Higgs Discovery Research Articles

Electroweak and supersymmetry breaking from the Higgs boson discovery

We will explore the consequences on the electroweak breaking condition, the mass of supersymmetric partners and the scale at which supersymmetry breaking is transmitted, for arbitrary values of the supersymmetric parameters $\mathrm{tan}\ensuremath{\beta}$ and the stop mixing ${X}_{t}$, which follow from the Higgs discovery with a mass ${m}_{H}\ensuremath{\simeq}126\text{ }\mathrm{GeV}$ at the LHC. Within the present uncertainty on the top quark mass we deduce that radiative breaking requires $\mathrm{tan}\ensuremath{\beta}\ensuremath{\gtrsim}8$ for maximal mixing ${X}_{t}\ensuremath{\simeq}\sqrt{6}$, and $\mathrm{tan}\ensuremath{\beta}\ensuremath{\gtrsim}20$ for small mixing ${X}_{t}\ensuremath{\lesssim}1.8$. The scale at which supersymmetry breaking is transmitted $\mathcal{M}$ can be of order the unification or Planck scale only for large values of $\mathrm{tan}\ensuremath{\beta}$ and negligible mixing ${X}_{t}\ensuremath{\simeq}0$. On the other hand for maximal mixing and large values of $\mathrm{tan}\ensuremath{\beta}$ supersymmetry should break at scales as low as $\mathcal{M}\ensuremath{\simeq}{10}^{5}\text{ }\mathrm{GeV}$. The uncertainty in those predictions stemming from the uncertainty in the top quark mass, i.e. the top Yukawa coupling, is small (large) for large (small) values of $\mathrm{tan}\ensuremath{\beta}$. In fact for $\mathrm{tan}\ensuremath{\beta}=1$ the uncertainty on the value of $\mathcal{M}$ is several orders of magnitude.

Probing the high scale SUSY in CP violations of K, [formula omitted] and [formula omitted] mesons

We probe the high scale SUSY at 10–50 TeV in the CP violations of K, B0 and Bs mesons. In order to estimate the contribution of the squark flavor mixing to these CP violations, we discuss the squark mass spectrum, which is consistent with the recent Higgs discovery. Taking the universal soft parameters at the SUSY breaking scale, we obtain the squark mass spectrum at 10 TeV and 50 TeV, where the SM emerges. Then, the 6×6 mixing matrix between down-squarks and down-quarks is discussed by input of the experimental data of K, B0 and Bs mesons. It is found that ϵK is most sensitive to the high scale SUSY. The SUSY contributions for the time-dependent CP asymmetries SJ/ψKS and SJ/ψϕ are 6–8% at the SUSY scale of 10 TeV. We also discuss the SUSY contribution to the chromo-EDM of the strange quark.

Cornering a hyper Higgs boson: Angular kinematics for boosted Higgs bosons with top pairs

In the wake of the Higgs discovery and over the long haul of the LHC run, one should keep a lookout for kinematic anomalies in the most massive known trio of coupled particles, $t\overline{t}h$. After surveying the scope of prior constraints on chromomagnetic dipole and Higgs-gluon kinetic couplings, we focus on surpluses of boosted-${p}_{T}$ Higgs bosons fomented by these momentum-dependent dimension-six operators in $t\overline{t}h$ final states. We uncover a number of simple, ${p}_{T}$-weighted angular variables useful for discriminating Standard Model from dimension-six boosted Higgs distributions, and we make headway by arguing that one of these variables may improve the reach of existing Standard Model top-Higgs searches. The approach we take is model independent because we just consider a set of effective operators that contribute to the same three-body final state.

Supersymmetry after the Higgs discovery

P. Ramond, early years (1966-1976).- P. Fayet, The Standard Model.- I. Melzer-Pellmann (CMS), P. Pralavorio (ATLAS), Lessons for from the LHC after the first run.- J. Ellis, Supersymmetric fits after the Higgs discovery and implications for model building.- A. Djouadi, Implications of the Higgs discovery for the MSSM.- G. G. Ross, SUSY: Quo Vadis?.- R. Catena, L. Covi, SUSY dark matter(s).- H. P. Nilles, The strings connection: MSSM-like models from strings.- B. Bellazzini, C. Csaki, J. Serra, Composite Higgses.

SUSY: Quo Vadis?

Given that there is currently no direct evidence for supersymmetric particles at the LHC it is timely to re-evaluate the need for low scale supersymmetry and to ask whether it is likely to be discoverable by the LHC running at its full energy. We review the status of simple SUSY extensions of the Standard Model in the light of the Higgs discovery and the non-observation of evidence for SUSY at the LHC. The need for large radiative corrections to drive the Higgs mass up to 126 GeV and for the coloured SUSY states to be heavy to explain their non-observation introduces a little hierarchy problem and we discuss how to quantify the associated fine tuning. The requirement of low fine tuning requires non-minimal SUSY extensions and we discuss the nature and phenomenology of models which still have perfectly acceptable low fine tuning. A brief discussion of SUSY flavour-changing and CP-violation problems and their resolution is presented.

SUSY dark matter(s)

We review the status of different dark-matter candidates in the context of supersymmetric models, in particular the neutralino as a realization of the WIMP mechanism and the gravitino. We give a summary of the recent bounds in direct and indirect detection and also of the LHC searches relevant for the dark-matter question. We also discuss the implications of the Higgs discovery for the supersymmetric dark-matter models and give the prospects for the future years.

Phenomenology of the Higgs effective Lagrangian via FeynRules

The Higgs discovery and the lack of any other hint for new physics favor a description of non-standard Higgs physics in terms of an effective field theory. We present an implementation of a general Higgs effective Lagrangian containing operators up to dimension six in the framework of FeynRules and provide details on the translation between the mass and interaction bases, in particular for three- and four-point interaction vertices involving Higgs and gauge bosons. We illustrate the strengths of this implementation by using the UFO interface of FeynRules capable to generate model files that can be understood by the MadGraph 5 event generator and that have the specificity to contain all interaction vertices, without any restriction on the number of external legs or on the complexity of the Lorentz structures. We then investigate several new physics effects in total rates and differential distributions for different Higgs production modes, including gluon fusion, associated production with a gauge boson and di-Higgs production. We finally study contact interactions of gauge and Higgs bosons to fermions.

A new avenue to charged Higgs discovery in multi-Higgs models

Current searches for the charged Higgs at the LHC focus only on the $\tau\nu$, $cs$, and $tb$ final states. Instead, we consider the process $pp\to \Phi\to W^\pm H^\mp \to W^+ W^- A$ where $\Phi$ is a heavy neutral Higgs boson, $H^\pm$ is a charged Higgs boson, and $A$ is a light Higgs boson, with mass either below or above the $b\bar{b}$ threshold. The cross-section for this process is typically large when kinematically open since $H^\pm \to W^\pm A$ can be the dominant decay mode of the charged Higgs. The final state we consider has two leptons and missing energy from the doubly leptonic decay of the $W^+ W^-$ and possibly additional jets; it is therefore constrained by existing SM Higgs searches in the $W^+ W^-$ channel. We extract these constraints on the cross-section for this process as a function of the masses of the particles involved. We also apply our results specifically to a type-II two Higgs doublet model with an extra Standard-Model-singlet and obtain new and powerful constraints on $m_{H^\pm}$ and $\tan\beta$. We point out that a slightly modified version of this search, with more dedicated cuts, could be used to possibly discover the charged Higgs, either with existing data or in the future.

Massively parallel computing and the search for jets and black holes at the LHC

Massively parallel computing at the LHC could be the next leap necessary to reach an era of new discoveries at the LHC after the Higgs discovery. Scientific computing is a critical component of the LHC experiment, including operation, trigger, LHC computing GRID, simulation, and analysis. One way to improve the physics reach of the LHC is to take advantage of the flexibility of the trigger system by integrating coprocessors based on Graphics Processing Units (GPUs) or the Many Integrated Core (MIC) architecture into its server farm. This cutting edge technology provides not only the means to accelerate existing algorithms, but also the opportunity to develop new algorithms that select events in the trigger that previously would have evaded detection. In this paper we describe new algorithms that would allow us to select in the trigger new topological signatures that include non-prompt jet and black hole-like objects in the silicon tracker.

Charge and color breaking constraints in MSSM after the Higgs discovery at LHC

Abstract We revisit the constraints on the parameter space of the Minimal Supersymmetric Standard Model (MSSM), from charge and color breaking minima in the light of information on the Higgs from the LHC so far. We study the behavior of the scalar potential keeping two light sfermion fields along with the Higgs in the pMSSM framework and analyze the stability of the vacuum. We find that for lightest stops ≲ 1 TeV and small μ ≲ 500 GeV, the absolute stability of the potential can be attained only for $ \left| {{X_t}} \right|\lesssim \sqrt{{6{m_{{\widetilde{t}1}}}{m_{{\widetilde{t}2}}}}} $. The bounds become stronger for larger values of the μ parameter. Note that this is approximately the value of Xt which maximizes the Higgs mass. Our bounds on the low scale MSSM parameters are more stringent than those reported earlier in literature. We reanalyze the stau sector as well, keeping both staus. We study the connections between the observed Higgs rates and vacuum (meta)stability. We show how a precision study of the ratio of signal strengths, (μ γγ /μ ZZ ) can shed further light.

Particle Fever: A look behind the scenes of the Higgs discovery

<i>Particle Fever</i>: A look behind the scenes of the Higgs discovery

Erratum: LHC explores what LEP hinted at: CP-violating type-I 2HDM

The Large Hadron Collider is shown to have great scope for a light charged Higgs discovery, in the context of the CP-violating type-I two Higgs doublet model. This scenario with similar masses of $H^\pm$ and W was suggested by the puzzling departure from charged current lepton universality found in the LEP data. With the lightest neutral Higgs mass set to 125 GeV, the charged-neutral Higgs associated production mechanism can cause a significant excess in the $\tau \nu b \bar{b}$ events over a vast range of tan beta as long as the Higgs mixing pattern avoids a few limiting cases. Thanks to the low $H^\pm$ mass, the charged Higgs loop can play a striking role in neutral Higgs decays into $\gamma \gamma$, thereby compensating for a suppressed gluon-gluon fusion rate. The effect of scalar-pseudo-scalar mixing on loop-induced Higgs signals is also discussed.

Decoupling MSSM Higgs sector and heavy Higgs decay

The decoupling limit in the MSSM Higgs sector is the most likely scenario in light of the Higgs discovery. This scenario is further constrained by MSSM Higgs search bounds and flavor observables. We perform a comprehensive scan of MSSM parameters and update the constraints on the decoupling MSSM Higgs sector in terms of 8 TeV LHC data. We highlight the effect of light SUSY spectrum in the heavy neutral Higgs decay in the decoupling limit. We find that the chargino and neutralino decay mode can reach at most 40% and 20% branching ratio, respectively. In particular, the invisible decay mode BR(H0(A0)→χ˜10χ˜10) increases with increasing Bino LSP mass and is between 12%–15% (13%–20%) for 30<mχ˜10<100 GeV. The leading branching fraction of heavy Higgses decay into sfermions can be as large as 80% for H0→t˜1t˜1⁎ and H0/A0→τ˜1τ˜2⁎+τ˜1⁎τ˜2. The branching fractions are less than 10% for H0→h0h0 and 1% for A0→h0Z for mA>400 GeV. The charged Higgs decays to neutralino plus chargino and sfermions with branching ratio as large as 40% and 60%, respectively. Moreover, the exclusion limit of leading MSSM Higgs search channel, namely gg,bb¯→H0, A0→τ+τ−, is extrapolated to 14 TeV LHC with high luminosities. It turns out that the ττ mode can essentially exclude regime with tanβ>20 for L=300 fb−1 and tanβ>15 for L=3000 fb−1.

Dark matter and Higgs bosons in the MSSM

We investigate dark matter (DM) in the context of the minimal supersymmetric extension of the standard model (MSSM). We scan through the MSSM parameter space and search for solutions that (a) are consistent with the Higgs discovery and other collider searches; (b) satisfy the flavor constraints from $B$ physics; (c) give a DM candidate with the correct thermal relic density; and (d) are allowed by the DM direct detection experiments. For the surviving models with our parameter scan, we find the following features: (1) The DM candidate is largely a Bino-like neutralino with non-zero but less than $20\%$ Wino and Higgsino fractions; (2) The relic density requirement clearly pins down the solutions from the $Z$ and Higgs resonances ($Z,h,H,A$ funnels) and co-annihilations; (3) Future direct search experiments will likely fully cover the $Z,h$ funnel regions, and $H,A$ funnel regions as well except for the "blind spots"; (4) Future indirect search experiments will be more sensitive to the CP-odd Higgs exchange due to its $s$-wave nature; (5) The branching fraction for the SM-like Higgs decay to DM can be as high as $10\%$, while those from heavier Higgs decays to neutralinos and charginos can be as high as $20\%$. We show that collider searches provide valuable information complementary to what may be obtained from direct detections and astroparticle observations. In particular, the $Z$- and $h$-funnels with a predicted low LSP mass should be accessible at future colliders. Overall, the Higgs bosons may play an essential role as the portal to the dark sector.

Status of Y = 0 triplet Higgs with supersymmetry in the light of ∼ 125 GeV Higgs discovery

We study the $Y=0$ triplet extended supersymmetric model in the light of the recent Higgs boson discovery. We calculate full one loop Higgs mass spectrum in this model where the possible doublet-triplet mixing is considered in the charged Higgs sector. This mixing changes the prediction of $\mathcal{B}r(B_s\to X_s \gamma)$ in this model, compared to the MSSM. The constraints from the $\sim 125$ GeV Higgs along with $\mathcal{B}r(B_s\to X_s \gamma)$ are incorporated to find out the allowed parameter space. The lower bounds on the third generation squark masses coming from 125 GeV Higgs are rather week in this scenario compared to most constrained supersymmetric scenarios, e.g. a 200 GeV squark mass is still possible.

Fixing the EW scale in supersymmetric models after the Higgs discovery

TeV-scale supersymmetry was originally introduced to solve the hierarchy problem and therefore fix the electroweak (EW) scale in the presence of quantum corrections. Numerical methods testing the SUSY models often report a good likelihood L (or χ2=−2lnL) to fit the data including the EW scale itself (mZ0) with a simultaneously large fine-tuning i.e. a large variation of this scale under a small variation of the SUSY parameters. We argue that this is inconsistent and we identify the origin of this problem. Our claim is that the likelihood (or χ2) to fit the data that is usually reported in such models does not account for the χ2 cost of fixing the EW scale. When this constraint is implemented, the likelihood (or χ2) receives a significant correction (δχ2) that worsens the current data fits of SUSY models. We estimate this correction for the models: constrained MSSM (CMSSM), models with non-universal gaugino masses (NUGM) or higgs soft masses (NUHM1, NUHM2), the NMSSM and the general NMSSM (GNMSSM). For a higgs mass mh≈126 GeV, one finds that in these models δχ2/ndf⩾1.5 (≈1 for GNMSSM), which violates the usual condition of a good fit (total χ2/ndf≈1) already before fitting observables other than the EW scale itself (ndf=number of degrees of freedom). This has (negative) implications for SUSY models and it is suggested that future data fits properly account for this effect, if one remains true to the original goal of SUSY. Since the expression of δχ2 that emerges from our calculation depends on a familiar measure of fine-tuning, one concludes that fine-tuning is an intrinsic part of the likelihood to fit the data that includes the EW scale (mZ0).

Implications of the Higgs discovery for SUSY

The implications of the discovery of the Higgs boson at the LHC with a mass of approximately 125 GeV are discussed in the context of minimal supersymmetric extension of the Standard Model, the MSSM.

The health of SUSY after the Higgs discovery and the XENON100 data

We analyze the implications for the status and prospects of supersymmetry of the Higgs discovery and the last XENON data. We focus mainly, but not only, on the CMSSM and NUHM models. Using a Bayesian approach we determine the distribution of probability in the parameter space of these scenarios. This shows that, most probably, they are now beyond the LHC reach. This negative chances increase further (at more than 95% c.l.) if one includes dark matter constraints in the analysis, in particular the last XENON100 data. However, the models would be probed completely by XENON1T. The mass of the LSP neutralino gets essentially fixed around 1 TeV. We do not incorporate ad hoc measures of the fine-tuning to penalize unnatural possibilities: such penalization arises automatically from the careful Bayesian analysis itself, and allows to scan the whole parameter space. In this way, we can explain and resolve the apparent discrepancies between the previous results in the literature. Although SUSY has become hard to detect at LHC, this does not necessarily mean that is very fine-tuned. We use Bayesian techniques to show the experimental Higgs mass is at ~ 2 σ off the CMSSM or NUHM expectation. This is substantial but not dramatic. Although the CMSSM or the NUHM are unlikely to show up at the LHC, they are still interesting and plausible models after the Higgs observation; and, if they are true, the chances of discovering them in future dark matter experiments are quite high.

Confirming the LHC Higgs discovery with WW

We investigate the prospects of observing a neutral Higgs boson decaying into a pair of W bosons (one real and the other virtual), followed by the W decays into qq′ℓν or jjℓν at the CERN Large Hadron Collider (LHC). Assuming that the missing transverse energy comes solely from the neutrino in W decay, we can reconstruct the W masses and then the Higgs mass. At the LHC with a center of mass energy (s) of 8 TeV and an integrated luminosity (L) of 25 fb−1, we can potentially establish a 6σ signal. A 5σ discovery of H→WW⁎→jjℓν for s=14 TeV can be achieved with L=6 fb−1. The discovery of H→WW implies that the recently discovered new boson is a CP-even scalar if its spin is zero. In addition, this channel will provide a good opportunity to study the HWW coupling.

Global fits of the cMSSM and NUHM including the LHC Higgs discovery and new XENON100 constraints

We present global fits of the constrained Minimal Supersymmetric Standard Model (cMSSM) and the Non-Universal Higgs Model (NUHM), including the most recent CMS constraint on the Higgs boson mass, 5.8 fb−1 integrated luminosity null Supersymmetry searches by ATLAS, the new LHCb measurement of BR(B̄s → μ+μ−) and the 7-year WMAP dark matter relic abundance determination. We include the latest dark matter constraints from the XENON100 experiment, marginalising over astrophysical and particle physics uncertainties. We present Bayesian posterior and profile likelihood maps of the highest resolution available today, obtained from up to 350M points. We find that the new constraint on the Higgs boson mass has a dramatic impact, ruling out large regions of previously favoured cMSSM and NUHM parameter space. In the cMSSM, light sparticles and predominantly gaugino-like dark matter with a mass of a few hundred GeV are favoured. The NUHM exhibits a strong preference for heavier sparticle masses and a Higgsino-like neutralino with a mass of 1 TeV. The future ton-scale XENON1T direct detection experiment will probe large portions of the currently favoured cMSSM and NUHM parameter space. The LHC operating at 14 TeV collision energy will explore the favoured regions in the cMSSM, while most of the regions favoured in the NUHM will remain inaccessible. Our best-fit points achieve a satisfactory quality-of-fit, with p-values ranging from 0.21 to 0.35, so that none of the two models studied can be presently excluded at any meaningful significance level.