4. Search for the SM Higgs Boson

Transcription

1 4. Search for the SM Higgs Boson i. Production and Decay ii. H J JJ iii. Associated production channels iv. H J ZZ* J 4 ", H J ZZ -> 4 " v. M(H) ~ 1 TeV : H J"" QQ, "" jet-jet vi. Measurement of Higgs properties vii. Other possibilities GIF Annecy

2 Production of SM Higgs Boson g t H o t g t g g fusion t g g t t H o t t fusion t q W,Z W,Z q H o W, Z bremsstrahlung q W,Z H o q W,Z WW, ZZ fusion q σ (pb) gg H qq Hqq qq' HW M. Spira et al. gg,qq Hbb NLO QCD gg,qq Htt qq HZ M H (GeV) σ(pp H+X) s = 14 TeV m t = 175 GeV CTEQ4M events for 10 5 pb 1 gg H : K= residual uncertainties on NLO cross-sections (PDF, NNLO, etc.) 20% (except tth) GIF Annecy

3 Decay Modes of the SM Higgs Decays & discovery channels Higgs couples to m f 2 Heaviest fermion (b quark) always dominates Until WW, ZZ thresholds open Low mass: b quarks jets; poor resolution ~ 15% Only chance is to use ECAL (use γγ decay mode) Once M H >2M Z, use ZZ mode W decays to jets or lepton+neutrino (missing E T ) GIF Annecy

4 Search for SM Higgs Boson Fully hadronic final states dominate but cannot be used due to large QCD bkg. Dlook for final states with isolated leptons and photons despite smaller BR Region 1: Intermediate mass region ( LEP limit < m H < 2 m Z ) m H < 120 GeV: pp J WH J "Q bb or tt H J "QX bb m H < 150 GeV: H J JJ, ZJ 130? < m H < 2 m Z : H J WW* J "ν "ν 130? < m H < 2 m Z : H J ZZ* J "" "" Region 2: High mass region (2 m Z <m H < 700) H J ZZ J "" "" Region 3: Very high mass region (700 < m H < 1 TeV) H J ZZ J "" νν, H J ZZ* J "" jet-jet H J WW J "ν jet-jet forward jet tagging Recently: qq J qqh with H J WW (mh~130 GeV), H J WW etc. GIF Annecy

5 H J JJ H t*,w* t*,w* Most promising channel in the range m H < 150 GeV t*,w* γ γ (σ.b ~ m H ~ 150 GeV) σ.b can be modified by heavy undiscovered fundamental fermions or bosons Backgrounds are large (2pb/GeV), H natural width is small (~MeV) D excellent mass resolution required σ m /m = 0.5 [σ E1 /E 1 O σ E2 /E 2 O cot(θ/2) θ] D energy resolution and precise vertex localisation Typical Cuts 2 isolated photons p T > 25, 40 GeV with η < 2.5 No track or em cluster with p T > 2.5 GeV in a cone size R = 0.3 around γs Signal: ~ 1000 s of events GIF Annecy

6 H J JJBackgrounds Main Backgrounds Irreducible: qq annihilation and gg box q q γ γ g g γ γ σ ( γγ ) σ ( H γγ ) ~ 60 Reducible: J-jet and jet-jet q g q γ π 0 γ (s) σ jj σ ( H γγ ) ~ 10 8 A need large J-jet separation (essentially J-S 0 separation) to reject jets faking photons GIF Annecy

7 H J JJ Background Rejection ATLAS EM calorimeter 4 mm η-strips in first compartment 3 longitudinal segments Detailed MC D (γ jet + jet-jet) < 40% γγ GIF Annecy

8 H J JJ Signal in CMS CMS CMS ATLAS, 100 fb -1 ATLAS + CMS m H (GeV) S (evts) S/B S/ B S/ B 30 fb GIF Annecy

9 H J JJ Associated Production γγ + " + X γγ + 2 jets p T > 40 GeV m H =120 GeV, 1 experiment, 100 fb -1 complementary to H γγ smaller S but better S/B needs 100 fb -1 confirm discovery, measure tth, WWH couplings γγ + jets : large theoretical uncertainties H direct γγ γγ + " γγ + jet S ~100 S/B S/ B ~5 GIF Annecy

10 H J bb in Associated Production I Dominant decay for m H < 2 m H is H J bb (σ ~ 20 pb) Signal for Higgs produced in isolation impossible to extract no Level-1 trigger and QCD production of bb pairs is v large N S /N B < 10-5 Associated production: pp J WH J "Q bb or tt H J "QX bb a high p T lepton from W or tt can provide the trigger (σ ~ 1 pb) ATLAS Study L-1 Trigger: muon (electron) with p T > 6 (20) GeV with η < 2.5 ATLAS ε b ~ 60% for rejection of 100 against light quarks (~ obtained in CDF) GIF Annecy

11 tth channel more powerful H J bb in Associated Production II Typical Cuts Jets retained if p T > 15 (30)GeV lo(hi)l No isolated lepton with p T > 6 GeV 4 tagged b-jets Reconstruct both top quarks ATLAS 100 fb -1 30(70) fb -1 at lo(hi)l m H = 120 GeV Signal (100 fb -1 ) 62 evts for m H = 120 GeV Background tt jj is the most important ~ 250 evts in a bin of width 30 GeV S/N ~ 0.2 depends critically on ε b and background rejection 2 nd observation of H in this mass range GIF Annecy

12 H J WW * J " + Q" - Q Important around m H ~170 GeV Where BR(HJZZ) reduced W W Large rate : σ x BR 700 fb BR (H WW (*) ) > 70% Counting channel (no mass peak) D precise knowledge of bkg needed Main Backgrounds -WW (*) (irreducible) σ 5pb -WZ "ν"", ZZ ""νν σ 1pb -Wt,WbbJ 2"+X σ 120 pb Typical Cuts 2 isolated opp sign leptons (e, µ) p T > 20, 10 GeV, 10 < m "" < 80 GeV with φ "" < 1 and η "" < 1.5 (rejects WZ, ZZ) no jets p T > 15 GeV in η < 3 (rejects tt,wt,wbb) E miss T > 40 GeV, m T ("" E miss T ) between m H -30 GeV and m H GIF Annecy

13 H J WW * J " + Q" - Q 1 experiment, 30 fb -1 m H (GeV) S S/B S/ B (*) S/ B (*) fb -1 (*) 5% background systematics included Count excess of events in signal region Signal and background have similar shapes very tight mass window to optimise S/ B ATLAS 30 fb -1 m H =150 GeV Conclusions: -5σ discovery at low L for 150 m H 200 GeV -complementary to H 4" larger rate, better sensitivity for 160 m H < 180 GeV, but no mass peak - crucial : background knowledge GIF Annecy

14 H J ZZ * J 4": Introduction σ x BR 3 fb Main backgrounds: ZZ*, Zγ* continuum (irreducible) Zb b 4" + X, tt 4" + X (2 " from b-decays) Z Z* 120 m H 2 m Z Typical Cuts Four isol leptons p T > 20, 20, 7, 7 GeV m (" 1 " 2 ) compatible with m Z (rejects tt ) m (" 3 " 4 ) > GeV lepton isolation and rejects b "X decays impact parameter t t + Zbb < 10% ZZ* ATLAS full simulation Largest normalised impact parameter of the four muons in the transverse plane σ (d 0 ) ~ 20 µm H 4 µ Zbb Normalised impact parameter tt GIF Annecy

15 H J ZZ * J 4": Resolution Intermediate m H : * H << V m High m H : * H ~ V m or * H > V m Additional complication: internal bremstrahlung 8% of reconstructed ZJµµ fall outside window m #2σ Z Z at m H =150 GeV Efficiencies: 70% per electron in CMS Incl internal, external bream, 5x7 array, m #2σ Z Z GIF Annecy

16 H J ZZ * J 4": Signal - Intermediate m H 1 experiment, 30 fb -1 ~90% of bkg comes from ZZ* m H (GeV) S S/B S/ B 30 fb (Poisson) S/ B 100 fb (Poisson) Conclusions -5σ discovery at low L for 130 < m H 180 GeV 1 expt (except GeV) - require excellent " reconstruction and identification efficiency and resolution down to p T ~ 5 GeV (low-rate signal) Note : -- m H > 2 m Z : gold-plated H ZZ 4" (background free) -- m H 160 GeV : dip due to H WW opening GIF Annecy

17 H J ZZ J 4": Signal - High m H 20 fb fb -1 GIF Annecy

18 m H ~ 1 TeV : H J ZZJ ""QQ As m H increases further, Γ H increases and σ falls D turn to higher BR modes Signal: Jacobian peak in E T miss in events with Z + large E T miss ATLAS : 100 fb -1 Typical Cuts 2isol" :p T" >20 GeV, p T (Z)>60 GeV E T miss > 100 GeV 1 tagging jet E j > 1 TeV, in η >2.5 Backgrounds: irreducible ZZ, reducible Z + jets Z+jets: parton level simulation Forward jets can be used GIF Annecy

19 m H ~ 1 TeV : HJ "" jj, "Q jj Larger statistics if use decay modes HJWWJ"ν+jets and HJZZJ""+jets BUT need to reduce enormous W+jets and Z+jets background Consider WW final state (ZZ similar) Find jets in R=0.2 with E T >50 GeV, reconstruct W J jj ε(wjjets) ~ 60%, E T (jj) > 150 GeV, m W -2σ <m jj < m W +2σ σ(m W ) ~ 7 GeV p T (") > 50 GeV, E miss T > 50 GeV p T (W) > 200 GeV Backgrounds from W+jets and ttjwbwb roughly equal but still large Use forward tagging jets from qq J Hqq E T tag > 15 GeV, E > 600 GeV with 2 < η < 5 E T cell > 3 GeV Low L : no additional jets with E T >20 GeV in η <2 Fake tag prob. from MinBias Single jet - 4.6%, double jet % GIF Annecy

20 m H ~ 1 TeV : H J ZZJ "" jj, Typical Cuts 2 isol " :p T" >50 GeV, p T (Z)>150 GeV M "" = m Z -10 GeV l.e. 2 central jets E Tj > 40 GeV in η <3 2 tagging jets E j > 400 GeV, E Tj >20 GeV CMS GIF Annecy

21 m H ~ 1 TeV : HJWW J "Q jj Typical Cuts 1 isol " :p T" >30 GeV in η <2.5 E T miss > 100 GeV l.e. 2 central jets E Tj > 40 GeV in η <3 2 tagging jets E j > 400 GeV, E Tj >20 GeV p TW >100 GeV in "ν and jj modes E tag >200 GeV ATLAS m H = 1TeV, 30fb -1 m H = 800 GeV, 30 fb -1 E tag >400 GeV GIF Annecy

22 Summary: Search for SM Higgs m H < 180 GeV many complementary channels (gg, bb, 2", 3", 4", etc.) m H > 180 GeV discovery is straightforward with gold-plated H ZZ 4" (S/B > 5). Complemented by H WW "ν jj, H ZZ ""νν, "" jj (forward jet tag) > 1 channel observable over most of range robustness, measurement of couplings GIF Annecy

23 Summary: Search for SM Higgs SM Higgs boson can be discovered at 5 σ after 1 year of operation (10 fb -1 / experiment) excluded at 95% CL after 1 month of running at cm -2 s -1. Results are conservative: - no K-factors - simple cut-based analyses - conservative assumptions on detector performance - channels where background control is difficult are not included e.g. WH " νbb (large systematics) L is per experiment LEP2 5σ GIF Annecy

24 Measurement of Higgs Properties: Mass Mass Favoured mass of SM Higgs < mh < 212 GeV In this range m H can be measured to 0.1% using γγ and 4" channels Energy scale can be calibrated to 0.1% using ZJe + e - and ZJµ + µ - GIF Annecy

25 Measurement of Higgs Properties: Cross-sections 10% of σ in intermediate mass region comes from WW fusion Identified by requiring forward tagging jets and no additional central jets Higgs production via WW fusion Zeppenfeld et. al. 100 fb -1 Errors Statistical: 5 20% γγ and 4" well understood Modes involving fwd jets more difficult to estimate 30fb -1 Corrected σ compared with perturbative QCD calculations Known to NLO for all and NNLO for ggjh processes GIF Annecy

26 Measurement of Couplings and BR g g g g t t t g g fusion t t t H o H o Use various Higgs production and decay modes In ratios luminosity uncertainty largely cancels Assuming 300 fb-1 σ. B( tth + WH γγ ) BR( H γγ ) σ. B( tth + WH bb ) BR( H bb ) t t t fusion q W,Z W,Z q H o W, Z bremsstrahlung W,Z q H o q W,Z WW, ZZ fusion q σ. B ( H γγ ) σ. B ( H ZZ *) σ. B ( tt H σ. B ( WH γγ / bb ) γγ / bb ) σ. B( H WW * / W ) σ. B( H ZZ */ Z) BR ( H γγ ) BR ( H ZZ *) g g g g 2 HWW 2 HZZ 2 Ht t 2 HWW GIF Annecy

27 Measurement of Higgs Properties: BR BR cannot be measured directly at the LHC But possible to infer ratios of couplings from measured rates Measure Error M H range BH ( γγ ) BH bb 30% ( ) ( ) ( ) BH γγ BH ZZ σ( tt H) σ( WH) ( ) ( ( ) ) BH WW ( ) BH ZZ 15% % % Error on σx BR (%) Open symbols : + / + = 10% Closed symbols : + / + = 5% H γγ tth (H bb) H WW lνlν H ZZ ( * ) M H (GeV/c 2 ) 10 3 GIF Annecy

28 5. Search for the Supersymmetric Higgs Boson i. Production and Decay ii. SM-like decays iii. H/A J WW iv. H/A J PP v. A J JJ vi. Charged Higgs vii. Other signatures GIF Annecy

29 SUSY Higgs: Particle Content Complex analysis; 5 Higgs (H ± ;H 0,h 0,A 0 ) At tree level, all masses & couplings depend on only two parameters; tradition says take M A &tanβ Modifications to tree-level mainly from top loops Important ones; e.g. at tree-level, M h <M Z cosβ; radiative corrections push this to 150 GeV. Important branch 1: SUSY particle masses (a) M>1 TeV (i.e. no decays of the Higgs to them); well-studied (b) M<1 TeV (i.e. allows decays of the Higgs to them); new Important branch 2: stop mixing; value of tanβ (a) Maximal No mixing (b) Low (1.5) and high ( YDOXHVRI tanβ GIF Annecy

30 SUSY Higgs Channels Studied H, h γγ, bb (H bb in WH, t t H) h γγ in WH, t t h γ γ h, H ZZ*, ZZ 4 h, H, A τ + τ (e/µ) + + h +E miss T e + + µ +E miss T h + + h +E miss T H + τ + ν from t t H + τ + ν and H + t b for M H >M top A Zh with h bb; A γγ inclusively and in bbh SUSY H, A χ 0 2 χ0 2, χ0 i χ0 j, χ+ i χ j H + χ + 2 χ0 2 qq qqh with H τ + τ H ττ, in WH, t t H using OO code (tough ) work started; tough GIF Annecy

31 Searches for SUSY Higgs Large variety of channels: e.g. h γγ, tth ttbb, H ZZ (*) 4" ± A/H µµ, ττ, tt, H τν, cs, tb H hh, A Zh also in SM typical of MSSM 0 A/H χ 0 0 χ h χ χ 1 2 if SUSY particles accessible Note : -- suppression/absence of WWH, ZZH, WWA, ZZA couplings -- strong enhancement of bba, bbh couplings for large tanβ A/H µµ, ττ accessible compared to SM GIF Annecy

32 SUSY Higgs: Mass Spectra Mass spectra for M SUSY >1TeV M HIGGS (GeV/c2 ) No stop mixing M SUSY = 1 TeV Two-loop / RGE-improved radiative corrections included Maximal stop mixing M SUSY = 1 GeV H, tan β= 2 H, tan β= 20 H, tan β= 20 H ±, tan β= 20 H, tan β= 2 H ±, tan β= 20 H ±, tan β= 2 H ±, tan β= 2 h, tan β= 20 h, tan β= 20 h, tan β= 2 h, tan β= M A (GeV/c 2 ) M A (GeV/c 2 ) GIF Annecy

33 SUSY Higgs: Production σ (pb) Biggest branch is tanβ g g gg h hbb hw hqq hz htt ~ ~ t,t,b,b h H h,h Hqq gg H HZ σ (pp h / H+X) [pb] s = 14 TeV M t = 175 GeV CTEQ4 tgβ= 1.5 Hbb HW W,z M. Spira et al. Htt σ (pb) q q M h/h (GeV/c 2 ) W,Z h,h hbb hw g g gg h hz b b hqq b b Hqq h,h g g gg H htt 10 HW 3 h H HZ Htt M h/h (GeV/c 2 ) b Hbb h,h σ (pp h / H+X) [pb] s = 14 TeV M t = 175 GeV CTEQ4 tgβ = 30 b GIF Annecy

34 SUSY Higgs: Decay Modes No mixing, M S =1TeV GIF Annecy

35 m A > 100 GeV: - h mass close to max value (~ 130 GeV) - h behaves as SM Higgs m A < 100 GeV: - h mass decreases -BR(h γγ) and tth prodn suppressed - large tanβ : bbh production enhanced bbh bb µµ channel observable Search for the h - different production mechanisms : gg h (loops), Wh, tth - different decays : h γγ(loops), h bb GIF Annecy

36 A/H owwo "QQ h # Q In MSSM, at large tanβ, H/A J ττ rates strongly enhanced over SM All final states accessible "", "-had, had-had A/H owwo "QQ h # Q Backgrounds Z ττ, W+ jets (dominant), tt,bb ATLAS σ m ~12% Cuts (e.g. CMS) 1 isolated lepton with p T > GeV 1 tau jet candidate, E T >40 GeV No jet with E T >25 GeV in η <2.4 CMS σ m ~14% m H =500 GeV tanβ=25 GIF Annecy

37 A/H J WWJ h Qh Q Provides best reach for large m A. Signature: two stiff opposite-sign isolated tracks and missing transverse energy. CMS 30 fb -1 Typical Cuts E Tj >60 GeV, p Th >40 GeV φ jj <175 o, E T miss >40 GeV Background: Main challenge: reject QCD jet background (already at L1 trigger!). Feasible for m A > 300 GeV: hadrons have high p T,E miss T is large, etc.. R QCD ~ QCD background << 10% (tt + Z/γ* ττ) B-tagging improves S/B, σ M ~ 10% For m A < 300 GeV : More study (trigger, background). Additional tools: calorimeter isolation, impact parameter GIF Annecy

38 +$J PP Dominant Backgrounds Z/γ*, tt Typical Cuts 2isolµ p Tµ > 10 GeV Df(mm) > 120 o E T miss >40 GeV b-tag in assoc. channel 1 b-tag GIF Annecy

39 Search for the A and H Large tane bbh, bba strongly enhanced e.g. σ (MSSM) / σ (SM) 5000 tanβ =30, m =300 GeV m A > 200 GeV: A and H are ~ degenerate H/A ττ, µµ observable and cover large part of parameter space Small tane large number of channel measurement of many couplings including Hhh, AZh GIF Annecy

40 Search for H # m Hr < m t -m b Production via gg J tt then (t b H +) and (H + τν) Signature violation of lepton universality in semi-leptonic top decays + BR( t τ ντb) R = = 1+ R + BR( t µ ν b) µ + + BR( t H b) BR( t τ ντ ) where R = + + BR( t W b) BR( W µ ν ) LEP: M H+ <78.6 GeV µ m Hr > m t gb H ± t tb t gb H ± t τν t g t t b H ± Due to τ polarisation π from τjπν is harder from τ produced in H + decay than in W decay GIF Annecy

41 Typical Cuts 1 isol " p T > 20 GeV in η <2.5 (trigger) 1 τ-jet E Tj >40 GeV η <2.5 1 isol hard track p Th > 30 GeV pointing to τ-jet ( R<0.1) ge. 3 jets with p T >20 in η <2.5 with ge. 2 b-jets ATLAS: 30 fb -1,tanE=5 m H+ (GeV) σ.br(pb) Signal Bkg Signif Search for H # (m H <m t ) 3000 W τν 4000 fake τ from W jj Syst error on bkg 3% GIF Annecy

42 Search for H # (m H >m t ) Backgrounds W+ jets, Wtb, QCD jets tt, gb H ± t Cuts 1. E T (τ-jet) > 100 GeV 2. τ-polarisation (p π / E τ-jet > 0.8) 3. E miss T > 100 GeV 4. reconstruct W, top 5. m T (τ-jet,e miss T ) >100 GeV 30fb -1 τν 200 tt W+jet Wtb Evts 4k Cut k k Cut k 26k 280 Cut k 7.7k 104 Cut Cut GIF Annecy

43 Search for H # GIF Annecy

44 H Decays to Sparticles If mass of charg(neutra)linos < 1 TeV e.g. Decays H 0 χ 0 2 χ0 2, χ+ i χ- j become important χ 0 2 χ0 1 + _ has spectacular edge on the dilepton mass distribution Example: χ 0 2 χ0 2. Four (!) leptons (isolated); plus two edges Four-lepton mass GIF Annecy

45 If M charg(neutra)linos < 1 TeV Adding bb on the W modes can close the plane Wh (e/p)q bb Area covered by H 0 of 0 2F 0 2, o4 eptons 100 fb -1 No stop mixing maximal stop mixing with 30 fb -1 maximal stop mixing with 300 fb -1 GIF Annecy

46 Summary: SUSY Higgs Plane fully covered (no holes) at low L (30 fb -1 ). Main channels : ± h γγ, bb, A/H µµ, ττ, H τν Two or more Higgs can be observed over most of parameter space D can disentangle SM / MSSM LHC will observe h, A, H, H r m A < 400 GeV for Uncertainties : m A ±30 GeV (e.g. from m h ~3 GeV), tanβ ± 0.7 Impact of mixing on couplings studied for minimal mixing but not for all possible mixing (evolving theory predictions) GIF Annecy

47 Minimal Mixing Minimal mixing (m h < GeV) NB: log scale Caveat: coverage depends strongly on exact upper bound on m h GIF Annecy

48 Maximal Mixing Maximal mixing (m h < 130 GeV) NB: linear scale Caveat: possible suppression of e.g. bbh coupling could affect significantly H observation at LHC GIF Annecy

49 MSSM Higgs bosons How Many Higgs Discoverable? h,a,h h,a,h,h ± h,h ± 4 Higgs observable 3 Higgs observable 2 Higgs observable 1 Higgs observable 5σ contours H,H ± h h,h Assuming decays to SM particles only h,,h,h ± h,a,h,h ± h,h ± In this region only h observable (h SM Higgs) disentangle SM /MSSM? GIF Annecy

50 SUSY Higgs Boson: Mass Maximal mixing (m h < 130 GeV) NB: linear scale 300 fb -1 MSSM Higgs m/m (%) h, A, H γγ H 4 " H/A µµ h bb 1 2 Η hh bb γγ 1-2 Α Zh bb "" 1 2 H/A ττ 1-10 Present theoretical error m h ~ 3 GeV Caveat: possible suppression of e.g. bbh coupling could affect significantly H observation at LHC GIF Annecy

51 Physics Reach? Discovery Luminosity [fb 1 ] σ Higgs Signals (statistical errors only) CMS LHC 14 TeV (SM NLO Cross Sections) M Higgs [GeV] H γγ H ZZ H WW lept. acceptance, lept. isol. lept. isol., jet veto, E t miss D_D_1285c ~ 1 34 ~ 1 33 ~ 1 33 m 1/2 (GeV) ~ one ~~ miss CMS q, g mass reach in E + jets inclusive channel T for various integrated luminosities CMS TH q(500) ~ h(110) EX Ωh 2 = 0.15 Ωh 2 = 0.4 g(500) ~ 500 Ωh 2 = 1 q(1000) ~ g(3000) ~ miss E T (100 fb -1 ) q(2000) ~ q(1500) ~ g(1500) ~ L dt = 1, 10, 100, 300 fb -1 A 0 = 0, tanβ= 35, µ > 0 miss E T (300 fb -1 ) g(2000) ~ miss E T (10 fb -1 ) miss E T (1 fb -1 ) g(1000) ~ h(123) g(2500) ~ q(2500) ~ m 0 (GeV) ~ one ~ one ~ one cosmologically plausible region Fermilab reach: < 500 GeV DD_2101 GIF Annecy

52 Conclusions Higgs is still missing Symmetry Breaking in the SM (and beyond!) still not understood LHC and ATLAS/CMS designed to find it Numerous challenges, mostly solved Physics at the LHC will be extremely rich SM Higgs (if there) in the pocket Now turning to measurements of couplings, etc. Supersymmetry (if there) ditto Can perform numerous accurate measurements Large com energy: new thresholds Compositeness, new bosons, large extra dimensions within reach LHC++? Just need to build machine/experiments. GIF Annecy