SM Higgs boson branching ratios

Hi,

You syntax for the decay is not correct.
> ( h > z1 z2 , ( z1 > l+ l- ) , ( z2 > l+ l- ) )
This force both Z to be on shell, and therefore the on shell cut bias your result.

The correct syntax is:
h > l+ l- l+ l-
Then they are not constraint on the intermediate Z.

More details on the above syntax can be found here:
https://cp3.irmp.ucl.ac.be/projects/madgraph/attachment/wiki/MGTalks/13_06_10_tutomg_tasi.pdf

Cheers,

Olivier

On Apr 30, 2014, at 2:32 PM, Matthew Conroy <email address hidden> wrote:

> New question #247928 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/247928
>
> We are trying to generate SM branching ratios of Higgs boson decay in the 4 lepton channel using cross sections generated by Madgraph, but cannot generate the expected value.
>
> We have generated:
> ggF
> import model heft
> generate p p > h
>
> pp->hjj
> import model heft
> generate p p > h j j
>
> VBF
> define v = z w+ w-
> generate p p > h j j $$v
>
> VH:
> define v = w+ w- z,
> define v’ = w+ | w- | z
> generate p p > v’ > v h
>
> We then generated all these processes with the Higgs decaying to four leptons, by using
> define z1 = z
> define z2 = z
>
> and then at the end of the generate line
> , ( h > z1 z2 , ( z1 > l+ l- ) , ( z2 > l+ l- ) )
>
> The cross sections that we found are at this link: http://imgur.com/3XJ0K0z where ratio indicates the branching ratio found by dividing taking (cross sectio with 4l decay) / (cross section with no decay).
>
> These values do not agree with the accepted value of 1.25E-4. We have removed all lepton related cuts from the run_card.dat file to generate this.
>
> Any advice on to generate the correct branching ratio using Madgraph is greatly appreciated!
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

I've followed your instructions and calculated p p > h and p p > h > l+ l- l+ l- using heft and have found cross sections of 18.43pb for p p > h and 0.0004662pb for p p > h >4l. This gives a BR of 2.52957E-05 which is still not what we expect. Is there anything else you think could be causing the discrepancy?

If you do
p p > h > 4l
You also have a non negligeable contribution of off-shell Higss.

So you need to use
p p > h, h > l+ l- l+ l-
such that you have a cut preventing the higgs to be too off shell.

Cheers,

Olivier

On May 1, 2014, at 1:56 PM, Xanthe Hoad <email address hidden> wrote:

> Question #247928 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/247928
>
> Xanthe Hoad requested more information:
> Hi Olivier,
>
> I've followed your instructions and calculated p p > h and p p > h > l+
> l- l+ l- using heft and have found cross sections of 18.43pb for p p > h
> and 0.0004662pb for p p > h >4l. This gives a BR of 2.52957E-05 which is
> still not what we expect. Is there anything else you think could be
> causing the discrepancy?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

generating p p > h, h > l+ l- l+ l- using heft, I get a cross section of 0.0003681pb and a BR of 1.99729E-05. Sorry to keep asking you but we're quite confused as to what would be causing this. We're trying to use madgraph to generate some more unusual processes and are using this decay as a test if we can find branching ratios reliably

Hi Xanthe,

How/Where do you get your “accepted number”?
In particular, did you assume one of the Z to be on shell? (pretty bad but ok) and does this number include tau in your lepton definition?

Also is this number include fully non resonant diagram like the Higgs decaying into 2 Higgs(or 2 photo) and then 4 leptons.

Our Higgs expert team check this part of the code very recently. So I’m sure that this part is fine.

Cheers,

Olivier

On May 1, 2014, at 4:41 PM, Xanthe Hoad <email address hidden> wrote:

> Question #247928 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/247928
>
> Xanthe Hoad posted a new comment:
> Hi Olivier,
>
> generating p p > h, h > l+ l- l+ l- using heft, I get a cross section of
> 0.0003681pb and a BR of 1.99729E-05. Sorry to keep asking you but we're
> quite confused as to what would be causing this. We're trying to use
> madgraph to generate some more unusual processes and are using this
> decay as a test if we can find branching ratios reliably
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Oliver,

To avoid confusion I should point out that Xanthe and I are working together on the same problem!

We have been using the branching ratio values on this CERN website here, which quotes h->Z Z->l+ l- l+ l- as 2.76E-04 (including tau) and h->ZZ->4l (excluding tau) as 1.25E-04.

Thanks,

Matthew.

Hi Oliver,

Sorry the link is here: https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CERNYellowReportPageAt8TeV

The spreadsheets with the values are at the bottom of the page, using a Higgs mass of 125 GeV.

Thanks,

Matthew.

Hi,

Sorry for the delay, I was very busy those days.
So I did the following:
generate
h > z > l+ l- l+ l-
output
launch -f

And it returns me a width of 5.085e-07.
In your table the total width for the h at 125 GeV is 0.00407
so the branching fraction is 5.085e-07/ 0.00407 = 0.00012493857493857494
So so far so good since it did not include the tau.

If I use the heft model instead then I have:
5.085e-07 ± 2e-09
so this is not linked to the model.

Now the problem is probably linked to the value use for the Higgs width.
In the heft model the default value is 6.382339e-03 and not 0.00407.
Did you change this value for your computation of the Higgs Decay?

Cheers,

Olivier

On May 4, 2014, at 3:51 PM, Matthew Conroy <email address hidden> wrote:

> Question #247928 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/247928
>
> Matthew Conroy posted a new comment:
> Hi Oliver,
>
> To avoid confusion I should point out that Xanthe and I are working
> together on the same problem!
>
> We have been using the branching ratio values on this CERN website here,
> which quotes h->Z Z->l+ l- l+ l- as 2.76E-04 (including tau) and
> h->ZZ->4l (excluding tau) as 1.25E-04.
>
> Thanks,
>
> Matthew.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.