serena oggero august 14th, 2007 cern summer student session ph - cmm università di torino (italy)
TRANSCRIPT
Serena Oggero
August 14th, 2007 CERN Summer Student Session
PH - CMM Università di Torino (Italy)
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
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 farmCMS Software
...so any offline analysis depends on the HLT efficiency…
My physics channel
Serena Oggero CERN Summer Student Session 2007
One of the most promising channelH Z Z* l+l- l+l-
and I focused onH Z Z* e+e- e+e-
How it is seen by the CMS detector:
140 < MH < 700 GeV140 < MH < 700 GeV
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 GeVH Z Z* e+e- e+e- Higgs mass 190 GeV
Filter ModuleFilter Module• selection of at least 2 e- and 2 e+ per event• acceptance cuts: pt > 5 GeV and |η| < 2.7
to preserve electron reconstruction efficiency
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 NtupleRoot Ntuple
HLT table for L = 1032cm-2s-1
Serena Oggero CERN Summer Student Session 2007
Single Electron Double Electron
Relaxed Single Electron
Relaxed Double Electron
L1 seed A_SingleIsoEG12 A_DoubleIsoEG8 A_SingleEG15 A_DoubleEG10
|η| < 2.5 < 2.5 < 2.5 < 2.5
Et < 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 - < 1.5 -
E/P endcaps < 2.45 - < 2.45 -
HLT pathsused
HLT pathsused
..relaxed paths only differ for Et thresholds that are matched with L1..
Serena Oggero CERN Summer Student Session 2007
Results: efficiency tests
Single Electron
Relaxed Single
Electron
Double Electron
Relaxed Double
Electron
Logical OR
Absolute 97,6% 97,3% 95,8% 97,4% (98,9±0,4)%
On L1 seed 97,6% 97,3% 95,9% 97,4%
Efficiency measured on 2 MC samples (~730 events for mH = 190 GeV and ~370 events for mH = 170 GeV):
Single Electron
Relaxed Single
Electron
Double Electron
Relaxed Double
Electron
Logical OR
Absolute 96,0% 96,2% 92,2% 95,0% (98,4±0,7)%
On L1 seed 96,0% 96,2% 93,2% 95,0%
mH = 170 GeV
mH = 190 GeV
HLT_events
All_eventsε =
HLT_events
L1_eventsε =
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:
Serena Oggero CERN Summer Student Session 2007
Some H 4e plots
Pt and eta spectrum for events chosen by my first Filter:
Serena Oggero CERN Summer Student Session 2007
Summary & Outlook
Written modules for HLT studies on H4e 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!