[Rivet] Rivet: populating high pT leading jet UE plots

[Andy Buckley]

On 16/04/14 23:53, Janssen Xavier wrote:
> 
> Dear Andy,
> 
> I am trying to find an economic way to produce leading jet UE plots
> and populate them with reasonable statistics at high jet pT (let say
> up to 50 GeV). I was thinking of doing many runs and keep 2D histo
> instead of profiles (yes I am still working with AIDA version within
> the CMS framework, so profile adding does not work … )

D'oh! The latest version, 2.1.1, is now working fine in ATLAS
(integrated into our ROOT histogram service and everything) so you can
let the CMS guys know that there shouldn't be any technical blockers to
upgrading...

> and then hack
> a bit to produce the summed profile out of all AIDA files.

In the past we used profiles for this in the usual way, but then used a
*nasty* script called something like rivet-mergeruns which was
hard-coded to paste together groups of bins which "safely" corresponded
to the incoming jet slices. Yuck, but it worked for us for a long time
-- enough to do all the Professor and ATLAS Pythia tunes! Rivet2 makes
it much easier, of course. But I just thought I'd mention that you can
still do run merging with AIDA profiles... it's just a lot more manual
than you'd like.

> As I am
> rather using rivet as a way to get fast through tunes but not really
> wanting to use the plotting functionality, I was thinking about doing
> also some run with some pTmin cuts. If I do that I am afraid I’ll
> have to bookkeep each events (tuple of ptHat, jet Pt, multiplicity,
> ptsum) and match them afterwards in different ptHat region, so is
> there a way to access the the actual pThat value of an event ?

Not really -- it doesn't exist as a well-defined thing beyond 2-parton
final states, and each generator writes the relevant partons in
different ways (or not at all). As mentioned above, sliced runs can
already be used but some bookkeeping is unavoidable.

However, I have a nicer suggestion: use a weighted run with pThat
enhancement, i.e. the sampled events will be distributed according to
dsigma/dpThat * pThat**4 or similar (and then each event down-weighted
by ~ pThat**-4). Certainly PYTHIA6, Pythia8, and Sherpa can all do
this... and I think I also used it in Herwig++ in the past. Such an
enhancement makes it quite easy to cover a very wide jet pT spectrum in
a single run because it distributes the statistics much more widely in
pT than in reality, where almost all will be at low pT (hence the usual
practice of slicing). This way is both faster and avoids the need for
bookkeeping sliced runs.

Hope that helps,
Andy

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

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