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

Submission Date: 
Article Information
Submission Form
2.76 TeV
Abstract Plain Text: 

We present measurements of two-particle correlations with neutral pions for transverse momenta $8 < \ptt < 16~\gmom$ as trigger and charged hadrons for $0.5 < \pta < 10~\gmom$ as associated particles versus azimuthal angle difference $\dphi$ at midrapidity in pp and central \PbPb\ collisions at $\snn$=2.76 TeV.
Our new measurement exploits associated hadrons down $0.5~\gmom$, and hence significantly extends our previous measurement which used charged hadrons above $3~\gmom$.
After subtracting the contributions of the relevant flow harmonics, $v_{2}$--$v_{5}$, the per-trigger yields are extracted for $|\dphi|<0.7$ on the near and for $|\dphi-\pi| < 1.1$ on the away side.
The per-trigger yield modification factor, \Iaa\, quantified as the ratio of per-trigger yields in \PbPb\ to that in pp collisions, is measured on the near and away side for $0$--$10$\% most central \PbPb\ collisions.
On the away side, the per-trigger yields in \PbPb\ are strongly suppressed to the level of $\Iaa \approx 0.6$ for $\pta > 3.0~\gmom$, while with decreasing momenta a enhancement develops reaching about $5.2$ at lowest \pta.
On the near side, an enhancement of $\Iaa$ between $1.2$ to $1.8$ at lowest \pta\ is observed.
The data are compared to predictions using the JEWEL and AMPT event generators, as well as a state-of-the-art pQCD calculation with medium-modified fragmentation functions.
While all predictions describe the away-side suppression, only AMPT is able to describe also the enhancement, both on the near and away side.