Dergi makalesi Açık Erişim

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

2016    CERN İşbirliği

We present measurements of two-particle correlations with neutral pion trigger particles of transverse momenta $8<{p}_{T}^{\mathrm{trig}}<16\text{}\text{GeV}/c$ and associated charged particles of $0.5<{p}_{T}^{\mathrm{assoc}}<10\text{}\text{GeV}/c$ versus the azimuthal angle difference Δφ at midrapidity in pp and central Pb–Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=2.76\text{TeV}$ with ALICE. The new measurements exploit associated charged hadrons down to $0.5\text{}\text{GeV}/c$, which significantly extends our previous measurement that only used charged hadrons above $3\text{}\text{GeV}/c$. After subtracting the contributions of the flow background, ${v}_{2}$ to ${v}_{5}$, the per-trigger yields are extracted for $|\Delta \phi |<0.7$ on the near and for $|\Delta \phi -\pi |<1.1$ 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 $0\text{–}10\text{%}$ 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 ${p}_{T}^{\mathrm{assoc}}>3\text{}\text{GeV}/c$, while with decreasing momenta an enhancement develops reaching about 5 at low ${p}_{T}^{\mathrm{assoc}}$. On the near side, an enhancement of ${I}_{\mathrm{AA}}$ between 1.2 at the highest to 1.8 at the lowest ${p}_{T}^{\mathrm{assoc}}$ 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 ${p}_{T}^{\mathrm{assoc}}$. Only AMPT captures the enhancement at low ${p}_{T}^{\mathrm{assoc}}$, both on the near and away side. However, it also underpredicts ${I}_{\mathrm{AA}}$ above $5\text{GeV/}c$, in particular on the near-side.