The work of REINVENT was organised into 3 different subprojects, each focusing on different
directions of improvement of the state-of-the-art for event simulation.
The first subproject focused on color-neutral production processes of high relevance for the LHC phenomenology. We have completed the studies for the cases of W-boson production, single and double Higgs production via gluon fusion, HiggsStrahlung and diboson pair production, including diphoton. This HiggsStrahlung process was not originally part of the proposal, but it was added after it was realized it was well suited for our approach and that it could be used as testing ground for a further extension of the method aiming at including also the Higgs boson decay. The diphoton pair production process was an important milestone because it delivered the first program with this level of accuracy for a genuine 2-to-2 process and was also a proof of the capability of the method to deal with processes which requires a nontrivial theoretical definition. The Higgs and diboson implementation established the method as a standard for color singlet production processes, signaling to the experimental community that the GENEVA approach was a viable alternative to other methods, delivering increased accuracy and reduced theoretical errors. For the case of the double Higgs pair production, our predictions are the only ones currently available at NNLO+PS accuracy, including the possibility to interface with different shower models.
Extending the Geneva approach to deal with more complicated processes, like vector boson plus one jet or Higgs boson plus one jet production was pursued in the second subproject . When a jet is already present at the leading order the principal resolution variable must distinguish between one or more jets: one-jettiness was the natural candidate. Here we were able to achieve the one-jettiness resummation accuracy to N3LL, the first resummation at this level of accuracy for a process involving three colored light partons at an hadron collider. We also developed a phase space map that preserves the value of zero and one jettiness while performing the necessary higher-order calculationsm which is required for the very definition of events used in our approach. We are suing this map for the full implementation for vector boson or Higgs plus jet production.
The last direction was the study of alternative resolution parameters. We first focused on the vector boson transverse momentum, interfacing to the N3LL resummation in RADISH. This proved the approach independence from the resolution variable Later on we studied the NNLL’ resummation of the jet veto (transverse momentum of the hardest jet) in the SCETlib framework and interfaced it to our implementation, delivering the first jet-veto resummation at this accuracy in an event generator.
We also explored the double differential resummation of zero-jettiness and the transverse momentum of the color singlet performing the resummation up to NNLL.
In addition we extended the method to heavy-quarks, both in pairs and in association with a heavy color singlet system, obtaining a factorization theorem for zero-jettiness with heavy-quarks, which opens up the additional possibility to study processes like ttW, ttZ or ttH. We calculated their NNLO corrections and started the work that will allow their implementation into GENEVA.
The results achieved by the project have been published in scientific journals, producing many well-received papers and presented at international and national conferences and workshops.
Our team has also been in regular contact with the LHC experimental collaborations for immediate usage of the new results in experimental analyses.
