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Determination of the Higgs-Fermion Yukawa couplings at future colliders

Determination of the Higgs-Fermion Yukawa couplings at future colliders. Markus Schumacher, Bonn University. Introduction Higgs boson discovery and 1st measurements at LHC Precision measurements at ILC Synergy of LHC and ILC for g t Conclusions.

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Determination of the Higgs-Fermion Yukawa couplings at future colliders

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  1. Determination of the Higgs-Fermion Yukawa couplings at future colliders Markus Schumacher, Bonn University • Introduction • Higgs boson discovery and 1st measurements at LHC • Precision measurements at ILC • Synergy of LHC and ILC for gt • Conclusions WE Heraeus Summer School on Flavour Physics and CP Violation Dresden, 29 August to 7 September

  2. The Higgs Mechanism in the Nut Shell The problem:(for details see lecture by Marek Jezabek) gauge symmetry  no masses for W and Z different reps. for left- a. rightchiral fields  no masses for fermions The „standard“ solution: • new doublet of scalar fields • with appropiately choosen potential V • vacuum spontaneously breaks gauge symmetry • one new particle: the Higgs boson H F =v+H v =247 GeV effective mass terms = friction of particles with omnipresent „Äther“ x gf fermion mf = gfv / sqrt(2) gf is Yukawa coupling Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  3. The Higgs Mechanism in the Nut Shell Higgs Boson couplings: v = (sqrt(2) Gm)-1/2 =247GeV Born level couplings: Fermions gf= mf / v W/Z Bosons: gV= 2 MV / v x H x 2 Loop induced effective couplings: (sensitive to new physics) Photon: gg = gW “+“ gt “+“… Gluon: gg = gt “+“ gb “+“… • one unknown parameter in SM: mass of Higgs boson MH • MH completely determines Higgs phenomenology in SM Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  4. The situation after LEP and from TEVATRON  direct search: MH<114.4 GeV excluded by LEP at 95% CL MH < 186 GeV  from EW fit (EPS05) MSSM: theory Mh <134 GeV (MSUSY=1TeV, mtop =175 GeV) LEP Mh<92.9 GeV MA<93.4 excluded at 95% CL Today: only discuss SM like Higgs boson with mass below 200 GeV Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  5. Higgs Boson Decays in SM bb WW ZZ tt cc tt gg gg HDECAY: Djouadi, Spira et al. for M<135 GeV: H bb, tt dominant for M>135 GeV: H WW, ZZ dominant channels which can be identified and observed: LHC: WW,ZZ,gg bb,tt ILC: WW,ZZ,gg,Zg bb,tt, cc udsg (mm) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  6. Higgs Physics at Future Colliders • discovery at LHC (SM like or at least one in MSSM) • investigation of Higgs boson profile start at LHC and continue with higher precision at ILC • mass (LHC, ILC) • quantum numbers: spin and CP (LHC, ILC dep. on MH) • BRs, total width, couplings • self coupling (non vanishing at SLHC?, meas. only at ILC) • future colliders: • LHC: pp collisions at 14 TeV start in 2007 • ILC: e+e- collisions between 90 and 800++ GEV start in 201x? Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  7. Why and how to access the couplings ? Why ? precision test of the hopefully discovered Higgs sector  look for deviations from SM prediction  hint towards new physics (SUSY, ED, Little H, TC) How ? • Higgs couplings enter production and decay sHx = const x GHxBR(Hyy) = GHy / Gtot 2 partial width:GHz ~ gHz • experiment measures rate: rate = Nsig+NBG Nsig=L x efficiency x sHx x BR  need to know: luminosity, efficiency, background prod decay GHX GHy sHx x BR ~ Gtot • tasks: disentangle contribution from production and decay • determine Gtot (Gtot << mass resolution for MH <200 GeV) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  8. pp collider /LHC and e+e- collider / ILC collision of composed particles with unknown energy ECM< 2 Ebeam high energies easily achievable quantum numbers of hard process not known, only PT=0 production via strong interaction  QCD uncertainty, PDF uncertainty complex final states, overlaping events, huge background sophisticated trigger needed purely hadronic final states can hardly be triggered and selected Higgs: need identification of decay for observation very high radiation level best suited for discoveries (energy frontier) and first measurements collision of pointlike particle with known energy ECM = 2 Ebeam high enery difficult to achieve well defined quantum numbers and four momentum of initial state production via el.-weak interaction  smaller theo. uncertainties “simple” final states, “moderate” background no trigger needed purely hadronic final states selectable and reconstructable Higgs: decay mode independent observation moderate radiation exposure suited for discoveries and precision measurements hadron and lepton collider are complementary !! Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  9. Comparison of cross sections ILC: Higgs 120 GeV S/B >= 10-2 LHC: Higgs 150 GeV S/B <= 10-10 Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  10. LHC pp collisions ECM = 14 TeV start: 2007 Dtbunch = 25 ns Luminosity: first years: L= 12 1033/(cm2s)  >10 fb-1 / year later: L= 1034/(cm2s)  100 fb-1 / year ~23 overlaying minimum bias events Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  11. Production of the SM Higgs Boson at LHC K = sNLO / sLO K~2.0 K~1.2 K~1.1 K~1.3 Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  12. Two multipurpose detectors at LHC: ATLAS and CMS CMS ATLAS euds = 0.005 detectors optimised for discovery of low mass Higgs boson • pixel vertex a. strip tracking detectors  b and t tagging (Htt, bb) • homogenous calorimeters up to h ~ 5 e/g meas. (Hgg,H4 lept.) (pseudorapidtiy h = -ln tanq/2)  forward jet tagging (VBF)  missing energy (Htt, Hinv.) • complex myon spectrometers  mmomentum accuracy and eff. trigger (HZZ4 m, A/Hmm) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  13. Discovery Potential for light SM Higgs boson • discovery channels: • GGF: H  gg • GGF: H  ZZ  4l+- • GGF: H WW2(ln) • tth: H  bb • VBF: H  tt • VBF: H  WW Excluded by LEP need identification of Higgs boson decay mode for observation !!! • need photon, lepton or missing energy for trigger a. background supp. • no sensitivity for fully hadronic final states • signal processes with largest rate not useable e.g. GGF with Hbb discovery with 10fb-1 for masses between LEP exclusion and 1 TeV Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  14. Gluon Fusion: H  gg and H ZZ 4 leptons 100 fb-1 MH=130GeV H  gg:signature two high Ptg • irreducible BG: ppgg +x • mass resolution sM: ~1% • precise background estimate from sidebands ~ 0.1% K=1.6 Events / GeV S/BG ~ 1/20 sM: ~1GeV HZZ4 leptons: • 4 high pt leptons • narrow mass peak, small and flat background • irreducible BG: ZZ reducible BG: tt, Zbb • rejection via lepton isolation and b-veto • mass resolution sM: ~1% Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  15. ttH with Hbb signature: 1 lepton, missing energy, 6 jets of which 4 b-tagged mbb ~ mH • reducible BG: tt+jets,W+jets  b-tagging • irreducible BG: ttbb  reconstruct mass peak • exp. issue: full reconstruction of ttH final state  b-tagging + jet/missing energy performance • understanding of whole detector needed ! 30 fb-1 • mass resolution sM: ~ 15% • difficult background estimate from • data foreseen, uncertainty ~ O(10%) S/BG ~ 1/6 only channel to see Hbb Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  16. Vector Boson Fusion Higgs Decay Forward tagging jets Jet f h Jet • signature: - 2 forward jets with large Dh • - only Higgs decay products • in central part of detector • exp. issues: - forward jet reconstruction - jet-veto fake rate due to pile up - missing energy resolution • only studied for low luminosity running results for 30 fb-1 • decay modes: H  WW  l l n n and l n j j • H  tt  l l n n n n and l n n had n Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  17. Vector Boson Fusion HWWe MH=120 GeV MH=160 GeV Httem 10 fb-1 ATLAS ATLAS 30 fb-1 • S/BG ~ 1 to 2 / 1 • background: Zjj • mass resolution ~ 10% • BG uncertainty ~ 5 to 10% • S/BG ~ 3.5/1 • background: tt • no mass peak  transverse mass • BG uncertainty ~ 10 % only channel to see Htt Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  18. Measurement of Higgs Boson Mass • Direct from mass peak: HggHbbHZZ4l • “Indirect”from Likelihood fit to transverse mass spectrum: HWWlnln WHWWWlnlnln • Uncertainties considered: i) statistical ii) absolute energy scale 0.1% (goal: 0.02%) for l,g 1% for jets iii) 5% on BG and signal rates for HWW channels ATLAS • No theoretical errors considered: • effect of PDF <<10 MeV DM/M: 0.1% to 1% VBF with Htt or WW not studied yet Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  19. Strategy of Coupling Determination at LHC • assumption:CP-even, Spin=0 (several mass degenerate states fine)  only measurement of rates • only one Higgs boson  ratios of BRs = ratios of partial decay widths = ratios of squared couplings, if only Born level couplings involved Direct: VBF old study, Zeppenfeld et al. Indirect: e.g. • further theoretical assumptions needed in order to constrain Gtot  measurement of couplings Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  20. Overview of 13 Channels used in new ATLAS Study * only studied for low lumi running, L= 30fb-1 Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  21. CP even Spin 0: Measurement of Rates Simultaneous fit of signal rates s x BR in all 13 channels • Takes into account: • cross talk between channels (e.g. GF events selected in VBF analysis) • statistical fluctuations • detector effects: D Lumi, D eff. tau, b-, forward jet tagging, g and e • background estimates: sidebands + shape + theoretical prediction • uncertainties to signal rate from PDFs and QCD corrections Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  22. One CP even Higgs Boson: Ratio of Partial Widths 9 fit parameters: all rates can be expressed by those 9 parameters H WW chosen as reference as best measured for MH>120 GeV For 30fb-1 worse by factor 1.5 to 2 Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  23. Total Decay Width GH • for MH>200 GeV, Gtot>1GeV  measurement from peak width in ZZ4 l • for MH<200 GeV, Gtot<< mass resolution  no direct determination  have to use indirect constraints onGtot • lower limit from rate measurements: Gtot > GW+GZ+Gt+Gg+.... • upper limit needs input from theory: mild assumption: gV<gVSM valid in models with only Higgs doublets and singlets rate(VBF, HWW) ~ GV2 / Gtot < (GV2 in SM)/ Gtot  Gtot< rate/(GV2 in SM) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  24. Fit of couplings with gV < gVSM constraint 8 fit parameters: • Ginvfor undetactable decays e.g. c, gluons,new • coupling to W, Z, t, b, t • Gphoton (new), Ggluon (new): non SM contribution to loops Dg/g = ½ D(g2)/g2 Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  25. ILC Superconducting cavities ECM:90 GeV bis 800++ GeV Lumi.: 3.4 to 5 x 1034cm-2s-1 (6000xLEP) L = 500 fb-1 @ 500 GeV ~ 2 to 3 years L = 1000 fb-1 @ 800 GeV ~ 3 to 4 years Polarisation: 80% electrons, 60% positrons 5 Bunch Trains/s Dtbunch=337 ns No hardware trigger  deadtime free contineous readout for bunch train Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  26. SM Higgs Boson Production at ILC Higgs-Strahlung WW-Fusion 17 Higgs events per hour ECM=500 GeV, MH=120 GeV  Higgs factory e+e-  qq 330/h e+e- WW 930/h e+e-  tt 70/h Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  27. Strategy for e+e- collider • decay mode independent observation in Higgs-Strahlung • from recoil mass spectrum model independent determination of mass, Spin, CP and coupling to Z boson gHZ • rate measurement in Higgs Strahlung with Hxx: gHZ x BR(Hxx)  branching ratios BR(Hxx) • indirect but model independent determination of total width Gtot • BR(Hxx) + Gtot  partial width Gx  coupling gHx • Yukawa coupling from rate in ttH associated production 2 need: accelerator with luminosity  ILC highly performing detector Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  28. Performance Requirements • Momentum: Higgs mass,… d(1/p) = 7 x 10-5/GeV (1/10xLEP 1/7xLHC) • Impact parameter :Yukawa couplings dd=5Å10/p(GeV)mm (1/3xSLD, 1/2,1/5LHC) • Jet energy:Higgs selfcoupling, ttH dE/E = 0.3/ÖE(GeV) (<1/2xLEP 2/3xLHC) • reconstruction of complex multi jet final states (even 8 or more) • hermeticity down to small angles q = 5 mrad • time structure of collisions and background vom beamstrahlung  read out speed / granularity • radiation hardness (almost) no problem compared to LHC 1st layer of vertex detector: 109 n/cm2/yr at TESLA = 0.00001LHC Design determined by precision physics, not by radiation hardness or event rate !!! Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  29. Detector Concept (TESLA/Large Detector) • tracking system and both calorimeters inside coil • magnetic field B = 4 Tesla • large gaseous central tracking device • precision vertex detector • instrumented mask for background shielding • no hardware trigger • different bunch separation / background level w.r.t to LHC  other technology options possible at ILC e.g. gaseous tracking • all silicium tracking also studied for ILC Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  30. Why d(1/p) = 7 x 10-5/GeV?  Higgs mass meas. Higgs-Strahlung independent of H decay  model independent recoil mass to ll:  MH, sZH, gZZH, Spin • e+e-gZgZHgll X precise measurement of lepton momenta goal: dMmm <0.1x GZad(1/p) < 7x10-5/GeV befficient supression of background good resolution for recoil mass c Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  31. Tracking System Barrel region: Pixel vertex detector (VTX) Silicon strip tracker (SIT) Time projection chamber (TPC) Forward region:Silicon Disks (FTD) Forward Tracking Chambers (FCH) (e.g. Strawtubes, Si strips) E and B field Momentum resolution: TPC only: d(1/p) = 2.0 x 10-4 /GeV (1/6 x LEP) TPC+VTX: d(1/p) = 0.7 x 10-4 /GeV (1/9 x LEP) TPC+VTX+SIT: d(1/p) = 0.5 x 10-4 /GeV (below the goal) Efficient and robust track reconstruction, seperately in TPC: 200 space point + VTX+SIT: 7 space points global track finding: e=98.4% (including background) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  32. Mass and Coupling to the Z Boson decay mode independent selection of ZH with Z mm or ee fit to spectrum of the recoil mass to leptons 500fb-1 peak position peak height Ds ~ 5 bis 6% Dm ~ 100 MeV sZH ~ gZH2model independent determination of gZH DgZH/gZH~ 2-3% Dm ~ 40 bis 80 MeV with complete reconstruction of the Higgs decay Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  33. Why dd=5Å10/p(GeV)mm?  Higgs Yukawa Couplings do . goal: determination of BR(Hbb, cc, light q+g) with O(%) precision • efficient ID of b,c and light jets • reconstruction of secondary vtx. with all tracks a M, l/sl , Q M Secundary vtx. l/sl l ~ 8 mm IP sd= a Åb/p(GeV) goal: 5mm 10mm LHC: 12mm 57mm Precise measurement of impact par.do IP sd=aÅb/p b: 300 mm „state of the art“ c,t: 75 mm „challenging“ <p> = 1 bis 2 GeV Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  34. Vertex detector: concept and expected performance M e.g. vertex mass l/sl • 5 pixel layers • R1 = 15 mm (1/2SLD, 1/4LEP,1/3LHC) • pixel size: 20x20mm2,  sPunkt < 3 mm • thin: 0.1 % X0 pro Lage (1/4 SLD) • read out at ladder ends  no hybrid pixels a la LHC Expected resolution: s= 4.2 Å4.0/p(GeV)mm • LEP-c Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  35. Fermionic Branching Ratios • Select ZHqq/ll qq events by kinematic cuts • calculate likelihood for Hbb,cc,gg from precise measurements of tracks at IP • perform fit of MC likelihood distributions to data  event rates data = Hcc Hgg background Hbb Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  36. Higgs Boson Branching Ratios TDR study: two independent measurements of Rel.Error Decay 23% -1 for 500 fb , m=120 GeV alternative approach: measure fraction of Hxx events within an unbiased sample of HZHll events disadvantage: smaller event sample advantage : binomial errors smaller than gaussian errors (one measurement instead of two) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  37. Total Decay Width needed for determination of Yukawa couplings to fermions gf2 ~ Gff = BR(Hff) x Gtot direct determination from peak width • Indirect determination for M < 180 GeV: • Gtot << detector resolution  no info in width of mass peak • Idea: use Gtot = G(Hxx) / BR(Hxx) • best precision: W Boson G(HWW): from measurement of cross section of WW fusion BR(HWW): from Higgs-Strahlung ZH with HWW Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  38. Coupling to W Boson and Total Width b b WW fusion process: • fit to missing mass spectrum: • s~ gw2xBR(Hbb) + meas. of BR(Hbb) in ZH model independent determination of gw DgW/gW ~ 3 to 13% +BR (H>WW) DG/G = 6 to 16 % for MH = 120 to 160 GeV LHC Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  39. Top Quark Yukawa Coupling small cross section and „a lot of mass“ in the final state • large ECM = 800 GeV • high luminosity L = 1 ab-1 challenging analysis (ANN): DgttH/gttH = 7 to 15 % for mH =120 to 200 GeV including 5% systematic uncertainty on BG Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  40. Top Quark Coupling:Synergy of LHC and ILC LHC:measurement of rate stth x BR(Hbb) stth x BR(HWW)  gt x BR(Hxx) 2 x x ILC at ?? x ILC:measurement of branching ratio BR(Hbb) BR(HWW) H x • combination of both measurements • model independent determination of top quark Yukawa coupling Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  41. Determination of gt 2 assume Born level relation: s ~ gt combination of LHC and ILC • synergy of LHC and ILC allows 1st model independent determination of top Yuakwa coupling Dgt ~ 13 to 17 % (7 to 11%) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  42. The Higgs Boson Profile from ILC PDG Booklet 201x ? E. Gross rel. error on Higgs boson couplings expected accuracy: 1 to 5 % 10-3 Dg/g = ½ DG/G !! • Why aim for this precision ? • precise test of the SM • discrimination between SM Higgs sector  extensions or alternatives • (SUSY, ED, Little H, TC, …) Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  43. SM or Extended Higgs Sector e.g. Minimal SUSY ? LHC: discrimination using rate measurements from VBF channels (30fb-1) 300 fb-1 BR(h WW) BR(h tt) R = systematic error from lumi, PDFs, QCD in production cancel compare expected measurement of R in MSSM with prediction from SM for same value of MH • assume Higgs mass well measured • no systematic errors considered Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  44. SM or Extended Higgs Sector ? similar study by Duehrssen et al.: VBF dominates discrimination ILC 300 fb-1 ATLAS prel. D=|RMSSM-RSM|/sexp c2 comparison of all couplings discrimination from profile measurements at 2s level observation of additional Higgs bosons at LHC and ILC500/800 Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

  45. Summary LHC: discovery over full mass range 110 to 1000 GeV 1st measurements e.g.: mass ~ 0.1%, CP, Spin ratios of partial width: W/Z, W/t, W/t, W/b ~10 to 60 % absolute couplings only with further theoretical input D = 5 to 45% depending on mass and particle ILC: decay mode independent observation mass, CP, Spin mass determination: ~ 0.04 % total width determinable w/o theoretical assumptions  absolute couplings (also 2nd generation) D =1 to 5 % LHC+ILC: 1st model independent determination of top quark coupling from synergy of data: ~15% Let’s hope for unexpected deviations from the SM at LHC and ILC and also other collider and non collider experiments! Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005

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