status of cms and the road to first physics results jordan nash for the cms collaboration – icfa...
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Status of CMS and the road to first physics results
Jordan Nash
For the CMS Collaboration – ICFA Seminar – SLAC October 2008
Outline
CMS Status Commissioning so far Commissioning plans with first data Physics Topics for the first fb-1
QCD/JETS Electroweak New Physics
Last detector to Install
When the detector was closed for the September beam running, all elements of CMS were installed except for the pre-Shower detector in front of the Crystal endcaps
The Preshower detector will soon be completed, and installed during the winter shutdown
“D’s” undergoing final assembly cold testing now
Commissioning with Cosmics
z
(at
surf
ace)
[c
m]
x (at surface) [cm]
Tracker
ECAL
HCAL
Muon System
3 T
Sept 10
0 T
Position of track extrapolated to
surface.Clearly see shaft
More than 300M events
recorded during
summer
Tracks passing through the ECAL
Cosmic running used to test triggers, operation of all detectors
Example: Trigger using Drift Tubes Validate Calorimeter e-gamma Trigger
Verify pre-calibration of ECAL
in detector units
i
n d
ete
cto
r un
its Reconstructed clusters matching muon tracks
(DT triggered events)
Energy deposited in 3x3 ECAL cluster matched to a muon track
Muon reconstruction at 3TReconstructed Muon Momentum using Drift Tubes
Magnet closed for the first time underground late in the summerBefore the Sept 10 Running field raised to 3 T
Tracker operation and alignment Cosmics used to align
tracking detectors Significant improvement
from construction parameters possible already
Multiple algorithms for alignment validated
Look at performance using “split” muons
CRUZET4
before alignment
after alignment
Calorimetric response
Splash on collimators 2 X 109 p hitting the collimator 150 m upstream from the detector
Tremendous amount of energy deposited in the detector DAQ able to cope with enormous
events
Ecal Endcap
Ecal Barrel
Correlation between total
energy in ECAL and HCAL
Conditions with beam captured
HCAL Endca
p
Endcap Muon Trigger Rate for circulation and then capture of
beam
Next Steps 300M events at 3.8 T (CRAFT) Goals
Improved alignment of tracking detectors Want sufficient events passing
through pixel detector Experience of continuous operation
of complete detector at full field Will then open CMS to install the
preshower detector
75 M events in first few
days
What do we expect to do with first collisions? Plan over the last year has
been to study what to extract from the first few pb-
1
Re-discover the SM Event rates for SM processes
are large Rate W ~108/fb-1
Rate Z ~107/fb-1
Rate tt ~106/fb-1
Understand detectors e.g. W/Z used for precision
calibrations Understand backgrounds in
searches for new physics, and precision measurements Concentrate on data driven
methods for determining backgrounds
Early studies of event properties
Enormous QCD Cross section New territory in terms of Jet ET
Underlying event measured with very first data Understand environment at 14
TeV Tune MC models Observables Nch, PT
SumTevatron
LHC
Different Tunes/Model
s
Jets/QCD
Potential for discovery of Contact interactions in Dijets, 4 TeV for 10 pb-1
7 TeV for 100 pb-1
10 TeV for 1 fb-1
Measurement of Inclusive Jet Cross Section Understanding of Jet
Energy scales, resolutions PDF Uncertainties
Energy Scale
Uncertainty100 pb-1
Calibrating Jets/Missing ET
Missing ET Vital for many physics channels
calibration is difficult Sensitive to Hot/Dead Channels
Instrumental effects can create large fake signals
Need Real data Need to correct for
Jet Energy , m t, e
Data Driven methods for Jet Energy Scale Corrections e.g. DiJet Balance –relative Z+Jets - absolute
Early Z Measurement 10 pb-1
~4.6K e+e- pairs in the 70<Me,e<110 mass
region
~5.5K μ+μ- pairs in the 70<Mμ,μ<140 mass
region.
The Z produces a very clean signal. Use Tag
and Probe to calculate efficiencies from Data
2 Isolated High PT (20 GeV) tracks (muons)2 Isolated High ET (20 GeV) electrons, loose electron ID
Early W Measurement Single Isolated High PT Lepton
Muon (>25 GeV), Electron (>30 GeV) QCD Background estimation from Data
Invert Isolation Cuts Missing ET Shape from Data
Use γ*/Ζll events Measure missing ET excluding the 2nd
lepton Event rates (at 10 TeV are about 70% the
rate at 14 Tev)
28K Weν events and ~ 6K QCD events
64K Wμν events and ~16K QCD events
W Mass –precision measurements 1 fb-1 gives MW to about 40 MeV/c2
Limit energy linearity(e), MET scale(m) 10 fb-1 measure MW to about 20 MeV/c2
(statistical uncertainty 15 Mev/c2) Ultimate precision about 15 MeV/c2
Limited by MET Scale, resolution Theoretical uncertainties PDFs, PT(W)
WZ/ZZ
Understanding vital for searches These are major irreducible backgrounds for searches Ultimately measure TGCs
300 pb-1
Events per fb-1
•Find Same Flavour Opposite Sign leptons for Z candidate• PT Leptons > 15 GeV•Add 3rd lepton with PT > 20 GeV• Form MT with Missing ET -Require MT > 50 GeV
Looking for Supersymmetry Signatures
Leptons Jets Missing Energy
Requires excellent understanding of the detector
Builds on our measurements of SM processes
SUSY parameter space Where to look? Detailed studies at a
set of potential SUSY mass scenarios Full MC analysis Understand analysis
strategies, systematic uncertainties
Extrapolate to cover the full plane using Fast simulation
Low Mass points for early discovery potential
High Mass points for looking near potential limits
Early SUSY searches Jets + Missing ET signature
>= 3 Jets (180, 110, 30 GeV) , HT > 500 GeV, Missing ET > 200 GeV
Must control backgrounds, and understand missing transverse energy – QCD events with mis-measurements have very different
topologies Irreducible background from Z to neutrino decays Use Z + Jets (Z to leptons) to estimate bkgd Also Use g + jets
Remove photon
LM1 1 fb-1
HM Points/DiJets
Jets+Missing ET at HM points HT > 1500 GeV, Missing ET > 600 GeV
Also looking at new variables Look at Dijet events using discriminator
suggested by Randall/Tucker-Smith Two High PT Jets (HT > 500 GeV) a > 0.55 Sensitive to squark pair production
HM1 1 fb-1
Missing ET + Jets + leptons
Two Same Sign Muons PT > 10 GeV >= 3 Jets (175/130/55) GeV Missing ET > 200 GeV
Backgrounds in these channels are very low SM Backgrounds produce
opposite sign leptons
At least 1 isolated Muon PT > 30 GeV
>= 3 Jets (440/440/50) GeV
Missing ET > 120 GeV Signal/Background High
Discovering SUSY parameters
No Mass peak, but kinematic edges possible to observe
Same Flavour Opposite Sign leptons PT > 10 GeV
>= 3 Jets (120/80/30) GeV Missing ET > 200 GeV Estimate backgrounds from
Opposite flavour events Fit for endpoint
Sensitivity (statistical) ~1 GeV/c2 for 1 fb-1
Signal
Bkgd
Cascade Higgs Decays
Other Possible BSM extensions have similar signatures (i.e. leptons, jets, large missing ET,) Technicolor ED Little Higgs
May be possible to see Hadronic h decays with large missing ET signatures
h02
bmissTE01
b
Heavy Stable Charged Particles
32
Models with Charged Stable Particles GMSB - staus Kaluza-Klein taus Long lived stop
ct of order meters Measure Time of Flight in the
Muon DT system Measure DE/Dx in the
Tracker Momentum from Tracking
Conclusions
CMS Detector will be complete and commissioned at the start of next year’s run Substantial data collected at full field with all
detectors Experience of 24/7 operation
Rapid understanding of first data will be vital to be ready for early discoveries Physics preparation concentrating on preparing
data-driven analysis to: Recover SM Understand detector performance Look for evidence of new physics
Many new physics signals detectable with a few fb-1