 # MC Study of B°  S Jianchun Wang Syracuse University BTeV meeting 06/27/01.

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MC Study of B°  S Jianchun Wang Syracuse University BTeV meeting 06/27/01

Jianchun (JC) Wang2 Introduction  Physics beyond the Standard Model  B (B°  K°) = 6.9    1.9  10 5 event/year   (CLEO), 8.1   (BaBar) B°  K S  K  K   K S     b d B° s d s s  KSKS WW tcu

06/27/01Jianchun (JC) Wang3 Reconstruction of    track selection:  Kaon hit RICH detector  Num of hits > 20  Silicon hits  4  P > 4 GeV, P T > 0.2 GeV  At least one P T > 0.4 GeV  Applied later:  DCA /  > 3  Vertex fit: prob > 0.01  | M   M  | < 3   Mass constraint fit: benefit B reconstruction   3.9 MeV

06/27/01Jianchun (JC) Wang4 Reconstruction of K S   track selection:  Num of hits > 10  P > 2 GeV, P T > 0.2 GeV  At least one P T > 0.4 GeV  Applied later:  Each  DCA /  > 3  K S : DCA /  > 3  Vertex fit: prob > 0.01  | M   M K s  | < 3   Mass constraint fit   3.7 MeV

06/27/01Jianchun (JC) Wang5  Vertex Reconstruction  K  very soft in  rest frame (P = 127 MeV/c)  Poor vertex resolution: (290, 290, 4800)  m  Compare:  J/     (26, 26, 250)  m  Primary vertex (13, 14, 108)  m  K S     (130, 130, 2000)  m  B vertex: use trajectories of reconstructed  and K S (63, 69, 1040)  m BB      KSKS Two methods for B vertex       vertex  B  K S  vertex

06/27/01Jianchun (JC) Wang6 B  Decay Length  Decay length resolution:   L ~ 4100  m using       L ~ 660  m using  K S  Vertex fit: prob > 0.01  Applied later: L decay /  L > 3  Efficiency of this cut  39% using      79% using  K S B    K S Use K + K  vertex Use  K S vertex

06/27/01Jianchun (JC) Wang7 Background Event  Main source: real  and K S from bb event   : narrow width, K ± identification with RICH  K S : long life time, narrow width  Decay branching ratio boost: (factor of 17.4) (D S, D , D +,  C )  X 2.9 ( 5 only on charm side) K  K S, K S    ,     5.9 = 1 / (0.5  0.6861  0.492)  Pre-selection: ( 2.2  10  )  Reject prompt  (80% of 0.51), and K S (83% of 3.1)  P, P T of tracks, same hemisphere,  K S invariant mass (5.0 - 5.5 GeV)  Background events generated 254K ( 10% of a year running)

06/27/01Jianchun (JC) Wang8 Further Reduction DCA/  (  ) DCA/  (K S ) DCA/  (  ) L decay /  (  ) Signal (|  M B | < 3  Bkg (|  M B | < 12  With all other cuts applied in the plots  ~ 26  m  ~ 50  m  ~ 27  m  ~ 660  m

06/27/01Jianchun (JC) Wang9 Signal Yield M  K S (GeV) Signal = 2360 / year Background 148/4  9.8 = 363 / year S/N = 6.5  = 18 MeV

06/27/01Jianchun (JC) Wang10 Effect of Smaller X-plane  Trade off: multiple scattering, secondary interaction hits  Trigger algorithm mainly rely on Y-plane (fixed at 10 cm) Size of X Plane (cm)

06/27/01Jianchun (JC) Wang11 Size of Both Planes  Change of efficiency and resolution is bigger  This is a special case ( very poor time resolution )  The trigger efficiency is very interesting Size of Both Planes (cm)

06/27/01Jianchun (JC) Wang12 Summary  Study Decay B°  K S,  K  K   K S      2400/year signals expected,  M = 18MeV, S/B  6.5  Pixel detector geometry has impact on reconstruction efficiency, time resolution and trigger efficiency  Since this is very special mode (poor time resolution), we need to study more channels on this issue

06/27/01Jianchun (JC) Wang13 Total Signal  B (B°  K S ) =   / 2  B (  K  K     B  K S        Total branching fraction = 1.16    Generic BB event = 2   / year  Number of neutral B = 2  0.4 / event  Signal yield = 1.86   / year  Reconstructed = 2360 / year B°  K S  K  K   K S    

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