MSSM Parameter Space Research Articles

MSSM: cornered and correlated

Abstract Inspired by the latest results of ATLAS and CMS on the search for the standard model (SM) Higgs scalar, we discuss in this article the correlations between Higgs-boson properties, low-energy observables, such as B → X sγ, B s → μ + μ −, and (g − 2)μ, and the dark matter (DM) relic density. We focus on the corners of the MSSM parameter space where the pp → h → γγ signal is enhanced due to the presence of a light stau state. In this region tan β, M A , A t, and μ take large values, and we find striking correlations between many of the considered observables. In particular, the B → X sγ branching fraction is enhanced, while the B s → μ + μ − rate tends to be below the SM expectation. In contrast, the Higgs-boson couplings show good overall agreement with the preliminary experimental determinations, the DM abundance is consistent with observation, and the discrepancy in (g − 2) μ is reduced. The predicted deviations and found correlations could be tested in the near future and hence may become very valuable as guidelines and consistency checks.

Properties of 125 GeV Higgs boson in non-decoupling MSSM scenarios

Tantalizing hints of the Higgs boson of mass around 125 GeV have been reported at the LHC. We explore the MSSM parameter space in which the 125 GeV state is identified as the heavier of the CP even Higgs bosons, and study two scenarios where the two photon production rate can be significantly larger than the standard model (SM). In one scenario, $\Gamma(H\to \gamma\gamma)$ is enhanced by a light stau contribution, while the $WW^{\ast}$ ($ZZ^{\ast}$) rate stays around the SM rate. In the other scenario, $\Gamma(H\to b\bar{b})$ is suppressed and not only the $\gamma\gamma$ but also the $WW^{\ast}$ ($ZZ^{\ast}$) rates should be enhanced. The $\tau\bar{\tau}$ rate can be significantly larger or smaller than the SM rate in both scenarios. Other common features of the scenarios include top quark decays into charged Higgs boson, single and pair production of all Higgs bosons in $e^+e^-$ collisions at $\sqrt{s}\lesssim 300$ GeV.

On the NLO QCD corrections to the production of the heaviest neutral Higgs scalar in the MSSM

We present a calculation of the two-loop top-stop-gluino contributions to Higgs production via gluon fusion in the MSSM. By means of an asymptotic expansion in the heavy particle masses, we obtain explicit and compact analytic formulae that are valid when the Higgs and the top quark are lighter than stops and gluino, without assuming a specific hierarchy between the Higgs mass and the top mass. Being applicable to the heaviest Higgs scalar in a significant region of the MSSM parameter space, our results complement earlier ones obtained with a Taylor expansion in the Higgs mass, and can be easily implemented in computer codes to provide an efficient and accurate determination of the Higgs production cross section.

Bayesian implications of current LHC and XENON100 search limits for the CMSSM

The CMS Collaboration has released the results of its search for supersymmetry, by applying an ${\ensuremath{\alpha}}_{T}$ method to $1.1/\mathrm{fb}$ of data at 7 TeV. The null result excludes (at 95% C.L.) a low-mass region of the Constrained MSSM's parameter space that was previously favored by other experiments. Additionally, the negative result of the XENON100 dark matter search has excluded (at 90% C.L.) values of the spin-independent scattering cross sections ${\ensuremath{\sigma}}_{p}^{\mathrm{SI}}$ as low as ${10}^{\ensuremath{-}8}\text{ }\text{ }\mathrm{pb}$. We incorporate these improved experimental constraints into a global Bayesian fit of the Constrained MSSM by constructing approximate likelihood functions. In the case of the ${\ensuremath{\alpha}}_{T}$ limit, we simulate detector efficiency for the CMS ${\ensuremath{\alpha}}_{T}1.1/\mathrm{fb}$ analysis and validate our method against the official 95% C.L. contour. We identify the 68% and 95% credible posterior regions of the CMSSM parameters, and also find the best-fit point. We find that the credible regions change considerably once a likelihood from ${\ensuremath{\alpha}}_{T}$ is included, in particular, the narrow light Higgs resonance region becomes excluded, but the focus point/horizontal branch region remains allowed at the $1\ensuremath{\sigma}$ level. Adding the limit from XENON100 has a weaker additional effect, in part due to large uncertainties in evaluating ${\ensuremath{\sigma}}_{p}^{\mathrm{SI}}$, which we include in a conservative way, although we find that it reduces the posterior probability of the focus point region to the $2\ensuremath{\sigma}$ level. The new regions of high posterior favor squarks lighter than the gluino and all but one Higgs bosons heavy. The dark matter neutralino mass is found in the range $250\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{\ensuremath{\chi}}\ensuremath{\lesssim}343\text{ }\text{ }\mathrm{GeV}$ (at $1\ensuremath{\sigma}$) while, as the result of improved limits from the LHC, the favored range of ${\ensuremath{\sigma}}_{p}^{\mathrm{SI}}$ is pushed down to values below ${10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{pb}$. We highlight tension between $\ensuremath{\delta}(g\ensuremath{-}2{)}_{\ensuremath{\mu}}^{\mathrm{SUSY}}$ and $\mathcal{B}\mathcal{R}(\overline{B}\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma})$, which is exacerbated by including the ${\ensuremath{\alpha}}_{T}$ limit; each constraint favors a different region of the CMSSM's mass parameters.

Upper Bounds on Superpartner Masses from Upper Bounds on the Higgs Boson Mass

The LHC is putting bounds on the Higgs boson mass. In this Letter we use those bounds to constrain the minimal supersymmetric standard model (MSSM) parameter space using the fact that, in supersymmetry, the Higgs mass is a function of the masses of sparticles, and therefore an upper bound on the Higgs mass translates into an upper bound for the masses for superpartners. We show that, although current bounds do not constrain the MSSM parameter space from above, once the Higgs mass bound improves big regions of this parameter space will be excluded, putting upper bounds on supersymmetry (SUSY) masses. On the other hand, for the case of split-SUSY we show that, for moderate or large tanβ, the present bounds on the Higgs mass imply that the common mass for scalars cannot be greater than 10(11) GeV. We show how these bounds will evolve as LHC continues to improve the limits on the Higgs mass.

Search for Neutral Minimal Supersymmetric Standard Model Higgs Bosons Decaying to Tau Pairs Produced in Association withbQuarks inpp¯Collisions ats=1.96 TeV

We report results from a search for neutral Higgs bosons produced in association with b quarks using data recorded by the D0 experiment at the Fermilab Tevatron Collider and corresponding to an integrated luminosity of 7.3 fb(-1). This production mode can be enhanced in several extensions of the standard model (SM) such as in its minimal supersymmetric extension (MSSM) at high tanβ. We search for Higgs bosons decaying to tau pairs with one tau decaying to a muon and neutrinos and the other to hadrons. The data are found to be consistent with SM expectations, and we set upper limits on the cross section times branching ratio in the Higgs boson mass range from 90 to 320 GeV/c(2). We interpret our result in the MSSM parameter space, excluding tanβ values down to 25 for Higgs boson masses below 170 GeV/c(2).

Light neutralino in the MSSM: a playground for dark matter, flavor physics and collider experiments

We investigate the constraints to the light neutralino dark matter scenario in the minimal supersymmetric standard model from available experimental observations such as decays of B and K meson, relic dark matter abundance, and the search for neutralino and Higgs production at colliders. We find that two regions of the MSSM parameter space fulfill all the constraints: a fine-tuned strip with large tanβ where the lightest neutralino can be a slight as 8 GeV, and alow tanβ region providing a neutralino mass larger than 16 GeV. The large tan β strip, which can be compatible with recently reported signals from direct detection experiments, can be fully tested by means of low-energy observables and, in particular, by B s → μμ and Higgs bosons searches at the LHC within the upcoming months.

Search for Neutral Minimal Supersymmetric Standard Model Higgs Bosons Decaying to Tau Pairs inppCollisions ats=7 TeV

A search for neutral MSSM Higgs bosons in pp collisions at the LHC at a center-of-mass energy of 7 TeV is presented. The results are based on a data sample corresponding to an integrated luminosity of 36 inverse picobarns recorded by the CMS experiment. The search uses decays of the Higgs bosons to tau pairs. No excess is observed in the tau-pair invariant-mass spectrum. The resulting upper limits on the Higgs boson production cross section times branching fraction to tau pairs, as a function of the pseudoscalar Higgs boson mass, yield stringent new bounds in the MSSM parameter space.

Positrons in cosmic rays from dark matter annihilations for uplifted Higgs regions in the MSSM

We point out that there are regions in the MSSM parameter space which successfully provide a dark matter (DM) annihilation explanation for observed positron excess (e.g. PAMELA), while still remaining in agreement with all other data sets. Such regions (e.g. the uplifted Higgs region) can realize an enhanced neutralino DM annihilation dominantly into leptons via a Breit-Wigner resonance through the CP-odd Higgs channel. Such regions can give the proper thermal relic DM abundance, and the DM annihilation products are compatible with current antiproton and gamma ray observations. This scenario can succeed without introducing any additional degrees of freedom beyond those already in the MSSM.

CP violation in sbottom decays

We study CP asymmetries in two-body decays of bottom squarks into charginos and tops. These asymmetries probe the SUSY CP phases of the sbottom and the chargino sector in the Minimal Supersymmetric Standard Model. We identify the MSSM parameter space where the CP asymmetries are sizeable, and analyze the feasibility of their observation at the LHC. As a result, potentially detectable CP asymmetries in sbottom decays are found, which motivates further detailed experimental studies for probing the SUSY CP phases.

MSSM forecast for the LHC

We perform a forecast of the MSSM with universal soft terms (CMSSM) for the LHC, based on an improved Bayesian analysis. We do not incorporate ad hoc measures of the fine-tuning to penalize unnatural possibilities: such penalization arises from the Bayesian analysis itself when the experimental value of M Z is considered. This allows to scan the whole parameter space, allowing arbitrarily large soft terms. Still the low-energy region is statistically favoured (even before including dark matter or g-2 constraints). Contrary to other studies, the results are almost unaffected by changing the upper limits taken for the soft terms. The results are also remarkable stable when using flat or logarithmic priors, a fact that arises from the larger statistical weight of the low-energy region in both cases. Then we incorporate all the important experimental constrains to the analysis, obtaining a map of the probability density of the MSSM parameter space, i.e. the forecast of the MSSM. Since not all the experimental information is equally robust, we perform separate analyses depending on the group of observables used. When only the most robust ones are used, the favoured region of the parameter space contains a significant portion outside the LHC reach. This effect gets reinforced if the Higgs mass is not close to its present experimental limit and persits when dark matter constraints are included. Only when the g-2 constraint (based on e + e − data) is considered, the preferred region (for μ > 0) is well inside the LHC scope. We also perform a Bayesian comparison of the positive- and negative-μ possibilities.

Comparing the predictions of two mixed neutralino dark matter models with the recent CDMS II candidate events

We consider two optimally mixed neutralino dark matter models, based on nonuniversal gaugino masses, which were recently proposed by us to achieve WMAP compatible relic density over a large part of the MSSM parameter space. We compare the resulting predictions for the spin-independent DM scattering cross-section with the recent CDMS II data, assuming the possibility of the two reported candidate events being signal events. For one model the predicted cross-section agrees with the putative signal over a small part of the parameter space, while for the other the agreement holds over the entire WMAP compatible parameter space of the model.

Strangephilic Higgs bosons in the MSSM

We suggest a new CPX-derived scenario for the search for strangephilic MSSM Higgs bosons at the Tevatron and the LHC, in which all neutral and charged Higgs bosons decay predominantly into pairs of strange quarks and into a strange and a charm quark, respectively. The proposed scenario is realized within a particular region of the MSSM parameter space and requires large values of tan β, where threshold radiative corrections are significant to render the effective strange-quark Yukawa coupling dominant. Experimental searches for neutral Higgs bosons based on the identification of b-quark jets or τ leptons may miss a strangephilic Higgs boson and its existence could be inferred indirectly by searching for hadronically decaying charged Higgs bosons. Potential strategies and experimental challenges to search for strangephilic Higgs bosons at the Tevatron and the LHC are discussed.

Gravitino dark matter and general neutralino NLSP

We study the scenario of gravitino DM with a general neutralino NLSP in a model independent way. We consider all neutralino decay channels and compare them with the most recent BBN constraints. We check how those bounds are relaxed for a Higgsino or a Wino NLSP in comparison to the Bino neutralino case and look for possible loopholes in the general MSSM parameter space. We determine constraints on the gravitino and neutralino NLSP mass and comment on the possibility of detecting these scenarios at colliders.

SUSY at the ILC and solving the LHC inverse problem

Recently a large-scale study of points in the MSSM parameter space which are problematic at the Large Hadron Collider (LHC) has been performed. This work was carried out in part to determine whether the proposed International Linear Collider (ILC) could be used to solve the LHC inverse problem. The results suggest that while the ILC will be a valuable tool, an energy upgrade may be crucial to its success, and that, in general, precision studies of the MSSM are more difficult at the ILC than has generally been believed.

Supersymmetry, the ILC, and the LHC inverse problem

We report the results of the first large scale examination of the MSSM parameter space at the International Linear Collider (ILC). In particular, we address the question of whether or not the ILC can help to resolve the LHC Inverse Problem within this context. We examine 242 randomly generated but representative points in the MSSM parameter space which were found to lead to somewhat difficult signatures at the LHC. Including full Standard Model backgrounds and a fast detector simulation, our study finds that only roughly one third of these scenarios lead to visible signatures of some kind with a significance ⩾5 at the ILC with s=500 GeV. However, kinematically accessible charged sparticles are visible over 90% of the time. Furthermore, we examine these points in the parameter space pairwise and find that only one third of the pairs produce distinguishable signatures at the ILC at 5σ. Going to a 1 TeV center of mass energy would substantially improve this situation since the dominant limitations are kinematic in origin.

Bayesian approach and naturalness in MSSM analyses for the LHC

The start of LHC has motivated an effort to determine the relative probability of the different regions of the MSSM parameter space, taking into account the present, theoretical and experimental, wisdom about the model. Since the present experimental data are not powerful enough to select a small region of the MSSM parameter space, the choice of a judicious prior probability for the parameters becomes most relevant. Previous studies have proposed theoretical priors that incorporate some (conventional) measure of the fine-tuning, to penalize unnatural possibilities. However, we show that such penalization arises from the Bayesian analysis itself (with no ad hoc assumptions), upon the marginalization of the mu-parameter. Furthermore the resulting effective prior contains precisely the Barbieri-Giudice measure, which is very satisfactory. On the other hand we carry on a rigorous treatment of the Yukawa couplings, showing in particular that the usual practice of taking the Yukawas "as required", approximately corresponds to taking logarithmically flat priors in the Yukawa couplings. Finally, we use an efficient set of variables to scan the MSSM parameter space, trading in particular B by tan beta, giving the effective prior in the new parameters. Beside the numerical results, we give accurate analytic expressions for the effective priors in all cases. Whatever experimental information one may use in the future, it is to be weighted by the Bayesian factors worked out here.

Search for Neutral Higgs Bosons at Hightanβin theb(h/H/A)→bτ+τ−Channel

The first search in pp[over ] collisions at sqrt[s]=1.96 TeV for the production of neutral Higgs bosons in association with bottom quarks and decaying in two tau leptons is presented. The cross section for this process is enhanced in many extensions of the standard model, such as its minimal supersymmetric extension (MSSM) at large tanbeta. The data, corresponding to an integrated luminosity of 328 pb;{-1}, were collected with the D0 detector at the Fermilab Tevatron Collider. An upper limit is set on the production cross section of neutral Higgs bosons in the mass range of 90 to 150 GeV, and this limit is used to exclude part of the MSSM parameter space.

SUSY AND DARK MATTER CONSTRAINTS FROM THE LHC

The LHC will have much to say about the mysteries of dark matter, and this talk reviews this potential within the context of supersymmetry (SUSY). The SUSY search reach of CMS and ATLAS is presented, followed by a brief introduction to the methods of SUSY parameter measurement. A representative ATLAS study is then used to explain how the LHC can be used to obtain a measurement of the relic density of a neutralino WIMP candidate. Finally, the prospect of success is considered by looking at different points in the MSSM parameter space.

Perspectives for the detection and measurement of supersymmetry in the focus point region of mSUGRA models with the ATLAS detector at LHC

This paper discusses the potential of ATLAS to study supersymmetry in the “focus point” region of the parameter space of mSUGRA models. The potential to discover a deviation from standard model expectations with the first few fb-1 of LHC data was studied using the parametrized simulation of the ATLAS detector. Several signatures were considered, involving hard jets, large missing energy, and either b-tagged jets, opposite-sign isolated electron or muon pairs, or top quarks reconstructed exploiting their fully-hadronic decays. With only 1 fb-1 of data each of these signatures may allow for observing an excess of events over standard model expectations with a statistical significance exceeding five standard deviations. Furthermore, each of the two invariant mass distributions of the two leptons produced by the \(\tilde\chi^0_3\rightarrow\tilde\chi^0_1 l^+ l^-\) and the \(\tilde\chi^0_2\rightarrow\tilde\chi^0_1 l^+ l^-\) three-body decays has a kinematic endpoint that measures the difference between the masses of the parent and daughter neutralino. An analytical expression was derived for the shape of this distribution and was used to fit the simulated LHC data. A measurement of the \(\tilde\chi^0_2-\tilde\chi^0_1\) and \(\tilde\chi^0_3-\tilde\chi^0_1\) mass differences was obtained and this information was used to constrain the MSSM parameter space.