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MC Study on B° S (Status Report) Jianchun Wang Syracuse University BTeV meeting 05/25/01
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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 WW tcu
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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
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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
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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
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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 BB KSKS
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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
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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
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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
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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
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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
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