calculations of higgs x-sections at n k lo
DESCRIPTION
Calculations of Higgs x-sections at N k LO. p. diff. observables Higgs HqT (NLO+NNLL) Resbos (NLO+NLL). Hard scattering. Higgs. …. gg H Higlu ggHTotal Fehip hnnlo resbos. VBF VV2H (NLO) VBFNLO (NLO). decay. Hdecay Prophecy4f FeynHiggs. W/Z H V2HV. bkg. p. gg diphox - PowerPoint PPT PresentationTRANSCRIPT
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Calculations of Higgs x-sections at NkLO
1 A.-C. Bourgaux, M. Escalier, L. Fayard
p
p
Hard scattering
Higgs
…decay
HdecayProphecy4fFeynHiggs
Cteq 2009Mstw 2008Uncertainties pdfs
diff. observables HiggsHqT (NLO+NNLL)Resbos (NLO+NLL)
ggHHigluggHTotalFehiphnnloresbos
VBFVV2H (NLO)VBFNLO (NLO)
W/Z HV2HV
ttHhQQ
bkg
/jetjetphox
jet jetnlojet++
diphoxresbos
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2 2/14
Why studying again cross-section ?
…but LHC accident : 14 TeV10 TeVConsequence expected on cross-sections
LHC to improve potential discovery…
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• Higlu (NLO), • HNNLO (NNLO, no mt correction),• FEHiP, HggTotal (NNLO+F(mt)) Anastasiou• HqT
Factorisation (µF) and renormalisation (µ
R) scales :
F=
R in [m
H/2 ; 2m
H ] to limit computations
Pdf: mstw2008CTEQ6L1/M for Higlu
default parameters used, while concluding for a common prescription:mt = 172.7 GeV for FEHiP,
172 GeV for Higlu178 GeV for HNNLO
Tools and parameters used
3
TeVs 10
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Integrated x-sections (100-800 GeV)
• HNNLO mt ∞No correction
• FEHiP mt ∞ + correction:
)(
)()(
tLO
tLOt m
mmF
4
tt
• HIGLU mt exact
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Integrated x-sections with HggTotalAvailable : http://www.phys.ethz.ch/~babis/Software/
Includes electroweack corrections,
Different choice for scales:R=F=0.5*mH
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*BR(H with HNNLO
× Br(H )
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Br(H )
(Br tables of HNNLO seem to be computed from Hdecay)
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Motivations:
-take into consideration acceptance of detector and change of ecmneed angular and pT distributions of photons
-Higgs pT is a powerful discriminating variable, need good knowledge of distributions especially at low pT where resummation is important to avoid fixed order Monte Carlo behavior
differential x-sections
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differential x-sections with HNNLO
gg fusion Higgs 2 photons γ
LO _ pT34 pT3 &pT4
y34 η3 & η4
NLO pT5 pT34 pT3 &pT4
y34 η3 & η4
NNLO pT5 pT34 pT3 & pT4
pT6 y34 η3 & η4
1
2
H3
4
5 (jet)
6 (jet)
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)(
d
d
For high masses, the photon is more central
9
mH=100 GeVstable observable / pert order
mH=100 GeV mH=800 GeVphoton
normalized:ATL-COM-PHYS-2009-161 Qian, Liu,
Mansoulie, Purdham, Strandberg, Thun
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)(
Tdp
dmH=100 GeV
fixed order calculation :LO bounded at pt=mH/2 NLO and NNLO unstables in this region
10
photon
normalized: ATL-COM-PHYS-2009-161
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)(Hdy
d
mH=100 GeV mH=800 GeV
Detector acceptance will limit the rapidity range that can be measured11
Higgs
stable observable / pert ordermH=100 GeVnormalized:
ATL-COM-PHYS-2009-161
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)(Hdp
d
T
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Higgs compatible with statistical error
mH=100 GeV
ATL-COM-PHYS-2009-161
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Higgs PT, @ LO and NLO, with HqT
mH=125 GeV )(Hdp
d
T
Correction to pT(H) : appendix
Normalized : ≠ from HNNLO
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HNNLOHqTresummation for low pT fix order for high pT
mrst2004
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Influence of R , F
mH/2
For low pT :dependance on scales decreases between LO and NLO
For high pT :dependance on scales remains almost constant : calculation is actually LO
LO
NLO
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Influence of resummation scale RS (@ LO)
Matched calculation is closer to fix order when resumation scale is lower
RS=mH
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Influence of RS @ LOlog scale:linear scale:
@ NLO
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Acceptances with FEHiP, PYTHIA and MC@NLO
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Conclusion
Gluon fusion: soon under control,
VBF: great work in progress from Nansi (vv2h, mass and scales dependances),
W/Z H: will be investigated and compared with Djouadi computation at NNLO,
tṫ H: will be investigated to close available programs study.
Up to now signal investigated, what about background?
jet: yet investigated by Pauline (NLO)
jet-jet : NLOjet++ could be investigated (NLO)
Differential cross-section feedback to statistic team (Nansi, Francesco, Louis)
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Appendix
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Construction of the curve :
• Resummed : divergent terms only « resummed »=exp(Sudakov factor)
• Asymptotic : limit of perturbative order when PT0 : divergent terms only
• Fix order : all perturbative developpement terms, including divergent terms
Matched = Resummed + Fix order - Asymptotic
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PT of Higgs : HqT
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Available tools