Abstract
Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution. This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500GeV, in pp and PbPb collisions at a center-of-mass energy of 5.02TeV per nucleon pair. In central PbPb collisions, the splitting function indicates a more unbalanced momentum ratio, compared to peripheral PbPb and pp collisions.. The measurements are compared to various predictions from event generators and analytical calculations.
Highlights
Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur
Jet quenching was first observed at the Relativistic Heavy Ion Collider [3,4,5,6,7,8,9] and at the Large Hadron Collider (LHC) [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]
This Letter reports a study of hard parton splittings in pp and PbPb collisions
Summary
The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500 GeV, in pp and PbPb collisions at a center-ofmass energy of 5.02 TeV per nucleon pair. This Letter reports an attempt to isolate parton splittings to two well separated partons with high transverse momentum (pT), probing medium induced effects during the parton shower evolution in the QGP Information about these leading partons of a hard splitting can be obtained by removing the softer wide-angle radiation contributions, done through the use of jet grooming algorithms that attempt to split (“decluster”) a single jet into two subjets [26,27,28,29,30].
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