Angles on CP-violation in Higgs boson interactions

Abstract

CP-violation in the Higgs sector remains a possible source of the baryon asymmetry of the universe. Recent differential measurements of signed angular distributions in Higgs boson production provide a general experimental probe of the CP structure of Higgs boson interactions. We interpret these measurements using the Standard Model Effective Field Theory and show that they do not distinguish the various CP-violating operators that couple the Higgs and gauge fields. However, the constraints can be sharpened by measuring additional CP-sensitive observables and exploiting phase-space-dependent effects. Using these observables, we demonstrate that perturbatively meaningful constraints on CP-violating operators can be obtained at the LHC with luminosities of O(100/fb). Our results provide a roadmap to a global Higgs boson coupling analysis that includes CP-violating effects.

CP Violation in Higgs-Gauge Interactions: From Tabletop Experiments to the LHC

“…This allows us to directly compare the low-energy limits to those of Ref. [30]. In this case there is one free direction left unconstrained by EDM measurements, even when neglecting theoretical uncertainties.…”

“…It has long been recognized that the required new CP -violating couplings can generate observable effects in both Higgs production and decay rates, i.e. CP -even observables [12][13][14][15][16][17][18][19][20][21][22][23][24], as well as genuinely CP -odd signatures at the Large Hadron Collider (LHC) [25][26][27][28][29][30][31][32][33][34][35][36][37]. Moreover, the interplay with low-energy CP -violating observables such as electric dipole moments (EDMs) has been explored, in either specific models [19,38] or SM effective field theory (SMEFT) [12-14, 16, 19-24], taking into account only subsets of the dimension-6 CP -odd operators.…”

“…Such dimension-8 contributions however still lead to significant constraints [27,32]. The Higgs-gauge operators contribute at O(v 2 /Λ 2 ) to CP -odd observables, such as the CP asymmetry in pp → h + 2j [28][29][30]34], angular distributions in associated HW and HZ production [27,31,32], or in h → 4l [25,33,34], while CW and C ϕW B contribute to CP -odd observables in diboson production [27,35]. CG gives tree-level corrections to pp → h + 2j and to multijet production [36].…”

“…In this Letter we set up the framework to include low-energy CP -violating probes and demonstrate that they put severe constraints on the CP -violating sector of universal theories. To establish the connection to existing collider bounds [30,37], we first concentrate the phenomenological analysis on the operators that involve the Higgs coupling, and later discuss the low-and highenergy input necessary for an analysis of all six parameters simultaneously.…”

“…We follow Ref. [23] and present limits in a variety of cases: (i) the "central" scenario, in which we neglect all hadronic and nuclear uncertainties, (ii) the "Rfit" strategy, in which all hadronic and nuclear matrix elements are varied within their allowed ranges to minimize the χ 2 value, and (iii) the "Gaussian" [30], while the low-energy limits assume improved matrix elements and future EDM measurements as described in the text. All four couplings were turned on at the scale Λ = 1 TeV, and the low-energy limits were obtained using the Gaussian strategy for the theoretical uncertainties.…”