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Opened 6 years ago

Closed 4 years ago

#250 closed defect (wontfix)

Comix/Amegic disagree for WW->ee

Reported by: Steffen Schumann Owned by: support@sherpa-mc.de
Priority: major Milestone: rel-2.2.0
Component: Unknown Version: 2.0.beta
Keywords: Cc:

Description

For the attached fixed energy, fixed order setup Comix & Amegic strongly disagree on the cross section for WW->ee, 8 vs. 0.4 pb. While a similar setup with IS Z's works fine I can't get this one to agree. I tried the various choices for the gauge in Amegic, no change.

Anyone any idea?

Attachments (1)

Run.dat (1.3 KB) - added by Steffen Schumann 6 years ago.

Download all attachments as: .zip

Change History (8)

Changed 6 years ago by Steffen Schumann

Attachment: Run.dat added

comment:1 Changed 6 years ago by Frank Siegert

Milestone: rel-2.0.0

comment:2 Changed 5 years ago by Stefan Hoeche

No idea, but I have checked that Comix gives the correct result pointwise. The test point is

p_lab[0]=Vec4D(1000,0,0,996.761147135561);
p_lab[1]=Vec4D(1000,0,0,-996.761147135561);
p_lab[2]=Vec4D(1000,9.5491248055827,-4.95020237239177,999.942153182833);
p_lab[3]=Vec4D(1000,-9.5491248055827,4.95020237239177,-999.942153182833);

For which Comix gives

// 2_2__W+__W-__e-__e+
double ME = 6.597330053016647e-05; // in GeV^2, incl. symfacs
// 2_2__e-__e+__W+__W-
double ME = 0.0001484399261928508; // in GeV^2, incl. symfacs

In the second case I have swaped momenta {0,1} and {2,3}, such that the ME is the same up to symmetry factors. In this process the ratio of symmetry factors is 9/4, which is exactly the ratio of the ME values.

Amegic gives

// 2_2__W+__W-__e-__e+
double ME = 5.635166056739648; // in GeV^2, incl. symfacs
// 2_2__e-__e+__W+__W-
double ME = 0.06433668100554696; // in GeV^2, incl. symfacs

The ratio is 0.0114169982495.

comment:3 Changed 5 years ago by Stefan Hoeche

Milestone: rel-2.0.0rel-2.1.0

comment:4 Changed 5 years ago by Stefan Hoeche

Milestone: rel-2.1.0rel-2.1.1

comment:5 Changed 5 years ago by Steffen Schumann

problem remains even with helicity mapping switched off now.

comment:6 Changed 5 years ago by Frank Siegert

Milestone: rel-2.1.1rel-2.2.0

comment:7 Changed 4 years ago by Stefan Hoeche

Resolution: wontfix
Status: newclosed

This needs to be re-checked on the bsm branch which is to supersede trunk in the near future.

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as closed The owner will remain support@sherpa-mc.de.

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