[Rivet] Tau decays from Particle guns

[Andy Buckley]

Hi all,

Holger and I chatted on Skype about this. I *think* this cut was an
attempt to stop beam particles from being considered as unstable
hadrons. If so, it should be done properly instead. Holger's going to
try hacking it now.


OTHER DEVELOPMENT NEWS:

For the record I'm also doing some Rivet and YODA hacking at the moment,
too. The release branch now has a first stab at improved Fastjet
interoperability of Jet and Particle, and FastJets tries to do
opportunistic c, b, and tau tagging using the ghost method. The tag
particles come from the HeavyHadrons and (Holger's new) TauFinder, but
I've implemented it so that actually anything can be passed as a "tag"
via the calc() method, or you could retrieve all the tag particles and
use them to implement your own deltaR-based jet tagging if you really
wanted. Still to be properly tested, but this is a very important
development for our Boost deadline.

I'm still hoping we can move to David's new Cuts framework before Boost;
even if we are just demonstrating a pre-release 2.2.0beta version. This
is the point at which the increasingly misnamed release-2-0 branch will
get deleted and we'll just develop on the default branch until 2.2.0 is out.

Making the interface changes (aka huge improvements!) for the Cuts
system will also make it feasible to fiddle a bit with the Projection
base classes: I would like to add a ParticleFinder base class /
interface for all projections which provide a particles() method, and
the TauFinder, UnstableFinalState, JpsiFinder, etc. could all trivially
derive from a single DecayedParticleFinder. This would topple FinalState
from its slightly artificial current position. Not urgent, but should be
a nice interface development when the Cuts and so-on are in place.

In YODA making 2D histo "outflows" work has been a frustrating business.
I think I've worked out now what needs to be done, but it's a big enough
job that it probably needs to wait until after the 2.2.0 Rivet release.
It turns out to be hard to get this stuff "right" from a UI point of
view, while still retaining power and performance, but we are slowly
getting there. I have just removed a bunch of function aliases from the
interface, since maintaining them was proving a nightmare: the next
version will hence need to be 1.2.0 due to the compatibility breaking.
Best to do it before it is *really* heavily used, I think.


Thanks if you managed to read this far! Please let me/us know if you are
also doing/planning any development, or could help out with the urgent
work for Boost.

Cheers,
Andy


On 03/08/14 00:09, Holger Schulz wrote:
> Hi again,
> 
> I narrowed it down to the UnstableFinalState Projection,
> source code, line 34:
> 
>     !isZero(p->momentum().perp())
> 
> If a gun produces tau decays, the taus are produced at rest, resulting
> in them being
> rejected from the accepted particles.
> 
> Any ideas how to cope with this? Simply dropping the cut on the
> transverse momentum
> makes my code work as expected but I have no feeling what it would break
> in other cases.
> 
> Alternatively, I could put some reconstruction code in the taufinder.
> 
> Holger
> 
> 
> 
> 
> On 02/08/14 22:16, Holger Schulz wrote:
>> Hi,
>>
>> I am doing some tau stuff and came across a problem I do not know how
>> to tackle.
>>
>> When I look for taus coming from, e.g. an electron-positron collision,
>> everything is fine.
>> However, when trying to do the same with a tau-gun, the taus
>> themselves are
>> to be found in the incoming particles of a vertex and the TauFinder is
>> unable to find
>> them. Can someone with some more experience with HepMC give me some
>> pointers
>> how to do this properly? It might also be a generator issue (Sherpa in
>> DECAYER mode).
>>
>> Thanks,
>> Holger
>>
>>     GenEvent: #1 ID=0 SignalProcessGenVertex BarcodisZero(e: 0
>>      Momenutm units:     GEV     Position units:      MM
>>      Cross Section: 0 +/- 0
>>      Entries this event: 2 vertices, 5 particles.
>>      Beam Particles are not defined.
>>      RndmState(0)=
>>      Wgts(1)=(0,1)
>>      EventScale -1 [energy]      alphaQCD=-1     alphaQED=-1
>>                                         GenParticle Legend
>>             Barcode   PDG ID      ( Px,       Py,       Pz,     E )
>>     Stat  DecayVtx
>>     ________________________________________________________________________________
>>     GenVertex:       -1 ID:    6 (X,cT):0
>>      Wgts(1)=1
>>      I: 1     10001       15 +0.00e+00,+0.00e+00,+0.00e+00,+1.78e+00  
>>     2        -1
>>      O: 1     10002       15 +0.00e+00,+0.00e+00,+0.00e+00,+1.78e+00  
>>     2        -2
>>     Vertex:       -2 ID:    6
>>     (X,cT)=+0.00e+00,+0.00e+00,+0.00e+00,+8.17e-02
>>      Wgts(1)=1
>>      I: 1     10002       15 +0.00e+00,+0.00e+00,+0.00e+00,+1.78e+00  
>>     2        -2
>>      O: 3     10003     -211 -4.88e-01,+1.27e-01,-1.85e-01,+5.55e-01   1
>>               10004      130 +1.86e-02,+3.71e-02,-2.53e-01,+5.60e-01   1
>>               10005       16 +4.69e-01,-1.64e-01,+4.38e-01,+6.62e-01   1
>>
>>
>>
>>
>> _______________________________________________
>> Rivet mailing list
>> Rivet at projects.hepforge.org
>> https://www.hepforge.org/lists/listinfo/rivet
> 
> 
> 
> _______________________________________________
> Rivet mailing list
> Rivet at projects.hepforge.org
> https://www.hepforge.org/lists/listinfo/rivet
> 


-- 
Dr Andy Buckley, Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow / PH Dept, CERN