[Rivet] Is it possible? Rivet and truth look different

[Andy Buckley]

On 09/11/13 19:21, Liron Barak wrote:
> Hi Andy,
> 
> On Fri, Nov 8, 2013 at 2:36 PM, Andy Buckley <andy.buckley at cern.ch
> <mailto:andy.buckley at cern.ch>> wrote:
> 
>     Ok, well the two sets of curves do look a bit different. Maybe this
>     could come from different eta acceptance and changes in Sherpa's
>     handling of beam remnant dipoles, etc.
> 
> But then, wouldn't it also be seen in the first plot? 
> 
>     In the Rivet plot it looks to me
>     like Sherpas 1 and 2 could be ~consistent in the high-stats part, and
>     maybe the deviations elsewhere are just statistical jitter: can you make
>     the plot again with the --mc-errs option flag, to show the MC error
>     bars?
> 
> It is attached... but surprised me is not that the 2 sherpa options are
> different, that is kind of expected, no? What worries me is why the
> Rivet gave different (actually opposite) answers than simple draw of the
> truth jets? If it is because the eta/pt are different, what should I
> "believe" to?

I suspect both are correct. There is no "right" definition of either jet
constituents, jet algorithm, or jet acceptance -- the ATLAS truth jets
are not *the* thruth jets, but just one definition, which I suspect
doesn't coincide with the one used in that validation Rivet analysis.

If you look at the ATLAS data analyses in Rivet, you'll find that the
jet setup often involves excluding muons from the jet inputs, and
applying an eta cut corresponding to the calorimeters. I'm not sure what
eta cut is used in the default ATLAS truth jet collection.

In short, "believe" both! And if you need a specific jet definition in
Rivet then make your own analysis plugin based on MC_TTBAR (or whatever)
with your preferred jet setup.

Cheers,
Andy

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