MadGraph5_aMC@NLO

total XS for "a a > mu mu" using PDF=2

Asked by Patricia Rebello Teles

Dear authors,

after computing the total XS for the process a a > mu mu, using EPA from protons in SM, I have noticed that it DECREASES with increasing Q**2 values.

After Calchep and LPAIR results, I was expecting an increasing total XS with increasing Q**2 values.

I would appreciate very much if you could clarify it?

I have changed the Q**2 following previous questions as, assuming Q**2 = 2 GeV**2,

T = fixed_ren_scale ! if .true. use fixed ren scale
T = fixed_fac_scale ! if .true. use fixed fac scale
 1.414213562 = scale ! fixed ren scale
 1.414213562 = dsqrt_q2fact1 ! fixed fact scale for pdf1
 1.414213562 = dsqrt_q2fact2 ! fixed fact scale for pdf2
 1 = scalefact ! scale factor for event-by-event scales

and used the following cuts
ptl > 15 GeV and etal < 3.13 for ECM=8TeV and asked 50K events.

Moreover, each time I run, it returns quite different XS values, although I am using exactly the same parameters. So, it looks very unstable.

Kind regards Patricia

Question information

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Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#1

Dear authors

I apologize but would you have any new about this topic. Should I give more details about it?

Thank you.

Kind regards Patricia

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#2

Dear Patricia,

When investigating this topic, I found that this topic had a huge bug introduced in 2.1.2.
The version that I release yesterday night (2.2.2) actually fix that bug. Sorry that I forget to react here.

Now independently of that bug, It’s clear that the integration error for that process is under-estimate and
that the function has some problem to converge correctly. One way which might help the integrator
is to put some cut on the maximum value of the pt of the lepton and of the lepton pair. In top of the minimal one.
But I did not test that one.

Concerning the dependencies in Q**2, I didn’t observe an effect which was large enough to confirm your point.
If you have some doubt on how this work, I would suggest to read the code handling that part:
Source/PDF/Photon_Flux.f

Cheers,

Olivier

On Nov 7, 2014, at 8:51 PM, Patricia Rebello Teles <email address hidden> wrote:

> Question #256728 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> Patricia Rebello Teles posted a new comment:
> Dear authors
>
> I apologize but would you have any new about this topic. Should I give
> more details about it?
>
> Thank you.
>
> Kind regards Patricia
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#3

Dear Olivier

thank you very much. In fact I was anxious about your answer because we are
using Madgraph for a CMS analysis.

In fact, the difference in the XS is quite big when we scan the Q**2.

For instance,

LPAIR is the benchmark XS for the "a a > mu mu" because the features of the
generator: XS_lpair = 6.49fb

In the Calchep we have

Q**2=1 GeV**2: XS= 6.47 fb

Q**2=2 GeV**2: XS=6.59 fb etc

Q**2=4 GeV**2: XS=6.62 fb etc

Q**2 = 10 GeV**2 XS= 6.64 fb

In the case of Madgraph

Q**2=1 GeV**2: XS= 5.52 fb

Q**2=2 GeV**2: XS=5.33 fb (that is dsqrt_q2fact1=1.414213562)

Q**2=4 GeV**2: XS=4.76 fb

Q**2 = not fixed (much bigger): XS= 3.75fb

You see, while Calchep tends to increase the XS, or at least is more
stable, with increasing Q**2, Madgraph does the opposite.

I have already taken a look in the PhotonFlux.f. In fact I have edit it for
getting the q2max, and epa_proton values.

Didn`t you observe any large effect? I will try the newest version as you
recommended.

Thank you.

Kind regards Patricia.

2014-11-08 1:06 GMT+01:00 Olivier Mattelaer <
<email address hidden>>:

> Your question #256728 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Dear Patricia,
>
> When investigating this topic, I found that this topic had a huge bug
> introduced in 2.1.2.
> The version that I release yesterday night (2.2.2) actually fix that bug.
> Sorry that I forget to react here.
>
> Now independently of that bug, It’s clear that the integration error for
> that process is under-estimate and
> that the function has some problem to converge correctly. One way which
> might help the integrator
> is to put some cut on the maximum value of the pt of the lepton and of the
> lepton pair. In top of the minimal one.
> But I did not test that one.
>
> Concerning the dependencies in Q**2, I didn’t observe an effect which was
> large enough to confirm your point.
> If you have some doubt on how this work, I would suggest to read the code
> handling that part:
> Source/PDF/Photon_Flux.f
>
> Cheers,
>
> Olivier
>
>
>
>
> On Nov 7, 2014, at 8:51 PM, Patricia Rebello Teles <
> <email address hidden>> wrote:
>
> > Question #256728 on MadGraph5_aMC@NLO changed:
> > https://answers.launchpad.net/mg5amcnlo/+question/256728
> >
> > Patricia Rebello Teles posted a new comment:
> > Dear authors
> >
> > I apologize but would you have any new about this topic. Should I give
> > more details about it?
> >
> > Thank you.
> >
> > Kind regards Patricia
> >
> > --
> > You received this question notification because you are an answer
> > contact for MadGraph5_aMC@NLO.
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=1
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> You received this question notification because you asked the question.
>

Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#4

Hi Olivier,

you have mentioned a "huge bug" on previous versions of MG5.

Should this bug be presented in "two-photon" using EPA processes in general
or only in the "a a > mu mu" channel?

Could you please clarify it?

Thank you.

Cheers Patricia.

2014-11-08 1:06 GMT+01:00 Olivier Mattelaer <
<email address hidden>>:

> Your question #256728 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Dear Patricia,
>
> When investigating this topic, I found that this topic had a huge bug
> introduced in 2.1.2.
> The version that I release yesterday night (2.2.2) actually fix that bug.
> Sorry that I forget to react here.
>
> Now independently of that bug, It’s clear that the integration error for
> that process is under-estimate and
> that the function has some problem to converge correctly. One way which
> might help the integrator
> is to put some cut on the maximum value of the pt of the lepton and of the
> lepton pair. In top of the minimal one.
> But I did not test that one.
>
> Concerning the dependencies in Q**2, I didn’t observe an effect which was
> large enough to confirm your point.
> If you have some doubt on how this work, I would suggest to read the code
> handling that part:
> Source/PDF/Photon_Flux.f
>
> Cheers,
>
> Olivier
>
>
>
>
> On Nov 7, 2014, at 8:51 PM, Patricia Rebello Teles <
> <email address hidden>> wrote:
>
> > Question #256728 on MadGraph5_aMC@NLO changed:
> > https://answers.launchpad.net/mg5amcnlo/+question/256728
> >
> > Patricia Rebello Teles posted a new comment:
> > Dear authors
> >
> > I apologize but would you have any new about this topic. Should I give
> > more details about it?
> >
> > Thank you.
> >
> > Kind regards Patricia
> >
> > --
> > You received this question notification because you are an answer
> > contact for MadGraph5_aMC@NLO.
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=1
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> You received this question notification because you asked the question.
>

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#5

Dear Patricia,

> Should this bug be presented in "two-photon" using EPA processes in general
> or only in the “a a > mu mu" channel?

This is difficult to make a general statement since massive particle in the final state and/or cut reduces the bug to a significant level.
But in general, I would be suspicious about all EPA processes generated with MG5 between version 2.1.2 and 2.2.1

Cheers,

Olivier

On Nov 10, 2014, at 10:01 PM, Patricia Rebello Teles <email address hidden> wrote:

> Question #256728 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> Patricia Rebello Teles gave more information on the question:
> Hi Olivier,
>
> you have mentioned a "huge bug" on previous versions of MG5.
>
> Should this bug be presented in "two-photon" using EPA processes in general
> or only in the "a a > mu mu" channel?
>
> Could you please clarify it?
>
> Thank you.
>
> Cheers Patricia.
>
>
> 2014-11-08 1:06 GMT+01:00 Olivier Mattelaer <
> <email address hidden>>:
>
>> Your question #256728 on MadGraph5_aMC@NLO changed:
>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>
>> Status: Open => Answered
>>
>> Olivier Mattelaer proposed the following answer:
>> Dear Patricia,
>>
>> When investigating this topic, I found that this topic had a huge bug
>> introduced in 2.1.2.
>> The version that I release yesterday night (2.2.2) actually fix that bug.
>> Sorry that I forget to react here.
>>
>> Now independently of that bug, It’s clear that the integration error for
>> that process is under-estimate and
>> that the function has some problem to converge correctly. One way which
>> might help the integrator
>> is to put some cut on the maximum value of the pt of the lepton and of the
>> lepton pair. In top of the minimal one.
>> But I did not test that one.
>>
>> Concerning the dependencies in Q**2, I didn’t observe an effect which was
>> large enough to confirm your point.
>> If you have some doubt on how this work, I would suggest to read the code
>> handling that part:
>> Source/PDF/Photon_Flux.f
>>
>> Cheers,
>>
>> Olivier
>>
>>
>>
>>
>> On Nov 7, 2014, at 8:51 PM, Patricia Rebello Teles <
>> <email address hidden>> wrote:
>>
>>> Question #256728 on MadGraph5_aMC@NLO changed:
>>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>>
>>> Patricia Rebello Teles posted a new comment:
>>> Dear authors
>>>
>>> I apologize but would you have any new about this topic. Should I give
>>> more details about it?
>>>
>>> Thank you.
>>>
>>> Kind regards Patricia
>>>
>>> --
>>> You received this question notification because you are an answer
>>> contact for MadGraph5_aMC@NLO.
>>
>> --
>> If this answers your question, please go to the following page to let us
>> know that it is solved:
>>
>> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=1
>>
>> If you still need help, you can reply to this email or go to the
>> following page to enter your feedback:
>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>
>> You received this question notification because you asked the question.
>>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#6

Hi Olivier

thank you very much.

My samples were generated in February 2014 with

<MGVersion>
# MG version : 5.2.0.0
</MGVersion>

which has no bug in the EPA, right?

Cheers, Patricia.

2014-11-11 0:01 GMT+01:00 Olivier Mattelaer <
<email address hidden>>:

> Your question #256728 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Dear Patricia,
>
> > Should this bug be presented in "two-photon" using EPA processes in
> general
> > or only in the “a a > mu mu" channel?
>
>
> This is difficult to make a general statement since massive particle in
> the final state and/or cut reduces the bug to a significant level.
> But in general, I would be suspicious about all EPA processes generated
> with MG5 between version 2.1.2 and 2.2.1
>
> Cheers,
>
> Olivier
>
>
> On Nov 10, 2014, at 10:01 PM, Patricia Rebello Teles
> <email address hidden> wrote:
>
> > Question #256728 on MadGraph5_aMC@NLO changed:
> > https://answers.launchpad.net/mg5amcnlo/+question/256728
> >
> > Patricia Rebello Teles gave more information on the question:
> > Hi Olivier,
> >
> > you have mentioned a "huge bug" on previous versions of MG5.
> >
> > Should this bug be presented in "two-photon" using EPA processes in
> general
> > or only in the "a a > mu mu" channel?
> >
> > Could you please clarify it?
> >
> > Thank you.
> >
> > Cheers Patricia.
> >
> >
> > 2014-11-08 1:06 GMT+01:00 Olivier Mattelaer <
> > <email address hidden>>:
> >
> >> Your question #256728 on MadGraph5_aMC@NLO changed:
> >> https://answers.launchpad.net/mg5amcnlo/+question/256728
> >>
> >> Status: Open => Answered
> >>
> >> Olivier Mattelaer proposed the following answer:
> >> Dear Patricia,
> >>
> >> When investigating this topic, I found that this topic had a huge bug
> >> introduced in 2.1.2.
> >> The version that I release yesterday night (2.2.2) actually fix that
> bug.
> >> Sorry that I forget to react here.
> >>
> >> Now independently of that bug, It’s clear that the integration error for
> >> that process is under-estimate and
> >> that the function has some problem to converge correctly. One way which
> >> might help the integrator
> >> is to put some cut on the maximum value of the pt of the lepton and of
> the
> >> lepton pair. In top of the minimal one.
> >> But I did not test that one.
> >>
> >> Concerning the dependencies in Q**2, I didn’t observe an effect which
> was
> >> large enough to confirm your point.
> >> If you have some doubt on how this work, I would suggest to read the
> code
> >> handling that part:
> >> Source/PDF/Photon_Flux.f
> >>
> >> Cheers,
> >>
> >> Olivier
> >>
> >>
> >>
> >>
> >> On Nov 7, 2014, at 8:51 PM, Patricia Rebello Teles <
> >> <email address hidden>> wrote:
> >>
> >>> Question #256728 on MadGraph5_aMC@NLO changed:
> >>> https://answers.launchpad.net/mg5amcnlo/+question/256728
> >>>
> >>> Patricia Rebello Teles posted a new comment:
> >>> Dear authors
> >>>
> >>> I apologize but would you have any new about this topic. Should I give
> >>> more details about it?
> >>>
> >>> Thank you.
> >>>
> >>> Kind regards Patricia
> >>>
> >>> --
> >>> You received this question notification because you are an answer
> >>> contact for MadGraph5_aMC@NLO.
> >>
> >> --
> >> If this answers your question, please go to the following page to let us
> >> know that it is solved:
> >>
> >>
> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=1
> >>
> >> If you still need help, you can reply to this email or go to the
> >> following page to enter your feedback:
> >> https://answers.launchpad.net/mg5amcnlo/+question/256728
> >>
> >> You received this question notification because you asked the question.
> >>
> >
> > --
> > You received this question notification because you are an answer
> > contact for MadGraph5_aMC@NLO.
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=4
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> You received this question notification because you asked the question.
>

Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#7

Hi again Olivier

I have tested the newest version 2.2.2

Nevertheless the decreasing in the XS with increasing Q**2 value persists,
or at least the run is very unstable... take a look below.

Results obtained for alpha_EM=1/137, pt_mu > 20 GeV, |eta_mu| < 2.4 and
m_mumu > 160 GeV for comparison with Calchep results (which remain stable
around 6.4fb, being compatible with LPAIR)

For instance: if I let Q**2 free (huge values like q2max =
5891015.2916062307)

 F = fixed_ren_scale ! if .true. use fixed ren scale
 F = fixed_fac_scale ! if .true. use fixed fac scale

the XS = 3.8fb

If I change for Q**2 = 2 GeV**2 (thus decreasing q2max = 2)

 T = fixed_ren_scale ! if .true. use fixed ren scale
 T = fixed_fac_scale ! if .true. use fixed fac scale
 1.414213562373095 = scale ! fixed ren scale
 1.414213562373095 = dsqrt_q2fact1 ! fixed fact scale for pdf1
 1.414213562373095 = dsqrt_q2fact2 ! fixed fact scale for pdf2

the XS = 4.8fb

If I change for Q**2 = 0.5 GeV**2 (thus decreasing even more q2max = 0.5)

T = fixed_ren_scale ! if .true. use fixed ren scale
 T = fixed_fac_scale ! if .true. use fixed fac scale
 0.7071067811865476 = scale ! fixed ren scale
 0.7071067811865476 = dsqrt_q2fact1 ! fixed fact scale for pdf1
 0.7071067811865476 = dsqrt_q2fact2 ! fixed fact scale for pdf2

the XS = 5.4fb

Any hint to control it?

Cheers Patricia

2014-11-11 13:09 GMT+01:00 Patricia Rebello Teles <email address hidden>:

> Hi Olivier
>
> thank you very much.
>
> My samples were generated in February 2014 with
>
> <MGVersion>
> # MG version : 5.2.0.0
> </MGVersion>
>
> which has no bug in the EPA, right?
>
> Cheers, Patricia.
>
>
>
>
>
>
>
> 2014-11-11 0:01 GMT+01:00 Olivier Mattelaer <
> <email address hidden>>:
>
>> Your question #256728 on MadGraph5_aMC@NLO changed:
>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>
>> Status: Open => Answered
>>
>> Olivier Mattelaer proposed the following answer:
>> Dear Patricia,
>>
>> > Should this bug be presented in "two-photon" using EPA processes in
>> general
>> > or only in the “a a > mu mu" channel?
>>
>>
>> This is difficult to make a general statement since massive particle in
>> the final state and/or cut reduces the bug to a significant level.
>> But in general, I would be suspicious about all EPA processes generated
>> with MG5 between version 2.1.2 and 2.2.1
>>
>> Cheers,
>>
>> Olivier
>>
>>
>> On Nov 10, 2014, at 10:01 PM, Patricia Rebello Teles
>> <email address hidden> wrote:
>>
>> > Question #256728 on MadGraph5_aMC@NLO changed:
>> > https://answers.launchpad.net/mg5amcnlo/+question/256728
>> >
>> > Patricia Rebello Teles gave more information on the question:
>> > Hi Olivier,
>> >
>> > you have mentioned a "huge bug" on previous versions of MG5.
>> >
>> > Should this bug be presented in "two-photon" using EPA processes in
>> general
>> > or only in the "a a > mu mu" channel?
>> >
>> > Could you please clarify it?
>> >
>> > Thank you.
>> >
>> > Cheers Patricia.
>> >
>> >
>> > 2014-11-08 1:06 GMT+01:00 Olivier Mattelaer <
>> > <email address hidden>>:
>> >
>> >> Your question #256728 on MadGraph5_aMC@NLO changed:
>> >> https://answers.launchpad.net/mg5amcnlo/+question/256728
>> >>
>> >> Status: Open => Answered
>> >>
>> >> Olivier Mattelaer proposed the following answer:
>> >> Dear Patricia,
>> >>
>> >> When investigating this topic, I found that this topic had a huge bug
>> >> introduced in 2.1.2.
>> >> The version that I release yesterday night (2.2.2) actually fix that
>> bug.
>> >> Sorry that I forget to react here.
>> >>
>> >> Now independently of that bug, It’s clear that the integration error
>> for
>> >> that process is under-estimate and
>> >> that the function has some problem to converge correctly. One way which
>> >> might help the integrator
>> >> is to put some cut on the maximum value of the pt of the lepton and of
>> the
>> >> lepton pair. In top of the minimal one.
>> >> But I did not test that one.
>> >>
>> >> Concerning the dependencies in Q**2, I didn’t observe an effect which
>> was
>> >> large enough to confirm your point.
>> >> If you have some doubt on how this work, I would suggest to read the
>> code
>> >> handling that part:
>> >> Source/PDF/Photon_Flux.f
>> >>
>> >> Cheers,
>> >>
>> >> Olivier
>> >>
>> >>
>> >>
>> >>
>> >> On Nov 7, 2014, at 8:51 PM, Patricia Rebello Teles <
>> >> <email address hidden>> wrote:
>> >>
>> >>> Question #256728 on MadGraph5_aMC@NLO changed:
>> >>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>> >>>
>> >>> Patricia Rebello Teles posted a new comment:
>> >>> Dear authors
>> >>>
>> >>> I apologize but would you have any new about this topic. Should I give
>> >>> more details about it?
>> >>>
>> >>> Thank you.
>> >>>
>> >>> Kind regards Patricia
>> >>>
>> >>> --
>> >>> You received this question notification because you are an answer
>> >>> contact for MadGraph5_aMC@NLO.
>> >>
>> >> --
>> >> If this answers your question, please go to the following page to let
>> us
>> >> know that it is solved:
>> >>
>> >>
>> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=1
>> >>
>> >> If you still need help, you can reply to this email or go to the
>> >> following page to enter your feedback:
>> >> https://answers.launchpad.net/mg5amcnlo/+question/256728
>> >>
>> >> You received this question notification because you asked the question.
>> >>
>> >
>> > --
>> > You received this question notification because you are an answer
>> > contact for MadGraph5_aMC@NLO.
>>
>> --
>> If this answers your question, please go to the following page to let us
>> know that it is solved:
>>
>> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=4
>>
>> If you still need help, you can reply to this email or go to the
>> following page to enter your feedback:
>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>
>> You received this question notification because you asked the question.
>>
>
>

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#8

Yes 2.0.0 is not affected by that bug.

I will not have the time this week to look more in details to your problem, but i should be able to do it next week

Cheers,

Olivier

On Nov 11, 2014, at 1:16 PM, Patricia Rebello Teles <email address hidden> wrote:

> Question #256728 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> Patricia Rebello Teles gave more information on the question:
> Hi again Olivier
>
> I have tested the newest version 2.2.2
>
> Nevertheless the decreasing in the XS with increasing Q**2 value persists,
> or at least the run is very unstable... take a look below.
>
> Results obtained for alpha_EM=1/137, pt_mu > 20 GeV, |eta_mu| < 2.4 and
> m_mumu > 160 GeV for comparison with Calchep results (which remain stable
> around 6.4fb, being compatible with LPAIR)
>
> For instance: if I let Q**2 free (huge values like q2max =
> 5891015.2916062307)
>
> F = fixed_ren_scale ! if .true. use fixed ren scale
> F = fixed_fac_scale ! if .true. use fixed fac scale
>
> the XS = 3.8fb
>
> If I change for Q**2 = 2 GeV**2 (thus decreasing q2max = 2)
>
> T = fixed_ren_scale ! if .true. use fixed ren scale
> T = fixed_fac_scale ! if .true. use fixed fac scale
> 1.414213562373095 = scale ! fixed ren scale
> 1.414213562373095 = dsqrt_q2fact1 ! fixed fact scale for pdf1
> 1.414213562373095 = dsqrt_q2fact2 ! fixed fact scale for pdf2
>
> the XS = 4.8fb
>
> If I change for Q**2 = 0.5 GeV**2 (thus decreasing even more q2max =
> 0.5)
>
> T = fixed_ren_scale ! if .true. use fixed ren scale
> T = fixed_fac_scale ! if .true. use fixed fac scale
> 0.7071067811865476 = scale ! fixed ren scale
> 0.7071067811865476 = dsqrt_q2fact1 ! fixed fact scale for pdf1
> 0.7071067811865476 = dsqrt_q2fact2 ! fixed fact scale for pdf2
>
> the XS = 5.4fb
>
> Any hint to control it?
>
> Cheers Patricia
>
>
> 2014-11-11 13:09 GMT+01:00 Patricia Rebello Teles <email address hidden>:
>
>> Hi Olivier
>>
>> thank you very much.
>>
>> My samples were generated in February 2014 with
>>
>> <MGVersion>
>> # MG version : 5.2.0.0
>> </MGVersion>
>>
>> which has no bug in the EPA, right?
>>
>> Cheers, Patricia.
>>
>>
>>
>>
>>
>>
>>
>> 2014-11-11 0:01 GMT+01:00 Olivier Mattelaer <
>> <email address hidden>>:
>>
>>> Your question #256728 on MadGraph5_aMC@NLO changed:
>>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>>
>>> Status: Open => Answered
>>>
>>> Olivier Mattelaer proposed the following answer:
>>> Dear Patricia,
>>>
>>>> Should this bug be presented in "two-photon" using EPA processes in
>>> general
>>>> or only in the “a a > mu mu" channel?
>>>
>>>
>>> This is difficult to make a general statement since massive particle in
>>> the final state and/or cut reduces the bug to a significant level.
>>> But in general, I would be suspicious about all EPA processes generated
>>> with MG5 between version 2.1.2 and 2.2.1
>>>
>>> Cheers,
>>>
>>> Olivier
>>>
>>>
>>> On Nov 10, 2014, at 10:01 PM, Patricia Rebello Teles
>>> <email address hidden> wrote:
>>>
>>>> Question #256728 on MadGraph5_aMC@NLO changed:
>>>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>>>
>>>> Patricia Rebello Teles gave more information on the question:
>>>> Hi Olivier,
>>>>
>>>> you have mentioned a "huge bug" on previous versions of MG5.
>>>>
>>>> Should this bug be presented in "two-photon" using EPA processes in
>>> general
>>>> or only in the "a a > mu mu" channel?
>>>>
>>>> Could you please clarify it?
>>>>
>>>> Thank you.
>>>>
>>>> Cheers Patricia.
>>>>
>>>>
>>>> 2014-11-08 1:06 GMT+01:00 Olivier Mattelaer <
>>>> <email address hidden>>:
>>>>
>>>>> Your question #256728 on MadGraph5_aMC@NLO changed:
>>>>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>>>>
>>>>> Status: Open => Answered
>>>>>
>>>>> Olivier Mattelaer proposed the following answer:
>>>>> Dear Patricia,
>>>>>
>>>>> When investigating this topic, I found that this topic had a huge bug
>>>>> introduced in 2.1.2.
>>>>> The version that I release yesterday night (2.2.2) actually fix that
>>> bug.
>>>>> Sorry that I forget to react here.
>>>>>
>>>>> Now independently of that bug, It’s clear that the integration error
>>> for
>>>>> that process is under-estimate and
>>>>> that the function has some problem to converge correctly. One way which
>>>>> might help the integrator
>>>>> is to put some cut on the maximum value of the pt of the lepton and of
>>> the
>>>>> lepton pair. In top of the minimal one.
>>>>> But I did not test that one.
>>>>>
>>>>> Concerning the dependencies in Q**2, I didn’t observe an effect which
>>> was
>>>>> large enough to confirm your point.
>>>>> If you have some doubt on how this work, I would suggest to read the
>>> code
>>>>> handling that part:
>>>>> Source/PDF/Photon_Flux.f
>>>>>
>>>>> Cheers,
>>>>>
>>>>> Olivier
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Nov 7, 2014, at 8:51 PM, Patricia Rebello Teles <
>>>>> <email address hidden>> wrote:
>>>>>
>>>>>> Question #256728 on MadGraph5_aMC@NLO changed:
>>>>>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>>>>>
>>>>>> Patricia Rebello Teles posted a new comment:
>>>>>> Dear authors
>>>>>>
>>>>>> I apologize but would you have any new about this topic. Should I give
>>>>>> more details about it?
>>>>>>
>>>>>> Thank you.
>>>>>>
>>>>>> Kind regards Patricia
>>>>>>
>>>>>> --
>>>>>> You received this question notification because you are an answer
>>>>>> contact for MadGraph5_aMC@NLO.
>>>>>
>>>>> --
>>>>> If this answers your question, please go to the following page to let
>>> us
>>>>> know that it is solved:
>>>>>
>>>>>
>>> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=1
>>>>>
>>>>> If you still need help, you can reply to this email or go to the
>>>>> following page to enter your feedback:
>>>>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>>>>
>>>>> You received this question notification because you asked the question.
>>>>>
>>>>
>>>> --
>>>> You received this question notification because you are an answer
>>>> contact for MadGraph5_aMC@NLO.
>>>
>>> --
>>> If this answers your question, please go to the following page to let us
>>> know that it is solved:
>>>
>>> https://answers.launchpad.net/mg5amcnlo/+question/256728/+confirm?answer_id=4
>>>
>>> If you still need help, you can reply to this email or go to the
>>> following page to enter your feedback:
>>> https://answers.launchpad.net/mg5amcnlo/+question/256728
>>>
>>> You received this question notification because you asked the question.
>>>
>>
>>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#9

Thank you Olivier.

Would you have any news about the control of the aa > mu mu cross section?

Cheers Patricia

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#10

Dear Patricia,

Sorry I was in paternity leave.

I just find one "workaround" which is to start to generate your process with
set group_subprocess False
generate a a > mu+ mu-
This produces much more stable result and therefore the integration is much faster.
I currently have no idea why the grouping slows down the code that much in this case, but I didn't search too long on this , since I didn't want to make you wait any longer.

Cheers,

Olivier

Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#11

Hi Olivier, congratulations !!! :-D

I have just tried your suggestion in MG5_2_2_2 but unfortunately the same behavior (increasing Q**2 => decreasing XS) persists.

Remembering that the XS value should increase when the Q**2 value increases, would you have any other idea about the reason of this not expected behavior?

Cheers Patricia

Revision history for this message
Launchpad Janitor (janitor) said : 		#12

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

Revision history for this message
Patricia Rebello Teles (athenafma) said : 		#13

Dear authors,

would you have any news about it?

Thank you.

Kind regards Patricia.

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#14

Dear Patricia,

I’m still trying to understand the stability issue for this process.
Concerning the scale dependence issue, I do not reproduce your problem.
One thing which is surprising is that the scale cut doesn’t cut that much (if at all).
since the expression M_p^2 * x^2/(1-x) is always very very small and in most of the case much below the cut-off scale.
Therefore the dependency in that cut seems very very mild.

Cheers,

Olivier

On 27 Dec 2014, at 12:16, Patricia Rebello Teles <email address hidden> wrote:

> Question #256728 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/256728
>
> Status: Expired => Open
>
> Patricia Rebello Teles is still having a problem:
> Dear authors,
>
> would you have any news about it?
>
> Thank you.
>
> Kind regards Patricia.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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