Search For Higgs Bosons Research Articles

Associated production of Higgs boson with a photon at electron-positron colliders

A complete one-loop prediction for the single production of the neutral Higgs bosons in association with a photon in electron-positron collisions is presented in the framework the minimal supersymmetric standard model (MSSM), paying special attention to the individual contribution from each type of diagram. This process has no amplitude at tree level and is hence directly sensitive to one-loop impacts and the underlying dynamics of Higgs. To investigate the effect of the new physics, four different scenarios, which include a Higgs boson with mass and couplings consistent with those of the discovered Higgs boson and a considerable part of parameter space allowed by the bounds from the searches for additional Higgs bosons and sparticles, are chosen in the MSSM. The dependence of the cross section in both the standard model(SM) and MSSM on the center-of-mass energy is examined by considering the polarizations of the initial electron and positron beams. The effect of individual contributions from each type of one-loop diagram on the total cross section is also investigated in detail. Furthermore, the total cross sections of $e^- e^+ \rightarrow \gamma h^0$ as well as $e^- e^+ \rightarrow \gamma A^0$ are scanned over the plane $m_A-\tan\beta$ for each scenario. The full one-loop contributions are crucial for the analysis of beyond the SM physics at a future electron-positron collider.

Search for neutral Higgs bosons decaying to bb¯ in the flipped 2HDM at future e−e+ linear colliders

In this study, assuming the Type-Y (flipped) 2HDM at the SM-like scenario as the theoretical framework, observability of the additional heavy neutral Higgs bosons $H$ and $A$ is investigated through the signal process chain $e^- e^+ \rightarrow AH \rightarrow b\bar{b}b\bar{b}$ at a linear collider operating at the center-of-mass energy of 1.5 TeV. The assumed signal process is highly motivated by the enhancements in the $A/H\rightarrow b\bar{b}$ decays at relatively high $\tb$ values. Such enhancements result in the dominance of the mentioned decay modes even for Higgs masses above the threshold of the on-shell top quark pair production. Taking advantage of such a unique feature, several benchmark scenarios are studied. Simulating the detector response based on the SiD detector at the ILC, simulated events are analyzed to reconstruct the $H$ and $A$ Higgs bosons. The top quark pair production and $Z/\gamma$ production are the main SM background processes and are well under control. Results indicate that, the $H$ and $A$ Higgs bosons are observable with signals exceeding $5\sigma$ with possibility of mass measurement in all the tested scenarios. Specifically, the parameter space region enclosed with the mass ranges $m_H$=150-500 GeV and $m_A$=230-580 GeV with the $A/H$ mass splitting of 80 GeV is observable at the integrated luminosity of 500 $fb^{-1}$.

Importance-based signal detection and parameter estimation with applications tonew particle search

One of the hardest challenges in data analysis is perhaps the detection of rare anomalous data buried in a huge normal background. We study this problem by constructing a novel method, which is a combination of the Kullback?Leibler importance estimation procedure based anomaly detection algorithm and linear discriminant classifier. We choose to illustrate it with the example of charged Higgs boson (CHB) search in particle physics. Indeed, the Large Hadron Collider experiments at CERN ensure that CHB signal must be a tiny effect within the irreducible W-boson background. In simulations, different CHB events with different characteristics are produced and judiciously mixed with the non-CHB data, and the proposed method is applied. Our results show that distribution parameters of weak CHB signals can be estimated with high performance. This anomaly detection method is general enough to apply to similar problems in other fields (e.g., astrophysical, medical, engineering problems).

MSSM Higgs boson searches at the LHC: benchmark scenarios for Run 2 and beyond

We propose six new benchmark scenarios for Higgs boson searches in the Minimal Supersymmetric Standard Model. Our calculations follow the recommendations of the LHC Higgs Cross Section Working Group, and benefit from recent developments in the predictions for the Higgs-boson masses and mixing. All of the proposed scenarios are compatible with the most recent results from Run 2 of the LHC. In particular, they feature a scalar with mass and couplings compatible with those of the observed Higgs boson, and a significant portion of their parameter space is allowed by the limits from the searches for SUSY particles and additional Higgs bosons. We define a scenario where all SUSY particles are relatively heavy, and two scenarios with light colorless SUSY particles (charginos, neutralinos and, in one case, staus). In addition, we present two scenarios featuring alignment without decoupling, realized with either the lighter or the heavier scalar being SM-like, and a scenario with mathcal {CP} violation.

Search for charged Higgs bosons in the H\xb1 \u2192 \u03c4\xb1\u03bd\u03c4 decay channel in proton-proton collisions at sqrt{s}=13 TeV

A search is presented for charged Higgs bosons in the H± → τ±ντ decay mode in the hadronic final state and in final states with an electron or a muon. The search is based on proton-proton collision data recorded by the CMS experiment in 2016 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The results agree with the background expectation from the standard model. Upper limits at 95% confidence level are set on the production cross section times branching fraction to τ±ντ for an H± in the mass range of 80GeV to 3TeV, including the region near the top quark mass. The observed limit ranges from 6 pb at 80 GeV to 5 fb at 3 TeV. The limits are interpreted in the context of the minimal supersymmetric standard model mhhod − scenario.

Combined measurements of Higgs boson couplings in proton\u2013proton collisions at sqrt{s}=13,text {Te}text {V}

Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton–proton collision data set recorded with the CMS detector in 2016 at sqrt{s}=13,text {Te}text {V} , corresponding to an integrated luminosity of 35.9{,text {fb}^{-1}} . The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a mathrm {W} or mathrm {Z} boson, or a top quark-antiquark pair) and the following decay modes: mathrm {H} rightarrow gamma gamma , mathrm {Z}mathrm {Z}, mathrm {W}mathrm {W}, mathrm {tau }mathrm {tau }, mathrm {b} mathrm {b} , and mathrm {mu }mathrm {mu }. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be mu =1.17pm 0.10, assuming a Higgs boson mass of 125.09,text {Ge}text {V} . Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.

Search for neutral Higgs bosons within type-I 2HDM at future linear colliders

In this study, we investigate observability of the neutral scalar (H) and pseudoscalar (A) Higgs bosons in the framework of the type-I 2HDM at SM-like scenario at a linear collider operating at sqrt{s}= 500 and 1000 GeV. The signal process is e^- e^+ rightarrow A H rightarrow ZHHrightarrow jj b{bar{b}}b{bar{b}} where jj is a di-jet resulting from the Z boson decay and b{bar{b}} is a b-jet pair from scalar Higgs boson decay. Several benchmark scenarios with different mass hypotheses are studied. The assumed signal process is mainly motivated by the large decay rate of Arightarrow ZH (at high tan beta and enough Higgs boson mass splitting) and Hrightarrow b{bar{b}} in the type-I. After event generation the detector response is simulated based on the SiD detector at the ILC. The ISR and beamstrahlung effects are also included for each center of mass energy assuming unpolarized beams. The simulated events are analyzed to obtain candidate mass distributions of the Higgs bosons. Among standard model backgrounds, the top quark pair production process is the main background but is under control. Results indicate that, in all considered scenarios, both Higgs bosons H and A are observable with signals exceeding 5sigma with possibility of mass measurement. Final results are shown as 5sigma contours in (m_H,m_A) or (m_A,tan beta ) space.

Search for invisible Higgs boson decays in vector boson fusion at [formula omitted] with the ATLAS detector

We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1)TeV and O(100)GeV missing transverse momentum. The analysis uses 36.1fb−1 of pp collision data at s=13TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the wimp–nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3–1.7pb.

Type-II 2HDM under the precision measurements at the Z-pole and a Higgs factory

Future precision measurements of the Standard Model (SM) parameters at the proposed Z-factories and Higgs factories may have significant impacts on new physics beyond the Standard Model in the electroweak sector. We illustrate this by focusing on the Type-II two Higgs doublet model (Type-II 2HDM). The contributions from the heavy Higgs bosons at the tree-level and at the one-loop level are included in a full model parameter space. We perform a multiple variable global fit and study the extent to which the parameters of non-alignment and non-degenerate masses can be probed by the precision measurements. We find that the allowed parameter ranges are tightly constrained by the future Higgs precision measurements, especially for small and large values of tan β. Indirect limits on the masses of heavy Higgs can be obtained, which can be complementary to the direct searches of the heavy Higgs bosons at hadron colliders. We also find that the expected accuracies at the Z-pole and at a Higgs factory are quite complementary in constraining mass splittings of heavy Higgs bosons. The typical results are | cos(β − α)| < 0.008, |ΔmΦ| < 200 GeV, and tan β ∼ 0.2 − 5. The reaches from CEPC, FCC-ee and ILC are also compared, for both Higgs and Z-pole precision measurements.

MSSM Higgs benchmark scenarios for Run 2 and beyond: the low tan beta region

We propose two new benchmark scenarios for Higgs-boson searches in the Minimal Supersymmetric Standard Model (MSSM ). These scenarios are specifically designed for the low tan beta region. A light Higgs-boson mass prediction compatible with the observed value of 125,hbox {GeV} is ensured in almost the entire parameter space by employing a flexible supersymmetric (SUSY) mass scale, reaching values of up to 10^{16},hbox {GeV}. The MSSM Higgs-sector predictions are evaluated in an effective field theory (EFT ) framework that exhibits a Two-Higgs-Doublet-Model at the low scale. In the first scenario all SUSY particles are relatively heavy, whereas the second scenario features light neutralinos and charginos. Both scenarios are largely compatible with the most recent results from Run 2 of the LHC , and we highlight the main phenomenological features relevant for future LHC searches. In particular, we provide a detailed discussion of heavy Higgs-boson decays to neutralinos and charginos in the second scenario, and the arising collider signatures, in order to facilitate the design of dedicated LHC searches in the near future.

Searches for additional Higgs bosons decaying to tau leptons at the LHC

The searches for additional Higgs bosons decaying to tau leptons in scenarios beyond the standard model will be summarised, from the pp collision data collected by the ATLAS and CMS experiments at LHC Run-2.

Further study of the global minimum constraint on the two-Higgs-doublet models: LHC searches for heavy Higgs bosons

The usually considered vacuum of the two-Higgs-doublet model (2HDM) could be unstable if it locates at a local but not global minimum (GM) of the scalar potential. By requiring the vacuum to be a GM, we obtain an additional constraint, namely the GM constraint, on the scalar potential. In this work, we explore the GM constraint on the $CP$-conserving general 2HDM. This constraint is found to put limits on the soft $\mathbb{Z}_2$ breaking mass parameter $m_{12}^2$ and also squeeze the heavy $CP$-even Higgs boson mass into larger values for the $m_{12}^2< 0$ case. Combined with the current global signal fits from the LHC measurements of the 125 GeV Higgs boson, we discuss the phenomenological implications for the heavy Higgs boson searches at the LHC.

Phenomenology of the inflation-inspired NMSSM at the electroweak scale

The concept of Higgs inflation can be elegantly incorporated in the Next-to-Minimal Supersymmetric Standard Model (NMSSM). A linear combination of the two Higgs-doublet fields plays the role of the inflaton which is non-minimally coupled to gravity. This non-minimal coupling appears in the low-energy effective superpotential and changes the phenomenology at the electroweak scale. While the field content of the inflation-inspired model is the same as in the NMSSM, there is another contribution to the mu term in addition to the vacuum expectation value of the singlet. We explore this extended parameter space and point out scenarios with phenomenological differences compared to the pure NMSSM. A special focus is set on the electroweak vacuum stability and the parameter dependence of the Higgs and neutralino sectors. We highlight regions which yield a SM-like 125,hbox {GeV} Higgs boson compatible with the experimental observations and are in accordance with the limits from searches for additional Higgs bosons. Finally, we study the impact of the non-minimal coupling to gravity on the Higgs mixing and in turn on the decays of the Higgs bosons in this model.

Machine Learning Techniques in the CMS Search for Higgs Decays to Dimuons

With the accumulation of large collision datasets at a center-of-mass energy of 13 TeV, the LHC experiments can search for rare processes, where the extraction of signal events from the copious Standard Model backgrounds poses an enormous challenge. Multivariate techniques promise to achieve the best sensitivities by isolating events with higher signal-to-background ratios. Using the search for Higgs bosons decaying to two muons in the CMS experiment as an example, we describe the use of Boosted Decision Trees coupled with automated categorization for optimal event classification, bringing an increase in sensitivity equivalent to 50% more data.

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.

Searching for charged Higgs bosons in the B − L supersymmetric standard model at the high luminosity large hadron collider

Upon assuming the B−L Supersymmetric Standard Model (BLSSM) as theoretical framework accommodating a multi-Higgs sector, we assess the scope of the High Luminosity Large Hadron Collider (HL-LHC) in accessing charged Higgs bosons (H±) produced in pairs from Z′ decays. We show that, by pursuing both di-jet and tau-neutrino decays, several signals can be established for H± masses ranging from about MW to above mt and Z′ masses between 2.5 TeV and 3.5 TeV. The discovery can be attained, in a nearly background free environment in some cases, owing to the fact that the very massive resonating Z′ ejects the charged Higgs bosons at very high transverse momentum, a kinematic region where any SM noise is hugely depleted.

Highlights from the CMS Experiment

During the LHC Run 2, the CMS experiment has so far recorded $$>95\,\hbox {fb}^{-1}$$ of proton–proton collision data at $$\sqrt{\hbox {s}}=13$$ TeV. With such a large volume of data-set at an unprecedented energy, CMS has updated most of its new physics searches while the precision on various Standard Model measurements has substantially improved. This proceeding features most recent results on Higgs boson, Top quark, and new physics searches and the status of the CMS detector in 2017.

A Higgs boson below 125 GeV?!

We briefly summarize some searches for Higgs bosons with a mass of [Formula: see text] GeV at LEP and the LHC. We discuss a possible signal in the diphoton decay mode at [Formula: see text] GeV as reported by CMS, together with a [Formula: see text] hint in the [Formula: see text] final state at LEP. We briefly review possible interpretation of such a new particle in various BSM models. We focus on possible explanations as reported within the NMSSM and the [Formula: see text]SSM. Conclusions for future collider projects are briefly outlined.

Search for charged Higgs bosons decaying into top and bottom quarks at sqrt{s}=13 TeV with the ATLAS detector

A search for charged Higgs bosons heavier than the top quark and decaying via H± → tb is presented. The data analysed corresponds to 36.1 fb−1 of pp collisions at sqrt{s}=13 TeV and was recorded with the ATLAS detector at the LHC in 2015 and 2016. The production of a charged Higgs boson in association with a top quark and a bottom quark, pp → tbH±, is explored in the mass range from mH± = 200 to 2000 GeV using multi-jet final states with one or two electrons or muons. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. Multivariate techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass, which range from 2.9 pb at mH± = 200 GeV to 0.070 pb at mH± = 2000 GeV. The results are interpreted in two benchmark scenarios of the Minimal Supersymmetric Standard Model.

Searching for the W\u03b3 decay of a charged Higgs boson

We study the prospects for charged Higgs boson searches in the Wγ decay channel. This loop-induced decay channel can be important if the charged Higgs is fermiophobic, particularly when its mass is below the WZ threshold. We identify useful kinematic observables and evaluate the future Large Hadron Collider sensitivity to this channel using the custodial-fiveplet charged Higgs in the Georgi-Machacek model as a fermiophobic benchmark. We show that the LHC with 300 fb−1 of data at 14 TeV will be able to exclude charged Higgs masses below about 130 GeV for almost any value of the SU(2)L-triplet vacuum expectation value in the model, and masses up to 200 GeV and beyond when the triplet vacuum expectation value is very small. We describe the signal simulation tools created for this analysis, which have been made publicly available.