Higgs production cross section

1. Jan 31, 2016

Safinaz

Hi all,

I try to find the exact calculated gluon- gluon fusion cross section for the SM- Higgs with mass 125 GeV, for instance at CME = 14 TeV.

I found on twiki page:
" https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CERNYellowReportPageAt1314TeV#s_14_0_TeV [Broken]"

$\sigma(gg \to h) = 49.47~ pb$

while in reference like "arXiv:hep-ph/0503172 ", table(3.2):

$\sigma(gg \to h) \sim 37 ~ pb$

Both calculations are NLO, but why there is this difference ?

Last edited by a moderator: May 7, 2017
2. Jan 31, 2016

Staff: Mentor

The first one is NNLO QCD. For electroweak processes it is just NLO but those should be a small contribution. The NLO calculation discusses some NNLO effects but I don't understand what exactly they do.

3. Jan 31, 2016

Safinaz

So I wonder can we calculate $\sigma (gg \to h)$ at LO or NLO like in " arXiv:hep-ph/0503172 ",

while take the uncertainties (the standard deviation ) from NNLO calculations ?

The following paper " arXiv:1206.5047 [hep-ph]" made that in Fig. (1). While they use LO formula for the production cross section Equ. (5), they cite the Cern twiki page for $\sigma1~ \mbox{and}~ \sigma2$,

is this consistent to take the uncertainty from NNLO calculation for a cross section calculated at LO?

Last edited: Jan 31, 2016
4. Jan 31, 2016

Staff Emeritus
Virtually nothing that is done is consistent. Your choice is a) the latest calculations, or b) a consistent set of calculations. Most people choose a).

For Higgs production, the state of the art is N3LO, Anastasiou et al. PRL 114, 212001 (2015)

5. Jan 31, 2016

Safinaz

Hi,

I added my last sentence :) , I hope it's clear enough.

6. Feb 1, 2016

Staff: Mentor

Here is the NNNLO calculation. They also compare LO, NLO, NNLO and NNNLO in figure 2. The difference between NLO and NNLO is ~10/pb, although both still show significant scale-dependence. NNNLO is significantly better in terms of scale-dependence. Note that the plot is for 13 TeV. Figure 3 includes 14 TeV bands, the same difference is visible there.

I don't understand how you would take a NNLO calculation for a LO uncertainty. Where is the point in having an uncertainty on LO if you have a NNLO calculation?

7. Feb 1, 2016

Safinaz

It's this paper " arXiv:1206.5047 [hep-ph]", as you see for Fig. (1), they take the uncertainty 14.7 % from [10] , which are NNLO. While they use LO formula, ( Equ.5 )for the new physics ( NP) $gg \to h$ cross section.

Even I don't know in Fig. (1), when they normalized $\sigma_{NP}$ by $\sigma_{SM}$ which value for $\sigma_{SM}$ they considered, did they calculate it at LO or they just take [10] value .

8. Feb 1, 2016

Staff: Mentor

Those are different things.
As far as I understand it, they compare the cross-section for (LO NP + NNLO SM) with (NNLO SM), and use the NNLO SM uncertainty (which is independent of new physics) as comparison: if the NP prediction is within the uncertainties of the SM calculation, the cross-section alone is not sufficient to see new physics.