Tracking performances & b-tagging commissioning Simone Montesano (Milano)

Simone Montesano - Milano Outline Motivation: Impact of b-tagging on ATLAS data analysis (top cross section) Plan for 2009 (PHD thesis) Pixels offline calibrations => effect on resolution Tracking performances using cosmics data Tracking performances from first collisions data (minimum bias events) Developments & perspectives (2010) Tracking performances from first collisions data (top events) b-tagging commissioning using ttbar events (see CSC note) Real data MC data 3 June 2018 Simone Montesano - Milano

Top cross section analysis - b-tagging impact - B-tagging is an important tool in ATLAS: From CSC note “Determination of Top Quark Pair Production Cross-Section” (Udine involved): 100 pb-1 data, 14 Tev STANDARD ANALYSIS: no b-tagging (S/B = 2.2. – 5.3) b-tagging (S/B = 9.6 – 20.1) B-tagging performances are tested for small misalignments: From CSC note “Effect of Misalignment on b-Tagging”: “The amount of misalignment remaining after applying the actual alignment procedures resulted in only a small loss of performances[..]” CSC analysis didn’t assumed a working b-tagging with first data (no time for full alignment and tracking commissioning before collisions) 3 June 2018 Simone Montesano - Milano

b-tagging status after commissioning with cosmics? Before reprocessing: impact parameter resolution Splitted tracks to estimate resolution on tracking parameters d0 resolution is already very near to the nominal one! 12 μm expected!!! 3 June 2018 Simone Montesano - Milano

Optimizing pixel resolution: offline calibrations This is done with preliminary alignment! 30 um improvement in eta direction! 3 June 2018 Simone Montesano - Milano

Simone Montesano - Milano Plans: before data Consider SIG/BKG ratio in the plane “b-tagging efficiency vs b-tagging rejection” (top cross section analysis): when b-tagging starts to be useful? requirements on tracking performances? where b-tagging algorithms curves are placed? Plans: First data Tracking performances using minimum bias: resolution, efficiency? is b-tagging ready? impact on data? 3 June 2018 Simone Montesano - Milano

b-tagging commissioning using ttbar events Work that could start on simulated data and be completed in 2010 using data “super pure” top events selection mainly interested in b-jet enriched sample no need to reconstruct the full event di-leptonic top events? 3 June 2018 Simone Montesano - Milano