[Rivet] pT cut on B hadrons

[Andy Buckley]

Hi Kevin,

Thanks for the ping -- this had gone off my radar / I thought I had 
answered. I've copied this to the Rivet developer list, which is a more 
reliable place to ask questions due to more people & more expertise on 
the receiving end.

I'm not quite sure why you are asking: have you noticed a change in 
behaviour without the cut across Rivet versions? In general I think 
making cuts explicit is the right thing to do.

But I guess when you say that you are doing it manually that you really 
mean you are explicitly making a list of "b" particles with some 
kinematic cuts, then deltaR-matching those to the jets? We could/should 
allow the user to specify tag-particle cuts when configuring the 
FastJets projection, but right now you can do something like:

const Jets& myjets = applyProjection<FastJets>(evt, "Jets").jets();
foreach (const Jet& j, jets) {
     foreach (const Particle& t, j.bTags()) {
         if (t.pT() > 5*GeV) // accept this jet
     }
}

We can make this nicer to use, e.g. I imagine something like this would 
be helpful:

foreach (const Jet& j, jets) {
     if (j.bTags(Cuts::pT > 5*GeV).size() > 0) // accept this jet
}

What do you think? It's an easy feature to add.

Andy


On 29/07/15 02:20, Kevin Finelli wrote:
> Hi Andy,
>
> Just pinging again to see if you have had the chance to read this.
>
> Thanks,
> Kevin
>
> On Fri, Jul 24, 2015 at 5:06 PM, Alexander Grohsjean
> <Alexander.Grohsjean at desy.de <mailto:Alexander.Grohsjean at desy.de>> wrote:
>
>     Hi Andy,
>
>     maybe to clarify. In the original code I provided, there was a cut
>     of 5 GeV.
>     When testing my implementation against the Rivet one using 50 k events,
>     as Kevin wrote, we got exactly the same yoda files out.
>     That's why it is not clear if this cut was dropped between versions
>     or if the 50k was not enough statistics to see any difference.
>
>     Cheers, Alexander.
>
>
>
>
>     Am 24.07.2015 um 04:31 schrieb Kevin Finelli:
>
>         Hi Andy,
>
>         We were hoping you could clarify the situation with pT cuts on B
>         hadrons used in truth jet b-tagging within Rivet.  In my own
>         tests, using 2.2, I have been "manually" applying the standard 5
>         GeV pT requirement on B hadrons needed for a jet to be
>         considered b-tagged.  This is now in the 7 TeV pseudotop
>         analysis (ATLAS_2015_I1345452), Chris G. submitted a patch about
>         a week ago.
>
>         Looking back, I noticed the tt+jets analysis
>         (ATLAS_2014_I1304688) doesn't make this cut explicitly.
>         Alexander mentioned that this cut was not needed when the
>         analysis was tested, as two implementations of the ghost
>         association gave identical results in 50k events.
>
>         Is it possible there was a cut in FastJets that changed in Rivet
>         2.2?  In any case it seems that we might want to go back now and
>         make this cut explicit in the tt+jets routine.
>
>         Regards,
>         Kevin
>
>
>


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