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

J. Adam , R. Vernet (1) , I. Belikov (2) , J.C. Hamon (2) , B. Hippolyte (2) , C. Kuhn (2) , A. Maire (2) , L. Molnar (2) , F. Rami (2) , C. Roy (2) , V. Barret (3) , N. Bastid (3) , A. Batista Camejo (3) , P. Crochet (3) , P. Dupieux (3) , V.J.G. Feuillard (3) , X. Lopez (3) , F. Manso (3) , S. Porteboeuf-Houssais (3) , P. Rosnet (3) , B. Vulpescu (3) , Laurent Aphecetche (4) , B. Audurier (4) , Guillaume Batigne (4) , B. Erazmus (4) , Magali Estienne (4) , A. Francisco (4) , Marie Germain (4) , Gines Martinez Garcia (4) , A. Morreale (4) , Philippe Pillot (4) , L. Ronflette (4) , Y. Schutz (4) , Alexandre Shabetai (4) , Diego Stocco (4) , J. Zhu (4) , C. Cheshkov (5) , B. Cheynis (5) , L. Ducroux (5) , B. Teyssier (5) , R. Tieulent (5) , A. Uras (5) , Z. Conesa Del Valle (6) , I. Das (6) , B. Espagnon (6) , C. Hadjidakis (6) , I. Lakomov (6) , C. Suire (6) , J. D. Tapia Takaki (6) , M. Tarhini (6) , L. Valencia Palomo (6) , G. Conesa Balbastre (7) , J. Faivre (7) , C. Furget (7) , R. Guernane (7) , C. Silvestre , A. Vauthier (7)

1 CC-IN2P3 - Centre de Calcul de l'IN2P3
2 DRS-IPHC - Département Recherches Subatomiques
3 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand
4 SUBATECH - Laboratoire SUBATECH Nantes
5 IPNL - Institut de Physique Nucléaire de Lyon
6 IPNO - Institut de Physique Nucléaire d'Orsay
7 LPSC - Laboratoire de Physique Subatomique et de Cosmologie

We present measurements of two-particle correlations with neutral pion trigger particles of transverse momenta $8 < p_{\mathrm{T}}^{\rm trig} < 16~\mathrm{GeV}/c$ and associated charged particles of $0.5 < p_{\mathrm{T}}^{\rm assoc} < 10~\mathrm{GeV}/c$ versus the azimuthal angle difference $\Delta\varphi$ at midrapidity in pp and central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with ALICE. The new measurements exploit associated charged hadrons down to $0.5~\mathrm{GeV}/c$, which significantly extends our previous measurement that only used charged hadrons above $3~\mathrm{GeV}/c$. After subtracting the contributions of the flow background, $v_2$ to $v_5$, the per-trigger yields are extracted for $|\Delta\varphi|<0.7$ on the near and for $|\Delta\varphi-\pi| < 1.1$ on the away side. The ratio of per-trigger yields in Pb--Pb to those in pp collisions, $I_{\mathrm{AA}}$, 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 $I_{\mathrm{AA}} \approx 0.6$ for $p_{\mathrm{T}}^{\rm assoc} > 3~\mathrm{GeV}/c$, while with decreasing momenta an enhancement develops reaching about $5$ at low $p_{\mathrm{T}}^{\rm assoc}$. On the near side, an enhancement of $I_{\mathrm{AA}}$ between $1.2$ at the highest to $1.8$ at the lowest $p_{\mathrm{T}}^{\rm assoc}$ 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 $p_{\mathrm{T}}^{\rm assoc}$. Only AMPT captures the enhancement at low $p_{\mathrm{T}}^{\rm assoc}$, both on the near and away side. However, it also underpredicts $I_{\mathrm{AA}}$ above $5$ GeV/$c$, in particular on the near-side.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique des Hautes Energies - Expérience [hep-ex]

J. Adam, R. Vernet, I. Belikov, J.C. Hamon, B. Hippolyte, et al.. Jet-like correlations with neutral pion triggers in pp and central Pb-Pb collisions at 2.76 TeV. Physics Letters B, 2016, 763, pp. 238-250. ⟨10.1016/j.physletb.2016.10.048⟩. ⟨in2p3-01360019⟩