Diphoton Channel Research Articles

95 GeV Higgs boson in the Georgi-Machacek model

CMS and ATLAS have reported small excesses in the search for low-mass Higgs bosons in the diphoton decay channel at exactly the same mass, 95.4 GeV. These searches rely on improved analysis techniques, enhancing in particular the discrimination against the Z→e+e− background. In models beyond the Standard Model (SM) that extend the Higgs sector with triplets, doubly charged Higgs bosons are predicted which can contribute substantially to the diphoton decay rate of a light Higgs boson. The Georgi-Machacek (GM) Model is of particular interest in this context, since despite containing Higgs triplets it preserves the electroweak ρ-parameter to be 1 at the tree level. We show that within the GM model, a Higgs boson with a mass of ∼95 GeV with a diphoton decay rate as observed by CMS and ATLAS can be well-described. We discuss the diphoton excess in conjunction with an excess in the bb¯ final state observed at LEP and an excess observed by CMS in the ditau final state, which have been found at comparable masses with local significances of about 2σ and 3σ, respectively. The presence of a Higgs boson at about 95 GeV within the GM model would imply good prospects of the searches for additional light Higgs bosons. In particular, the observed excess in the diphoton channel would be expected to be correlated in the GM model with a light doubly charged Higgs boson in the mass range between 100 and 200 GeV, which motivates dedicated searches in upcoming LHC Runs. Published by the American Physical Society 2024

95 GeV light Higgs in the top-pair-associated diphoton channel at the LHC in the minimal dilaton model* *Supported by the National Natural Science Foundation of China (12275066, 11605123)

Motivated by experimental hints and theoretical frameworks indicating the existence of an extended Higgs sector, we explore the feasibility of detecting a 95 GeV light Higgs boson decaying into a diphoton within the minimal dilaton model at the 14 TeV LHC. Initially, we identify the correlations between the production cross section, decay branching ratios, and model parameters, e.g., the scalar mixing angle . Subsequently, we utilize Monte Carlo simulations to generate the signal of the light Higgs boson via the process, along with the corresponding backgrounds. To effectively separate the signal from the dominant backgrounds , we employ a meticulous cut-based selection process. Ultimately, we find that with an integrated luminosity of , the regions of can be covered over the level.

Additional Higgs Bosons near 95 and 650 GeV in the NMSSM

Hints for an additional Higgs boson with a mass of about 95 GeV originate from LEP and searches in the diphoton channel by CMS and ATLAS. A search for resonant production of SM plus BSM Higgs bosons in the diphoton plus bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$b\\bar{b}$$\\end{document} channel by CMS showed some excess for a 650 GeV resonance decaying into the SM Higgs plus a 95 GeV Higgs boson. We investigate whether these phenomena can be interpreted simultaneously within the NMSSM subject to the latest constraints on couplings of the SM Higgs boson, on extra Higgs bosons from the LHC, and on dark matter direct detection cross sections. We find that the hints for a 95 GeV Higgs boson in the diphoton channel by CMS and ATLAS and in the diphoton plus bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$b\\bar{b}$$\\end{document} channel by CMS can be fitted simultaneously within the 2σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2\\,\\sigma $$\\end{document} level.

Higgs probes of axion-like particles

We study axion-like particle contributions to the Higgs boson decays. The particle is assumed to couple with the standard model electroweak gauge bosons. Although direct productions of axion-like particles have often been discussed, we investigate indirect contributions to the Higgs boson decays into fermions, photons, W, and Z bosons at the one-loop level. It is found that the corrections to the fermions are suppressed, whereas precise measurements of the di-photon channel of the Higgs boson decay can provide a significant probe of the model especially when the axion-like particle is heavy and its coupling to di-photon is suppressed.

Measurement of the properties of Higgs boson production at sqrt{s} = 13 TeV in the H → γγ channel using 139 fb−1 of pp collision data with the ATLAS experiment

Measurements of Higgs boson production cross-sections are carried out in the diphoton decay channel using 139 fb−1 of pp collision data at sqrt{s} = 13 TeV collected by the ATLAS experiment at the LHC. The analysis is based on the definition of 101 distinct signal regions using machine-learning techniques. The inclusive Higgs boson signal strength in the diphoton channel is measured to be {1.04}_{-0.09}^{+0.10} . Cross-sections for gluon-gluon fusion, vector-boson fusion, associated production with a W or Z boson, and top associated production processes are reported. An upper limit of 10 times the Standard Model prediction is set for the associated production process of a Higgs boson with a single top quark, which has a unique sensitivity to the sign of the top quark Yukawa coupling. Higgs boson production is further characterized through measurements of Simplified Template Cross-Sections (STXS). In total, cross-sections of 28 STXS regions are measured. The measured STXS cross-sections are compatible with their Standard Model predictions, with a p-value of 93%. The measurements are also used to set constraints on Higgs boson coupling strengths, as well as on new interactions beyond the Standard Model in an effective field theory approach. No significant deviations from the Standard Model predictions are observed in these measurements, which provide significant sensitivity improvements compared to the previous ATLAS results.

Signal-background interference effects in Higgs-mediated diphoton production beyond NLO

In this paper we consider signal-background interference effects in Higgs-mediated diphoton production at the LHC. After reviewing earlier works that show how to use these effects to constrain the Higgs boson total decay width, we provide predictions beyond NLO accuracy for the interference and related observables, and study the impact of QCD radiative corrections on the Higgs width determination. In particular, we use the so-called soft-virtual approximation to estimate interference effects at NNLO in QCD. The inclusion of these effects reduces the NNLO prediction for the total Higgs cross-section in the diphoton channel by about 1.7%. We study in detail the impact of QCD corrections on the Higgs-boson line-shape and its implications for the Higgs boson width extraction. In particular, we find that the shift of the Higgs resonance peak arising from interference effects gets reduced by about 30% with respect to the NLO prediction. Assuming an experimental resolution of about 150 textrm{MeV} on interference-induced modifications of the Higgs-boson line-shape, our NNLO analysis shows that one could constrain the Higgs-boson total width to about 10–20 times its Standard Model value.

Di-photon decay of a light Higgs state in the BLSSM

In the context of the B−L Supersymmetric Standard Model (BLSSM), we investigate the consistency of a scenario with a light Higgs boson with mass in the range 94−98 GeV and a Standard Model (SM) Higgs state at 125 GeV with the results of a search performed by the CMS Collaboration in the di-photon channel primarily involving data at an integrated luminosity of 35.9 fb−1 and an energy of s = 13 TeV. In this study, we present a Monte Carlo (MC) analysis of signal and background mimicking the experimental one and showing acceptable consistency with data, at both the integral and differential level.

Unambiguously Testing Positivity at Lepton Colliders.

The diphoton channel at lepton colliders, e^{+}e^{-}(μ^{+}μ^{-})→γγ, has a remarkable feature that the leading new physics contribution comes only from dimension-eight operators. This contribution is subject to a set of positivity bounds, derived from the fundamental principles of quantum field theory, such as unitarity, locality, analyticity and Lorentz invariance. These positivity bounds are thus applicable to the most direct observable: the diphoton cross section. This unique feature provides a clear, robust, and unambiguous test of these principles. We estimate the capability of various future lepton colliders in probing the dimension-eight operators and testing the positivity bounds in this channel. We show that positivity bounds can lift certain flat directions among the effective operators and significantly change the perspectives of a global analysis. We also discuss the positivity bounds of the Zγ/ZZ processes which are related to the γγ ones, but are more complicated due to the massive Z boson.

LHC constraints on hidden gravitons

We analyze LHC data in order to constrain the parameter space of new spin-2 particles universally coupled to the energy-momentum tensor. These new hypothetical particles are the so-called hidden gravitons, whose phenomenology at low energies is determined by two parameters: its mass and its dimensional coupling constant. Hidden gravitons arise in many different extensions of the Standard Model of particles and interactions and General Relativity. Their phenomenology has been studied mainly in relation to modifications of gravity and astrophysical signatures. In this work, we extend the constraints for heavy hidden gravitons, with masses larger than 1 GeV, by taking into account events collected by ATLAS and CMS in the WW channel, Drell-Yan processes, and the diphoton channel from proton-proton collisions at sqrt{s} = 8 TeV.

SiPM dynamic range for CEPC scintillator-based electromagnetic calorimeter

A high-granularity scintillator calorimeter readout with silicon photomultipliers (SiPMs) is an electromagnetic calorimeter (ECAL) candidate for experiments at the Circular Electron Positron Collider (CEPC). A critical design parameter of this ECAL candidate is the dynamic range of the SiPMs. This study investigates the SiPM dynamic range required for the CEPC scintillator ECAL. A model is developed on the basis of the operation principles of SiPMs to describe the response of an SiPM to light pulses within one recovery period by considering the cross-talk effect, photon detection efficiency, and number of pixels. The response curve of a 10000-pixel SiPM predicted by the model is consistent with the measured curve within 2% for an incident light pulse of up to 12000 photons. The intrinsic fluctuations of the SiPM response naturally exist in this model, and the correction of the saturation effect in the SiPM response is investigated. Monte Carlo (MC) simulation shows that the algorithm can restore the response linearity of an SiPM for an incident light pulse in which the number of photons is up to around six times the number of SiPM pixels. The model and correction program are implemented for full simulation of the ZH production Z → νν, H → γγ channel to evaluate the impact of the SiPM dynamic range of the CEPC scintillator ECAL on the reconstructed Higgs boson mass and the sensitivity to the Higgs signal in this channel. The results show that the CEPC scintillator ECAL equipped with no less than 4000 SiPM pixels and operated with a light yield of 20 photon-electrons per channel for a single minimum ionizing particle can meet the requirements for Higgs boson precision measurement in the di-photon channel at the CEPC.

Searching for monopoles via monopolium multiphoton decays

We explore the phenomenology of a model of monopolium based on an electromagnetic dual formulation of Zwanziger and lattice gauge theory. The monopole is assumed to have a finite-sized inner structure based on a 't Hooft-Polyakov like solution, with the magnetic charge uniformly distributed on the surface of a sphere. The monopole and anti-monopole potential becomes linear plus Coulomb outside the sphere, analogous to the Cornell potential utilised in the study of quarkonium states. Discovery of a resonance feature in the diphoton channel as well as in a higher multiplicity photon channel would be a smoking gun for the existence of monopoles within this monopolium construction, with the mass and bound state properties extractable. Utilising the current LHC results in the diphoton channel, constraints on the monopole mass are determined for a wide range of model parameters. These are compared to the most recent MoEDAL results and found to be significantly more stringent in certain parameter regions, providing strong motivation for exploring higher multiplicity photon final state searches.

Fiducial Higgs and Drell-Yan distributions at N3LL\u2032+NNLO with RadISH

We present state-of-the-art predictions for transverse observables relevant to colour-singlet production at the LHC, in particular the transverse momentum of the colour singlet in gluon-fusion Higgs production and in neutral Drell-Yan lepton-pair production, as well as the {phi}_{eta}^{ast } observable in Drell Yan. We perform a next-to-next-to-next-to-leading logarithmic (N3LL) resummation of such observables in momentum space according to the RadISH formalism, consistently including in our prediction all constant terms of relative order {alpha}_s^3 with respect to the Born, thereby achieving N3LL′ accuracy. The calculation is fully exclusive with respect to the Born kinematics, which allows the application of arbitrary fiducial selection cuts on the decay products of the colour singlet. We supplement our results with a transverse-recoil prescription, accounting for dominant classes of subleading-power corrections in a fiducial setup. The resummed predictions are matched with fixed-order differential spectra at next-to-next-to-leading order (NNLO) accuracy. A phenomenological comparison is carried out with 13 TeV LHC data relevant to the Higgs to di-photon channel, as well as to neutral Drell-Yan lepton-pair production. Overall, the inclusion of mathcal{O} ( {alpha}_s^3 ) constant terms, and to a lesser extent of transverse-recoil effects, proves beneficial for the comparison of theoretical predictions to data, leaving a residual theoretical uncertainty in the resummation region at the 2–5% level for Drell-Yan observables, and 5–7% in Higgs production.

Discovering the origin of Yukawa couplings at the LHC with a singlet Higgs and vector-like quarks

Although the 125 GeV Higgs boson discovered at the LHC is often heralded as the origin of mass, it may not in fact be the origin of Yukawa couplings. In alternative models, Yukawa couplings may instead arise from a seesaw type mechanism involving the mixing of Standard Model (SM) chiral fermions with new vector-like fermions, controlled by the vacuum expectation value (VEV) of a new complex Higgs singlet field 〈Φ〉. For example, the largest third family (t, b) quark Yukawa couplings may be forbidden by a U(1)′ gauge or global symmetry, broken by 〈Φ〉, and generated effectively via mixing with a vector-like fourth family quark doublet (T, B). Such theories predict a new physical Higgs singlet ϕ, which we refer to as the Yukon, resulting from 〈Φ〉, in the same way that the Higgs boson h0 results from 〈H〉. In a simplified model we discuss the prospects for discovering the Yukon ϕ in gluon-gluon fusion production, with (t, b) and (T, B) quarks in the loops, and decaying in the channels ϕ → γγ, Zγ and ϕ → tT → tth0, ttZ. The potential for discovery of the Yukon ϕ is studied at present or future hadron colliders such as the LHC (Run 3), HL-LHC, HE-LHC and/or FCC. For example, we find that a 300–350 GeV Yukon ϕ could be accessed at LHC Run 3 in the di-photon channel in the global model, providing a smoking gun signature of the origin of Yukawa couplings. The tth0, ttZ channels are more involved and warrant a more sophisticated analysis.

A comparative study of the anomalous tHq couplings via the diphoton channel at the LHC

We present a comparative study about the flavor changing neutral Higgs (FCNH) interactions of top quark, i.e., tqh (q=u,c), from two processes with the h→γγ decay channel: top quark pair production pp→tt¯ with one top decaying to hq, and the anomalous single top plus Higgs production process pp→th. We perform a full simulation for the signals and the relevant SM backgrounds based on two separate cut selections at the future 14 TeV High Luminosity LHC (HL-LHC). The results show that the SM background can be greatly reduced for both selection methods. The branching ratios of t→uh and t→ch can be, respectively, probed to 1.4×10−4 and 1.5×10−4 at the 95% Confidence Level (CL), which is consistent with the dedicated study performed by the ATLAS collaboration. The advantage of the pp→th process is that the origin of the signal from tuh or tch couplings could be clarified by studying the diphoton pseudo-rapidity and the charges of the charged lepton from the top decay. If we only consider the signal coming from this process, the upper limit on the branching ratio of about Br(t→uh)=2.4×10−4 at the 95% CL is obtained. Altogether, these limits are one order of magnitude better than the current 13 TeV LHC experimental results.

Physics object performance of the FCC-hh calorimeter system

The feasibility of a future proton-proton collider (FCC-hh) has been outined in Conceptual Design Reports published early 2019. FCC-hh would deliver collisions at a center of mass energy up to 100 TeV and unprecedented instantaneous luminosity (L=3 × 1034), resulting in extremely challenging radiation conditions up to a maximum of 5× 1018 neq/cm2 and a dose up to 5 GGy in the forward calorimeters (up to |η|=6) and up to 1000 simultaneous proton-proton interactions per bunch-crossing. By delivering an integrated luminosity of few tens of ab−1, the FCC-hh would provide an unrivalled discovery potential for new physics. Requiring high sensitivity for resonant searches at masses up to tens of TeV imposes strong constraints on the design of the calorimeters. Resonant searches in final states containing jets, taus and electrons require both excellent energy resolution at multi-TeV energies as well as outstanding ability to resolve highly collimated decay products resulting from extreme boosts. In addition, the FCC-hh provides the unique opportunity to precisely measure the Higgs self-coupling in the di-photon and b-jets channel. Excellent photon and jet energy resolution at low energies as well as excellent angular resolution for pion background rejection are required in this challenging environment. In this talk we will briefly review the electromagnetic and hadronic calorimeter current design and requirements (granularity, energy resolution, acceptance, …) and discuss the expected performance of the physics objects based on calorimeter reconstruction. We will then examine the impact of the object performance on the final sensitivity of the relevant benchmark physics analyses.

Discussing 125 GeV and 95 GeV excess in light radion model

Even if the LHC observations are consistent with the Standard model (SM), current LHC results are not precise enough to rule out the presence of new physics. Taking a contrarian view of the SM Higgs fandom, we look out for a more suitable candidate for the 125 GeV boson observed at the LHC. At the same time, a recent result from CMS hints toward an excess near 95 GeV in the diphoton ($\ensuremath{\gamma}\ensuremath{\gamma}$) channel. Given these aspects, we revisit the Higgs-radion mixing model to explore the viability of the radion mixed Higgs to be the 125 GeV boson along with the presence of a light radion (to be precise, Higgs mixed radion) that can show up in future experiments in the $\ensuremath{\gamma}\ensuremath{\gamma}$ channel. We find that the mixed radion-Higgs scenario gives a better fit than the SM, with the radion mixed Higgs as a more suitable 125 GeV scalar candidate. It also gives rise to a diphoton excess from the light radion, consistent with the LHC observations.

Bayesian and frequentist approaches to resonance searches

We investigate Bayesian and frequentist approaches to resonance searches using a toy model based on an ATLAS search for the Higgs boson in the diphoton channel. We draw pseudo-data from the background only model and background plus signal model at multiple luminosities, from 10−3/ fb to 107/ fb. We chart the change in the Bayesian posterior of the background only model and the global p-value. We find that, as anticipated, the posterior converges to certainty about the model as luminosity increases. The p-value, on the other hand, randomly walks between 0 and 1 if the background only model is true, and otherwise converges to 0. After briefly commenting on the frequentist properties of the posterior, we make a direct comparison of the significances obtained in Bayesian and frequentist frameworks. We find that the well-known look-elsewhere effect reduces local significances by about 1σ. We furthermore find that significances from our Bayesian framework are typically about 1−2σ smaller than the global significances, though the reduction depends on the prior, global significance and integrated luminosity. This suggests that even global significances could significantly overstate the evidence against the background only model. We checked that this effect—the Bayes effect—was robust with respect to fourteen choices of prior and investigated the Jeffreys-Lindley paradox for three of them.

A light scalar in the Minimal Dilaton Model in light of the LHC constraints * * Supported by the National Natural Science Foundation of China (NNSFC)(11605123, 11547103, 11674253, 11547310), the China Scholarship Council (CSC) (201706275160) and the US National Science Foundation (NSF) (PHY-0855561)

Whether an additional light scalar exists is an interesting topic in particle physics beyond the Standard Model (SM), as we do not know as yet the nature of physics beyond the SM in the low mass region in view of the inconsistent results of the ATLAS and CMS collaborations in their search for light resonances around 95 GeV in the diphoton channel. We study a light scalar in the Minimal Dilaton Model (MDM). Under the theoretical and the latest experimental constraints, we sort the selected data samples into two scenarios according to the diphoton rate of the light scalar: the large-diphoton scenario (with ) and the small-diphoton scenario (with ), which are favored by the CMS and ATLAS results, respectively. We compare the two scenarios, test the characteristics of the model parameters, the scalar couplings, production and decay, and consider how they could be further discerned at colliders. We draw the following conclusions for the two scenarios: (i) The large-diphoton scenario has in general a small Higgs-dilaton mixing angle ( ) and a small dilaton vacuum expectation value (VEV) ( ), and the small-diphoton scenario has large mixing ( ) or large VEV ( ). (ii) The large-diphoton scenario in general predicts small coupling ( ) and large coupling ( ), while the small-diphoton scenario predicts small coupling ( ). (iii) The large-diphoton scenario can interpret the small diphoton excess seen by CMS at its central value, when GeV, and . (iv) The large-diphoton scenario in general predicts a negative correlation between the Higgs couplings and , while the small-diphoton scenario predicts that both couplings are smaller than 1, or .

Physics requirements for the FCC-hh calorimeter system

The future proton-proton collider (FCC-hh) will deliver collisions at a center of mass energies up to √s = 100 TeV at an unprecedented instantaneous luminosity of L = 3 1035cm−2s−1, resulting in extremely challenging radiation conditions up to a maximum of 5 1018cm2MeV neutron equivalent fluence and dose up to 5 GGy in the forward calorimeters (up to |η| = 6) and up to 1000 simultaneous proton-proton interactions per bunch-crossing. By delivering an integrated luminosity of few tens of ab−1, the FCC-hh will provide an unrivalled discovery potential for new physics. Requiring high sensitivity for resonant searches at masses up to tens of TeV imposes strong constraints on the design of the calorimeters. Resonant searches in final states containing jets, taus and electrons require both excellent energy resolution at multi-TeV energies as well as outstanding ability to resolve highly collimated decay products resulting from extreme boosts. In addition, the FCC-hh provides the unique opportunity to precisely measure the Higgs self-coupling in the di-photon and b-jets channel. Excellent photon and jet energy resolution at low energies as well as excellent angular resolution for pion background rejection are required in this challenging environment.

Connection between diphoton and triboson channels in new physics searches

Diphoton channel provides a clean signature in searches for new physics. In this paper, we discuss a connection between the diphoton channel (γγ) and triboson channels (Zγγ, ZZγ, WWγ) imposed by the SU(2)L×U(1)Y symmetry of the Standard Model (SM) in certain classes of models. To illustrate this idea we choose a simple model that has all these channels. In this model, the same physics can give rise to γ+MET instead of γγ and 2 bosons plus missing energy instead of 3-boson channels. We analyze existing constraints and previous searches and show that channels WWγ and especially Zγ+MET have a potential to discover new physics at the LHC.