1 ZVTOP algorithm (based on part of March ’04 Vienna talk) Overview Vertex finding with ZVTOP More details on the algorithm OO development plans Dave Jackson LCFI Physics Meeting 19 th April 2005

2 Vertices formed from charged tracks in the decay chain of a b-quark flavour jet Interaction Point (IP) location and Gaussian ellipsoid error determined by beam and event tracks

3 For each track i a function f i ( r ) represents a Gaussian probability tube for the track trajectory σ XY σZσZ

4 Track FunctionsVertex Function The 3D functions have been integrated over Z and shown in 2D only here The ∑ is over the tracks ( i = 0 for IP) in the jet The jet above includes a B decay 1.5mm from the IP PrimaryB

5 1)Find all maxima for f i (r) f j (r) with i, j = 0…N and collect spatial points r ij for cases of good vertex fit, χ 2 i,j < X 0 2)Search in 3D for maxima in V(r) near each such r ij 3)If two such maxima fail ‘resolubility criterion’ they are merged together r1r1 r2r2 V(r) 4) Spatially resolved clusters of V(r) maxima form candidate vertices 5) Track to vertex association ambiguities are decided according to largest V(r) after χ 2 i < X 0 trimming 6) Vertex that includes the IP ellipsoid is called the Primary ZVTOP algorithm

6 TRACKS + IP SPATIAL POINTS (MERGED SUBSET) CANDIDATE VERTICES VERTICES 1) 2) 3,4) 5,6) xyz iteration resolubility 2-prong fits decide track-vertex ambiguities N+1 objects (for N tracks in jet) each associated with a list from: up to ½N(N+1) objects b-jet at SLD: on average ~4 ‘vertex’ objects at this stage where here: a vertex contains an arbitrary no. of tracks, ≥2 each track belongs to arbitrary no. of vertices, ≥0 (this is the tricky step in terms of object relations) Primary, secondary, tertiary…

7 All non-primary vertices found must be n-prong with n ≥ 2 For IP→B→D decay chain can have 1-prong B or D decay Can consider n-prong ZVTOP vertex as a Seed vertex A track not directly associated with the Primary or Seed vertex, but with small T, is likely to come from B decay chain

8 ZVKON3 OPTIONS+ TUNABLE PARAMETERS ZVTOP3 ‘TIDY’ CUTS SELECT ALGO ZVRES3 ‘CONVENTIONAL ZVTOP’ ZVKIN ‘GHOST TRACK’ ALGORITHM ZVTOPL3 TOPOLOGICAL VERTEX STRUCTURE ZVSIG3 CALCULATE V(r) ZVGST FIND GHOST TRACK MONTE CARLO TRUTH ZVTOP3 CODE STRUCTURE

9 Compare ‘ZVTOP’ with ‘Ghost Track Algorithm’ Number of Found Vertices ‘B Decay’ Invariant Mass GeV/c 2 ZVRES ZVKIN For SLD VXD3 MC

10 Summary ZVTOP designed to be an efficient, fast and user-friendly topological vertex finder, developed at SLD for hadronic jets. The Ghost Track algorithm designed for clean B decay chain reconstruction, aided by kinematic information For LCFI OO implementation of ZVTOP3 – it makes sense to use the SLD algorithm for ZVRES (the original ZVTOP), but possible applications for ZVKIN (b-tagging/dipole) should be initially studied at the ILC Monte Carlo level.