Search for the Higgs Boson at the LHC W. Adam Institut für Hochenergiephysik der ÖAW Micro-summary of the Higgs discovery potential at LHC on the occasion of FAKT-Tagung, Weyer, 26./27. Sep Second “Physics at LHC” conference Emphasis on the physics programme & presentations by young physicists All 5 LHC experiments + theory Organised by HEPHY (LOC: J.Hrubec,G.Mitselmakher, C.-E.Wulz) Held at the main building of the ÖAW ~ 180 participants The talk is based on material shown at PHLHC04 and other summer conferences

FAKT2004Search for the Higgs Boson at the LHC2 SM Higgs: experimental status LEP EWWG, summer ‘04 The situation after LEP: Indirect (full EW fit) Preferred value: m H = GeV (exp. errors only) Limit: m H < %CL Precise values might still change, but message is clear: a light Higgs is favoured by the measurements. Direct (LEP searches) Observed (expected) limit m H > GeV (115.3GeV) preferred value from -2lnQ ~115GeV 129GeV 114GeV

FAKT2004Search for the Higgs Boson at the LHC3 SM Higgs: experimental status News from the Tevatron Signatures:HW  Wbb  (e )/(  )bb, HW  Zbb  (ee/  / )bb(m H <130) gg  H  WW*  (e /  )(e /  )(m H >130)  (WH) x B(H  bb) for m H =115GeV< 12.4 pb (D0, e-channel) < 5 pb (CDF)

FAKT2004Search for the Higgs Boson at the LHC4 SM Higgs: experimental status  xB(H-WW*) for m H =160GeV: < 5.7pb (D0), < 5.6pb (CDF) Available summer ‘04: ~400 pb -1 /exp (recorded) ~200 pb -1 /exp (used) 2009: fb -1

FAKT2004Search for the Higgs Boson at the LHC5 The SM LHC Production: mainly via gluon fusion tt-fusion W,Z fusion: increasingly important at high masses associated production in the low mass region

FAKT2004Search for the Higgs Boson at the LHC6 SM Higgs: low mass Decay: bb dominates, but high multi-jet backgrounds and low mass resolution  : BR low (10 -3 to ) - use small Higgs width and high resolution EM calorimetry Material in front of calorimetry (e.g. CMS: full-Si tracker): will need to complement with reconstruction of converted photons (under study)

FAKT2004Search for the Higgs Boson at the LHC7 SM Higgs: low mass H   signal (CMS, m H =130GeV, 100fb -1 ) ATL-PHYS H  bb much more challenging: use tt-fusion and top decay products

FAKT2004Search for the Higgs Boson at the LHC8 SM Higgs: production via VBF Contributes ~10% at low masses, dominates at very high masses Special topology allows for easy tagging: Forward jets Central Higgs decay products Low mass analysis decay channels: WW*,  and  Taus: need trigger (leptons and narrow jets) and offline enhancement (  -lifetime  tracking) Contribution of VBF analysis to total significance

FAKT2004Search for the Higgs Boson at the LHC9 SM Higgs: intermediate mass Decay modes to WW and ZZ become important

FAKT2004Search for the Higgs Boson at the LHC10 SM Higgs: intermediate mass H  WW  ll’X strong background from top decays need to use WW spin correlation veto on central jets tt-background: 1 st jet pt vs.  For m H =170±10GeV: 10 fb -1 are sufficient for discovery pTpT 

FAKT2004Search for the Higgs Boson at the LHC11 SM Higgs: intermediate to high mass The “easy” region: high probability for decays to ZZ (*)

FAKT2004Search for the Higgs Boson at the LHC12 SM Higgs: intermediate to high mass Golden channel H  ZZ  4  high energy muons Z mass constraint(s) irreducible background: ZZ production H  4 , CMS preliminary for high mass: decreasing sigma - need more BR: use llqq or ll

FAKT2004Search for the Higgs Boson at the LHC13 SM Higgs: summary Full range of Higgs boson masses can be covered - most of it already at low luminosity CERN/LHCC ATLAS TDR 15 CMS NOTE 2003/033

FAKT2004Search for the Higgs Boson at the LHC14 MSSM Higgs Boson 5 Higgs bosons (h,H,A,H ± ) Usually parametrised using m A and tan  (tree level). Stop-mixing at loop level! Important difference to searches at previous experiments: cascades via SUSY particles are possible! LEP HWG preliminary

FAKT2004Search for the Higgs Boson at the LHC15 MSSM Higgs: H, A “Decoupling regime” High m A, high tan  decays to  : high BR, analyse leptonic and hadronic channels! decays to  : lower BR, but ~1% mass resolution “Intermediate regime” m A <500GeV, tan  <5-10 transition region between couplings to u- and d-type use A  ZH, H  Wh, H/A  tt for very low tan  “Intense coupling regime” Low m A, high tan  Higgses are almost degenerate 5  discovery reach

FAKT2004Search for the Higgs Boson at the LHC16 MSSM Higgses: h “Decoupling regime” High m A, high tan  h is SM-like (m h <150GeV!) “Intermediate regime” m A <500GeV, tan  <5-10 h-couplings to VB and u-type suppressed  bb,  decays Large parts of the plane covered VBF modes are important

FAKT2004Search for the Higgs Boson at the LHC17 MSSM Higgses: H ± Production: for low mass: t  bH ± for high mass:gb  tH ± qq’  H ± gg  H ± H ± gg  W ± H ± Decay for m H >~130GeV: H ±  t (*) b dominates interesting for analyses: H ±  

FAKT2004Search for the Higgs Boson at the LHC18 MSSM Higgses: cascade decays In the MSSM Higgs bosons can decay to SUSY particles and/or be produced in SUSY decay cascades. One scenario: M 2 = 2*M 1 = 350GeV,  = 1TeV m(gluino) = 1200GeV ms(squark) = 800GeV “long” cascades via  0 3,4 and  0 1,2  m H <~200GeV accessible SUSY signal SUSY bkg SM bkg

FAKT2004Search for the Higgs Boson at the LHC19 More exotic scenarios Still more Higgs bosons … CP-violation Can add phases to MSSM parameters - major changes to all signatures Invisible decays, e.g. to LSPs excess would be visible, but interpretation? Extra dimensions e.g. Radion decays to Higgs bosons Fermiophobic, gluophobic scenarios Specific points in SUSY parameter space or in more general 2HDM models Other scenarios Technicolor still alive.. LHC could look for decays of  T to vector bosons. Strong V L -V L -coupling the no-Higgs scenario: look for resonant WZ and non-resonant W + W + scattering

FAKT2004Search for the Higgs Boson at the LHC20 Radion decays Randall-Sundrum model: warped extra dimensions; two branes (Planck & TeV plane) Radion: scalar representation of the 5d gravitational field Most promising channel:  hh  bb : look for mass peaks in the  (narrow) and jj (broader) system Other channels studied:  bb, 4b

FAKT2004Search for the Higgs Boson at the LHC21 Conclusions In the Standard Model LHC covers the full mass range If discovered need to measure parameters (mass, spin, CP, couplings,..): major field of activity In the MSSM: The light Higgs is detectable in the full range Some regions of parameter space are tricky Analyses looking for SUSY decay chains are being developped What’s about extensions? CP-violation? Substantial progress also on the theoretical side, e.g. K NNLO for the SM Higgs production full one-loop + 2-loop RCs for large couplings in the MSSM Still quite some work to be done before LHC startup!