Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “HIGGS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28

Search for invisible decays of Higgs bosons in the vector boson fusion and associated ZH production modes

A search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a b b-bar quark pair. The searches use the 8 TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7 inverse femtobarns. Certain channels include data from 7 TeV collisions corresponding to an integrated luminosity of 4.9 inverse femtobarns. The searches are sensitive to non-standard-model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. In all channels, the observed data are consistent with the expected standard model backgrounds. Limits are set on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, for the vector boson fusion and ZH production modes. By combining all channels, and assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the invisible branching fraction at m[H] = 125 GeV is found to be 0.58 (0.44) at 95% confidence level. We interpret this limit in terms of a Higgs-portal model of dark matter interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

New LHC benchmarks for the $\mathcal{CP}$-conserving two-Higgs-doublet model

We introduce a strategy to study the parameter space of the general, CP-conserving, two-Higgs-doublet Model (2HDM) with a softly broken $\mathbb Z_{2}$-symmetry by means of a new “hybrid” basis. In this basis the input parameters are the measured values of the mass of the observed Standard Model (SM)-like Higgs boson and its coupling strength to vector boson pairs, the mass of the second CP-even Higgs boson, the ratio of neutral Higgs vacuum expectation values, and three additional dimensionless parameters. Here, using the hybrid basis, we present numerical scans of the 2HDM parameter space where we survey available parameter regions and analyze model constraints. From these results, we define a number of benchmark scenarios that capture different aspects of non-standard Higgs phenomenology that are of interest for future LHC Higgs searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

A Correlation between the Higgs Mass and Dark Matter

Depending on the value of the Higgs mass, the Standard Model acquires an unstable region at large Higgs field values due to RG running of couplings, which we evaluate at 2-loop order. For currently favored values of the Higgs mass, this renders the electroweak vacuum only metastable with a long lifetime. We argue on statistical grounds that the Higgs field would be highly unlikely to begin in the small field metastable region in the early universe, and thus some new physics should enter in the energy range of order of, or lower than, the instability scale to remove the large field unstable region. We assume that Peccei-Quinn (PQ) dynamics enters to solve the strong CP problem and, for a PQ-scale in this energy range, may also remove the unstable region. We allow the PQ-scale to scan and argue, again on statistical grounds, that its value in our universe should be of order of the instability scale, rather than (significantly) lower. Since the Higgs mass determines the instability scale, which is argued to set the PQ-scale, and since the PQ-scale determines the axion properties, including its dark matter abundance, we are led to a correlation between the Higgs mass and the abundance of dark matter. We thus find the correlation to be in good agreement with current data.

43 PARTICLE ACCELERATORS↗

A search for the Higgs boson in H→WW→lvlv with 802 fb -1

This thesis documents a search for Standard Model (SM) Higgs boson to WW production in the final state of two charged leptons (e, μ) and two neutrino final state resulting from in pp collisions at √ s = 1.96 TeV. The data collected by the CDF II detector at the Tevatron collider at Fermilab, corresponds to an integrated luminosity of 8.2 fb -1 . This iteration of the analysis incorporated several improvements to increase Higgs sensitivity. We reevaluated lepton isolation values to recover signal events in which leptons mutually spoil each other’s isolation requirements. We additionally incorporated new lepton identification selections, namely likelihood based forward electrons and a better recovery of electrons passing through detector cracks. The base analysis searches for opposite-sign dilepton events. We employed three separately trained neural networks to distinguish signal from background processes for events with 0, one, or two jets. To further increase sensitivity for 0-jet events, we constructed a likelihood ratio discriminant based on Matrix Element calculations as an additional input to the neural network. For the base opposite-sign analysis, summing over all jet multiplicities, we observed 3513 events in data compared with a background expectation of 3409 ± 233 and a signal expectation of 53.6 ± 9.4 for a mass of 165 GeV/c 2 . To further increase signal acceptance, we incorporated several separate search regions in addition to the base analysis. We include subchannels searching for Higgs production in events with low dilepton invariant mass and in events having final states with either same-sign dileptons or trileptons With the combination of the separate analyses, we observed a 95% C.L. upper production limit of 0.77 times the SM expectation for a Higgs mass of 165 GeV/c 2 to be compared with the value for the median of the expected limit (0.78). We additionally present results for eighteen Higgs masses ranging from 110 GeV/c 2 to 200 GeV/c 2 . We excluded at the 95% C.L., a SM Higgs boson in the mass range between 156 and 175 GeV/c 2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for the Higgs Boson Produced in Association with a Vector Boson Using Like-Sign Dilepton Events in 1.96-TeV Proton-Antiproton Collisions

This thesis presents a search for the standard model and fermiophobic Higgs bosons produced in association with a vector boson using like-sign dilepton events collected by Collider Detector at Fermilab (CDF II). This analysis uses the data corresponding to an integrated luminosity of 9.4 fb -1 . The search is characterized by minimally biased cuts which maximize the acceptance of the Higgs bosons. The numbers of expected signal events passing requirements for like-sign dilepton are 5.6 for the fermiophobic Higgs on the mass of 110 GeV/c 2 assuming the standard model production cross section, and 1.7 for the standard model on the mass of 160 GeV/c 2 . The expectation of background events are 696.1, while the number of observed events are 624. To discriminate signal events from backgrounds, the search employs a multivariate analysis based on boosted decision trees. There are no significant disagreements in the BDT outputs, then, upper limits at a 95% confidence level are set on σ(p$\bar{p}$→V h) × B(h→WW ) for both Higgs bosons scenarios. The expected and observed limits are 5.9 and 9.2, respectively, relative to the standard model expectation for the standard model Higgs boson mass of 160 GeV/c 2 . For the fermiophobic Higgs boson corresponding to the mass of 110 GeV/c 2 , the expected and observed limits are 2.6 and 4.4, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Updated Combination of CDF and D0 Searches for Standard Model Higgs Boson Production with up to 10.0 fb$^{-1}$ of Data

We combine results from the CDF and D0 Collaborations on direct searches for the standard model (SM) Higgs boson (H) in ppbar collisions at the Fermilab Tevatron at sqrt(s)=1.96 TeV. Compared to the previous Tevatron Higgs boson search combination, more data have been included, additional channels have been incorporated, and some previously used channels have been reanalyzed to gain sensitivity. Searches are carried out for hypothesized Higgs boson masses between 100 and 200 GeV/c^2. With up to 10 fb-1 of luminosity analyzed, the 95% C.L. median expected upper limits on Higgs boson production are factors of 0.89, 1.08, and 0.48 times the values of the SM cross section for Higgs bosons of mass m_H=115 GeV/c^2, 125 GeV/c^2, and 165 GeV/c^2, respectively. In the absence of signal, we expect to exclude the regions 100<m_{H}<120 GeV/c^2 and 139<m_H<184 GeV/c^2. We exclude, at the 95% CL, two regions: 100<m_H<103 GeV/c^2, and 147<m_H<180 GeV/c^2. There is a significant excess of data events with respect to the background estimation in the mass range 115<m_H<140 GeV/c^2, which causes our observed limits to not be as stringent as expected. At m_H=120 GeV/c^2, the p-value for a background fluctuation to produce this excess is \sim1.5x10^-3, corresponding to a local significance of 3.0 standard deviations. The global significance for such an excess anywhere in the full mass range investigated is approximately 2.5 standard deviations. We also combine separately searches for H to bb and H to WW. We find that the excess is concentrated in the H to bb channel, appearing in the searches over a broad range of m_H. The maximum local significance of 3.2 standard deviations corresponds to a global significance of approximately 2.9 standard deviations. Our results in the H to WW channels are also consistent with the possible presence of a low-mass Higgs boson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Enabling U.S. participation in Future Higgs Factories

Exciting proposals for a new Higgs factory collider, aimed at the search for new physics and precision studies of particles and forces, especially measurement of the Higgs boson couplings at the loop level, will be evaluated as part of the Snowmass process. Potential facilities include (among others) ILC, FCC-ee, C3, CEPC, CLIC, muon collider and advanced accelerator concepts being investigated by Snowmass topical group AF6, potentially located in Asia, Europe, or the United States. The European Strategy has endorsed an electron-positron Higgs factory as its highest priority after HL-LHC. Much of the detector, software, and physics preparative studies needed for these machines is in common, and is currently being implemented by physicists world-wide. In this white paper for the 2021 Snowmass process we look at current global activity on future Higgs factories and give examples of investments that could be made in these common areas over the next five years to establish a leadership role for the U.S. in a future Higgs factory, wherever it is built. The U.S. high energy physics program confronts a number of challenges that a strong role in the study of the Higgs boson can address. These include, in addition to the scientific results, maintaining leading roles in international partnerships, nurturing and advancing world-leading capabilities and expert resources, and maintaining and attracting talent. The international effort would benefit from increased U.S. participation, and the U.S., in turn, would maintain stature through the partnership.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Rare Higgs Processes at CMS and Precision Timing Detector Studies for HL-LHC CMS Upgrade

This thesis describes the search for two rare Higgs processes. The first analysis describes the CMS Run 2 search for $H$ $\rightarrow$ $\mu$$\mu$ decays, with 137.3 fb$^{-1}$ of data at $\sqrt{s}$ = 13 TeV. The analysis targeted four different Higgs production modes: the gluon fusion (ggH), the vector boson fusion (VBF), the Higgs-strahlung process (VH), and the production in association with a pair of top quarks (ttH). Each category used a dedicated machine learning based classifier to separate the signal from the background processes. A combined fit from all these categories saw a slight excess in the data corresponding to 3.0 standard deviations at $M$$_{H}$ = 125.38 GeV, and gave the first evidence for the Higgs boson decay to second-generation fermions. The best-fit signal strength and the corresponding 68% CL interval was found to be +0.17?????? = 1.19 $_{-0.39}^{+0.41}$ (stat)$_{-0.16}^{+0.17}$(syst) at $M$$_{H}$ = 125.38 GeV. The second analysis describes the CMS Run 2 search for 𝐻𝐻 → 𝑏𝑏𝑏𝑏 with highly boosted Higgs bosons. This analysis used a dedicated jet identification algorithm based on graph neural networks (ParticleNet) to identify boosted H→ bb jets. This search targeted the gluon fusion and the vector boson fusion HH production modes, and put constraints on the allowed values of the various Higgs couplings as: 𝜅𝜆 ∈ [−9.9, 16.9] when 𝜅𝑉 = 1, 𝜅2𝑉 = 1; 𝜅𝑉 ∈ [−1.17, −0.79] ∪ [0.81, 1.18] when 𝜅𝜆 = 1, 𝜅2𝑉 = 1; 𝜅2𝑉 ∈ [0.62, 1.41] when 𝜅𝜆 = 1, 𝜅𝑉 = 1. A scenario with 𝜅2𝑉 = 0 was excluded with a significance of 6.3 standard deviations for the first time, when other H couplings are fixed to their SM values. The combined observed (expected) 95% upper limit on the HH production cross section was found to be 9.9 (5.1) × SM. Finally, this thesis also discusses the planned MIP Timing Detector (MTD) upgrade for CMS at the HL-LHC. The MTD will be a time-of-flight (TOF) detector, designed to provide a precision timing information for charged particles using SiPMs + LYSO scintillating crystals, with a time resolution of ∼30 ps. This thesis describes several R&D tests that have been performed for characterizing the sensor properties (time resolution, light yield, etc.) and optimizing the sensor design geometry. This thesis also contains a description of mock test setups for cooling the sensors, since it is known to be an effective way of mitigating the increased dark current rates in the sensors due to radiation damage.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Search for Low mass Higgs Portal Scalars at the MicroBooNE Detector in the NuMI Beam

The MicroBooNE experiment exploits Liquid Argon Time Projection Chamber (LArTPC) technology to detect neutrinos from two beams at Fermilab, Chicago: on-axis Booster Neutrino Beam (BNB) and the off-axis Neutrinos at the Main Injector (NuMI) beam. While the aim of the experiment is to study the low-energy excess of electron neutrino events observed by the MiniBooNE experiment, to search for eV-scale sterile neutrinos and to characterise neutrino interactions on argon, it could also be exploited to probe Beyond Standard Model (BSM) Physics. This thesis presents a BSM search for low-mass Higgs Portal Scalars at MicroBooNE in the NuMI beam using data collected during the Run 1 and Run 3 data-taking periods with a total exposure corresponding to $7.01 \times 10^{20}$ protons on target (POT). The Higgs Portal Model is an extension to the Standard Model in which a dark-sector scalar, $S$, mixes with the Higgs boson with mixing angle $\theta$ and acquires a coupling to the Standard Model fermions via the Higgs Yukawa coupling. We search for low-mass Higgs Portal scalars, in the mass range $100-200$ MeV, at MicroBooNE via the production channel $K \rightarrow \pi + S$, where scalars are produced from kaons decaying at rest in the NuMI target and beam dump, as well as kaons decaying in flight in the decay pipe of the NuMI beam. In the MicroBooNE detector, we search for the decay channel $S \rightarrow e^+e^-$, which is the only decay channel available to the scalars in the mass range of our search. The results are expressed as limits, at the 95\% confidence level, on the scalar-Higgs mixing angle $\theta$ for scalars in the mass range $100-200$ MeV.Date of Award1 Aug 2023Original languageEnglishAwarding InstitutionThe University of ManchesterSupervisorStefan Soldner-Rembold (Supervisor) & Justin Evans (Supervisor)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Understanding the High Energy Higgs Sector with the CMS Experiment and Artificial Intelligence

This dissertation describes efforts towards understanding the Higgs boson at the highest energies humanly accessible, using the CMS experiment at the Large Hadron Collider and advances in artificial intelligence (AI) and machine learning (ML). We present searches for resonant and nonresonant Higgs-boson (H) pair production in the all-hadronic two beauty-quark and two vector boson (V) final state, using a novel strategy to measure the quartic HHVV coupling and search for new Higgs-like bosons. By targeting highly Lorentz-boosted Higgs pairs, we probe effects of potential new physics in the high energy Higgs sector, which could hold answers to fundamental mysteries of nature such as baryon asymmetry. To enable these and future searches, we introduce as well significant developments in AI/ML, including in the identification of boosted H$\rightarrow$VV decays with deep transformer networks and advances in AI-accelerated fast simulations of the CMS detector. The latter notably includes the development of the first, highly performant generative models for point-cloud data in high energy physics, which have the potential to improve CMS' computational efficiency by up to three orders of magnitude. We also highlight novel solutions to the important and challenging problems of calibrating and validating these ML techniques. Finally, we present new approaches to search for new physics in a model-agnostic manner, using physics-informed ML methods equivariant to Lorentz transformations. The quartic HHVV coupling is observed (expected) to be constrained to $[-0.04, 2.05]$ ($[0.05, 1.98]$) at the 95% confidence level relative to the standard model prediction, representing the second-most sensitive measurement of this coupling by CMS to date. Exclusion limits on the production cross section of new heavy resonances decaying to two Higgs-like bosons are expected to be as low as 0.3 fb for high resonance masses.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Higgs boson physics and broken flavor symmetry – LHC phenomenology

The LHC implications are presented of a simplified model of broken flavor symmetry in which a new scalar (a flavon) emerges with mass in the TeV range. We summarize the influence of the model on Higgs boson physics, notably on the production cross section and decay branching fractions. Limits are obtained on the flavon φ from heavy Higgs boson searches at the LHC at 7 and 8 TeV. The branching fractions of the flavon are computed as a function of the flavon mass and the Higgs-flavon mixing angle. We explore possible discovery of the flavon at 14 TeV, particularly via the φ→Z 0 Z 0 decay channel in the 2ℓ2ℓ' final state, and through standard model Higgs boson pair production φ→hh in the $b\bar{b}$γγ final state. 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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

COSMOLOGICAL CONSTRAINTS ON THE HIGGS BOSON MASS

For a robust interpretation of upcoming observations from PLANCK and Large Hadron Collider experiments it is imperative to understand how the inflationary dynamics of a non-minimally coupled Higgs scalar field with gravity may affect the determination of the inflationary observables. We make a full proper analysis of the Wilkinson Microwave Anisotropy Probe, Type Ia supernova distance-redshift relation, and the baryon acoustic oscillations data sets in a context of the non-minimally coupled Higgs inflation field with gravity. For the central value of the top quark pole mass m{sub T} = 171.3 GeV, the fit of the inflation model with a non-minimally coupled Higgs scalar field leads to a Higgs boson mass in the range 143.7 GeV {<=} m{sub H} {<=} 167 GeV (95% CL). We show that the inflation driven by a non-minimally coupled scalar field to the Einstein gravity leads to significant constraints on the scalar spectral index n{sub S} and the tensor-to-scalar ratio R when compared with a tensor with similar constraints to form the standard inflation with a minimally coupled scalar field. We also show that an accurate reconstruction of the Higgs potential in terms of inflationary observables requires an improved accuracy of other parameters of the standard model of particle physics such as the top quark mass and the effective QCD coupling constant.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Late and early time phenomenology of Higgs-dependent cutoff

The analysis of theories with non-minimal coupling of Higgs field to gravity revealed that they enter into strong coupling regime above certain Higgs-dependent cutoff, which may be considerably below the Planck scale. Assuming that the effective theory, complementing the Standard Model or its minimal extension — the νMSM — contains a set of higher dimensional operators suppressed by the Higgs-dependent cutoff, we analyse the reheating of the Universe after the Higgs inflation. We show that extra terms do not spoil the Higgs inflation, but can lead to baryogenesis and to warm sterile neutrino dark matter production at the reheating stage of the Universe expansion. They can also result in neutrino mass generation and proton decay.

79 ASTRONOMY AND ASTROPHYSICS↗

Inflation from the Higgs field false vacuum with hybrid potential

We have recently suggested [1,2] that Inflation could have started in a local minimum of the Higgs potential at field values of about 10{sup 15}–10{sup 17} GeV, which exists for a narrow band of values of the top quark and Higgs masses and thus gives rise to a prediction on the Higgs mass to be in the range 123–129 GeV, together with a prediction on the the top mass and the cosmological tensor-to-scalar ratio r. Inflation can be achieved provided there is an additional degree of freedom which allows the transition to a radiation era. In [1] we had proposed such field to be a Brans-Dicke scalar. Here we present an alternative possibility with an additional subdominant scalar very weakly coupled to the Higgs, realizing an (inverted) hybrid Inflation scenario. Interestingly, we show that such model has an additional constraint m{sub H} < 125.3±3{sub th}, where 3{sub th} is the present theoretical uncertainty on the Standard Model RGEs. The tensor-to-scalar ratio has to be within the narrow range 10{sup −4}∼<r < 0.007, and values of the scalar spectral index compatible with the observed range can be obtained. Moreover, if we impose the model to have subplanckian field excursion, this selects a narrower range 10{sup −4}∼<r < 0.001 and an upper bound on the Higgs mass of about m{sub H} < 124±3{sub th}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Curvaton decay by resonant production of the Standard Model higgs

We investigate in detail a model where the curvaton is coupled to the Standard Model higgs. Parametric resonance might be expected to cause a fast decay of the curvaton, so that it would not have time to build up the curvature perturbation. However, we show that this is not the case, and that the resonant decay of the curvaton may be delayed even down to electroweak symmetry breaking. This delay is due to the coupling of the higgs to the thermal background, which is formed by the Standard Model degrees of freedom created from the inflaton decay. We establish the occurrence of the delay by considering the curvaton evolution and the structure of the higgs resonances. We then provide analytical expressions for the delay time, and for the subsequent resonant production of the higgs, which ultimately leads to the curvaton effective decay width. Contrary to expectations, it is possible to obtain the observed curvature perturbation for values of the curvaton-higgs coupling as large as 10{sup −1}. Our calculations also apply in the general case of curvaton decay into any non Standard Model species coupled to the thermal background.

79 ASTRONOMY AND ASTROPHYSICS↗

Dark Higgs channel for Fermi GeV γ-ray excess

Dark Higgs is very generic in dark matter models where DM is stabilized by some spontaneously broken dark gauge symmetries. Motivated by tentative GeV scale γ-ray excess from the galactic center (GC), we investigate a scenario where a pair of dark matter X annihilates into a pair of dark Higgs H{sub 2}, which subsequently decays into standard model particles through its mixing with SM Higgs boson. Besides the two-body decay of H{sub 2}, we also include multibody decay channels of the dark Higgs. We find that the best-fit point is around M{sub X} ≅ 95.0 GeV, M{sub H{sub 2}} ≅ 86.7 GeV, (σ v) ≅ 4.0 × 10{sup −26}cm{sup 3}/s and gives a p-value ≅ 0.40. Implication of this result is described in the context of dark matter models with dark gauge symmetries. Since such a dark Higgs boson is very difficult to produce at colliders, indirect DM detections of cosmic γ-rays could be an important probe of dark sectors, complementary to collider searches.

79 ASTRONOMY AND ASTROPHYSICS↗

Leptogenesis, radiative neutrino masses and inert Higgs triplet dark matter

We extend the standard model by three types of inert fields including Majorana fermion singlets/triplets, real Higgs singlets/triplets and leptonic Higgs doublets. In the presence of a softly broken lepton number and an exactly conserved Z{sub 2} discrete symmetry, these inert fields together can mediate a one-loop diagram for a Majorana neutrino mass generation. The heavier inert fields can decay to realize a successful leptogenesis while the lightest inert field can provide a stable dark matter candidate. As an example, we demonstrate the leptogenesis by the inert Higgs doublet decays. We also perform a systematic study on the inert Higgs triplet dark matter scenario where the interference between the gauge and Higgs portal interactions can significantly affect the dark matter properties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

A global fit of the γ-ray galactic center excess within the scalar singlet Higgs portal model

We analyse the excess in the γ-ray emission from the center of our galaxy observed by Fermi-LAT in terms of dark matter annihilation within the scalar Higgs portal model. In particular, we include the astrophysical uncertainties from the dark matter distribution and allow for unspecified additional dark matter components. We demonstrate through a detailed numerical fit that the strength and shape of the γ-ray spectrum can indeed be described by the model in various regions of dark matter masses and couplings. Constraints from invisible Higgs decays, direct dark matter searches, indirect searches in dwarf galaxies and for γ-ray lines, and constraints from the dark matter relic density reduce the parameter space to dark matter masses near the Higgs resonance. We find two viable regions: one where the Higgs-dark matter coupling is of O(10{sup −2}), and an additional dark matter component beyond the scalar WIMP of our model is preferred, and one region where the Higgs-dark matter coupling may be significantly smaller, but where the scalar WIMP constitutes a significant fraction or even all of dark matter. Both viable regions are hard to probe in future direct detection and collider experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗