H γγ. Sean Simon UC San Diego (on behalf of the H γγ WG) Photon Workshop July 23 rd 2008

Transcription

1 H γγ Sean Simon UC San Diego (on behalf of the H γγ WG) Photon Workshop July 23 rd 2008 Contributing and interested groups Caltech, Lyon, Notre Dame, Rome, Saclay, UC Riverside, UCSD

2 Signal and Background in H γγ SIGNAL 2 Isolated, High E T photons Gluon fusion Vector Boson fusion Associated Production with Z,W,tt BR(H γγ) ~.002 Process (M H =120) σxbr (fb) gg H 80 VV H 10 pp ZWttH 7 BACKGROUND irreducible backgrounds gg γγ (box diagram) qq γγ (born diagram) pp γ+jets (2 prompt γ) reducible backgrounds pp γ+jets (1 fake γ) pp jets (1 or 2 fake γ) pp ee (Drell Yan) when electrons are misidentified as photons Process pp γγ (born) pp γγ (box) pp γ+jets pp jets Drell Yan ee P that (GeV) >25 >25 >25 >50 - σ (pb) x x10 6 4x10 3 Events/1 fb -1 68K 43K 90M 24x10 9 4M Handles for Irreducible BG Kinematics Handles for Reducible BG Isolation, shower shape, conversions 23-Jul-08 Sean Simon 2

3 Analysis Steps Reconstruction Level Trigger and Skims L1 Trigger HLT Di-photon Skim Photon isolation Primary Vertex estimation Energy Measurement Photon conversion identification and π 0 rejection To carry out the analysis the different groups are still using standalone root trees written by a CMSSW analyzer 23-Jul-08 Sean Simon 3

4 Level-1 Trigger L1 electromagnetic trigger towers are classified into two categories depending on the energy deposition in the calorimeter trigger towers: non-isolated, isolated. Level-1 trigger efficiency for H γγ almost 100% for reasonable thresholds Isolated EM triggers not important for H γγ L1 Et Thresholds Physics TDR Lumi 2x10 33 cm -2 s -1 Startup Lumi 2x10 30 cm -2 s -1 Startup Lumi 2x10 31 cm -2 s -1 Lumi 2x10 32 cm 2 s -1 Single isolated 23 GeV 5-25 GeV 8-25 GeV 12 GeV Single non isolated GeV 8-25 GeV 15 GeV Double isolated 12 GeV 8-10 GeV 8-10 GeV 8 GeV Double non isolated 19 GeV 5-15 GeV 5-15 GeV 10 GeV 23-Jul-08 Sean Simon 4

5 HLT for Photons H γγ signal has two isolated photons Dominant background from di-jets and γ+jet has at least one fake photon candidate that is not well isolated PTDR HLT photon selection Nominal Low Lumi (2x10 33 cm -2 s -1 ) We keep early conversions in the double stream HLT trigger efficiency almost 100% for events selected in the analysis Trigger is relatively easy for H γγ because of high E t photons PTDR Ecal isolation may be too tight Total rate for photons after HLT ~5 Hz 23-Jul-08 Sean Simon 5

6 HLT for Photons As they are, the single photon paths have an E T cut that is too tight for H γγ (80GeV, rate limited) Try to add the double photon HLT path seeded from single L1 (look for second high-e T SC in events passing single L1 trigger) Should be possible without increasing the timing much Easier to study double trigger efficiency More robust in case some trigger towers are noisy or malfunctioning Also introduce the possibility of having different isolation for the two photons (one tight and one loose) 23-Jul-08 Sean Simon 6

7 Skim for H γγ A very simple Two-photon skim selection was developed last summer Want to keep it very simple: Double.OR. Single Photon HLT with an additional high Et SC (currently > 15 GeV) Possible single photon stream May use another one or we could make one ourselves May want prescaled single photon with same E T threshold as double Currently using RECO format for photon conversion and pizero ID studies 23-Jul-08 Sean Simon 7

8 SPLIT INTO 2 SLIDES Selection & Isolation for Cut-Based Analysis Photon selection: photon candidates are reconstructed using the hybrid clustering algorithm in the barrel and the island clustering algorithm in the endcaps E T1, E T2 > 40, 35 GeV η <2.5 Track isolation (same as PTDR) No tracks with p t>1.5 GeV present within ΔR<0.3 around the direction of the photon candidate Calorimeter isolation (same as PTDR) 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 either candidate is in the endcap, both are required to satisfy the tighter encap isolation thresholds Working to improve isolation May introduce different requirements for the 2 photons Still need tracker,ecal, and Hcal isolation variables Maybe with different cone sizes,. No Pileup After Selection+Isolation Efficiency Events/fb -1 Signal 33.6% 31.6 Comparable to PTDR BG AS WELL 23-Jul-08 Sean Simon 8

9 PLOTS OF 1 st and 2 nd photons AFTER ISOLATION Lead and sublead photon P T spectra after selection and isolation E T1 >40GeV && E T2 >35GeV Both Photons Pass Isolation Scaled to 1 fb -1 Signals are scaled by Jul-08 Sean Simon 9

10 Current Results for Cut-Based Analysis Photon Categories: Improve sensitivity by splitting events into categories having different s/b ratios 3 Categories in R9 x 4 Categories in η (same as PTDR) Large sidebands will allow us to estimate the BG precisely Signal x 10 Integrated luminosity for discovery/exclusion Analysis M H =120 GeV 1 category 12 categories 5σ discovery 32 fb fb -1 3σ evidence 12 fb -1 9 fb -1 95% exclusion 3.6 fb fb -1 Systematic errors not included No Pileup Still working on the optimized analysis Worse than PTDR due to worse mass resolution from miscalibration Sensitivity of the H γγ channel to new physics could increase the signal by a factor of 10, giving results within 1 fb -1 (Manohar-Wise hep-ph/ ) 23-Jul-08 Sean Simon 10

11 Photon Conversions and Pizero ID Photon conversion reconstruction provided in CMSSW by N. Marinelli (see also talk by her) Pizero rejection from Aris Kyriakis et al. for converted and unconverted case Lyon group while reproducing PTDR results with CSA07 data has shown a first indication of small improvement in the analysis using the pi-zero id NN Links to presentations by zhang 23-Jul-08 Sean Simon 11

12 What we expect from 2008 data taking Mainly look at the properties of BG Fake rate from data (important even if not crucial for H γγ) Using sidebands, separation of reducible/irreducible BGs in not important Study signal efficiency with data Efficiency very important to be measured from data Must use (Z->ee, Z->eeγ, Z->µµγ) Standard tools to be put in place Real analysis take as much as possible from data Exercise usage data (sidebands) to optimize the selection and to estimate the BG properties Related Analyses (to be studied from the beginning) γ+jet (Fake rate needed) γγ (Fake rate needed) 23-Jul-08 Sean Simon 12

13 Z->µµγ See for example talk by S. Gascon at: ALPGEN Not very many events, must also study photon efficiency with Z-> ee events 23-Jul-08 Sean Simon 13

14 Primary Vertex Determination In PTDR vertex was estimated from the underlying event and recoiling jet and the efficiency of determining the right vertex was ~83% for H γγ events after selection Currently we only have datasets with no pileup Efficiency of reconstructing the right primary vertex ~99% on H γγ events Need pileup to study it again 100 pb -1 calibration CMSSW_1_6_7 CSA07 MC 23-Jul-08 Sean Simon 14

15 Primary Vertex From Photon Conversions Selected converted photons: Choose Converted Photon with best e/p H γγ events passing PTDR selection At least 1 convpho identified 1 or 2 tracks At least 1 selected convpho identified All 51.1% 17.9% Vtx within 1 cm 20.1% 13.7% 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 23-Jul-08 Sean Simon 15

16 PAT and Needs for Photons Different people are working on the Photon PAT analysis (See Yuri Gershtein s presentation). For Photon candidates we would like to get: R9 Isolation variables (most likely to be optimized at the last step of analysis) Energy scale checked It would be good to have the error on the energy measurement Photon conversion information Pizero Id variables For Vertices from tracks from converted photons Combined (should think of how best to combine) We will soon implement preselection, vertex finding, and final selection in PAT 23-Jul-08 Sean Simon 16

17 Summary and Outlook Results somewhat worse than PTDR from reduced mass resolution from 100pb -1 calibration scenario Improve HLT for Higgs to gammagamma Potential sensitivity of H γγ could yield results within 1fb mainly Study BG and optimize tools Get tools into PAT format What Do we need MC - Pileup is important, we should look at it as soon as possible More precise simulation of backgrounds Not clear when we will have sufficiently large BG samples (unless we only use fast simulation - no conv yet) Until then, would like that the 1_6_7 CSA07 data remain available 23-Jul-08 Sean Simon 17

18 End of the talk End of the talk 23-Jul-08 Sean Simon 18

19 Higgs Mass Resolution ECAL calibration for 100 pb -1 Peak resolution all selected events σ fit 1.45 GeV, σ fit 1.75 GeV Much worse than with ideal calibration, especially in endcaps Barrel Endcap s CMSSW_1_6_7 CSA07 MC R9>0.93 R9< Jul-08 Sean Simon 19

20 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 23-Jul-08 Sean Simon 20

21 NEW EXTRA NEW EXTRA 23-Jul-08 Sean Simon 21

22 Introduction Different people/groups are contributing or interested: Caltech, Lyon, Notre Dame, Rome, Saclay, UC Riverside, UCSD For 2008 not much to be expected in H γγ channel for SM Higgs Anyway we should carry out the analysis as well as possible Also look at related analyses: SM γ+jet, γγ, Z->μμγ, Z->eeγ Photon reconstruction (15') Nancy Marinelli (Univ. of Notre Dame) Photon triggers (15') Alessio Ghezzi (Univ. + INFN) Status of Photon ID (15') Yuri Gershtein (Florida State University) EWK : W, Z +photons (15') Chia-Ming Kuo (NCU, Taiwan) EXOTICA: channels with photons (20') Higgs to gamma gamma (15') 23-Jul-08 Sean Simon 22

23 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 Process P that (GeV) Cross section (pb) Events/1 fb -1 pp γγ (born) > K pp γγ (box) > K pp γ+jets >30 90x M pp jets >25 1x10 8 1x10 11 Drell Yan ee - 4x10 3 4M Handles for Irredicible BG Kinematics Handles for Reducible BG Until now only Isolation Should add photon identification (converted) and π 0 rejection 23-Jul-08 Sean Simon 23

24 Photon Isolation Reducible backrounds (π 0 s and mis-identified jets) have other particles near at least one photon candidate We are in process of repeating and improving the study that was carried out for the PTDR Some plots are shown in the extra slides For low p that, isolation much less effective, needs further studies Note that pre-selected QCD events below 50 GeV p that have not been simulated Study the correlation between isolation variables and specify benchmark selections for photons For the PTDR analysis we also used a Neural Network for isolation No use of kinematical information, easy to combine these variables with reconstructed mass and photons E t in an optimized analysis Also repeat this study in the near future 23-Jul-08 Sean Simon 24

25 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 E T1, E T2 > 40, 35 GeV η <2.5 Both photon candidates should match L1 isolated triggers with E T > 12 GeV within ΔR < 0.5 Track isolation No tracks with p t >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 23-Jul-08 Sean Simon 25

26 Higgs M H =120 GeV PTDR Selection for cut based analysis applied now We will soon improve the photon selection Results are in basic agreement with PTDR Still no pileup, efficiency will be somewhat lower Again may provide a first estimate adding minimum bias events Efficiency Nevts/100 pb-1 Gluon-fusion IVB fusion WH, ZH, tth Total 33.7% 31.9% 24.3% 30.0% BG rate, still to be evaluated 23-Jul-08 Sean Simon 26

27 ECAL Calibration and Photon Energy Scale Crystal Intercalibration Electrons from W eν decays Also π 0 (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 See for example talk by S. Gascon at: 23-Jul-08 Sean Simon 27

28 Photon Conversion Reconstruction Photon conversion reconstruction provided in CMSSW by N. Marinelli Studies of converted photons in progress Exploring methods to remove ambiguities See for example the talk by T. Kolberg at: Likelihood built with The following variables: 23-Jul-08 Sean Simon 28

29 Converted Photons and π 0 rejection Recovery of early conversions currently removed by track isolation Probably difficult Barrel Endcap s Converted photons can also be used for π 0 rejection Start looking at the performance of the π 0 rejection variables that are provided in CMSSW since version 1_6_7 See for example presentation by A. Kyriakis in: 23-Jul-08 Sean Simon 29

30 Primary Vertex Determination Vertex was 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 Currently we have datasets with no pileup Efficiency of reconstructing the right primary vertex ~99% on H γγ events We can compare the Primary vertex variables with those in minimum bias events Check of usage of identified converted photons very preliminary 23-Jul-08 Sean Simon 30

31 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 Process H γγ (gg fusion) H γγ (IVB fusion) pp γγ (born) pp γγ (box) pp γ+jet (2 prompt) pp γ+jet (1 prompt + 1fake) pp jets Eff (%) PTDR analysis 23-Jul-08 Sean Simon 31

32 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 convpho identified Nearest convpho (or track) used (Cheat) All 51.1% 17.9% 51.1% 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 23-Jul-08 Sean Simon 32

33 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 p t 23-Jul-08 Sean Simon 33

34 Important points Analysis Level Simulation Signal an Background Real analysis on data and related channels Optimization of the Analysis 23-Jul-08 Sean Simon 34

35 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 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 23-Jul-08 Sean Simon 35

36 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 23-Jul-08 Sean Simon 36

37 Outlook CSA07 MC basically available now (it took a lot of time) Organizing the work between the different groups Study and re-optimize HLT Study and re-optimize Isolation Study and re-optimize the primary vertex finding (adding conversions) Re-optimize the basic selection for the cut-based analysis Study converted photons and π 0 rejection tools and integrate them in the analysis Get NLO/NNLO description of the signal and NLO description of the irreducible backgrounds Look at all issues of the real analysis on data Fake rate Trigger efficiency from data Photon id efficiency from data Look again at the optimization of the analysis possibly including more kinematic variables such as P thiggs Contribute to other photon analyses SM γ+jet and γγ 23-Jul-08 Sean Simon 37

38 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 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 36 pb 1 1M 1M ~28 qq->gamgam (born) pthat>25 GeV none 45 pb 45 pb 1 1M 1M ~22 pp->gam +jet pthat>25 GeV Special cuts (~sel B' in CMS IN 2005/018) 90 nb 0.6 nb ~ M 2M ~3.3 pp->jets pthat>50 GeV Special cuts (~sel C' CMS IN 2005/018) 24 ub 4.8 nb ~ G 10M ~2.1 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 23-Jul-08 Sean Simon 38

39 ORIGINAL EXTRA ORIGINAL EXTRA 23-Jul-08 Sean Simon 39

40 H γγ Signal SIGNAL: two isolated photons with large E t Gluon-gluon fusion WW and ZZ fusion (Weak Boson Fusion) WH, ZH, tth (additional leptons and MET) Total σ x BR ~95 fb for M H = GeV Very good mass resolution Photons from Higgs decay qqh qqγγ MH = 120 GeV H γγ M H = 115 GeV Jets from qq are at high rapidity and large Δη forward jets 23-Jul-08 Sean Simon 40

41 Cross section and K-factors Signal cross sections and BR used for the PTDR (NLO M. Spira) M=115 GeV M=120 GeV M=130 GeV M=140 GeV M=150 GeV σ (gg fusion)(pb) σ (IVB fusion) (pb) σ (HW, HZ, Hqq) (pb) Total (pb) BR (H γγ) 2.08x x x x x10-3 Inclusive σ x BR (fb) K-factors for the background used for the PTDR (to be re-evaluated if needed) pp γγ (born) pp γγ (box) pp γ+jets (2 prompt) pp γ+ jets (1 prompt+ 1 fake) pp jets Jul-08 Sean Simon 41

42 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 if needed and precise BG estimation 23-Jul-08 Sean Simon 42

43 Photon Isolation Reducible backrounds (π 0 s and mis-identified jets) have other particles near at least one photon candidate We are in process of repeating and improving the study that was carried out for the PTDR Most of discriminating variables are built by summing up the E t or P t of calorimeter deposits or tracks within a cone ΔR ΔR = (Δη 2 + Δφ 2 ) To study the performance of isolation variables we use individual photon candidates matched or not to a prompt generator level photon In the next plots signal is: 120 GeV H γγ gg-fusion reconstructed photon with E t >30 GeV matched with a generated photon within ΔR<0.2, background is: a super-cluster with E t >30 GeV NOT matched with a generated photon Low statistics in these plots, cannot really look at correlations Trigger (L1 and HLT) not included 23-Jul-08 Sean Simon 43

44 Photon Isolation Barrel QCD p that GeV Two possible views, first better for high purity, second better for high efficiency Trigger not included CMSSW_1_6_7 CSA07 MC 23-Jul-08 Sean Simon 44

45 Photon Isolation Endcaps QCD p that GeV Trigger not included CMSSW_1_6_7 CSA07 MC 23-Jul-08 Sean Simon 45

46 Photon Isolation Barrel QCD pthat GeV Trigger not included 23-Jul-08 Sean Simon 46

47 Photon Isolation Endcaps QCD p that GeV Trigger not included 23-Jul-08 Sean Simon 47

48 Primary Vertex Determination III CMSSW_1_6_7 CSA07 MC 23-Jul-08 Sean Simon 48

49 Higgs Photons Efficiency Plots Top plots photon finding efficiency Bottom plots photon isolation efficiency (PTDR cuts) 23-Jul-08 Sean Simon 49