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

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

3 SM Higgs discovery H→μeνν Asai et al.

4 What if no Higgs? 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 ?

5 Boson-Boson scattering and Unitarity

6 Unitarity Expand Amp in partial waves M= ∑ j a j (s) Pj (cos( ϑ )) SS † =1 ⇒ |a j (s)|≤1 Low Energy Th. M (VV→VV) ∝ s/v 2 No H Unitarization : one example a j = a 0j /(1-ia 0j ) a 0j ∝ s Small s ⇒ LET Large s ⇒ a j →1 NOT UNIQUE!! Works well in ππ

7 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 V T V T

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

9 Phantom Ballestrero, Belhouari,Bevilacqua,E.M. Dedicated event generator O(α 6 )+O(α 4 α s 2 ) All q 1 q 2 →f 1 f 2 f 3 f 4 f 5 f 6, gg →f 1 f 2 f 3 f 4 f 5 f 6, 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 q 1 q 2 →q 1 q 2 q 3 q 4 lv covered in Phase1.0 Accomando,Ballestrero,E.M. hep-ph/

10 Phantom 0.9 : qq→4qlv At O(α 6 ) All particles outgoing Adding ud↔cs, e ↔μ, CC ⇒ 1K processes All processes generated simultaneously Two step procedure As in Phase 1.0

11 Phantom 0.9: qq→4ql ⁺ l ⁻ O(α 6 ) Good generation efficiency ≈ 10 -3

12 PHACT PLB350(95)225 hep-ph/

13 I= 〈 f 〉 A ΔI ∝〈 (f− 〈 f 〉 ) 2 〉

14 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! Adapts well to cuts Rough estimate of integrand shape enough Small number of channels required (Multimapping) Channels are integrated separately Good efficiency

15 An interesting example: 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 1046 diagrams

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

17 Tag vs decay quarks Selection

18 Signal vs Bkg Bad

19 PHASE vs PYTHIA PYTHIA has only LL in EVBA approximation After: Top rejection W mass mH=500 GeVNo Higgs

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

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

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

23 M(VZ)>800GeV +p T +E+η+M ij cuts Red lines: |η Z | < 2 |η qc | < 2 η qc Full: noH Dash:mh=200 GeV

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

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