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Status of Secondary Vertex Reconstruction in BESIII Analysis Software Group

This document provides an outline of the status of secondary vertex reconstruction in BESIII analysis software, including the algorithm used and preliminary results. The reconstruction and selection of K0S, Λ, J/ψ->ΛΛ, and J/ψ->K0S.K0L are discussed.

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Status of Secondary Vertex Reconstruction in BESIII Analysis Software Group

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  1. Status of Secondary Vertex Reconstruction Liu BeijiangBESIII Analysis Software Group

  2. Outline • Introduction • Algorithm • BKlamsVTX (C++ implementation for BES III) • Preliminary results • KS reconstruction • Λ reconstruction • J/ψ-> ΛΛ selection • J/ψ-> KS KL selection • Summary Status of Secondary Vertex Reconstruction BESIII Analysis Tools

  3. Introduction • To select candidates for K0S-> π+π- or Λ -> p π-, a subroutine named KLAMS is used on BESII, which is based on an iterative, nonlinear least squares technique. • We accomplished its counterpart for BESIII : BKlamsVTX BESIII Analysis Tools

  4. AlgorithmSecondary Vertex Finding (Geometry calculation) • Get the point (s) of intersection of two circles (two helices’ projection in transverse plane) • Check if the 2nd vertex candidate is located in reasonable region • If there two points of intersection, the one closer to the interaction point is chosen as the 2nd vertex candidate BESIII Analysis Tools

  5. AlgorithmFormulas for fitting (adopted from MARKIII MEMO) xb is beam position, the measurement uncertainty is described by σb xv is secondary vertex location, the measurement uncertainty is described by σv ub is vector from xb to the primary vertex uv is vector from xv to the secondary vertex t is vector of the decaying track BESIII Analysis Tools

  6. AlgorithmFormulas for decay length (adopt from MARKIII MEMO) BESIII Analysis Tools

  7. BKlamsVTX Class Input: IP parameters Trk mass,charge, Trk parameters, Error matrix Secondary Vertex Finding LS fitting Swimming Output: Swum Trk parameters, error matrix Parent’s Trk parameters, error matrix Lxy, Chi-sqare， ctau BESIII Analysis Tools

  8. Secondary Vertex Reconstruction in BOSS BParticle BKlamsVTX BVertex BComposedParticle GoodKShortSelection GoodLambdaSelection VeeVtxReconstruction KShortReconstructionklams LambdaReconstructionklams BESIII Analysis Tools

  9. PreliminaryresultsKS reconstruction [ inclusive 1M J/ψ toanything events ] Decay Length/Error of Decay Length Decay Length in XY Plane(cm) Distance of 2 trks at secondary vertex in Z direction (cm) BESIII Analysis Tools

  10. PreliminaryresultsΛ reconstruction [ inclusive 1M J/ψ toanything events ] Decay Length/Error of Decay Length Decay Length in XY Plane(cm) Distance of 2 trks at secondary vertex in Z direction (cm) BESIII Analysis Tools

  11. PreliminaryresultsKS reconstruction [ inclusive 1M J/ψ toanything events ] --σ> 0 --σ> 1 --σ> 2 --σ> 3 • Good KShort Selection Criteria: • δz<2.0cm; (δz=Distance of 2 trks at secondary vertex in Z direction ) • χ2 < 20; • σ> 2; (σ=Decay Length/Error of Decay Length) • |M(KS) - 0.49765|<0.01; BESIII Analysis Tools

  12. PreliminaryresultsΛ reconstruction [ inclusive 1M J/ψ toanything events ] --σ> 0 --σ> 1 --σ> 2 • Good Lambda Selection Criteria: • δz<2.5cm; (δz=Distance of 2 trks at secondary vertex in Z direction ) • χ2 < 20; • σ> 1; (σ=Decay Length/Error of Decay Length) • |M(Λ) - 1.115683|<0.003; BESIII Analysis Tools

  13. PreliminaryresultsKS reconstruction [ inclusive 1M J/ψ toanything events ] mass resolution ~3 MeV BESIII Analysis Tools

  14. PreliminaryresultsΛ reconstruction [ inclusive 1M J/ψ toanything events ] mass resolution ~1 MeV BESIII Analysis Tools

  15. PreliminaryresultsJ/ψ->K0S K0L • To estimate the K0Smomentum resolution, following selection criteria are used: • Two good charged tracks with zero total charge are required • The two tracks shared one K0S secondary vertex • Mass of reconstructed K0S satisfy|M(KS) - 0.49765|<0.01; BESIII Analysis Tools

  16. PreliminaryresultsJ/ψ->K0S K0L [ 10000 MC events ] J/ψ-> K0S K0L (K0S-> π+π-) selection efficiency 23.3% momentum resolution ~8 MeV BESIII Analysis Tools

  17. PreliminaryresultsJ/ψ->K0S K0L [ 1M J/ψ toanything events ] Result at BESII signal J/ψ->K* K background BESIII Analysis Tools

  18. PreliminaryresultsJ/ψ-> ΛΛ • To estimate the Λ momentum resolution, following selection criteria are used: • 4 good charged tracks with zero total charge are required • 2 tracks shared one Λ secondary vertex, the other 2 tracks shared one Λ secondary vertex • Mass of reconstructed Λ satisfy |M(Λ) – 1.115683|<0.003; BESIII Analysis Tools

  19. PreliminaryresultsJ/ψ-> ΛΛ [ 10000 MC events ] J/ψ-> ΛΛ (Λ -> p π- , Λ -> p π+ ) selection efficiency 22.3% momentum resolution ~6 MeV BESIII Analysis Tools

  20. Summary • BKlamsVTX is accomplished with reasonable output. • Secondary vertex reconstruction is available in BOSS. BESIII Analysis Tools

  21. Thank you BESIII Analysis Tools

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