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On The Nature Of The Higgs Boson

On The Nature Of The Higgs Boson

Several particles are not observed directly, but only through their decay products. We consider the possibility that they might be fakeons, i.e. fake particles, which mediate interactions but are not asymptotic states. A crucial role to determine the true nature of a particle is played by the imaginary parts of the one-loop radiative corrections, which are affected in nontrivial ways by the presence of fakeons in the loop. The knowledge we have today is sufficient to prove that most non directly observed particles are true physical particles. However, in the case of the Higgs boson the possibility that it might be a fakeon remains open. The issue can be resolved by means of precision measurements in existing and future accelerators.
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A search for the Standard Model Higgs boson at OPAL

A search for the Standard Model Higgs boson at OPAL

For the Standard Model sh 11 to describe the interactions of the particles observed in nature, the symmetry will have to be broken in a subtle way thus accomTAO j t l t | the particles’ masses, as well as still preserving the Model’s renormalizability. The subtle breaking of the symmetry is done spontaneously, this involves finding suit­ able Lagrangians in which the sym m etry is broken only in the ground state. The Standard Model introduces a doublet of fields, the Higgs doublet, into the family of known particle fields to achieve this purpose. It is thought th at these fields perm eate the whole of the universe. After spontaneous symm etry breaking has occurred in the ground state, only one of the fields has a non-vanishing value. Particle masses are generated by their interactions with this residual Higgs field. A quantum of this residual field is called the Higgs boson.
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Sgoldstino physics and flavor-violating Higgs boson decays

Sgoldstino physics and flavor-violating Higgs boson decays

respectively. This remark is important since corresponding physical masses can differ drastically from the mentioned ones in case of large of mixing angles and this will be the case for most of the interesting points in the parameter space of our model. We will denote mass states as ˜ s and ˜ h keeping notations s and h for non-physical states. Next, the second term in (7) is suppressed compared to the first one. In this way the sign of the mixing angle is dictated by the sign of μ parameter. Unlike Higgs boson sgoldstino has flavour-violating couplings to the SM fermions

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Measurements of the properties of the Higgs boson using the ATLAS detector

Measurements of the properties of the Higgs boson using the ATLAS detector

Measurements probing the properties of the Higgs boson at the LHC are reported, based on pp col- lision data collected by the ATLAS detector corresponding to an integrated luminosity of 4.7 fb −1 at centre-of-mass energy √ s = 7 TeV, and 20.3 fb −1 at √ s = 8 TeV. The compatibility of the data with different spin, parity and tensor coupling scenarios of the Higgs boson are tested in the H → γγ, H → ZZ ∗ → 4 and H → WW ∗ → eνμν decay channels. Fiducial and differential cross sections for Higgs boson production in the H → γγ, H → ZZ ∗ → 4 decay channels are presented. In the H → γγ channel a selection of the measured differential cross sections are used to set limits on anomalous Higgs boson couplings using an effective Lagrangian. No significant deviations from the SM predictions are observed in any of the measurements discussed.
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Search for rare and exotic Higgs Boson decay modes

Search for rare and exotic Higgs Boson decay modes

A number of models for physics beyond the SM allow for invisible decay modes of the Higgs boson, such as decays to neutralinos in supersymmetric models [18] or graviscalars in models with extra spatial dimensions [19, 20]. More generally, invisible Higgs boson decays can be realised through interactions between the Higgs boson and dark matter (DM) [21]. Direct searches for invisible decays of the Higgs boson increase the sensitivity to the invisible Higgs boson width beyond the indirect con- straints. The typical signature at the LHC is a large missing transverse momentum recoiling against a distinctive visible system. Firstly a combination of searches for invisible decays of the Higgs boson using data collected during 2011, 2012, and 2015 are presented [22]. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 fb −1 at centre-of-mass
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Spin Forms and Spin Interactions among Higgs Bosons, between Higgs Boson and Graviton

Spin Forms and Spin Interactions among Higgs Bosons, between Higgs Boson and Graviton

In traditional views, there are no any spin interactions among spin zero particles. However, by means of STS concept, on the contrary, it is shown there are the spin interactions. 0 Spin zero particle not only possesses spin phenomena but also appears out right-circumrotation and left-circumrotation, such kind of properties may exist in Higgs Boson world of the Standard Model.

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Search for an Invisibly Decaying Higgs Boson Produced via Vector Boson Fusion

Search for an Invisibly Decaying Higgs Boson Produced via Vector Boson Fusion

The discovery of the Higgs in July 2012 at the Large Hadron Collider opened the possibility of using the Higgs as a vehicle for other discoveries. The analysis presented here attempts to use the Higgs boson to explore the very active research area of dark matter. Dark matter accounts for most of the mass in the universe, but little is known about its properties. The existence of dark matter is inferred from many astrophysical observations originating from as early as 1931 with galaxy rotation curves. The most promising explanation for dark matter is that it is composed of Weakly Interactive Massive Particles (WIMPs), which interact only through gravity and the weak force. Since the Higgs boson couples to massive particles, there is motivation to believe that it should couple to dark matter candidates as well.
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A new implementation of the NMSSM Higgs boson decays

A new implementation of the NMSSM Higgs boson decays

pure CP–even or CP–odd states anymore. In order to compare with recent experimental results it is mandatory to assess, besides the spectrum, the decay pattern of the NMSSM Higgs bosons. In the following, we will present our implementation of the NMSSM Higgs boson decays either with real (CP–conserving R –NMSSM) or complex (CP–violating C –NMSSM) parameters. In particular the state-of-the-art higher–order corrections will be included as well as the renormalization group evolution of the pa- rameters.

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Search for the standard model Higgs boson at LEP

Search for the standard model Higgs boson at LEP

are expected at the end of the kinematic range of the Higgsstrahlung process from W and Z boson fusion, which produce a Higgs boson and a pair of neutrinos or electrons, respectively, in the final state [15]. The signal processes are simulated using the HZHA generator [16], which includes the fusion processes and their interference with the HZ final states. For Higgs boson masses which are relevant at LEP, the Standard Model Higgs boson is expected to decay mainly into b¯ b quark pairs (the branching ratio is 74% for a mass of 115 GeV/c 2

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A light Higgs boson would invite supersymmetry

A light Higgs boson would invite supersymmetry

If the Higgs boson weighs about 115 GeV, the effective potential of the Standard Model becomes unstable above a scale of about 10 6 GeV. This instability may be rectified only by new bosonic particles such as stop squarks. However, avoiding the instability requires fine-tuning of the model couplings, in particular if the theory is not to become non-perturbative before the Planck scale. Such fine-tuning is automatic in a supersymmetric model, but is lost if there are no higgsinos. A light Higgs boson would be prima facie evidence for supersymmetry in the top-quark and Higgs sectors.  2001 Elsevier Science B.V. All rights reserved.
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CMS standard model Higgs boson results

CMS standard model Higgs boson results

shape, isolation, kinematic variables, and the m γγ resolu- tion. As a cross-check, a cut-based selection is performed applying cuts on the γ pseudo-rapidity and the γ conver- sion probability. The events are classified in 4 categories with di ff erent signal over background (S / B) and mass res- olution. To gain sensitivity on the Higgs boson production modes, 5 exclusive analyses are done: 3 channels with ei- ther one electron, one muon or MET tagged in the event (sensitive to VH), and 2 dijet categories (sensitive to VBF). The di-photon mass distribution, with each event weighted by the S /(S + B) value of its category, is dis- played in figure 1. The Higgs boson signal shows up at m γγ = 125.4 ± 0.5 (stat.) ± 0.6 (syst.) GeV / c 2 , where the first uncertainty is statistical and the second systematic.
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Setting limits and application to Higgs boson search

Setting limits and application to Higgs boson search

The concerns about frequentist limits discussed at the end of the previous section have been addressed in the definition of a new procedure that was adopted for the first time in the combination of the results of the search for the Higgs boson [14] of the four LEP experiments, Aleph, Delphi, Opal and L3. The modification of the purely frequentist confidence level by a conservative correction factor can cure, as will be presented in the following, the counterintuitive peculiarities of the frequentist limit procedure. The original proposal of the modified frequentist approach adopted a test statistics based on the ratio of the likelihood functions evaluated under two di ff erent hypotheses: the presence of signal plus background, and the presence of background only:
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Measurements of Higgs Boson Properties using the ATLAS Detector

Measurements of Higgs Boson Properties using the ATLAS Detector

The discovery of a new particle with a mass of about 125 GeV in the search for the Standard Model (SM) Higgs boson at the CERN Large Hadron Collider (LHC) was reported in July 2012 by the ATLAS and CMS Collaborations[1]. The present experimental challenge is to compare its properties with those predicted by the Standard Model. This proceeding presents measurements of the main properties of the newly observed particle, including its mass, production strengths and couplings to fermions and bosons, as well as spin and parity, using diboson final states: γγ, ZZ ∗ → 4 and WW ∗ → νν.
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Higgs boson production in association with a single top quark at the LHC

Higgs boson production in association with a single top quark at the LHC

Abstract. Higgs boson production in association with a single top quark is the only pro- cess sensitive to the sign of the Top Yukawa coupling. We present a Monte-Carlo study of the pp → tHqb process and discuss the esperimental signatures that can help to dis- cover it at the LHC. Two scenarios have been considered, the Standard Model case and the Inverted Top Coupling scenario.

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Neural Networks Search for Charged Higgs Boson in Two Doublet Higgs Model at the Hadrons Colliders

Neural Networks Search for Charged Higgs Boson in Two Doublet Higgs Model at the Hadrons Colliders

The neural network method used for b-tagging in the OPAL SM Higgs-boson search [27] is used to calculate the discriminating the charged Higgs signal from the SM background. The inputs to the neural network include in- formation about the electrons and the muons as transverse momentum, transverse mass and pseudorapidity. The main background in this search comes from decay of w ± to electron and muons. The signal depends on the Higgs-boson masses and is very clean via electron and muon in the event. For purely leptonic events the first two candidates were retained and the rest were neglected as τ particles. For semileptonic events, only the first one was retained as a τ candidate. The resulting samples are completely dominated by background, the contribu- tion of a Higgs signal being at most 0.5%. The statistical analysis is based on weighted event counting, with the weights computed from physical observables, also called discriminating variables of the candidate events. An improved analysis has been designed for the fully leptonic channel where BR H ( + → τ τ + ν ) = 1 and the rejec- tion of the w w + − background has been refined with Artificial Neural Networks (ANNs) discrimination. When dealing with semileptonic final states, the τ candidate jet definition was refined removing particles that were not likely to come from τ decay.
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Search for a high mass Higgs boson using the ATLAS detector

Search for a high mass Higgs boson using the ATLAS detector

A search for a SM Higgs boson decaying via H → ZZ → ll j j (where l can be either an electron or a muon) has been performed over the mass range 200 GeV ≤ m H ≤ 600 GeV [25]. It is based on proton proton collision data recorded at a centre-of-mass energy of 7 TeV and corresponding to an integrated luminosity of 4.7 fb −1 . In order to optimise the expected sensitivity a distinction between events containing at least two or less than two b tagged jets has been applied as well as a different selection criteria for events with m H < 300 GeV or m H ≥ 300 GeV. The main background to this analysis comes from the Z boson production in association with jets. The shapes of the relevant kinematic distributions for this background are taken from MC simulation, with a small data-driven correction for the low-m H less than two b-tagged jets selection, while the normalisations for all selections are derived directly from data. The flavor composition of the Z+jets events is derived from MC and the overall Z jets normalisation is obtained by fitting the m ll j j distribution in m j j sidebands. The main systematic uncertainties in this channel are the same as discussed in the previous session: JES, JER, b-tagging e ffi ciency as experimental contributions, lineshape and interference e ff ects from the theory. The signal is extracted by fitting the ll j j invariant mass m ll j j . Finally the upper limits at 95% CL on SM Higgs production cross section are derived. This channel allows to exclude at 95% CL a SM Higgs boson within a mass range of 300 GeV ≤ m H ≤ 322 GeV or 353 GeV ≤ m H ≤ 410 GeV.
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Evidence for the Higgs boson in the H->WW->lnulnu decay channel

Evidence for the Higgs boson in the H->WW->lnulnu decay channel

For 8 TeV proton-proton collisions, the collisions producing Higgs bosons are x ⇠ 0.01 0.02, which are mostly gluons as shown in red on the PDF in Figure 2.4. The large amount of gluon collisions makes them a more desirable production method than through quarks; however, gluons are massless. Therefore, the Higgs does not couple directly to them, but the gluons can split into top quarks that are massive and do couple to the Higgs. Hence, the Higgs boson production on the LHC is dominated by a pair of gluons going through a mainly top quark loop to a Higgs boson as shown in Figure 2.5. There are some small corrections for the b-quark in the loop, but the other quark flavors are too light to contribute significantly. The production method with two gluons is referred to as gluon-gluon fusion or ggF and was the primary production method used to discover the Higgs boson. ggF, which is in blue in Figure 2.6, has the advantage of a relatively large cross-section compared to the other Higgs production mechanism; however, ggF is that it is theoretically difficult to calculate because of the gluon-gluon initial state and the color-charged particles with non-negligible mass in the loop. This makes it difficult to know that there is not a new particle hiding in that loop, which would increase the ggF cross-section.
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The Journey Through Time Towards the Discovery of the Higgs Boson - A Review

The Journey Through Time Towards the Discovery of the Higgs Boson - A Review

In the standard model the fundamental particles are divided into the three families of fermions (6leptons and 6 quarks) and the bosons responsible for the electromagnetic (photon), the weak (W ± /Z 0 bosons), and the strong nuclear interactions (gluons). Under local transformations, these physical interactions are invariant, hence the corresponding field theories are gauge-invariant and the carriers of these interactions are called gauge bosons. Since these gauge bosons all have a spin of 1, they are classified as vector bosons, e.g. the photon is a massless gauge vector boson. The Higgs boson on the other side has a spin of 0 and is therefore classified as a scalar boson. The W ± /Z 0 bosons are originally massless but they obtain a mass through the (scalar) Higgs boson which interacts with all fundamental particles through the universal Higgs field. The addition of the Higgs boson is required to remove the infinities in the field equations by enabling the formulation of a renormalizable quantum field theory for the electroweak interaction. As a result, the standard model and the Higgs boson are inextricably intertwined. Therefore, it is clear that the detection of the Higgs boson in 2012 was an important milestone for the experimental verification of the standard model (“the breakthrough of theyear”). (Cho, A., 2012).
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Evidence for Decays of the Higgs Boson to Tau Leptons at atlas

Evidence for Decays of the Higgs Boson to Tau Leptons at atlas

The collection of fundamental SM particles, including the Higgs boson, are shown in Figs. 2.1 and 2.2. The bosons of the SM are mediators of the theory, and the fermions compose the matter we observe. The fermions are grouped into the quarks, which compose objects like protons and neutrons, and the leptons, such as electrons. Quarks have fractional electric charge and three possible color charges, typically called red, blue, and green. They therefore interact with all of the SM gauge bosons. The leptons are colorless and only interact with the electroweak gauge bosons. Among the leptons, neutrinos are electrically neutral and thus only participate in weak interactions. They are also have small mass relative to the other SM fermions, though they are not massless. Understanding the properties of neutrinos is an active area of current research.
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Search for the Higgs boson produced in association with top quarks

Search for the Higgs boson produced in association with top quarks

As can be seen from the the Feynman diagram in Fig. 1 the ttH process has a very complex final state from the experimental point of view. The presence of other tagging objects (either b-jets, jets or leptons) in addition to the Higgs boson allows us to e ff ectively reduce the background, reaching a good sensitivity despite the low cross section of this process.

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