QCD background for studies with SIMDET

1
QCD background for studieswith SIMDET

• A De Roeck
• CERN
• A few technical comments

2
QCD background

• The QCD background in a ?? collider can be large
• Eg. for Lgeom 1035 cm-2 s-1, 400 nb ??
  cross section
• ? 3 ?? events/bunch
  crossing
• Many events boosted and/or low mass no problems
• V. Telnov (TESLA TDR appendix) 1.5 central high
  energy ?? events for L??(z gt 0.8zmax) 1.1 .1034
  cm-2 s-1
• Should include QCD background for studies and see
  how relevant variables smear because of this
  background
• Can use CLIC tools for TESLA

3
HADES Background files

• 
  CLIC study
• In ee- mode ? 4 ?? events per bunch crossing
  overlaid on average
• Tool developed HADES (D. Schulte)
• Take photon input spectra and generate data base
  of events
• of the type ?? ? hadrons with
  PYTHIA
• Presently PYTHIA 6.136 used (default soft
  hard processes)
• Now included in SIMDET_V4 (M.Battaglia/HJ.
  Schreiber)
• Steering via 3 cards
• BKGR 0 no background (D) /1
  include background
• NBKG Average number of background
  events (REAL/D0.)
• of events is generated
  according to a Poisson
  . distribution
• BKGF UNIT input file name for the
  background file

4
HADES Background files

• for TESLA gamma
  collider study
• Files for TESLA have been prepared
• ee- and ??
  files
• So far catalogued on the CLIC page
• //clicphysics.web.cern.ch/CLICp
  hysics
• Only the 200 GeV files done so far
• ?? file contains 5000 events
• Selection events W2 gt 5 GeV2 ,
• tracks Ptgt 150 MeV, ? gt
  80 mrad (can be changed)
• photon polarization not
  taken into account
• Note NOT for background to signal study/only for
  smearing
• A more detailed revisit of QCD tuning planned
  for later this year
• (R. Godbole
  visiting CERN)
• Further requirements ?

5
Examples of particles/event
5000 events sampled
63
95
36
lteventsgt 0.5
lteventsgt 1
lteventsgt 3
Number of particles in the detector
Only events with non-zero activity in the detector
6
Example Missing ET/event
events
events
ET (GeV)
ET (GeV)
lteventsgt 1
lteventsgt 3
Et tails to several 10s of GeV, but on average
not much Et
7
Example transverse and total energy
lteventsgt 3
? gt 80 mrad
? gt 250 mrad
Etot (GeV)
? gt 250 mrad
? gt 80 mrad
Etrans (GeV)
8
Example transverse and total energy
lteventsgt 1
? gt 80 mrad
? gt 250 mrad
Tails! but average values not so bad
Etot (GeV)
? gt 80 mrad
? gt 250 mrad
Etrans (GeV)
9
Example of jets
lteventsgt
lteventsgt 3
? gt 80 mrad
Jet selection Cluster algorithm ET(JET) gt 5 GeV
? gt 250 mrad
of jets
? gt 250 mrad
? gt 80 mrad
About 5-10 of the events with 1 or more jets
Etot of each jet (GeV)
10
Example of jets
lteventsgt 1
? gt 80 mrad
? gt 250 mrad
of jets