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? 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 ?

5. Boson-Boson scattering and Unitarity

6. 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

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 VTVT

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
No full EW six fermion MC :
enter PHASE, PHANTOM
QCD is flavour blind: smaller number of basic amps

9. 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 Phase Accomando,Ballestrero,E.M. hep-ph/

10. 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

11. Phantom 0.9: qq→4ql⁺l⁻
O(α6)
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!
Rough estimate of integrand shape enough
Small number of channels required (Multimapping)
Channels are integrated separately
Good efficiency

15. 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

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

17. Selection
Tag vs decay quarks

18. Signal vs Bkg
Bad

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

20. 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

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

22. 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

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

24. 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

25. Improvements and projects Phantom 1.0 qq→6f O(α6) as first step
2q → 2q4l ready WW&ZW&ZZ final states lept
2q → O(αs2 αw4) first results available
2g → 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