Long-range and short-range dihadron angular correlations in central PbPb collisions at √^s_NN= 2.76 TeV

Abstract

First measurements of dihadron correlationsfor charged particles are presented for central PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76TeV over a broad range in relative pseudorapidity (Δη ) and the full range of relative azimuthal angle (ΔΦ ). The data were collected with the CMS detector, at the LHC. A broadening of the away-side (ΔΦ≈ π ) azimuthal correlation is observed at all Δη, as compared to the measurements in pp collisions. Furthermore, long-range dihadron correlations in Δη are observed for particles with similar Φ values. This phenomenon, also known as the "ridge", persists up to at least |Δη|=4. For particles with transverse momenta (p T) of2-4 GeV/c, the ridge is found to be most prominent when these particles are correlated with particles of p _T=2-6 GeV/c, and to be much reduced when paired with particles of p _T=10-12 GeV/c.