Supersymmetric%20Particle%20Reconstructions%20at%20CMS

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Supersymmetric Particle Reconstructions at CMS

• Massimiliano Chiorboli
• INFN Catania

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• Up to a couple of years ago, most of attention
  devoted to inclusive studies
• I started working in the Physics group on
  sparticle reconstruction
• Sbottom, squark ad gluino mass peaks in 3 mSUGRA
  points

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Decay Chains
p
b
b
p

• ? 2 high pt isolated leptons OS
• (leptons e,m)
• ? 2 high pt non-b jets
• missing Et

• ? 2 high pt isolated leptons OS
• (leptons e,m)
• ? 2 high pt b jets
• missing Et

SM bkg tt, Zjet, Wjet, ZZ, WW, ZW, QCD jets
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Generation and Simulation

• SUSY events generated with ISAJET 7.51 PYTHIA
  6.158
• SM bkg events (tt, Zjet, Wjet, ZZ, WW, ZW, QCD
  jets) generated with PYTHIA 6.158
• Detector simulated with CMSJET 4.801

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Benchmark Points
Proposed Post-LEP Benchmarks for Supersymmetry,
M. Battaglia et al. (hep-ph/0106204)

• Rather low m0 and m1/2 values in order to have
  high SUSY cross section
• Three different tan b values (tan b 10, 20, 35)
  since BR(c20 ? ll- c10) depends on tan b

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Reconstruction Method
At the end-point

• ?2 isolated leptons, pTgt15 GeV, hlt2.4
• ? 2 b-jets, pTgt20 GeV, hlt2.4

• assuming M(c10) known
• Selecting events in edge
• Combining the c20 obtained from the two leptons
  with the most energetic b-jet in the event

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Reconstruction Method
Once the sbottom (or the squark) is reconstructed

• SM bkg can be reduced cutting on ETmiss
• The main problem is combinatorial

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Results _at_ Point B
sSUSY 57.77 pb
Sbottom Chain Sbottom Chain Sbottom Chain Sbottom Chain Squark Chain Squark Chain Squark Chain Squark Chain
10 fb-1 60 fb-1 300 fb-1 10 fb-1 60 fb-1 300 fb-1
M(sbottom) 5007 5024 4972 M(squark) 53610 5322 5361
s(sbottom) 425 414 363 s(squark) 609 361 311
M(gluino) 5947 5924 5913 M(gluino) 5927 5952 5902
s(gluino) 427 463 393 s(gluino) 755 592 592
gluino
Result of the fit
Result of the fit

• Squark mass peaks can be reconstructed in the
  first few weeks (resolution 12)
• Sbottom and gluino in the first year (resolution
  68)
• Two independent gluino mass measurements
• The resolution can be improved with larger
  statistics (56 at 300 fb-1)

Generated values
Generated value
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Results _at_ Point G

• With respect to the Point B
• Lower total SUSY cross section (8.25 pb)
• Lower BRs of useful decays
• Higher BRs of competitive decays
• Lower BR of the last decay

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Results _at_ Point G
Sbottom Chain Sbottom Chain
300 fb-1
M(sbottom) 72026
s(sbottom) 8118
M(gluino) 85140
s(gluino) 13043
Squark Chain Squark Chain
300 fb-1
M(squark) 7749
s(squark) 849
M(gluino) 85311
s(gluino) 12611
300 fb-1
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Point I

• The tau channel is the main one also in the other
  points
• Tau-pair edge is not as sharp as in the e and m
  case, but could help to cover points in which the
  reconstruction is problematic
• It could be exploited in regions with too low
  leptonic BR

Neutralino BRs Neutralino BRs Neutralino BRs Neutralino BRs
B G I
BR(c20?ll) 16.44 2.26 0.25
BR(c20?tt) 83.22 75.88 98.13
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Conclusions

• Supersymmetric Spectroscopy has been attempted
• CMS will be capable to reconstruct sparticles
  with favourable parameters
• Point B
• squark in the first few weeks (1 fb-1)
• sbottom and gluino in the first year (10 fb-1)
• Point G
• squark, sbottom and gluino with 300 fb-1
• Point I
• no recontruction possible with the lepton
  channel, but it could be useful to investigate
  other decay chains (e.g. c?tt)
• CMS Note in preparation

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Future perspectives

• What can be done
• Re-run the analysis in full simulation
• Try to look fo other sparticles in the same
  points
• stop
• non-strongly interacting sparticles
• Investigate other decay channels
• c?tt at Point I (high tan b points)
• Explore reconstruction capability at different
  points