Measurement of jet fragmentation in Pb+Pb and

Area of Science:

• High-energy nuclear physics
• Particle physics
• Quantum chromodynamics

Background:

• Heavy-ion collisions create a hot, dense medium.
• Jets are produced by energetic partons.
• Understanding jet modification in the medium is crucial for probing its properties.

Purpose of the Study:

• To measure charged particle distributions within jets in Pb+Pb and pp collisions.
• To investigate the impact of the hot, dense medium on jet fragmentation functions.
• To quantify modifications in jet structure due to parton energy loss.

Main Methods:

• Utilized ATLAS detector at the LHC.
• Analyzed Pb+Pb and pp collision data at 2.76 TeV.
• Measured transverse momentum and longitudinal momentum fraction of charged particles in jets.
• Used pp collisions as a reference for Pb+Pb collisions.

Main Results:

• Observed modest but significant centrality-dependent modifications of fragmentation functions in Pb+Pb collisions compared to pp collisions.
• No significant dependence of modifications on jet transverse momentum (pT) and rapidity was found.
• A reduction in yields for high transverse momentum fragments was observed for more forward jets.

Conclusions:

• The hot, dense medium created in heavy-ion collisions modifies the internal structure of jets.
• Jet fragmentation functions are sensitive to the energy loss of partons traversing the medium.
• These findings provide insights into the properties of the quark-gluon plasma.