Showing papers on "Elementary particle published in 2014"

REVIEW OF PARTICLE PHYSICS Particle Data Group

Abstract: The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,283 new measurements from 899 Japers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as heavy neutrinos, supersymmetric and technicolor particles, axions, dark photons, etc. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as Supersymmetry, Extra Dimensions, Particle Detectors, Probability, and Statistics. Among the 112 reviews are many that are new or heavily revised including those on: Dark Energy, Higgs Boson Physics, Electroweak Model, Neutrino Cross Section Measurements, Monte Carlo Neutrino Generators, Top Quark, Dark Matter, Dynamical Electroweak Symmetry Breaking, Accelerator Physics of Colliders, High-Energy Collider Parameters, Big Bang Nucleosynthesis, Astrophysical Constants and Cosmological Parameters.

The universal Higgs fit

Abstract: We perform a state-of-the-art global fit to all Higgs data. We synthesise them into a ‘universal’ form, which allows to easily test any desired model. We apply the proposed methodology to extract from data the Higgs branching ratios, production cross sections, couplings and to analyse composite Higgs models, models with extra Higgs doublets, supersymmetry, extra particles in the loops, anomalous top couplings, and invisible Higgs decays into Dark Matter. Best fit regions lie around the Standard Model predictions and are well approximated by our ‘universal’ fit. Latest data exclude the dilaton as an alternative to the Higgs, and disfavour fits with negative Yukawa couplings. We derive for the first time the SM Higgs boson mass from the measured rates, rather than from the peak positions, obtaining M h = 124.4 ± 1.6 GeV.

Impersonating the Standard Model Higgs boson: Alignment without decoupling

Abstract: In models with an extended Higgs sector there exists an alignment limit, in which the lightest CP-even Higgs boson mimics the Standard Model Higgs. The alignment limit is commonly associated with the decoupling limit, where all non-standard scalars are significantly heavier than the Z boson. However, alignment can occur irrespective of the mass scale of the rest of the Higgs sector. In this work we discuss the general conditions that lead to “alignment without decoupling”, therefore allowing for the existence of additional non-standard Higgs bosons at the weak scale. The values of tan β for which this happens are derived in terms of the effective Higgs quartic couplings in general two-Higgs-doublet models as well as in supersymmetric theories, including the MSSM and the NMSSM. Moreover, we study the information encoded in the variations of the SM Higgs-fermion couplings to explore regions in the m A − tan β parameter space.

Precision Measurements of Higgs Couplings: Implications for New Physics Scales

Abstract: The measured properties of the recently discovered Higgs boson are in good agreement with predictions from the Standard Model. However, small deviations in the Higgs couplings may manifest themselves once the currently large uncertainties will be improved as part of the LHC program and at a future Higgs factory. We review typical new physics scenarios that lead to observable modications of the Higgs interactions. They can be divided into two broad categories: mixing eects as in portal models or extended Higgs sectors, and vertex loop eects from new matter or gauge elds. In each model we relate coupling deviations to their eective new physics scale. It turns out that with percent level precision the Higgs couplings will be sensitive to the multi-TeV regime.

Evidence for the direct decay of the 125 GeV Higgs boson to fermions

Abstract: The discovery of a new boson with a mass of approximately 125 GeV in 2012 at the LHC has heralded a new era in understanding the nature of electroweak symmetry breaking and possibly completing the standard model of particle physics. Since the first observation in decays to gamma gamma, WW, and ZZ boson pairs, an extensive set of measurements of the mass and couplings to W and Z bosons, as well as multiple tests of the spin-parity quantum numbers, have revealed that the properties of the new boson are consistent with those of the long-sought agent responsible for electroweak symmetry breaking. An important open question is whether the new particle also couples to fermions, and in particular to down-type fermions, since the current measurements mainly constrain the couplings to the up-type top quark. Determination of the couplings to down-type fermions requires direct measurement of the corresponding Higgs boson decays, as recently reported by the CMS experiment in the study of Higgs decays to bottom quarks and tau leptons. In this paper we report the combination of these two channels which results, for the first time, in strong evidence for the direct coupling of the 125 GeV Higgs boson to down-type fermions, with an observed significance of 3.8 standard deviations, when 4.4 are expected.

Higgs portal vector dark matter for GeV scale γ-ray excess from galactic center

Abstract: We show that the GeV scale -ray excess from the direction of the Galactic Center can be naturally explained by the pair annihilation of Abelian vector dark matter (VDM) into a pair of dark Higgs bosons V V → ��, followed by the subsequent decay of � into � → bb,�¯ �. All the processes are described by a renormalizable VDM model with the Higgs portal, which is naturally flavor-dependent. Some parameter space of this scenario can be tested at the near future direct dark matter search experiments such as LUX and XENON1T.

Benchmarks for Higgs boson pair production and heavy Higgs boson searches in the two-Higgs-doublet model of type II

Abstract: The search for additional Higgs particles and the exact measurements of Higgs (self-)couplings is a major goal of future collider experiments. In this paper we investigate the possible sizes of new physics signals in these searches in the context of the $CP$-conserving two-Higgs-doublet model (2HDM) of type II. Using current constraints from flavor, electroweak precision, and Higgs signal strength data, we determine the allowed sizes of the triple-Higgs couplings and the branching fractions of the heavy Higgs bosons into lighter Higgs bosons. Identifying the observed Higgs resonance with the light $CP$-even 2HDM Higgs boson $h$, we find that the $hhh$ coupling cannot exceed its Standard Model (SM) value, but can be reduced by a factor of 0.56 at the $2\ensuremath{\sigma}$ level. The branching fractions of the heavy neutral Higgs bosons $H$ and $A$ into two-fermion or two-vector-boson final states can be reduced by factors of 0.4 and 0.01, respectively, if decays into a lighter Higgs boson are possible and if the mass of the decaying Higgs is below the $t\overline{t}$ threshold. To facilitate future studies of collider signatures in 2HDM scenarios with large triple-Higgs couplings or decay modes of the heavy Higgs bosons not covered by the SM Higgs searches we provide a set of benchmark points which exhibit these features and agree with all current constraints. We also discuss the effect of the heavy Higgs bosons on the $gg\ensuremath{\rightarrow}hh$ cross section at a 14 TeV LHC for some of these benchmarks. For ${m}_{H}$ below the $hh$ threshold we see a reduction of the SM $gg\ensuremath{\rightarrow}hh$ cross section due to destructive interference, but for ${m}_{H}$ above the $hh$ threshold current constraints allow enhancement factors above 50. An enhancement factor of 6 is still possible in scenarios in which the heavy Higgs particles would not be discovered by standard searches after $300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data.

Survey of vector-like fermion extensions of the Standard Model and their phenomenological implications

Abstract: With the renewed interest in vector-like fermion extensions of the Standard Model, we present here a study of multiple vector-like theories and their phenomenological implications. Our focus is mostly on minimal flavor conserving theories that couple the vector-like fermions to the SM gauge fields and mix only weakly with SM fermions so as to avoid flavor problems. We present calculations for precision electroweak and vector-like state decays, which are needed to investigate compatibility with currently known data. We investigate the impact of vector-like fermions on Higgs boson production and decay, including loop contributions, in a wide variety of vector-like extensions and their parameter spaces.

Discovery prospects for NMSSM Higgs bosons at the high-energy Large Hadron Collider

Abstract: We investigate the discovery prospects for Higgs bosons in the next-to-mininmal supersymmetric extension of the Standard Model (NMSSM) during the 13 TeV run of the LHC. While one of the neutral Higgs bosons is demanded to have a mass around 125 GeV and Standard Model-like properties, there can be substantially lighter, nearby or heavier Higgs bosons that have not been excluded yet by LEP, Tevatron or the 8 TeV run of the LHC. The challenge consists in discovering the whole NMSSM Higgs mass spectrum. We present the rates for production and subsequent decay of the neutral NMSSM Higgs bosons in the most promising final states and discuss their possible discovery. The prospects for pinning down the Higgs sector of the natural NMSSM will be analyzed taking into account alternative search channels. We give a series of benchmark scenarios compatible with the experimental constraints, that feature Higgs-to-Higgs decays and entail (exotic) signatures with multifermion and/or multiphoton final states. These decay chains furthermore give access to the trilinear Higgs self-couplings. We briefly discuss the possibility of exploiting coupling sum rules in case not all the NMSSM Higgs bosons are discovered.

Scaling and tuning of EW and Higgs observables

Abstract: We study deformations of the SM via higher dimensional operators. In particular, we explicitly calculate the one-loop anomalous dimension matrix for 13 bosonic dimension-6 operators relevant for electroweak and Higgs physics. These scaling equations allow us to derive RG-induced bounds, stronger than the direct constraints, on a universal shift of the Higgs couplings and some anomalous triple gauge couplings by assuming no tuning at the scale of new physics, i.e. by requiring that their individual contributions to the running of other severely constrained observables, like the electroweak oblique parameters or Γ(h → γγ), do not exceed their experimental direct bounds. We also study operators involving the Higgs and gluon fields.

Constraints on and future prospects for Two-Higgs-Doublet Models in light of the LHC Higgs signal

Abstract: We analyze the Two-Higgs-Doublet Models (2HDMs) of Type I and II for consistency with the latest measurements of the ~125.5 GeV Higgs-like signal at the LHC. To this end, we perform scans of the 2HDM parameter space taking into account all relevant pre-LHC constraints as well as the most recent limits coming from searches for heavy Higgs-like states at the LHC. The current status of the 2HDMs of Type I and II is discussed assuming that the observed 125.5 GeV state is one of the two CP-even Higgs bosons, either the lighter h or the heavier H. Implications for future experiments, including expectations regarding other lighter or heavier Higgs bosons are given. The possible importance of heavier Higgs bosons feeding the signals for the 125.5 GeV state is also evaluated.

Minimal composite Higgs models at the LHC

Abstract: We consider composite Higgs models where the Higgs is a pseudo-Nambu Goldstone boson arising from the spontaneous breaking of an approximate global symmetry by some underlying strong dynamics. We focus on the SO(5)! SO(4) symmetry breaking pattern, assuming the \partial compositeness" paradigm. We study the consequences on Higgs physics of the fermionic representations produced by the strong dynamics, that mix with the Standard Model (SM) degrees of freedom. We consider models based on the lowest-dimensional representations of SO(5) that allow for the custodial protection of the Zbb coupling, i.e. the 5, 10 and 14. Wend a generic suppression of the gluon fusion process, while the Higgs branching fractions can be enhanced or suppressed compared to the SM. Interestingly, a precise measurement of the Higgs boson couplings can distinguish between dierent realizations in the fermionic sector, thus providing crucial information about the nature of the UV dynamics.

Constraining CP-violating Higgs sectors at the LHC using gluon fusion.

Abstract: We investigate the constraints that the LHC can set on a 126 GeV Higgs boson that is an admixture of $CP$ eigenstates. Traditional analyses rely on Higgs couplings to massive vector bosons, which are suppressed for $CP$-odd couplings, so that these analyses have limited sensitivity. Instead we focus on Higgs production in gluon fusion, which occurs at the same order in ${\ensuremath{\alpha}}_{S}$ for both $CP$-even and -odd Higgs couplings to top quarks. We study the Higgs plus two jet final state followed by Higgs decay into a pair of tau leptons. We show that using the 8 TeV data set it is possible to rule out the pure $CP$-odd hypothesis in this channel alone at nearly 95% C.L, assuming that the Higgs is $CP$-even. We also provide projected limits for the 14 TeV LHC run.

Gluon-initiated associated production boosts Higgs physics

Abstract: Analyses of boosted Higgs bosons from associated production comprise some of the main search channels for the Higgs boson at the LHC. The gluon-initiated gg→hZ subprocess has largely been ignored in phenomenological analyses of boosted associated production although this contribution is sizable as the pT spectrum for this process is maximized in the boosted regime due to the top quark loop threshold. In this paper, we discuss this contribution to boosted pp→hZ analyses in detail. We find there are previously overlooked modifications of standard model Higgs rates at the LHC which depend on the pT cuts applied and can be significant. There are also important consequences for physics beyond the standard model as the gg→hZ process introduces significant dependence on the magnitude and sign of the Higgs-top quark coupling ct, which is overlooked if it is assumed that associated production depends only on the Higgs-Z boson coupling as c2V. This new dependence on ct impacts interpretations of Higgs rates in the contexts of supersymmetry, two Higgs doublet models, and general scenarios with modified couplings. We suggest that these effects be included in current and future LHC boosted Higgs analyses.

Implications of improved Higgs mass calculations for supersymmetric models

Abstract: We discuss the allowed parameter spaces of supersymmetric scenarios in light of improved Higgs mass predictions provided by FeynHiggs 2.10.0. The Higgs mass predictions combine Feynman-diagrammatic results with a resummation of leading and subleading logarithmic corrections from the stop/top sector, which yield a significant improvement in the region of large stop masses. Scans in the pMSSM parameter space show that, for given values of the soft supersymmetry-breaking parameters, the new logarithmic contributions beyond the two-loop order implemented in FeynHiggs tend to give larger values of the light CP-even Higgs mass, [Formula: see text], in the region of large stop masses than previous predictions that were based on a fixed-order Feynman-diagrammatic result, though the differences are generally consistent with the previous estimates of theoretical uncertainties. We re-analyse the parameter spaces of the CMSSM, NUHM1 and NUHM2, taking into account also the constraints from CMS and LHCb measurements of [Formula: see text]and ATLAS searches for [Formula: see text] events using 20/fb of LHC data at 8 TeV. Within the CMSSM, the Higgs mass constraint disfavours [Formula: see text], though not in the NUHM1 or NUHM2.

Hidden sector monopole, vector dark matter and dark radiation with Higgs portal

Abstract: We show that the 't Hooft-Polyakov monopole model in the hidden sector with Higgs portal interaction makes a viable dark matter model, where monopole and massive vector dark matter (VDM) are stable due to topological conservation and the unbroken subgroup U(1 X. We show that, even though observed CMB data requires the dark gauge coupling to be quite small, a right amount of VDM thermal relic can be obtained via s-channel resonant annihilation for the mass of VDM close to or smaller than the half of SM higgs mass, thanks to Higgs portal interaction. Monopole relic density turns out to be several orders of magnitude smaller than the observed dark matter relic density. Direct detection experiments, particularly, the projected XENON1T experiment, may probe the parameter space where the dark Higgs is lighter than 50 GeV. In addition, the dark photon associated with the unbroken U(1 X contributes to the radiation energy density at present, giving Δ Neffν ~ 0.1 as the extra relativistic neutrino species.

Is the Higgs Boson Associated with Coleman-Weinberg Dynamical Symmetry Breaking?

Abstract: The Higgs mechanism may be a quantum phenomenon, i.e., a Coleman-Weinberg potential generated by the explicit breaking of scale symmetry in Feynman loops. We review the relationship of scale symmetry and trace anomalies, and we show that the Coleman-Weinberg potential can be defined as the solution to a differential renormalization group equation that follows from the trace of the improved stress tensor. We propose a simple phenomenological model with ``maximal visibility'' at the LHC containing a ``dormant'' Higgs doublet [no VEV, coupled to standard model gauge interactions $SU(2)\ifmmode\times\else\texttimes\fi{}U(1)$] with a mass of $\ensuremath{\sim}380\text{ }\text{ }\mathrm{GeV}$. We discuss the LHC phenomenology and UV challenges of such a model. We also give a schematic model in which new heavy fermions, with masses $\ensuremath{\sim}230\text{ }\text{ }\mathrm{GeV}$, can drive a Coleman-Weinberg potential at two loops. The role of the ``improved stress tensor'' is emphasized, and we propose a nongravitational term, analogous to the $\ensuremath{\theta}$ term in QCD, which generates it from a scalar action.

Double take on new physics in double Higgs boson production

Abstract: Gluon-initiated double Higgs production is the most important channel to extract the Higgs self-coupling at hadron colliders However, new physics could enter into this channel in several distinctive ways including, but not limited to, the Higgs self-coupling, a modified top Yukawa coupling, and an anomalous Higgs-top quartic coupling In this work we initiate a study on the interplay of these effects in the kinematic distributions of the Higgs bosons More specifically, we divide the ${p}_{T}$ and the total invariant mass spectra into two bins and use the differential rates in each bin to constrain the magnitude of the aforementioned effects Significantly improved results could be obtained over those using the total cross section alone However, some degeneracy remains, especially in the determination of the Higgs trilinear coupling Therefore, an accurate measurement of the Higgs self-coupling in this channel would require precise knowledge of the magnitudes of other new physics effects We base our analysis on a future $pp$ collider at $\sqrt{s}=100\text{ }\text{ }\mathrm{TeV}$

Confronting Higgcision with Electric Dipole Moments

Abstract: Current data on the signal strengths and angular spectrum of the 125.5 GeV Higgs boson still allow a CP-mixed state, namely, the pseudoscalar coupling to the top quark can be as sizable as the scalar coupling: C ≈ C = 1/2. CP violation can then arise and manifest in sizable electric dipole moments (EDMs). In the framework of two-Higgs-doublet models, we not only update the Higgs precision (Higgcision) study on the couplings with the most updated Higgs signal strength data, but also compute all the Higgs-mediated contributions from the 125.5 GeV Higgs boson to the EDMs, and confront the allowed parameter space against the existing constraints from the EDM measurements of Thallium, neutron, Mercury, and Thorium monoxide. We found that the combined EDM constraints restrict the pseudoscalar coupling to be less than about 10−2, unless there are contributions from other Higgs bosons, supersymmetric particles, or other exotic particles that delicately cancel the current Higgs-mediated contributions.

Resolving the Higgs-gluon coupling with jets.

Abstract: In the Standard Model, the Higgs coupling to gluons is almost entirely induced by top quark loops. We derive the logarithmic structure of Higgs production in association with two jets. Just like in the one-jet case, the transverse momentum distributions exhibit logarithms of the top quark mass and can be used to test the nature of the loop–induced Higgs coupling to gluons. Using Higgs decays to W bosons and to tau leptons, we show how the corresponding analyses hugely benefit from the second jet in the relevant signal rate as well as in the background rejection.

Higgs precision analysis updates 2014

Abstract: During the 2014 summer conferences, both the ATLAS and CMS Collaborations of the LHC experiments have demonstrated tremendous efforts in treatment of data and processing more data such that most data on signal strengths have improved, especially the diphoton and fermionic modes of both experiments. Here in this paper we perform an update to our previous model-independent Higgs precision analysis---Higgcision. We found the following: (i) the uncertainties on most couplings shrink about 10%--20%, (ii) the nonstandard (e.g. invisible) decay branching ratio of the Higgs boson is constrained to be less than 19% if only the width is allowed to vary, (iii) the gauge-Higgs coupling ${C}_{v}$ is constrained to be ${0.94}_{\ensuremath{-}0.12}^{+0.11}$, in which the uncertainty is reduced by about 10%, and (iv) the standard model (SM) Higgs boson still provides the best fit to all the Higgs boson data, and compared to the previous results the SM Higgs boson now enjoys a higher $p$ value than the last year.

h → Zγ in the complex two Higgs doublet model

Abstract: The latest LHC data confirmed the existence of a Higgs-like particle and made interesting measurements on its decays into γγ, ZZ *, W W *, τ + τ − , and $$ b\overline{b} $$ . It is expected that a decay into Zγ might be measured at the next LHC round, for which there already exists an upper bound. The Higgs-like particle could be a mixture of scalar with a relatively large component of pseudoscalar. We compute the decay of such a mixed state into Zγ, and we study its properties in the context of the complex two Higgs doublet model, analysing the effect of the current measurements on the four versions of this model. We show that a measurement of the h → Zγ rate at a level consistent with the SM can be used to place interesting constraints on the pseudoscalar component. We also comment on the issue of a wrong sign Yukawa coupling for the bottom in Type II models.

Supersymmetric subelectroweak scale dark matter, the Galactic Center gamma-ray excess, and exotic decays of the 125 GeV Higgs boson

Abstract: We continue our exploration of the nearly Peccei-Quinn symmetric limit shared by common singlet extensions of the minimal supersymmetric standard model. This limit has been established as a viable framework for studying subelectroweak scale dark matter phenomenology and has interesting and direct connections to new exotic Higgs decay physics. We present analytic calculations to motivate the important phenomenological features mentioned above. We also discuss benchmark points in this model framework that accommodate the observed Galactic center gamma-ray excess. We emphasize connections between phenomenology of dark matter direct detection and indirect detection, and new exotic decay channels for the 125 GeV Higgs boson. We conclude by identifying two benchmark modes of exotic Higgs decays for $h\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}{\overline{)E}}_{\mathrm{T}}$ and $h\ensuremath{\rightarrow}b\overline{b}{\overline{)E}}_{\mathrm{T}}$ final states and estimate their sensitivity prospects at the LHC.

Minimal semi-annihilating $\mathbb{Z}_N$ scalar dark matter

Abstract: We study the dark matter from an inert doublet and a complex scalar singlet stabilized by Z{sub N} symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for N > 2. We consider explicitly the Z{sub 3} and Z{sub 4} cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak Z{sub N} preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

A light pseudoscalar of 2HDM confronted with muon g-2 and experimental constraints

Abstract: A light pseudoscalar of the lepton-specific 2HDM can enhance the muon g-2, but suffer from various constraints easily, such as the 125.5 GeV Higgs signals, non-observation of additional Higgs at the collider and even $B_s\to \mu^+\mu^-$. In this paper, we take the light CP-even Higgs as the 125.5 GeV Higgs, and examine the implications of those observables on a pseudoscalar with the mass below the half of 125.5 GeV. Also the other relevant theoretical and experimental constraints are considered. We find that the pseudoscalar can be allowed to be as low as 10 GeV, but the corresponding $\tan\beta$, $\sin(\beta-\alpha)$ and the mass of charged Higgs are strongly constrained. In addition, the surviving samples favor the wrong-sign Yukawa coupling region, namely that the 125.5 GeV Higgs couplings to leptons have opposite sign to the couplings to gauge bosons and quarks.

Higgs boson mass in the standard model at two-loop order and beyond

Abstract: We calculate the mass of the Higgs boson in the Standard Model in terms of the underlying Lagrangian parameters at complete 2-loop order with leading 3-loop corrections. A computer program implementing the results is provided. The program also computes and minimizes the Standard Model effective potential in Landau gauge at 2-loop order with leading 3-loop corrections.

Higgs couplings: disentangling new physics with off-shell measurements.

Abstract: After the discovery of a scalar resonance, resembling the Higgs boson, its couplings have been extensively studied via the measurement of various production and decay channels on the invariant mass peak. Recently, the possibility of using off-shell measurements has been suggested: in particular, the CMS Collaboration has published results based on the high-invariant mass cross section of the process $gg\ensuremath{\rightarrow}ZZ$, which contains a contribution from the Higgs boson. While this measurement has been interpreted as a constraint on the Higgs width after very specific assumptions are taken on the Higgs couplings, in this Letter, we show that a much more model-independent interpretation is possible.