Measurements Of Higgs Boson Properties Research Articles

Testing complex singlet scalar cosmology at the Large Hadron Collider

The Standard Model extended with a complex singlet scalar (cxSM) can admit a strong first order electroweak phase transition (SFOEWPT) as needed for electroweak baryogenesis and provide a dark matter (DM) candidate. The presence of both a DM candidate and a singlet-like scalar that mixes with the Standard Model Higgs boson leads to the possibility of a bb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ b\\overline{b} $$\\end{document} + MET final state in pp collisions. Focusing on this channel, we analyze the prospective reach at the Large Hadron Collider (LHC) for a heavy singlet-like scalar in regions of cxSM parameter space compatible with a SFOEWPT and DM phenomenology. We identify this parameter space while implementing current constraints from electroweak precision observable and Higgs boson property measurements as well as those implied by LHC heavy resonance searches. Implementing a proposed search strategy, we find that the heavy scalar and DM candidate can be probed up to 1 TeV and 450 GeV at 2σ level respectively.

Jet performance at the circular electron-positron collider

Jet reconstruction is critical for the precision measurement of Higgs boson properties and the electroweak observables at the CEPC. We analyze the jet energy and angular responses of benchmark 2- and 4-jet processes with fully simulated samples with the CEPC baseline detector geometry. We observe a relative resolution of 3.5% and 1% on the jet energy and angular measurement for jets in the detector barrel region (|cos θ| < 0.6) with energy greater than 60 GeV. Meanwhile, the jet energy/angular scale can be controlled within 0.5/0.01%. The differential dependences of the jet response on the jet direction and energy are extracted. We also analyze the impact on the jet responses induced by different jet clustering algorithms and matching criteria, which yields a relative difference of up to 8%.

Measurement of the Higgs boson properties using the ATLAS detector

With the proton-proton collision dataset collected at with the ATLAS detector at LHC, an integrated luminosity of 139 fb−1 has been achieved and detailed measurements of Higgs boson properties can be performed. The measurements of Higgs boson properties using various decay modes of the Higgs boson is presented. The different production mode cross sections are determined, simplified template cross sections are measured, and interpretations of the results in different frameworks are obtained.

Precision inclusive Higgs physics at e+e\u2212 colliders with tracking detectors and without calorimetry

A primary goal of a future e+e− collider program will be the precision measurement of Higgs boson properties. For practical reasons it is of interest to determine the minimal set of detector specifications required to reach this and other scientific goals. Here we investigate the precision obtainable for the e+e−→Zh→μ+μ−X inclusive cross section and the Higgs boson mass using the di-muon recoil method, considering a detector that has only an inner tracking system within a solenoidal magnetic field, surrounded by many nuclear interaction lengths of absorbing material, and an outer muon identification system. We find that the sensitivity achievable in these measurements with such a tracking detector is only marginally reduced compared to that expected for a general purpose detector with additional electromagnetic and hadronic calorimeter systems. The difference results mainly from multi-photon backgrounds that are not as easily rejected with tracking detectors. We also comment on the prospects for an analogous measurement of the e+e−→Zh→e+e−X inclusive cross section. Finally, we study searches for light scalars utilizing the di-muon recoil method, estimating the projected reach with a tracking or general purpose detector.

Measurements of decay branching fractions of in associated production at the CEPC * * Supported by the National Key Program for S&T Research and Development (2016YFA0400400), National Natural Science Foundation of China (NSFC) (11705028), Fundamental Research Funds for the Central Universities (2242015K40027 and 2242017K40018), Provincial Innovation and Entrepreneurship Training Program for Undergraduate (201710286068X), and Beijing Municipal Science and Technology Commission

The high-precision measurement of Higgs boson properties is one of the primary goals of the Circular Electron Positron Collider (CEPC). The measurements of decay branching fraction in the CEPC experiment is presented, considering a scenario of analysing 5000 fb-1 collision data with the center-of-mass energy of 250 GeV. In this study the Higgs bosons are produced in association with a pair of leptons, dominantly mediated by the ZH production process. The statistical uncertainty of the signal cross section is estimated to be about 1% in the final state, and approximately 5%-10% in the final states. In addition, the main sources of the systematic uncertainties and their impacts to the measurements of branching fractions are discussed. This study demonstrates the potential of precise measurement of the hadronic final states of the Higgs boson decay at the CEPC, and will provide key information to understand the Yukawa couplings between the Higgs boson and quarks, which are predicted to be the origin of quarks’ masses in the standard model.

Precision Higgs physics at the CEPC * *Supported by the National Key Program for S&T Researh and Development (2016YFA0400400); CAS Center for Excellence in Particle Physics; Yifang Wang’s Science Studio of the Ten Thousand Talents Project; the CAS/SAFEA International Partnership Program for Creative Research Teams (H751S018S5); IHEP Innovation Grant (Y4545170Y2); Key Research Program of Frontier Sciences, CAS (XQYZDY-SSW-SLH002); Chinese Academy

The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics. The Higgs boson will be the subject of extensive studies of the ongoing LHC program. At the same time, lepton collider based Higgs factories have been proposed as a possible next step beyond the LHC, with its main goal to precisely measure the properties of the Higgs boson and probe potential new physics associated with the Higgs boson. The Circular Electron Positron Collider (CEPC) is one of such proposed Higgs factories. The CEPC is an e + e − circular collider proposed by and to be hosted in China. Located in a tunnel of approximately 100 km in circumference, it will operate at a center-of-mass energy of 240 GeV as the Higgs factory. In this paper, we present the first estimates on the precision of the Higgs boson property measurements achievable at the CEPC and discuss implications of these measurements.

Collider probes of singlet fermionic dark matter scenarios for the Fermi gamma-ray excess

We investigate the collider signatures of three benchmark points in the singlet fermionic dark matter model motivated by the Fermi gamma-ray excess at the Galactic center. The benchmark points are classified according to the final state of the main dark annihilation process: a pair of b quarks, Higgs bosons and new scalar bosons. Since the dark sector in the model communicates with the visible sector through a mixing between the new scalar and the Higgs boson, collider observables related to the measurements of Higgs boson properties and searches for the new scalar boson are essential to probe the benchmark scenarios at colliders. In this paper, we consider four collider observables: (1) Higgs signal strength (essentially hZZ coupling), (2) triple Higgs coupling, (3) exotic Higgs decay, and (4) direct production of the new scalar particle. We find that the benchmark points have distinctive collider signatures that can be well tested by the interplay of future lepton and hadron colliders.

Electroweak and QCD corrections to Z -boson production with one b jet in a massive five-flavor scheme

We compute the $O(\alpha_s \alpha^2)$ and $O(\alpha_s^2 \alpha)$ contributions to the production cross section of a $Z$ boson with one $b$ jet at the Large Hadron Collider (LHC), and study their phenomenological relevance for LHC physics. The accurate prediction of hadronic $Z+b$-jet production is needed to control a background that greatly affects both the measurement of Higgs-boson properties and searches of new physics at the LHC. At the same time it could enable the first precise measurement of the $b$-quark parton distribution function. In this context $b$-quark mass effects become relevant and need to be studied with care, both at the level of the hard process and at the level of the initial- and final-state parton evolution. It is the aim of this paper to explore some of these issues in the framework of a massive 5 Flavor Scheme and to assess the need for both the inclusion of electroweak corrections, in addition to QCD corrections, and $b$-quark mass effects in the prediction of total and differential cross sections for hadronic $Z+b$-jet production.

Measurements of Higgs boson properties in the diphoton decay channel in proton-proton collisions at sqrt{s}=13 TeV

Measurements of Higgs boson properties in the H → γγ decay channel are reported. The analysis is based on data collected by the CMS experiment in proton-proton collisions at sqrt{s}=13 TeV during the 2016 LHC running period, corresponding to an integrated luminosity of 35.9 fb−1. Allowing the Higgs mass to float, the measurement yields a signal strength relative to the standard model prediction of 1.18− 0.14+ 0.17 = 1.18− 0.11+ 0.12(stat)− 0.07+ 0.09(syst)− 0.06+ 0.07(theo), which is largely insensitive to the exact Higgs mass around 125 GeV. Signal strengths associated with the different Higgs boson production mechanisms, couplings to bosons and fermions, and effective couplings to photons and gluons are also measured.

Probing extra Yukawa couplings by precision measurements of Higgs boson properties

If one removes any \emph{ad hoc} symmetry assumptions, the general two Higgs doublet model should have additional Yukawa interactions independent from fermion mass generation, in general involving flavor changing neutral Higgs couplings. These extra couplings can affect the discovered Higgs boson $h$ through fermion loop contributions. We calculate the renormalized $hZZ$ coupling at one-loop level %by on-shell and minimal subtraction scheme, and evaluate the dependence on heavy Higgs boson mass and extra Yukawa coupling $\rho_{tt}$. Precision measurements at future colliders can explore the parameter space, and can give stronger bound on $\rho_{tt}$ than the current bound from flavor experiments. As a side result, we find that if $\rho_{tt}\cos\gamma < 0$, where $\cos\gamma$ is the exotic Higgs component of $h$, the $\rho_{tt}$-induced top loop contribution cancels against bosonic loop contributions, and one may have alignment without decoupling, namely $\sin(-\gamma) \simeq 1$, but exotic scalar bosons could have masses at several hundred GeV.

Quark-gluon tagging with shower deconstruction: Unearthing dark matter and Higgs couplings

The separation of quark and gluon initiated jets can be an important way to improve the sensitivity in searches for new physics or in measurements of Higgs boson properties. We present a simplified version of the shower deconstruction approach as a novel observable for quark-gluon tagging. Assuming topocluster-like objects as input, we compare our observable with energy correlation functions and find a favorable performance for a large variety of jet definitions. When applied to dark matter searches in mono-jet final states limitations from small signal-to-background ratios can be overcome. We also show that quark-gluon tagging is an alternative way of separating weak boson from gluon-fusion production in the process p + p -> H + jet + jet + X

Higgs boson properties and tests of the Standard Model at CMS

The measurements of Higgs boson properties, mass, spin/CP, couplings, off-shell cross sections and constraints on invisible width are summarized and compared with standard model expectations. The analysis is based on pp collision data collected at centre-of-mass energies of 7 and 8 TeV by the CMS experiment at the LHC, corresponding to integrated luminosities of 5 fb−1 and 20 fb−1, respectively.

Reconstruction and Identification of Tau Leptons in ATLAS

These proceedings describe the reconstruction and identification of tau leptons in the ATLAS experiment at the LHC. Tau leptons play an important role in the measurement of Standard Model processes, in the search for new physics (Supersymmetry, heavy resonances) and in the measurement of Higgs boson properties. Hadronic tau lepton decays are reconstructed calorimeter based and separation against QCD-induced jets is done relying on shapes of energy depositions in the calorimeter as well as tracking based variables. The energy scale of tau leptons is obtained by scaling the measured momentum to the simulated one and is cross-checked in data. The tau trigger makes use of the collimated nature of tau decays and relies on a combination of objects (e.g. tau + muon) to reduce the rates and thresholds. An outlook to the improved tau reconstruction to be used in the next data-taking period of ATLAS concludes the proceedings.

CP -violating phenomenology of flavor conserving two Higgs doublet models

We analyze the constraints on $CP$-violating, flavor conserving two Higgs doublet models implied by measurements of Higgs boson properties at the Large Hadron Collider (LHC) and by the nonobservation of permanent electric dipole moments (EDMs) of molecules, atoms, and neutrons. We find that the LHC and EDM constraints are largely complementary, with the LHC studies constraining the mixing between the neutral $CP$-even states and the EDMs probing the effect of mixing between the $CP$-even and $CP$-odd scalars. Presently, the most stringent constraints are implied by the nonobservation of the ThO molecule EDM signal. Future improvements in the sensitivity of neutron and diamagnetic atom EDM searches could yield competitive or even more severe constraints. We analyze the quantitative impact of hadronic and nuclear theory uncertainties on the interpretation of the latter systems and conclude that these uncertainties cloud the impact of projected improvements in the corresponding experimental sensitivities.

Phenomenology of light fermionic asymmetric dark matter

Asymmetric dark matter (ADM) has been an attractive possibility attempting to explain the observed ratio of baryon to dark matter abundance in the universe. While a bosonic ADM is constrained by the limits from existence of old neutron stars, a fermionic ADM requires an additional light particle in order to annihilate its symmetric component in the early universe. We revisit the phenomenology of a minimal GeV scale fermionic ADM model including a light scalar state. The current constraints on this scenario from cosmology, dark matter direct detection, flavour physics and collider searches are investigated in detail. We estimate the future reach on the model parameter space from next-generation dark matter direct detection experiments, Higgs boson property measurements and search for light scalars at the LHC, as well as the determination of Higgs invisible branching ratio at the proposed ILC.

Higgs decay width in multiscalar doublet models

We show that there are regions of parameter space in multiscalar doublet models where, in the first few hundred inverse femtobarns of data, the new charged and neutral scalars are not directly observable at the LHC and yet the Higgs decay rate to $b\overline{b}$ is changed significantly from its standard model value. For a light Higgs with a mass less than 140 GeV, this can cause a large change in the number of two photon and ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ Higgs decay events expected at the LHC compared to the minimal standard model. In the models we consider, the principle of minimal flavor violation is used to suppress flavor changing neutral currents. This paper emphasizes the importance of measuring the properties of the Higgs boson at the LHC; for a range of parameters the model considered has new physics at the TeV scale that is invisible, in the first few hundred inverse femtobarns of integrated luminosity at the LHC, except indirectly through the measurement of Higgs boson properties.

Higgs Boson theory and phenomenology

Precision electroweak data presently favors a weakly-coupled Higgs sector as the mechanism responsible for electroweak symmetry breaking. Low-energy supersymmetry provides a natural framework for weakly-coupled elementary scalars. In this review, we summarize the theoretical properties of the Standard Model (SM) Higgs boson and the Higgs sector of the minimal super-symmetric extension of the Standard Model (MSSM). We then survey the phenomenology of the SM and MSSM Higgs bosons at the Tevatron, LHC and a future e + e − linear collider. We focus on the Higgs discovery potential of present and future colliders and stress the importance of precision measurements of Higgs boson properties.