Hi Jeremy.

a point was made before that no one actually runs with free nucleon targets. A change to reproduce ANL/BNL in the default tune is by itself unwarranted if not supported by comparisons to nuclear data. So we need to study the suggested model configurations against all data, before deciding whether we want to introduce a similar change in one or more configurations (default or not).

The issue was not unknown to GENIE before the Rodrigues paper, and their tuning can not be copied into GENIE as a host of things have changed wrt to the version of GENIE used by Rodrigues et al. So we need to investigate our own independent solution. For one, Rodrigues et al have not investigated -I think- the impact of their tune on other data/MC comparisons where GENIE did well.

As for the reweighting: Will look at it, but there is no guarantee whatsoever that a weight calculator (with its default initialisation) works for any configuration of GENIE. The GENIE reweighting needs a major upgrade to properly initialise itself with configuration data stored in the event file it reweighs. Otherwise, it is all too easy for differences to creep in. I always wanted to do this upgrade, which is very substantial, but i do not see the motivation for this any more. Professor does not need reweighting, so our tunes won't depend critically upon it. So it is certain that there will be a increasingly widening gap between the amount of tuning and error estimation done in GENIE, and the amount of it that can be supported via reweighting. Users need to develop own solutions for their analysis needs.

Talk to you tomorrow.

cheers
Costas

--
Dr Constantinos Andreopoulos
Reader (Assoc. Professor) in Particle Physics
Univ. of Liverpool & STFC Rutherford Appleton Lab
+44-(0)7540 847333 (Mobile)
+44-(0)1235 445091 (Office/RAL)
+44-(0)1517 943201 (Office/Liverpool)
http://costas.andreopoulos.eu
https://valor.pp.rl.ac.uk
https://genie.hepforge.org

Sent from my iPhone

On 21 Nov 2016, at 17:47, Jeremy Wolcott <[log in to unmask]<mailto:[log in to unmask]>> wrote:


Hi all,

After an extended discussion Hugh & I had this morning, we'd like to add another candidate item for this meeting: the reweighting knobs for nonresonant pion production (RvnCC1pi, etc.).  After the paper from Rodrigues et al. describing how they were able to make GENIE agree much better with revised bubble chamber data from ANL & BNL (https://inspirehep.net/record/1414604) by reducing the predicted nonresonant pion production at low W, this has become something of a front-line issue.  I know of at least two experiments (MINERvA and NOvA) who are applying post facto corrections to GENIE according to that paper because it substantially affects their predictions, and it's probably worth our trying to decide how we can incorporate it into the default tune.

Perhaps more immediately, in looking through the reweight knobs to understand exactly what Rodrigues et al.'s tuning was doing, I noticed something which seemed kind of unusual: the R{v,vbar}{n,p}{CC,NC}{1,2}pi knobs all apparently affect DIS events with W < 2.0 GeV (see Doxygen for GReWeightNonResonanceBkg<https://genie.hepforge.org/doxygen/html/classgenie_1_1rew_1_1GReWeightNonResonanceBkg.html>; note that member fWmin, which should probably actually be called fWmax, is set to 2.0 GeV in Init()).  This seems sort of unusual in that the usual crossover point for things of this nature (e.g., cutoff of resonant pion production) is W=1.7 GeV.  We were lead to a few questions, which we can discuss tomorrow:

  1.  Was this (upper bound of 2.0 GeV instead of 1.7 GeV) the intent?  If so, what was the rationale?
  2.  The usual philosophy for the reweight knobs is that by turning them, one arrives at the same effective event sample as one would have by running GENIE with a modification to some config parameter(s).  On the face of it, this situation seems to break that prescription.  Is that actually the case?
  3.  Does the current situation double-count uncertainties (especially in the 1.7 < W/GeV < 2.0 region) that are handled by some other knobs?
  4.  Are there known users who depend on the current behavior, or could it be modified if we decide that any of (1)-(3) represent problems?

-Jeremy

On 11/11/2016 07:04 AM, Costas Andreopoulos wrote:

Hi all

Are you available for a GENIE meeting on Nov 22 (at the regular GENIE slot) focussing
on work for v3 and v4?

Could discuss:

-----
1) Quantitative characterisation of proposed model configurations for v3

A report is now being drafted by Marco, Anselmo and Rhiannon as they start to see and
digest the comparisons outputs. Hopefully this can be circulated a couple of days before
the meeting.

2) Next steps with v3

- Identifying and sorting out problems with model configurations.
- Deploying code to support multiple comprehensive model configurations
- Reiterating on v3 scope.

3) Progress with Prof/GENIE interface and plans for v4

We have a staged QE+MEC tuning exercise (6 stages from a trivial fit to a full analysis)
in order to sort out the Prof/GENIE interface specifics and develop all production scripts.
There is also now, I think, a quite good understanding of what is needed from our side.
Recent and ongoing devel in the Comparisons in order to be able to include all possible
correlations simplifies the interface to Professor. Depending on how responsive the Professor
authors are, we may have stage 1 done, so could discuss experience / issues.

cheers
Costas


--
Dr. Constantinos Andreopoulos
Reader (Associate Professor) in Experimental Particle Physics
University of Liverpool & STFC Rutherford Appleton Laboratory
+44-(0)7540-847333 (Mobile)
+44-(0)1235-445091 (Office/RAL)
+44-(0)1517-943201 (Office/Liverpool)
http://costas.andreopoulos.eu
https://valor.pp.rl.ac.uk
https://genie.hepforge.org