Measurement of jet quenching with semi-inclusive hadron-jet distributions in central Pb-Pb collisios at sqrt(NN)=2.76 TeV

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2.76 TeV
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The ALICE Collaboration at the LHC reports a new measurement of jet
quenching in central PbPb collisions at sqrtsNN=2.76 TeV, based
on the semi-inclusive distribution of jets recoiling from a high
pT hadron trigger. The difference between recoil jet distributions
for two exclusive intervals of hadron trigger pT measures the
evolution of jet yield coincident with the trigger. This measurement
can be carried out with collinear-safe jet reconstruction and low
infrared cutoff on jet constituents, even in the complex environment
of heavy ion collisions, resulting in minimal jet selection bias. We
report the differential recoil distribution of charged jets in
central PbPb collisions at sqrtsNN=2.76 TeV over the kinematic
range 20<pTjet<100 GeV, with jet resolution parameter R=0.2,
0.4, and 0.5.  The effects of jet quenching are quantified by
comparison of the PbPb measurements to Next-to-Leading-Order
calculations for pp collisions, and by comparison of recoil jet
yields measured in PbPb collsiions for different R. The angular
distribution of coincidence recoil jets relative to the trigger
hadron direction is measured and the rate of large-angle scatterings
in the hot and dense medium is characterized.

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