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MSSM H 0 3 prong using vertexing at CMS

MSSM H 0 3 prong using vertexing at CMS. Helsinki b/tau workshop 30.05.-01.06.2002 Lauri A. Wendland / HIP. Outline. Motivation Tools & methods Secondary vertex (SV) reconstruction Charge reconstruction Effective mass reconstruction Conclusions Future plans. Motivation.

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MSSM H 0 3 prong using vertexing at CMS

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  1. MSSM H03 prongusing vertexing at CMS Helsinki b/tau workshop 30.05.-01.06.2002 Lauri A. Wendland / HIP

  2. Outline • Motivation • Tools & methods • Secondary vertex (SV) reconstruction • Charge reconstruction • Effective mass reconstruction • Conclusions • Future plans

  3. Motivation • If 3-prong  events can be used in addition to 1-prong  decays, a factor of 1.7 of signal events are gained

  4. Tools & methods • Software • ORCA_5_4_1 • CMSIM 123 • Reconstruction • Lvl1,2 calo selections (L2cut = 3.4 GeV (lowlumi)) • Lvl3 pixel selection (RS = 0.07, RM = 0.1, RI = 0.4) • full tracker reconstruction (Reco) • pixel lines from Lvl3 used as seeds • at least 8 hits per track demanded

  5. Used event samples Events produced with ORCA_4_5_0, L=2·1033 cm-2s-1

  6. -jet axis  axis  axis SVRECO SVMC PVMC SV reconstruction • The residual of the SV is divided into components along and transverse to the jet axis • A double gaussian fit is used to estimate the tails of the residuals

  7. SV residual along -jet axis H500 2, 3 tracks H200 2, 3 tracks  = 5.4 ± 0.5 mm s = 1.3 ± 0.1 mm ±2 = 62 %  = 1.6 ± 0.2 mm s = 0.65 ± 0.03 mm ±2 = 69 % cm cm H500 3 tracks H200 3 tracks  = 5.9 ± 2.4 mm s = 1.0 ± 0.1 mm ±2 = 73 %  = 1.4 ± 0.4 mm s = 0.60 ± 0.04 mm ±2 = 80 % cm cm

  8. Why are there tails? R = sqrt(2 + 2) H500 2, 3 tracks H500 2, 3 tracks cm cm • Tails come predominantly from jets with low R • Hit mismatching because of narrowness of jet?

  9. Initial number of prongs Number of pixel lines Number of reconstructed tracks (at least 8 hits) Track reconstruction efficiency H500 H200 0.5 0.5 number of tracks number of tracks

  10. SV residual transverse to -jet axis H500 2, 3 tracks H200 2, 3 tracks  = 50 ± 11 µm s = 25 ± 3 µm ±2 = 78 %  = 43 ± 66 µm s = 22 ± 2 µm ±2 = 87 % cm cm H500 3 tracks H200 3 tracks s = 21 ± 1 µm ±2 = 93 % s = 20 ± 1 µm ±2 = 93 % cm cm

  11. Flightpath reconstruction Signal efficiency 3D reconstructed flightpath in cm Background efficiency • Signed flightpath is fine for making cuts • D-mesons could be a concern

  12. Charge reconstruction H500, 3-prong H500 bin 0: 55 % others: 45 % q q Reconstructed charge - MC charge Total charge of two -jets • Low reliability, because currently tracks are lost

  13. Effective mass reconstruction H500, 3-prong QCD, 80-120 GeV m m m cut-off GeV GeV • meff = sqrt(( sqrt(pi2 + m2))2 -  pi2) • QCD background should contain heavier particles

  14. Conclusions • SV resolution (without tails) of • 600-1000 µm can be reached in jet axis direction for 200 and 500 GeV Higgs events respectively • 20-21 µm can be reached transverse to jet axis • resolution dominated by high boost of the -jets • More efficient track reconstruction method has to be used • The signal resolution as well as background rejection will improve if efficiency of reconstructing all 3 prongs is high

  15. Future plans • Move to ORCA_6_x_x • To use regional track finding instead of pixel seeds • To use deterministic annealing filter (DAF)

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