Electroweak bounds on Higgs pseudo-observables and $$h\rightarrow 4\ell $$ h → 4 ℓ decays

It is well-known but sometimes overlooked that constraints on the oblique parameters (most notably S and T parameters) are generally speaking only applicable to a special class of new physics scenarios known as universal theories. In the effective field theory (EFT) framework, the oblique parameters should not be associated with Wilson coefficients in a particular operator basis, unless restrictions have been imposed on the EFT so that it describes universal theories. We work out these restrictions, and present a detailed EFT analysis of universal theories. We find that at the dimension-6 level, universal theories are completely characterized by 16 parameters. They are conveniently chosen to be: 5 oblique parameters that agree with the commonly-adopted ones, 4 anomalous triple-gauge couplings, 3 rescaling factors for the h 3 , hf f , hV V vertices, 3 parameters for hV V vertices absent in the Standard Model, and 1 four-fermion coupling of order y 2 f . All these parameters are defined in an unambiguous and basis-independent way, allowing for consistent constraints on the universal theories parameter space from precision electroweak and Higgs data.

Section: 2mentioning

confidence: 99%

Effective theories of universal theories

Wells

Zhang

2016

“…These couplings are thus highly constrained by LEP allowing us to set the coefficient of this contact operator to zero [44,47,48]. Exploring its effects in a non-linearly realized EFT would of course also be interesting [39,49]. However, since this operator does not involve a photon mediating the decay to leptons, we do not expect it to qualitatively change our results for the sensitivity to the A Zγ 2−3 , A γγ 2−3 operators and therefore do not include it for now.…”

Section: Jhep09(2015)185mentioning

confidence: 99%

New opportunities in h → 4ℓ

Chen

Harnik

Vega-Morales

2015

104

The Higgs decay h → 4 has played an important role in discovering the Higgs and measuring its mass thanks to low background and excellent resolution. Current cuts in this channel have been optimized for Higgs discovery via the dominant tree level ZZ contribution arising from electroweak symmetry breaking. Going forward, one of the primary objectives of this sensitive channel will be to probe other Higgs couplings and search for new physics on top of the tree level ZZ 'background'. Thanks to interference between these small couplings and the large tree level contribution to ZZ, the h → 4 decay is uniquely capable of probing the magnitude and CP phases of the Higgs couplings to γγ and Zγ as well as, to a lesser extent, ZZ couplings arising from higher dimensional operators. With this in mind we examine how much relaxing current cuts can enhance the sensitivity while also accounting for the dominant non-Higgs continuum qq → 4 background. We find the largest enhancement in sensitivity for the hZγ couplings ( 100%) followed by hγγ ( 40%) and less so for the higher dimensional hZZ couplings (a few percent). With these enhancements, we show that couplings of order Standard Model values for hγγ may optimistically be probed by end of Run-II at the LHC while for hZγ perhaps towards the end of a high luminosity LHC. Thus an appropriately optimized h → 4 analysis can complement direct decays of the Higgs to on-shell γγ and Zγ pairs giving a unique opportunity to directly access the CP properties of these couplings.

“…In the absence of significant deviations from the SM predictions, limits are set on modified Higgs boson interactions within the framework of pseudo- Figure 11. Limits on modified Higgs boson decays within the framework of pseudo-observables [15,81]. In (a), the limits are extracted in the plane of ε L and ε R , which modify the contact terms between the Higgs boson and left-and right-handed leptons, assuming lepton-flavour universality.…”

Section: Jhep10(2017)132mentioning

confidence: 99%

“…observables [15,81]. In this paper, the couplings related to the contact interaction of the Higgs boson decay are considered, ε L and ε R , which modify, in a flavour-universal way, the contact terms between the Higgs boson, the Z boson, and left-or right-handed leptons.…”

Section: Jhep10(2017)132mentioning

confidence: 99%

See 1 more Smart Citation

Measurement of inclusive and differential cross sections in the H → ZZ * → 4ℓ decay channel in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV with the ATLAS detector

Aaboud¹,

Aad²,

Abbott³

et al. 2017

Inclusive and differential fiducial cross sections of Higgs boson production in proton-proton collisions are measured in the H → ZZ * → 4 decay channel. The protonproton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb −1 . The inclusive fiducial cross section in the H → ZZ * → 4 decay channel is measured to be 3.62 ± 0.50 (stat) +0.25 −0.20 (sys) fb, in agreement with the Standard Model prediction of 2.91 ± 0.13 fb. The cross section is also extrapolated to the total phase space including all Standard Model Higgs boson decays. Several differential fiducial cross sections are measured for observables sensitive to the Higgs boson production and decay, including kinematic distributions of jets produced in association with the Higgs boson. Good agreement is found between data and Standard Model predictions. The results are used to put constraints on anomalous Higgs boson interactions with Standard Model particles, using the pseudo-observable extension to the kappa-framework. The ATLAS collaboration 32 IntroductionThe ATLAS and CMS Collaborations at the Large Hadron Collider (LHC) have performed extensive studies of the Higgs boson properties in the past few years. The Higgs boson mass has been measured to be m H = 125.09 ± 0.24 GeV [1] and no significant deviations from Standard Model (SM) predictions have been found in the cross sections measured per production mode, the branching ratios [2], or spin and parity quantum numbers [3][4][5][6]. Furthermore, inclusive and differential fiducial cross sections of Higgs boson production, defined as background-subtracted event yields corrected for the detector response, have been measured in proton-proton (pp) collisions at a centre-of-mass energy of √ s = 8 TeV, using the 4 ( = e, µ), γγ, and eνµν final states [7][8][9][10][11][12]. The measured differential cross sections are also in good agreement with the SM predictions.This paper presents a measurement of inclusive and differential fiducial cross sections in the H → ZZ * → 4 decay channel using pp collisions at √ s = 13 TeV recorded with the ATLAS detector. The combined effect of a higher centre-of-mass energy and an integrated luminosity of 36.1 fb −1 is expected to increase the number of Higgs boson events by a factor -1 - JHEP10(2017)132of almost four compared to the previous analysis at √ s = 8 TeV. Significantly larger gains are expected in the regions of the differential distributions that probe higher momentum scales due to increased parton-parton luminosities. The differential cross sections presented in this paper are measured in a fiducial phase space to avoid model-dependent extrapolations. The observed distributions are corrected for detector inefficiency and resolution.Fiducial cross sections are presented both inclusively and separately for each of the final states of the H → ZZ * → 4 decay (4µ, 2e2µ, 2µ2e, 4e). Differential fiducial cross sect...