P. Bechtle, O. Brein, S. Heinemeyer, G. Weiglein, K. Williams
We review the program HiggsBounds that tests theoretical predictions of models with arbitrary Higgs sectors against the exclusion bounds obtained from the Higgs searches at LEP and the Tevatron. We explicitly list the bounds that have been added after the first release of HiggsBounds.
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HiggsBounds is a computer code which tests the Higgs sectors of new models against the current exclusion bounds from the Higgs searches at LEP and the Tevatron. As input, it requires a selection of model predictions, such as Higgs masses, branching ratios, effective couplings and total decay widths. HiggsBounds then uses the expected and observed topological cross section limits from the Higgs searches to determine which points in the parameter space have already been excluded at 95% CL. HiggsBounds will be updated to include new results as they become available.
We describe the new developments in version 4 of the public computer code HiggsBounds. HiggsBounds is a tool to test models with arbitrary Higgs sectors, containing both neutral and charged Higgs bosons, against the published exclusion bounds from Higgs searches at the LEP, Tevatron and LHC experiments. From the model predictions for the Higgs masses, branching ratios, production cross sections and total decay widths - which are specified by the user in the input for the program - the code calculates the predicted signal rates for the search channels considered in the experimental data. The si…
HiggsBounds is a computer code that tests theoretical predictions of models with arbitrary Higgs sectors against the exclusion bounds obtained from the Higgs searches at LEP and the Tevatron. The included experimental information comprises exclusion bounds at 95% C.L. on topological cross sections. In order to determine which search topology has the highest exclusion power, the program also includes, for each topology, information from the experiments on the expected exclusion bound, which would have been observed in case of a pure background distribution. Using the predictions of the desired …
HiggsBounds 2.0.0 is a computer code which tests both neutral and charged Higgs sectors of arbitrary models against the current exclusion bounds from the Higgs searches at LEP and the Tevatron. As input, it requires a selection of model predictions, such as Higgs masses, branching ratios, effective couplings and total decay widths. HiggsBounds 2.0.0 then uses the expected and observed topological cross section limits from the Higgs searches to determine whether a given parameter scenario of a model is excluded at the 95% C.L. by those searches. Version 2.0.0 represents a significant extension …
We introduce version 2.0.0 of the computer program HiggsBounds. The program tests neutral and charged Higgs sectors of new models against the current exclusion bounds from LEP and the Tevatron. As input, it requires a selection of model predictions, such as Higgs masses, branching ratios, effective couplings and total decay widths. The program then uses the expected and observed topological cross section limits from the Higgs searches to determine whether a given parameter scenario of a model is excluded at the 95% C.L. by those searches. Version 2.0.0 includes 39/53 LEP/Tevatron Higgs search …
We report on recent developments in the public computer code HiggsBounds, which confronts arbitrary Higgs sector predictions with 95% C.L. exclusion limits from Higgs searches at the LEP, Tevatron and LHC experiments. We discuss in detail the performance of the Standard Model (SM) likeness test as implemented in the latest version HiggsBounds-3.8.0, whose outcome decides whether a search for a SM Higgs boson can be applied to a model beyond the SM. Furthermore, we give a preview of features in the upcoming version HiggsBounds-4.0.0 and the new program HiggsSignals, which performs a chi-squared…
The program HiggsBounds is a well-established tool for testing Beyond-the-Standard Model (BSM) theories with an extended Higgs sector against experimental limits from collider searches at LEP, Tevatron and LHC. Thus far, it could be applied to any neutral or charged Higgs bosons originating from the modified Higgs sector. Implicitly, these particles were assumed to exhibit a somewhat hierarchical Yukawa structure as present in the Standard Model, where in particular the couplings to first generation fermions could be neglected. In this work, we extend the HiggsBounds functionalities to go beyo…
I briefly review the progress in perturbative QCD calculations in LEP era and discuss the prospects for the extension of their accuracy to higher orders.
A completely model-independent method of obtaining information on the spin using the quantum interference effect among various helicity states was proposed in a recent paper. Here we point out that this effect should be demonstrable in the existing data on e^-e^+ \to W^+ W^- at LEP-II and p \bar{p} \to Z^0 + j at Tevatron.
A complete set of dimension-6 effective contact interactions involving Higgs, gauge bosons and quarks is studied. Limits on the coefficients of these new operators are obtained from the experimental values of the $Z$ and $W$ gauge bosons widths.
HiggsSignals is a Fortran90 computer code that allows to test the compatibility of Higgs sector predictions against Higgs rates and masses measured at the LHC or the Tevatron. Arbitrary models with any number of Higgs bosons can be investigated using a model-independent input scheme based on HiggsBounds. The test is based on the calculation of a chi-squared measure from the predictions and the measured Higgs rates and masses, with the ability of fully taking into account systematics and correlations for the signal rate predictions, luminosity and Higgs mass predictions. It features two complem…
We point out that charged Higgs bosons can decay into final states different than $τ^+ ν_τ$ and $c \bar{s}$, even when they are light enough to be produced at LEPII or at the Tevatron, through top-quark decays. These additional decay modes are overlooked in ongoing searches even though they alter the existing lower bounds on the mass of charged Higgs bosons that are present in supersymmetric and two Higgs doublets models.
I present a brief review of prospects for discovering supersymmetry, focusing primarily on the Tevatron and LEPII, but commenting on the LHC and a next linear $\epem$ collider. Special emphasis is given to expectations in the context of models with GUT boundary conditions motivated by Supergravity and Superstrings. An overview of related conference contributions is given.
If the $R_b$ excess at LEP is real, then any explanation in terms of renormalizable loop corrections leads to important new decay modes of the $t$ quark and suppresses the $t \to bW$ branching ratio. In the two-Higgs-doublet model, the branching ratio of $Z \to b \bar b$ + a light boson which decays itself predominantly into $b \bar b$ is at least of order $10^{-4}$.
Using the Bose-Einstein correlations (BEC) implemented in PYTHIA we investigated a possibility of the CDF experiment at the Tevatron to see the two-particle correlations in the final state of interactions. The approach based on quantum field theory at finite temperature was applied to the ALEPH data at LEP, and the BEC important parameters were retrieved.
Searches for SUSY particles are the main physics focus of the ongoing Run IIa of the Tevatron. LEP results have constrained heavily the Minimal Supersymmetric Standard Model. In this paper the results obtained at LEP and the Tevatron Run I are analysed within two consistent scenarios: the gravity-mediated MSSM framework and the minimal SUGRA scenario. In these frameworks limits much beyond the kinematic reach of LEP are set, and the allowed mass range for particles which are not directly observable at LEP is explored. These results can be used to evaluate searches at the Tevatron Run II. Both …
If next generations of heavy quarks and leptons exist within the standard model (SM), they can manifest themselves in Higgs boson production at the Tevatron and the LHC, before being actually observed. This generation leads to an increase of the Higgs boson production cross section via gluon fusion at hadron colliders by a factor 6-9. So, the study of this process at the Tevatron and LHC can finally fix the number of generations in the SM. Using the $WW^*$ Higgs boson decay channel, the studies at the upgraded Tevatron will answer the question about the next generation for mass values 135 GeV …
We study the properties of the Higgs boson sector in the MSSM, putting special emphasis on radiative effects which can affect the discovery potential of the LHC, Tevatron and/or LEP colliders. We concentrate on the V b b-bar channel, with V=Z or W, and on the channels with diphoton final states, which are the dominant ones for the search for a light Standard Model Higgs boson at LEP/Tevatron and LHC, respectively. By analyzing the regions of parameter space for which the searches in at least one of these colliders can be particularly difficult, we demonstrate the complementarity of these three…
Within the paradigm of warped extra dimensions, third generation quarks are expected to be the most sensitive to effects beyond the Standard Model. The anomalies observed at the LEP and Tevatron colliders in the forward-backward asymmetries of the bottom (A_FB^b) and top (A_FB^t) quarks can thus be seen as early signatures of warped extra-dimensional scenarios. We propose a realization of such a scenario, with a gauge custodial symmetry in the bulk, which allows to address simultaneously the A_FB^b anomaly and the discrepancies observed recently on A_FB^t at high top quark rapidities and ttbar…
We study extensions of the Standard Model where the Higgs boson dominantly decays via a cascade to four tau leptons, and discuss whether this decay is visible at the Tevatron. We find that with an integrated luminosity of 6 fb^-1, there can be excesses in multi-lepton events in several channels for a Higgs boson of a mass = 110 GeV.
Luminosity upgrades of the Fermilab Tevatron pbar-p collider have been shown to allow experimental detection of a Standard Model (SM) Higgs boson up to $m_{H_{SM}}\sim 120$ GeV via $WH_{SM} \to \ellνb\bar{b}$ events. This limit nearly saturates the parameter space for many models of weak scale supersymmetry (SUSY) with a minimal particle content. It is therefore interesting to examine the SUSY Higgs reach of future Tevatron experiments. Contours are presented of Higgs boson reach for CERN LEP2 and Tevatron luminosity upgrades for three models of weak scale SUSY: the Minimal Supersymmetric Stan…
We explore the ability of the Tevatron to probe Minimal Supersymmetry with high energy scale boundary conditions motivated by supersymmetry breaking in the context of supergravity/superstring theory. A number of boundary condition possibilities are considered: dilaton-like string boundary conditions applied at the standard GUT unification scale or alternatively at the string scale; and extreme (``no-scale'') minimal supergravity boundary conditions imposed at the GUT scale or string scale. For numerous specific cases within each scenario the sparticle spectra are computed and then fed into ISA…
We explore the prospects for detection of sparticles and Higgs bosons at the Tevatron, LEP-200 and the LHC in the allowed parameter space of a `yukawa unified' ($λ_b(M_U)=λ_τ(M_U)$) minimal supergravity (YUMS) model, where the only non-zero unification scale soft-SUSY-breaking terms are a universal gaugino mass and a Higgs mixing term. In a bottom-up approach, just two weak scale parameters, $\tanb$ and $\mha$, (along with the sign of the Higgs mixing parameter $μ$) completely parameterize the model. Many interesting `special' situations regarding sparticle and Higgs discovery arise, such as t…
During the last few years the Tevatron has dramatically improved the bounds on rare B-meson decays into two leptons. In the case of B_s --> mu+ mu-, the current bound is only ten times greater than the Standard Model expectation. Sensitivity to this decay is one of the benchmark goals for LHCb performance and physics. The Higgs penguin dominates this rate in the region of large tan(beta) of the MSSM. This is not necessarily the case in the region of low tan(beta), since box and Z-penguin diagrams may contribute at a comparable rate. In this article, we compute the complete one-loop MSSM contri…
We study the constraints on the Lee-Wick Higgs sector arising from direct collider searches. We work in an effective-field theory framework, where all of the Lee-Wick partners are integrated out, with the sole exception of the Lee-Wick Higgs bosons. The resulting theory is a two-Higgs doublet model where the second doublet has wrong-sign kinetic and mass terms. We include the bounds coming from direct Higgs searches at both LEP and Tevatron using the code HiggsBounds, and show the currently excluded parameter space. We also analyze the prospects of LHC Run-I, finding that with a total integrat…
Over the last years the Tevatron Run-II has extended several limits on Higgs boson masses and coupling which were pioneered during the LEP accelerator operation between 1989 and 2000. Higgs boson searches will also be at the forefront of research at the LHC. This review concisely discusses the experimental constraints set by the CDF and D0 collaborations in winter 2008/2009 at the beginning of the LHC era. Model-independent and model-dependent limits on Higgs boson masses and couplings have been set and interpretations are discussed both in the Standard Model and in extended models. Recently, …
If $c$ and $t$ quarks are strongly mixed with a weak singlet charge $2/3$ quark, $BR(t\to \ellν+ X)$ could be suppressed via the $t\to cH^0$ mode, thereby the top quark could still hide below $M_W$, whereas the heavy quark signal observed at the Tevatron is due to the dominantly singlet quark $Q$. This may occur without affecting the small $m_c$ value. Demanding $m_Q \simeq 175$ GeV and $m_t \ltap M_W$, we find that $BR(t\to \ellν+ X)$ cannot be too suppressed. The heavy quark $Q$ decays via $W,\ H$, and $Z$ bosons. The latter can lead to $b$-tagged $Z + 4$ jet events, while the strong $c$--$Q…
Data from HERA, LEP and the Tevatron, as well as from low energy experiments are used to constrain the scale of possible electron-quark contact interactions. Different models are considered, including the most general one, in which all new couplings can vary independently. Limits on couplings and mass scales are extracted and upper limits on possible effects to be observed in future HERA, LEP and Tevatron running are estimated. Total hadronic cross-section at LEP and e-p scattering cross-section at HERA are strongly constrained by existing data, whereas large cross-section deviations are still…
Limits are derived on models with extended Higgs sectors, including the Minimal Supersymmetric Standard Model (MSSM), by exploiting the data on $τ^+ τ^- + $ 2 jets final states, used by the CDF collaboration to place limits on third generation leptoquarks. The main observation here is that both leptoquark production and associated $b \bar{b}$ Higgs production can lead to $b \bar{b} τ^+ τ^-$ final states.
We analyze the prospect for observing the intermediate neutral Higgs ($h_2$) boson in its decay to two lighter Higgs bosons ($h_1$) at the Tevatron in the framework of the CP violating MSSM using the PYTHIA event generator. We consider the lepton+ 4-jets+ $\met$ channel from $p \bar p \ra W h_2 \ra W h_1 h_1 \ra l ν_l b \bar b b\bar b$, with two or three tagged $b$ jets. We found that it is very hard to observe this signature in the LEP-allowed region of parameter space, due to the small signal efficiency.
n this letter we investigate the various processes that can contribute to a final state consisting of a lepton, missing transverse momentum and two jets at Next to Leading Order (NLO) at the Tevatron. In particular we consider the production of W/Z + 2 jets, diboson pairs, single top and the tt process with both fully leptonic and semi-leptonic decays. We present distributions for the invariant mass of the dijet system and normalisations of the various processes, accurate to NLO.
We study the Higgs boson decay to W+W-, where one boson decays to leptons, and the other decays to c+jet at Tevatron. Given the current charm tagging acceptances, this channel can help improve and confirm the current combined Tevatron exclusion limit on a standard model-like Higgs boson. If charm acceptance can be improved to at least 24%, this channel could provide the second tightest limits on a Higgs boson mass between 140-190 GeV from a single channel measurement.
We analyze the signal at the Tevatron for the doubly charged Higgs superfield of supersymmetric left-right models with gauge mediated supersymmetry breaking. Due to the presence of a new coupling, the lighter stau is usually less massive than the lightest neutralino and is frequently the NLSP. The fermionic part of the doubly charged Higgs field decays dominantly into two tau leptons plus missing energy (gravitino). We find that the inclusive two tau jets and three tau jets plus missing energy signatures could be observable at Run II of the Tevatron. We also find that the distribution in angle…
We investigate the potentiality of CERN LEP and Fermilab Tevatron colliders to establish bounds on new couplings involving the bosonic sector of the standard model. A combined exclusion plot for the coefficients of different dimension-6 anomalous operators is presented. We also discuss the sensitivity that can be achieved at the upgraded Tevatron.
The top quark data in the lepton plus $τ$ channel offers a viable probe for the charged Higgs boson signal. We analyse the recent Tevatron collider data in this channel to obtain a significant limit on the $H^\pm$ mass in the large $\tanβ$ region.
The model-independent constraints on the Abelian Z' couplings from the LEP data are applied to estimate the Z' production in experiments at the Tevatron and LHC. The Z' total and partial decay widths are analyzed. The results are compared with model-dependent predictions and present experimental data from the Tevatron. If we assume the 1-2sigma hints from the LEP data to be a signal of the Abelian Z' boson, then the Tevatron data constrain the Z' mass between 400 GeV and 1.2 TeV.
We analyze the prospects for discovering supersymmetry at the Fermilab Tevatron and CERN LEP colliders in the scenario that the lightest supersymmetric particle is a gravitino of mass < 1 keV. We consider in particular the case that the lightest neutralino has a nearly 100% branching fraction into gravitino + photon within the detector. This implies that supersymmetric events should contain both missing (transverse) energy and two energetic photons. Therefore one can search for supersymmetry simply through inclusive production of superpartners. We consider the exclusion and reach capabilities …
Recently, several astrophysical data or would-be signals has been observed in different dark-matter oriented experiments. In each case, one could fit the data at the price of specific nature of the coupling between the Standard Model (SM) particles and a light Dark Matter candidate: hadrophobic (INTEGRAL, PAMELA) or leptophobic (WMAP Haze, dijet anomalies of CDF, FERMI Galactic Center observation). In this work, we show that when one takes into account the more recent LEP and Tevatron analysis, a light thermal fermionic Dark Matte (\lesssim 10 GeV) that couples to electrons is mainly ruled out…
We analyze the prospect for observing the intermediate neutral Higgs boson ($h_2$) in its decay to two lighter Higgs bosons ($h_1$) at the presently operating hadron colliders in the framework of the CP violating MSSM using the PYTHIA event generator. We consider the lepton+ 4-jets+ $\met$ channel from associate $W h_2$ production, with $W h_2 \ra W h_1 h_1 \ra \ell ν_\ell b \bar b b\bar b$. We require two or three tagged $b$-jets. We explicitly consider all relevant Standard Model backgrounds, treating $c$-jets separately from light flavor and gluon jets and allowing for mistagging. We find t…
Z' bosons that couple preferentially to the third generation fermions can arise in models with extended weak (SU(2)xSU(2)) or hypercharge (U(1)xU(1)) gauge groups. We show that existing limits on quark-lepton compositeness set by the LEP and Tevatron experiments translate into lower bounds of order a few hundred GeV on the masses of these Z' bosons. Resonances of this mass can be directly produced at the Tevatron. Accordingly, we explore in detail the limits that can be set at Run II using the process p pbar -> Z' -> tau tau -> e mu. We also comment on the possibility of using hadronically-dec…
A review of searches for physics beyond the Standard Model carried out at high energy lepton-hadron and hadron-hadron facilities is presented, with emphasis on topics of interest for future data taking at the upgraded Tevatron $p{\bar p}$ and HERA $ep$ colliders. The status and discovery prospects are discussed for leptoquarks, Technicolour and supersymmetry, forbidden lepton and quark flavour-changing processes, extra gauge bosons, excited states of composite fermions, generic contact interactions and extra compactified dimensions.
We perform a joint analysis of the prediction of composite Higgs models for the discrepancies of the forward-backward asymmetries of top and bottom quarks at Tevatron and LEP+SLC, respectively. We build a two sector model which can be thought as an effective low energy description of 5D warped models and choose the quantum numbers of the fermionic resonances to protect the Z-couplings of the partially composite Standard Model light quarks. We analyze the cross section, forward-backward asymmetry and invariant mass distribution of the top anti-top production at Tevatron, as well as the bottom f…
The Higgs and some of the Standard Model superpartners may have been copiously produced at LEP and the Tevatron without being detected. We study a novel scenario of this type in which the Higgs decays predominantly into a light hidden sector either directly or through light SUSY states. Subsequent cascades increase the multiplicity of hidden sector particles which, after decaying back into the Standard Model, appear in the detector as clusters of collimated leptons known as lepton jets. We identify the relevant collider observables that characterize this scenario, and study a wide range of LEP…
The mixing of a new $Z'$ boson with the $Z$ significantly improves the fit to the LEP precision electroweak data, provided that the $Z'$ couples mainly to quarks. If $M_{Z_2}<200$~GeV, the $s$-channel $Z_2$ production and $(W,Z,γ)Z_2$ pair production cross sections at the Tevatron give an excess above QCD of $b\bar b$ and $(W,Z,γ)b\bar b$ events, respectively, with invariant mass $m(b\bar b)\approx M_{Z_2}$, which provide viable signals for detection of the $Z_2$. The interference of the $Z_2$ with $γ,Z_1$ in $e^+e^-\to \bar bb(\bar cc)$ at LEP\,1.5 energies is correlated with $R_b(R_c)$ and m…
We analyze the accelerator constraints on the parameter space of the Minimal Supersymmetric extension of the Standard Model, comparing those now available from LEP II and anticipating the likely sensitivity of Tevatron Run II. The most important limits are those from searches for charginos, neutralinos and Higgs bosons at LEP, and searches for stop squarks, charginos and neutralinos at the Tevatron Collider. We also incorporate the constraints derived from b --> s + gamma decay, and discuss the relevance of charge- and colour-breaking minima in the effective potential. We combine and compare t…
It has been recently shown that the observed baryon number may originate at the electroweak phase transition, provided that the Higgs boson and the lightest stop are sufficiently light. In this work, we perform a detailed analysis, including all dominant two-loop finite temperature corrections to the Higgs effective potential, as well as the non-trivial effects proceeding from the mixing in the stop sector, to define the region of parameter space for which electroweak baryogenesis can happen. The limits on the stop and Higgs masses are obtained by taking into account the experimental bounds on…
Recent Tevatron exclusion interval of the masses of Higgs boson considerably reduces in case of the light quasistable fourth generation neutral lepton.
We examine the scenario where a leptophobic Z' boson accounts for the excess of events in the Wjj channel as observed by CDF. We assume generation independent couplings for the Z' and obtain allowed regions for the four hadronic couplings using the cross section range quoted by CDF as well as constraints from dijet production at UA2. These coupling regions translate into well-determined rates for the associated production of Z/γ+Z' at the Tevatron and LHC, as well as W+Z' at the LHC,that are directly correlated with the Wjj rate observed at the Tevatron. The Wjj rate at the LHC is large and th…
We analyze the prospect for observing the intermediate neutral Higgs boson ($h_2$) in its decay to two lighter Higgs bosons ($h_1$) at the presently operating hadron colliders in the framework of the CP violating MSSM using the PYTHIA event generator. We consider the lepton+ 4-jets+ $\met$ channel from associate $W h_2$ production, with $W h_2 \ra W h_1 h_1 \ra \ell ν_\ell b \bar b b\bar b$. We require two, three or four tagged $b$-jets. We explicitly consider all relevant Standard Model backgrounds, treating $c$-jets separately from light flavor and gluon jets and allowing for mistagging. We …
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