MC Study on B°  S (Status Report) Jianchun Wang Syracuse University BTeV meeting 05/25/01

Jianchun (JC) Wang2 Introduction  Physics ( see Sheldon’s talk )  B (B°  K S ) =   / 2 ( By Tomasz and Bayar)  Events per year: 1.5  10 5 B°  K S  K  K   K S     b d B° s d s s  KSKS WW tcu

05/25/01Jianchun (JC) Wang3 Reconstruction of K S   track selection:  Covariant matrix exists  Num of hits > 10  P > 2 GeV  Applied later: (???)  DCA /  > 10  Distance (K S to primary vertex)  Vertex fit: prob(  2, 1) > 0.01  | M   M K s  | < 3   Mass constraint fit  = 3.3 MeV

05/25/01Jianchun (JC) Wang4 K S Vertex Reconstruction  Vertex fitting: prob(  2, 1) > 0.01  Vertex Resolution: (29, 27, 330)  m  Primary Vertex: (12, 12, 80)  m  L: distance between Ks vertex and primary vertex  L/  can be used to reject bkg (similar as DCA/  of  )  S     

05/25/01Jianchun (JC) Wang5 Reconstruction of    track selection:  P > 4 GeV  Num of hits > 20  Silicon hits  4  At least one hit RICH  Applied later: (?)  DCA  Vertex fit: prob(  2, 1) > 0.01  | M   M  | < 3   Mass constraint fit (benefit B reconstruction)  = 3.6 MeV

05/25/01Jianchun (JC) Wang6  Vertex Reconstruction  K  very soft in  rest frame (P = 127 MeV/c)  Poor vertex resolution: (220, 210, 3000)  m  Compare with J/     (22, 22, 154)  m  Use reconstructed  and K S to reconstruct B(  ) vertex (28, 27, 340)  m BB      KSKS

05/25/01Jianchun (JC) Wang7 B  Decay Length  Decay length resolution:   L ~ 2900  m using       L ~ 380  m using  K S  Possible cut: ( ? ) L decay /  L > 4  Efficiency of this cut  28% using      76% using  K S B    K S Use K + K  vertex Use  K S vertex

05/25/01Jianchun (JC) Wang8 Possible Criteria To Be Studied  DCA of tracks, DCA of reconstructed  and K S  Decay length of B and K S  Angle between momentum and vertex (B, K S )  P T of B with respect to vertex direction  Vertex veto to reject  produced in other mode

05/25/01Jianchun (JC) Wang9 Distribution of M B  = 15 MeV B    K S Current Signal: 2800 / year Background: not studied yet Further reduction ~ 30% Signal ~ 2000 / year

05/25/01Jianchun (JC) Wang10 Background Event  Main source: real  and K S from B decay   : narrow width, K ± identification with RICH  K S : detached vertex, narrow width, vertex veto  Difficulty in background simulation   and K S are very popular in generic BB events  Reduction: forcing  and K s decay mode, selections on P track, decay length, K S vertex, and M  K S  Current reduction ratio: 4  10   8  10  events/year  Further reduction needed

05/25/01Jianchun (JC) Wang11 Summary  Study Decay B°  K S,  K  K   K S      B  mass resolution: 15 MeV  2000/year signals expected  S/N unknown yet  Background study need to be done