Jet-like correlations with neutral pion triggers in pp and central Pb–Pb collisions at 2.76 TeVстатья
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Аннотация:We present measurements of two-particle correlations with neutral pion trigger particles of transverse momenta 8<pTtrig<16 GeV/c and associated charged particles of 0.5<pTassoc<10 GeV/c versus the azimuthal angle difference Δ φ at midrapidity in pp and central Pb–Pb collisions at sNN=2.76 TeV with ALICE. The new measurements exploit associated charged hadrons down to 0.5 GeV/c , which significantly extends our previous measurement that only used charged hadrons above 3 GeV/c . After subtracting the contributions of the flow background, v2 to v5 , the per-trigger yields are extracted for |Δφ|<0.7 on the near and for |Δφ−π|<1.1 on the away side. The ratio of per-trigger yields in Pb–Pb to those in pp collisions, IAA , 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 IAA≈0.6 for pTassoc>3 GeV/c , while with decreasing momenta an enhancement develops reaching about 5 at low pTassoc . On the near side, an enhancement of IAA between 1.2 at the highest to 1.8 at the lowest pTassoc 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 pTassoc . Only AMPT captures the enhancement at low pTassoc , both on the near and away side. However, it also underpredicts IAA above 5 GeV/c , in particular on the near-side.