Higgs constraints from vector boson fusion and scattering

Abstract

We present results on 4-lepton + 2-jet production, the partonic processes most commonly described as vector boson pair production in the Vector Boson Fusion (VBF) mode. This final state contains diagrams that are mediated by Higgs boson exchange. We focus particularly on the high-mass behaviour of the Higgs boson mediated diagrams, which unlike on-shell production, gives information about the Higgs couplings without assumptions on the Higgs boson total width. We assess the sensitivity of the high-mass region to Higgs coupling strengths, considering all vector boson pair channels, $W^-W^+$, $W^\pm W^\pm$, $W^\pm Z$ and $ZZ$. Because of the small background, the most promising mode is $W^+ W^+$ which has sensitivity to Higgs couplings because of Higgs boson exchange in the $t$-channel. Using the Caola-Melnikov (CM) method, the off-shell couplings can be interpreted as bounds on the Higgs boson total width. We estimate the bound that can be obtained with current data, as well as the bounds that could be obtained at $\sqrt{s}=13$~TeV in the VBF channel for data samples of 100 and 300 fb$^{-1}$. The CM method has already been successfully applied in the gluon fusion (GGF) production channel. The VBF production channel gives important complementary information, because both production and decay of the Higgs boson occur already at tree graph level.Comment: 17 pages, 5 figures, 4 table

Complete NLO corrections to W+W+ scattering and its irreducible background at the LHC

“…The contraction is illustrated at the level of squared amplitudes in Fig. 4 via the cut along the dashed line number (1). Second, the EW corrections to the EW tree-level amplitude at O g 8 contracted with the QCD-induced LO amplitude at O g 2 s g 4 lead to yet another contribution of order O α s α 6 .…”

“…The leptonic decay products of the scattered bosons in association with two jets radiated from the incoming partons in forward direction give rise to a typical signature that can be enhanced over the irreducible background with dedicated VBS event selections. Among the various leptonic final states, the channel with two equally charged leptons and two neutrinos, the so-called samesign WW channel, has been identified as the most promising candidate for discovery [1,2]. Owing to the limited number of partonic channels that allow for such a leptonic final state, the irreducible QCD background is smaller than in the other VBS channels.…”

Interference effects in Higgs production through Vector Boson Fusion in the Standard Model and its singlet extension

“…(4.3) with the ones obtained with the more realistic requirement proposed in [15,68] m l 1 j 2 , m l 2 j 1 > 200 GeV, where l 1 , l 2 (j 1 , j 2 ) represent the leptons (jets) of highest and lowest transverse momentum respectively. The blue and red lines refer to the first case for the O(α 6 EM ) and O(α 4 EM α 2 S ) cross section, while the gray and purple lines refer to the second set of cuts.…”

“…are expected to be small [15,56]. A careful investigation of all channels, including the semileptonic ones and exploiting all techniques to identify vector bosons decaying hadronically, will be required to assess the observability of the 1HSM through VBF in Run II and beyond.…”

“…On the one hand, at large energies, Higgs exchange unitarizes processes like Vector Boson Scattering (VBS) and fermion pair annihilation to Vector Bosons which would otherwise diverge. On the other hand, the comparison of off-shell and peak cross sections can provide limits on the total width of the Higgs [9][10][11][12][13][14][15]. Both aspects are sensitive to BSM physics through direct production of new states and through their contributions in loops.…”