charged particles of 0.5 < p(T)(assoc) < 10 GeV/c versus the azimuthal angle difference Delta phi at midrapidity in pp and central Pb-Pb collisions at root sNN= 2.76 TeV with ALICE. The new measurements exploit associated charged hadrons down to 0.5GeV/c, which significantly extends our previous measurement that only used charged hadrons above 3GeV/c. After subtracting the contributions of the flow background, v2to v(5), the per-trigger yields are extracted for vertical bar Delta phi vertical bar < 0.7 on the near and for vertical bar Delta phi - pi vertical bar < 1.1 on the away side. The ratio of per-trigger yields in Pb-Pb to those in pp collisions, I-AA, is measured on the near and away side for the 0-10% most central Pb-Pb collisions. On the away side, the per-trigger yields in Pb-Pb are strongly suppressed to the level of I-AA approximate to 0.6 for p(T)(assoc) > 3GeV/c, while with decreasing momenta an enhancement develops reaching about 5 at low p(T)(assoc) . On the near side, an enhancement of I-AA between 1.2 at the highest to 1.8 at the lowest p(T)(assoc) is observed. The data are compared to parton-energy-loss predictions of the JEWEL and AMPT event generators, as well as to a perturbative QCD calculation with medium-modified fragmentation functions. All calculations qualitatively describe the away-side suppression at high p(T)(assoc). Only AMPT captures the enhancement at low p(T)(assoc) , both on the near and away side. However, it also underpredicts IAAabove 5GeV/c, in particular on the near-side. (C) 2016 The Author(s). Published by Elsevier B.V.