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Prospects for a Low-Mass Higgs Boson

Prospects for a Low-Mass Higgs Boson. Thomas R. Junk University of Illinois at Urbana-Champaign C2CR07, February 25, 2007. Theoretical Motivation What we Know from LEP and SLC Higgs Searches at the Tevatron Higgs Searches at the LHC.

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Prospects for a Low-Mass Higgs Boson

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  1. Prospects for a Low-Mass Higgs Boson Thomas R. Junk University of Illinois at Urbana-Champaign C2CR07, February 25, 2007 • Theoretical Motivation • What we Know from LEP and SLC • Higgs Searches at the Tevatron • Higgs Searches at the LHC Thomas R. Junk, C2CR07 Feb. 25, 2007

  2. The Goal: Test the Hypothesis of Spontaneous Symmetry Breaking • SU(2)LU(1)Y is extremely well tested in • collider experiments • But it cannot be a symmetry of our vacuum – otherwise • quarks, leptons, and gauge bosons would all be massless • Simplest model – one complex doublet • with a VEV – W and Z get three DOF, • one left over: fundamental scalar HSM • Not the only possibility • SUSY Higgs • General 2HDM • Higgs Triplets • Technicolor • Little Higgs • Higgs Boson couples preferentially to massive • particles – a window to new physics! Thomas R. Junk, C2CR07 Feb. 25, 2007

  3. Why is a Low-Mass Higgs Boson Interesting? Define Low-Mass to be mH<200 GeV or so. It’s preferred by the Electroweak Fits! New LEP+SLD+Tevatron EW Fit New MW measurement from CDF (Jan 2007) See W. Trischuk’s talk Jan 2007’s blue-band plot (does not include CDF mW) New Fit numbers Thomas R. Junk, C2CR07 Feb. 25, 2007

  4. SM Decays LEP Exclusions for Higgsstrahlung with specific Higgs decay modes  bb Phys. Lett. B565 (2003) 61-75 Thomas R. Junk, C2CR07 Feb. 25, 2007

  5. Higgs Coupling to the Z with SM couplings Excluded all the way down to mH=0 Decay-mode Independent Search in e+e-! Z+anything (CP-even Higgs component!) Including invisible decay products. Mass reach extends down to exactly zero. Many “stealthy Higgs” and continuous-spectrum Higgs models ruled out too. Assumes Higgsstrahlung production. k=1: SM Higgs production rate. Separate dedicated searches for CP-even Higgses decaying to bb, , jets, , invisible done at LEP2. Limits all ~110 GeV Eur. Phys. J C27 (2003) 311-329 Thomas R. Junk, C2CR07 Feb. 25, 2007

  6. Higgs Self-Coupling Diverges with Increasing Energy Allowed Mexican Hat Brim Turns Over Vacuum Stability and Triviality Bounds on SM mH Finding a Higgs boson with mH~120 GeV is powerful evidence for TeV-scale New Physics mH too light! hep-ph/9708416 Hambye and Riesselman Thomas R. Junk, C2CR07 Feb. 25, 2007

  7. The Higgs Bosons of the MSSM • Two Complex Higgs Doublets! Needed to avoid • anomalies. • Five Degrees of Freedom plus W+,-, Z0 longitudinal • polarization states • Five scalars predicted: h, H, A, H+, H- • CP-conserving models: h, H are CP-even, A is CP-odd • Independent Parameters: • mA • tan = ratio of VEV’s •  • M0, M1/2 (parameterizes squark, gaugino masses in CMSSM) • Trilinear couplings A (mostly through stop mixing) • And a real prediction: Let’s test it! Thomas R. Junk, C2CR07 Feb. 25, 2007

  8. Precision Measurements of MW and Mt Favor a Light Higgs Boson Has new mW from CDF in it Thomas R. Junk, C2CR07 Feb. 25, 2007

  9. LEP Exclusions for MSSM Higgs bosons ~114.4 GeV mh-max Scenario (<0) Eur.Phys.J.C47:547-587,2006 (and many more scenarios) Thomas R. Junk, C2CR07 Feb. 25, 2007

  10. LEP Exclusions are Weaker in CP-Violating Scenarios Eur.Phys.J.C47:547-587,2006 Thomas R. Junk, C2CR07 Feb. 25, 2007

  11. CMSSM Favors mH <120 GeV • Bayesian scan over CMSSM • parameter space. • Inputs • Direct LEP2 Higgs searches • Precision EW • Muon g-2 • WMAP assuming • CDM=neutralinos:  h2 • Bs Mixing Rate:  MBs • Br(B! s ) • Br(Bs!+-) • Sophisticated MCMC guided • search for high-posterior-probability • parameter values • CMSSM parameters (flat prior) • 50 GeV < m0 < 4 TeV • 50 GeV < m1/2 < 4 TEV • |A0| < 7 TeV 2 < tan < 62 MSSM h is SM-like for these models (production, decay) hep-ph/0611173v2 (Feb. 27, 2007) Thomas R. Junk, C2CR07 Feb. 25, 2007

  12. Heavier Higgs Bosons are, Well, Heavier hep-ph/0611173 v2(Feb. 27, 2007) They could be out of reach at the LHC New estimations of SM br(b! s) lowered these predictions. More on this later. Thomas R. Junk, C2CR07 Feb. 25, 2007

  13. An Old SM Posterior Density Plot from 2001 Jens Erler, hep-ph/0010153 Includes ~3 excess at mH=115 GeV from LEP2 which now has a p-value of 9% (not even 2 now) But: Precision EW has pulled in the long, high tail. Mt has decreased, MW has risen. Errors are smaller. No vacuum stability or triviality bounds. At that time, precision EW gave Thomas R. Junk, C2CR07 Feb. 25, 2007

  14. Sensitivity Projections from 2000 and 2003 hep-ph/0010338 2003: Realistic detector models Data-based backgrounds @ Run II energies Analysis upgrades assumed Acceptance upgrades Sophisticated s/b separation No systematic uncertainties! No WW channel! 1999: Run I extrapolations Attempt at syst. errors: scale with 1/sqrt(L) Includes WW channel MC models of Run II detector performance Fermilab-Pub-03/320-E Thomas R. Junk, C2CR07 Feb. 25, 2007

  15. The State of the Individual Channels as of ICHEP 2006 Getting close at mH=160 GeV! Thomas R. Junk, C2CR07 Feb. 25, 2007

  16. Just a Short While ago, It looked like THIS La Thuile/Moriond 2005 In just over a year, we analyzed 6 the data, optimized the analyses, and combined them together to close in on the SM. Searches gaining staff and momentum! Thomas R. Junk, C2CR07 Feb. 25, 2007

  17. CDF and DØ’s Contributions for ICHEP06 were “Complementary” DØ: Hbb (<= 400 pb-1) HWW (1 fb-1) CDF: Hbb (1 fb-1) HWW (360 pb-1) Different analyses ready at different times: A snapshot of the horse-race. Much much more data to come! Even though CDF+DØ were combined, factor of sqrt(2) not realized for ICHEP2006 due to non-overlap in most sensitive searches. Thomas R. Junk, C2CR07 Feb. 25, 2007

  18. We’ve Come a Long Way Since Run I Thomas R. Junk, C2CR07 Feb. 25, 2007

  19. The Old To-Do List, of October 2005 SM Channels only Doesn’t specify what WW people should do. We thought they were pretty optimal already. We are learning there is much more to be gained in WW Much has been learned in the last year. Lots left to learn, and do. Thomas R. Junk, C2CR07 Feb. 25, 2007

  20. Newly Released (Jan 2007) CDF H! WW Search with 1 fb-1 • Cut-based for now. • NN and Matrix Element analyses in the works • More sensitivity from the same data sample. • To do: Combination with DØ Thomas R. Junk, C2CR07 Feb. 25, 2007

  21. Accomplishments and Ideas – Mass Resolution MET resolution too.. • Current Status: • Many tools available: • NN Jet tools • Hyperball (kind of like an NN) • Track-Cluster Association • B-specific Corrections • Wider Jet Cones (llbb already • uses these) • Selection nets implicitly • optimize mjj resolution if they • include such things as MET • and EM fraction and other • things a NN needs (llbb). • Double-tagged events have • better mjj resolution than single- • tagged events (less combinatorics, • less semileptonic decay) Many of these we have tools for, but need to convince ourselves in data that they perform as promised. Watch out for multiple collision effects.. Thomas R. Junk, C2CR07 Feb. 25, 2007

  22. Sensitivity gain from B-tag Improvements ~20% improvement by separating single and double tagging Significance: *S, B are number of events in 3 window in dijet mass distribution ~10% improvement by NN tagging Focus on =1 SECVTX tag w/ NN tag 2 SECVTX tag Example: WH! l bb channel *Find the most sensitive b-tagging option a priori Still more to gain. Thomas R. Junk, C2CR07 Feb. 25, 2007

  23. Example – Splitting WH! l bb Channel into single and double-tags • Different s/b in the two sub-channels: • lower fraction of mistags, W+jets in double-tagged sample • better mjj resolution • General Strategy – If you can classify events in two or more ways with • different s/b, sensitivity is gained by separating them and combining the • results. Thomas R. Junk, C2CR07 Feb. 25, 2007

  24. A Continuous Job: NN Selection llbb Channel already has a 2D NN! WHlvbb tried a NN analysis already. Claim: 1.75 factor in HSWG note; Run I NN gets 1.2 factor in s/sqrt(b)). Single top NN’s have shown tremendous improvements in sensitivity over simple variables like Mlvb and HT. We learn as we go: Matrix Element Techniques perform very well and give results not 100% correlated with NN’s. But – some measured quantities are not input to the Matrix Element, like NN b-tags. Many kinds of backgrounds lack convincing matrix elements Non-W Thomas R. Junk, C2CR07 Feb. 25, 2007

  25. Tevatron Performance Getting Impressive! Higher peak luminosity – mainly due to higher pbar stacking rates. Thomas R. Junk, C2CR07 Feb. 25, 2007

  26. And a Concern: Trigger Rates Rise Faster than Luminosity • Example: Muon triggers at • inermediate : multiply • cross-section by instantaneous • luminosity to get trigger rate. • At least a cubic dependence on • luminosity! • Hit deadtime wall at a L2 trigger rate of • ~1 KHz. • Fake track rate grows with occupancy. • CDF has a stereo trigger upgrade (L1 • already done, L2 in test) to reject fake • tracks. Works very well! • MET trigger upgrade in progress – sharpen • the MET trigger turnon. • L2 Cluster upgrade • Still compromises to be made at • Lumi = 300E30 cm2s-1. • CDF Has a working group dedicated to the Higgs • triggers. • More high-lumi concerns: • B-tagging degrades with increasing • # primary vertices/BX • MET resolution degrades • Some good news: • Only a fraction of data collected at • the highest luminosities though • (beginnings of stores) Would like to • make the best use of it, though. Thomas R. Junk, C2CR07 Feb. 25, 2007

  27. Expected Signal Significance CDF+DØ vs Luminosity It’s possible to be lucky or unlucky! per experiment per experiment mH=115 GeV assumed Date Thomas R. Junk, C2CR07 Feb. 25, 2007

  28. Parton Distribution Functions of the Proton “The LHC is a gluon-gluon collider” (approximately). Thomas R. Junk, C2CR07 Feb. 25, 2007

  29. SM Higgs Boson Production Rates at the LHC Thomas R. Junk, C2CR07 Feb. 25, 2007

  30. q q q p p q l  q q W W q H p p q l  Backgrounds and Signals at the LHC Backgrounds dominated by strong processes ATLAS TDR Signals much smaller Thomas R. Junk, C2CR07 Feb. 25, 2007

  31. excluded by LEP SM Higgs Discovery Potential with ATLAS • discovery channels • GGF: H  gg • GGF: H  ZZ  4l+- • GGF: HWW2(ln) • ttH: H  bb • VBF: H  tt • VBF: H  WW since 2000 For MH>300 GeV also: VBF: H  ZZ  llnn VBF: WW  lnqq ? • Some Channels allow very precise mH measurement (ZZ,) • Calibration of backgrounds with data • k-factors increase signal rates (and backgrounds) Thomas R. Junk, C2CR07 Feb. 25, 2007

  32. CMS Higgs Search Similar to ATLAS Thomas R. Junk, C2CR07 Feb. 25, 2007

  33. Low-mass SM Higgs Boson Searches at the LHC H: Low s/b, but good mass resolution allows for a peak. Large irreducible background: ppX Measure background with sidebands Optimizing signal resolution – conversions, dead material Can reduce Jets faking photons with cuts ttH, Hbb: Only channel where Hbb is possible (WH, ZH, Hbb are hopeless) • Jet Combinatorics • Energy Resolution • Background Rate and Shape • (get from data as much as possible) ATLAS TDR, 100 fb-1 Thomas R. Junk, C2CR07 Feb. 25, 2007

  34. ATLAS TDR A Very Clean Mode: ggHZZ(*)l+l-l+l- at ATLAS, CMS Simulated H  ZZ  e+e-+- Event in ATLAS Expect to measure mH to 1% with this mode if it’s there. NLO k-factor may improve expected significance by ~25% Small and flat background: estimate with data I Isolation, anti-B veto (lepton impact parameters) use m4l to discriminate Thomas R. Junk, C2CR07 Feb. 25, 2007

  35. Luminosity Required to Discovery a SM Higgs boson at LHC • VBF HWW strongest channel for 130 < mH< 200 GeV • Sensitivity all the way up to 1 TeV with HZZ • mH<130 GeV – several difficult channels in combination, >5 fb-1 needed (N)NLO k-factors increase signal rates Data needed to calibrate backgrounds Analyses are cut-based: Advanced separation techniques to be applied ATLAS Thomas R. Junk, C2CR07 Feb. 25, 2007

  36. Higgs Boson Production and Decay in MSSM at High tan • Interesting feature of many MSSM scenarios (but not • all!): • [mh ,mH]  mA at high tan (most benchmark scenarios..) • Two for the price of one! • At leading order, (A0bb) and (A0+-) are both • proportional to tan2. • Decays to W, Z are not enhanced • and so Br. falls with increasing tan (even at high mA) • Br(A0 bb) ~ 90% and Br(A0+-) ~ 10% almost • independent of tan (some gg too). Thomas R. Junk, C2CR07 Feb. 25, 2007

  37. 0 0 t b b 0 b Higgs Boson Production Mechanisms + Amplitude  1/tan Amplitude  tan enhanced! suppressed! And many other diagrams At high tan, (h,A+X)  tan2 (low tan and SM case: cross-sections too small to test with current data.) Amplitude  tan enhanced! Thomas R. Junk, C2CR07 Feb. 25, 2007

  38. CDF’S h! Search ~ 2 excess around mH=160 New! Released Feb. 2, 2007 Thomas R. Junk, C2CR07 Feb. 25, 2007

  39. CDF’s h! Search: Limits and Interpretations ~300 pb-1 results This analysis is one to watch closely: Backgrounds are small for mH>150 GeV. Probing tan of 40! (interesting value) Still a lot of mileage left in this analysis – benefits greatly from luminosity and combination Thomas R. Junk, C2CR07 Feb. 25, 2007

  40. DØ Doesn’t See Anything Though Sensitivity is similar to CDF’s analysis, even with the NN Thomas R. Junk, C2CR07 Feb. 25, 2007

  41. We Would Like to Observe More than One Higgs Boson ATLAS, 300 fb-1(VBF 30 fb-1 only in plot) • At least one Higgs boson visible • over entire plane • Many models for which only one • Higgs boson is detectable. • Decays of H? Typical CPX scenario: Other CPC Scenarios Similar Thomas R. Junk, C2CR07 Feb. 25, 2007

  42. Cascade Decays and a Low-Mass Higgs h! AA! bbbb,bb, , photons Example: Dermisek,Gunion hep-ph/0611197 h! AA! bbbb LEP Interprets h! bb searches in h! bbbb with extra signal MC. No analysis re-optimization. Some NMSSM models with low fine-tuning just sneaking under the LEP exclusion. Still pretty hard at the Tevatron. Maybe taus? But low mAtaus together, not isolated. Look like jets! 3 channel: DØ 4\gamma channel: CDF just getting started Thomas R. Junk, C2CR07 Feb. 25, 2007

  43. Interesting A0 decay modes: taus, charm, gluons. Could extend this if we could get someone interested in reading old LEP data. Thomas R. Junk, C2CR07 Feb. 25, 2007

  44. A New Exotic Channel pp! H+hf! W+hfhf! W+ DØ Sought this in 3+X (hf is fermiophobic and decays to photons) DØ Note 5067-CONF Signal proposed by Akeroyd, Diaz Phys.Rev.D67:095007,2003. hep-ph/0301203 CDF wants to look at the 4 final state. Thomas R. Junk, C2CR07 Feb. 25, 2007

  45. Summary and Prospects • SM Higgs Searches at the Tevatron are going full speed ahead • We are getting smarter in many ways (foreseen and unforeseen) • Chance of Evidence/Discovery of a light Higgs boson at the Tevatron • Difficult range of mH for LHC. Light Higgs preferred by EW fits, • Preferred by MSSM. • MSSM Higgs Searches at Tevatron • Complementary to LEP Searches • Tau channels benefit greatly from additional data. • LHC: Full coverage of entire allowed SM Higgs mass range • Discovery guaranteed if it’s there! • Measurement of mH • May only see one of five MSSM Higgses though • MSSM covered for many scenarios with the LHC. Tevatron is testing • interesting parts of model space. May need ILC to disentangle • ambiguities in LHC discoveries. By 2009 we will know quite a lot about Gauge Symmetry Breaking Thomas R. Junk, C2CR07 Feb. 25, 2007

  46. Backup Slides Follow Thomas R. Junk, C2CR07 Feb. 25, 2007

  47. Thomas R. Junk, C2CR07 Feb. 25, 2007

  48. Higgs Decay Forward tagging jets Jet f h Jet Vector-Boson Fusion with HWW • signature: • 2 forward jets with • large rapidity gap - only Higgs decay products • in central part of detector Thomas R. Junk, C2CR07 Feb. 25, 2007

  49. VBF: Forward Jet Reconstruction, Backgrounds, Pileup Signal and Background Discrimination Does it still hold up @NLO?   Background due to Pileup High Luminosity Jet Reconstruction Efficiency Low Luminosity Need to see how first data look Jet  Thomas R. Junk, C2CR07 Feb. 25, 2007

  50. Couplings of MSSM Higgs Bosons Relative to SM W and Z couplings to H, h are suppressed relative to SM (but the sum of squares of h0, H0 couplings are the SM coupling). Yukawa couplings (scalar-fermion) can be enhanced Thomas R. Junk, C2CR07 Feb. 25, 2007

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