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Higgs, Top and Boson Boson Scattering Six fermion

simulations at the LHC

E. MainaU. Torino

MCWG Frascati Feb 27, 2006

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LHC Physics Agenda Higgs (SM?) SUSY No Higgs nor SUSY

Top QCD …………

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SM Higgs discovery

H→μeνν

Asai et al.

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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 ?

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Boson-Boson scattering and Unitarity

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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 a⇒ j→1

NOT UNIQUE!!Works well in ππ

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Unitarization: eg: Butterworth,Cox,Forshaw PRD65(02)96014different ways of constructing amplitudes which are unitary from low order amp

Must be prepared for the unexpectedMust know SM “background” e.g VTVT

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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

QCD is flavour blind: smaller number of basic amps

No full EW six fermion MC : enter PHASE, PHANTOM

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PhantomBallestrero, 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

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Phantom 0.9 : qq→4qlv At O(α6)

All particles outgoingAdding ud↔cs, e ↔μ, CC ⇒1K processes

All processes generated simultaneously

Two step procedure

As in Phase 1.0

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Phantom 0.9: qq→4ql⁺l⁻O(α6)

Good generation efficiency≈ 10-3

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PHACT PLB350(95)225hep-ph/9911318

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I= 〈 f 〉 A

ΔI∝〈 (f−〈 f 〉 )2 〉

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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

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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

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

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Tag vs decay quarks

Selection

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Signal vs Bkg

Bad

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PHASE vs PYTHIA

PYTHIA has only LL in EVBA approximation

After: Top rejection W mass

mH=500 GeV No Higgs

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PHASE vs MADEVENTuu→uuqqμν Not the full set of processesqq=u-dbar,c-sbar

MADEVENT: qqWV Decay⊗

VVV production vetoed

Could produce exact resultLong CPU time

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

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qq→qqH, H→ZZ, ZZ→llqqAccomando, Ballestrero, Belhouari, E.M. in preparation

EW bkg + interference included exactlybkg ≈ 10% exact spin correlations

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M(VZ)>800GeV +pT+E+η+Mij cuts

Red lines:|ηZ| < 2|ηqc| < 2

ηqc

Full: noHDash:mh=200 GeV

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Internal gluon QCD correctionswith G. Bevilacqua (Torino)

Includes qq-->tt No external g

First results: no real analysis 70<M(jcjc)<90GeV

All qq→4qlv processes

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Improvements and projects

Phantom 1.0qq→6f O(α6) as first step

2q --> 2q4l ready WW&ZW&ZZ final states lept 2q --> 4qlnu @ O(αs

2 αw4) first results available

2g --> 4qlnu @ O(αs2 αw

4) ready Main TOP channel! Good control of tails is essential 2g --> 4ql⁺l⁻ ready 2g --> 2q4l ready 2q --> 4ql⁺l ⁻@ O(αs

2 αw4)

t-tbar: spin correlations qqWW→qqlνlν Alternative models of EWSB Standard candle