cms 2008:2014 michael murray kansas, athens,basel, cern, demokritos, dubna, ioannina, kent state,...
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CMS 2008:2014 Michael MurrayMichael Murray
Athens,Basel, CERN, Demokritos, Dubna, Ioannina, Kent State, Kiev, Lyon, MIT, Moscow, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, Kansas,Kansas, Tbilisi, UC Davis, UC Riverside, UI Chicago, U. Iowa, Yerevan, Warsaw
Are our projections reliable?
“There are known knowns. These are things we
know that we know. There are known unknowns.
That is to say, there are things we know we don't
know. But, there are also unknown unknowns.
These are things we don't know we don't know.”
Donald Rumsfeld Washington 2002
“These theories (this talk) ain’t worth a
bucket of worm piss”
Bill Willis CERN Council 1982
It’s the unexpected stuff that is fun.
Muons
Hadron Calorimeter
Cyrostat
EM
Tracker
A Generic Detector
17 pp collisions each 25ns = 20% of a PbPb collision
What do we want to run?The first pp collisions should be April 2007 andPbPb expected one year later. Each year expectseveral weeks of ion beams (106s effective). TheCERN HI community wants a short exploratoryrun in 2007 Future includes other ion species andpA. Start off with surveys of such as flow, J/ etc.We will then move onto statistics limited
measurements such as, , high pT, jets, and
correlations of jets with and Z.
It is vital to understand pp well
At RHIC we had some idea what to expect but still had to learn pp. At LHC pp √S is 7 times greater than FNAL.
Measure leptons, hadrons & neutrals
Abundant hard probes
J/
Balancing or Z0 vs Jets: Quark Energy Loss
# E
ven
ts/4
GeV
ET/0-ET
Jet (GeV)
<E>=8 GeV<E>=4 GeV<E>=0 GeV
Background
Isol. 0+jet
Suppression (or enhancement) of quarkonia can tell us about the medium.
J/
AA pp
Di-muon mass
J/
Energy Density (GeV/fm3)
m = 50MeV for the .
Jets in the calorimeters: ||<5
100 GeV JetPbPb dN/d =5000
Jet ET (GeV)
E %
Eff %
1. Subtract average pileup2. Find jets with sliding window3. Build a cone around Etmax 4. Recalculate pileup outside the cone5. Recalculate jet energy
Spatial resolution: = 0.045 = 0.051
Jet Reconstruction
Use calorimeters and tracking to measure V2
=0.1 rad
Event plane determination
CMS
Fragmentation & hydrodynamics
dNdNpartD
Calos cover 14 units of
Event by Event Multiplicity (and ET)
PHOBOS: Single Layer ~15000 channels
CMS: Three Layers ~60 Million channels
dN
/d
Min pT=26 MeV
Measure multiplicity on day 1
LHC?
Extrapolated to LHC:dN/d~1400
Evidence for Saturation
NdAuNpp
Kinematics at the LHC
J/
Z0
SaturationGluon density has to saturate at low x
Access to widest range of Q2 and x
Where do the protons go?
At RHIC the protons lose about two units of rapidity.
Rap
idit
y L
oss
Beam Rapidity
CASTOR covers 5< <7. This should cover the maximum baryon density
Beam pipe splits 140m from IR
ZDC LOCATION
BEAMS
b2R ~ 15fm
Spectators
Spectators
Participant Region
At zero degrees study energy flow and trigger on ultraperipheral
~7*107 J/ and can be made
Fragmentation of jets
A jet covers ~ 9000 crystals
pTjet
dN
dpTjet
dNdZ
Physics Goals of CMS 2008:2014
Observe the weakly interacting QGP. This state may be characterized by a collapse of directed flow, thermalization of charm and stronger energy loss. Use jets, resonances Z0 and photons to measure its properties. Pin down the color glass condensate by measuring the saturation scale as a function of rapidity (x) and system size. Be ready for unknown unknowns.
Backups
Si Tracker Performance with Heavy Ions
6 layersOuterBarrel
4 layersInnerBarrel
3 disks 9 disks in the End Cap
1 Single Detector
2 Detectors Back to Back
Pixel Layers Crucial for Heavy Ions
pT Inside a Jet
100 GeV
Heavy Ion Trigger
• Main types of trigger as required by physics:– multiplicity/centrality:”min-bias”, “central-only”
– high pT probes: muons, jets, photons, quarkonia etc.
• High occupancy but low luminosity !– many low level trigger objects may be present, but less isolated than in p+p, Level 1
might be difficult for high pT particles
– but we can read most of the events up to High Level Trigger and do partial reconstruction
• HLT for HI needs significant software/simulation effort.
L1
HLT
Tracking works well for pT > 1GeV
Refinement of RHIC results at the LHC:
What lies beyond ?
• Many phenomena measured at RHIC have surprisingly simple energy dependence, will this continue at the LHC ?
• Hydrodynamic limit, will it hold?
beamy−≡′
dN
ch/d
′/<
Np
art>
/2
Flow
Charged particle multiplicity, scaling, limited fragmentation
CASTOR
5.32 < η < 6.86
T2 Tracker
5.32 < η < 6.71
CASTOR and Totem T2
Forward coverage: 1. Access to region of relatively high baryon density in HI
collisions2. Study diffractive & low-x (<106) Physics in p-p interactions
ZDC integration with TAN
Level-1 Trigger• Fast algorithms: 3 s with coarse local data
• Only Calorimetry and Muon Detectors
• Special purpose hardware (ASICS)
• Centrality with ECAL, HCAL (including HF)
• ZDC for minbias.
• Trigger on e, , jets, Missing ET. Rates steep function of pT thresholds
• AA higher backgrounds
Electromagnetic Hadron
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
Illustration Of Online Farm Power: Low pT J/ψ
• Only a small fraction of produced J/ψ are seen in LHC detectors– E.g. CMS J/ψ→ acceptance 0.1-0.2%, ~O(104) per LHC run
• Detection of low pT J/ψ requires efficient selection of low momentum, forward going muons. Simple hardware L1 dimuon trigger is not sufficient
L1 trigger Two 60 Hz
L2 trigger None 60 Hz
L3 trigger None 60 Hz
J/ψ pT >3 GeV/c
L1 trigger Single ~2 kHz
L2 trigger Re-fit 70 Hz
L3 trigger Match tracker
<40 Hz
J/ψ pT >1 GeV/c
Without online farm (HLT) With online farm (HLT)
Online farm
pT
Online farmImprovement
Acceptance x2.5
PILE UP SUBTRACTION PILE UP SUBTRACTION
ALGORITHMALGORITHM1. Subtract average pileup2. Find jets with iterative cone algorithm3. Recalculate pileup outside the cone4. Recalculate jet energy
Jet spatial resolution: (rec
- gen
) = 0.032; (rec
- gen
) = 0.028
It is better, than , size of tower (0.087 x0.087)
Measured jet energy Efficiency, purity Jet energy resolution
Calorimetric Jet reconstruction
CMS coverage
Finding charged tracks
Occupancy in central Pb+Pb Event:• 1-3% in Pixel Layers• Up to 70% in Strip Layers @
dNdy 7000
Efficiency and fake rates
Jet fragmentationLongitudinal momentum fraction z along the thrust axis of a jet:
pT relative to thrust axis:
Using ECAL clusters~0 in CMS
• Fragmentation function for 100GeV Jets embedded in dN/dy ~5000 events.
• Use charged particles and electromagnetic clusters