Spin and parity of a single-produced resonance at the LHC

Abstract

The experimental determination of the properties of the newly discovered boson at the Large Hadron Collider is currently the most crucial task in high energy physics. We show how information about the spin, parity, and, more generally, the tensor structure of the boson couplings can be obtained by studying angular and mass distributions of events in which the resonance decays to pairs of gauge bosons, ZZ, W W , and γγ. A complete Monte Carlo simulation of the process pp → X → V V → 4f is performed and verified by comparing it to an analytic calculation of the decay amplitudes X → V V → 4f . Our studies account for all spin correlations and include general couplings of a spin J = 0, 1, 2 resonance to Standard Model particles. We also discuss how to use angular and mass distributions of the resonance decay products for optimal background rejection. It is shown that by the end of the 8 TeV run of the LHC, it might be possible to separate extreme hypotheses of the spin and parity of the new boson with a confidence level of 99% or better for a wide range of models. We briefly discuss the feasibility of testing scenarios where the resonances is not a parity eigenstate.

Limits on the Higgs boson lifetime and width from its decay to four charged leptons

“…(4) in the off-shell H boson production is performed by reweighting the SM-like samples. An extended MCFM library provided as part of the Matrix Element Likelihood Approach (MELA) package, [35][36][37], allows for both reweighting and event simulation with anomalous couplings in off-shell H production, and the analytical reweighting for the f ΛQ parametrization used in this analysis is identical to reweighting via the MELA package. Figure 1 illustrates the simulation of the gg → 4l process with the above technique, which includes H boson off-shell production, its background, and their interference for the five signal models with the a 1 (SM), a 2 , a 3 , Λ 1 , and Λ Q terms in Eq.…”

“…Therefore, different techniques and tools have been used for on-shell and off-shell simulation. The simulation of the H boson signal is performed at the measured value of the H boson pole mass m H ¼ 125.6 GeV in the 4l The two dominant H boson production mechanisms, gluon fusion and VBF, are generated on-shell at next-toleading order (NLO) in perturbative quantum chromodynamics (QCD) using the POWHEG [32][33][34] [35][36][37]. In addition, gluon fusion production with up to two jets at NLO in QCD has been generated using POWHEG with the HJJ program [38], where the MINLO procedure [39] is used to resum all large logarithms associated with the presence of a scale for merging the matrix element and the parton shower contributions.…”

Scrutinizing the Higgs signal and background in the 2e2μ golden channel

“…If ϕ is the Standard Model Higgs, then g h = i, while g Z , g Zγ and g γγ are = 0, but loop induced and small. Detailed studies of the ZZ contribution to the golden channel mediated through the operators with coefficients g h , g Z were conducted in [4,6,22]. The operators corresponding to g Zγ were studied in [8] for the golden channel final state and in [23] for the + − γ final state and both were shown to be useful discriminators.…”

“…It has been shown in recent studies [3][4][5][6][7][8] and also emphasized for quite some time [9][10][11][12][13], that the decay to four charged leptons is a powerful channel in accomplishing this goal. Because of the experimental precision with which this channel is measured, it offers one of the few opportunities to use analytic methods to analyze the data.…”

A fast track towards the ‘Higgs’ spin and parity

“…Various strategies have been proposed for determining the spin and parity of a Higgs candidate in hadron-hadron collisions, including angular distributions and kinematic correlations in X → ZZ * , W W * and γγ decays [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Historically, the problem of determining the spin and parity of a Higgs candidate was first considered in the context of e + e − collisions, and the point was made that the threshold behaviour of the cross section for the 'Higgs'-strahlung process e + e − → Z + X would depend on the spin and parity of the X particle, offering potential discrimination between different spin-parity assignments [23].…”