Revisiting Vh(→ $$ b\overline{b} $$) at the LHC and FCC-hh

Abstract

Diboson production processes provide good targets for precision measurements at present and future hadron colliders. We consider Vh production, focusing on the h → $$ b\overline{b} $$ b b ¯ decay channel, whose sizeable cross section makes it accessible at the LHC. We perform an improved analysis by combining the 0-, 1- and 2-lepton channels with a scale-invariant b-tagging algorithm that allows us to exploit events with either a boosted Higgs via mass-drop tagging or resolved b-jets. This strategy gives sensitivity to 4 dimension-6 SMEFT operators that modify the W and Z couplings to quarks and is competitive with the bounds obtained from global fits. The benefit of the h → $$ b\overline{b} $$ b b ¯ decay channel is the fact that it is the only Vh channel accessible at the LHC Run 3 and HL-LHC, while at FCC-hh it is competitive with the effectively background-free h → γγ channel assuming ≲ 5% systematic uncertainty. Combining the boosted and resolved categories yields a 17% improvement on the most strongly bounded Wilson coefficient at the LHC Run 3 with respect to the boosted category alone (and a 7% improvement at FCC-hh). We also show that, at FCC-hh, a binning in the rapidity of the Vh system can significantly reduce correlations between some EFT operators. The bounds we obtain translate to a lower bound on the new physics scale of 5, 8, and 20 TeV at the LHC Run 3, HL-LHC, and FCC-hh respectively, assuming new-physics couplings of order unity. Finally, we assess the impact of the Vh production channel on anomalous triple gauge coupling measurements, comparing with their determination at lepton colliders.

Gluon-induced diboson production in the SMEFT

“…The quark induced channel enters at tree-level and is sensitive to O (−) 𝜑𝑄 and O (3) 𝜑𝑄 , while the gluon channel is subdominant as it enters at NNLO and is sensitive to O (−) 𝜑𝑄 , O 𝜑𝑡 and O 𝑡 𝜑 . We added the gluon-initiated signal contribution to an analysis originally focused on quark-initiated diboson production [17] and we relaxed the flavour assumption in said analysis from its original Flavour Universality to U(2) 𝑞 ×U(3) 𝑑 ×U(2) 𝑢 × (U(1) ℓ × U(1) 𝑒 ) 3 . We simulated the contribution of the 𝑔𝑔 → 𝑍 𝐻 process using Madgraph5 and SMEFTatNLO [4] at LO in QCD for a centre-of-mass energy of 13 TeV and in the presence of one operator at a time.…”

Diboson production in the SMEFT from gluon fusion

“…To then demonstrate in a realistic manner how the loop induced component of the diboson process plays a special role, we focus on ZH production. Previous studies of this process focused on one of the initial states, either gg or q q, and set the other to its SM value to play the role of a background [24,31,32,42]. This methodology can be justified by the fact that quark-and gluon-initiated ZH production probe disjoint sets of SMEFT dimension-6 operators.…”

“…To assess the sensitivity of this process to the aforementioned operators, we add the gluon-initiated signal contribution to an analysis originally focused on quark-initiated diboson production [32]. This addition is meaningful only after relaxing the flavour assumption in said analysis from its original Flavour Universality to the one mentioned in the previous paragraph.…”

“…The final-state configuration of ZH/W H production that is most useful for precision differential measurements is that in which the weak gauge boson decays to charged leptons or neutrinos and the Higgs boson decays to a b-quark pair. Several studies have highlighted this process as a powerful BSM probe, in particular in the boosted Higgs regime [15,18,23,24,32,78]. However, the limited cross-section at high energies allows for a noticeable gain of sensitivity when the boosted and resolved regimes are combined, as shown in ref.…”

“…However, the limited cross-section at high energies allows for a noticeable gain of sensitivity when the boosted and resolved regimes are combined, as shown in ref. [32]. We adopt the analysis strategy developed in the latter reference, which exploits the high-energy tails of p T distributions and reproduces published ATLAS ZH/W H analyses [79,80].…”