MC Study on B°  J/  ° With J/      °     Jianchun Wang Syracuse University BTeV meeting 03/04/01

Jianchun (JC) Wang2 Introduction  Test of CPT conservation and measurement of cos(2  ) ( see Sheldon’s last month talk )  Events per year: 1.14  10 6  Difficult to detector: c  =15.51 m (K L ), 2.68 cm (K S )  Generated within  (0.5, 0.5, 1.5)m  K S : (89.9  0.3)% 1.76    K L : (0.97  0.01)% 1.11    Total: (1.13  0.01)% 1.28   B°  J/  °, J/      °     Kaon Decay Time [  S ] ( K L /K S ~ 580 )

03/04/01Jianchun (JC) Wang3 Reconstruction With Missing  Only  not reconstructed ( 4 free parameters )  K  direction determined by K  and J/  vertices ( 2 constraints )  Known K  and masses ( 2 constraints )  Two solutions BB     (J/  ) K S / K L

03/04/01Jianchun (JC) Wang4 MC Events  Signal events: 12.8K events with K  decay within detection volume, corresponds to one year run  Main background source is real J/  from B decay  Small J/  width  Reject fake J/   Detached vertex criteria  Reject prompt J/   Background events:  Generic BB events, J/  fully decays into      Events preselected after QQ simulation  A quarter of a year events simulated  MCFast simulation used, no multiple interaction yet

03/04/01Jianchun (JC) Wang5 Primary Vertex Reconstruction  Based on Rob’s primary vertex subroutine, modification of primary vertex seeds selection  Resolution and efficiency improved: eff = 99.2% (90.8%) 11.4 (12.1)  m 11.9 (12.5)  m  79.9 (89.7)  m

03/04/01Jianchun (JC) Wang6 Reconstruction of J/    track selection:  Real MC   Covariant matrix exists  Num of hits > 20  Silicon hits  4  Applied later:  P > 3GeV, max(P) > 8 GeV  At least one  has muon hit  Vertex fitting: prob(  2, 1) > 0.01  | M   M J/  | < 3   Mass constraint fit  = 11.7 MeV Efficiency ~ 20%

03/04/01Jianchun (JC) Wang7 B  Decay Vertex  Vertex resolution  Primary vertex: (11.4, 11.9, 79.9)  m  B  (w/o M J/  constraint): (22.0, 22.9, 163)  m  B  (with M J/  constraint): (21.6, 22.2, 154)  m  Decay length resolution:  L ~ 190  m  Detached vertex: L decay /  L > 4 B   J/  K 

03/04/01Jianchun (JC) Wang8 K  Vertex Reconstruction   selection:  Covariant matrix exists  Num of hits > 10  MC real   Selection later   has muon hit  DCA > 1 mm, max(DCA) > 2 mm  P > 1 GeV, max(P) > 2GeV  Vertex fitting: prob(  2, 1) > 0.01  M  < 0.5 GeV,  M ~ 2.5 MeV  Vertex Resolution: (62, 52, 450)  m  L decay /  L > 20, (  L ~ 450  m)  °    

03/04/01Jianchun (JC) Wang9 Determination of K  momentum  p  in K° rest frame = p  in Lab frame  cos 2  = ( p 2  p  2 ) / p 2  Selection of two solutions:  Matching momentum with vertex direction  Select one with mass close to B  m, p)  K  (M,  ) Negative due to resolution Cut: cos 2  >  0.2

03/04/01Jianchun (JC) Wang10 B° Directions  B  directions:  Momentum reconstructed  B  vertex to primary vertex  Open angle between two directions:  B < 20 mrad  The solution with M close to M B selected  Signal is of one year run, background is for ¼ year  B (mrad) B  Signal Background cut With all other cuts applied

03/04/01Jianchun (JC) Wang11 J/  Vertex Veto  To reject events with B  J/  + tracks  Add extra track to J/  vertex, require  2 > 10  Track selection:  Covariant matrix exists  Silicon hits  4  P > 0.5 GeV  Not from primary vertex  2 B  signal Background cut With all other cuts applied

03/04/01Jianchun (JC) Wang12 Distribution of M B M B  (GeV)  = 31 MeV Signal: 132 Background: 14  4 S/N: 2.36

03/04/01Jianchun (JC) Wang13 Background Events 5/14 B  J/  K  X (X =  ) 7/14 B  J/  X, K  (from fragmentation, or decay) 1/14 B  J/  X, B    X, K S      1/14 B  J/  X,    , K S      Classification of 14 Background Events

03/04/01Jianchun (JC) Wang14 Summary  No flavor tagging applied  B  mass resolution: 31 MeV  132/year signals for  channel only, adding e’s will increase the number by a factor of 2~4  S/N = 2.36  To be done: multiple interaction, GEANT

03/04/01Jianchun (JC) Wang15 Primary Vertex Reconstruction  Based on Rob’s primary vertex subroutine, improvement on primary vertex seeds selection  Track selections: 4 silicon hits, P > 0.5 GeV, covariance matrix defined, N track >2  Group two tracks together, select about 10 vertices consistent with beam spread:  2 < 5,  (  x/  ) 2 < 25  Among vertices, reject those far away from majority | Z – Z average | < 1.5  (two iterations)  Use tracks from selected vertices as seed, and add all tracks left one by one:  (  2 ) < 12  N track  3,  2 / N track < 4.0  99.2%  Resolution:  x =11.4  m,  y =11.9  m,  z = 80  m

03/04/01Jianchun (JC) Wang16 Pre-selection of Signal Events  Decay channels boosted:  B  J/  K    J/     5.88     K  K S (0.173%), K L (99.827%)  K S /K L     1.36    Event Selection:  At least one B  in the event3.96    Primary vertex simulation (moved from MCFast)  K  vertex within (  0.5m,  0.5m,  1.5m)1.13    One year run 2    BB events  12.8 K pre-selected events for further study

03/04/01Jianchun (JC) Wang17 Pre-selection of Background Events  BB events produced in one year run2.00    Decay channels boosted:  B +, B , B S,  b  J/    C0  C1  C2 + X4.23    J/      5.88    Event Selection:  J/  : dkl > 400  m, P  >3 GeV, max(P ,P  )>8 GeV1.65     of K  : generated within (  0.4m,  0.4m,  1.5 m) P > 1GeV, DCA > 1 mm, same side of J/  2.77     of K  : generated within (  0.4m,  0.4m,  1.5 m) P > 1GeV, DCA > 1 mm, same side of J/  8.50     and  pair: opposite charge, mass(  ) 2GeV, max(DCA) > 2 mm1.50    J/     : mass(J/  ) < 5.5 GeV7.90    Events selected for one year run2.24  

03/04/01Jianchun (JC) Wang18 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/  efficiency improvement, with one lepton identification:   (106%): MUON P>5 GeV  MUON P>5GeV + RICH 2<p<15GeV  e (110%): ECAL  ECAL + RICH p < 17 GeV J/     

03/04/01Jianchun (JC) Wang19 Yield of Events Per Year  Number of b event   cm  s   10  s  100  b 2.00    With B0/B0b  0.4     With B0  J/  K  (8.9  1.2)   1.42    With J/       (5.88  0.10)   8.37    With K      1.14   via K S  0.5  4.69   1.96   via K L  0.5  (27.18  0.25)   1.14    With K  decays in  (0.5,0.5,1.5)m   1.28   via K S  0.899(1.76   ) via K L  (0.97  0.01)   (1.11   

03/04/01Jianchun (JC) Wang20 Detection of Signal Events  Generated and pre-selected events per year (2 arms)12800  Primary vertex selection( )  ( All tracks detected1331  Tracks quality (no mu)1202 )  J/  after primary vertex selection, and after four tracks requirement (!!!)  Two tracks pass track quality 2729  Prob > 0.01, 3  mass cut, constraint fit2482  K° after J/  selection  Two tracks pass track quality1093  Vertex Prob >  M   (0.24, 0.70 )445  Missing fit cos 2  >   Further Cut  B decay length: L > 400 um, L/  L > 4302  B directions from two methods:  B < 20 mrad255  J/  vertex veto223  J/  p  > 3, max(p  )>8 GeV218  K° p  > 1, max(p  )>2 GeV192  K° DCA  > 1mm, max>2mm (for BKG purpose only)167   M B within 3  142  Include e modes (  2.43  2), with one arm (/2)345