# QM 2011 - XXII International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

May 22 – 28, 2011
Centre Bonlieu
Europe/Zurich timezone

## Dijet fragmentation functions measured in PbPb collisions with CMS

May 27, 2011, 5:30 PM
20m
Salon Verdi AB (Imperial Palace)

### Salon Verdi AB

#### Imperial Palace

Allée Impérial 74000 Annecy, France Tél. : +33 4 50 09 30 00 Salle de l'Europe, Imperial Palace
Parallel Jets

### Speaker

Yetkin Yilmaz (Massachusetts Inst. of Technology (MIT))

### Description

The energy loss of fast partons traversing the strongly interacting matter produced in high-energy nuclear collisions is one of the most interesting observables to probe the nature of the produced medium. Analyzing data from PbPb collisions at a center-of-mass energy of 2.76 TeV, recorded with the Compact Muon Solenoid (CMS) detector, parton energy loss is observed as a significant imbalance of dijet transverse momentum. To gain further understanding of the parton energy loss mechanism and how it manifests itself in the distribution of final state particles, parton fragmentation functions are studied for the leading and subleading jet in bins of centrality and dijet imbalance. Dijets are reconstructed using the anti-kT jet algorithm, with the particle flow method of event reconstruction. Particle flow, which is applied to heavy-ion collisions for the first time in this measurement, allows for improved jet reconstruction by combining track and calorimeter information at the particle level. The fragmentation functions for leading and subleading jets are compared to model calculations and measurements in pp collisions. The results confirm and complement earlier CMS results based on calorimeter jets and yield a detailed picture of parton propagation in the hot QCD medium.

 Slides