us participation in heavy ion physics with compact muon solenoid at lhc m. ballintijn,k barish,r...
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US participation in Heavy Ion Physics with Compact Muon Solenoid at LHC
M. Ballintijn,K Barish,R Betts, BE Bonner, W.Busza, D.Cebra, G.Eppley, E.Garcia, F.Geurts, C.Halliwell, D.Hofman, P.Kulinich, W.Llope, M.Murray, G. van Nieuwenhuizen, E.Norbeck, R.Nouicer, Y.Onel, C.Roland, G.Roland,
R.Seto, G.S.F.Stephans, B. Wyslouch, P.Yepes
MIT, Rice, TAMU, UC Davis, UC Riverside, UI Chicago, U Iowa
CMS HI workshopwas held at MITFebruary 2002
US Heavy Ion physics today
• RHIC has completed first long run of Au-Au at (sNN) =200 GeV/c (Its highest energy)– Expect to run for many years
• It has reached design luminosity– Expect improvements
• The four detectors: BRAHMS, PHENIX, PHOBOS and STAR– BRAHMS and PHOBOS have short lifetime (<4 y)
• Much better detectors and running conditions than ever before in the field of relativistic heavy ions
• Practically no involvement at LHC
Main RHIC physics and tools
• Equation of state of QCD: connection to lattice results predicting phase transitions
• Chiral symmetry restoration• Quark Gluon Plasma, How does a high-temperature
quark-gluon state emerge from the collision of nuclei?• Photon and di-lepton probes ( J/), studying effects of
the plasma on particle production and survival• Production of high pt particles is affected by the energy
loss in nuclear matter
Early results are accumulating. No large, obvious effects seen, but some puzzles start to appear
Integrated Au-Au luminosity
FY2000(66 GeV/amu)
FY2001 – 02100 GeV/amu
PHENIX during last 10 days:24 (b)-1/week
Lave(week) = 0.4 1026 cm-2 s-1
Lave(week)/Lave(store) = 27 %
Multiplicity per nucleon-nucleon interaction as a function of collision energy for heavy ions and for proton-antiproton collisions
Preliminary
Comparison of momentum spectra of particles AuAu vs ppToo few high pt particles ?
ppN
AuAuR
binaryAA
STAR
Production of high pT particles, e.g. 0
Heavy Ion physics at the LHCIncrease energy (sNN) 200->5500 GeV
• Saturated gluon distributions in colliding nuclei, initial state of the system calculable in perturbative QCD
• Plasma has higher temperature and lives longer in partonic state
• Spectrum of quarkonia produced with high statistics
• Jets clearly visible and identifiable
• Z0 produced in large numbers
HI group in CMS has produced many excellent physics studiesResults need some update and extensions to take into account RHIC results
The experiments
ATLAS: pp experiment, recent HI interest
ALICE: dedicated HI experiment
CMS: pp experiment with HI program
Design of LHC experiments is affected by the multiplicity of charged particles
Peter Steinberg, 2002
LHC?
Extrapolated to LHC:dN/d~1400
LHC detectors are being designed for
dN/dy~8000
Quarkonia, CMS is very good here
J/ family
’/ ratioaffected by the initial conditions: a plasma thermometer(Ramona Vogt)
Detailed studies using full simulation,reconstruction, background subtractiondN/dy studied from 2500 to 8000
Very large event rate
Uses muon detector, outer tracker, pixels
Pb+Pb Sn+Sn Kr+Kr Ar+ArJ/psi 28.7 210 470 2200psi' 0.8 5.5 12 57Upsilon 22.6 150 320 1400Upsilon' 12.4 80 180 770Upsilon'' 7 45 100 440
Yield/month (kevents, 50% eff)
Can we use tracker ? CMS Tracker Occupancy
• Calculated for PbPb dNch/dy=5000
• For reference: STAR TPC occupancy reaches 22%
Jet fragmentation
• Find jets using calorimetry• Study charged particle momenta inside of a jet using the tracker• For this study use 4-5 outer layers of the tracker (use
conservative resolution obtained in pp studies: AA plausible with low occupancy in outer layers)
Particles in jet
Background
Field OFFField OFF Field ONField ON
Field OFFField OFFField ONField ON
Global observables e.g. Et
Our proposal to DoE/Nuclear
• Extend the physics reach of the US heavy ion community beyond RHIC’s energy scale
• Concentrate US physics effort on the study of phenomena most likely to be affected by the energy increase, the “hard probes”:– Quarkonia and heavy quark production– Jet production, jet-jet, jet-gamma and jet-Z0
correlations
• Provide US/RHIC expertise and tools to study high pt processes in AA collisions at the LHC
• Use detector designed for high pt physics: CMS
• LHC starts in mid-2007 with pp, AA to follow in 2008(?): Be ready with strong group in 2008
Our proposal to DoE/NuclearSpecific plans of the existing groups
• Physics studies, software development• High Level Trigger code development +
request to fund 2/8 slices of Event Filter Farm (Rice, MIT, UC Davis, UCR)
• Zero degree calorimeter (U Iowa, UIC, TAMU)
• Total ~ 5 M$ from DoE/Nuclear• review took place 2&3 of April @ DoE, no final
report yet. Closeout conclusion: “continue studies, come back later”
• competing with ALICE and ATLAS(!)
Centrality: Participants vs. Spectators
“Spectators”
Zero-degreeCalorimeter
“Spectators”
Many things scale with Npart:• Transverse Energy• Particle Multiplicity• Particle Spectra
“Participants”
Only ZDCs measure Npart
specpart NAN
Detectors at 90o
The collision geometry (i.e. the impact parameter) determines the number of nucleons that participate in the collision
Beam pipe splits 140m from IR.
INNER WALL
Z-AXIS
ZDC LOCATION
BEAM
BEAMPAIR OF PANTS(POP)
ALIGNMENT PINS
Zero Degree Calorimetry for CMS
RHIC ZDCs work very well
High Level Trigger (HLT)
• All event data available:– Fine data for
Calorimetry and Muon Detectors
– Tracker
• Refine triggered object
• Allows to go lower in pT
• Processing time O(s)• Filtering Farms of
commodity processors (Linux)
• L1 in AA has larger backgrounds than in pp due to underlying event.
• Efficiency trigger requires more careful analysis. HLT can do a better job than L1.
• HLT to play a greater role in AA
AA Event Size & Data Flow
0
500
1000
1500
2000
2500
3000
pp OO ArAr SnSn PbPb
Eve
nt S
ize
(Kby
tes)
Pixel Si TrackerECAL HCALMuon
Event Size Detector # Channels(1000)
Pixel 45,000
Si Tracker 12,000
ECAL 230HCAL 14
Muon Det. 400
Total 57,644
Data Flow and Rates
L1
HLT
HLT better
trigger job
CPU Estimate of HI Online Tracking
June 16, 2000 First STAR event
tracked on line
STAR CMS ScalingdN/dy 600 3000 5.0Acceptance, ||< 1.5 2.5 1.7Max. Number Layers 45 13 0.3Clustering 1 2 2.0Clustering Type 1 2 2.0All Factors 9.6
STAR CMSMIP s/event 386 3706MIP s/ CPU 460 13800Event/CPU/s 1.2 3.7Max Input L3/HLT (Hz) 100 7400Minimum Number CPUs 84 1987
Moore’s Law: double/18 months
for ~8 years
• Use STAR (Rice) experience
• Scale linearly with # clusters from STAR AuAu to CMS PbPb
• Assume Moore’s Law
Near term plan
• Work together with heavy ion group in CMS on expanding the physics scope of the heavy ion program
• Develop good physics case for tracking in CMS, at HLT level and in offline analysis
• Develop and possibly prototype Zero degree calorimeter.
• Fight for funding from DoE, expand collaboration
Summary
• CMS has a potential to be an excellent detector for heavy ion physics
• RHIC results will really determine the scope of interesting physics, the US community will have direct access to the RHIC experience
• HI physicists could provide useful expertise, manpower and source of funding
Z0 production
• Z0- can be reconstructed with high efficiency
• A probe to study nuclear shadowing and parton energy loss
• Z0 also proposed as reference to production.– Nuclear effects may
depend on mass MZ>M
– Different production mechanisms:
• Z0: antiquark-quark, quark-gluon and antiquark-gluon.
: gluon-gluon.
Open b: high mass +- : medium modification, energy loss for b-quarks
Muon tracking (muon+tracker)
Displaced vertices(pixels)