Nuclear Particle Astrophysics (NPA) Seminar, Yen-Jie Lee, MIT, “Measurement of quenched energy relative to dijet systems in PbPb collisions at 2.76 TeV with CMS”

Thursday Oct 15, 2015, 3:00 PM → 4:00 PM US/Eastern

WLC 108

One of the first observations of the “flow” of the quenched energy in imbalanced dijet events in PbPb collisions has been through the studies of transverse vector sum of particles with the CMS detector, namely the missing transverse momentum (pT) measurement. The results have led to new theoretical insights to order to explain the wide angle radiation, such as “jet collimation”, “color decoherence”, “turbulence cascade”, “third jet quenching” and “hydrodynamical expansion of quenched energy”. These mechanisms could give different angular distributions of quenched energy relative to dijet systems. In this talk, an updated analysis of dijet events in PbPb and pp collisions is presented. Data are collected at a nucleon-nucleon center-of-mass energy of 2.76 TeV at the LHC. The distribution of transverse momentum surrounding dijet systems is measured by selecting charged particles in different ranges of pT and at different angular cones of pseudorapidity and azimuth. The measurement is performed as a function of centrality of the PbPb collisions, the pT asymmetry of the jets in the dijet pair, and the distance parameter R used in the anti-kt jet clustering algorithm. In events with unbalanced dijets, PbPb collisions show an enhanced multiplicity in the hemisphere of the subleading jet, with the pT imbalance compensated by an excess of low-pT particles at large angles from the jet axes. These results constrain the redistribution of transverse momentum in the modeling of QCD energy loss processes of partons traversing the hot and dense medium created in heavy-ion collisions.

Yen-Jie_Lee_NPA_Seminar_10152015.pdf