High-density QCD with CMS at the LHC

Haidong Liufor the CMS Collaboration

OutLine•Detectors Overview•Bulk Observables•Hard Probes•Summary

2008-10-24 Haidong Liu (UCD) / DNP2008 2

CMS Detectors

Coverage of main detectors

Silicon tracker |η|<2.5

Muon tracker |η|<2.4

ECAL |η|<3.0

HCAL |η|<5.2

CASTOR 5.2<|η|<6.7

2008-10-24 Haidong Liu (UCD) / DNP2008 3

Tracking in Si Pixels and low pT PID in Pb+Pb 5.5 TeV collisions

Reconstructed hits in the Si pixel tracker

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455

2008-10-24 Haidong Liu (UCD) / DNP2008 4

Low pT PID spectra for Pb+Pb @ 5.5 TeV

Acceptance|η|<1

Efficiency|η|<1

pT_reco/pT_sim

|η|<1

pT resolution|η|<1

pT (GeV/c)

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455

pT (GeV/c)

pTsim (GeV/c) pTsim (GeV/c)

2008-10-24 Haidong Liu (UCD) / DNP2008 5

Event plane resolutionb=9fm of Pb+Pb collisions --the expected resolution is 0.37 rad with ECAL

NA49 Phys. Rev. C 68 034903 PHOBOS nucl-ex/0610037PHOBOS Nucl. Phys. A 774 523–26 STAR AIP Conf. Proc. 870 691–4Voloshin S A and Poskanzer A M Phys. Lett. B 474 27–32Kolb P F, Sollfrank J and Heinz U W ,Phys. Rev. C 62 054909Teaney D, Lauret J and Shuryak E V nucl-th/0110037

will the v2 reach the hydro limit?

Φsimu-Φreco

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455

2008-10-24 Haidong Liu (UCD) / DNP2008 6

Hard probe triggeringLevel 1 Trigger

Collision Rate 3 kHz (8 kHz peak)

Event Rate 3 kHz (8 kHz peak)

Rejection 0%

High-Level Triggers

Input events rate 3 kHz (8 kHz peak)

Output rate 10 - 100 Hz

rejection 97 – 99.7%

HLT significantly enhanced statistics for hard processes

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455

2008-10-24 Haidong Liu (UCD) / DNP2008 7

Jets and high pT spectra

Leading jet ET distribution in one month data

ET threshold 50, 75, 100 GeV

Charged particle spectra and RAA

Very small errorsbelow 200 GeV

Jet

ET R

esol

utio

n [%

]J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455

Expected reach (0.5 nb-1): pT~ 300 GeV/c (inclusive hadrons)pT~ 500 GeV/c (jets)

2008-10-24 Haidong Liu (UCD) / DNP2008 8

Expected quarkonia signalsin one month data (di-muon)

Assuming no quarkonia suppression dN/dη|η=0=5000Both μ |η|<2.4

dN/dη|η=0=2500Both μ |η|<0.8

Solid line: Both μ |η|<2.4 dashed line: Both μ |η|<0.8

Acceptance

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455

Expected stats (0.5 nb-1): ~1.8e+5 (J/Psi) & ~2.5e+4 (Upsilon)

2008-10-24 Haidong Liu (UCD) / DNP2008 9

Z0 signals

Expected stats (0.5 nb-1): ~11000 (Z-->μμ) ~1000 (Z-jet with pT>25 GeV/c)

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455

2008-10-24 Haidong Liu (UCD) / DNP2008 10

Photon tagged jets

Isolated photon+

away side jet

CMS NOTE HIN-07-002

Unquenched FF Quenched FF

models used in this analysisPYQUEN: selected QCD channels w/ jet quenchingPYTHIA: selected QCD channels w/o jet quenchingHYDJET: underlying corresponding Pb+Pb events

Ratio of quenchedand unquenched FF

Detailed quantitative studies of medium-induced parton energy-loss possible.

2008-10-24 Haidong Liu (UCD) / DNP2008 11

Summary

• CMS detector has – High-resolution trackers, calorimeters and muon

chambers– Large acceptance

• This makes CMS an ideal experiment to measure various hard probes in Pb+Pb at 5.5 TeV and a competitive experiment for soft properties study at the LHC

Thanks!