Rivet release 2.3.0

This new release of Rivet adds an amazing 15 new analysis routines, as well as validating several long-standing analyses from the UNVALIDATED set (and two re-UNVALIDATions!) and making a variety of minor analysis fixes and improvements.

We’re very pleased to announce the release of Rivet 2.3.0 and an accompanying release of version 1.4.0 of the YODA histogramming package.

This new release of Rivet adds an amazing 15 new analysis routines, as well as validating several long-standing analyses from the UNVALIDATED set (and two re-UNVALIDATions!) and making a variety of minor analysis fixes and improvements. As you’d expect from the non-trivial release number change, the framework has also received some significant improvements.

One long-standing issue has been whether neutrinos are to be included in jet finding or not: detectors do not see them, of course, but MC-driven calibrations can add their average contributions back to the 4-vectors. But telling the FastJets projection to useInvisibles() would include hard-process neutrinos (and invisible BSM hypotheticals), while calibrations would typically only be intended to account for neutrinos from hadron decays. We have changed the behaviour of useInvisibles() to only accept non-prompt stable invisibles, and added both an optional argument to that method and the FastJets constructor to allow any of the three sane invisibles strategies to be specified via enums. A similar method, enum, and optional constructor parameter has been added for the treatment of muons. We’ve checked that there are no substantial changes to any VALIDATED analyses. Some very specific jet-splitting analysis features have also been removed from FastJets — it’s nowadays better to use FastJet’s API directly — and we’ve added a convenient extra constructor from a FastJet::JetDefinition.

The second major change has been to the behaviour of the WFinder. Previously this used a missing ET cut to decide whether an event could be considered as containing a leptonic W, but then a specific neutrino was selected in an l+nu pair used to build the pseudo-W. That’s not experimentally possible, of course, and given Rivet’s emphasis on observable measurements we have changed the default to allocate all the MET to the W candidate. No significant changes in analysis outputs were found by our testing system. This has, however, introduced a discussion on whether a W finder is a sensible object for us to provide: neither leptonic or hadronic W’s are fully constructible from final-state observables via an unambiguous procedure, and we expect that each analysis that tries may have a different approach. Hence in a later release the WFinder may disappear entirely, but for now it is still in place, but with a more portable — but less accurate — behaviour.

Other technical improvements have been made to e.g. protect against accidental ‘slicing’ of C++ objects when using the remainingFinalState() method. Please see the ChangeLog for the full list of substantial changes since release 2.2.0.

As always, this new version is recommended for immediate use. Please keep sending us your feedback and analysis codes!