MC Study on B

1
MC Study on B?J/?KWith J/??mm-, K?p?m?n
BTeV meeting 03/04/01

• Jianchun Wang
• Syracuse University

2
Introduction
B?J/?K, J/??mm-, K?p?m?n

• Test of CPT conservation and measurement of
  cos(2b) ( see Sheldons last month talk )
• Events per year 1.14 ? 106
• Difficult to detector ct 15.51 m (KL),
  2.68 cm (KS)
• Generated within ?(0.5, 0.5, 1.5)m
• KS (89.9 ?0.3) 1.76?103
• KL (0.97?0.01) 1.11?104
• Total (1.13?0.01) 1.28?104

3
Reconstruction With n Missing

• Only n not reconstructed ( 4 free
  parameters )
• K? direction determined by K? and J/y vertices (
  2 constraints )
• Known K? and n masses ( 2 constraints )
• Two solutions

4
MC Events

• Signal events 12.8K events with K? decay
  within detection volume, corresponds to one
  year run
• Main background source is real J/y from B decay
• Small J/y width ? Reject fake J/y
• Detached vertex criteria ? Reject prompt J/y
• Background events
• Generic BB events, J/y fully decays into mm-
• Events preselected after QQ simulation
• A quarter of a year events simulated
• MCFast simulation used, no multiple interaction
  yet

5
Primary Vertex Reconstruction

• Based on Robs primary vertex subroutine,
  modification of primary vertex seeds selection
• Resolution and efficiency improved eff 99.2
  (90.8)

6
Reconstruction of J/y
Efficiency 20

• m track selection
• Real MC m
• Covariant matrix exists
• Num of hits gt 20
• Silicon hits ? 4
• Applied later
• P gt 3GeV, max(P) gt 8 GeV
• At least one m has muon hit
• Vertex fitting prob(c2, 1) gt 0.01
• Mmm-M J/y lt 3s
• Mass constraint fit

s 11.7 MeV
7
B? Decay Vertex

• Vertex resolution
• Primary vertex (11.4, 11.9, 79.9) mm
• B? (w/o MJ/y constraint) (22.0, 22.9, 163) mm
• B? (with MJ/y constraint) (21.6, 22.2, 154) mm
• Decay length resolution sL 190 mm
• Detached vertex Ldecay / sL gt 4

B? ? J/? K?
8
K? Vertex Reconstruction

• p, m selection
• Covariant matrix exists
• Num of hits gt 10
• MC real m
• Selection later
• m has muon hit
• DCA gt 1 mm, max(DCA) gt 2 mm
• P gt 1 GeV, max(P) gt 2GeV
• Vertex fitting prob(c2, 1) gt 0.01
• Mmp lt 0.5 GeV, sM 2.5 MeV
• Vertex Resolution (62, 52, 450) mm
• Ldecay/sL gt 20, ( sL 450 mm)

K?p?m?n
9
Determination of K? momentum

• p? in K rest frame p? in Lab frame
• cos2q ( p2 - p?2) / p2
• Selection of two solutions
• Matching momentum with vertex direction
• Select one with mass close to B

Negative due to resolution Cut cos2q gt -0.2
10
B Directions
With all other cuts applied

• B? directions
• Momentum reconstructed
• B? vertex to primary vertex
• Open angle between two directions qB lt 20 mrad
• The solution with M close to MB selected
• Signal is of one year run, background is for ¼
  year

11
J/y Vertex Veto
With all other cuts applied

• To reject events with B?J/y tracks
• Add extra track to J/y vertex, require Dc2 gt 10
• Track selection
• Covariant matrix exists
• Silicon hits ? 4
• P gt 0.5 GeV
• Not from primary vertex

12
Distribution of MB
Signal 132 Background 14 ? 4
S/N 2.36
13
Background Events
Classification of 14 Background Events

• 5/14 B ? J/y K? X (X p?, p, g)
• 7/14 B ? J/y X, K? (from fragmentation,
  or decay)
• 1/14 B ? J/y X, B ? m X, KS ? p
  p-
• 1/14 B ? J/y X, p-? m- n , KS ? p
  p-

14
Summary

• No flavor tagging applied
• B? mass resolution 31 MeV
• 132/year signals for m channel only, adding
  es will increase the number by a factor of 24
• S/N 2.36
• To be done multiple interaction, GEANT

15
Primary Vertex Reconstruction

• Based on Robs primary vertex subroutine,
  improvement on primary vertex seeds selection
• Track selections 4 silicon hits,
  P gt 0.5 GeV,
  covariance matrix defined, Ntrackgt2
• Group two tracks together, select about 10
  vertices consistent with beam spread ?2 lt
  5, S(Dx/s)2 lt 25
• Among vertices, reject those far away from
  majority Z Zaverage lt 1.5
  s (two iterations)
• Use tracks from selected vertices as seed, and
  add all tracks left one by one D(?2) lt 12
• Ntrack ? 3, c2 / Ntrack lt 4.0 ?
  99.2
• Resolution sx 11.4 mm, sy 11.9 mm, sz
  80 mm

16
Pre-selection of Signal Events

• Decay channels boosted
• B??J/y K? 8.90?10-4
• J/y?mm- 5.88?10-2
• K??KS (0.173), KL (99.827)
• KS/KL ?p-mn 1.36?10-1
• Event Selection
• At least one B? in the event 3.96?10-1
• Primary vertex simulation (moved from MCFast)
• K? vertex within (?0.5m, ?0.5m,
  ?1.5m) 1.13?10-2
• One year run 2?1011 BB events ? 12.8 K
  pre-selected events for further study

17
Pre-selection of Background Events

• BB events produced in one year run 2.00?1011
• Decay channels boosted
• B, B?, BS, Lb ? J/y, y2, cC0, cC1, cC2
  X 4.23?10-2
• J/y ? mm- 5.88?10-2
• Event Selection
• J/y dkl gt 400mm, Pmgt3 GeV, max(Pm1,Pm2)gt8
  GeV 1.65?10-1
• m of K? generated within (?0.4m, ?0.4m, ?1.5
  m) P gt 1GeV, DCA gt
  1 mm, same side of J/y 2.77?10-2
• p of K? generated within (?0.4m, ?0.4m, ?1.5
  m) P gt 1GeV, DCA
  gt 1 mm, same side of J/y 8.50?10-1
• m and p pair opposite charge, mass(m p) lt 0.5
  GeV max(P) gt 2GeV, max(DCA) gt 2
  mm 1.50?10-1
• J/y, m,p- mass(J/y m p) lt 5.5
  GeV 7.90?10-1
• Events selected for one year run 2.24?105

18
Lepton Identification With RICH

• Perfect detection efficiency assumed
• Detector size
• RICH z 386 cm, ? 135 cm square, 2.28 cm
  inner radius
• ECAL z 739 cm, 160cm outer radius, ? 9.88 cm
  square hole
• MUON z 890 cm, 240 cm outer radius , 6 cm
  inner radius
• J/y efficiency improvement, with one lepton
  identification
• m (106) MUON Pgt5 GeV ?
• MUON Pgt5GeV RICH 2ltplt15GeV
• e (110) ECAL ?
• ECAL RICH p lt 17 GeV

J/y ?????
19
Yield of Events Per Year

• Number of b event 2?1032cm-2s-1 ? 107s ? 100 mb
  2.00?1011
• With B0/B0b ? 0.4 ? 2 1.60?1011
• With B0?J/y K? ? (8.9?1.2)?10-4 1.42?108
• With J/y? mm- ? (5.88?0.10)?10-2 8.37?106
• With K?? p?m?n 1.14?106
• via KS ? 0.5 ? 4.69?10-4 1.96?103
• via KL ? 0.5 ? (27.18?0.25)?10-2 1.14?106
• With K? decays in ?(0.5,0.5,1.5)m ?
  1.13?10-2 1.28?104
• via KS ? 0.899 (1.76?103)
• via KL ? (0.97?0.01)?10-2 (1.11?104)

20
Detection of Signal Events

• Generated and pre-selected events per year (2
  arms) 12800
• Primary vertex selection (1269720)
• ( All tracks detected 1331
• Tracks quality (no mu) 1202 )
• J/y after primary vertex selection, and after
  four tracks requirement (!!!)
• Two tracks pass track quality 2729
• Prob gt 0.01, 3s mass cut, constraint fit 2482
• K after J/y selection
• Two tracks pass track quality 1093
• Vertex Prob gt 0.01 450
• Mmp ? (0.24, 0.70 ) 445
• Missing n fit cos2q gt -0.2 363
• Further Cut
• B decay length L gt 400 um, L/ sL gt 4 302
• B directions from two methods qB lt 20 mrad 255
• J/y vertex veto 223
• J/y pm gt 3, max(pm)gt8 GeV 218
• K pm,p gt 1, max(pm,p)gt2 GeV 192
• K DCA u,p gt 1mm, maxgt2mm (for BKG purpose
  only) 167