Matrix Element Method Research Articles

Bounding the Higgs width at the LHC using full analytic results for gg → e − e + μ − μ +

We revisit the hadronic production of the four-lepton final state, e^- e^+ \mu^- \mu^+, through the fusion of initial state gluons. This process is mediated by loops of quarks and we provide first full analytic results for helicity amplitudes that account for both the effects of the quark mass in the loop and off-shell vector bosons. The analytic results have been implemented in the Monte Carlo program MCFM and are both fast, and numerically stable in the region of low Z transverse momentum. We use our results to study the interference between Higgs-mediated and continuum production of four-lepton final states, which is necessary in order to obtain accurate theoretical predictions outside the Higgs resonance region. We have confirmed and extended a recent analysis of Caola and Melnikov that proposes to use a measurement of the off-shell region to constrain the total width of the Higgs boson. Using a simple cut-and-count method, existing LHC data should bound the width at the level of 25-45 times the Standard Model expectation. We investigate the power of using a matrix element method to construct a kinematic discriminant to sharpen the constraint. In our analysis the bound on the Higgs width is improved by a factor of about 1.6 using a simple cut on the MEM discriminant, compared to an invariant mass cut m_{4l} > 300 GeV.

Study on the simplified numerical spot welding simulation by using the flexibility influence coefficient method

In this study, the spot welding procedures were simulated in detail using the finite element method (FEM). The stiffness matrix of any element that may reflect residual stress and residual displacement was obtained from the simulation based on calculations with the flexibility influence coefficient method. The results of static analysis on existing models and modal analysis were also compared using the spot welding elements proposed in this paper. The purpose of this study is to improve the reliability of the analysis by reflecting the residual stress of the spot welds and to design a simplified spot weld model to allow faster and more accurate analysis of structures with multiple spot welds. In analysis of structures with multiple weld points and the equivalent stiffness matrix element method for spot welds presented in this paper is expected to reduce the analysis time and produce more accurate results compared to existing analysis methods.

Unravellingtt¯hvia the Matrix Element Method

Associated production of the Higgs boson with a top-antitop pair is a key channel to gather further information on the nature of the newly discovered boson at the LHC. Experimentally, however, its observation is very challenging due to the combination of small rates, difficult multi-jet final states and overwhelming backgrounds. In the Standard Model the largest number of events is expected when h->bb, giving rise to a WWbbbb signature, deluged in tt+jets. A promising strategy to improve the sensitivity is to maximally exploit the theoretical information on the signal and background processes by means of the matrix element method. We show how, despite the complexity of the final state, the method can be efficiently applied to discriminate the signal against combinatorial and tt+jets backgrounds. Remarkably, we find that a moderate integrated luminosity in the next LHC run will be enough to make the signature involving both W's decaying leptonically as sensitive as the single-lepton one.

High energyWWscattering at the LHC with the matrix element method

Perhaps the most important question in particle physics today is whether the boson with mass near 125 GeV discovered at the Large Hadron Collider (LHC) is the Higgs Boson of the Standard Model. Since a particularly important property of the Standard Model Higgs is its role in unitarizing longitudinal WW scattering, we study the ability of the LHC to probe this process in the case of same-sign W pair production. We find that the use of the Matrix Element Method increases the significance with which the Higgs sector can be probed in this channel. In particular, it allows one to distinguish between a light and heavy SM Higgs in this channel alone with a high degree of significance, as well as to set important limits in the parameter space of the Two Higgs Doublet Model and the Strongly-Interacting Light Higgs Model with less than 200/fb at the 14-TeV LHC, thus providing crucial information about the putative Higgs boson's role in electroweak symmetry breaking.

Finding the Higgs boson in decays toZγusing the matrix element method at next-to-leading order

We illustrate how the matrix element method at next-to-leading order can be used to discriminate between events arising from the production of a Higgs boson, which subsequently decays to a final state consisting of ${\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}\ensuremath{\gamma}$, and the background production of the same final state. We illustrate how the method could be used in an experimental analysis by devising cuts on the signal (${P}_{S}$) and background (${P}_{B}$) weights that are computed event by event in this approach. We find that we can increase the $S/\sqrt{B}$ ratio by around 50% compared to an invariant mass fit on its own. Considering only statistical uncertainty, this is equivalent to recording a factor of around two times more integrated luminosity.

Study of irregular behavior of shear waves in layered soil using matrix and finite element methods

This study uses both the theoretical matrix and finite element methods to simulate the three-dimensional (3D) wave propagation in elastic layered soils with a harmonic point load acting on the surface. Choosing different multi-layer cases (two, four and eight layers) where the point load is in horizontal or vertical direction, we first investigated the accuracy of the two methods, and the comparisons indicate that the results from both are in good agreement. Few authors have investigated the irregular wave amplitude of the Love wave induced in layered soils. This study indicates that the Love wave, unlike the Rayleigh wave, might generate larger ground vibrations for a wave located far away from the source, which is called wave hump in this paper. A ratio of the Young’s modulus between the top and bottom soil layers larger than three may cause obvious this condition. Moreover, a layer thickness between 0.5 and 1.5times the wave length in the first soil layer can significantly change the magnitude of the wave hump.

Precision studies of the Higgs boson decay channelH→ZZ→4ℓwith MEKD

The importance of the H -> ZZ -> 4l "golden" channel was shown by its major role in the discovery, by the ATLAS and CMS collaborations, of a Higgs-like boson with mass near 125 GeV. We analyze the discrimination power of the matrix element method both for separating the signal from the irreducible ZZ background and for distinguishing various spin and parity hypotheses describing a signal in this channel. We show that the proper treatment of interference effects associated with permutations of identical leptons in the four electron and four muon final states plays an important role in achieving the best sensitivity in measuring the properties of the newly discovered boson. We provide a code, MEKD, that calculates kinematic discriminants based on the full leading order matrix elements and which will aid experimentalists and phenomenologists in their continuing studies of the H -> ZZ -> 4l channel.

Extracting precise Higgs couplings by using the matrix element method

After the recent discovery of a Standard Model Higgs boson-like particle at the LHC, the question of its couplings to known and unknown matter is eminent. In this letter, we present a method that allows for an enhancement in S/B(irreducible) of the order of 100% in $pp\to (h\to \gamma\gamma) jj$ for a center of mass energy of 8 and 14 TeV. This is achieved by applying the matrix element method. We discuss the implications of detector resolution effects and various approximations of the involved event simulation and reconstruction. The matrix element method provides a reliable, stable, and efficient handle to separate signal from background, and the gluon and weak boson fusion components involved in this process. Employing this method, a more precise Higgs boson coupling extraction can be obtained, and our results are of immediate relevance for current searches.

Comparison of Cut-based and Matrix Element Method Results for Beyond Standard Model Quarks

In this work, two different methods for extracting the mass of a new quark from the (pseudo) data are compared: the classical cut-based method and the matrix element method. As a concrete example a fourth family up type quark is searched in p-p collisions of 7 TeV center of mass energy. We have shown that even with very small number of events, Matrix Element Method gives better estimations for the mass value and its error, especially for event samples in which Signal to Background ratio is greater than 0.2.

The matrix element method at next-to-leading order

AbstractThis paper presents an extension of the matrix element method to next-to-leading order in perturbation theory, for electro-weak final states. To accomplish this we have developed a method to calculate next-to-leading order weights on an event-by-event basis. This allows for the definition of next-to-leading order likelihoods in exactly the same fashion as at leading order, thus extending the matrix element method to next-to-leading order. A welcome by-product of the method is the straightforward and efficient generation of unweighted next-to-leading order events. As examples of the application of our next-to-leading order matrix element method we consider the measurement of the mass of theZboson and also the search for the Higgs boson in the four lepton channel.

Improving the sensitivity of Higgs boson searches in the golden channel

Leptonic decays of the Higgs boson in the ZZ* channel yield what is known as the golden channel due to its clean signature and good total invariant mass resolution. In addition, the full kinematic distribution of the decay products can be reconstructed, which, nonetheless, is not taken into account in traditional search strategy relying only on measurements of the total invariant mass. In this work we implement a type of multivariate analysis known as the matrix element method, which exploits differences in the full production and decay matrix elements between the Higgs boson and the dominant irreducible background from q bar{q} -> ZZ*. Analytic expressions of the differential distributions for both the signal and the background are also presented. We perform a study for the Large Hadron Collider at sqrt{s}=7 TeV for Higgs masses between 175 and 350 GeV. We find that, with an integrated luminosity of 2.5 fb^-1 or higher, improvements in the order of 10 - 20 % could be obtained for both discovery significance and exclusion limits in the high mass region, where the differences in the angular correlations between signal and background are most pronounced.

Precise measurement of the top-quark mass fromlepton+jetsevents at D0

We report a measurement of the mass of the top quark in lepton+jets final states of pp¯→tt¯ data corresponding to 2.6 fb−1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. A matrix-element method is developed that combines an in situ jet energy calibration with our standard jet energy scale derived from studies of γ+jet and dijet events. We then implement a flavor-dependent jet-response correction through a novel approach. This method is used to measure a top-quark mass of mt=176.01±1.64 GeV. Combining this result with our previous result obtained on an independent data set, we measure a top-quark mass of mt=174.94±1.49 GeV for a total integrated luminosity of 3.6 fb−1.3 MoreReceived 31 May 2011DOI:https://doi.org/10.1103/PhysRevD.84.032004© 2011 American Physical Society

Matrix element method and QCD radiation

The matrix element method has been extensively used for the analysis of top-quark and $W$-boson physics at the Tevatron but in general without dedicated treatment of initial-state QCD radiation. At the LHC, the increased center-of-mass energy leads to a significant increase in the amount of QCD radiation, which makes it mandatory to carefully account for its effects. We here present several methods for inclusion of QCD radiation effects in the matrix element method and apply them to mass determination in the presence of multiple invisible particles in the final state. We demonstrate significantly improved results compared to the standard treatment.

Top Quark Mass Measurement in thelepton+jetsChannel Using a Matrix Element Method andin situJet Energy Calibration

A precision measurement of the top quark mass m_t is obtained using a sample of ttbar events from ppbar collisions at the Fermilab Tevatron with the CDF II detector. Selected events require an electron or muon, large missing transverse energy, and exactly four high-energy jets, at least one of which is tagged as coming from a b quark. A likelihood is calculated using a matrix element method with quasi-Monte Carlo integration taking into account finite detector resolution and jet mass effects. The event likelihood is a function of m_t and a parameter DJES to calibrate the jet energy scale /in situ/. Using a total of 1087 events, a value of m_t = 173.0 +/- 1.2 GeV/c^2 is measured.

Three-Dimensional Heat Transfer Analysis of Pin-Bushing System With Oscillatory Motion: Theory and Experiment

A three-dimensional computational thermal contact model is developed. The approach utilizes a combination of the transfer matrix and finite element methods. The frictional heat generated at the contact interface is instantaneously partitioned between the bushing and the shaft. Two methods to couple the heat and temperature at the contact interface are presented. One method automatically accounts for the heat division between contacting bodies by satisfying the heat equilibrium and temperature continuity at interactive surfaces. The other method introduces a fictitious layer between contacting bodies with a specified gap conductance to partition the frictional heat. Application of the model to the heat transfer analysis of journal bearing systems experiencing oscillatory motion is presented. Nonuniformly distributed frictional heat along the axial direction is considered. The model is capable of predicting the transient temperature field for journal bearings. It can also be used to determine the maximum contact temperature, which is difficult to be measured experimentally. Comparison of the simulated resulted along with experimental tests conducted in a laboratory is presented.

The matrix element method and its application to measurements of the top quark mass

The most precise measurements of the top quark mass are based on the matrix element method. We present a detailed description of this analysis method, taking the measurements of the top quark mass in final states with one and two charged leptons as concrete examples. In addition, we show how the matrix element method is suitable to reduce the dominant systematic uncertainties related to detector effects, by treating the absolute energy scales for b-quark and light-quark jets independently as free parameters in a simultaneous fit together with the top quark mass. While the determination of the light-quark jet energy scale has already been applied in several recent measurements, the separate determination of the absolute b-quark jet energy scale is a novel technique with the prospect of reducing the overall uncertainty on the top quark mass in the final measurements at the Tevatron and in analyses at the LHC experiments. The procedure is tested on Monte Carlo generated events with a realistic detector resolution.

The top quark, others new phenomena observed at the CDF in {ie359-1} collisions at √s = 1.96 TeV (Review)

Upgraded Tevatron luminosity in Run-II (started 2001) has opened a new level of modern heavy-quark studies compared to that one of Run-I. Now top event samples contain hundreds of event statistics for investigation. This review mainly covers the mass measurements of the top quark produced at √s = 1.96 TeV in {ie359-2} collisions at the Collider Detector of Fermilab with the integrated luminosity samples up to 1 fb−1. As an example of the top quark mass measurements we consider so-called Matrix Element method in “lepton + jets” and “dilepton” channels of the top-quark decay. The CDF top quark mass obtained in lepton +jets mode is the world most precise single measurement of this important physics parameter. The review summarizes the essential results of the CDF top-quark mass measurement achieved and published for the recent 2003–2008 period. We consider also b-quark baryon discoveries like Σb, Σb*, Θb as well as first observation of {ie359-3} oscillations. Let us mention here that a CDF/JINR-group created significant contribution to the new CDF complex and physics investigation.

Search for the Higgs boson produced in association withZ→ℓ+ℓ−using the matrix element method at CDF II

We present a search for associated production of the standard model (SM) Higgs boson and a $Z$ boson where the $Z$ boson decays to two leptons and the Higgs decays to a pair of $b$ quarks in $p\bar{p}$ collisions at the Fermilab Tevatron. We use event probabilities based on SM matrix elements to construct a likelihood function of the Higgs content of the data sample. In a CDF data sample corresponding to an integrated luminosity of 2.7 fb$^{-1}$ we see no evidence of a Higgs boson with a mass between 100 GeV$/c^2$ and 150 GeV$/c^2$. We set 95% confidence level (C.L.) upper limits on the cross-section for $ZH$ production as a function of the Higgs boson mass $m_H$; the limit is 8.2 times the SM prediction at $m_H = 115$ GeV$/c^2$.

THE DISCOVERY OF AN ANGLO-SAXONGRUBENHAUSAT NEW BEWICK, NORTHERN UK USING ELECTRICAL SURVEYING AND PREDICTIVE DECONVOLUTION

Twin-probe and 33-fold multiplexed Wenner electrical resistivity surveys were carried out at New Bewick, northern UK to examine the extent of crop marks and potential Grubenhauser (sunken-featured buildings, sunken-floored buildings or SFBs). The twin-probe method was faster, but provided data with a lower spatial resolution. However, the Wenner array data was affected by characteristic ‘M’- or ‘W’-shaped responses over filled excavations such as those expected to represent a Grubenhaus. The raw Wenner array data have been analysed using one-dimensional and two-dimensional predictive deconvolution in order to remove these artefacts. The deconvolution was carried out using an inverse matrix element method. The filtered results indicate the presence of anomalies consistent with the presence of at least six Grubenhauser and other anomalies concurrent with the linear crop-marks. One particular anomaly measured about 5 m by 4 m and with a pit depth of 0.6 m below 0.3 m of topsoil. This anomaly was subsequently excavated and a Grubenhaus was discovered at the site. The excavated Grubenhaus measured 4.7 m by 3.9 m with a pit depth of 0.5 m below the base of the topsoil, confirming the electrical survey results.

Top quark mass measurement in the lepton plus jets channel using a modified matrix element method

We report a measurement of the top quark mass, m_t, obtained from ppbar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron using the CDF II detector. We analyze a sample corresponding to an integrated luminosity of 1.9 fb^-1. We select events with an electron or muon, large missing transverse energy, and exactly four high-energy jets in the central region of the detector, at least one of which is tagged as coming from a b quark. We calculate a signal likelihood using a matrix element integration method, with effective propagators to take into account assumptions on event kinematics. Our event likelihood is a function of m_t and a parameter JES that determines /in situ/ the calibration of the jet energies. We use a neural network discriminant to distinguish signal from background events. We also apply a cut on the peak value of each event likelihood curve to reduce the contribution of background and badly reconstructed events. Using the 318 events that pass all selection criteria, we find m_t = 172.7 +/- 1.8 (stat. + JES) +/- 1.2 (syst.) GeV/c^2.