First measurement of large area jet transverse momentum spectra in heavy-ion collisions

Jet production in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02TeV is studied with the CMS detector at the LHC, using PbPb and pp data samples corresponding to integrated luminosities of 404 mu b(-1) and 27.4 pb(-1), respectively. Jets with different areas are reconstructed using the anti-k(T) algorithm by varying the distance parameter R. The measurements are performed using jets with transverse momenta (p(T)) greater than 200 GeV and in a pseudorapidity range of vertical bar eta vertical bar < 2. To reveal the medium modification of the jet spectra in PbPb collisions, the properly normalized ratio of spectra from PbPb and pp data is used to extract jet nuclear modification factors as functions of the PbPb collision centrality, p(T) and, for the first time, as a function of R up to 1.0. For the most central collisions, a strong suppression is observed for high-p(T) jets reconstructed with all distance parameters, implying that a significant amount of jet energy is scattered to large angles. The dependence of jet suppression on R is expected to be sensitive to both the jet energy loss mechanism and the medium response, and so the data are compared to several modern event generators and analytic calculations. The models considered do not fully reproduce the data.

Automated summary

The production of jets in PbPb and pp collisions at a center-of-mass energy of 5.02TeV was studied using the CMS detector at the LHC. The study revealed a strong suppression of high-p(T) jets in the most central collisions, with the jet nuclear modification factors extracted from properly normalized spectra. Various modern event generators and analytic calculations were compared to the data, however, none fully reproduced the observed results.