1. ATLAS Physics Potential II Borut Kersevan Jozef Stefan Inst. Univ. of Ljubljana ATLAS Physics Potential: Standard Model Higgs & Susy BSM: Susy & Exotics On behalf of the ATLAS collaboration

2. 2 The experimental observation of one (or several) Higgs bosons will be fundamental to understand the mechanism of electroweak symmetry-breaking and may probe physics beyond the SM.. LHC offers the potential for such a discovery. There is a very rich variety of search channels for the discovery of the SM Higgs and even more for the non-SM Higgs bosons. An overview of the most relevant channels will be given. It must be stated from the beginning that the “all hadronic” states are impossible to separate from the background and very difficult to be triggered. Very good understanding of the detector is mandatory ! Main points

3. 3 SM Higgs Searches (benchmark analyses) H  ZZ* H  WW* H  Vector Boson Fusion ttH(H  bb) Additional MSSM Higgs Searches Example: H/A  τ + τ -, H/A  μ + μ - Higgs properties Mass, couplings, … Other scenaria: Little Higgs Higgs@LHC

4. 4 SM Higgs at the TeV scale Many theoretical arguments predict a Higgs mass at the TeV scale: WW scattering violates unitarity if only Z/  are exchanged  For Higgs to be able to restore it at any s: G F m 2 H ~< O(1) Triviality bound:  Scalar sector is a  4 theory  Energy cut off  C where SM is not trivial   C ~10 16(3) GeV  m H <200(1000) GeV Vacuum stability bound:  Fermionic contributions could lead to negative self coupling for too small  Vacuum not a minimum anymore   C ~10 3(16) GeV  m H > 70 (130) GeV

5. 5 Current SM Higgs Limits LEP direct search m H >114.4 GeV @95% CL Tevatron Direct search LEP, SLD, Tevatron e/w fit m H <182 GeV

6. 6 Higgs @ LHC: production Gluon Gluon fusion:  Dominant production mode  NLO correction important  K = 1.7  Main contribution is gluon radiation  many events with at least one jet  NNLO cross section known  Sig(NNLO)/Sig(NLO) = 1.3 Vector Boson Fusion:  small K factor ~ 1.1  Small jet multiplicity in final state  No color exchange between quarks  large energetic jets at small p T  Low hadronic activity in central region from hard event  a part from Higgs decay Production with Gauge boson:  Known NNLO for QCD and EW corrections Production with heavy quarks:  More complicated final state  More than 10 diagrams, known at NLO Typical uncertainties on cross-sections gg 10-20 % (NNLO) VBF ~ 5% (NLO) WH,ZH ~< 5% (NNLO) ttH 10-20 % (NLO) (A.Djouadi) q q g g H g g t t H H q q W W H

7. 7 Higgs decay channels Uncertainties on branching ratios: few % (NLO) Inclusive search channels: H → ZZ for m H ≥ 130 GeV → 4 l H → WW for m H ≥ 145 GeV → lνlν H → γγ for m H ≤ 150 GeV Exclusive search channels: VBF H → WW for m H ≥ 115 GeV VBF H → ττ for m H ≤ 150 GeV ttH, H → bb for m H ≤ 135 GeV

8. 8 SM Higgs Search H → ZZ(ZZ*) → l + l - l + l - ZZ(*) → 4l is very clean (also → lljj, llνν are studied) All H decay products are reconstructed Very sensitive for m H >130 GeV Golden channel for m H >2m Z Signature: two opposite sign pair of leptons coming from the primary vertex compatible with Z mass (at least 1 couple) ATLAS Exploits the excellent e/μ identification and momentum resolution of the detectors σ=1.4 GeV

9. 9 Irreducible Background: continuum ZZ(*) → 4 leptons Reducible Backgrounds: Zbb  4 leptons tt  4 leptons suppressed by impact parameter and isolation criteria gg->ZZ is added as 20% of LO qq->ZZ ZZ NLO k factor depends on m 4l Background control: a) from side bands b) from ZZ  4l / Z  2l Discovery with less than 10 fb -1 130<m H <160 GeV, 2m Z < m H < 550 GeV SM Higgs Search H → ZZ(ZZ*) → l + l - l + l -

10. 10 SM Higgs Search H → WW → l + νl - ν Important channel for 2m W <m H <2m Z H  WW BR ~ 95% Exclusive VBF also sensitive in lower mass regions Inclusive H  WW Using dilepton final state Signature l + l - and MET no mass peak, have to use transverse mass l + l - E Tmis need to determine shape of background Leptons anti-correlated W+, W- opposite spin Leptons tend to be close

11. 11 Backgrounds: tt, tWb : rejected by vetoing the jets WW,WZ,ZZ: rejected by kinematical cuts i.e. - ETmiss > 50 GeV - jet veto in  < 2.5 - 30 <pT max <55 GeV - pT min > 25 GeV - 12 < m ll < 40 GeV Background Control a) Invert cut on l + l - proximity b) Create control samples for tt,WW,WZ For 1,2 and 10 fb-1 syst err ~19,16 and 11% Discovery may happen within ~1fb -1 SM Higgs Search H → WW → l + νl - ν

12. 12 SM Higgs Search H → γγ With H  BR  10 -3 only: Still, very important in the mass range m H ≤ 150 GeV Requires good energy resolution of the EM calo Signature: 2 isolated high Et gammas from PV Need of excellent energy resolution Irreducible Background: Continuum gamma-gamma Reducible Backgrounds: jet-jet and gamma-jet events Need of Excellent jet rejection factor (> 10 3 for 80%  efficiency) good π 0 rejection 5000 Jet rejection 80 % γ efficiency σ=1.36 GeV Mass γγ

13. 13 Event Selection Kinematical cuts p T 1 >40 GeV, p T 2 >25 GeV, |  |<2.5 Photon identification cuts Photon reconstruction and calibration Photons direction corrected for PV resbos ATLAS Improve the discovery potential using the shape of kinematical variables Likelihood ratio method based on kinematical variables of signal and background SM Higgs Search H → γγ

14. 14 ATLAS Significance change LO -> NLO Carminati L., Physics at LHC 2006 SM Higgs Search H → γγ Impact of kinematical variables not shown in this plot

15. 15 SM Higgs search VBF with H → ττ and H → WW At low Higgs masses the largest sensitivity search channels are found in the vector boson fusion production mode. The two jet of the quarks are energetic and distributed in the forward region. The Higgs decay products in between.. Signature: two tag jets in the forward region One of the W or τ decay leptonicaly Irreducible Background qq Z/W Reducible backgrounds QCD multi-jet, W+jet, Z+jet, g+jet and tt

16. 16 Significant background suppression by Two tag jets in forward region sn-atlas-2003-024 SM Higgs search VBF with H → ττ and H → WW Forward tagging jets: energetic jets at high  No color flow between initial partons No jet radiation Central Jet Veto

17. 17 SM Higgs search VBF with H → WW m H =120 GeV m H =160 GeV Signal to background with VBF increases by a factor >3

18. 18 SM Higgs search VBF with H → ττ Backgrounds : QCD ττ +jets, EW ττ +jets, W+jets, tt Selection: VBF tag jets τ selection ΜΕΤ reconstruction, Kinematical cuts Background Control Side bands Relaxed cuts ττ → lνν+jν ATLAS ττ → eνν+μνν PRELIMINARY

19. 19 SM Higgs search ttH (H → bb) → lνbbbbjj Signature 4b-jets + lepton + 2 jets +MET Irreducible background: Non resonant ttbb Reducible backgrounds: ttZ, ttjj, WWjj Event Selection: Reconstruction of at least 6 jets B-tagging of exactly 4 jets Kinematical cuts Invariant Mass of bb from H Use of Likelihood functions To associate bs from t decays To discriminate ttbb bkg Very challenging channel Significant for very low Higgs masses Difficult to control the background with the use of the data m H = 120 GeV, L = 30 fb -1 S/  B = 2.8, with LO

20. 20 ATLAS Summary for the the SM Higgs discovery ATLAS uses LO cross-sections in the plot, NLO cross sections ‘in reserve’ ATLAS new sensitivity study is ongoing.. PRELIMINARY

21. 21 F.Gianotti, ICHEP06 5σ discovery over all allowed mass range with ≤ 5 fb -1 More than one channel must be combined for early discovery at low masses (~ 115 GeV) LHC Summary for the the SM Higgs discovery

22. 22 large loop corrections to masses and couplings mainly dependent on t/ t sector parameters: M top and X t, M SUSY, M 2, , M gluino mass prediction M h < 133 GeV (for M t = 175GeV) large loop corrections to masses and couplings mainly dependent on t/ t sector parameters: M top and X t, M SUSY, M 2, , M gluino mass prediction M h < 133 GeV (for M t = 175GeV) MSSM Higgs Sector  MSSM: 2 Higgs doublets  5 physical bosons: h, H, A, H +, H -  phenomenology at Born level described by tan , m A  mass prediction: M h < M Z  couplings: g MSSM = ξ · g SM  no coupling of A to W/Z  large tan  large BR(h,H,A  ,bb)  MSSM: 2 Higgs doublets  5 physical bosons: h, H, A, H +, H -  phenomenology at Born level described by tan , m A  mass prediction: M h < M Z  couplings: g MSSM = ξ · g SM  no coupling of A to W/Z  large tan  large BR(h,H,A  ,bb) ξtb/  W/Z hcos  /sin  -sin  /cos  sin(  -  ) Hsin  /sin  cos  /cos  cos(  -  ) Acot  tan  -----  : mixing angle between CP even Higgs bosons (calculable from tan  and M A ) for exclusion bounds and discovery potential: fix the 5 parameters in benchmark scenarios and scan (tan , M A )- plane for exclusion bounds and discovery potential: fix the 5 parameters in benchmark scenarios and scan (tan , M A )- plane ~

23. 23 current exclusion in (tan ,M A )-plane:  LEP excludes low tan  and low M A region  note: no exclusion from LEP for M t larger ~183 GeV current exclusion in (tan ,M A )-plane:  LEP excludes low tan  and low M A region  note: no exclusion from LEP for M t larger ~183 GeV main questions for LHC/ ATLAS:  Can at least 1 Higgs be discovered in the allowed parameter space?  How many Higgs bosons can be observed ?  Can the SM be discriminated from models with extended Higgs sectors (like MSSM) ? main questions for LHC/ ATLAS:  Can at least 1 Higgs be discovered in the allowed parameter space?  How many Higgs bosons can be observed ?  Can the SM be discriminated from models with extended Higgs sectors (like MSSM) ? The (tan , M A )-Plane

24. 24 Benchmark Scenarios 1)MHMAX scenario maximal M h < 133 GeV 2)Nomixing scenario small M h < 116 GeV 3)Gluophobic scenario M h < 119 GeV coupling of h to gluons suppressed designed to affect discovery via gg  h, h   and h  ZZ  4l 4)Small  scenario M h < 123 GeV coupling of h to b (  ) suppressed (for large tan  and M A 150  500GeV) designed to affect discovery via VBF, h   and tth, h  bb 1)MHMAX scenario maximal M h < 133 GeV 2)Nomixing scenario small M h < 116 GeV 3)Gluophobic scenario M h < 119 GeV coupling of h to gluons suppressed designed to affect discovery via gg  h, h   and h  ZZ  4l 4)Small  scenario M h < 123 GeV coupling of h to b (  ) suppressed (for large tan  and M A 150  500GeV) designed to affect discovery via VBF, h   and tth, h  bb 4 CP conserving scenarios considered to examplify the discovery potential mainly influence on phenomenology of h masses, coupling and BRs calculated with FeynHiggs ( Heinemeyer et al. ) NameM SUSY (GeV)  (GeV)M 2 (GeV)X t (GeV)M gluino (GeV) m h -max1000200 2000800 no mixing2000200 0800 gluophobic350300 -750500 small  8002000500-1100500 suggested by Carena et al., EPJ C26, 601(2003) eff. hg - coupling hbb - coupling already at LEP Newly designed for hadron colliders

25. 25 MSSM Higgs Production  Higgs sector of the MSSM: physical states h,H,A,H ±  Described by two parameters at lowest order: M A, tanb  Discovery of extended Higgs sector leads to physics beyond SM At high tan  associated bbH production is greatly enhanced! tan  = 3 MSSM neutral Higgs production tan  =30

26. 26 MSSM Higgs search Channels taken into consideration …and BR to WW,ZZ strongly suppressed

27. 27  most important channels: VBF  differences mainly due to M h almost entire (tan , M A )- plane covered  most important channels: VBF  differences mainly due to M h almost entire (tan , M A )- plane covered Light Higgs Boson (30 fb -1 ) h observable in entire parameter space and for all benchmark scenarios? ATLAS (prel.) See talk of P. Conde for SM Higgs searches with ATLAS

28. 28 hole due to reduced BR for H   Light Higgs in Small a Scenario (30 fb -1 ) Complementarity of search channels almost guarantees the discovery of h Complementarity of search channels almost guarantees the discovery of h ATLAS (prel.) covered by enhanced BR to gauge bosons

29. 29 Light Higgs Boson (300 fb -1 ) VBF: only 30 fb -1 also h  , h  ZZ  4 leptons, tth  bb contribute large area covered by several channels  stable discovery and parameter determination possible small area uncovered (M h = 90 to 100 GeV) also h  , h  ZZ  4 leptons, tth  bb contribute large area covered by several channels  stable discovery and parameter determination possible small area uncovered (M h = 90 to 100 GeV) ATLAS (prel.)

30. 30 rec. mass for   had.had. Neutral Heavy Higgs Bosons (H/A)   prod ~ (tan  ) 2 ; important at large tan   new analysis:   had. had.  BR(H/A   ) ~ 10 %, rest is bb   prod ~ (tan  ) 2 ; important at large tan   new analysis:   had. had.  BR(H/A   ) ~ 10 %, rest is bb  example: bbH/A, H/A    bb H/A  bb  covers large tan  region  other scenarios similar  intermediate tan  region not covered  bb H/A  bb  covers large tan  region  other scenarios similar  intermediate tan  region not covered New: take running b- quark mass for  prod 30fb -1 discovery reach for H/A: ATLAS (prel.) ATLAS (prel.)  only very few events remain after cuts (acceptance ~10 -3 )  LVL1 trigger performance crucial  detailed study: >90% LVL1 efficiency for M A >450GeV via “jet+E T,miss ” and “  + E T,miss ” triggers with a rate of ~1.4 kHz (within rate limit)  only very few events remain after cuts (acceptance ~10 -3 )  LVL1 trigger performance crucial  detailed study: >90% LVL1 efficiency for M A >450GeV via “jet+E T,miss ” and “  + E T,miss ” triggers with a rate of ~1.4 kHz (within rate limit)

31. 31 VBF channels, H/A   only 30fb -1 300 fb -1 Overall Discovery Potential (300 fb -1 ) ATLAS (prel.)  at least one Higgs boson is observable for all parameter points (in all four benchmark scenarios)  in some parts: >1 Higgs bosons observable  distinguish between SM and extended Higgs sector  but: significant area where only h is observable.  basic conclusions independent of m top  at least one Higgs boson is observable for all parameter points (in all four benchmark scenarios)  in some parts: >1 Higgs bosons observable  distinguish between SM and extended Higgs sector  but: significant area where only h is observable.  basic conclusions independent of m top ongoing:  including SUSY decay modes to increase areas for heavy Higgs bosons, e.g. H          3l + E T,miss  can SM be discriminated from extended Higgs sector by parameter determination e.g. via rate measurements? ongoing:  including SUSY decay modes to increase areas for heavy Higgs bosons, e.g. H          3l + E T,miss  can SM be discriminated from extended Higgs sector by parameter determination e.g. via rate measurements?

32. 32 Relatively easy from H  or 4leptons. The channel H  can also contribute at low luminosity  (H) only directly accessible for m>200 GeV Higgs mass measurement HWW no mass peak High mass region: larger Width, weaker statistical power

33. 33  Z polarization  plane angle Atlas-sn-2003-025 Higgs spin, CP Observation of gg  H or H  excludes spin 1 For M H >200 GeV, study spin/CP from H  ZZ  4l Exclusion can be deduced from  and  distributions

34. 34 Concentrate on “low” M H Series of assumption needed: Assume spin 0: allow to use angular distribution on HWW (most precise measure) measure .BR in different channels: .BR = (N S+B - )/L Uncertainties:  Selection efficiencies  Background subtraction  Luminosity Second step: assume only one Higgs boson BR(Hx)/BR(HWW) =  x / W Reduced number of fitted parameters  smaller errors Atlas note phys-2003-030 Couplings

35. 35 Third step, more assumptions: -No new particles in loop -Light mass  H not accessible -Absolute scale not measurable, measure g x /g W Express all rates and BR as a function of 5 couplings:  g W,g Z,g top,g b,g   Examples:  (VBF): a WF.g W 2 +a ZF.g Z 2  BR(): (b 1.g W 2 – b 2.g top 2 )/ H Syst uncertainties from exp+theory Couplings

36. 36 Higgs Parameters – Couplings to Weak Bosons sn-atlas-2007-060 VBF H->WW, H->ττ Δφ jj : azimuthal angle of tag jets Determination of the dominant coupling term Put limits on anomalous couplings

37. 37 SM or extended Higgs Sector ? BR(h  WW) BR(h  )  estimate of sensitivity from rate measurements in VBF channels (30 fb -1 )  only statistical errors  assume M h exactly known potential for discrimination  seems promising  needs further study incl. sys. errors  compare expected measurement of R in MSSM with prediction from SM =|R MSSM -R SM | exp R = ATLAS (prel.) ATLAS (prel.)

38. 38 Charged Higgs Bosons

39. 39 A “Little” Higgs ? Seeks to solve the radiative instability of the SM Higgs sector In the “Little Higgs” model, the massless Higgs is generated (in analogy of the pion in QCD) through SSB of a new symmetry It’s mass is acquired during EWSB. The new symmetry being still approximately valid, the mass is protected and stays small Breaking SU(5) requires at least one heavy, O(TeV), new particle for each particle contributing to the radiative corrections of the Higgs, which cancel the SM corrections By construction: the W ± H, Z H cancel the weak divergence, a new quark T cancels the top- quark divergence, the new Higgs triplet cancels the SM Higgs divergence The new heavy top and gauge bosons decay into their SM partners through associated Higgs production. These and the new Higgs fields could be discovered at ATLAS, studies performed! As new symmetry one could use SU(5), embedding the unified gauge group (SU(2)  U(1)) 2 Breaking SU(5) by a VEV into SO(5) creates 14 “Goldstone” bosons Then, the group (SU(2)  U(1)) 2 is broken into SU(2) L  U(1) Y, where 4 of the 14 Goldstone bosons are used to create massive longitudinal SM gauge fields (W ± H, Z H, A H ) of the broken gauge group Among the remaining Goldstone bosons one finds a complex scalar doublet (SM Higgs), and a scalar triplet with 5 Higgs bosons:  0,  ±,  ±±

40. 40 Two other modes: Z H  Zh  + -  ZZ  + - jj + - W H  Wh   ZZ   jj + - 1.5 TeV 1 TeV 18.6  S= 92 Mass reco. bias: 1% Mass resolution: 4% ~same all modes cot  = 0.5 300 fb -1 9.2  S= 31  S ≈21%  B <1%  S ≈24%  B <1% Z H  Zh  + - WW  + - jj V H decays to Higgs (mh=200 GeV)

41. 41 If the Standard model Higgs boson exists, it cannot escape detection at the LHC. Discovering the Higgs boson is just the first step, the next step is to measure its mass and couplings. Discovery of enhanced Higgs sector directly prompts to physics beyond the SM. … the adventure is about to start Higgs summary