[Rivet] delta phi of jets with sherpa

[Ulrike Schnoor]

Hi Andy,

thanks for your hints, I will try again with debugging switched on.

There might actually be a related issue with the xsec override. When
running on a sherpa file with -x 1.0 option, it says at the beginning
(before the event loop):
User-supplied cross-section = 1.000000e+00 pb
but after the event loop:
Cross-section = 2.335586e-03 pb
(which is the sample's correct cross section, but I am wondering if it
shouldn't say 1 pb since I did -x 1.0)
whereas for the Whizard file both statements say:
User-supplied cross-section = 1.000000e+00 pb
and after the event loop:
Cross-section = 1.000000e+00 pb
Does that mean there is a problem with the xsec override? Also for
other plots, I have to do rivet-rescale in order to get the bin
entries on the same order. Btw, I am using rivet 1.5.0.

Thanks!
Ulrike


2011/9/15 Andy Buckley <andy.buckley at ed.ac.uk>:
> Hi Ulrike,
>
> That (pb vs. fb) could certainly lead to discrepancies, but hopefully not if
> you are explicitly specifying -x 1.0 ... unless there is a bug in Rivet's
> xsec override option.
>
> By the way, I think that HepMC specifies that the cross-section should be
> entered as pb: we certainly made sure that a definite unit was specified (as
> opposed to the older vertex and particle 4-vectors) when we added
> cross-section support to HepMC.
>
> Can you try enabling the debug output on rivet, i.e. either -lDEBUG,
> -lAnalysis=DEBUG or -lProjection=DEBUG? This would help to get a picture of
> how many particles and jets are being found in the events from Sherpa and
> Whizard: an obvious disagreement might help to identify the source of the
> problem.
>
> Andy
>
>
> On 15/09/11 11:54, Ulrike Schnoor wrote:
>>
>> Hi Frank,
>>
>> no, the generators don't give the same total cross section, but they
>> are in the same order of magnitude. Also I am using the option -x 1.0
>> and normalizing to cross-section/sumofweights.
>>
>> The units line in the hepmc files show GEV and MM for both. Whizard
>> gives its cross-sections in fb, whereas Sherpa gives them in pb,
>> perhaps that is the reason for the large difference? Is there a way to
>> tell rivet the unit that the generator is using? (Sorry if this is an
>> ignorant question.)
>>
>> Thanks,
>> Ulrike
>>
>>
>> 2011/9/15 Frank Siegert<frank.siegert at cern.ch>:
>>>
>>> Hi Ulrike,
>>>
>>> this is clearly not a Rivet question, but a generator question. Have you
>>> checked whether both generators give the same total cross section for the
>>> same cuts? Also, is it possible that the units in the HepMC file are
>>> accidently inconsistent with what the generator claims (normally pb and
>>> GeV)?
>>>
>>> Frank
>>>
>>> On 15/09/11 11:10, Ulrike Schnoor wrote:
>>>>
>>>> Dear RIVET experts,
>>>>
>>>> When using RIVET to compare WHIZARD (hepmc files) to SHERPA (hepmc2g
>>>> files) I ran into the following problem with the azimuthal angle of
>>>> the jets' FourMomentum, which is happening with my own analysis as
>>>> well as with MC_WWJETS:
>>>> There are far less entries in the jets' phi or delta phi plots for
>>>> Sherpa than for Whizard. You can see this in the following plot made
>>>> with MC_WWJETS:
>>>> http://iktp.tu-dresden.de/~schnoor/rivet/jets_dphi_12.pdf. Has this
>>>> happened before, and what could I do to avoid this? I have already
>>>> tried to rescale the histograms, with no effect.
>>>> The same is happening in my private analysis that also needs the
>>>> azimuthal angle of jets. In addition, the MET distributions of the two
>>>> generators look rather different as shown in this plot:
>>>> http://iktp.tu-dresden.de/~schnoor/rivet/MC_VBS/missingET.pdf
>>>> Could this be related to the problem with the jets' phi coordinates?
>>>>
>>>> Please have a look at this and let me know if you need more information.
>>>> Many thanks,
>>>> Ulrike
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>>>
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>
>
> --
> Dr Andy Buckley
> SUPA Advanced Research Fellow
> Particle Physics Experiment Group, University of Edinburgh
>
> The University of Edinburgh is a charitable body, registered in
> Scotland, with registration number SC005336.
>
>