Extracting K factor

Hi,

Do you want the NLO K factor?
if so generate the NLO code, when running that one, you can run the same code (with same cut) at Leading Order and therefore compute your K-factor.

Cheers,

Olivier

On 26 May 2015, at 21:26, John <email address hidden> wrote:

> New question #267410 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/267410
>
> Dear Staff,
>
> I am trying to simulate the standard model diboson production from a proton and anti-proton collision such as
>
> proton + antiproton -> WW + X, where X is an initial state radiation such as a gluon. (a.k.a K factor); I want to extract an
>
> enhancement factor in the cross section without X.
>
> Could you tell me how to implement this?
>
> Thank you.
>
> John
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear John,

Could you confirm that you are interested in the NLO K-factor?

If yes, then what you need to do is:

generate p p > w+ w- [QCD]
output PATH

Then you will need to run twice the code (running twice “launch PATH”).

It starts by the following question:
The following switches determine which operations are executed:
 1 Perturbative order of the calculation: order=NLO
 2 Fixed order (no event generation and no MC@[N]LO matching): fixed_order=OFF
 3 Shower the generated events: shower=ON
 4 Decay particles with the MadSpin module: madspin=OFF
  Either type the switch number (1 to 4) to change its default setting,
  or set any switch explicitly (e.g. type 'order=LO' at the prompt)
  Type '0', 'auto', 'done' or just press enter when you are done.
 [0, 1, 2, 3, 4, auto, done, order=LO, order=NLO, ... ][60s to answer]

For the first run, I would choose
order=NLO
and fixed_order=ON
While for the second, I would choose
order=LO and fixed_order=ON

The ratio of the cross-section is the global K-factor.

> One last question is, after I change parameters for a collision, how do
> I exit from that screen so that I can launch the process?

If you did not specify a text editor, then it is likely that the one used is “vi”. to quit “vi” you need to use the following command:
1) press escape
2) type :x
3) press enter
It is also possible that you use “emacs”.
in that case the following command should do it:
1) (save your modification) ctrl-x ctrl-s
2) (quite the program) ctrl-x ctrl-c

Note that you can edit most of the file without opening the file: https://answers.launchpad.net/mg5amcnlo/+faq/2186

Cheers,

Olivier

On 27 May 2015, at 19:11, John <email address hidden> wrote:

> Question #267410 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/267410
>
> Summary changed to:
> Extracting K factor
>
> Description changed to:
> Dear Staff,
>
> I received the reply from a staff, "if so generate the NLO code, when
> running that one, you can run the same code (with same cut) at Leading
> Order and therefore compute your K-factor."
>
> My question was
>
> I am trying to simulate the standard model diboson production from a
> proton and anti-proton collision such as
>
> proton + antiproton -> WW + X, where X is an initial state
> radiation,ISR, such as a gluon. (a.k.a K factor); I want to extract an
>
> enhancement factor in the cross section with X.
>
> My questions are
>
> In order to include X as an ISR, do I need to type in a special command
> or can the madgraph figure this out automatically?
>
> How would I go about running two processes, NLO and LO at the same time?
> (as written in the reply)
>
> One last question is, after I change parameters for a collision, how do
> I exit from that screen so that I can launch the process?
>
> Thank you so much!
>
> John
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.