Substructuring Technique Research Articles

Uncovering light scalars with exotic Higgs decays to b b ¯ μ + μ − $$ b\overline{b}{\mu}^{+}{\mu}^{-} $$

The search for exotic Higgs decays are an essential probe of new physics. In particular, the small width of the Higgs boson makes its decay uniquely sensitive to the existence of light hidden sectors. Here we assess the potential of an exotic Higgs decay search for h -> 2X -> bbmumu to constrain theories with light CP-even (X = s) and CP-odd (X = a) singlet scalars in the mass range of 15 to 60 GeV. This decay channel arises naturally in many scenarios, such as the Standard Model augmented with a singlet, the two-Higgs-doublet model with a singlet (2HDM+S) -- which includes the Next-to-Minimal Supersymmetric Standard Model (NMSSM) -- and in hidden valley models. The 2b2mu channel may represent the best discovery avenue for many models. It has competitive reach, and is less reliant on low-pT b- and tau-reconstruction compared to other channels like 4b, 4tau, and 2tau2mu. We analyze the sensitivity of a 2b2mu search for the 8 and 14 TeV LHC, including the HL-LHC. We consider three types of analyses, employing conventional resolved b-jets with a clustering radius of R ~ 0.4, thin b-jets with R=0.2, and jet substructure techniques, respectively. The latter two analyses improve the reach for m_X ~ 15 GeV, for which the two b-jets are boosted and often merged. We find that Br(h -> 2X -> 2b2mu) can be constrained at the few x 10^-5 level across the entire considered mass range of X at the HL-LHC. This corresponds to a 1 - 10% reach in Br(h->2X) in 2HDM+S models, including the NMSSM, depending on the type of Higgs Yukawa couplings.

Search for [Formula: see text] decays in [Formula: see text] collisions at [Formula: see text]=8TeV with the ATLAS detector.

A search for a massive W' gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in pp collisions at the LHC. The dataset was taken at a centre-of-mass energy of sqrt{s} = 8{mathrm { TeV}} and corresponds to 20.3,text{ fb }^{-1} of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass W' bosons in the range 1.5–3.0 {mathrm { TeV}}. b-tagging is used to identify jets originating from b-quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the W'rightarrow tb cross section times branching ratio ranging from 0.16,mathrm {pb} to 0.33,mathrm {pb} for left-handed W' bosons, and ranging from 0.10,mathrm {pb} to 0.21,mathrm {pb} for W' bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the W'-boson coupling to tb as a function of the W' mass using an effective field theory approach, which is independent of details of particular models predicting a W' boson.

Identifying boosted new physics with non-isolated leptons

We demonstrate the utility of leptons which fail standard isolation criteria in searches for new physics at the LHC. Such leptons can arise in any event containing a highly boosted particle which decays to both leptons and quarks. We begin by considering multiple extensions to the Standard Model which primarily lead to events with non-isolated leptons and are therefore missed by current search strategies. We emphasize the failure of standard isolation variables to adequately discriminate between signal and SM background for any value of the isolation cuts. We then introduce a new approach which makes use of jet substructure techniques to distinguish a broad range of signals from QCD events. We proceed with a simulated, proof-of-principle search for R-parity violating supersymmetry to demonstrate both the experimental reach possible with the use of non-isolated leptons and the utility of new substructure variables over existing techniques

Band structure and transmission characteristics of complex phononic crystals by multi-level substructure scheme

A fast scheme based on the multi-level substructure technique is proposed for the band structure and transmission characteristics calculation of phononic crystals uniformly. The main idea is that finite element models of phononic crystals are divided into several domains by a special multi-level decomposition. For the band structure calculation, the upscaling calculation is employed to condense the internal stiffness matrix of the unit cell into the Bloch boundary. Due to the internal stiffness matrix does not change along with reduced wave vectors in an iteration process, the scheme can reduce the computational scale and improve the efficiency greatly, meanwhile it does not introduce approximation into the traditional finite element model. For the transmission characteristics calculation, the unit cell of the phononic crystal is periodic which is taken as a substructure with the same coefficient matrix. Moreover, the downscaling calculation of internal displacements can be selected flexibly. Some closely watched examples of the three-dimensional locally resonant, defect state of Lamb wave and Bragg waveguide are analyzed. Numerical results indicate that the proposed scheme is efficient and accurate, which may widely be applicable and suitable for complex phononic crystal problems, and provides a reliable numerical tool to optimize and design crystal devices.

Reduction in the moan noise by frequency-response-function-based substructuring and optimization techniques

‘Moan’ noise in a vehicle causes discomfort and anxiety to passengers. In the previous study, the causes of moan noise were identified, and a coherence analysis of the components was conducted. It was found that moan noise was generated by the attribution of resonance when the exciting force produced by the stick–slip motion in a brake system was transmitted to a coupled torsional beam axle module. The analysis involved calculation of the response of the coupled torsional beam axle module on a full suspension brake system reconstructed by consideration of the transfer functions and the joint conditions of the coupled torsional beam axle module and the brake system. Each transfer function is decomposed by a frequency-response-function-based substructuring technique. In this study, when using the sensitivity analysis and optimization techniques for moan-noise reduction, the frequency-response-function-based substructuring technique was performed to calculate the response of the modified coupled torsional beam axle module by considering the joint conditions and the transfer functions of the brake system. Highly sensitive design parameters regarding the response of the coupled torsional beam axle module were identified after the sensitivity analysis. The most sensitive design parameters were selected to enhance the efficiency and the robustness of optimization. The optimal values for the design variables were obtained by applying a progressive quadratic response surface method as a optimization algorithm. The application of an optimization technique was possible using the finite element model and the results of the finite element analysis from the previous study. After optimization, a prototype was re-designed, manufactured and tested. Finally, it was verified that the moan noise was reduced, as the natural frequency of 387 Hz for the coupled torsional beam axle module was moved to a higher frequency.

Numerical Solution of Two Phase Solidification Problem Using Dynamic Substructuring Based on Adaptive Error Estimation

Numerical solution of solidification of metals with a sharp front, in particular solidification of lead, is investigated. Considering the fact that the associated CPU time and memory requirement may be costly for large domains, alternatives are searched. It is observed that using a substructuring technique with a local mesh refinement is promising. Following, by the use of an adaptive error estimation algorithm to find the location of solidification front and mushy zone, dynamic substructuring technique is developed to decrease the computational cost and to increase the accuracy of results. Superconvergent patch recovery technique is used to obtain the heat fluxes to evaluate the error energy norm of elements at each analysis step. Solidification front, mushy zone and elements having errors above a threshold value are captured with the error estimator. Then, elements having errors above the threshold value are refined by creating a substructure which is independent from the original global mesh. Equations of the global coarse mesh are augmented with the equations of the substructure. Employing the equations of the original coarse mesh help reduce the computational cost. Numerical solutions are presented and it is shown that the proposed approach has advantages over the alternative methods and, by the virtue of the adaptive error estimation algorithm, significantly decreases the CPU time of numerical solutions while it increases the accuracy of solutions and locates precisely the solidification front and mushy zone. Keywords: Solidification; Finite Element Methods; Substructuring; Stefan Problem; Error Estimation DOI: 10.17350/HJSE19030000017 Full Text:

Numerical modeling and active noise control of impact road noise inside a vehicle compartment

Even though active noise control (ANC) technique has been widely investigated and proven its efficiency for low-frequency vehicle interior noise control, current applications are mainly for the steady noise process such as powertrain noise and uniform road noise. When impulsive road disturbances due to road bumps or potholes are present, they may hinder the performance of the ANC system. One of the reasons is that the prevalent ANC algorithm, namely the filtered- x least mean square (FxLMS) algorithm, has been developed assuming that the signals follow the normal distribution. The impact road noise due to a sudden impact may exhibit a non-Gaussian characteristic. Hence, the FxLMS algorithm may not be appropriate for controlling this type of impulsive noise. In this study, a robust ANC system configured with a modified FxLMS (MFxLMS) algorithm by incorporating thresholds on reference and error signal paths is proposed for impact road noise control. To aid in the control system design, the spectral-based substructuring technique is implemented to develop a coupled vehicle system model to simulate the impulsive interior acoustic response due to road unevenness. The vehicle passenger compartment is simplified as a 3-dimensional flexible-panel backed cavity model, which is coupled with the tire-wheel system modeled as a flexible ring element and rigid wheel through the suspension system represented by a spring-damper model. The tire-road interaction is modeled as a set of flexible elements with certain stiffness over a half-cosine wave road bump. Numerical simulation results show that the proposed ANC system can effectively deal with the interior impact road noise without instability issue that may occur in the existing FxLMS algorithm. In fact, results show that approximately 8 dB reductions are achieved at the driver's ear position.

Top Partner Discovery in the T → tZ channel at the LHC

In this paper we study the discovery potential of the LHC run II for heavy vector-like top quarks in the decay channel to a top and a $Z$ boson. Despite the usually smaller branching ratio compared to charged-current decays, this channel is rather clean and allows for a complete mass reconstruction of the heavy top. The latter is achieved in the leptonic decay channel of the $Z$ boson and in the fully hadronic top channel using boosted jet and jet substructure techniques. To be as model-independent as possible, a simplified model approach with only two free parameters has been applied. The results are presented in terms of parameter space regions for $3\sigma$ evidence or $5\sigma$ discovery for such new states in that channel.

Review of physics results using jet substructure techniques in LHC Run1

The possible existence of phenomena beyond the standard model of particle physics at the TeV scale implies the production of highly boosted heavy objects, whose decay products tend to be collimated and can be reconstructed as jets with large radius parameter. Jet substructure analysis techniques have been developed and successfully applied to LHC Run1 data to perform cross section measurements in the high transverse momentum regime and searches for new physics phenomena. An overview of selected physics results obtained by ATLAS and CMS using jet substructure techniques is presented.

Online hybrid test using a finite element program and an explicit integration scheme

A new online hybrid test system combined with substructuring techniques and incorporating finite element methods is developed. In the proposed system, numerical substructure analysis is conducted by ABAQUS/Explicit. An ABAQUS user subroutine is used as the interface between the main control program and ABAQUS to impose the target displacements and determine the reaction forces. No iteration is needed in this system, making it suitable for physical testing. As the approach also avoids the need to modify source code, it will be appealing to a number of real engineering applications. The proposed system adopts a separated-model framework, operator-splitting integration scheme, and data exchange through a socket mechanism. The earthquake responses of a simple steel moment-resisting frame are simulated, and the results obtained from the new system are compared to those obtained from the conventional analysis. It is found that the results obtained from the new system are accurate, demonstrating the applicability and efficiency of the proposed approach. The optimal test parameters are also studied to gain the most accurate results in the minimum time.

Numerical Simulation of Seepage Control Effects at a Gravity Dam Site

Located at a narrow and deeply-cut valley in the middle reach of Yalong River in Southwestern China, the Kala Hydropower Station is subjected to serious seepage and leakage problems due to complex geological conditions at the dam site. A numerical method combining a substructure technique, a variational inequality formulation of Signorini’s type and an adaptive penalized Heaviside function (short for SVA method) was adopted for the simulation and assessment of seepage control effects at the dam site in Kala Hydropower Project. Numerical modeling of a typical overflow dam section and the whole dam site demonstrated that the primary design was a proper scheme for seepage control, and furthermore, optimization of the seepage control system can be performed in designing the layout.

AN EXTENDED SUBSTRUCTURING TECHNIQUE FOR EFFICIENT EVALUATION OF NONLINEAR LOAD-BEARING STRUCTURES IN THE CONCEPTUAL DESIGN STAGE

The research presented in this paper has extended the substructuring technique into the nonlinear domain in order to apply the finite element analysis (FEA) method to complex nonlinear structural design problems in the conceptual design stage. As conventional FE models based on substructures allow only linear analysis, it was necessary in this research to introduce a new algorithm capable of linearizing nonlinear structural problems with sufficient accuracy in order to enable evaluation of engineering design concepts in a more objective and rigorous manner in the early stages of design. The developed method was implemented within a commercial FE solver, and validated using a select number of case studies. The results obtained for the two sample solutions indicate that the new method has achieved an improvement in accuracy of 90% and 98% respectively compared to the conventional FE-based approach applied to the same class of design problems.

Better hadronic top quark polarimetry

Observables sensitive to top quark polarization are important for characterizing or even discovering new physics. The most powerful spin analyzer in top decay is the down-type fermion from the W, which in the case of leptonic decay allows for very clean measurements. However, in many applications it is useful to measure the polarization of hadronically decaying top quarks. Usually it is assumed that at most 50% of the spin analyzing power can be recovered in this case. This paper introduces a simple and truly optimal hadronic spin analyzer, with a power of 64% at leading-order. The improvement is demonstrated to be robust at next-to-leading order, and in a handful of simulated measurements including the spins and spin correlations of boosted top quarks from multi-TeV top-antitop resonances, the spins of semi-boosted tops from chiral stop decays, and the potentially CP-violating spin correlations induced in continuum top pairs by color dipole operators. For the boosted studies, we explore jet substructure techniques that exhibit improved mapping between subjets and quarks.

Sequential analysis coupled with optimized substructure technique modeled on 3D-frame construction process

This paper deals with sequential analysis coupled with an optimized substructure technique modeled on 3D-frame construction process. This model handles the hypothesis that any subpart of the entire structure can be constructed at a time. On a realistic 3D-frame building, permanent gravity load (dead load), variable gravity loads (construction load, live load) and non-gravity loads or effects (time dependence, temperature, and earthquake) are either applied sequentially or following the conventional method. Their individual contributions on bending moments, key of design, are investigated. To implement this analysis, some additional computational efforts can be justified. However, an optimized procedure using substructure technique is proposed, based on a smart but simple choice of the substructure size. The proposed procedure tends to minimize the required memory used while reducing the required time as well. The sequential analysis as presented herewith reveals many salient features and more accurate results that should be employed in analyzing buildings, more so tall ones.

BAND STRUCTURE AND TRANSMISSION CHARACTERISTICS CALCULATION OF PHONONIC CRYSTALS BASED ON MULTI-LEVEL SUBSTRUCTURE TECHNIQUE

A fast scheme based on multi-level substructure technique is proposed to analyze band structure and transmission characteristics of phononic crystals. The main idea is that the finite element model of phononic crystal is divided into several substructures by a special multi-level decomposition. For the calculation of band structure, tree travelling technique and static condensation method are used to convert the internal stiffness matrix into the Bloch boundary of unit cell. Because the internal stiffness matrix does not change along with reduced wave vector, the scheme can reduce computation budget and improve efficiency greatly, while it does not introduce approximation into traditional finite element model. For the calculation of transmission characteristics, the proposed scheme can be also used to reduce computation, because unit cell of phononic crystal is periodic which has the same coefficient matrix. Moreover, the back substitution of internal displacements of unit cell can be selected flexibly. Some examples of three-dimensional locally resonant system and two-dimensional Bragg scattering phononic crystal are analyzed. Numerical results indicate that the proposed scheme is efficient and accurate, and suitable for complex phononic crystal problems.

Partitioned fluid-structure methods applied to the solution of elastohydrodynamic conformal contacts

The functional characteristics of statically-loaded journal bearings operating in the elastohydrodynamic lubrication (EHL) regime are evaluated by means of three partitioned fluid-structure coupling methods. Widely used in other areas but yet unexplored in the context of EHL problems related to journal bearings, these methods permit the use of optimized codes to solve the hydrodynamic and structural equations separately employing different techniques specialized in each type of equation. In this study, lubricant pressures are calculated using the isothermal Reynolds equation and the p−θ mass-conserving formulation is adopted for the computation of cavitation effects. An appropriate substructuring technique is applied in order to reduce the order of the bearing 3D linear-elastic finite element model. The efficiency and robustness of the partitioned fluid-structure coupling methods presented are assessed for two extreme situations of high deformation and high load conditions of a typical internal combustion engine connecting-rod big-end bearing. Numerical results evidence that partitioned fluid-structure coupling methods consist in a very efficient simulation tool for EHL journal bearing analyses.

Standard model Higgs boson pair production in the ( b b ¯ $$ b\overline{b} $$ )( b b ¯ $$ b\overline{b} $$ ) final state

Measuring the Higgs boson couplings as precisely as possible is one of the major goals of the High Luminosity LHC. We show that the $(b\bar{b})(b\bar{b})$ final state in Higgs boson pair production can be exploited in the boosted regime to give constraints on the trilinear Higgs boson self-coupling. In these exclusive phase space regions, novel jet substructure techniques can be used to separate the signal from the large QCD and electroweak backgrounds. New developments on trigger and b-tagging strategies for the upcoming LHC runs are necessary in order to reconstruct the Higgs bosons in boosted final states, where the trilinear self-coupling sensitivity is reduced. We find that using our approach one can set a limit for $\lambda \leq 1.2$ at $95 \%$ CL after $3000~\mathrm{fb}^{-1}$. As the signal-to-background ratio is small we propose a data-driven side-band analysis to improve on the coupling measurement.

Comparisons of Elasto-Fiber and Fiber & Bernoulli-Euler reinforced concrete beam-column elements

In this study, two beam-column elements based on the Elasto-Fiber element theory for reinforced concrete (RC) element have been developed and compared with each other. The first element is based on Elasto Fiber Approach (EFA) was initially developed for steel structures and this theory was applied for RC element in there and the second element is called as Fiber & Bernoulli-Euler element approach (FBEA). In this element, Cubic Hermitian polynomials are used for obtaining stiffness matrix. The beams or columns element in both approaches are divided into a sub-element called the segment for obtaining element stiffness matrix. The internal freedoms of this segment are dynamically condensed to the external freedoms at the ends of the element by using a dynamic substructure technique. Thus, nonlinear dynamic analysis of high RC building can be obtained within short times. In addition to, external loads of the segment are assumed to be distributed along to element. Therefore, damages can be taken account of along to element and redistributions of the loading for solutions. Bossak-a integration with predicted-corrected method is used for the nonlinear seismic analysis of RC frames. For numerical application, seismic damage analyses for a 4-story frame and an 8-story RC frame with soft-story are obtained to comparisons of RC element according to both approaches. Damages evaluation and propagation in the frame elements are studied and response quantities from obtained both approaches are investigated in the detail.

Disentangling flavor violation in the top-Higgs sector at the LHC

We study the LHC phenomenology of flavor changing Yukawa couplings between top quark, Higgs boson, and either an up or charm quark. Such $tuh$ or $tch$ couplings arise for instance in models in which Higgs sector is extended by the existence of additional Higgs bosons or by higher dimensional operators. We emphasize the importance of anomalous single top plus Higgs production in these scenarios, in addition to the more widely studied $t \to h j$ decays. By recasting existing CMS searches in multilepton and diphoton plus lepton final states, we show that bounds on $tuh$ couplings are improved by a factor of 1.5 when single top plus Higgs production is accounted for. We also recast the CMS search for vector boson plus Higgs production into new, competitive constraints on $tuh$ and $tch$ couplings, setting the limits of $BR(t\to hu) < 0.7%$ and $BR(t\to hc) <1.2%$. We then investigate the sensitivity of future searches in multilepton channel and in fully hadronic channel. In multilepton searches, studying the lepton rapidity distributions and charge assignments can be used to discriminate between $tuh$ couplings, for which anomalous single top production is relevant, and $tch$ couplings, for which it is suppressed by the parton distribution function of the charm quark. An analysis of fully hadronic $t+h$ production and $t\to h j$ decay can be competitive with the multilepton search at 100 fb$^{-1}$ of 13 TeV data if jet substructure techniques are employed to reconstruct boosted top quarks and Higgs bosons. To show this we develop a modified version of the HEPTopTagger algorithm, optimized for tagging $t \to h j$ decays. Our sensitivity estimates on $BR(t\to hu)$ ($BR(t\to hc)$) at 100 fb$^{-1}$ of 13 TeV data for multilepton searches, vector boson plus Higgs search and fully hadronic search are $0.22%$ ($0.33%$), $0.15%$ ($0.19%$) and $0.36%$ ($0.48%$), respectively.

Study of the baryonicR-parity violating MSSM using the jet substructure technique at the 14 TeV LHC

We study the discovery reach of the gluino ($\widetilde{g}$) and the lightest stop squark ($\widetilde{t}_1$) with baryonic R-parity violation (UDD type) in the context of Minimal Supersymmetric Standard Model (MSSM) at the 14 TeV run of the LHC. We consider the gluino pair production process followed by its decay to a top quark and a real or virtual stop squark. The top quark produced from the decay of the gluino can have sufficient transverse momentum to appear as a single fat jet. We apply the jet substructure technique to tag such a hadronically decaying boosted top quark and find that gluino mass up to 1.65 TeV can be discovered whereas exclusion limit extends up to 1.9 TeV at the 14 TeV LHC with 300 $\rm fb^{-1}$ luminosity. We also briefly discuss the discovery prospect of the boosted stop squark which may be identified as a narrow resonance in the jet mass distribution.