1 / 17

E. Soldatov

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.

ull
Download Presentation

E. Soldatov

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Tight photon efficiency study using FSR photons fromZll decays 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 17.10.2011

  2. Introduction 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: A “minor” problem: a small production cross section. E. Soldatov Photon ID efficiencies meeting 17.10.2011 №2

  3. Introduction: 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 MCTruthClassifier used for truth matching E. Soldatov Photon ID efficiencies meeting 17.10.2011 №3

  4. Introduction: Selection A kinematic approach of the photon selection Three body mass spectrum (Z) Signal -FSR Background -ISR -Brem -Jets Kinematics approach is based on a simple criteria of the event selection. 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 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 3. Isolation: Etcone20_ptcorrected<5 GeV && Nucone20=0. E. Soldatov Photon ID efficiencies meeting 17.10.2011 №4

  5. Tightcut efficiency study MCTruthClassifier check of the background There are many of FSR in bkg!!! E. Soldatov Photon ID efficiencies meeting 17.10.2011 №5

  6. Tightcut efficiency study MCTruthClassifier check of the background after tight cut There are many of FSR in bkg!!! E. Soldatov Photon ID efficiencies meeting 17.10.2011 №6

  7. Photon purity after all cuts applied Differential purity for each bin. Purity=Signal/(Signal+Background) Z-> Z->ee Syst=0.3% Syst=1.0% Converted photons Converted photons Et [GeV] Et [GeV] Z->ee Z-> Syst=0.5% Unconverted photons Unconverted photons Syst=0.1% Et [GeV] Et [GeV] E. Soldatov Photon ID efficiencies meeting 17.10.2011 №7

  8. Introduction 3 body mass spectrum with constrains on the mass of two leptons (Data and MC) Z->ee ET()>5 GeV ET()>15 GeV Signal/background ration is much better at for higher photon energies. (Electrons pass Medium cut) E. Soldatov Photon ID efficiencies meeting 17.10.2011 №8

  9. Introduction Photon spectrum after selection of the signal area applying 3 body mass cut 80 < m(ee)< 94 GeV 81 < m() < 95 GeV Z->ee Z-> E. Soldatov Photon ID efficiencies meeting 17.10.2011 №9

  10. Tightcut efficiency study Efficiency of robust tight cut on photons vs Et spectrum Z->ee Converted photons Unconverted photons - Sgn sample MC - Data 2011 - Sgn sample MC - Data 2011   ET [GeV] ET [GeV] E. Soldatov Photon ID efficiencies meeting 17.10.2011 №10

  11. Tightcut efficiency study Efficiency of robust tight cut on photons vs Et spectrum Nominal MC Z-> Fudge factor correction Converted photons - Sgn sample MC - Data 2011 Converted photons  - Sgn sample ffMC - Data 2011  ET [GeV] ET [GeV] - Sgn sample ffMC - Data 2011 - Sgn sample MC - Data 2011   Unconverted photons Unconverted photons ET [GeV] ET [GeV] E. Soldatov Photon ID efficiencies meeting 17.10.2011 №11

  12. Data driven background estimation Work of the background estimation method on real data Z->ee ET()>5 GeV, ET()<10 GeV Syst~2-3% N (tracks in cone20) E. Soldatov Photon ID efficiencies meeting 17.10.2011 №12

  13. Conclusions 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. E. Soldatov Photon ID efficiencies meeting 17.10.2011 №13

  14. Back-up slides E. Soldatov Photon ID efficiencies meeting 17.10.2011 №14

  15. Tightcut efficiency study Multiplicity for data E. Soldatov Photon ID efficiencies meeting 17.10.2011 №15

  16. Data driven background estimation Crosscheck on a larger statistics! ET()>5 GeV Excellent agreement! In order to obtain more background photons under in a signal sample less stringent kinematic conditions where taken: 40 < m() < 88 GeV 75 < m() < 105 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. E. Soldatov Photon ID efficiencies meeting 17.10.2011 №16

  17. MC: Study of the pure background sample. Background photon spectrums Cut Et (in cone 0.2)<3 GeV Applying 3 body mass cut we deform a bit the photon spectrum. Does it affect the background estimation? ET [GeV] Spectrum of background photons from the signal sample after 3 body mass CUT applied Spectrum of background photons from the background sample E. Soldatov Photon ID efficiencies meeting 17.10.2011 №17

More Related