# QM 2011 - XXII International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

May 22 – 28, 2011
Centre Bonlieu
Europe/Zurich timezone

## Triggered di-hadron correlations in PbPb collisions from the ALICE experiment

May 24, 2011, 3:00 PM
20m
Rotonde de l'Europe (Imperial Palace)

### Rotonde de l'Europe

#### Imperial Palace

Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00
Parallel Correlations and fluctuations

### Speaker

Angular correlations between unidentified hadron trigger and associated particles are measured by the ALICE experiment for $0.5 < p_{t}^{(t),(a)} < 15$ GeV/c, where $p_t^{(t)} > p_t^{(a)}$. The modification of conditional yields in central Pb--Pb collisions is measured with respect to p--p ($I_{AA}$) and with respect to peripheral events ($I_{CP}$). Significant suppression is observed on the side opposing the trigger, while an enhancement is measured on the near side. The latter result is a notable departure from RHIC measurements. In addition, the shape of the pair azimuthal distribution is examined in a variety of centrality categories for pairs in $|\eta| < 0.8$ where $|\eta^{(t)} - \eta^{(a)}| > 0.8$. A set of two-particle Fourier components $V_{n\Delta} \equiv \langle \cos(n\Delta\phi)\rangle$ are computed directly from the long-range azimuthal correlation functions. A series including $V_{1\Delta}$ to $V_{5\Delta}$ describes the data. For each $n$, a fit is applied over all $p_{T}$ bins simultaneously to test the collectivity hypothesis $V_{n\Delta} \simeq v_n^{(t)} \, v_n^{(a)}$. This factorization hypothesis is satisfied at low $p_{T}$ but not at higher $p_{T}$. The divergence between the data and the global fit provides a new measure of the onset of nonflow dominance in long-range correlations due to the away side jet. The first five single-particle $v_n$ coefficients are presented as new results from the global fit, and are compared to $v_n$ values measured by more established methods.