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# Physics at LHC 2012

4-9 June 2012
Life Sciences Centre, UBC
<strong><font color="#cc0000">Abstract submission has closed</font></strong>

## Hard probes used in heavy ion collisions to study QCD at extreme energy densities

5 Jun 2012, 15:30
20m
LSC-3 (Life Sciences Centre, UBC)

### LSC-3

#### Life Sciences Centre, UBC

University of British Columbia Vancouver, BC Canada
Parallel Talk Heavy Ion Physics

### Speaker

Dr Jim Pivarski (Fermi National Accelerator Lab. (US))

### Description

We present results of the CMS experiment from PbPb collisions at $\sqrt{s_{NN}} = 2.76$ TeV, probing quark and gluon matter at unprecedented values of energy density. The capabilities of the CMS apparatus allows us to investigate various hard probes, using the calorimetry, muon and tracking systems covering a large range in pseudorapidity, complemented by a flexible two-level trigger system. One of the most important early observations was that dijets at high pT are found to be increasingly unbalanced as a function of collision centrality. The overall pT-imbalance can be recovered by including tracks found at low pT and at large angles with respect to the jet axis. Furthermore, the pT-distribution of charged tracks (jet fragments) has been measured using various jet triggers in pp collisions at 7 TeV, and a reference spectrum is constructed to compare to PbPb collisions at 2.76 TeV/nucleon pair. The inclusive production of isolated prompt photons has also been studied in pp and PbPb collisions. CMS is also well equipped to measure muons and dimuons in the high multiplicity environment of heavy ion collisions. Inclusive and differential measurements of the Z and W boson yields show no sign of modification with respect to NLO pQCD calculations. Dimuon decays of the J/psi particle and the Upsilon family are also investigated and results will be presented.

### <strong>Collaboration Name</strong><br /><font color="#000099">Please enter the name of<br />the collaboration or group<br />using the acronym, as in:<br /><font color="#ff0000">ABC Collaboration</font>

CMS Collaboration