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

J. Adam, D. Adamov�, M.M. Aggarwal, G. Aglieri Rinella, M. Agnello, N. Agrawal, Z. Ahammed, S. Ahmad, S.U. Ahn, S. Aiola, …
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 卷.763, 頁碼.238-250
12/2016
DOI: https://doi.org/10.1016/j.physletb.2016.10.048

摘要

Nuclear and High Energy Physics
We present measurements of two-particle correlations with neutral pion trigger particles of transverse momenta 8>p <sub>T</sub> <sup>trig</sup> >16 GeV/c and associated charged particles of 0.5>p <sub>T</sub> <sup>assoc</sup> >10 GeV/c versus the azimuthal angle difference Δφ at midrapidity in pp and central Pb–Pb collisions at s <sub>NN</sub> =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, v <sub>2</sub> to v <sub>5</sub> , 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, I <sub>AA</sub> , 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 <sub>AA</sub> ≈0.6 for p <sub>T</sub> <sup>assoc</sup> <3 GeV/c, while with decreasing momenta an enhancement develops reaching about 5 at low p <sub>T</sub> <sup>assoc</sup> . On the near side, an enhancement of I <sub>AA</sub> between 1.2 at the highest to 1.8 at the lowest p <sub>T</sub> <sup>assoc</sup> 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 <sub>T</sub> <sup>assoc</sup> . Only AMPT captures the enhancement at low p <sub>T</sub> <sup>assoc</sup> , both on the near and away side. However, it also underpredicts I <sub>AA</sub> above 5 GeV/c, in particular on the near-side.

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