Analyse des Zerfalles KS p pp0 bei NA48

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Analyse des ZerfallesKS ? pp-p0 bei NA48

• Manfred Jeitler
• PDA-Seminar
• HEPHY, 2. Mai 2003

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the experimental situation

• Fermilab experiment E621
• 1.1 million pp-p0
• 0.6 to 7.6 KS lifetimes
• BR ( 4.8 2.2-1.6 (stat.) ? 1.1 (syst.) ) ?
  10-7
• CPLEAR
• BR ( 2.5 1.3-1.0 (stat.) 0.5-0.6 (syst.) ) ?
  10-7
• Martin Wache (Diplomarbeit NA48)
• BR ( 6.0 ? 2.5 (stat.) ? 2.5 (syst.) ) ? 10-7
• he thinks one can improve the systematic error

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the CP-violating part

• rate expected to be about 300 times smaller than
  for the CP-conserving part
• only limit given by CPLEAR
• Re (h-0) ( -2 ? 7 (stat.) 4-1 (syst.) ) ?
  10-3
• Im (h-0) ( -2 ? 9 (stat.) 2-1 (syst.) ) ?
  10-3
• do not yet know if we could be competitive
• difficult analysis
• detailed MonteCarlo needed

4
the approach

• different from KL ? pp and KS ? p0p0p0
• those are purely CP-violating decays
• KS ? pp-p0 has CP-conserving and CP-violating
  part
• L1 is CP 1 (CP-conserving), has
  centrifugal barrier
• L0 is CP -1 (CP-violating)
• distinguish them by Dalitz-plot distribution

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parity and charge conjugation for three particles
L1
-
P
L1
-


- (-)L1 (-)L2
L2
L2
-
0
0
B. dEspagnat, 1958 CERN lectures found by Don
Cundy
L1
-
L1
C
-
L1
-



(-)L1
L2
L2
L2
0
0
0
? CP - (-)2L1 (-)L2 -(-)L2 -(-)L
kaon spin is 0 ? L1 L2 L
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the original Dalitz plot
p- kinetic energy in CMS
p0 kinetic energy in CMS
kinematically allowed region
p kinetic energy in CMS
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the usual Dalitz plot
Y is scaled and upside down compared to previous
plot !
Y
X
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the usual Dalitz plot variables

• si ... the invariant mass squared of the other
  two particles the higher the si, the smaller
  the kinetic energy of that (i-th) pion in
  the CMS system
• X ... the difference between the si of the p
  and the p- (in units of mp2)
• Y ... the difference between the si of the p0
  and the mean
• of all the si (in units of mp 2)
  

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distinguish CP-conserving from CP-violating
distribution is odd in X for CP-conserving
even
violating
X gt 0
X lt 0
Y
X
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look at some KS data
p0 kinetic energy in CMS system
p kinetic energy in CMS system
p- kinetic energy in CMS system
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original Dalitz plot
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usual Dalitz plot
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COG ?
part of slope due to acceptance
Y ?
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... but most of it also in Monte Carlo - both
in accepted and generated data!
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the same for the charged (odd pion takes place
of p0 ) K ? ppp-
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background
pp- invariant mass ?
? p / p-
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pp- invariant mass ?
? p / p-
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energy sharing between LKr clusters and tracks
close-by tracks distort the photon energy and the
calculated p0 mass ? systematic error?
p0 mass in GeV/c2 ?
cluster track distance in cm ?
cluster track distance in cm ?
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ct spectra for the various kaon energy
ranges dilution (K0 / K0 ratio) is energy
dependent ? fit separately
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30 lt EK lt 47 GeV
Dalitz X gt 0
Dalitz X lt 0
fit ct distribution for Xgt0 - Xlt0 Xgt0 Xlt0 to
extract the l parameter and branching ratio
difference
difference normalized to sum
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98 lt EK lt 115 GeV
Dalitz X gt 0
Dalitz X lt 0
fit ct distribution for Xgt0 - Xlt0 Xgt0 Xlt0 to
extract the l parameter and branching ratio
difference
difference normalized to sum
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relative excess
V-0 for literature values dilution
0.28 Re (l) 0.031 Im (l) - 0.006
ct in units of KS lifetimes
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