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 11th 2008 Updated for March 18th aaaaa

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 11-Mar-08 Marco Pieri

H→ γγ Signal Gluon-gluon fusion WW and ZZ fusion (Weak Boson Fusion)
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 = GeV Very good mass resolution forward jets Photons from Higgs decay qqH → qqγγ MH = 120 GeV H → γγ MH = 115 GeV Jets from qq are at high rapidity and large Δη 11-Mar-08 Marco Pieri

Background to H→ γγ Handles for Irredicible BG – Kinematics
‘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 Process Pthat (GeV) Cross section (pb) Events/1 fb-1 pp→γγ (born) >25 82 82K pp→γγ (box) pp→ γ+jets >30 90x104 90M pp→jets 1x108 1x1011 Drell Yan ee - 4x103 4M 11-Mar-08 Marco Pieri

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) M=115 GeV M=120 GeV M=130 GeV M=140 GeV M=150 GeV σ (gg fusion)(pb) 39.2 36.4 31.6 27.7 24.5 σ (IVB fusion) (pb) 4.7 4.5 4.1 3.8 3.6 σ (HW, HZ, Hqq) (pb) 3.3 2.6 2.1 1.7 Total (pb) 47.6 44.2 38.3 33.6 29.7 BR (H→ γγ) 2.08x10-3 2.21x10-3 2.24x10-3 1.95x10-3 1.40x10-3 Inclusive σ x BR (fb) 99.3 97.5 86.0 65.5 41.5 pp→γγ (born) 1.5 pp→γγ (box) 1.2 pp→ γ+jets (2 prompt) 1.72 pp→γ+ jets (1 prompt+ 1 fake) 1 pp→jets 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

gen level cuts reduction factor
CSA07 MC Samples Requests at: 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 process pythia lev cuts gen level cuts gen sigma sim sigma gen level cuts reduction factor # of gen evts # of sim evts Int L (fb-1) gg->gamgam (box) pthat>25 GeV none 36 pb 1 1M ~28 qq->gamgam (born) 45 pb ~22 pp->gam +jet Special cuts (~sel B' in CMS IN 2005/018) 90 nb 0.6 nb ~150 300M 2M ~3.3 pp->jets pthat>50 GeV Special cuts (~sel C' CMS IN 2005/018) 24 ub 4.8 nb ~5000 50G 10M ~2.1 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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→ γγ larger than 99% Perhaps could still optimize the threshold at which all Isolation L1 cuts are removed 11-Mar-08 Marco Pieri

PTDR HLT photon selectionNominal Low Lumi (2x1033 cm-2s-1)
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→ γγ because 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) 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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 ΔR 11-Mar-08 Marco Pieri

Photon Isolation – Barrel – QCD pthat 80 – 120 GeV
Two possible views, first better for high purity, second better for high efficiency Trigger not included 11-Mar-08 Marco Pieri

Photon Isolation – Barrel – QCD pthat 50 – 80 GeV
Trigger not included 11-Mar-08 Marco Pieri

Photon Isolation – Endcaps – QCD pthat 80 – 120 GeV

Photon Isolation – Endcaps – QCD pthat 50 – 80 GeV

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 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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 Process Eff (%) H→γγ (gg fusion) 82 H→γγ (IVB fusion) 89 pp→γγ (born) 71 pp→γγ (box) 72 pp→γ+jet (2 prompt) 78 pp→γ+jet (1 prompt + 1fake) 86 pp→jets 90 11-Mar-08 Marco Pieri

Primary Vertex Determination III
Generator level plots for different track pt cuts are provided in the Extra slides 11-Mar-08 Marco Pieri

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 At least 1 convpho identified 1 or 2 tracks At least 1 selected Nearest convpho (or track) used (Cheat) All 51.1% 17.9% Vtx within 1 cm 20.1% 13.7% 24.3% Vtx within 2 mm 12.3% 8.7% 15.7% All reconstructed converted photons, 1 or 2 tracks Best e/p Selected reconstructed converted photons, with 2 tracks Best e/p 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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|> 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 11-Mar-08 Marco Pieri

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 Barrel Endcaps CMSSW_1_6_7 CSA07 MC R9>0.93 R9<0.93 11-Mar-08 Marco Pieri

Higgs Photons Efficiency Plots
Top plots photon finding efficiency Bottom plots photon isolation efficiency (PTDR cuts) 11-Mar-08 Marco Pieri

Higgs Mass – Primary Vertex Effect
Barrel Endcaps R9>0.93 R9<0.93 11-Mar-08 Marco Pieri

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 Barrel Endcaps 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

QCD Fake Photon Rate – 1 pb-1
Fake Photon Rate after isolation Trigger not included 11-Mar-08 Marco Pieri

Photon+jet Fake Photon Rate – 1 pb-1
Fake Photon Rate after isolation ??? Should check Trigger not included 11-Mar-08 Marco Pieri

Fake Photon Isolation Efficiency

One Photon Rate – 1 pb-1 Trigger not included 11-Mar-08 Marco Pieri

ECAL Calibration and Photon Energy Scale
Crystal Intercalibration Electrons from W→eν decays 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 11-Mar-08 Marco Pieri

ECAL Calibration and Photon Energy Scale
Crystal Intercalibration Electrons from W→eν decays Also π0 (and perhaps η) will be used See for example presentation by V. Litvin at: 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: 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: 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

Converted Photons and π0 rejection
Recovery of early conversions currently removed by track isolation Probably difficult Barrel Endcaps 11-Mar-08 Marco Pieri

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: Start looking at the π0 rejection NN variables provided in CMSSW 11-Mar-08 Marco Pieri

Important points – Analysis Level
Simulation – Signal an Background Real analysis on data and related channels Optimization of the Analysis 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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) 11-Mar-08 Marco Pieri

Z + g, Zmm : A clean source of photons,
See for example talk by S. Gascon at: 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 11-Mar-08 Marco Pieri

Z->eeγ See presentation by Marat Gataullin at:
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 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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 11-Mar-08 Marco Pieri

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, Look at all issues of the real analysis on data Look again at the optimization of the analysis 11-Mar-08 Marco Pieri

End of the talk End of the talk 11-Mar-08 Marco Pieri

EXTRA EXTRA 11-Mar-08 Marco Pieri

Barrel – pthat 80 – 120 GeV Trigger not included 11-Mar-08 Marco Pieri

Track Isolation Barrel

Track Isolation Endcaps

Ecal Isolation Barrel Trigger not included 11-Mar-08 Marco Pieri

Ecal Isolation Endcaps

Hcal Isolation Barrel Trigger not included 11-Mar-08 Marco Pieri

Hcal Isolation Endcaps

Generator Level, charged pt>1.5 GeV |eta|<2.5
11-Mar-08 Marco Pieri

Generator Level, charged pt>0.3 GeV |eta|<2.5
11-Mar-08 Marco Pieri

Just to remember – IVB fusion
Sasha Nikitenko: 11-Mar-08 Marco Pieri

Status and Prospects of the H→γγ Analysis

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Status and Prospects of the H→γγ Analysis

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