Calculations of Higgs x-sections at NkLO

1 A.-C. Bourgaux, M. Escalier, L. Fayard

p

p

Hard scattering

Higgs

…decay

HdecayProphecy4fFeynHiggs

pdf

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

2 2/14

Why studying again cross-section ?

…but LHC accident : 14 TeV10 TeVConsequence expected on cross-sections

LHC to improve potential discovery…

• 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

Integrated x-sections (100-800 GeV)

• HNNLO mt ∞No correction

• FEHiP mt ∞ + correction:

)(

)()(

tLO

tLOt m

mmF

4

tt

• HIGLU mt exact

5

Integrated x-sections with HggTotalAvailable : http://www.phys.ethz.ch/~babis/Software/

Includes electroweack corrections,

Different choice for scales:R=F=0.5*mH

*BR(H with HNNLO

× Br(H )

6

Br(H )

(Br tables of HNNLO seem to be computed from Hdecay)

7

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

8

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)

)(

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

)(

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

)(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

)(Hdp

d

T

12

Higgs compatible with statistical error

mH=100 GeV

ATL-COM-PHYS-2009-161

13

Higgs PT, @ LO and NLO, with HqT

mH=125 GeV )(Hdp

d

T

Correction to pT(H) : appendix

Normalized : ≠ from HNNLO

14

HNNLOHqTresummation for low pT fix order for high pT

mrst2004

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

Influence of resummation scale RS (@ LO)

Matched calculation is closer to fix order when resumation scale is lower

RS=mH

Influence of RS @ LOlog scale:linear scale:

@ NLO

18

Acceptances with FEHiP, PYTHIA and MC@NLO

19

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)

Appendix

20

21

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