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Photon purity measurement on JF17 Di jet sample using Direct photon working Group ntuple Z.Liang (Academia Sinica,TaiWan) 6/24/20161.

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Presentation on theme: "Photon purity measurement on JF17 Di jet sample using Direct photon working Group ntuple Z.Liang (Academia Sinica,TaiWan) 6/24/20161."— Presentation transcript:

1 Photon purity measurement on JF17 Di jet sample using Direct photon working Group ntuple Z.Liang (Academia Sinica,TaiWan) 6/24/20161

2 Introduction to Direct photon ntuple Made by HiggsAnalysisUtils package, size 2.5k/evt Ntuple maker can run in DPD and AOD format Official tools are embedded into ntuple dumper,conversion recovery tool Truth matching information are done for photon and electron and jets objects. Wiki page : https://twiki.cern.ch/twiki/bin/view/AtlasProtected/SMDirectPhotonsPro duction1 https://twiki.cern.ch/twiki/bin/view/AtlasProtected/SMDirectPhotonsPro duction1 Central production of these ntuple for JF17 Dijet sample and photon jet sample are available on grid, more detailed are in the wiki page Trigger information are also included. 6/24/20162

3 Outline Photon purity measurement in JF17 dijet sample (Direct photon group ntuple) Two method to estimate photon purity after IsEM cut ph_isEM%65536==0) and track isolation cut (ph_PtIsolationCone==0)  Method1 : two dimensional side band  Method2 : photon conversion Comparison between method 1 and 2 and truth information 6/24/20163

4 Pt distribution of photon candidate with truth information Photon Pt[GeV] 6/24/20164 Photon candidate PT after IsEM cut ( ph_isEM%65536==0 ) Photon candidate Pt after IsEM cut ( ph_isEM%65536==0 ) and track isolation (ph_PtIsolationCone==0) Purity[Pt]= (Area under red curve )/ (Area under blue curve+ Area under red curve )[Pt] The question is : how we estimate the purity from data without any truth information ? Truth photon : photon from hard process and quark/gluon bremstrahlung

5 Method 1: 2 dimensional sideband method Select 2 different photon ID variable(ph_PtIsolation and ph_shwr_fracm), Try something like 2 dimensional sideband,3 control region, 1 signal region. Try to make use of information of 3 control region to get number of events in signal region. 6/24/20165

6 Photon ID variable 6/24/20166 Ph_shwr_fracm: fraction of Energy in LAr strip layer outside core, in formular [E(+-7)-E(+-3)]/E(+-7) Ph_PtIsolationCone: scalar sum of track pt (DR<0.3) around photon cluster Ph_shwr_fracm Ph_PtIsolationCone[GeV] Plots of Barrel region,Pt of photon >15GeV

7 Correlation between these two variables 6/24/2016 7 Ph_shwr_fracm Plots of Barrel region,Pt of photon >15GeV Ph_shwr_fracm is not sensitive to isolation cut for fake photon object Meaning that these two variables are not correlated to each other for fake photon object.

8 Control region and signal region 6/24/20168 C AD B Control region A : ph_shwr_fracm> 1.2* isemcut value && track isolation <1GeV Control region B : ph_shwr_fracm 2GeV Control region D : ph_shwr_fracm> 1.2* isemcut value && track isolation >2GeV Signal region C : ph_shwr_fracm< isemcut value && track isolation <1GeV

9 Purity measurement Assume number of background in region all region is NA’,NB’,NC’,ND’ Since two ID variables are not correlated for fake photon object. So NA’/NC’=ND’/NB’ Our signal (real photon ) only in region C,assume NC’’ is number of signal events in region C So NC=NC’+NC’’ Purity =NC’’/NC=1-NC’/NC=1-NA’*NB’/ND’/NC If A,D,B dominated by background (NB’=NB,ND’=ND,NA’=NA), purity=1-NA*NB/ND/NC 6/24/2016 9 9 C AD B

10 Validation of this method using truth information Pt~[5GeV,10GeV] 6/24/201610 Total eventsReal Photon (N’’)Truth fake photon (N’) Control region A4868106 (NA’’)4762 (NA’) Control region B56053123 (NB’’)55930 (NB’) Signal region C18326835 (NC’’)17491 (NC’) Control region D1616418 (ND’’)16146 (ND’) The truth information shows: Background events in region A B D is much at least 20 time larger than signal events NA’>>NA’’ and NB’>>NB’’ This formular for background events NA’/NC’=ND’/NB’ can be validated Table for photon candidate Pt~[5GeV,10GeV] C AD B

11 Validation of this method using truth information Pt~[30GeV,35GeV] 6/24/201611 Total eventsReal Photon (N’’)Truth fake photon (N’) Control region A1847 (NA’’)177 (NA’) Control region B120267 (NB’’)1135 (NB’) Signal region C1211542 (NC’’)669 (NC’) Control region D3380 (ND’’)338 (ND’) The truth information shows: Background events in region A B D is much at least 20 time larger than signal events NA’>>NA’’ and NB’>>NB’’ This formular for background events NA’/NC’=ND’/NB’ can be validated Table for photon candidate Pt~[30GeV,35GeV] C AD B

12 Purity of method 1 for photon in barrel region(|eta|<1.37) 6/24/201612 purity Red: truth information Blue :method 1 measurement Photon Pt[MeV] Purity measured by method 1 increase with Pt, consistent with truth information

13 Method 2: conversion method After all IsEm cut and track isolation cut main background of photon is pi0 or other neutral meson They tend to decay to two photon or more. And the key point of method 2 is that two photon have more possibility to converse into at least one electron. Define converted fraction ( called it F ) is the probability of at least one electron was created by conversion of neutral em object before LAr presample layer F(data)=(1-purity)*F(fake photon) +purity*F(real photon ) 6/24/201613

14 Converted fraction Measurement using LAr presample layer 6/24/201614 We can measure conversion fraction using Pre-sample layer of Lar EM Calo. If neutral EM object converted into at least one electron before LAr Calo, it deposit its energy in presample layer like a landau distribution If not, neutral EM object can not loss energy by ionization,so energy loss is close to zero in pre-sample layer Ph_ES0/ph_E Peak Created by Converted neutral EM object Peak Created by Non-Converted neutral EM object

15 Template of Converted component In order to separate this two Component, we need template for One of the component to make a fit We can use inner detector vertexing Information to get this template The best choice of template for Converted component is photon candidate Matched with single track or double track conversion vertex( ph_Conv%10==1) 6/24/201615 Ph_ES0/ph_E Converted component Non-Converted component Ph_ES0/ph_E Ph_isEM%65536==0 && Track isolation ==0 && Ph_Conv%10>=1 Ph_isEM%65536==0 && Track isolation ==0 Template distribution for converted Component of ph_ES0/ph_E

16 Calculate converted fraction 6/24/201616 Converted neutral EM object Non-Converted neutral EM object Ph_ES0/ph_E 1.Plot ph_ES0/ph_E for Photon candidated That pass all the cuts 2. Get template distributon Of converted component Plot ph_ES0/ph_E with the cut ph_Conv%10==1 3. Fit data point of step 1 using Template from step 2 with the Help of TFractionFitter in Root 4. Conversion fraction F= red /(red+blue)

17 6/24/201617 With Truth info Real photon With Truth info Real Fake photon Data info(without truth ) photon candidate pass Isem and isolation cut Ph_ES0/ph_E

18 Control sample In real data,we can not trust distribution of Real Fake photon from MC simulation since jet simulation is not so easy. possible choice is to use a control sample which is dominated by Fake photon object Define a control sample with photon candidates which pass IsEM (itune1) cut but fail track isolation cut, This control sample is dominated by neutral meson background (has been validated in slide 9,10) Replace the third column of previous slide with control sample distribution 6/24/201618

19 6/24/201619 With Truth info Real photon Data info(without truth ) photon candidates pass Isem but fail isolation cut Real Fake photon Data info(without truth ) photon candidate pass Isem and isolation cut Ph_ES0/ph_E

20 Ph_ES0/ph_E VS Eta 6/24/201620 Eta Ph_ES0/ph_E In very central region |eta|<0.8 (As indicated by red line) Ph_ES0/ph_E do not have strong eta dependence in that region,relatively easy to handle. So we try method 2 in region |eta|<0.8 at very beginning. All the plots for method 2 in previous page is made in this very central region

21 Conversion fraction and purity in barrel region (|eta|<0.8) Pt of photon F(data)F(control sample)F(real phton) Truth info from MC Purity 5-10GeV0.865+-0.0070.886+-0.0060.75+-0.020.16+-0.04 10-15GeV0.82+-0.020.850+-0.0080.69+-0.020.21+-0.04 15-20GeV0.73+-0.020.81+-0.020.58+-0.030.31+-0.05 20-25GeV0.60+-0.020.710+-0.0090.51+-0.020.53+-0.05 25-30GeV0.59+-0.040.72+-0.040.49+-0.040.57+-0.15 30-35GeV0.51+-0.020.64+-0.020.42+-0.020.59+-0.07 35-40GeV0.51+-0.020.59+-0.040.41+-0.020.46+-0.07 6/24/201621

22 (1-purity) of method 1,2 for photon in barrel region (|eta|<0.8) 6/24/201622 Red: truth information Blue :method 1 measurement Black :method 2 measurement Photon Pt [MeV]

23 Conversion fraction and purity in barrel region (|eta|<1.37) Pt of photon F(data)F(control sample)F(real phton) Truth info from MC Purity 5-10GeV0.946+-0.0020.954+-0.0020.82+-0.010.047+-0.004 10-15GeV0.89+-0.020.91+-0.020.77+-0.010.10+-0.03 15-20GeV0.86+-0.030.90+-0.020.71+-0.020.19+-0.05 20-25GeV0.74+-0.030.82+-0.020.66+-0.020.44+-0.09 25-30GeV0.67+-0.020.78+-0.020.60+-0.020.58+-0.09 30-35GeV0.65+-0.020.76+-0.020.57+-0.030.56+-0.09 35-40GeV0.67+-0.030.74+-0.020.60+-0.030.46+-0.14 6/24/201623

24 Purity of method 1,2 for photon in barrel region (|eta|<1.37) 6/24/201624 Red: truth information Blue :method 1 measurement Black :method 2 measurement Photon Pt [MeV] try method 2 in full barrel, seems still reasonable

25 Summary Purity measurement Method 1 and 2 is more or less consistent with truth purity Purity increase with photon Pt increase. Next step : Running out of events in high Pt region,may try other high Pt dijet sample, or change binning of photon Pt to test methods in high Pt region Try Calo base isolation instead of track isolation 6/24/201625

26 Backup F(real photon)=1-Exp[-X/X0] F(fake photon from neutral meson)=1-Exp[-m*X/X0], where m is effective background neutral meson decay multiplicity. Since most of background is pi0, m is close to 2,but not exactly, m is lower than 2 in low pt region since two photon from pi0 is not collinear in low pt region m is larger than 2 in high pt region since back scattering will increase effective multiplicity Try to test method in endcap region 6/24/201626

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