Wrong cross section when I specify the polarisation of final W boson

Asked by Da Liu on 2018-01-23

Hi,

I want to calculate the cross section for the longitudinal W cross section in the sm W+1jet process at the 14 TeV LHC, so I modify the matrix.f in the subprocess folder after I output the process. For the g u > w+ d process, the results seem reasonable, when I put pt larger than 500 GeV, the results for the longitudinal is 0.00085pb, which is as expected, because at high-pt, the W should be mainly transverse. But when I do the same thing for the process u g > w+ d, the cross section with pt > 500 GeV for the longitudinal W is 5.9pb, which is not possible, as the total rate for pt > 500 GeV in this process is 0.6085pb.
Below is the part I modify the polarisation of W boson.

      INTEGER ISUM_HEL
      LOGICAL MULTI_CHANNEL
      COMMON/TO_MATRIX/ISUM_HEL, MULTI_CHANNEL
      INTEGER MAPCONFIG(0:LMAXCONFIGS), ICONFIG
      COMMON/TO_MCONFIGS/MAPCONFIG, ICONFIG
      INTEGER SUBDIAG(MAXSPROC),IB(2)
      COMMON/TO_SUB_DIAG/SUBDIAG,IB
      DATA XTRY, XREJ /0,0/
      DATA NGOOD /0,0/
      DATA ISHEL/0,0/
      SAVE YFRAC, IGOOD, JHEL
      DATA (NHEL(I, 1),I=1,4) / 1,-1, 0,-1/
      DATA (NHEL(I, 2),I=1,4) / 1,-1, 0, 1/
      DATA (NHEL(I, 3),I=1,4) / 1, 1, 0,-1/
      DATA (NHEL(I, 4),I=1,4) / 1, 1, 0, 1/
      DATA (NHEL(I, 5),I=1,4) /-1,-1, 0,-1/
      DATA (NHEL(I, 6),I=1,4) /-1,-1, 0, 1/
      DATA (NHEL(I, 7),I=1,4) /-1, 1, 0,-1/
      DATA (NHEL(I, 8),I=1,4) /-1, 1, 0, 1/
      DATA IDEN/96/

Could you please help me have a look at it? Thanks a lot.

Best wishes,
Da Liu

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
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Last query:
2018-01-23
Last reply:
2018-01-24

Hi,

I have tested this but with a slightly different change to the matrix.f compare to yours.
In my case, I have replace the following line (present at different stage of the file):
T=MATRIX1(P ,NHEL(1,I),JC(1))
by either
            if(NHEL(3,I).ne.0) then
               T=MATRIX1(P ,NHEL(1,I),JC(1))
            else
               T =0
            endif
or by
            if(NHEL(3,I).eq.0) then
               T=MATRIX1(P ,NHEL(1,I),JC(1))
            else
               T =0
            endif

I have done this both for ug and gu initial state. Here are my results:

1) Whith default cut ( ug vs gu initial state):
no restriction: 5088 +- 2 vs 5088 +-2
transverse : 4427 +-2. vs 4426 +-2
long: 657 +-1. vs 660+=1

2) with a pt cut at 500 GeV ( ug vs gu initial state):
no restriction: 0.511 vs 0.5109
transverse: 0.5090 vs 0.5084
long: 0.00073 vs 0.00074

This is 13 TeV but should not have any impact on the result, those results clearly indicate that your modification of (at least) u g initial state is not done correctly.

Cheers,

Olivier

> On 23 Jan 2018, at 08:48, Da Liu <email address hidden> wrote:
>
> New question #663424 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/663424
>
> Hi,
>
> I want to calculate the cross section for the longitudinal W cross section in the sm W+1jet process at the 14 TeV LHC, so I modify the matrix.f in the subprocess folder after I output the process. For the g u > w+ d process, the results seem reasonable, when I put pt larger than 500 GeV, the results for the longitudinal is 0.00085pb, which is as expected, because at high-pt, the W should be mainly transverse. But when I do the same thing for the process u g > w+ d, the cross section with pt > 500 GeV for the longitudinal W is 5.9pb, which is not possible, as the total rate for pt > 500 GeV in this process is 0.6085pb.
> Below is the part I modify the polarisation of W boson.
>
> INTEGER ISUM_HEL
> LOGICAL MULTI_CHANNEL
> COMMON/TO_MATRIX/ISUM_HEL, MULTI_CHANNEL
> INTEGER MAPCONFIG(0:LMAXCONFIGS), ICONFIG
> COMMON/TO_MCONFIGS/MAPCONFIG, ICONFIG
> INTEGER SUBDIAG(MAXSPROC),IB(2)
> COMMON/TO_SUB_DIAG/SUBDIAG,IB
> DATA XTRY, XREJ /0,0/
> DATA NGOOD /0,0/
> DATA ISHEL/0,0/
> SAVE YFRAC, IGOOD, JHEL
> DATA (NHEL(I, 1),I=1,4) / 1,-1, 0,-1/
> DATA (NHEL(I, 2),I=1,4) / 1,-1, 0, 1/
> DATA (NHEL(I, 3),I=1,4) / 1, 1, 0,-1/
> DATA (NHEL(I, 4),I=1,4) / 1, 1, 0, 1/
> DATA (NHEL(I, 5),I=1,4) /-1,-1, 0,-1/
> DATA (NHEL(I, 6),I=1,4) /-1,-1, 0, 1/
> DATA (NHEL(I, 7),I=1,4) /-1, 1, 0,-1/
> DATA (NHEL(I, 8),I=1,4) /-1, 1, 0, 1/
> DATA IDEN/96/
>
> Could you please help me have a look at it? Thanks a lot.
>
> Best wishes,
> Da Liu
>
> --
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> contact for MadGraph5_aMC@NLO.

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