1. Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006

2. 2 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Outline the Higgs Mechanism and SM Higgs phenomenology at LHC discovery of 1 neutral scalar SM like Higgs boson (determination of mass, spin, CP) quantum numbers: spin and CP BRs, total width, couplings self coupling at SLHC direct observation of additional Higgs bosons determination of Higgs profile: deviations from SM prediction - > 1 neutral Higgs boson - charged Higgs boson - exotic decays:H invisible Higgs physics program at the LHC discrimination: SM or extended Higgs sectors (e.g. MSSM)

3. 3 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 The Higgs Mechanism in the Nut Shell consistent description of nature seems to be based on gauge symmetry SU(2) L xU(1) gauge symmetry no masses for W and Z and fermions ad hoc mass terms spoil The problem: The standard solution: new doublet of complex scalar fields with appropiately choosen potential V vacuum spontaneously breaks gauge symmetry one new particle: the Higgs boson H = v + H renormalisibility no precise calculation of observables bad high energy behaviour W L W L scattering violates unitarity at E CM ~1.2 TeV Higgs boson mass unknown: theory: unitarity M H <1TeV LEP search: M H <114.4 GeV electroweak fit: M H <186 GeV excluded at 95% CL at 95%CL

4. 4 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Mass generation and Higgs couplings: = v + H effective mass = friction of particles with omnipresent Äther v =247 GeV x fermion gfgf m f ~ g f v Yukawa coupling M V ~ g v gauge coupling x x W/Z boson g gauge Interaction of particles with v=247 GeV Fermions g f ~ m f / v W/Z Bosons: g V ~ 2 M V / v Interaction of particles with Higgs H fermion gfgf x W/Z boson g gauge Higgs v 2 2 VVH coupling ~ vev only present after EWSB breaking !!! unknown Higgs mass fixes Higgs profile completely

5. 5 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 bW ZZ tt cc gg Higgs Boson Decays in SM for M<135 GeV: H bb, dominant for M>135 GeV: H WW, ZZ dominant tiny: H also important HDECAY: Djouadi, Spira et al.

6. 6 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 LHC SPPS pp collisions at the Large Hadron Collider start in 2007 at E CM of 14 TeV first years: low lumi running 10 fb -1 /year later (x10): high lumi running 100 fb -1 /year

7. 7 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Complexity of a LHC event + ~23 additional pp-interactions per bunch crossing at high lumi ~10 9 proton-proton collisions / sec ~1600 charged particles in detector per event hard process + ISR,FSR + underlying event

8. 8 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 The challenge of reconstruction low lumi. high lumi.

9. 9 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Production of the SM Higgs Boson at LHC K = (N)NLO / LO K ~ 1.2 K ~ 2 K ~ 1.4 K ~ 1.1 ~4 to 15% + from PDF (5 to15%) signal MC at NLO only avaiable for GGF background: NLO calculations often not avaiable ATLAS: use K=1 and LO MC for signal and BG CMS:K-factor for GGF + guestimated K for BG

10. 10 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Cross sections for background processes Higgs 150 GeV: S/B <= 10 -10 overwhelming background trigger: 10 -7 reduction on leptons, photons, missing E p p q q q pp q q q q H WW l l background: mainly QCD driven signal: often electroweak interaction photons, leptons, … q

11. 11 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Considerations for Discovery Channels sufficient signal rate no sensitivity to H in SM efficient trigger (,e,, …) no sensitivity for: GGF, WBF: H bb H mass reconstructable? yes: H, ZZ, bb, no: H WW control of background - signal-to-background ratio - estimate of BG from data possible? - sometimes: shape from MC needed excluded by LEP main discovery channels GGF: H GGF: H ZZ 4l +- GGF: H WW 2(l) ttH: H bb VBF: H VBF: H WW ATLAS since 2000

12. 12 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 H 2 Photons signal: two photons background: - reducible: pp j+x, jj+x,.. photon vs. jet seperation - irreducible: pp+X diphoton mass mass resolution M /M = 0.7% - uniformity/understanding of ECAL - dead material: % of unconverted - pile up: vtx constraint background estimate from sidebands no Monte Carlo needed exp. uncertainty: O(0.1%) S/BG ~ 1/10 CMS 100fb -1 red./irred. BG: 2 to 1 after final cut LO NLO: increase of S/ B ~ 50 60% (K-factor ~ 2, larger Higgs P t ) NLO CMS

13. 13 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 H ZZ (*) 4 Leptons reducible BG: tt, Zbb 4 leptons lepton isolation and veto against b-jets good mass resolution M : <~1% muon spectrometer + tracking detectors small and flat background easy estimate from sidebands no Monte Carlo needed CMS 100fb -1 NLO signal: 4 iso. leptons 1(2) dilepton mass = M Z irreducible BG: ZZ 4 leptons four lepton mass

14. 14 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 signal: - 2 leptons + missing E T - lepton spin corrleations - no mass peak transverse mass H WW l l ATLAS M=160GeV 30fb -1 transverse mass BG: WW, WZ, tt lepton iso., missing E resolution jet (b-jet) veto against tt BG estimate in data from ll normalisation rom sideband shape from MC NLO effect on spin corr. gg WW contribution signal like Dührssen, prel. ll

15. 15 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Vector Boson Fusion: pp qqH signature: 2 forward jets with large rapidity gap only Higgs decay products in central part of detector rapidity of tag jets rapidity difference

16. 16 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Vector Boson Fusion: pp qqH

17. 17 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Vector Boson Fusion: challenges p T >20GeV forward jet reconstruction influence of UE and pile up? so far only for low lumi ATLAS central jet veto: influence of UE and pile up? so far only for low lumi efficiency of jet veto at NLO.? distributions at NLO calculated but: need NLO MC generator for signal and BG Zeppenfeld et al.

18. 18 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Vector Boson Fusion: H tau tau ll 4 (or l had 3 ) signature: tagging jets + 2 high p t leptons + large missing E T backgrounds: tt,Zjj central jet veto reconstruction of m mass resolution ~ 10% dominated bei E miss resolution H e ATLAS 30 fb -1 expected BG uncertainty ~ 5 to 10% for M H > 125 GeV: flat sideband for M H < 125 normalisation from Z peak, but shape? collinear approximation

19. 19 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Idea: jjZandjjZ look almost the same, esp. in calos same missing energy only momenta different Method: select Z events randomise momenta apply normal mass reco. Vector Boson Fusion, Hestimate of BG shape from data PT miss,final (GeV)M (GeV) promising prel. results from ongoing diploma thesis in BN (M. Schmitz)

20. 20 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Weak Boson Fusion: H WW ll (lqq) H WW e ATLAS 10 fb -1 M H =160 GeV H 2 photons S/BG ~ 1/1 S/BG ~1/10 VBF versus inclusive channel ATLAS M=160GeV 30fb -1 H WW ll S/BG ~ 4/1 S/BG ~ 2/3 smaller rate larger sig-to-BG ratio smaller K-factor more challenging for detector understanding order of significance depends on channel and Higgs mass CMS

21. 21 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Discovery Potential for light SM Higgs boson excluded by LEP for GGF: raise of significance by ~ 50% from LO to NLO results for cut based analysis improvement by multivariate methods discovery from LEP exclusion until 1 TeV from combination of search channels with 15 fb -1 of well understood data with individual search channels with 30 fb -1 of well understood data

22. 22 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Measurement of Higgs Boson Mass ATLAS M/M: 0.1% to 1% Uncertainties considered: Indirect from Likelihood fit to transverse mass spectrum: H WW ll WH WWW lll Direct from mass peak: HH bb H ZZ 4l VBF with H or WW not studied yet ! i) statistical ii) absolute energy scale 0.1 (0.02) % for l,,1% for jets iii) 5% on BG + signal for H WW

23. 23 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Determination of Higgs boson couplings couplings in production Hx = const x Hx and decay BR(H yy) = Hy / tot Hx x BR ~ HX Hy tot prod decay partial width: Hz ~ g Hz 2 tasks: - disentangle contribution from production and decay - determine tot H WW chosen as reference as best measured for M H >120 GeV for 30fb -1 worse by factor 1.5 to 2 model independent: only ratio or partial decay widths 13 signal rates used in global fit (incl. various syst. uncertainties)

24. 24 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 for M H <200 GeV, tot <<mass resolution no direct determination have to use indirect constraints on tot Absolute couplings with g V < g V SM constraint coupling to W, Z,, b, t Dührssen et al. lower limit from observable rates: tot > W + Z + t + g +.... upper limit needs input from theory: mild assumption: g V <g V SM rate(VBF,H WW)~ V 2 / tot <( V 2 in SM )/ tot tot < rate/( V 2 in SM)

25. 25 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 M H 2 = 2 =M Planck Motivation for Supersymmetry from Higgs Sector Higgs mass problem in SM: 2 solves hierarchy problem: why v=246 GeV << M Pl =10 19 GeV ? M H 2 = (M SM- M SUSY ) 22 WW + H H natural value ~ M Pl vs electroweak fit M H ~O(100GeV) SUSY solution: - partner with spin difference by ½ cancel divergence exactly if same M - SUSY broken in nature, but hierarchy still fine if M SUSY ~1 TeV H H - SUSY breaking in MSSM: parametrised by 105 additional parameters too many constrained MSSM with O(5) additional parameters

26. 26 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 The MSSM Higgs sector in a tiny Nut Shell SUSY: 2 Higgs doublets 5 physical bosons real MSSM: 2 CP even h, H, 1 CP odd A, charged H +, H - at Born level 2 parameters: tan, m A m h < M Z large corrections: m h < 133 GeV for m top =175 GeV, M SUSY =1TeV corrections depend on 5 SUSY parameters: X t, M 0, M 2, M gluino, fixed in the benchmark scenarios e.g. MHMAX scenario maximal M h conservative LEP exclusion M top =174.3 GeV main questions for LHC: at least 1 Higgs boson observable in the entire parameter space? how many Higgs bosons can be observed? can the SM be discriminated from extended Higgs sectors? calculated with FeynHiggs

27. 27 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Light Higgs Boson h large area covered by many channels sure discovery and parameter determination possible small area uncovered @ m h ~95 GeV 300 fb -1 30 fb -1 VBF dominates observation small area from bbh,h for small M h ATLAS preliminary VBF, H covers hole plane from either H or h observation with 30fb -1

28. 28 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Overall Discovery Potential: 300 fb -1 at least one Higgs boson observable for all parameters in all CPC benchmark scenarios significant area where only lightest Higgs boson h is observable can H SUSY decays or Higgs from SUSY decays provide observation? discrimination via h profile determination? similar results in other benchmark scenarios VBF channels, H/Aonly used with 30fb -1 300 fb -1 ATLAS preliminary

29. 29 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Higgs Decays to Gauginos M sleptons =250 GeV e.g. H 0 2 0 2 0 1 0 1 0 +4l dominant background from SUSY results for most optimistic scenarios shown fine tuned require small slepton masses for large BR( 2 1 +2 leptons ) reduced sensitivity for other channels, consistent interpretation needed CMS 100fb -1

30. 30 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 ATLAS prel. 300 fb -1 SM or Extended Higgs Sector e.g. Minimal SUSY ? discrimination via rates from VBF R = BR(h WW) BR(h ) assume Higgs mass well measured no systematic errors considered same contribution from GGF compare expected measurement of R in MSSM with prediction from SM for same value of M H =|R MSSM -R SM | exp

31. 31 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 CP-Violating MSSM: Overall Discovery Potential M H1 : < 70 GeV M H2 : 105 to 120 GeV M H3 : 140 to 180 GeV small masses below 70 GeV not yet studied in ATLAS 300 fb -1 yet uncovered area size and location of hole depends on M top and program for calculation ATLAS preliminary at Born level: CP symmetry conserved in Higgs sector complex SUSY parameters mixing between neutral CP eigenstates no absolute mass limit from LEP

32. 32 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 Conclusion and Outlook Standard model: discovery of SM Higgs boson with 15 fb -1 requires good understanding of whole detector multiple channels with larger luminosity Higgs profile investigaton CP conserving MSSM: at least one Higgs boson observable only h observable in wedge area at intermediate tan maybe Higgs to SUSY or SUSY to Higgs observable? discrimination via Higgs parameter determination seems promising CP violating MSSM: probably a hole with current MC studies promising MC studies on the way see 2nd next talk more realistic MC studies: influence of miscalibrated and misaligned detector improved methods for background estimation from data use of NLO calcluations and MCs for signal and background additional extended models + seach channels: CPV MSSM, NMSSM, 2HDM Higgs SUSY, SUSY Higgs VBF, H bb (b-trigger at LV2), VBF,H inv. (add. forward jet trigger)