heavy ion physics with the cms experiment at the lhc
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Heavy Ion Physics with the CMS Experiment at the LHC. G á bor Veres Eötvös Loránd University, Budapest, Hungary Massachusetts Institute of Technology, Cambridge, USA for the CMS Collaboration. Strangeness in Quark Matter ’06 UCLA, California, March 26, 2006. - PowerPoint PPT PresentationTRANSCRIPT
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Heavy Ion Physics with the CMS Experiment at the LHC
Gábor VeresEötvös Loránd University, Budapest, Hungary
Massachusetts Institute of Technology, Cambridge, USAfor the CMS Collaboration
Strangeness in Quark Matter ’06UCLA, California, March 26, 2006
CMS HI groups: Adana, Athens, Basel, Budapest, CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon, MIT, Moscow, Mumbai, New Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, U Kansas,
Tbilisi, UC Davis, UC Riverside, UI Chicago, U Iowa, Yerevan, Warsaw, Zagreb
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Physics opportunities at the LHC LHC: a large increase in collision energy compared to
existing accelerators:• Extended kinematical reach (y, pT) for p+p, p+A, A+A collisions
• New properties of initial state, saturation even at mid-rapidity
• A hotter and longer lived partonic phase
• Increased cross sections of hard probes, heavy quarks
• Last but not least: unknown territory/surprises?
New energy regime will open a new window on hot and dense matter physics: another large energy jump!
AGS SPS RHIC LHC (Pb+Pb)
sNN [GeV] 5 17 200 5500
increase in sNN 3-4 12 28
y range 1.6 2.9 5.4 8.7
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Heavy Ion Physics Topics at the LHC
High pT: modification by the medium
Copious production of high pT particles
Large jet production cross section
RHIC
LHCRHICLHC
J/ψ Different “melting” for the family
members, depending on binding energyLarge production cross section for the J/ψ and family
Correlations, scattering in mediumjets clearly identifiable, for the first time in heavy ion collisions
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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CMS, as a heavy ion experiment
Calorimeters: high resolution and segmentation
Hermetic coverage up to ||<5 (||<7 with the proposed CASTOR)Zero Degree Calorimeter (approved)
Muon tracking: from Z0, J/, Wide rapidity coverage: ||<2.4 σm 50 MeV at the mass in the barrel
Silicon Tracker Good efficiency and purity for pT>1 GeV Pixel occupancy: <2% at dNch/d 3500 p/p 2% for pT<70 GeV
Functional at the highest expected multiplicities: studied in detail at dNch/d 3000-5000 and cross-checked at 7000-8000
DAQ and TriggerHigh rate capability for A+A, p+A, p+p
High Level Trigger: real time HI event reconstruction
CASTORCASTOR(5.32 < η < 6.86)
ZDCZDC(z = 140 m)
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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HLT
Lvl-1
Data Acquisition and Trigger
Level 1 hardware trigger Muon track segmentsCalorimetric towersNo tracker dataOutput rate (Pb+Pb): 1-2 kHz comparable to collision rate
High level trigger Full event information available Every event accepted by L1 sent to an online farm of 2000 PCsOutput rate (Pb+Pb): 40 HzTrigger algorithm: similar to offline reconstruction
- Every event must pass the whole chain- Selectivity depends on available CPU power
switchswitch
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Centrality and forward detectors
Energy in the forward hadronic calorimeter
Zero Degree Calorimeter
Tungsten-quartz fibre structure electromagnetic section: 19X
0
hadronic section 5.6λ0
Rad. hard to 20 Grad (AA, pp low lum.) Energy resolution: 10% at 2.75 TeV Position resolution: 2 mm (EM sect.)
Centrality (impact parameter) determination is needed for physics analysis
impact parameter [fm]
ET [
GeV
]
Pb+Pb
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Charged particle multiplicityWill be one of the first results, important for initial energy density, saturation, detector performance etc.
ch
Muon detection, tracking, jet finding performance checked up to dNch/d5000
high granularity pixel detectors pulse height measurement in each pixel
reduces background Very low pT reach, pT>26 MeV (counting hits)
W. Busza, CMS Workshop, June 2004
Simple extrapolation from RHIC data
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Track reconstruction
MomentumResolution [%]
Transverse Impact Parameter Resolution
[cm]
(Event sample: dn/dy3000 + one 100GeV jet/event)
Excellent performance, even at the highest particle densities
Efficiency and fake rate [%]
-0.5<<0.5
2.0<<2.5
-0.5<<0.5
2.0<<2.5
-0.5<<0.5
efficiency
fake rate
%
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Quarkonia in CMS Heavy Ions
J/ acceptance
J/ familyM+- spectrum, family
Y=50 MeV
in the barrel
Expected: 24000 J/and ~ 18000/5000/3000 /’/’’
After one month of Pb+Pb running at L=1027cm-2s-
1
with 50% efficiencyOnline HLT farm improves acceptanceby 2.5 at high and low pT
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Jets – a new observable at LHC
Hard, perturbative scale: Q>>QCD. Hard parton production unaffected by medium
Parton shower development affected by the medium At LHC in Pb+Pb collisions:
– wider pT range for suppression, quenching studies
– jet structure will likely be modified, compared to jets produced in p+p– comparison to p+p and p+A is essential
Observables:High pT particles and particle correlations (similar to RHIC analyses)
Jet rates: single and multi-jets (quenching studies)Jet fragmentation and shape:
Distance R to leading particle (in - space) forward-backward correlation: (particle, jet axis)– Fragmentation function: F(z)=1/NjdNch/dz where z=pt/pjet
correlations with non-hadronic particles: jets+, jets+ZJets originating from heavy quarks (b, c)
c
d
ab
Extensive theoretical and experimental preparatory workpresently in progress
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Jet reconstruction in the calorimeters
||<0.3
1.6<||<1.9||<0.3
1.6<||<1.9
resolution resolution
efficiency efficiency
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Jet studies using the tracking
Centrality dependence of pT specra can be studied:Azimuthal correlations (as studied at RHIC):
Fragmentation functions: pT with respect to jet axis:
Tracking is a very important capability for jet physics
dN/d
p T1/
Nje
tsdN
ch/d
z
1/N
jetsdN
ch/d
p Tje
tdN
/d(
)
Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006
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Advantages of CMS over other HI experiments
CASTORCASTOR TOTEMTOTEM
ZDCZDC
(5.32 < η < 6.86)
(z = 140 m)
Hermeticity, Resolution, GranularityCentral region: tracker, electromagnetic and hadronic calorimeters and muon detector
Forward coverage calorimeters extend to 10 Proposed CASTOR calorimeter to 14
High data taking speed and trigger versatility
Two-level triggerAbility to “inspect” every heavy ion event on the High Level Trigger computer farm