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Status and Prospects of the H → γγ Analysis

Status and Prospects of the H → γγ Analysis. Jim Branson - Marco Pieri - Sean Simon. UCSD Meeting March 11 th 2008 Updated for March 18th. Introduction. H → γγ analysis will start to be more important for Int L >~ 1 fb -1

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Status and Prospects of the H → γγ Analysis

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  1. Status and Prospects of the H→γγ Analysis Jim Branson - Marco Pieri - Sean Simon UCSD Meeting March 11th 2008 Updated for March 18th

  2. Introduction • H→γγ analysis will start to be more important for Int L >~ 1 fb-1 • UCSD has played a major role in the PTDR studies and is expected to play a major role in the next years • Other people/groups contributing are: • Caltech, Lyon, Notre Dame, Rome, Saclay, UC Riverside, UCSD • For 2008 not much to be expected in H→γγ channel • In addition the ECAL calibration will not be optimal • Related analyses: γ+jet, γγ from SM (except Higgs) – Should collaborate more with people working on them • Since about 1 month started revisiting the analysis framework to have it more flexible and common with other analyses • For now we ran over small MC samples: ~100k GamJet + ~100k Higgs + ~ 100k QCD + photonsJets + ~50k Dy • All what shown here very preliminary • News: In CMSSW 2_0_0 photons a 5 GeV Et cut an H/E cut at 0.2 is proposed to be applied for reconstructing photons Marco Pieri

  3. qqH → qqγγMH = 120 GeV Photons from Higgs decay forward jets H→γγ Signal SIGNAL: two isolated photons with large Et • Gluon-gluon fusion • WW and ZZ fusion (Weak Boson Fusion) • WH, ZH, ttH (additional leptons and MET) • Total σ x BR ~95 fb for MH = 110-130 GeV • Very good mass resolution H →γγMH = 115 GeV Jets from qq are at high rapidity and large Δη Marco Pieri

  4. Background to H→γγ BACKGROUND • ‘irreducible’ backgrounds, two real photons • gg→ γγ (box diagram) • qq→ γγ (born diagram) • pp→ γ+jets (2 prompt γ) • ‘reducible’ backgrounds, at least one fake photons or electrons • pp→ γ+jets (1 prompt γ + 1 fake γ) • pp→ jets (2 fake γ) • pp→ ee (Drell Yan) when electrons are mis-identified as photons • Handles for Irredicible BG – Kinematics • Handles for Reducible BG – Until now only Isolation • Should add photon identification (converted) and π0 rejection Marco Pieri

  5. Cross section and K-factors • Signal cross sections and BR used for the PTDR (NLO M. Spira) • K-factors for the background used for the PTDR (to be re-evaluated if needed) Marco Pieri

  6. PTDR Mass Spectrum of Selected Events • All plots are normalized to an integrated luminosity of 1 fb-1 and the signal is scaled by a factor 10 • Fraction of signal is very small (signal/background ~0.1) • Use of background MC can be avoided when we will have data • Data + signal MC can be used for optimizing cuts, training NN and precise BG estimation Marco Pieri

  7. CSA07 MC Samples • Requests at: https://twiki.cern.ch/twiki//bin/view/CMS/HiggsWGMCRequestsForHiggsToGamGam • Higgs Signal (Pythia) masses between 60 and 160 GeV (at Fnal, Cern, Lyon) • gluon-gluon fusion, • IVB fusion , • WH, ZH, ttH • Background (and even Signal) started to came very late in 2007 at it is not yet complete + Two samples were forgotten and resubmitted at the end of January • GamJet, Twophoton_Box, DY - OK • Twophoton_Born 450 K events Lyon - 1/2 of requested • Jets_Pt50up 1.4 M events Cern - 1/6 of requested • It would probably be good if the production was finished • HiggsTo2Gamma Skims of the soups available, we should start running on them Marco Pieri

  8. Important Points – Reconstruction Level • Trigger and Skims • L1 Trigger • HLT • Skims • Photon isolation • Primary Vertex estimation • Energy Measurement • Ecal crystal calibration • SuperCluster calibration • Photon energy scale • Energy Resolution and Error (maybe optional, was done before) • Photon conversion identification and π0 rejection Marco Pieri

  9. Level-1 Trigger • Electromagnetic trigger towers are classified in two categories depending on the energy deposition in the calorimeter trigger towers: non-isolated, isolated. Nominal Low Lumi (2x1033 cm-2s-1) • Single isolated • Et>23 GeV • Double isolated • Et>12 GeV • Double non-isolated • Et>19 GeV • At startup thresholds lower • Total electron+photon Level-1 trigger rate ~ 4 kHz • Level-1 trigger efficiency for H→γγlarger than 99% • Perhaps could still optimize the threshold at which all Isolation L1 cuts are removed Marco Pieri

  10. HLT for Photons • H → γγ signal has two isolated photons • Dominant background from di-jets and γ+jet has at least one candidate from jet fragmentation that is not well isolated • We keep early conversions in the double stream • HLT trigger efficiency 88% - almost 100% for events selected in the analysis • Trigger is relatively easy for H→γγbecause of high Et photons • Total rate for photons after HLT ~5 Hz • Need to make some improvements, particularly for pre-scaled triggers, try to add the double from single L1 HTL paths (also for electrons?) PTDR HLT photon selectionNominal Low Lumi (2x1033 cm-2s-1) Marco Pieri

  11. Skim for H→γγ • I made a very simple skim selection last summer • For now very simple: • Double Photon HLT .OR. Single Photon HLT with an additional SC – to easily study trigger efficiency • Will hopefully keep it simple forever • Skimmed datasets not too large ~1-3 Hz for photons • RECO format planned to be used for now • PDPhoton Skim higgsTo2Gamma files are at UCSD now • We should run on them • No veto for electrons – Stream can also be useful to study electrons Marco Pieri

  12. ΔR Photon Isolation • Reducible backrounds (π0’s and mis-identified jets) have other particles near at least one photon candidate • We are in process of repeating and improving the study we carried out for the PTDR • Most of discriminating variables are built by summing up the Et or Pt of calorimeter deposits or tracks within a cone ΔR =  (Δη2+ Δφ2) • To study the performance of isolation variables we use individual photon candidates match or not within ΔR < 0.2 to a prompt generator level photon • Signal is: 120 GeV H→γγ gg-fusion reconstructed photon with Et>30 GeV matched with a generated photon within ΔR<0.2, background is: a super-cluster with Et>30 GeV NOT matched with a generated photon • Low statistics for now, cannot really look at correlations • Trigger (L1 and HLT) not included Marco Pieri

  13. Photon Isolation – Barrel – QCD pthat 80 – 120 GeV • Two possible views, first better for high purity, second better for high efficiency Trigger not included Marco Pieri

  14. Photon Isolation – Barrel – QCD pthat 50 – 80 GeV Trigger not included Marco Pieri

  15. Photon Isolation – Endcaps – QCD pthat 80 – 120 GeV Trigger not included Marco Pieri

  16. Photon Isolation – Endcaps – QCD pthat 50 – 80 GeV Trigger not included Marco Pieri

  17. Photon Isolation II • For low pthat, isolation much less effective • Should study it better – need more statistics at low pthat • Note that pre-selected QCD events below 50 GeV pthat not simulated • Run on Gumbo skims – already at UCSD • Some more checks must still be carried out • Study the correlation between isolation variables and specify benchmark selections for photons • For the PTDR analysis we used a Neural Network with 2, 3 or 5 of following inputs: • ΔR of the 1st track with Pt>1.5 GeV/c • Sum ECAL Et within ΔR<0.3 • The shower shape variable R9 • Sum HCAL Et within ΔR<0.35 • Sum tracks Et within ΔR<0.2 • We did not use kinematical information, easy to combine these variables with reconstructed mass and photons Et in an optimized H→γγ analysis • Repeat the study in the near future Marco Pieri

  18. Primary Vertex Determination • New longitudinal interaction spread σ~7.5 cm (was 5 cm) • Vertex estimated from the underlying event and recoiling jet • In PTDR analysis the efficiency of determining the right vertex was ~83% for H→γγ events after selection • Efficiency for the different types of background is similar and basically irrelevant • First check of usage of identified converted photons – very preliminary • Currently we have datasets with no pileup • Efficiency of reconstructing the right primary vertex ~98% on all generated H→γγ events • Must be compared with minimum bias events Marco Pieri

  19. Primary Vertex Determination II Use old z beam spot 100 pb-1 calibration CMSSW_1_6_7 CSA07 MC PTDR low luminosity Efficiency of determining the primary vertex within 5 mm from the true one PTDR analysis Marco Pieri

  20. Primary Vertex Determination III • Generator level plots for different track pt cuts are provided in the Extra slides Marco Pieri

  21. Primary Vertex From Photon Conversions • Selected converted photons: use only thosewith Mass <2 GeV, |z1-z2|<2cm • Choose Converted Photon with best e/p • H→γγ events passing PTDR selection CMSSW_1_6_7 CSA07 MC All reconstructed converted photons, 1 or 2 tracks Best e/p Selected reconstructed converted photons, with 2 tracks Best e/p Marco Pieri

  22. Primary Vertex Studies • Wider longitudinal beam spot will: • Worsen the Mass resolution for events with the wrong primary vertex or no vertex • Make easier the discrimination between different vertices using tracks from converted photons • Even with no pileup can already superimpose Higgs events and minimum bias events and carry out all studies • When we want to optimize primary vertex finding we can also use the direction of the total tracks transverse momentum that should be opposite to the Higgs pt Marco Pieri

  23. PTDR Selection for Cut-Based Inclusive Analysis • Photon selection: photon candidates are reconstructed using the hybrid clustering algorithm in the barrel and the island clustering algorithm in the endcaps • ET1, ET2 > 40, 35 GeV • |η|<2.5 • Both photon candidates should match L1 isolated triggers with ET > 12 GeV within ΔR < 0.5 • Track isolation • No tracks with pt>1.5 GeV present within ΔR<0.3 around the direction of the photon candidate • Calorimeter isolation • Sum of Et of the ECAL basic clusters within 0.06<ΔR<0.35 around the direction of the photon candidate <6 GeV in barrel, <3 GeV in endcaps • Sum of Et of the HCAL towers within ΔR<0.3 around the direction of the photon candidate<6 GeV(5 GeV) in barrel (endcaps) • If one of the candidate has |eta|>1.4442 the other has to satisfy also: Sum of Et of the ECAL<3, Sum of Et of the HCAL<6 GeV • L1 + HLT inefficiency negligible after selection Marco Pieri

  24. Higgs Mass Resolution • ECAL calibration for 100 pb-1 • Peak resolution all selected events σfit 1.45 GeV, σfit 1.75 GeV • Much worse than with ideal calibration, especially in endcaps Endcaps Barrel CMSSW_1_6_7 CSA07 MC R9>0.93 R9<0.93 Marco Pieri

  25. Higgs Photons Efficiency Plots • Top plots photon finding efficiency • Bottom plots photon isolation efficiency (PTDR cuts) Marco Pieri

  26. Higgs Mass – Primary Vertex Effect Barrel Endcaps R9>0.93 R9<0.93 Marco Pieri

  27. γ+jet Background • Plots are normalized to an integrated luminosity of 1 fb-1 and the signal is scaled by a factor 10 • BG seems similar to PTDR Endcaps Barrel Marco Pieri

  28. Fake Photons from Jets • We ran on very low BG statistics, did not yet estimate the two photon BG • Start studying the single photon efficiency and fake rate • Will compare between QCD and γ + jets • Should evaluate the needs in terms of BG rejection and consequently optimize isolation Marco Pieri

  29. QCD Fake Photon Rate – 1 pb-1 Fake Photon Rate Fake Photon Rate after isolation Trigger not included Marco Pieri

  30. Photon+jet Fake Photon Rate – 1 pb-1 Fake Photon Rate Fake Photon Rate after isolation ??? Should check Trigger not included Marco Pieri

  31. Fake Photon Isolation Efficiency Trigger not included Marco Pieri

  32. One Photon Rate – 1 pb-1 Trigger not included Marco Pieri

  33. ECAL Calibration and Photon Energy Scale • Crystal Intercalibration • Electrons from W→eνdecays will be used • Also π0 and/or η will be used • In CMSSW 2_0_0 there will only be SC corrections, no photon nor electron corrections anymore • Photon energy scale being studied from μμγ by Lyon, Florida State University and Kansas State University • μμγ events can also be used for efficiency studies Marco Pieri

  34. ECAL Calibration and Photon Energy Scale • Crystal Intercalibration • Electrons from W→eνdecays • Also π0 (and perhaps η) will be used • See for example presentation by V. Litvin at: http://indico.cern.ch/conferenceDisplay.py?confId=29156 • In CMSSW 2_0_0 there should only be new SC corrections, no photon nor electron corrections anymore unless it will be shown that they are needed • See for example presentation by Y. Maravin in: http://indico.cern.ch/conferenceDisplay.py?confId=27059 • Basically ready for Barrel, in progress for endcaps • Photon energy scale being studied from Z->μμγ (and Z->eeγ) • See for example talk by S. Gascon at: http://indico.cern.ch/conferenceDisplay.py?confId=27555 Marco Pieri

  35. Photon Conversions • Most of the work carried out by Nancy Marinelli and Notre Dame University • They are currently trying to choose the best candidate • Some changes Photon Objects in CMSSW 2_0_0 • In my opinion much more word needed in order to use them for photon identification Marco Pieri

  36. Converted Photons and π0 rejection • Recovery of early conversions currently removed by track isolation • Probably difficult Barrel Endcaps Marco Pieri

  37. π0 Rejection • Converted photons can also be used for π0 rejection • Start looking at the performance of the π0 rejection variables that are provided in CMSSW since version 1_6_7 • See for example presentation by A. Kyriakis in: http://indico.cern.ch/conferenceDisplay.py?confId=20797 • Start looking at the π0 rejection NN variables provided in CMSSW Marco Pieri

  38. Important points – Analysis Level • Simulation – Signal an Background • Real analysis on data and related channels • Optimization of the Analysis Marco Pieri

  39. Simulation • Background simulation • Generator level preselection for fake photons has been studied and used for CSA07 MC production • The Lyon group is working with DiPhox authors to have a full NLO irreducible BG simulation • Anyway, be ready to carry out the analysis using the BG from data, enough events from sidebands • Signal Simulation (common with other Higgs channels) • We should get NLO/NNLO calculations in order to exploit at best the signal topology: • HNNLO for gluon fusion, M. Grazzini et al. • VBFNLO for IVB fusion, D. Zeppenfeld et al. • Think about the requests for the next MC production with CMSSW Version 2 Marco Pieri

  40. Real analysis • Real analysis – take as much as possible from data • Efficiency from data (Z->ee , Z->eeγ, Z->μμγ) • Fake rate from data (important even if not crucial for H→γγ) • Use data (sidebands) to optimize the selection and to estimate the BG properties • Study of systematic errors • Only sources of tagged high Et photons • Z->μμγ • Z->eeγ • Related Analyses (to be studied since the beginning) • γ+jet (Fake rate needed) • γγ (Fake rate needed) Marco Pieri

  41. Z->μμγ • See for example talk by S. Gascon at: http://indico.cern.ch/conferenceDisplay.py?confId=27555 • Z + g, Zmm : A clean source of photons, • can determine, with real data: • Efficiency of photon triggers • Determination of photon energy scale • Determination of photon id efficiency • Determination of photon energy corrections ALPGEN Marco Pieri

  42. Z->eeγ • See presentation by Marat Gataullin at: http://indico.cern.ch/conferenceDisplay.py?confId=29791 Efficiency of the Photon ID cuts is 88%, but the background is almost gone, 96% purity in the window 85 GeV < M(eeγ) < 95 GeV. Total yield: 4.6K events per 1fb-1 Marco Pieri

  43. Optimized Analysis • Coherently exploit the different production modes (signatures 1l, 2l, MET, VBF) • See if possible avoid using MC background also for these • Add additional variables that were not used in the PTDR because of the poor description of the LO generators that were used • Carry out optimized multivariate/multicategorized analysis Marco Pieri

  44. Effect of Systematic Errors - PTDR Input for CL calculation is: • Background expectation from fit to the data (sidebands) • Signal expectation from MC Origin of systematic errors • Error on the BG estimation (statistical from fit of sidebands + uncertainty of the form of the fitted function) • Error on the signal (theoretical σxBR, integrated luminosity, detector + selection efficiency) Effect of systematic errors • Systematic errors on the signal do not change the expected discovery CL • Systematic error on the signal makes exclusion more difficult • Systematic error on the BG makes exclusion and discovery more difficult Marco Pieri

  45. Main Systematic Errors - PTDR SIGNAL • Theoretical error on cross section times BR (~15%) • Integrated luminosity (~5%) • Higgs Qt distribution – effect to be evaluated • Selection efficiency (~10%) • Can assume a total of 20% (anyway not important in case of discovery) • Nevertheless systematic errors on the signal may cause the analysis to be less optimized BACKGROUND • Statistical error on the fit of the sidebands (~0.3% for ~20 fb-1) • Systematic error on the shape of the fitted function (~0.3%) • No other errors when data available Marco Pieri

  46. Outlook • We started revising the H→γγ analysis framework so that it can also be used for all other analyses • We only ran over small samples for now • We can now run on larger samples • We are also trying to organize the CMS-wide effort in order not to be alone in the analysis as it was for the PTDR • Getting other groups to contribute to the H→γγ analysis NEXT STEPS • Continue the studies presented here • Include HLT (and re-optimize it) in our analysis • Need to re-optimize the basic selection for the cut-based analysis • Study more converted photons and π0 rejection to see if they can be used in the analysis • Get NLO/NNLO description of the signal and rescale Pythia – Also check ALPGEN, MC@NLO • Look at all issues of the real analysis on data • Look again at the optimization of the analysis Marco Pieri

  47. End of the talk End of the talk Marco Pieri

  48. EXTRA EXTRA Marco Pieri

  49. Barrel – pthat 80 – 120 GeV Trigger not included Marco Pieri

  50. Barrel – pthat 80 – 120 GeV Trigger not included Marco Pieri

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