Minimal Supersymmetric Extension Of The Standard Model Parameter Research Articles

MSSM WIMPs–Nucleon cross-section for Eχ < 500GeV

Among dark matter candidates are the Weakly Interacting Massive Particles (WIMPs). Low-threshold detectors could directly detect dark matter by measuring the energy deposited by the particles. In this work, we examine the cross-section for the elastic scattering of WIMPs on nucleons, in the spin-dependent and spin-independent channels. WIMPs are taken as neutralinos in the context of the minimal super-symmetric extension of the standard model (MSSM). The dependence of the results with the adopted MSSM parameters is discussed.

Fully covering the MSSM Higgs sector at the LHC

In the context of the Minimal Supersymmetric extension of the Standard Model (MSSM), we reanalyze the search for the heavier CP-even $H$ and CP-odd $A$ neutral Higgs bosons at the LHC in their production in the gluon-fusion mechanism and their decays into gauge and lighter $h$ bosons and into top quark pairs. We show that only when considering these processes, that one can fully cover the entire parameter space of the Higgs sector of the model. Indeed, they are sensitive to the low $\tan\beta$ and high Higgs mass ranges, complementing the traditional searches for high mass resonances decaying into $\tau$-lepton pairs which are instead sensitive to the large and moderate $\tan\beta$ regions. The complementarity of the various channels in the probing of the complete $[\tan\beta, M_A]$ MSSM parameter space at the previous and upcoming phases of the LHC is illustrated in a recently proposed simple and model independent approach for the Higgs sector, the $h$MSSM, that we also refine in this paper.

Search for neutral MSSM Higgs bosons decaying to a pair of tau leptons in pp collisions

A search for neutral Higgs bosons in the minimal supersymmetric extension of the standard model (MSSM) decaying to tau-lepton pairs in pp collisions is performed, using events recorded by the CMS experiment at the LHC. The dataset corresponds to an integrated luminosity of 24.6 inverse femtobarns, with 4.9 inverse femtobarns at 7 TeV and 19.7 inverse femtobarns at 8 TeV. To enhance the sensitivity to neutral MSSM Higgs bosons, the search includes the case where the Higgs boson is produced in association with a b-quark jet. No excess is observed in the tau-lepton-pair invariant mass spectrum. Exclusion limits are presented in the MSSM parameter space for different benchmark scenarios, m[h,max}, m[h,mod+], m[h,mod-], light-stop, light-stau, tau-phobic, and low-m[H]. Upper limits on the cross section times branching fraction for gluon fusion and b-quark associated Higgs boson production are also given.

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.

Study of charged and neutral minimal supersymmetric standard model Higgs boson decays and measurement of tan β at the compact linear collider

The minimal supersymmetric extension of the standard model (MSSM) predicts the existence of new charged and neutral Higgs bosons. The pair creation of these new particles at the multi-TeV e + e − compact linear collider (CLIC), followed by decays into standard model particles, were simulated along with the corresponding background. High-energy beam-beam effects such as ISR, beamstrahlung and hadronic background were included. We have investigated the possibility of using the ratio between the number of events found in various decay channels to determine the MSSM parameter tan β and we have derived the corresponding statistical error from the uncertainties on the measured cross-sections and Higgs boson masses.

The MSSM parameter space with non-universal Higgs masses

Without assuming that Higgs masses have the same values as other scalar masses at the input GUT scale, we combine constraints on the minimal supersymmetric extension of the Standard Model (MSSM) coming from the cold dark matter density with the limits from direct searches at accelerators such as LEP, indirect measurements such as b→ sγ decay and the anomalous magnetic moment of the muon. The requirement that Higgs masses-squared be positive at the GUT scale imposes important restrictions on the MSSM parameter space, as does the requirement that the LSP be neutral. We analyze the interplay of these constraints in the ( μ, m A ), ( μ, m 1/2), ( m 1/2, m 0) and ( m A ,tan β) planes. These exhibit new features not seen in the corresponding planes in the constrained MSSM in which universality is extended to Higgs masses.

Exploration of elastic scattering rates for supersymmetric dark matter

We explore the possible cross sections for the elastic scattering of neutralinos $\ensuremath{\chi}$ on nucleons $p,n$ in the minimal supersymmetric extension of the standard model (MSSM). Universality of the soft supersymmetry-breaking scalar masses for the Higgs multiplets is not assumed, but the MSSM parameters are nevertheless required to lead consistently to an electroweak vacuum. We explore systematically the region of MSSM parameter space where CERN LEP and other accelerator constraints are respected, and the relic neutralino density lies in the range $0.1<~{\ensuremath{\Omega}}_{\ensuremath{\chi}}{h}^{2}<~0.3$ preferred by cosmology. We also discuss models with ${\ensuremath{\Omega}}_{\ensuremath{\chi}}{h}^{2}<0.1,$ in which case we scale the density of supersymmetric dark matter in our galactic halo by ${\ensuremath{\Omega}}_{\ensuremath{\chi}}{h}^{2}/0.1,$ allowing for the possible existence of some complementary form of cold dark matter. We restrict our attention to $\mathrm{tan}\ensuremath{\beta}<~10,$ for which reliable relic-density calculations are available. Within this range of $\mathrm{tan}\ensuremath{\beta},$ we find values of the cross sections that are considerably lower than the present experimental sensitivities. At low neutralino masses, ${m}_{\ensuremath{\chi}}\ensuremath{\lesssim}100$ GeV, the cross sections may be somewhat higher than in the constrained MSSM with universal soft Higgs boson masses, though they are generally lower. In the case of large ${m}_{\ensuremath{\chi}},$ the cross sections we find may be considerably larger than in the constrained model, but still well below the present experimental sensitivity.

Variations of the neutralino elastic cross-section with CP-violating phases

We analyze the neutralino–nucleus elastic cross-section in the minimal supersymmetric extension of the standard model (MSSM), including contributions from CP-violating phases, using the four-fermi neutralino–quark interaction. Over a wide range of the MSSM parameter space, we show the variations in the cross-sections due to these phases. We further concentrate on the regions which are consistent with constraints from the electric dipole moment of the electron, neutron and mercury atom. In the regions we examine in detail, we find suppressions by up to a factor of two, while enhancements in the cross-sections are no greater than ∼10%.

The Higgs boson mass as a probe of the minimal supersymmetric standard model

Recently, the LEP collaborations have reported a lower bound on a Standard Model-like Higgs boson of order 89 GeV. We discuss the implications of this bound for the minimal supersymmetric extension of the Standard Model (MSSM). In particular, we show that the lower bound on tan β, which can be obtained from the presently allowed Higgs boson mass value, becomes stronger than the one set by the requirement of perturbative consistency of the theory up to scales of order M GUT (associated with the infrared fixed-point solution of the top quark Yukawa coupling) in a large fraction of the allowed parameter space. The potentiality of future LEP2 searches to further probe the MSSM parameter space is also discussed.

Searches for the neutral Higgs bosons of the MSSM in e +e − collisions at centre-of-mass energies of 181–184 GeV

The data collected by ALEPH at LEP at centre-of-mass energies ranging from 181 to 184 GeV, corresponding to an integrated luminosity of 57 pb −1, are analysed to search for pair-produced neutral Higgs bosons h and A, in the b b ̄ b b ̄ and τ + τ − b b ̄ final states. Two events are found in the data with 2.5 expected from standard model processes. When combined with the lower energy data collected by ALEPH and with earlier reported searches for associated hZ production, these analyses are interpreted in the context of the minimal supersymmetric extension of the standard model (MSSM). For standard choices of MSSM parameter sets, this combination results in 95% C.L. exclusion lower limits of 72.2 and 76.1 GeV/ c 2 for m h and m A, irrespective of tan β. A scan of the MSSM parameter space is performed in which the model parameters are varied over wide ranges. For low values of tan β, i.e., for 1< tanβ≲ 2 , the limit on m h of ∼88 GeV/ c 2 is shown to be robust, being satisfied in essentially all of the physically allowed domain.

The fine-tuning price of LEP

We quantify the amount of fine tuning of input parameters of the Minimal Supersymmetric Extension of the Standard Model (MSSM) that is needed to respect the lower limits on sparticle and Higgs masses imposed by precision electroweak measurements at LEP, measurements of b→ X s γ, and searches at LEP 2. If universal input scalar masses are assumed in a gravity-mediated scenario, a factor of ≳180 is required at tan β∼1.65, decreasing to ∼20 at tan β∼10. The amount of fine tuning is not greatly reduced if non-universal input scalar Higgs masses are allowed, but may be significantly reduced if some theoretical relations between MSSM parameters are assumed.

Precision electroweak data, supersymmetry and GUTs

Following an update of indirect constraints on m t , M H and α s (M Z) ∥ MS from precision electroweak measurements in the Standard Model, we analyze the data within the context of the Minimal Supersymmetric extension of the Standard Model (MSSM), including the constraint from supersymmetric grand unification. Within the Standard Model, we find somewhat larger values of m t and M H than previously, and a somewhat lower value of α s (M Z) ∥ MS . The favoured value of m t can be decreased (increased) by O (10 to 20) GeV if the scalar particle masses (lightest chargino mass) are close to the direct experimental limits. We find for the first time a significant lower limit on supersymmetric Higgs masses. The supersymmetric GUT constraint gives a coupled upper limit on the scalar and gaugino masses that depends sensitively on the other MSSM parameters.

Search for neutral Higgs bosons in the minimal supersymmetric extension of the standard model

A search for the neutral Higgs bosons h0 and A0, predicted by the Minimal Supersymmetric Extension of the Standard Model (MSSM), has been performed by the OPAL Collaboration at LEP. The analysis was based on approximately 75 pb−1 of data taken at centre-of-mass energies in the vicinity of the Z0 resonance. No Higgs boson signals have been detected. Using, in addition, an upper limit on the contribution of non-Standard Model processes to the Z0 boson width, almost the entire MSSM parameter space that can be reached at present LEP energies has been excluded. In particular, at the 95% confidence level, our results imply that\(m_{h^0 } > 44.5\) GeV/c2 and\(m_{A^0 } > 24.3\) GeV/c2, for tan β≥1. The sensitivity to this assumption is discussed and the search results are also interpreted in the context of general two-doublet models.