Higgs Boson Physics Research Articles

Specialized minimal PDFs for optimized LHC calculations.

We present a methodology for the construction of parton distribution functions (PDFs) designed to provide an accurate representation of PDF uncertainties for specific processes or classes of processes with a minimal number of PDF error sets: specialized minimal PDF sets, or SM-PDFs. We construct these SM-PDFs in such a way that sets corresponding to different input processes can be combined without losing information, specifically as regards their correlations, and that they are robust upon smooth variations of the kinematic cuts. The proposed strategy never discards information, so that the SM-PDF sets can be enlarged by the addition of new processes, until the prior PDF set is eventually recovered for a large enough set of processes. We illustrate the method by producing SM-PDFs tailored to Higgs, top-quark pair, and electroweak gauge boson physics, and we determine that, when the PDF4LHC15 combined set is used as the prior, around 11, 4, and 11 Hessian eigenvectors, respectively, are enough to fully describe the corresponding processes.

HistFitter: a flexible framework for statistical data analysis

HistFitter is a software framework for statistical data analysis that has been used extensively in the ATLAS Collaboration to analyze data of proton-proton collisions produced by the Large Hadron Collider at CERN. Most notably, HistFitter has become a de-facto standard in searches for supersymmetric particles since 2012, with some usage for Exotic and Higgs boson physics. HistFitter coherently combines several statistics tools in a programmable and flexible framework that is capable of bookkeeping hundreds of data models under study using thousands of generated input histograms.HistFitter interfaces with the statistics tools HistFactory and RooStats to construct parametric models and to perform statistical tests of the data, and extends these tools in four key areas. The key innovations are to weave the concepts of control, validation and signal regions into the very fabric of HistFitter, and to treat these with rigorous methods. Multiple tools to visualize and interpret the results through a simple configuration interface are also provided.

Higgs physics: Review of recent results and prospects from ATLAS and CMS

An overview of recent results in Higgs boson physics obtained with the ATLAS and CMS experiments at the Large Hadron Collider located at CERN, Geneva, is presented. The focus is on measurements of the properties of the recently discovered Higgs boson with a mass of about 125 GeV. A brief selection of results in searches for Higgs bosons beyond the Standard Model is given, and prospects of future Higgs boson measurements and searches at the LHC are discussed.

HistFitter - A flexible framework for statistical data analysis

We present a software framework for statistical data analysis, called HistFitter, that has extensively been used in the ATLAS Collaboration to analyze data of proton-proton collisions produced by the Large Hadron Collider at CERN. Most notably, HistFitter has become a de-facto standard in searches for supersymmetric particles since 2012, with some usage for Exotic and Higgs boson physics. HistFitter coherently combines several statistics tools in a programmable and flexible framework that is capable of bookkeeping hundreds of data models under study using thousands of generated input histograms. The key innovations of HistFitter are to weave the concepts of control, validation and signal regions into its very fabric, and to treat them with rigorous statistical methods, while providing multiple tools to visualize and interpret the results through a simple configuration interface.

B-jet identification at High Level Trigger in CMS

The CMS experiment at the CERN LHC has been designed with a 2-level trigger system. The Level 1 Trigger (L1) is implemented on custom-designed electronics. The High Level Trigger (HLT) is a streamlined version of the CMS offline reconstruction software running on a computer farm. Being able to identify b-quark jets (b-tagging) at trigger level will play a crucial role during the Run II data taking to ensure the top quark, beyond the Standard Model and Higgs boson physics program of the experiment. It will help to significantly reduce the trigger output rate which will increase due to the higher instantaneous luminosity and higher cross sections at 13 TeV. B-tagging algorithms based on the identification of tracks displaced from the primary proton-proton collision and/or on the reconstruction of secondary vertices have been successfully used during Run I. We will present their design and performance with an emphasis on the dedicated aspects of track and primary vertex reconstruction, as well as the improvements foreseen to meet the challenges of the Run II data taking.

Review of physics results from the Tevatron: Higgs boson physics

We review the techniques and results of the searches for the Higgs boson performed by the two Tevatron collaborations, CDF and DØ. The Higgs boson predicted by the Standard Model was sought in the mass range 90 GeV < mH < 200 GeV in all main production modes at the Tevatron: gluon–gluon fusion, WH and ZH associated production, vector boson fusion, and [Formula: see text] production, and in five main decay modes: [Formula: see text], H→τ+τ-, H→WW(*), H→ZZ(*) and H→γγ. An excess of events was seen in the [Formula: see text] searches consistent with a Standard Model Higgs boson with a mass in the range 115 GeV < mH < 135 GeV . Assuming a Higgs boson mass of mH = 125 GeV , studies of Higgs boson properties were performed, including measurements of the product of the cross section times the branching ratio in various production and decay modes, constraints on Higgs boson couplings to fermions and vector bosons, and tests of spin and parity. We also summarize the results of searches for supersymmetric Higgs bosons, and Higgs bosons in other extensions of the Standard Model.

Latest Higgs Physics Results from ATLAS

Selected recent results on Higgs boson physics obtained with the ATLAS experiment at the LHC are presented. These include preliminary evidence for the Higgs Yukawa interaction with fermions based on ττ final states, results from an updated combined analyses of Higgs boson couplings, new mass measurements, constraints on the total width, differential cross section measurements as well as the search for rare production and decay modes.

Higgs-flavon mixing and LHC phenomenology in a simplified model of broken flavor symmetry

The LHC phenomenology of a low-scale gauged flavor symmetry model with inverted hierarchy is studied, through introduction of a simplified model of broken flavor symmetry. A new scalar (a flavon) and a new neutral top-philic massive gauge boson emerge with mass in the TeV range along with a new heavy fermion associated with the standard model top quark. After checking constraints from electroweak precision observables, we investigate the influence of the model on Higgs boson physics, notably on its production cross section and decay branching fractions. Limits on the flavon $\varphi$ from heavy Higgs boson searches at the LHC at 7 and 8 TeV are presented. The branching fractions of the flavon are computed as a function of the flavon mass and the Higgs-flavon mixing angle. We also explore possible discovery of the flavon at 14 TeV, particularly via the $\varphi \rightarrow Z^0Z^0$ decay channel in the $2\ell2\ell'$ final state, and through standard model Higgs boson pair production $\varphi \rightarrow hh$ in the $b\bar{b}\gamma\gamma$ final state. We conclude that the flavon mass range up to $500$ GeV could probed down to quite small values of the Higgs-flavon mixing angle with 100 fb$^{-1}$ of integrated luminosity at 14 TeV.

Some recent theoretical progress in Higgs boson and top quark physics at hadron colliders

The test of the Standard Model and search for New Physics signal are main aim of LHC experiment. With the increasing of the measurement accuracy at the LHC, it is a major task in future to exceed the current accuracy of the theoretical predictions for important processes, in particular ones involving Higgs boson and top quark. In this review we briefly summarize some recent theoretical progress in Higgs boson and top quark physics, especially the fixed-order and resummation predictions in QCD at both the Tevatron and the LHC.

Results of searches for Higgs Boson and New Physics at LHC

An overview of the recent results from the LHC experiments is given for the searches for a Higgs Boson and New Physics with √s = 7 and 8 TeV data. Studies of Standard Model processes, including polarization measurements, are also presented.

Isospin violating dark matter being asymmetric

The isospin violating dark matter (IVDM) scenario offers an interesting possibility to reconcile conflicting results among direct dark matter search experiments for a mass range around 10 GeV. We consider two simple renormalizable IVDM models with a complex scalar dark matter and a Dirac fermion dark matter, respectively, whose stability is ensured by the conservation of ``dark matter number.'' Although both models successfully work as the IVDM scenario with destructive interference between effective couplings to proton and neutron, the dark matter annihilation cross section is found to exceed the cosmological/astrophysical upper bounds. Then, we propose a simple scenario to reconcile the IVDM scenario with the cosmological/astrophysical bounds, namely, the IVDM being asymmetric. Assuming a suitable amount of dark matter asymmetry has been generated in the early Universe, the annihilation cross section beyond the cosmological/astrophysical upper bound nicely works to dramatically reduce the antidark matter relic density and as a result, the constraints from dark matter indirect searches are avoided. We also discuss collider experimental constraints on the models and an implication to Higgs boson physics.

Higgs couplings beyond the standard model

Abstract We consider the Higgs boson decay processes and its production, and provide a parameterisation tailored for testing models of new physics beyond the Standard Model. We also compare our formalism to other existing parameterisations based on scaling factors in front of the couplings and to effective Lagrangian approaches. Different formalisms allow to best address different aspects of the Higgs boson physics. The choice of a particular parameterisation depends on a non-obvious balance of quantity and quality of the available experimental data, envisaged purpose for the parameterisation and degree of model independence, importance of the radiative corrections, scale at which new particles appear explicitly in the physical spectrum. At present only simple parameterisations with a limited number of fit parameters can be performed, but this situation will improve with the forthcoming experimental LHC data. Detailed fits can only be performed by the experimental collaborations at present, as the full information on the different decay modes is not completely available in the public domain. It is therefore important that different approaches are considered and that the most detailed information is made available to allow testing the different aspects of the Higgs boson physics and the possible hints beyond the Standard Model.

Top quark and Higgs boson physics at the Tevatron

The search for the Higgs boson and the study of the heaviest known fundamental particle, the top quark, have been at the center of the Tevatron research program. The Higgs boson is yet to be discovered and the top quark was discovered in 1995. Both of these particles have a very special place in the "periodic table" of fundamental particles. With Tevatron having delivered more than 11 fb−1 of data at 1.96 TeV and the Large Hadron Collider also rapidly collecting data at 7 TeV, we are entering a very exciting era where many interesting questions about these intriguing particles will be answered. Here I summarize the current status of Higgs boson and top quark studies at the Tevatron.

Diboson Production at Colliders

This article is devoted to the physics of pairs of electroweak gauge bosons (dibosons) produced at high-energy particle colliders. Particular emphasis is placed on published results on diboson production from the CDF and DØ experiments at the Fermilab Tevatron and the CMS and ATLAS experiments at the CERN Large Hadron Collider (LHC). The study of diboson production at colliders plays an important role in tests of electroweak theory and searches for new phenomena at the TeV-energy scale and beyond. The diboson physics program has been a highlight of Run II at the Fermilab Tevatron. The progress made on analysis methods through the study of Standard Model diboson signals has had a direct and positive impact on the sensitivity of Higgs boson and New Physics searches in the Tevatron experiments. It is anticipated that diboson physics will play an even bigger role in the TeV-scale exploration now under way at the LHC.

Single Higgs-boson production at a photon–photon collider: General 2HDM versus MSSM

We revisit the production of a single Higgs boson from direct γγ-scattering at a photon collider. We compute the total cross-section σ(γγ→h) (for h=h0,H0,A0), and the strength of the effective gh0γγ coupling normalized to the Standard Model (SM), for both the general Two-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric Standard Model (MSSM). In both cases the predicted production rates for the CP-even (odd) states render up to 104 (103) events per 500 fb−1 of integrated luminosity, in full consistency with all the theoretical and phenomenological constraints. Depending on the channel the maximum rates can be larger or smaller than the SM expectations, but in most of the parameter space they should be well measurable. We analyze how these departures depend on the dynamics underlying each of the models, supersymmetric and non-supersymmetric, and highlight the possible distinctive phenomenological signatures. We demonstrate that this process could be extremely useful to discern non-supersymmetric Higgs bosons from supersymmetric ones. Furthermore, in the MSSM case, we show that γγ-physics could decisively help to overcome the serious impasse afflicting Higgs boson physics at the infamous “LHC wedge”.

Standard Model, Higgs Boson(s) and New Physics at the LHC in Run I

A overview of the ATLAS and CMS detectors and first physics results from the 2010 data taking campaign at the LHC collider is presented. Measurements with pp collisions at s = 7 TeV and for integrated luminosities reaching up to about 40 pb −1 are summarized for weak bosons and top quark production, as well as for the search of the Higgs Boson(s), supersymmetry and new interactions at the TeV scale. The physics prospects for the complete Run I from 2010 to 2012 with a few fb −1 of luminosity collected per experiment are discussed.

Unanswered Questions in the Electroweak Theory

This article is devoted to the status of the electroweak theory on the eve of experimentation at CERN's Large Hadron Collider (LHC). A compact summary of the logic and structure of the electroweak theory precedes an examination of what experimental tests have established so far. The outstanding unconfirmed prediction is the existence of the Higgs boson, a weakly interacting spin-zero agent of electroweak symmetry breaking and the giver of mass to the weak gauge bosons, the quarks, and the leptons. General arguments imply that the Higgs boson or other new physics is required on the 1-TeV energy scale.Even if a “standard” Higgs boson is found, new physics will be implicated by many questions about the physical world that the Standard Model cannot answer. Some puzzles and possible resolutions are recalled. The LHC moves experiments squarely into the 1-TeV scale, where answers to important outstanding questions will be found.

Measurement of the W Boson Mass at the Tevatron

Over the past four decades, the standard model of electroweak interactions has achieved tremendous success in describing the experimental data. One of the key observables is the mass MW of the W boson. The experimental measurements, including MW, have reached a level of precision that tests the theory at the quantum loop level, providing indirect constraints on the hypothetical Higgs boson and other new physics. Improved measurements of MW are driven by new data from Run II of the Fermilab Tevatron ([Formula: see text] collider at [Formula: see text] TeV). We discuss the techniques used for measuring MW at hadron colliders, summarize the measurements from Run I of the Tevatron, and review the state of the art of the Run II analyses, which are based on significantly larger data sets collected with upgraded detectors. We discuss the constraints on the Higgs boson, and conclude with a discussion of the ultimate precision in MW that can be expected from Run II.

The road towards the international linear collider: Higgs, top/quantum chromodynamics, loops

The international linear e + e − collider (ILC) could go into operation in the second half of the upcoming decade. Experimental analyses and theory calculations for the physics at the ILC are currently performed. We review recent progress, as presented at the LCWS06 in Bangalore, India, in the fields of Higgs boson physics and top/QCD. Also the area of loop calculations, necessary to achieve the required theory precision, is included.

Dark matter and Higgs boson physics

A vectorlike colorless fermion doublet and a singlet added to the standard model allow a consistent interpretation of dark matter in terms of the lightest neutral particle, as they may help in obtaining successful gauge coupling unification. We analyze in detail the mass range of the lightest neutral particle below the W mass, i.e. in a range of the parameters where the physics of the standard model Higgs boson may be substantially affected either directly or indirectly.