Search for high-mass VH resonances in the fully hadronic channel with full Run 2 data

The results of a new search for high-mass VH resonances in the fully hadronic channel (qqbb) have been submitted for publication in Phys. Rev. D. The submitted paper and additional figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2018-11/. These results are the culmination of UMass student Zac Meadows’ graduate work and forms the basis of his PhD dissertation (CERN-THESIS-2020-062) under the direction of Prof. Willocq. Congratulations to Zac for a successful completion of this extensive work and a well-deserved PhD degree!

The analysis extends a previous search performed on 36 fb-1 of proton-proton collision data collected at sqrt(s) = 13 TeV with the full 139 fb-1 integrated luminosity collected between 2015 and 2018. Several improvements have been introduced to significantly increase the sensitivity of the search. These include: (i) more powerful W/Z tagging based on jets combining tracking and calorimeter measurements; (ii) variable-radius track jets to identify H -> bb decay; (iii) addition of the number of tracks associated with the Higgs candidate jet to suppress gluon-initiated jet background; (iv) boosted decision tree to correct kinematic biases in the data-derived background estimate.

The observed distributions of the WH and ZH candidate invariant masses are found to agree with the background prediction and upper limits are set on the cross section for production of W’ and Z’ bosons, in the context of the Heavy Vector Triplet (HVT) model. Several limits are shown below.

Observed and expected 95% CL upper limits on the cross section for pp? W? ? WH. The red solid (dashed) lines show the cross-section predictions as a function of the resonance mass in the context of HVT model B (A).
Limits at 95% CL in the gf vs. gH plane for resonance masses of 2, 3, and 4 TeV for the WH channel in the context of the HVT model. The coupling values corresponding to HVT models A and B are indicated by filled circles. The gray region indicates values of the couplings corresponding to V? resonances with ?/m greater than 5%. In that region, the assumption that the W? signal mJJ shape is dominated by the experimental resolution is no longer valid.