Higgs, Top and Boson Boson Scattering Six fermion simulations at the LHC E. Maina U. Torino MCWG Frascati Feb 27, 2006

LHC Physics Agenda Higgs (SM?) SUSY No Higgs nor SUSY Top QCD …………

SM Higgs discovery H→μeνν Asai et al.

What if no Higgs? Where do we look for clues to what lies beyond SM ? Consistency of SM is lost SM Effective theory Why does SM with weak radiative corrections work so well? MSSM not a viable replacement EWWG 05 Where do we look for clues to what lies beyond SM ?

Boson-Boson scattering and Unitarity

Expand Amp in partial waves M=∑j aj (s) Pj (cos(ϑ)) SS†=1 ⇒ |aj(s)|≤1 Unitarity Expand Amp in partial waves M=∑j aj (s) Pj (cos(ϑ)) SS†=1 ⇒ |aj(s)|≤1 Low Energy Th. M(VV→VV)∝s/v2 No H Unitarization: one example aj = a0j /(1-ia0j) a0j∝s Small s ⇒ LET Large s ⇒ aj→1 NOT UNIQUE!! Works well in ππ

Unitarization: eg: Butterworth,Cox,Forshaw PRD65(02)96014 different ways of constructing amplitudes which are unitary from low order amp Must be prepared for the unexpected Must know SM “background” e.g VTVT

t-tbar, qqH, VV→VV require Multiparton ME MC’s Dedicated: ALPGEN, GR@PPA …. General purpose, automatic: MADEVENT, COMPHEP, GRACE, AMEGIC …. NLO: MC@NLO match NLO calculation with PS No full EW six fermion MC : enter PHASE, PHANTOM QCD is flavour blind: smaller number of basic amps

Phantom Ballestrero, Belhouari,Bevilacqua,E.M. Dedicated event generator O(α6)+O(α4αs2) All q1q2→f1f2 f3 f4 f5f6, gg →f1f2 f3 f4 f5f6 , gq→…… Exact matrix elements. No production ⊗decay or EVBA One-shot: generates unweighted events for all processes simultaneously Efficient: good coverage of phase-space Interfaced with showering/hadronization via LH protocol Interfaced with FAMOS (as Phase1.0) Overcomes Problems due to Large number of processes Large number of diagrams/process Large number of channels/enhanced regions q1q2→q1q2 q3 q4 lv covered in Phase1.0 Accomando,Ballestrero,E.M. hep-ph/0504009

Phantom 0.9 : qq→4qlv At O(α6) All particles outgoing Adding ud↔cs, e ↔μ, CC ⇒1K processes All processes generated simultaneously Two step procedure As in Phase 1.0

Phantom 0.9: qq→4ql⁺l⁻ O(α6) Good generation efficiency ≈ 10-3

PHACT PLB350(95)225 hep-ph/9911318

I=〈f〉A ΔI∝〈(f−〈f〉)2 〉

Adaptive integration (VEGAS) Adapts well to cuts Rough estimate of integrand shape usually enough Fails if too many peaks or along diagonals Multichannel Requires a large number of channels All channels are integrated over simultaneously Sensitive to cuts, efficiency generally small Adapts varying the channel relative weight Iterative-Adaptive Multichannel NEW! (Phase+Phantom) Merges best feautures of both! Rough estimate of integrand shape enough Small number of channels required (Multimapping) Channels are integrated separately Good efficiency

An interesting example: 1046 diagrams It includes: ZZ → W+W- Higgs → WW ZW- → ZW- W-Z → ZW- W-W- → W-W- W- → W-W+W- 2 Higgs → WW chanls W- → ZZW- Higgs → ZZ Homework: check it out

First results qq→4qlv Accomando,Ballestrero,Bolognesi,E.M.,Mariotti hep-ph/0512219

Selection Tag vs decay quarks

Signal vs Bkg Bad

PHASE vs PYTHIA After: Top rejection W mass mH=500 GeV No Higgs PYTHIA has only LL in EVBA approximation

PHASE vs MADEVENT MADEVENT: qqWV⊗Decay Could produce exact result uu→uuqqμν Not the full set of processes qq=u-dbar,c-sbar MADEVENT: qqWV⊗Decay Could produce exact result Long CPU time VVV production vetoed

M(VW)>800GeV +pT+E+η+Mij cuts Small sensitivity to MH in SM range ⇒ SM predictions well defined. Not just counting exp

qq→qqH, H→ZZ, ZZ→llqq EW bkg + interference included exactly Accomando, Ballestrero, Belhouari, E.M. in preparation EW bkg + interference included exactly bkg ≈ 10% exact spin correlations

M(VZ)>800GeV +pT+E+η+Mij cuts ηqc Red lines: |ηZ| < 2 |ηqc| < 2 Full: noH Dash:mh=200 GeV

Internal gluon QCD corrections with G. Bevilacqua (Torino) Includes qq→tt No external g All qq→4qlv processes First results: no real analysis 70<M(jcjc)<90GeV

Improvements and projects Phantom 1.0 qq→6f O(α6) as first step 2q → 2q4l ready WW&ZW&ZZ final states lept 2q → 4qlnu @ O(αs2 αw4) first results available 2g → 4qlnu @ O(αs2 αw4) ready Main TOP channel! Good control of tails is essential 2g → 4ql⁺l⁻ ready 2g → 2q4l ready 2q → 4ql⁺l ⁻@ O(αs2 αw4) t-tbar: spin correlations qqWW→qqlνlν Alternative models of EWSB Standard candle