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
J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455
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 machine for soft properties study at the LHC
Thanks!
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