Alpha_em in the LHE output file

[Kazuhiro Yamamoto]

Dear MG/ME authors,

According to the manual of LHE format for event record, the 1st line of every event record
should have "NUP, IDPRUP, XWGTUP, SCALUP, AQEDUP, AQCDUP" of HEPUEP common block.
But I found the 5th element of this line is something different from Alpha_EM like below,

<event>
 5 0 0.2322800E+01 0.7955208E+02 0.7957747E-01 0.1328773E+00
        2 -1 0 0 501 0 0.00000000000E+00 0.00000000000E+00 0.39575137121E+01 0.39575137121E+01 0.00000000000E+00 0. -1.
       -1 -1 0 0 0 501 0.00000000000E+00 0.00000000000E+00 -0.39977966292E+03 0.39977966292E+03 0.00000000000E+00 0. 1.
       24 2 1 2 0 0 0.00000000000E+00 0.00000000000E+00 -0.39582214921E+03 0.40373717663E+03 0.79552083513E+02 0. 0.
      -13 1 3 3 0 0 0.14539702790E+02 -0.36320249214E+02 -0.23435674198E+03 0.23759976004E+03 0.00000000000E+00 0. 1.
       14 1 3 3 0 0 -0.14539702790E+02 0.36320249214E+02 -0.16146540723E+03 0.16613741659E+03 0.00000000000E+00 0. -1.
# 0.1400000E+05 0.1400000E+05
</event>

The 5th element "0.7957747E-01" is something far from 1/137 (Alpha(0)) or 1/127 (Alpha(Z0)).
(If it is 0.79E-02, not 0.79E-01, it would be reasonable.)
This is an output of MG/ME v5. But the one from MG/ME v4, the event record is like

<event>
11 100 0.5848300E+09 0.9118800E+02 0.7818608E-02 0.1300000E+00
        2 -1 0 0 501 0 0.00000000000E+00 0.00000000000E+00 0.32276682981E+03 0.32276682981E+03 0.00000000000E+00 0. -1.
       -1 -1 0 0 0 501 0.00000000000E+00 0.00000000000E+00 -0.28508745348E+03 0.28508745348E+03 0.00000000000E+00 0. 1.
       25 2 1 2 0 0 -0.91817605887E+02 -0.19599186764E+03 0.78358910151E+02 0.25958399215E+03 0.12000185519E+03 0. 0.
       24 2 1 2 0 0 -0.32559371594E+02 0.78245194025E+01 0.12565486544E+02 0.87298932506E+02 0.79635898828E+02 0. 0.
       25 2 1 2 0 0 0.12437697748E+03 0.18816734824E+03 -0.53245020366E+02 0.26097135863E+03 0.11997680760E+03 0. 0.
       22 1 3 3 0 0 0.28404088468E+02 -0.33955643721E+02 0.36036189247E+01 0.44415808577E+02 0.00000000000E+00 0. -1.
       22 1 5 5 0 0 0.50905311909E+02 0.17057407518E+03 -0.22572285894E+02 0.17943348069E+03 0.00000000000E+00 0. -1.
       22 1 5 5 0 0 0.73471665572E+02 0.17593273063E+02 -0.30672734472E+02 0.81537877940E+02 0.00000000000E+00 0. -1.
       22 1 3 3 0 0 -0.12022169436E+03 -0.16203622392E+03 0.74755291226E+02 0.21516818358E+03 0.00000000000E+00 0. -1.
       -3 1 4 4 0 502 -0.87473183642E+01 -0.24236538248E+02 -0.22458201604E+02 0.34180347923E+02 0.00000000000E+00 0. 1.
        4 1 4 4 502 0 -0.23812053230E+02 0.32061057650E+02 0.35023688148E+02 0.53118584584E+02 0.00000000000E+00 0. -1.
</event>

and the 5th element of the 1st line is "0.7818608E-02" (=~ 1/127) as is expected.
So, is there something wrong ?

Best regards,
Kazuhiro Yamamoto

[Olivier Mattelaer (olivier-mattelaer)]

Hi Kazuhiro,

Thanks so much for having pointing this to us.
Nobody notice this points before.
The problem is in the interface with the UFO model.
So a quick fix is to use the MG4 model:
(import model sm_v4)
with this model this is working fine.

I'm going to discuss this point with FR author in order to have an agreement on how identify alpha_ew from the UFO model such that this value can be accurate.

Cheers and thanks,

Olivier

[Olivier Mattelaer (olivier-mattelaer)]

Hi,

I'm waiting some confirmation from the FR team, but this is apriori the patch to the code in order to have it right for most of the UFO model (all of those who pass by alpha_ew^-1 for the definition of alpha_ew)

Cheers,

Olivier