[EvtGen] Problem with EvtGen R01-07-00

[Martin Ritter]

Hi John,

Thanks for the quick work. Yes, I received mail updates without 
problems. I commented directly on the issue to keep the discussion in 
one place.

Best Regards,

Martin


On 13/03/18 12:43, John Back wrote:
> Hi Martin, all,
> 
> I have updated the code (master git repository) to hopefully fix the 
> problems and have updated the ticket. Let me know if a) the code is 
> working for you and if b) you are getting emails regarding ticket 
> updates, since we are still tweaking the setup of the bug reporting 
> feature to make sure it is working as intended.
> 
> Thanks,
>      John.
> 
> On 09/03/18 15:02, Martin Ritter wrote:
>> Hi John,
>>
>> of course, here you go: https://evtgen.hepforge.org/trac/ticket/1
>>
>> I could not really fill out component/milestones as they are not
>> configured yet but everything else worked fine.
>>
>> Cheers,
>>
>> Martin
>>
>> On 09/03/18 15:35, John Back wrote:
>>> Hi Martin,
>>>
>>> Thanks for your report and I agree with your assessments:
>>>
>>> a) EvtPDL::getMass() needs to be replaced with EvtPDL::getMeanMass().
>>>
>>> The getMass() function returns a mass sampled from the particle's
>>> resonance shape, but we need the pole mass. I'm not sure how this
>>> mistake was done, but I guess it was only tested on particles with
>>> very small or zero widths, so getMass() would be the same as
>>> getMeanMass(), and we should have done more testing.
>>>
>>> b) For particles with Pythia id = 0, we should add a check in the
>>> entry_generic and entry_alias conditional statements to also require
>>> the id to be non-zero. This will then avoid the issue of redefining
>>> the void particle many times.
>>>
>>> Could you please create a bug report for these issues on our HepForge
>>> webpage:
>>>
>>> http://evtgen.hepforge.org/trac/report/3
>>>
>>> using the "guest" account (password = evtgen)? This is so that we can
>>> i) test that our bug reporting feature works for users such as
>>> yourself and we can ii) keep a record of the bug and its required fix.
>>> Let us know if you are having problems creating the bug report.
>>>
>>> Thanks,
>>>      John.
>>>
>>> On 09/03/18 13:01, Martin Ritter wrote:
>>>> Dear EvtGen Developers,
>>>>
>>>> I was trying to use EvtGen R01-07-00 for Belle II and I found some
>>>> problems with the synchronization of particle properties between EvtGen
>>>> and Pythia which was introduced with the following commit:
>>>>
>>>>> commit 48a86cf7d8c45cf026beac84df6e204d6eb42b1d
>>>>> Author: John Back <J.J.Back at warwick.ac.uk>
>>>>> Date:   Fri Apr 7 16:03:30 2017 +0100
>>>>>
>>>>>     Make sure Pythia8 uses the same particle properties as EvtGen.
>>>>>     Modified EvtGenExternal/EvtPythiaEngine to ensure that the
>>>>> EvtGen-based
>>>>>     instances of Pythia8 (for generic and alias decays) use the same
>>>>>     particle properties as defined by EvtGen, courtesy Patrick Robbe
>>>>> (LHCb).
>>>>
>>>> I modified the evtgen code to provide some additional output (see
>>>> attached output.patch). As you can see from the attached log output
>>>> (evtgen_output.txt) this produces very weird results (with Pythia
>>>> 8.215):
>>>>
>>>> 1. The Pythia particle with id 0 (void) gets redefined ~160 times,
>>>>     probably because the particles are not known to Pythia.
>>>> 2. The assigned masses are not correct. For example in line 142 the 
>>>> rho0
>>>>     is set to 1.023 GeV. This is due to the fact that the code uses
>>>>     EvtPDL::getMass() instead of EvtPDL::getMeanMass().
>>>>
>>>> I was wondering if (1) is an effect of the Pythia version we use but I
>>>> haven't seen anything in the Pythia Changelog or in the EvtGen 
>>>> README so
>>>> maybe you know more.
>>>>
>>>> For (2) I really believe this is a bug in the code.
>>>>
>>>> Best Regards,
>>>>
>>>> Martin
>>>>
>>

-- 
Dr. Martin Ritter

LMU München, Excellence Cluster Universe
Boltzmannstrasse 2, 85748 Garching

Tel: (+49) 89 35831-7152
Fax: (+49) 89 3299-4002