Vertex fitting Franco Bedeschi INFN FCCee topical meeting

Vertex fitting Franco Bedeschi, INFN FCC-ee topical meeting February, 2021 OUTLINE v Intro/Caveats v Vertex fitting Ø Performance checks v Way forward FCCee topical meeting, February 2021 1 F. Bedeschi, INFN-Pisa

Introduction v Vertex fit is already available in many existing packages Ø …. . That’s the problem: Ø Using it usually means you also buy a complex infrastructure v Goal here is to provide a simple standalone code Ø Easy to insert in FCC framework Ø More complex implementations can come later FCCee topical meeting, February 2021 2 F. Bedeschi, INFN-Pisa

Vertex fit (1) v Input: Ø Array of observed tracks 5 parameters + Cov. Matrix Assume perfect helix D, f 0, C, cot q, z 0 v Output: Ø 3 D vertex + covariance v Method: Ø c 2 minimization with constraints Vary parameters and phase and force all tracks to cross at same point FCCee topical meeting, February 2021 3 F. Bedeschi, INFN-Pisa

Vertex fit (2) v FCCee topical meeting, February 2021 4 F. Bedeschi, INFN-Pisa

Performance (1) v Example: 100, 000 events, 3 tracks, RV (0 -1. 5 cm), pt (0. 5 -1. 0 Ge. V) FCCee topical meeting, February 2021 5 F. Bedeschi, INFN-Pisa

Performance (2) v Example: 100, 000 events, 2 tracks, RV (0 -1. 5 cm), pt (0. 5 -1. 0 Ge. V) FCCee topical meeting, February 2021 6 F. Bedeschi, INFN-Pisa

Way forward v Can turn routine into a class with additional features: Ø External vertex constraint (easy): useful for primary vertex Ø Adding/removing individual tracks (easy) Ø Calculate updated track parameters and their error matrix Large matrix with correlations (easy) Ø Setup for tertiary vertices (more complex) Calculate total vertex momentum /covariance Allow for vertices with neutral tracks v In general strong interaction with track class format v Simple track/vertex structure to be refined FCCee topical meeting, February 2021 7 F. Bedeschi, INFN-Pisa