Physics with the CMS Experiment at LHC Start-up

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Physics with the CMS Experiment at LHC Start-up

• Dimitri Bourilkov
• University of Florida
• CMS Collaboration
• Meeting of SES of APS, November 11, 2004, Oak
  Ridge, TN, USA

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CMS Detector

• TRACKER ? lt 2.4, ?/pT 1.5x10-4 pT ? 0.005
• MUON ? lt 2.4, ?/pT 5 at 1TeV

• ECAL ? lt 3, ?/E 1.5/vE ? 0.5 ? 0.15/E
• HCAL ? lt 5, ?/E 120 / vE ? 5

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CMS Muon System

• Three types of gaseous detectors
• Drift Tubes in barrel region
• 4 stations interleaved with iron return yoke
• Self triggering and bunch crossing ID
• Cathod Strip Chambers in endcap regions
• 4 stations interleaved with iron return yoke
• Up to ? lt 2.4
• Resistive Plate Chambers in both barrel and
  endcaps
• precise bunch crossing ID for Trigger
• Up to ? lt 2.1

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LHC Start-up

• April 2007 start machine cool-down followed
  by machine commissioning
• (mainly with single beam)
• Summer 2007 two beams in the machine ? first
  collisions
• -- 43 43 bunches, L6 x 1031 cm-2 s-1
  (possible scenario tuning machine parameters)
• -- pilot run 936936 bunches (75 ns ? no
  electron cloud), Lgt5x 1032
• -- 2-3 month shut-down ?
• -- 2808 2808 bunches (bunch spacing 25 ns),
  L up to 2x1033 (goal of first year)
• ? 7 months of physics run

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Start-up and Staging

• Start-up Staging
• deferrals of high-level Trigger/DAQ processors
  50 Hz instead of 100 Hz
• pixel and Ecal endcap installed during first
  shut-down
• muon endcap RPCs ? lt 1.6 instead of ? lt 2.1
• 4th Muon CSC Endcap (ME4/1 Restored! 4/2 staged)

• Expected
  performance day 1 Physics samples to improve
  (examples)
• ECAL uniformity 4
  Minimum-bias, Z? ee
• e/? scale 1-2 ?
  Z ? ee
• HCAL uniformity 2-3
  Single pions, QCD jets
• Jet scale lt 10
  Z (? ll) 1j, W ? jj in tt
  events
• Tracking alignment 20-500 ?m in R? ?
  Generic tracks, isolated m , Z ? mm

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Event Rates
Expected in the first year LHC rates 103 larger
in area of asymptotic TEVATRON reach ? Large
samples of SM events understand (calibrate,
align etc) detector and LHC physics (check SM at
highest Q2)
Channels (examples ) Events to tape for 10 fb-1 (per experiment)
W ? m n 70 x 106
Z ? m m 11 x 106
tt ?W b W b ? m n X 0.8 x 106
QCD jets pTgt150 107
Minimum bias 107
gg m 1 TeV 103 - 104
few PB of data per year/experiment ? challenge
for software and computing (esp. _at_ beginning )
Computing GRID underway
assuming 1 of trigger bandwidth
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Early Discoveries? Fix Scale for New Physics

• Easy new resonance decaying into ee- or µµ-,
  e.g. Z ? µµ- of mass 1-2 TeV compositeness,
  extra dimensions, surprises
• Not-so-easy SUSY proving a direct link between
  SUSY, dark matter and cosmology probably higher
  importance than Higgs !
• Far-from-easy light Higgs (m 115-140 GeV)

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Z ? µµ-

• Excellent benchmark analysis for CMS Muon
  Detector
• Clean (small Drell-Yan background)
• Very high pT muons (TeV specific problems
  showering etc)
• Mass Reach (SL gt 5?)
• Full CMS simulation and reconstruction
• Un-binned Likelihood Ratio Approach
• SL v 2 ln( Lsb/Lb)

Mass Reach (TeV) Luminosity (fb-1)
gt 1 0.1
2.6 3.4 10
3.4 4.3 100
No systematic effects
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Supersymmetry

• Most important task in early days

• Most sensitive channel
• jets missing ET (MET resolution is KEY)
• squarks / gluinos
• (clean final states, large rate, favorable
  signal/bg ratio)

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Standard Model Higgs
M lt 140 GeV low rates, high bg, difficult

• Advancing detailed studies (large scale full
  detector simulations, lots of CPU)

CMS Full simulation
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Outlook

• When Carlo Rubia came to Sofia at the end of
  1989, he was expecting LHC to start in 1996
• For some time, it was always 6 years from now
• Now we expect data taking in 2007-8, and the
  first year can bring major discoveries, fix the
  scale of new physics (ILC, dark matter )
• The situation is similar to the jump from the ISR
  to the SppbarS and the W/Z discovery
• So we better be ready fast after day 1