Poles do not cancel problem for p p > w+ w- h[QCD] in 5fs

Asked by Debashis on 2019-07-05

Dear Madgraph Authors,

I am trying to generate p p > w+ w- h [QCD] FO process in 5fs using the 2.6.6 version of madgraph. But each time, I got this error message for the folder P0_bbx_wpwmh:

...
...
INFO: P0_dxd_wpwmh
INFO: Result for test_ME:
INFO: Passed.
INFO: Result for check_poles:
INFO: Poles successfully cancel for 20 points over 20 (tolerance=1.0e-05)
INFO: P0_bbx_wpwmh
INFO: Result for test_ME:
INFO: Passed.
INFO: Result for check_poles:
Error detected in "launch auto "
write debug file /data/DOC/debashis/work/tar/MG5_aMC_v2_6_6/bin/out/tmp/test/ppwwh_5fs/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
aMCatNLOError : Poles do not cancel, run cannot continue

I suspect that the error is coming from btw- vertex, t being massive. There is also tth vertex. But I got the same error message for pp > w+ w- [QCD] process as well, where tth vertex is not present.

I have read various threads on "Poles do not cancel" on launchpad:
https://answers.launchpad.net/mg5amcnlo/+faq/2720
https://answers.launchpad.net/mg5amcnlo/+question/238819
https://answers.launchpad.net/mg5amcnlo/+question/251302
https://answers.launchpad.net/mg5amcnlo/+question/668490
https://answers.launchpad.net/mg5amcnlo/+question/268184
https://answers.launchpad.net/mg5amcnlo/+question/265667
https://answers.launchpad.net/mg5amcnlo/+question/254144

Most of them suggest that the absence of some EW correction diagram to the QCD born level diagram at the same order is the reason for the problem. In that case switching off IR check by setting IRPoleCheckThreshold to -1d0 in FKS_params.dat is a way out as the EW corrections are usually small. In some cases setting complex_mass_scheme to True also solved this pole cancellation problem. But in my case both gave abnormally large NLO correction. And also I didn't get any warning message like some diagrams are being discarded.

Here are the contents of proc_card_mg5.dat for p p > w+ w- [QCD] and p p > w+ w- h [QCD]
-----------------------------------------------------------------------------------------
set default_unset_couplings 99
set group_subprocesses Auto
set ignore_six_quark_processes False
set loop_color_flows False
set gauge unitary
set complex_mass_scheme False
set max_npoint_for_channel 0
import model sm
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
import model loop_sm-no_b_mass
define p = 21 2 4 1 3 -2 -4 -1 -3 5 -5 # pass to 5 flavors
define j = p
generate p p > W+ W- [QCD]
output out/tmp/test/ppww_5fs
-------------------------------------------------------------------------------
------------------------------------------------------------------------------
set default_unset_couplings 99
set group_subprocesses Auto
set ignore_six_quark_processes False
set loop_color_flows False
set gauge unitary
set complex_mass_scheme False
set max_npoint_for_channel 0
import model sm
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
import model loop_sm-no_b_mass
define p = 21 2 4 1 3 -2 -4 -1 -3 5 -5 # pass to 5 flavors
define j = p
generate p p > W+ W- h [QCD]
output out/tmp/test/ppwwh_5fs

Thank you in advance!

Debashis

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
2019-07-08
Last reply:
2019-07-08

Hi,

Indeed this process does not cancel pole due to the onshell contribution of the top quark.
Such computation can not be done in 5FS but can be done in 4FS.

This being said, They are some paper computing this in 5FS but this require some special handling of the top quark propagator. Such handling is not part of any official version. You can contact the author of such paper if you are interested.

Cheers,

Olivier

> On 5 Jul 2019, at 21:13, Debashis <email address hidden> wrote:
>
> New question #681817 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/681817
>
> Dear Madgraph Authors,
>
> I am trying to generate p p > w+ w- h [QCD] FO process in 5fs using the 2.6.6 version of madgraph. But each time, I got this error message for the folder P0_bbx_wpwmh:
>
> ...
> ...
> INFO: P0_dxd_wpwmh
> INFO: Result for test_ME:
> INFO: Passed.
> INFO: Result for check_poles:
> INFO: Poles successfully cancel for 20 points over 20 (tolerance=1.0e-05)
> INFO: P0_bbx_wpwmh
> INFO: Result for test_ME:
> INFO: Passed.
> INFO: Result for check_poles:
> Error detected in "launch auto "
> write debug file /data/DOC/debashis/work/tar/MG5_aMC_v2_6_6/bin/out/tmp/test/ppwwh_5fs/run_01_tag_1_debug.log
> If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
> aMCatNLOError : Poles do not cancel, run cannot continue
>
> I suspect that the error is coming from btw- vertex, t being massive. There is also tth vertex. But I got the same error message for pp > w+ w- [QCD] process as well, where tth vertex is not present.
>
> I have read various threads on "Poles do not cancel" on launchpad:
> https://answers.launchpad.net/mg5amcnlo/+faq/2720
> https://answers.launchpad.net/mg5amcnlo/+question/238819
> https://answers.launchpad.net/mg5amcnlo/+question/251302
> https://answers.launchpad.net/mg5amcnlo/+question/668490
> https://answers.launchpad.net/mg5amcnlo/+question/268184
> https://answers.launchpad.net/mg5amcnlo/+question/265667
> https://answers.launchpad.net/mg5amcnlo/+question/254144
>
> Most of them suggest that the absence of some EW correction diagram to the QCD born level diagram at the same order is the reason for the problem. In that case switching off IR check by setting IRPoleCheckThreshold to -1d0 in FKS_params.dat is a way out as the EW corrections are usually small. In some cases setting complex_mass_scheme to True also solved this pole cancellation problem. But in my case both gave abnormally large NLO correction. And also I didn't get any warning message like some diagrams are being discarded.
>
> Here are the contents of proc_card_mg5.dat for p p > w+ w- [QCD] and p p > w+ w- h [QCD]
> -----------------------------------------------------------------------------------------
> set default_unset_couplings 99
> set group_subprocesses Auto
> set ignore_six_quark_processes False
> set loop_color_flows False
> set gauge unitary
> set complex_mass_scheme False
> set max_npoint_for_channel 0
> import model sm
> define p = g u c d s u~ c~ d~ s~
> define j = g u c d s u~ c~ d~ s~
> define l+ = e+ mu+
> define l- = e- mu-
> define vl = ve vm vt
> define vl~ = ve~ vm~ vt~
> import model loop_sm-no_b_mass
> define p = 21 2 4 1 3 -2 -4 -1 -3 5 -5 # pass to 5 flavors
> define j = p
> generate p p > W+ W- [QCD]
> output out/tmp/test/ppww_5fs
> -------------------------------------------------------------------------------
> ------------------------------------------------------------------------------
> set default_unset_couplings 99
> set group_subprocesses Auto
> set ignore_six_quark_processes False
> set loop_color_flows False
> set gauge unitary
> set complex_mass_scheme False
> set max_npoint_for_channel 0
> import model sm
> define p = g u c d s u~ c~ d~ s~
> define j = g u c d s u~ c~ d~ s~
> define l+ = e+ mu+
> define l- = e- mu-
> define vl = ve vm vt
> define vl~ = ve~ vm~ vt~
> import model loop_sm-no_b_mass
> define p = 21 2 4 1 3 -2 -4 -1 -3 5 -5 # pass to 5 flavors
> define j = p
> generate p p > W+ W- h [QCD]
> output out/tmp/test/ppwwh_5fs
>
>
> Thank you in advance!
>
> Debashis
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Debashis (deba672) said : #2

Dear Olivier,
Thanks for the reply. I have some queries:

(1) I don't get why it is possible to do it in 4fs, but not in 5fs, if the pole cancellation problem is caused because of the on shell contribution of the top quark. Maybe you are saying when both b and t are massive, the problem goes away?

(2) I was suspecting that QCD correction to btw- vertex had not been taken care of properly. There is also box diagram in NLO QCD correction for p p > w+ w- [QCD]. Can you confirm that they are not causing any issue for the pole cancellation?

(3) I have found this paper https://arxiv.org/abs/1409.5301 and this page https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/bbH#no1 where they have considered MSbar renormalisation scheme, instead of default onshell renormalisation scheme of madgraph, for bottom yukawa in bbH production.

I tried to search some papers where top quark propagator has been handled specially to solve this pole cancellation problem but could not find them with some mild attempts. If those papers are handy to you, could you please refer me to those.

Thanks
Debashis

Hi,

> (1) I don't get why it is possible to do it in 4fs, but not in 5fs, if
> the pole cancellation problem is caused because of the on shell
> contribution of the top quark. Maybe you are saying when both b and t
> are massive, the problem goes away?

If the b is massive, the b quark radiation is not part of the NLO radiation concequently
in 5 flavor you have the following final state (for the real contribution)
w+ w- b
that you do not have within the 4 flavor (and therefore you do not have the issue with the onshell top.

> (2) I was suspecting that QCD correction to btw- vertex had not been
> taken care of properly. There is also box diagram in NLO QCD correction
> for p p > w+ w- [QCD]. Can you confirm that they are not causing any
> issue for the pole cancellation?

Do not know what you are talking about.

> (3) I have found this paper https://arxiv.org/abs/1409.5301 and this
> page https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/bbH#no1 where
> they have considered MSbar renormalisation scheme, instead of default
> onshell renormalisation scheme of madgraph, for bottom yukawa in bbH
> production.

Not fully sure but I think that this is the paper:
https://arxiv.org/pdf/1607.05862.pdf

Cheers,

Olivier

> On 6 Jul 2019, at 22:02, Debashis <email address hidden> wrote:
>
> Question #681817 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/681817
>
> Status: Answered => Open
>
> Debashis is still having a problem:
> Dear Olivier,
> Thanks for the reply. I have some queries:
>
> (1) I don't get why it is possible to do it in 4fs, but not in 5fs, if
> the pole cancellation problem is caused because of the on shell
> contribution of the top quark. Maybe you are saying when both b and t
> are massive, the problem goes away?
>
> (2) I was suspecting that QCD correction to btw- vertex had not been
> taken care of properly. There is also box diagram in NLO QCD correction
> for p p > w+ w- [QCD]. Can you confirm that they are not causing any
> issue for the pole cancellation?
>
> (3) I have found this paper https://arxiv.org/abs/1409.5301 and this
> page https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/bbH#no1 where
> they have considered MSbar renormalisation scheme, instead of default
> onshell renormalisation scheme of madgraph, for bottom yukawa in bbH
> production.
>
> I tried to search some papers where top quark propagator has been
> handled specially to solve this pole cancellation problem but could not
> find them with some mild attempts. If those papers are handy to you,
> could you please refer me to those.
>
> Thanks
> Debashis
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Debashis (deba672) said : #4

Thanks Olivier for the elucidation and sharing the paper.

Debashis (deba672) said : #5

Dear Olivier,

Sorry for re-opening this thread. I am again little confused. In 4fs, if we want to see bottom quark contribution to w+w- production, we will have to take b b~ in the final state as well. In that case on-shell top will be both in virtual diagram and real diagram, in addition to being present at tree level. Maybe you are saying as on-shell top is present both in virtual and real diagram in 4fs, but only in real diagrams in 5fs, poles do not cancel in 5fs?

Thanks
Debashis

Hi,

As stated in the FAQ:

http://amcatnlo.web.cern.ch/amcatnlo/list_detailed.htm

A consistent SU(2)×U(1) gauge invariant treatment of width effects (such as the complex mass scheme) is still under validation when unstable colored particles appear in the loop. Therefore processes that feature resonances charged in QCD are not yet supported, e.g. p p > W+ W- b b~ [QCD] that has top quark resonant contributions.

You also have a line for resonance opening:

Processes in which new resonances open up in the real-emission diagrams give unstable results that are usually wrong. For example p p > W+ W- [QCD] in the five-flavor scheme has top quark resonant contributions in the real emission diagrams that the phase-space integration is not able to handle, leading to a non-converging integral. (Note that for this particular case, p p > W+ W- [QCD], the solution is to use the four-flavor scheme with a diagonal CKM matrix to prevent the top quark resonance from appearing.) It is under investigation what the best solution is in the context of NLO event generation and therefore these processes are not yet supported.

Cheers,

Olivier

On 8 Jul 2019, at 17:17, Debashis <<email address hidden><mailto:<email address hidden>>> wrote:

Question #681817 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/681817

   Status: Answered => Open

Debashis is still having a problem:
Dear Olivier,

Sorry for re-opening this thread. I am again little confused. In 4fs, if
we want to see bottom quark contribution to w+w- production, we will
have to take b b~ in the final state as well. In that case on-shell top
will be both in virtual diagram and real diagram, in addition to being
present at tree level. Maybe you are saying as on-shell top is present
both in virtual and real diagram in 4fs, but only in real diagrams in
5fs, poles do not cancel in 5fs?

Thanks
Debashis

--
You received this question notification because you are an answer
contact for MadGraph5_aMC@NLO.

Can you help with this problem?

Provide an answer of your own, or ask Debashis for more information if necessary.

To post a message you must log in.