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B. Scurlock, Y. Pakhotin D. Acosta, P. Bartalini, R. Cavanaugh ,

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

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B. Scurlock, Y. Pakhotin D. Acosta, P. Bartalini, R. Cavanaugh ,

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  1. CMS Discovery Potential for mSUGRA inSingle-muon&Same-sign di-muonEvents 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 !

  3. 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: > 440 GeV • SS di-muon analysis: > 170 GeV • The 3rd jet is softer: • required to be > 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 ttbar+jet • 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

  5. 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 > 100 for comparisons between PS and ME • In order to properly compare LO with NLO, one requires a full NLO generator • MC@NLO

  6. 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 > 50 GeV • Result:  5% 5% Cut on

  7. 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

  8. Conclusion • Rough Estimate (likely conservative for ttbar) of the Effects from Matrix Element Calculated ISR/FSR in ttbar+jet compared with Parton Shower method  +5%  / LO  +57%

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