Post on 29-Jan-2016
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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