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

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


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


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)


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)


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


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..


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 =


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:


Some H 4e plots

Pt and eta spectrum for events chosen by my first Filter:


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!

Documents

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