Vladimir Litvin, Harvey Newman,

1
Preliminary study of QCD background preselection
for diphoton RS graviton decay Status and plans

• Vladimir Litvin, Harvey Newman,
• Sergei Shevchenko
• Caltech CMS

2
Introduction

• Two main updates since last CMS week
• PYTHIA version with bugfix (from M.-C. Lemaire)
  was used to double-check our parameters for
  generator level cuts nothing changed in our case
  as was preliminary reported on previous CMS week
• 70k preselected events of QCD background were
  generated by PYTHIA and we are ready to start
  OSCAR/ORCA simulation and reconstruction

3
PYTHIA bugfix

• PYTHIA bugfix was reported during March CMS week
  by C.Collard and M.-C. Lemaire
• http//agenda.cern.ch/askArchive.php?baseagendac
  atega04983ida04983s5t52Ftransparencies2Fbsm_m
  ars2004.ppt
•  Saclay D0 members( Marc Besançon, Nadia
  Lahrichi and Emmanuelle Perez) working on the
  same topic mentioned a problem with Pythia as the
  squared amplitude was varying as s2 while it
  should be s4 dependent
• From J. Bijnens et al. hep-ph/0101316
• ds/dt varies as s2 , so s should vary as s3
  and the squared amplitude as s4.
• With the help from Torbjon Sjostrand it was
  suggested that we should multiply the squared
  amplitude in the code with a factor s2/MG4
• An independent calculation of the
  cross-section from Michael Spira has convinced
  that we should use the corrected version.   
• We are using PYTHIA version with bugfix, obtained
  from M.-C. Lemaire until official version will be
  released

4
Parameters

• Main goal is to find out the optimal parameters
  for QCD generator level cuts. Looking for events
  with at least one pair of any two of the
  following particles, p0, e, g, w, r, h, h,
  satisfying
• Minv gt 900 GeV
• Pthat gt 100 GeV
• EgT1 gt 150 GeV
• EgT2 gt 100 GeV
• h 1,2 lt 2.4
• Key parameter is c - dimensionless coupling c
  k/MPl. Theoretically, 0.01 lt c lt 0.1 for
  graviton masses gt 1TeV.
• Subsets of 1000 events each have been produced in
  c0.01 - 0.2 range and for different graviton
  masses starting from 1 TeV

5
Pthat

• MG 1TeV, Pthat gt 100 GeV

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EgT1

• MG 1TeV, EgT1 gt 150 GeV

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EgT2

• MG 1TeV, EgT2 gt 100 GeV

8
Conclusion

• Preselection parameters have been confirmed for C
  lt 0.2 area and MG gt 1 TeV
• Minv gt 900 GeV
• h 1,2 lt 2.4
• Ephoton1 gt 150 GeV
• Ephoton2 gt 100 GeV
• Pthat gt 100 GeV
• 70k for 10 fb-1 of selected events have been
  produced by PYTHIA and ready to go into
  OSCAR/ORCA production.
• ADD model is under investigation now in
  collaboration with JINR (Dubna) and IHEP
  (Protvino)
• We shall make a cross-check with another
  generators in a second half of this year. CompHEP
  (and probably ALPGEN) will be used for the
  comparison, because the selection factor is very
  large and very sensitive at that extreme
  kinematics.