LHC Higgs XS VBF+VH Subgroup Meeting (21 Oct 2014)
Chaired by: Nielsen, Jason; Prof. Dittmaier, Stefan; Tramontano, Francesco; Pianori, Elisabetta; Rizzi, Andrea; Govoni, Pietro; Jaeger, Barbara
Approximately 40 people attended by Vidyo
1. News from ATLAS/CMS (E. Pianori et al.)
Elisabetta Pianori shared updates from the experiments. Most urgent questions involve the choice of generators for upcoming 13 TeV MC generation campaigns.
Stefan Dittmaier commented that the K-factor for ggZH is only known in the heavy top limit, and there are other uncertainties. Nevertheless, it is better to include the flat K-factor=2 than to omit it, even if this approach
Marco Zaro commented that the aMC@NLO authors are working on the NLO EWK corrections, including the possibility to match with the parton shower. He confirmed that NLO re-weighting is not available yet, although LO reweighting.
Barbara Jager reminded everyone that VBFNLO already includes gamma + VBF Higgs production. It is available in the current public version.
2. Resummation for GG->HZ (A. Kulesza et al.)
Massimiliano Grazzini commented that perhaps the uncertainties from the EFT itself are more significant than the higher-order uncertainties in the EFT framework. He also reminded us that the analyses are done in a restricted phase space, and not in the inclusive phase space treated here. Anna suggested that this could be a next step, with a differential cross section as a function of Higgs boson pT.
There was some discussion about how the theory community might estimate the uncertainties due to the effective field theory framework itself. This will probably require a full loop calculation outside EFT, but there is some hope that an estimate could be made on a shorter timescale.
3. HVNNLO (G. Ferrera et al.)
Giancarlo announced that the HVNNLO parton-level numerical code will be available soon, including the NNLO QCD corrections to the H decay to bb.
4. VBF and VH in MadGraph5_aMC@NLO (M. Zaro et al.)
Jason Nielsen asked about the special process gamma + VBF H. Marco said that it has not been validated and that there are some tricky points that may be incompatible with the standard approach.
Eleni Vryonidou confirmed that the special process-specific ggZH code on the MadGraph TWiki should work in the usual framework and connect to LHEF output and parton showers. Marco pointed out that a more general loop treatment is on the way.
Bruce Mellado asked whether there are any issues with unitarization for the effective operators. Marco said that there are no specific constraints on the operators, but the results prove that things are reasonable. For the spin-2 case, there is of course a bad breakdown of unitarity.
Biagio di Micco asked about the inclusion of EWK corrections, and Marco responded that they are a work in progress, probably several months away.
5. HAWK for VBF/VH (A. Mueck, R. Roth et al.)
Jason asked about the implementation of the Les Houches Accord 3, which allows for a common format for effects of scale uncertainties and PDFs. Alexander said that HAWK holds outputs all of the relevant weights so that only one pass of the program is needed. Michael Rauch said that VBFNLO can use the variations but not in the LHA3 format. Marco Zaro confirmed that MadEvent also provides all of the weights for scale and PDF variations.
6. VBFNLO (M. Rauch et al.)
VBFNLO is not just for VBF anymore!
Elisabetta asked why REPOLO and other reweighting tools are using the LO matrix element and not NLO. The answer from Michael was that the extra jet complicates things. Generating at NLO and then reweighting with LO seems to match well the pure re-generation at NLO, as long as the reweighting factors do not become too large.
Bruce asked if the LHA output would eventually use the Binoth LHA for NLO event generators. Michael responded that combining with parton shower would eliminate the need for this step.
7. Gluon fusion H+3j as a background to VBF (G. Luisoni et al.)
Gionata showed the NLO calculation of H+3-jets, with a significant reduction of scale uncertainties. There are significant NLO corrections to the distributions, especially when applying VBF cuts. The output at the moment is at the ntuple level. Work to interface to parton shower is proceeding in parallel. Joey Huston suggested that this may be fast, due to the use of Comix. Gionata also reminded the group of the Powheg HV+1j process.
Paolo Francavilla asked if there are any plans to include hadronic decays of the vector bosons, in POWHEG specifically. Gionata said that it could be considered if it is shown to be useful.
Minutes submitted by Jason Nielsen.