Search

Abstract Inspired by the new TOTEM data on elastic pp scattering at 13 TeV, we study the possibility to describe all the diffractive collider data (σ tot , d σ el / d t , ρ ≡ Re A / Im A , σ low M D) in a wide interval of energy (0.0625 to 13 TeV) in the framework of a two-channel eikonal model. We show that a satisfactory description can be achieved without an odd-signature (Odderon) exchange contribution. We consider the possible role of the QCD Odderon which may improve the description of ρ and discuss the importance of the odd-signature term if the amplitude were to exceed the black disc limit. [ABSTRACT FROM AUTHOR]

Abstract The observation of Higgs boson production in association with a top quark pair (t t ¯ H), based on the analysis of proton–proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider, is presented. Using data corresponding to integrated luminosities of up to 79.8 fb−1, and considering Higgs boson decays into b b ¯ , W W ⁎ , τ + τ − , γγ , and Z Z ⁎ , the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the t t ¯ H searches using a dataset corresponding to integrated luminosities of 4.5 fb−1 at 7 TeV and 20.3 fb−1 at 8 TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total t t ¯ H production cross section at 13 TeV is measured to be 670 ± 90 (stat.) − 100 + 110 (syst.) fb, in agreement with the Standard Model prediction. [ABSTRACT FROM AUTHOR]

We evaluate the QED corrections due to initial state radiation (ISR) to associated Higgs boson production in electron–positron ( e + e − ) annihilation at typical energies of interest for the measurement of the Higgs properties at future e + e − colliders, such as CEPC and FCC–ee. We apply the QED Structure Function approach to the four-fermion production process e + e − → μ + μ − b b ¯ , including both signal and background contributions. We emphasize the relevance of the ISR corrections particularly near threshold and show that finite third order collinear contributions are mandatory to meet the expected experimental accuracy. We analyze in turn the rôle played by a full four-fermion calculation and beam energy spread in precision calculations for Higgs physics at future e + e − colliders. [ABSTRACT FROM AUTHOR]

A search for heavy resonances decaying to a W or Z boson and a Higgs boson in the q q ¯ ( ′ ) b b ¯ final state is described. The search uses 36.1 fb − 1 of proton–proton collision data at s = 13 TeV collected by the ATLAS detector at the CERN Large Hadron Collider in 2015 and 2016. The data are in agreement with the Standard Model expectations, with the largest excess found at a resonance mass of 3.0 TeV with a local (global) significance of 3.3 (2.1) σ . The results are presented in terms of constraints on a simplified model with a heavy vector triplet. Upper limits are set on the production cross-section times branching ratio for resonances decaying to a W ( Z ) boson and a Higgs boson, itself decaying to b b ¯ , in the mass range between 1.1 and 3.8 TeV at 95% confidence level; the limits range between 83 and 1.6 fb (77 and 1.1 fb) at 95% confidence level. [ABSTRACT FROM AUTHOR]

We study the effects of the initial state radiation on the s -channel Higgs boson resonant production at μ + μ − and e + e − colliders by convoluting with the beam energy spread profile of the collider and the Breit–Wigner resonance profile of the signal. We assess their impact on both the Higgs signal and SM backgrounds for the leading decay channels h → b b ¯ , W W ⁎ . Our study improves the existing analyses of the proposed future resonant Higgs factories and provides further guidance for the accelerator designs with respect to the physical goals. [ABSTRACT FROM AUTHOR]

In the simplest Higgs-portal scalar dark matter model, the dark matter mass has been restricted to be either near the resonant mass ( m h / 2 ) or in a large-mass region by the direct detection at LHC Run 1 and LUX. While the large-mass region below roughly 3 TeV can be probed by the future Xenon1T experiment, most of the resonant mass region is beyond the scope of Xenon1T. In this paper, we study the direct detection of such scalar dark matter in the narrow resonant mass region at the 14 TeV LHC and the future 100 TeV hadron collider. We show the luminosities required for the 2 σ exclusion and 5 σ discovery. [ABSTRACT FROM AUTHOR]

Direct detection of and LHC search for the singlet fermion dark matter (SFDM) model with Higgs portal interaction are considered in a renormalizable model where the full Standard Model (SM) gauge symmetry is imposed by introducing a singlet scalar messenger. In this model, direct detection is described by an effective operator m q q ¯ q χ ¯ χ as usual, but the full amplitude for monojet + E̸ T involves two intermediate scalar propagators, which cannot be seen within the effective field theory (EFT) or in the simplified model without the full SM gauge symmetry. We derive the collider bounds from the ATLAS monojet + E̸ T as well as the CMS t t ¯ + E̸ T data, finding out that the bounds and the interpretation of the results are completely different from those obtained within the EFT or simplified models. It is pointed out that it is important to respect unitarity, renormalizability and local gauge invariance of the SM. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the prospects for detecting a hidden sector at an collider. The hidden sector is assumed to be composed of invisible particles that carry no charges under the Standard Model gauge interactions, and whose primary interactions with ordinary matter are through the Higgs portal. We consider both the cases when the decays of an on-shell Higgs into a pair of hidden sector particles are kinematically allowed, and the case when such decays are kinematically forbidden. We find that at collider energies below a TeV, the most sensitive channel involves production of an on-shell or off-shell Higgs in association with a Z boson, and the subsequent decay of the Higgs into invisible hidden sector states. Focusing on this channel, we find that with order a thousand inverse fb of data at 250 GeV, the decay branching fraction of an on-shell Higgs to invisible hidden sector states can be constrained to lie below half a percent. The corresponding limits on Higgs portal dark matter will be stronger than the bounds from current and upcoming direct detection experiments in much of parameter space. With the same amount of data at 500 GeV, assuming order one couplings, decays of an off-shell Higgs to hidden sector states with a total mass up to about 200 GeV can also be probed. Both the on-shell and off-shell cases represent a significant improvement in sensitivity when compared to the Large Hadron Collider (LHC). [Copyright &y& Elsevier]

Abstract: We show that a muon collider is ideally suited for the study of heavy scalars, cousins of the Higgs boson found in two-Higgs-doublet models and required in supersymmetric models. The key aspects of are: (1) they are narrow, yet have a width-to-mass ratio far larger than the expected muon collider beam-energy resolution, and (2) the larger muon Yukawa allows efficient s-channel production. We study in detail a representative Natural Supersymmetry model which has a with . The large event rates at resonant peak allow the determination of the individual H and A resonance parameters (including CP) and the decays into electroweakinos provide a wealth of information unavailable to any other present or planned collider. [Copyright &y& Elsevier]

Abstract: We present a search for the standard model Higgs boson in 9.5 fb−1 of collisions at collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered contains a pair of b jets and is characterized by an imbalance in transverse energy, as expected from production. The search is also sensitive to the channel when the charged lepton is not identified. The data are found to be in good agreement with the expected background. For a Higgs boson mass of 125 GeV, we set a limit at the 95% C.L. on the cross section , assuming standard model branching fractions, that is a factor of 4.3 times larger than the theoretical standard model value, while the expected factor is 3.9. The search is also used to measure a combined WZ and ZZ production cross section that is a factor of times the standard model prediction of 4.4 pb, with an observed significance of 2.0 standard deviations. [Copyright &y& Elsevier]

Abstract: We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with zero, one, or two or more jets using data corresponding to an integrated luminosity of up to collected with the D0 detector at the Fermilab Tevatron collider. The analysis is sensitive to Higgs boson production via gluon–gluon fusion, associated vector boson production, and vector boson fusion, and to Higgs boson decays to ττ, WW, ZZ and pairs. Observed (expected) limits are set on the ratio of 95% C.L. upper limits on the cross section times branching ratio, relative to those predicted by the Standard Model, of 22 (14) at a Higgs boson mass of 115 GeV and 6.8 (7.7) at 165 GeV. [Copyright &y& Elsevier]

Abstract: We propose a novel left–right symmetric model where the standard model fermion and Higgs fields are doublets or singlets while their mirror partners are doublets or singlets. The scalar fields also include a real singlet for dark matter and two triplets for seesaw. The mixing between the standard model and mirror fermions is forbidden by a discrete symmetry. The mirror charged fermions can decay into their standard model partners with the dark-matter scalar while the mirror neutrinos can decay into the mirror charged fermions through the right-handed gauge interactions. Our model can have new implications on the strong CP problem, leptogenesis, collider phenomenology and dark matter detection. [Copyright &y& Elsevier]

Abstract: We examine the parameter space of the constrained MSSM by considering various experimental constraints. For the dark matter sector, we require the neutralino dark matter to account for the relic density measured by the WMAP and satisfy the XENON limits on its scattering rate with the nucleon. For the collider constraints, we consider all relevant direct and indirect limits from LEP, Tevatron and LHC as well as the muon anomalous magnetic moment. Especially, for the limits from , we either directly consider its branching ratio with the latest LHC data or alternatively consider the double ratio of the purely leptonic decays defined by . We find that under these constraints, the mass of the lightest Higgs boson (h) in both the CMSSM and the NUHM2 is upper bounded by about 124 GeV (126 GeV) before (after) considering its theoretical uncertainty. We also find that for these models the di-photon Higgs signal at the LHC is suppressed relative to the SM prediction, and that the lower bound of the top-squark mass goes up with , reaching 600 GeV for . [Copyright &y& Elsevier]

Abstract: We describe a model named No-Scale which is simultaneously capable of explaining the dual signals emerging at the LHC of (i) a 124–126 GeV Higgs boson mass , and (ii) tantalizing low-statistics excesses in the multi-jet data which may attributable to supersymmetry. These targets tend to be mutually exclusive in more conventional approaches. The unified mechanism responsible for both effects is the introduction of a rather unique set of vector-like multiplets at the TeV scale, dubbed flippons, which (i) can elevate by around 3–4 GeV via radiative loop corrections, and (ii) flatten the running of the strong coupling and color-charged gaugino, resulting in a prominent collider signal from production of light gluino pairs. This well-motivated theoretical framework maintains consistency with all key phenomenological constraints, and all residual parameterization freedom may in principle be fixed by a combination of the two experiments described. We project that the already collected luminosity of may be sufficient to definitively establish the status of this model, given appropriate data selection cuts. [Copyright &y& Elsevier]

Abstract: We examine the exclusion limits set by the CDF and D0 experiments on the Standard Model Higgs boson mass from their searches at the Tevatron in the light of large theoretical uncertainties on the signal and background cross sections. We show that when these uncertainties are consistently taken into account, the sensitivity of the experiments becomes significantly lower and the currently excluded mass range could be entirely reopened. The necessary luminosity required to recover the current sensitivity is found to be a factor of two higher than the present one. [Copyright &y& Elsevier]

Abstract: The Higgs sector is extended in R-symmetric supersymmetry theories by two iso-doublets which complement the standard iso-doublets . We have analyzed masses and interactions of these novel states and describe their [non-standard] decay modes and their production channels at the LHC and colliders. [Copyright &y& Elsevier]

Abstract: Recent fits of electroweak precision data to the Standard Model (SM) with a 4th sequential family (SM4) point to a possible “three-prong composite solution”: (1) the Higgs mass is at the TeV-scale, (2) the masses of the 4th family quarks are of and (3) the mixing angle between the 4th and 3rd generation quarks is of the order of the Cabibbo angle, . Such a manifestation of the SM4 is of particular interest as it may suggest that the Higgs is a composite state, predominantly of the 4th generation heavy quarks. Motivated by the above, we show that the three-prong composite solution to the SM4 can have interesting new implications for Higgs phenomenology. For example, the Higgs can decay to a single heavy 4th generation quark via the 3-body decays (through an off-shell or ) and . These flavor diagonal decays can be dramatically enhanced at the LHC (by several orders of magnitudes) due to the large width effects of the resonating heavy Higgs in the processes and , thus yielding a viable signal above the corresponding continuum QCD production rates. In addition, the Higgs can decay to a single and in the loop-generated flavor changing (FC) channels . These FC decays are essentially “GIM-free” and can, therefore, have branching ratios as large as . [Copyright &y& Elsevier]

Abstract: We present a search for charged Higgs bosons in top quark decays. We analyze the , , ee, eμ, μμ, τe and τμ final states from top quark pair production events, using data from about 1 fb−1 of integrated luminosity recorded by the DØ experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a τ lepton and a τ neutrino and a third one where both decays appear. We extract limits on the branching ratio for all these models. We use two methods, one where the production cross section is fixed, and one where the cross section is fitted simultaneously with . Based on the extracted limits, we exclude regions in the charged Higgs boson mass and parameter space for different scenarios of the minimal supersymmetric standard model. [Copyright &y& Elsevier]

Abstract: If the sparticles are relatively heavy (a few TeV) while the Higgs sector is not so heavy ( is not so large), the Higgs boson Yukawa couplings can harbor sizable quantum effects of sparticles and these large residual effects may play a special role in probing supersymmetry at foreseeable colliders. In this work, focusing on the supersymmetric QCD effects in the coupling (h is the lightest CP-even Higgs boson), we give a comparative study for the two popular supersymmetric models: the MSSM and NMSSM. While for both models the supersymmetric QCD can leave over large residual quantum effects in coupling, the NMSSM can allow for a much broader region of such effects. Since these residual effects can be over 20% for the coupling (and thus over 40% for the ratio ), future measurements may unravel the effects of heavy sparticles or even distinguish the two models. [Copyright &y& Elsevier]

Abstract: The production of a single neutral Higgs boson h through (loop-induced) γγ collisions is explored in the context of the linear colliders within the general Two-Higgs-Doublet Model (2HDM). Two different mechanisms are analyzed: on the one hand, the scattering of two real photons in a γγ collider; on the other, the more traditional mechanism of virtual photon fusion, . Owing to the peculiar properties of the Higgs boson self-interactions within the general 2HDM, we find that the overall production rates can be boosted up significantly, provided the charged Higgs mass is not too heavy. For example, if and, in addition, falls in the ballpark of the LEP bound on the SM Higgs mass up to a few hundred GeV, the cross-sections may typically render and – in both cases well above the SM prediction. Although for the rates become virtually insensitive to the Higgs boson self-couplings, a significant tail of non-SM effects produced by the combined contribution of the Yukawa couplings and gauge bosons could still reveal a smoking gun. [Copyright &y& Elsevier]

Abstract: In models with extended Higgs sectors, Higgs-boson-mediated Lepton Flavour Violation (LFV) can naturally appear. We study the physics potential of an electron–photon collider on searching LFV processes (; ) where H and A are extra CP even and odd Higgs bosons, respectively, in the minimal supersymmetric standard model and the effective two Higgs doublet model. The production cross section can be significantly large for the maximal allowed values of the LFV coupling constants under the current experimental data. Present experimental upper bounds on the effective LFV coupling constants would be considerably improved by searching these processes, which would be better than MEG and COMET experiments and also those at LHCb and SuperKEKB. Moreover, one can separately measure chirality of effective LFV coupling constants via these processes by selecting electron polarizations. [Copyright &y& Elsevier]

Abstract: We calculate the cross section of Higgs boson pair production at a photon collider in the two Higgs doublet model. We focus on the scenario in which the lightest CP even Higgs boson (h) has the Standard Model like couplings to the gauge bosons. We take into account the one-loop correction to the hhh coupling as well as additional one-loop diagrams due to charged Higgs bosons to the helicity amplitudes. It is found that the full cross section can be enhanced by both these effects to a considerable level. We discuss the impact of these corrections on the hhh coupling measurement at the photon collider. [Copyright &y& Elsevier]

Abstract: Results for the complete NLO electroweak corrections to Standard Model Higgs production via gluon fusion are included in the total cross section for hadronic collisions. Artificially large threshold effects are avoided working in the complex-mass scheme. The numerical impact at LHC (Tevatron) energies is explored for Higgs mass values up to 500 GeV (200 GeV). Assuming a complete factorization of the electroweak corrections, one finds a +5% shift with respect to the NNLO QCD cross section for a Higgs mass of 120 GeV both at the LHC and the Tevatron. Adopting two different factorization schemes for the electroweak effects, an estimate of the corresponding total theoretical uncertainty is computed. [Copyright &y& Elsevier]

Abstract: The dileptonic decays of doubly-charged Higgs bosons are investigated in the minimal type-II seesaw model with one Higgs triplet Δ and one heavy Majorana neutrino at the TeV scale. We show that the branching ratios depend not only on the mass and mixing parameters of three light neutrinos (for ), but also on those of . Assuming the mass of to lie in the range 200 GeV–1 TeV, we figure out the generous interference bands for the contributions of and to : , where and measure the strength of charged-current interactions of . We illustrate some salient features of the interference bands by considering three typical mass patterns of , and stress that it is very difficult to distinguish the type-II seesaw model from the triplet seesaw model in such a parameter region at the Large Hadron Collider. [Copyright &y& Elsevier]

Abstract: If scale invariance is exact, unparticles are unlikely to be probed in colliders since there are stringent constraints from astrophysics and cosmology. However these constraints are inapplicable if scale invariance is broken at a scale . The case is particularly interesting since it allows unparticles to be probed at and below the Z pole. We show that μ can naturally be in this range if only vector unparticles exist, and briefly remark on implications for Higgs phenomenology. We then obtain constraints on unparticle parameters from cross-section and forward–backward asymmetry data, and compare with the constraints from mono-photon production and the Z hadronic width. [Copyright &y& Elsevier]

Abstract: We propose a model that introduces a supersymmetric unparticle operator in the minimal supersymmetric Standard Model. We analyze the lowest dimension operator involving an unparticle. This operator behaves as a Standard Model gauge singlet and it introduces a new parameter into the Higgs potential which can provide an alternative way to relax the upper limit on the lightest Higgs boson mass. This operator also introduces several unparticle interactions which can induce a neutral Higgsino to decay into a spinor unparticle. It also induces violation of scale invariance around the electroweak scale. It is necessary for the scale of this violation to be larger than the lightest supersymmetric particle mass to maintain the latter as the usual weakly interacting massive particle dark matter candidate. An alternative is to have unparticle state as dark matter candidate. We also comment on some collider implications. [Copyright &y& Elsevier]

Abstract: We present a method to investigate the quantum numbers of the Higgs boson in the process at a future linear collider (LC), where ϕ, a generic Higgs boson, is a mixture of -even and -odd states. The procedure consists of a comparison of the data with predictions obtained from Monte Carlo simulations corresponding to the productions of scalar and pseudoscalar Higgs and the interference term which constitutes a distinctive signal of violation. We present estimates of the sensitivity of the method from Monte Carlo studies using hypothetical data samples with a full LC detector simulation taking into account the background signals. [Copyright &y& Elsevier]

Higgs boson production via weak boson fusion is sensitive to the tensor structure of the HVV (V=W,Z) couplings, which distinguishes loop induced vertices from SM expectations. At the CERN large hadron collider this information shows up most clearly in the azimuthal angle correlations of the two forward and backward quark jets which are typical for weak boson fusion. We calculate the next-to-leading order QCD corrections to this process, in the presence of anomalous HVV couplings. Gluon emission does not significantly change the azimuthal jet correlations. [Copyright &y& Elsevier]

Abstract: We propose to identify the excess of events with four charged leptons at seen by the CDF Collaboration (2012) [1] and CMS Collaboration (2012) [2] with a new ‘sterile’ scalar particle characterized by a very narrow resonance of the same height and branching ratios as the Standard Model Higgs boson, as predicted in the framework of the so-called Conformal Standard Model (K.A. Meissner and H. Nicolai 2007) [3]. [Copyright &y& Elsevier]