We present transverse momentum distributions of inclusive charged particles and identified hadrons in $pp$ and Pb--Pb collisions at $rs= 2.76$ TeV, measured by ALICE at the LHC. The Pb--Pb data are presented in intervals of collision centrality and c
over transverse momenta up to 50 GeV/$c$. Nuclear medium effects are studied in terms of the nuclear modification factor raa. The results indicate a strong suppression of high-$p_T$ particles in Pb--Pb collisions, consistent with a large energy loss of hard-scattered partons in the hot, dense and long-lived medium created at the LHC. We compare the preliminary results for inclusive charged particles to previous results from RHIC and calculations from energy loss models. Furthermore, we compare the nuclear modification factors of inclusive charged particles to those of identified $pi^0$, $pi^{pm}$, K$^0_s$, and $Lambda$.
A high statistics study of high-$p_t$ two-particle azimuthal correlations in Pb-Au at $sqrt{s_{rm NN}}=17.2$ GeV, performed by the CERES experiment at the CERN-SPS, is presented. A broad away-side correlation with significant dip at $Deltaphiapproxpi
$ is observed. The shape and magnitude of the correlation is similar to measurements at RHIC. In comparison to PYTHIA calculations, we observe a significant excess of soft particles at the away-side. A study of charge correlations between trigger and associated particles disfavors vacuum fragmentation of the away-side jet and suggests significant energy transfer of the hard-scattered parton to the medium.
Results of a two-particle correlation analysis of high-$p_t$ charged particles in Pb-Au collisions at 158$A$ GeV/$c$ are presented. The data have been recorded by the CERES experiment at the CERN-SPS. The correlations are studied as function of trans
verse momentum, particle charge and collision centrality. We observe a jet-like structure in the vicinity of a high-$p_t$ trigger particle and a broad back-to-back distribution. The yields of associated particles per trigger show a strong dependence on the trigger/associate charge combination. A comparison to PYTHIA confirms the jet-like pattern at the near-side but suggests a strong modification at the away-side, implying significant energy transfer of the hard-scattered parton to the medium.
We present results on transverse momentum correlations of charged particle pairs produced in Pb-Au collisions at 158$A$ GeV/$c$ at the Super Proton Synchrotron. The transverse momentum correlations have been studied as a function of collision central
ity, angular separation of the particle pairs, transverse momentum and charge sign. We demonstrate that the results are in agreement with previous findings in scale-independent analyses at the same beam energy. Employing the two-particle momentum correlator $<Delta p_{t,i}, Delta p_{t,j}>$ and the cumulative $p_t$ variable $x(p_t)$, we identify, using the scale-dependent approach presented in this paper, different sources contributing to the measured correlations, such as quantum and Coulomb correlations, elliptic flow and mini-jet fragmentation.
