1. Lighting up the Higgs sector with photons at CDF Fermilab Joint Experimental-Theoretical Seminar Karen Bland for the CDF collaboration May 20, 2011 1

2. Tevatron and CDF Performance Thanks to accelerator division for delivering luminosity! And CDF for keeping the detector running well! Delivered luminosity ~11.0 fb -1 !! CDF acquired luminosity: ~9.2 fb -1 Using 7.0fb -1 for results shown here 2 7.0 fb -1

3. Outline 3 Introduction Photon ID and Efficiency SM H  γγ Search Fermiophobic h  γγ Search Summary and Conclusions

4. Outline 4 Introduction – Theoretical Overview – Motivation Photon ID and Efficiency SM H  γγ Search Fermiophobic h  γγ Search Summary and Conclusions

5. The Standard Model Higgs boson is only SM particle that hasn’t been observed! Through the Higgs mechanism: (1) Electroweak symmetry is broken (2) Other SM particles acquire mass But mass of Higgs boson a free parameter… Has to be determined experimentally if exists What we know so far: Tevatron exclusion regions mostly based on search channels other than H  γγ H  γγ plays a role in the low mass region… Which is the favored Higgs mass region from electroweak constraints 5 Tevatron exclusion also reaching LEP limit at low mass  H  γγ contributes sensitivity here

6. The Standard Model Higgs boson is only SM particle that hasn’t been observed! Through the Higgs mechanism: (1) Electroweak symmetry is broken (2) Other SM particles acquire mass But mass of Higgs boson a free parameter… Has to be determined experimentally if exists What we know so far: 6 Tevatron exclusion also reaching LEP limit at low mass  There is a lot of work being done still at the Tevatron experiments to extend this exclusion region, so stay tuned! A new combination will come out this summer

7. SM Higgs Production at the Tevatron Gluon Fusion Associated Production Vector Boson Fusion 7Introduction: Theoretical Overview gg  H is largest cross section Excluded from channels where Higgs decays to quarks due to multijet backgrounds (like H  bb) gg  H is largest cross section Excluded from channels where Higgs decays to quarks due to multijet backgrounds (like H  bb)

8. SM Higgs Production at the Tevatron Gluon Fusion ~ 1000 fb @ 120 GeV Associated Production ~ 225 fb @ 120 GeV Vector Boson Fusion ~ 70 fb @ 120 GeV 8 Produced only rarely: ◦ One out of every 10 12 collisions ◦ That’s about 2 Higgs bosons produced each week gg  H is largest cross section Excluded from channels where Higgs decays to quarks due to multijet backgrounds (like H  bb) H  γγ gains by using all three production methods (~1300 fb) gg  H is largest cross section Excluded from channels where Higgs decays to quarks due to multijet backgrounds (like H  bb) H  γγ gains by using all three production methods (~1300 fb) Introduction: Theoretical Overview

9. SM H  γγ Decay Dominant low mass decay mode is H  bb 9 H  γγ Br < 0.25% Signal expectation @ 120 GeV: N = σ × L × Br = 1300fb × 7.0fb -1 × 0.002 ~ 18 H  γγ events produced (~ 6 reconstructed) Introduction: Theoretical Overview

10. No SM H  γγ observation expected at the Tevatron! However, contributes sensitivity to Tevatron search in difficult region ~125 GeV Even has sensitivity comparable to ZH  llbb ~140 – 150 GeV: – Br(H  bb) falls steeply for m H > 140 GeV – Br(H  γγ) relatively flat – Translates to relatively flat sensitivity compared to other channels Introduction: Motivation10 Many beyond SM scenarios include a larger Br(H  γγ) New results for one such scenario shown later in the talk Is a H  γγ search interesting at the Tevatron?

11. Clean signature compared to H  bb – Photons (or electrons from photon conversions) easier to identify/reconstruct than b-jets – Larger fraction of H  γγ events accepted in comparison – Total acceptance: ~35% accepted for gg  H ~30% accepted for VH and VBF – Largest efficiency losses from fiducial requirements and ID efficiency – Also improves reconstructed mass resolution… 11Introduction: Motivation Is a H  γγ search interesting at the Tevatron?

12. Great mass resolution: – Mass resolution limited only by electromagnetic (EM) calorimeter – 1σ width ~3 GeV or less (M jj width is ~16 GeV) – Resolution ~5x better than best jet algorithms for H  bb – Great background discrimination using M γγ alone – Search for narrow resonance – Sideband fits can be used to estimate background 12Introduction: Motivation Is a H  γγ search interesting at the Tevatron?

13. Outline 13 Introduction Photon ID and Efficiency – Introduction – Central Photons – Forward Photons – Conversion Photons SM H  γγ Search Fermiophobic h  γγ Search Summary and Conclusions

14. pp Silicon Vertex Detector Central Tracker Muon Chambers Electromagnetic Calorimeter CDF Detector Solenoid Hadronic Calorimeter Photon ID and Efficiency - Introduction

15. Photon Identification “Central” – |η|<1.1 “Plug” – 1.2<|η|<2.8 – Tracking efficiency lower than in central region – Easier to miss a track and reconstruct fake object as a photon – Higher backgrounds then for plug photons 15 Central Plug Cross sectional view of one detector quadrant Photon ID and Efficiency - Introduction

16. Photon Identification Basic Photon Signature: – Compact EM cluster – Isolated – No high momentum track associated with cluster – Profile (lateral shower shape) consistent with that of a prompt photon Unlike that of π 0 /η  γγ decays (the largest background for prompt photons) Hard to do this with calorimeters alone 16 Inside jets Background Signal Photon ID and Efficiency - Introduction

17. Photon Identification ΕΜ calorimeter segmentation: – Δη×Δ ϕ ~ 0.1×15° (|η|<1) – Not fine enough to fully reject π 0 /η jets 17 Hadronic Calorimeter Electromagnetic Calorimeter Shower maximum detector Signal Background Shower max detector – ~6 radiation lengths into EM calorimeter – Finely segmented – Gives resolution to better reject π 0 /η  γγ – Αlso refines EM cluster position measurement to better match associated tracks Photon ID and Efficiency - Introduction

18. Central Photon Identification Three level selection (1) Loose requirements – Fiducial in shower max detector – Ratio of hadronic to electromagnetic transverse energy (Had/EM) < 12.5% – Calorimeter isolation. Cut slides with – Track isolation < 5 GeV (2) Track veto – Number tracks ≤ 1 – If 1, then p T trk1 < 1 GeV (3) Cut on NN Output – More details on next slides 18Photon ID and Efficiency – Central Photons

19. Central Electron Identification Three level selection (1) Loose requirements – Fiducial in shower max detector – Ratio of hadronic to electromagnetic transverse energy (Had/EM) < 12.5% – Calorimeter isolation. Cut slides with – Track isolation – p T trk1 < 5 GeV 19Photon ID and Efficiency – Central Photons (2) Track veto – Number tracks ≤ 2 – If 2, then p T trk2 < 1 GeV (3) Cut on NN Output – More details on next slides No pure high statistics data sample of photons to validate ID efficiency Selection chosen so can be modified for electrons Then use Z  e + e – decays (more detail later)

20. 98% signal efficiency (8% better than standard ID cuts) 87% background rejection (23% better than standard ID cuts) Central Photon Identification NN discriminant constructed from seven well understood variables: – Ratio of hadronic to EM transverse energy – Shape in shower max compared to expectation – Calorimeter Isolation – Track isolation – Ratio of energy at shower max to total EM energy – Lateral sharing of energy between towers compared to expectation 20 s/sqrt(b) for H  γγ vs NN cut gives optimum cut of 0.74 Trained using inclusive photon MC and jet MC (with ISR photons removed and energy reweighting)

21. ID efficiency checked in data and MC from Z  e + e – decays Z mass constraint applied to get a pure sample of electrons to probe Effect of pile-up seen through N vtx dependence Net efficiencies obtained by folding ε vtx into N vtx distribution of diphoton data and signal MC (a weighted average) Central Photon ID Efficiency Net photon ID efficiency: Data: 83.2% MC: 87.8% MC scale factor of 94.8% applied Total systematic uncertainty of 2% applied from: – Differences between electron vs photon response (checked in MC) – Data taking period dependence – Fits made to Z mass distribution Small uncertainties using this method! 21Photon ID and Efficiency – Central Photons

22. Plug Photon ID and Efficiency Standard CDF Cut-Based ID Fiducial in shower max detector Ratio of hadronic to EM transverse energy * < 5% Calorimeter isolation * < 2 GeV Track isolation * < 2 GeV Shape in shower max compared to expectation Same Efficiency Technique as for Central Photons 22 Net photon ID efficiency: – Data: 73.2% – MC: 80.6% MC scale factor of 90.7% applied Total systematic uncertainty of 4.5% * Slides with EM energy or E T Photon ID and Efficiency – Foward Photons

23. Photon Conversions γ  e + e – Colinear tracks moving in approximately same direction Occurs in presence of detector material More material, higher the probability of converting 23 COT inner cylinder port cards, cables ISL outer screen L7 L6 L00, L0-L4

24. Photon Conversions Conversion probability at CMS substantially higher * … ~70% of H  γγ events have at least one photon that converts!! Similarly for ATLAS Much more important at LHC experiments! * J. Nysten, Nuclear Instruments and Methods in Physics Research A 534 (2004) 194-198 Photon ID and Efficiency – Conversion Photons24 Use central only Then for two photons, % of events lost from a single central photon converting is: – 26% for CC channel – 15% for CP channel CDF had only one Run I measurement using converted photons: γ cross section  PRD,70, 074008 (2004) H  γγ is the first Run II CDF photon analysis using conversions p ≈ 15% for central γ

25. Conversion ID 25 r- ϕ separation (cm) cotθ = p z /p T cut ~94% efficient cut ~95% efficient Δcotθ Photon ID and Efficiency – Conversion Photons Example trident

26. Outline 26 Introduction Photon ID and Efficiency SM H  γγ Search – Event Selection – Background Modeling – Results – Tevatron Combination Fermiophobic h  γγ Search Summary and Conclusions

27. Event Selection Inclusive photon trigger – Single photon E T > 25 GeV – Trigger efficiency after offline selection obtained from trigger simulation assuming z vtx = 0 and trigger tower clustering Use photon ID as previously described Photon p T > 15 GeV Four orthogonal diphoton categories: – Central-central photons (CC) – Central-plug photons (CP) – Central-central conversion photons (CC conv) where one converts – Central-plug conversion photons (CP conv) where central converts SM H  γγ Search27

28. Signal Shapes Widths ~3 GeV (or less) for each channel Use 2σ width to determine signal window  12 GeV Shapes used to fit for signal in the data when setting limits 28

29. Systematic Uncertainties on H  γγ Signal 29

30. Primary Background Composition Regular Photon Backgrounds – Real SM photons via QCD interactions – Jets faking a photon (mostly from π 0 /η  γγ) – Misidentified electrons such as in Drell-Yan Z/γ *  e + e – Conversion backgrounds – Real SM photons converting – Photons from π 0 /η jets converting – Combinatorics – Prompt conversions from Dalitz decays π 0  e + e – γ at small radius 30

31. Data-Driven Background Model Assume a null hypothesis Fit made to sideband regions of M γγ distribution We use a 6 parameter polynomial times exponential to model smooth portion of the data Fit is then interpolated into the 12 GeV signal region Example shown here for a test mass at 115 GeV for CC channel 31

32. Data-Driven Background Model CP and CP conversion channels also contaminated by Z background Breit-Wigner function added to smooth distribution to model this, where mean and width are bounded in fit Example shown here for a test mass at 115 GeV for CP channel 32

33. Background Model Windowed fit shown to indicate Higgs mass region being tested Interpolated fit used to obtain data-fit residuals Used to inspect for signs of a resonance for each mass and channel No significant resonance observed so will set limits on σ×Br(H  γγ) 33 CC Channel CC Conversion Channel

34. 34 CP Channel CP Conversion Channel Background Model Windowed fit shown to indicate Higgs mass region being tested Interpolated fit used to obtain data-fit residuals Used to inspect for signs of a resonance for each mass and channel No significant resonance observed so will set limits on σ×Br(H  γγ)

35. Background Rate Uncertainty Parameters of fit function varied within uncertainties to obtain a new test fit Integral in 12 GeV signal region calculated for test fit Repeated millions of times Largest upper and lower differences from standard fit stored Then symmetrized to obtain rate uncertainty for each test mass and channel 35 Model dependence checked by testing alternate fit functions Variation in normalization as compared to standard found to be within uncertainties already obtained Approximate Systematic Errors on Background (%) CC4 CP1 CC Conv8 CP Conv4

36. Mass Distributions 36

37. 12 GeV/c 2 signal region for each test mass used to set upper limits set on σ×Br relative to SM prediction Expected limit of 13.0xSM @ 120 GeV An improvement of ~33% on last result! Observed limit outside 2σ band @ 120 GeV, but reduced to < 2σ after trial factor taken into account 37 Will be added to SM Higgs Tevatron combination this summer New Limits on H  γγ at CDF using 7.0/fb

38. DØ’s SM H→γγ Search Uses a boosted decision tree as final H  γγ discriminant Βased on five kinematic inputs: M γγ, p T γγ, E T 1, E T 2, Δφ γγ Example output shown for mass of 120 GeV From March 2011 Using 8.2fb -1 Observed @ 120: 12.4xSM Expected @ 120: 11.3xSM 38

39. Observed @ 120: 16.9xSM Expected @ 120: 9.1xSM Combination significantly extends the sensitivity of the separate CDF/DØ results This is deepest existing investigation into this channel – a channel that’s very different from H  bb 39 Reaching within one order of magnitude of SM prediction… for an analysis that wasn’t expected to happen at the Tevatron! Tevatron SM H  γγ Combination

40. Tevatron vs LHC Due to higher jet backgrounds, the LHC is betting on the H  γγ channel rather than H  bb for a low mass Higgs discovery… But how are LHC experiments currently doing compared to the Tevatron? CMS has no public results yet, so we can look at ATLAS 40

41. ATLAS SM H  γγ First preliminary result uses 38pb -1 95% upper C.L. limits @ ~25xSM 41

42. ATLAS SM H  γγ Here with 94pb -1 from 2011 only Here with 131pb -1 from both 2010 and 2011 42 Atlas expecting to be near ~4 times SM prediction with 1 fb -1

43. Outline 43 Introduction Photon ID and Efficiency SM H  γγ Search Fermiophobic h  γγ Search – Theory Motivation – Differences in search from SM – Results Summary and Conclusions

44. Fermiophobic Higgs (h f ) It’s likely nature doesn’t follow the SM Higgs mechanism… We also consider a “benchmark” fermiophobic model A two-Higgs doublet model extension to the SM Spontaneous symmetry breaking mechanism different for fermions and bosons  5 Higges We search for one in which: – No Higgs coupling to fermions – SM Higgs coupling to bosons – SM production cross sections assumed Introduction44

45. Gluon Fusion ~ 1000 fb @ 120 GeV Fermiophobic Higgs (h f ) Production Introduction45 Associated Production ~ 225 fb @ 120 GeV Vector Boson Fusion ~ 70 fb @ 120 GeV No gg  h f σ ~ 300 fb @ 120 GeV

46. Fermiophobic Higgs (h f ) Decay 46Introduction Suppressed by m 2 b /m 2 W h  bb no longer dominant Dominant low mass decay mode is now h  γγ Signal expectation @ 120 GeV: N = σ × L × Br = 300fb × 7.0fb -1 × 0.03 ~63 (22) h f  γγ events produced (reconstructed) ~4x higher than SM expectation Br ~ 13x (120x) higher than SM @ 120 GeV (100 GeV)

47. Fermiophobic Higgs (h f ) Decay 47Introduction h  bb no longer dominant Dominant low mass decay mode is h  γγ Signal expectation @ 100 GeV: N = σ × L × Br = 560fb × 7.0fb -1 × 0.18 ~700 (245) h f  γγ events produced (reconstructed) ~30x higher than SM expectation Br ~ 13x (120x) higher than SM @ 120 GeV (100 GeV) Suppressed by m 2 b /m 2 W

48. Event Selection Inclusive photon trigger – Single photon E T > 25 GeV – Trigger efficiency after offline selection obtained from trigger simulation assuming z vtx = 0 and trigger tower clustering Use photon ID as previously described Photon p T > 15 GeV Four orthogonal diphoton categories: – Central-central photons (CC) – Central-plug photons (CP) – Central-central conversion photons (CC conv) where one converts – Central-plug conversion photons (CP conv) where central converts gg  h f suppressed Optimize for VH/VBF Split into three diphoton pt bins: – High: p T > 75 GeV – Medium: 35 < p T < 75 GeV – Low: p T < 35 GeV 4 diphoton categories x 3 Pt bins = 12 total channels 48 Greatest sensitivity! Same as SM SearchDifferent for h f search

49. Background Model Example fits for CC for each p T γγ bin 49 Same approach for background model as done for SM High p T γγ Bin N signal = 2.9 s/sqrt(b) = 0.66 Medium p T γγ Bin N signal = 2.5 s/sqrt(b) = 0.37 Low p T γγ Bin N signal = 1.3 s/sqrt(b) = 0.09

50. Results For comparison: LEP Limit: 109.7 GeV Previous CDF PRL result (3.0/fb): 106 GeV DØ’s recent (8.2/fb): 112 GeV Observed (expected) 95% C.L. limits on σ×B(h f  γγ) exclude a Fermiophobic Higgs boson with a mass < 114 GeV (111 GeV) A limit of 114 GeV is currently the world’s best limit on a h f Higgs 50

51. Summary and Conclusions Improvements for current results: – Inclusion of forward and conversion photons – Better central ID from a NN SM H  γγ search: – Observed (expected) 95% C.L. upper limits on σ×Br are 28.3xSM (13.0xSM) @ a mass of 120 GeV – Approximate 33% improvement from the 5.4fb -1 result Tevatron SM combination: – Shows significant gains when combined with DØ – Observed (expected) limits of 13.3 (8.5) at a mass of 120 GeV Fermiophobic h f  γγ: – Excludes h f mass below 114 GeV (111 GeV) from observed (expected) limits – A limit of 114 GeV is currently the best limits on h f mass 51

52. Backup 52

53. Used two central photons from cut-based ID 12 GeV/c 2 signal region for each test mass used to set upper limits set on σ  Br relative to SM prediction Expected and observed limits in good agreement Expected limits of 19.4xSM @ 120 GeV Most sensitive for range 110 – 130 GeV/c 2 53 Added to SM Higgs Tevatron combination this past summer Previous Limits on H  γγ at CDF using 5.4/fb

54. Fermiophobic Higgs (h f ) It’s likely nature doesn’t follow the SM Higgs mechanism… We also consider a “benchmark” fermiophobic model A Two Higgs Doublet Model (2HDM) extension to SM: With vacuum expectation values: 5 Physical Higgs Particles: h 0, H 0, A 0, H +, and H – 2HDM type-I – Scalar field mixing angle α can lead to different couplings to fermions for h 0 and H 0 – sin(α) for H 0 and cos(α) for h 0 – Limit of α  π/2 yields a Higgs with enhanced coupling to bosons: h 0  h f Standard model cross sections assumed Not present in MSSM 1 1 Akeroyd, hep-ph/9511347, 1995Introduction54

55. Tight Conversion ID Primary electron: – Fiducial – Had/EM < ~5.5% Secondary electron: – Fiducial – p T > 1.0 GeV Conversion photon – pT > 15 GeV – E/P ratio (optimized for Η  γγ) – Calorimeter isolation (optimized for H  γγ) – Rconv > 2.0 cm 55 ~24% of events ~72% of events Photon ID and Efficiency – Conversion Photons

56. Conversion ID Efficiency Search for “tridents” where one electron leg brems a photon which then converts Probed conversions of lower momentum range than those from H  γγ Obtain an uncertainty on conversion ID rather than MC scale factor In data and MC calculate ratio: R data /R MC  7% uncertainty 56Photon ID and Efficiency – Conversion Photons