mmllcut/addmasses issue

Hi Josh,

The fact that you don't have enough events indicates that your matrix element is divergent for such cut.
Indeed your photon might be soft and therefore creating a divergencies which should be cure by NLO process.

Concerning the bug in addmasses.py this is probably due to the fact that the energy of the lepton is smaller than the mass that you want to restore.

Cheers,

Olivier

On Aug 1, 2013, at 9:01 AM, Josh McFayden <email address hidden> wrote:

> New question #233378 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/233378
>
> Hi,
>
> I'm having a problem that appears to be related to low or zero mmllcut values.
>
> When I try to generate the process
> p p > t t~ l+ l-
> (ttbar+Z with Z->ll and gamma*->ll contributions)
>
> with the following modifications to the default cuts:
>
> ptl=1.0
> etal=5.0
> drll=0.0
> drjl=0.0
> mmll=0.0
>
> In normal running mode I don't see any errors but I don't get enough events generated: 61 are generated when asking for 40000.
> But if I generate a gridpack and then run the event generation from that gridpack I get the following error:
>
> Now generating 40000 events with random seed 200222 and granularity -1
> P0_gg_ttxtaptam
> P0_gg_ttxll
> P0_bbx_ttxtaptam
> P0_qq_ttxtaptam
> P0_qq_ttxll
> P0_bbx_ttxll
> N subproc = 6
> N jobs = 3
> N jobs = 3
> N jobs = 4
> DONE
> Moving events from events.lhe
> Running addmasses.py to add masses and correct kinematics of fixed particles
> Traceback (most recent call last):
> File "./madevent/bin/internal/addmasses.py", line 268, in <module>
> pmagNew=math.sqrt(p1.mom.E**2-p1.mom.m**2)
> ValueError: math domain error
>
> However, if I repeat this step with mmll=5.0 then everything runs with no problem.
>
> Is there an issue with going very low with the min mll cut?
>
> Cheers,
>
> Josh.
>
>
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