CMS Discovery Potential for mSUGRA in Singlemuon

1
CMS Discovery Potential for mSUGRA in
Single-muon Same-sign di-muon Events with
Jets and Large Missing Transverse Energy

• B. Scurlock, Y. Pakhotin
• D. Acosta, P. Bartalini, R. Cavanaugh,
• A. Drozdetskiy, A. Korytov, K. Kotov,
• K. Matchev, G. Mitselmakher, M. Schmitt
• University of Florida
• Reprise Talk for Analysis Notes AN2006-083
  AN2006-087

Short Update
2
First a short announcement

• Emilia Scurlock arrived on 26 April at a healthy
  3.8 kg !
• Mother (and Father) are reportedly tired but
  doing great !

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Discussion about estimating the effect of ALPGEN

• ttbar is a common background to both analyses
• Hence, we chose to look at ttbar
• Both analyses require 3 jets
• The leading two jets are hard
• Inclusive muon analysis gt 440 GeV
• SS di-muon analysis gt 170 GeV
• The 3rd jet is softer
• required to be gt 50 GeV
• We assume that ISR/FSR primarily affects the 3rd
  Jet
• The effect on the analyses may be two-fold
• Change in the cut efficiency for the 3rd jet
• Change in the overall ttbar cross section

4
Strategy

• Investigate at generator level
• Compare
• matrix element calculation for ttbarjet
• parton shower calculation for inclusive ttbar
• Roughly Estimate
• ?? the difference in efficiency to select an
  event with a 3rd jet
• ?? the difference in cross section, resulting
  from differences in matrix element versus parton
  shower

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Difficulties How to compare?

• Parton Shower (PS) method in Pythia is
• IR safe
• UV incorrect
• Matrix Element (ME) method in Alpgen, Comphep,
  Madgraph, etc is
• IR divergent
• UV correct
• Some theory papers require pT gt 100 for
  comparisons between PS and ME
• In order to properly compare LO with NLO, one
  requires a full NLO generator
• MC_at_NLO

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Estimate Difference in Efficiency

• Form normalised PDFs for pT distributions
• PS ME
• Integrate PDFs from cut on pT upwards (plot on
  the right)
• Represents the probability that the ISR/FSR
  parton would pass that cut
• Conservatively assume that the ISR/FSR parton is
  always the 3rd jet (could, of course, be 4th,
  5th, etc)
• Compare probabilities for a
  pT gt 50 GeV
• Result ?? ? 5

5
Cut on
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Estimate Difference in Cross Section

• A full NLO calculation would be necessary to
  achieve a fair comparison with LO
• Exemplified by the IR divergence of ME
  calculation
• Assume difference in cross section is simply
  given by the ttbar NLO k-factor k ? 1.6
• Hence, ??tt ? 57 ?LO
• Reminder to be fair, one should also consider
  the NLO k-factor estimation for the signal
• ??sig ? 27 ?LO

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Conclusion

• Rough Estimate (likely conservative for ttbar) of
  the Effects from Matrix Element Calculated
  ISR/FSR in ttbarjet compared with Parton Shower
  method
• ?? ? 5
• ?? / ?LO ? 57