CP-violating Supersymmetric Higgs at the Tevatron and LHC

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 \nu_\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 find that it is very hard to observe this signature at the Tevatron, even with 20 fb$^{-1}$ of data, in the LEP--allowed region of parameter space due to the small signal efficiency, even though the background is manageable. At the LHC, a priori huge SM backgrounds can be suppressed by applying judiciously chosen kinematical selections. After all cuts, we are left with a signal cross section of around 0.5 fb, and a signal to background ratio between 1.2 and 2.9. According to our analysis this Higgs signal should be viable at the LHC in the vicinity of present LEP exclusion once 20 to 50 fb$^{-1}$ of data have been accumulated at $\sqrt{s}=14$ TeV.Comment: 27 pages, 12 figure

Mitigation of the LHC Inverse Problem

The LHC inverse problem refers to the difficulties in determining the parameters of an underlying theory from data (to be) taken by the LHC experiments: if they find signals of new physics, and an underlying theory is assumed, could its parameters be determined uniquely, or do different parameter choices give indistinguishable experimental signatures? This inverse problem was studied before for a supersymmetric Standard Model with 15 free parameters. This earlier study found 283 indistinguishable pairs of parameter choices, called degenerate pairs, even if backgrounds are ignored. We can resolve all but 23 of those pairs by constructing a true \chi^2 distribution using mostly counting observables. The elimination of systematic errors would even allow separating the residual degeneracies. Taking the Standard Model background into account we still can resolve 237 of the 283 "degenerate" pairs. This indicates that (some of) our observables should also be useful for the purpose of determining the values of SUSY parameters.Comment: 32 pages, 13 figures, typo in (3.6) corrected, version to appear in Phys. Rev.

Direct and Indirect Detection of Neutralino Dark Matter and Collider Signatures in an SO(10)SO(10) Model with Two Intermediate Scales

We investigate the detectability of neutralino Dark Matter via direct and indirect searches as well as collider signatures of an $SO(10)$ model with two intermediate scales. We compare the direct Dark Matter detection cross section and the muon flux due to neutralino annihilation in the Sun that we obtain in this model with mSUGRA predictions and with the sensitivity of current and future experiments. In both cases, we find that the detectability improves as the model deviates more from mSUGRA. In order to study collider signatures, we choose two benchmark points that represent the main phenomenological features of the model: a lower value of $|\mu|$ and reduced third generation sfermion masses due to extra Yukawa coupling contributions in the Renormalization Group Equations, and increased first and second generation slepton masses due to new gaugino loop contributions. We show that measurements at the LHC can distinguish this model from mSUGRA in both cases, by counting events containing leptonically decaying $Z^0$ bosons, heavy neutral Higgs bosons, or like--sign lepton pairs.Comment: 21 pages, 16 figure

Determining the Mass of Dark Matter Particles with Direct Detection Experiments

In this article I review two data analysis methods for determining the mass (and eventually the spin-independent cross section on nucleons) of Weakly Interacting Massive Particles with positive signals from direct Dark Matter detection experiments: a maximum likelihood analysis with only one experiment and a model-independent method requiring at least two experiments. Uncertainties and caveats of these methods will also be discussed.Comment: 24 pages, 10 figures, 1 reference added, typos fixed, published version, to appear in the NJP Focus Issue on "Dark Matter and Particle Physics

Implications of SUSY Model Building

We discuss the motivations and implications of models of low-energy supersymmetry. We present the case for the minimal supersymmetric standard model, which we define to include the minimal particle content and soft supersymmetry-breaking interactions which are universal at the GUT or Planck scale. This model is in agreement with all present experimental results, and yet depends on only a few unknown parameters and therefore maintains considerable predictive power. From the theoretical side, it arises naturally in the context of supergravity models. We discuss radiative electroweak symmetry breaking and the superpartner spectrum in this scenario, with some added emphasis on regions of parameter space leading to unusual or interesting experimental signals at future colliders. We then examine how these results may be affected by various modifications and extensions of the minimal model, including GUT effects, extended gauge, Higgs, and matter sectors, non-universal supersymmetry breaking, non-conservation of R-parity, and dynamical supersymmetry breaking at low energies.Comment: Contribution to the DPF long range study, working group on 'Electroweak Symmetry Breaking and Beyond the SM Physics'; LaTeX file without figures, 60 pages. The complete PS file, including figures, can be obtained by anonymous ftp from ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-879.ps.

Modification of the Equivalent Photon Approximation for Resolved Photon Processes

We propose a modification of the equivalent photon approximation (EPA) for processes which involve the parton content of the photon, to take into account the suppression of the photonic parton fluxes due to the virtuality of the photon. We present simple, physically motivated ans\"atze to model this suppression and show that even though the parton content of the electron no longer factorizes into an electron flux function and a photon structure function, it is still possible to express it as a single integral. We also show that for the TRISTAN experiments its effect can be numerically of the same size as that of the NLO corrections. Further, we discuss a possible measurement at HERA, which can provide an experimental handle on the effect we model through our ans\"atze.Comment: 8 pages, LaTeX with equations.sty, 3 figures (not included); to appear in the Proceedings of "Photon95", Sheffield, April 1995. A complete compressed PS file, including figures, is available via anonymous ftp from ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-891.ps.