K0/?0 production in Min Bias events

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K0/?0 production in Min Bias events

• Data analyzed
• 1800 GeV run 1A 1B 1C
  3,300,000 triggers
• 630 GeV run 1C
  2,600,000 triggers
• Offline event selection reject ?
• -events containing cosmic rays (central
  calorimeter, TOF)
• events with no tracks
• -events with calorimeter problems
• events with a single CTC track, but no central
  calorimeter tower with at
• least 100 MeV
• events with more than one primary vertex
• events with a primary vertex more than 60 cm
  from the detector center
• - events with no primary vertex

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F.Rimondi QCD Meeting May 16,2002
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K0/?0 production in Min Bias events
After selection 2,079,558 triggers _at_ 1800
GeV 1,963,157 triggers _at_ 630 GeV

• Track selection
• standard CTCSEL selection
• - d 0.5 cm
• - z0trk - zver 5 cm

1 Nch pTgt ?
pTi Nch
Mult n. of good CTC tracks Nch
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F.Rimondi QCD Meeting May 16,2002
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K0/?0 production in Min Bias events

• K0/?0 selection
• use full sample of reconstructed CTC tracks
• make opposite sign pairs and look for pairs
  converging
• to a common secondary vertex
• fit secondary vertex with the hypothesis of
  K0/?0 decay
• K0/?0 were accepted if
• secondary vertex 3-C fit has probability gt 5
• the fitted mass is within 3 ? from K0/?0 mass
• the projected vertex displacement in xy plane
  Lxy gt 1 cm
• - the decay track ?lt 1.5 and pT(V0) ? 0.2 GeV/c

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F.Rimondi QCD Meeting May 16,2002
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K0/?0 production in Min Bias events

• K0/?0 efficiency correction
• Efficiency for finding K0/?0 evaluated in two
  ways
• simulated V0 embedded in real MB events
• full MB events with K0/?0 generated with
  Pythia, then
• simulated (QFL simulation) and reconstructed.

F.Rimondi QCD Meeting May 16,2002
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K0/?0 production in Min Bias events
Efficiency evaluated inclusively for each
single distribution Experimental distribution
?N/?I vs I is corrected for
Rec. (?N/?I) ?(I)
vs I Gen. (?N/?I)
where I is a generic inclusive variable (pT, ?,
mult) and ?N either the number of events or
tracks in ?I ?(I) is so integrated over all the
other variables
F.Rimondi QCD Meeting May 16,2002
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K0/?0 production in Min Bias events
Soft and Hard Interactions Soft events with no
cluster of minimum energy of 1.1 GeV in
the whole calorimeter Hard events with at least
one cluster of minimum energy of 1.1
GeV anywhere in the calorimeter A track cluster
algorithm is used to compensate energy loss in
the cracks
F.Rimondi QCD Meeting May 16,2002
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