NOvARwgt -- NOvA collaboration neutrino event generator reweight tools

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Original author: J. Wolcott jwolcott@fnal.gov

Last update to this document: May 2020

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This document briefly describes the configuration and usage of the NOvA reweighting tools contained in this package.

For build and installation instructions, see INSTALL.md.

Contents:

1. Getting and installing NOvARWGT
2. How to use
3. Contributing to NOvARwgt
4. Support

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1. GETTING AND INSTALLING

Please see INSTALL.md for further instructions.

2. HOW TO USE

1. PATH SETUP

   No matter how you have obtained the package, you will need to do the following:

   • include NOvARwgt's inc directory in your C++ header path (e.g., -I/path/to/NOvARwgt/inc)
   • load NOvARwgt's library during linking (e.g., -L/path/to/NOvARwgt/lib -lNOvARwgt)
   • ensure NOvARwgt's library is accessible when your compiled code is run (e.g., add /path/to/NOvARwgt/lib to $LD_LIBRARY_PATH).
   • ensure the environment variable $NOVARWGT_DATA points to the data subdirectory of your installation and is available at runtime

   If you are using an installation of NOvARwgt in FNAL UPS activated via setup novarwgt, these paths can be simplified by using

   • /path/to/NOvARwgt/inc --> ${NOVARWGT_INC}
   • /path/to/NOvARwgt/lib --> ${NOVARWGT_LIB}

   and $LD_LIBRARY_PATH, $NOVARWGT_DATA should be set for you automatically.

2. WRITING CODE USING NOVARWGT

   • External users

     Users external to the NOvA collaboration will likely be most interested in the novarwgt::Tune interface. Named tunes (which correspond to specific public analyses) can be accessed via

     #include "NOvARwgt/rwgt/tunes/Tunes<year of tune>.h"

     Then, either construct a novarwgt::EventRecord (see inc/NOvARwgt/rwgt/EventRecord.h) directly, or use one of the interfaces (see the headers in inc/NOvARwgt/interfaces) to convert an event record you already have into a novarwgt::EventRecord.

     Obtaining event weights is then simple:

     #include "NOvARwgt/interfaces/GenieInterface.h
     
     ...
     
     double GetWeight(const genie::EventRecord * genieEvt)
     {
       return novarwgt::kCVTune2018.EventWeight(novarwgt::ConvertGenieEvent(genieEvt));
     }
     
     // note that you probably want to cache the converted event record
     // rather than repeating it from above, but this is just an example
     double GetSystsWgt(const genie::EventRecord * genieEvt,
                        const std::map<std::string, double> & systPulls)
     {
       double wgt = 1.0;
       auto evt = novarwgt::ConvertGenieEvent(genieEvt);
       for (const auto & pullPair : systPulls)
       {
         if (pullPair.second == 0)
           continue;
         wgt *= novarwgt::kCVTune2018.SystKnobs().at(pullPair.first)->GetWeight(pullPair.second, evt);
       }
       return wgt;
     }

     If desired, novarwgt::Tune can also return a vector of the individual weights that contribute to the total for an individual event by calling Tune::EventWeightComponents() on the event (see inc/NOvARwgt/rwgt/Tune.h). This returns a vector of novarwgt::NamedWeight objects, each of which contains the weight itself as well as a short name to identify the knob. Similarly, the novarwgt::Tune contains a collections of the names of the systematic knobs it supports, which can be retrieved with Tune::KnobNames(). The knobs can then be addressed individually by name as in the code example above.

   • NOvA users

     NOvA users can of course use the Tune interface above. This is encouraged for the final tune used for major analyses. (Both CAFAna/Vars/XsecTunes.h and the art MCReweight service expose these tunes, so check there to see if you can reuse what's already available.)

     However, there may be situations where the individual weighters or systematic knobs themselves are desired. The best way to obtain them is to use the const instances of the various types sprinkled throughout the header files. Please see CAFAna/Vars/GenieWeights.h and CAFAna/Systs/XSecSysts.h for examples of how to do this.

     (You can also make use of the GetWeighter() function in inc/NOvARwgt/rwgt/IWeightGenerator.h, or the analogous GetSystKnob() in inc/NOvARwgt/rwgt/ISystKnob.h, which ensures there are not duplicate instances of any individual object, if the one you need was not instantiated. However, if the one you need is not available, also consider submitting a GitHub issue to request it be included in a future version.)

     Please see HACKING.md for instructions on how to prototype new weights or syst knobs that are not yet ready to be deployed publicly in NOvARwgt.

3. CONTRIBUTING TO NOVARWGT

Please see HACKING.md for discussion on how to contribute to NOvARwgt.

4. SUPPORT

If you are a user of NOvARwgt outside of the NOvA collaboration, and need help or clarification regarding the package, please contact the conveners of the NOvA Cross Section Tuning working group. As of May 2020, they are:

• Kirk Bays kirk.r.bays@gmail.com
• Aaron Mislivec misli002@umn.edu

If you are unable to reach the conveners, the NOvA co-spokespersons can direct you to the correct experts. The current co-spokespersons and their contact information are listed at http://novaexperiment.fnal.gov/collaboration.

If you are a member of the NOvA collaboration, please consult with the Cross Section Tuning working group via the mailing list or Slack.