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Enhancing 3-Prong Tau Event Reconstruction at CMS: Vertexing Techniques and Future Directions

This presentation discusses advancements in 3-prong tau event reconstruction techniques at CMS, focusing on motivation, tools, and methods. Key methods include secondary vertex (SV) reconstruction, charge reconstruction, and effective mass reconstruction, demonstrating a significant increase in signal events. The study highlights the software tools utilized, event samples, and challenges faced such as tails in SV residual analysis. Conclusions drawn point to the need for improved track reconstruction methods and future plans for software upgrades to enhance signal resolution and background rejection efficiency.

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Enhancing 3-Prong Tau Event Reconstruction at CMS: Vertexing Techniques and Future Directions

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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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