e. soldatov
DESCRIPTION
Tight photon efficiency study using FSR photons from Z ll decay s. E.Yu.Soldatov* *National Research Nuclear University “MEPhI”. Outline: Selection criteria Puries of samples Tight cut efficiency from Z->ee / Background estimation method. E. Soldatov. Photon ID efficiencies meeting. - PowerPoint PPT PresentationTRANSCRIPT
E. Soldatov 17.10.2011
Tight photon efficiency study using FSR photons Tight photon efficiency study using FSR photons fromfrom ZZllll decay decayss
E.Yu.Soldatov*
*National Research Nuclear University “MEPhI”
Outline:
1. Selection criteria
2. Puries of samples
3. Tight cut efficiency from Z->ee/
4. Background estimation method
Photon ID efficiencies meeting
E. Soldatov
IntroductionIntroduction
A “minor” problem: a small production cross section.
What do we want?
The main idea is to obtain a photon sample with maximum purity with the method decoupled from the standard analysis
methods. Why do we want this?
Studies of the ATLAS detector performance with tagged photons and first of all study and optimization of the tight cut criteria.
Very important for analysis all photon containing processes.
The best source of such kind of photons is a production of
FSR photons from Z-lepton decay:
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Introduction: Samples&PreselectionsIntroduction: Samples&Preselections
5M sample of Z-boson decays to electrons and muons from mc10 was used (ATHENA Release 16.6.4.3) :
Electron channel:MC: mc10_7TeV.106046.PythiaZee_no_filter.merge.AOD.e574_s933_s946_r2399_r2300/Data: 2011 Periods D-L5 (Egamma stream) – 2.14 fb-1 Muon channel:MC: mc10_7TeV.106047.PythiaZmumu_no_filter.recon.AOD.e574_s933_s946_r2399/Data: 2011 Periods D-K (Muons stream) – 2.03 fb-1
For all particles the initial requirements are: •ET>5 GeV for photons,
•PT>20 GeV for electrons and muons, •||<2.47, excluding the crack region (1.37<||<1.52) between the barrel and end-cap calorimeters.•deltaR(l)>0.2&& for leptons applied preselection consistent with EPS recommendations
Photon ID efficiencies meeting
17.10.2011MCTruthClassifier used for truth matching
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Introduction: SelectionIntroduction: Selection
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1. Mass of two leptons should have a missing part e.g. < Z bozon mass
For electron channel 60 < m(ee) < 83 GeV, and for muon channel 40 < m() < 82 GeV
A kinematic approach of the photon selection
2. And 3 body mass should correspond to a mass of Z bozon
For electron channel 80 < m(ee)< 94 GeV and for muon channel 81 < m() < 95 GeV
Kinematics approach is based on a simple criteria of the event selection.
Background-ISR-Brem-Jets
-FSRSignal
Three body mass spectrum (Z)
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3. Isolation: Etcone20_ptcorrected<5 GeV && Nucone20=0.
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TightTight cut efficiency studycut efficiency study
MCTruthClassifier check of the background
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17.10.2011There are many of FSR in bkg!!!
E. Soldatov
TightTight cut efficiency studycut efficiency study
MCTruthClassifier check of the background after tight cut
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17.10.2011There are many of FSR in bkg!!!
Photon purity after all cuts appliedPhoton purity after all cuts applied
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Differential purity for each bin.
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Purity=Signal/(Signal+Background)
Et [GeV]
Z->ee
Et [GeV] Et [GeV]
Et [GeV]
Unconverted photons
Unconverted photons
Converted photons
Converted photons
Z->ee Z->
Z->
Syst=1.0%
Syst=0.5%
Syst=0.3%
Syst=0.1%
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Signal/background ration is much better at for higher photon energies.
IntroductionIntroduction
3 body mass spectrum with constrains on the mass of two leptons (Data and MC)
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Z->ee
ET()>15 GeVET()>5 GeV
Photon ID efficiencies meeting
(Electrons pass Medium cut)
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IntroductionIntroductionPhoton spectrum after selection of the signal area
applying 3 body mass cut80 < m(ee)< 94 GeV
81 < m() < 95 GeV
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Z->ee Z->
Photon ID efficiencies meeting
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TightTight cut efficiency studycut efficiency study
Efficiency of robust tight cut on photons vs Et spectrum
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ET [GeV]
Z->ee
- Sgn sample MC
- Data 2011
- Sgn sample MC
- Data 2011
ET [GeV]
Converted photons
Unconverted photons
E. Soldatov
TightTight cut efficiency studycut efficiency study
Efficiency of robust tight cut on photons vs Et spectrum
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ET [GeV]
ET [GeV]
- Sgn sample MC
- Data 2011
ET [GeV]
ET [GeV]
Converted photons
Converted photons
Unconverted photons Unconverted photons
- Sgn sample MC
- Data 2011
- Sgn sample ffMC
- Data 2011
- Sgn sample ffMC
- Data 2011
Z-> Fudge factor correctionNominal MC
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Data driven background estimationData driven background estimationWork of the background estimation method on real data
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ET()>5 GeV, ET()<10 GeV
Syst~2-3%
Z->ee
N (tracks in cone20)
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ConclusionsConclusions
Correction of truth matching for signal selection has been done. The purity became larger than 98% for 15 GeV photon sample.
Monte Carlo simulation has been compared with the 2011 Data (periods D-K with ~2 fb-1 of integral luminocity).
To improve the agreement between simulation and data background estimation method from data has been proposed and implemented.
Tight cut efficiency has been estimated using two methods.
MC and Data descrepancy became very small after fudge factor MC correction.
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Back-up slidesBack-up slides
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TightTight cut efficiency studycut efficiency study
Multiplicity for data
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Data driven background estimationData driven background estimation
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Crosscheck on a larger statistics!
In order to obtain more background photons under in a signal sample less stringent kinematic conditions where taken:
40 < m() < 88 GeV75 < m() < 105 GeV
Excellent agreement!
ET()>5 GeV
N (tracks in cone20)
Number of tracks in cone 0.2 around photon vector in ID.
Again the black line shows the background estimate using extrapolation method described above.
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E. Soldatov
MC: Study of the pure background sample.MC: Study of the pure background sample.
Spectrum of background photons from the signal sample after 3 body
mass CUT applied
ET [GeV]
Spectrum of background photons from the background sample
Applying 3 body mass cutwe deform a bit the photon
spectrum.
Does it affect the background estimation?
Background photon spectrums
Cut Et (in cone 0.2)<3 GeV
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