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Serena Oggero August 14th, 2007 CERN Summer Student Session PH - CMM Università di Torino (Italy)

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Presentation on theme: "Serena Oggero August 14th, 2007 CERN Summer Student Session PH - CMM Università di Torino (Italy)"— Presentation transcript:

1 Serena Oggero August 14th, 2007 CERN Summer Student Session PH - CMM Università di Torino (Italy)

2 Outline Serena Oggero CERN Summer Student Session 2007  The CMS High Level Trigger  My physics channel  My work on CMS software with MC data  First results: efficiency measurements  Summary

3 The CMS HLT Serena Oggero CERN Summer Student Session 2007 Why? most of events produced at LHC are not interesting the interaction rate is larger than what can be recorded How? takes events already accepted by the first level trigger (L1) decides whether the event should be kept, based on sequences of more elaborated algorithms What? CMS online event selection code CMS detector (40 MHz) CMS detector (40 MHz) L1 Trigger (100 kHz) L1 Trigger (100 kHz) HL Trigger (100 Hz) HL Trigger (100 Hz) Custom-made Hardware Pc farm CMS Software...so any offline analysis depends on the HLT efficiency…

4 My physics channel Serena Oggero CERN Summer Student Session 2007 One of the most promising channel H  Z Z*  l + l - l + l - and I focused on H  Z Z*  e + e - e + e - How it is seen by the CMS detector: 140 < M H < 700 GeV

5 My work (I) Serena Oggero CERN Summer Student Session 2007 Event sources (Montecarlo) Event sources (Montecarlo) Set of complete events of: H  Z Z*  l + l - l + l - Higgs mass 170 GeV H  Z Z*  e + e - e + e - Higgs mass 190 GeV Filter Module selection of at least 2 e - and 2 e + per event acceptance cuts: p t > 5 GeV and |η| < 2.7 to preserve electron reconstruction efficiency

6 My work (II) Serena Oggero CERN Summer Student Session 2007 Analyzer module Analyzer module - Offline electron reconstruction in several steps: starting from the SuperCluster using information from pixel detector, tracker, HCAL - Run HLT Egamma paths: each path iterates over a collection of reconstructed physics objects and applies cuts Root Ntuple

7 HLT table for L = 10 32 cm -2 s -1 Serena Oggero CERN Summer Student Session 2007 Single ElectronDouble Electron Relaxed Single Electron Relaxed Double Electron L1 seed A_SingleIsoEG12 A_DoubleIsoEG8A_SingleEG15A_DoubleEG10 |η||η| < 2.5 EtEt < 15 GeV< 10 GeV< 17 GeV< 12 GeV Tk isol < 0.06< 0.4< 0.06< 0.4 HCAL isol barrel < 3 GeV< 9 GeV< 3 GeV< 9 GeV HCAL isol endcaps < 3 GeV< 9 GeV< 3 GeV< 9 GeV E/P barrel < 1.5- - E/P endcaps < 2.45- - HLT paths used HLT paths used..relaxed paths only differ for Et thresholds that are matched with L1..

8 Serena Oggero CERN Summer Student Session 2007 Results: efficiency tests Single Electron Relaxed Single Electron Double Electron Relaxed Double Electron Logical OR Absolute97,6%97,3%95,8%97,4%(98,9±0,4)% On L1 seed97,6%97,3%95,9%97,4% Efficiency measured on 2 MC samples (~730 events for m H = 190 GeV and ~370 events for m H = 170 GeV): Single Electron Relaxed Single Electron Double Electron Relaxed Double Electron Logical OR Absolute96,0%96,2%92,2%95,0%(98,4±0,7)% On L1 seed96,0%96,2%93,2%95,0% m H = 170 GeV m H = 190 GeV HLT_events All_events ε = HLT_events L1_events ε =

9 Serena Oggero CERN Summer Student Session 2007 Main sources of inefficiency L1 double seed (double electrons) Pixel match (single and double electrons) Electron E/p cut (single and double electrons) Checking HLT report:

10 Serena Oggero CERN Summer Student Session 2007 Some H  4e plots Pt and eta spectrum for events chosen by my first Filter:

11 Serena Oggero CERN Summer Student Session 2007 Summary & Outlook  Written modules for HLT studies on H  4e channel  efficiency measured on two different MC samples  results look promising… …still to do:  improve Ntuple structure for a more detailed study  study signal and background rates  work with higher statistics and other Higgs mass points Many thanks to Roberta Arcidiacono and Nadia Pastrone!


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