arXiv subjects
Publications and source records attributed to H. Baer.
We use the quantum corrected chargino production cross section, including information on the beam polarization and chargino helicities, to estimate the precision achievable at a 1 TeV, 500 ${\mathrm fb}^{-1}$ Linear Collider on the determination of fundamental supersymmetric parameters from measurements of light chargino mass and production cross sections. We show that to get meaningful results higher order corrections should be included.
Recently, refinements have been made on both the theoretical and experimental determinations of the i.) mass of the lightest Higgs scalar (m_h), ii.) relic density of cold dark matter in the universe (Omega_CDM h^2), iii.) branching fraction for radiative B decay BF(b \to s γ), iv.) muon anomalous magnetic moment (a_μ), and v.) flavor violating decay B_s \to μ^+μ^-. Each of these quantities can be predicted in the MSSM, and each depends in a non-trivial way on the spectra of SUSY particles. In this paper, we present updated constraints from each of these quantities on the minimal supergravity (mSUGRA) model as embedded in the computer program ISAJET. The combination of constraints points to certain favored regions of model parameter space where collider and non-accelerator SUSY searches may be more focussed.
The value of the bottom quark mass at M_Z in the DR-bar scheme is an important input for the analysis of supersymmetric models with a large value of tan(beta). Conventionally, however, the running bottom quark mass extracted from experimental data is quoted in the MS-bar scheme at the bottom mass scale. We describe a two loop procedure for the conversion of the bottom quark mass from MS-bar to DR-bar scheme. The Particle Data Group value m_b(m_b) = 4.2 \pm 0.2 GeV in the MS-bar scheme corresponds to a range of 2.65-3.03 GeV for m_b(M_Z) in the DR-bar scheme.
Recently, extra dimensional SUSY GUT models have been proposed in which compactification of the extra dimension(s) leads to a breakdown of the gauge symmetry and/or supersymmetry. We examine a particular class of higher-dimensional models exhibiting supersymmetry and SU(5) or SO(10) GUT symmetry. SUSY breaking occurs on a hidden brane, and is communicated to the visible brane via gaugino mediation. Non-universal gaugino masses are developed at the compactification scale as a consequence of a restricted gauge symmetry on the hidden brane. In this case, the compactification scale is at or slightly below the GUT scale. We examine the parameter space of such models where gaugino masses are related due to a Pati-Salam symmetry on the hidden brane. We find limited but significant regions of model parameter space where a viable spectra of SUSY matter is generated. Our results are extended to the more general case of three independent gaugino masses; here we find that large parameter space regions open up for large values of the U(1) gaugino mass M_1. We also find the relic density of neutralinos for these models to be generally below expectations from cosmological observations, thus leaving room for hidden sector states to make up the bulk of cold dark matter. Finally, we evaluate the branching fraction BF(b -> s gamma) and muon anomalous magnetic moment a_μ.
There are many low-energy models of supersymmetry breaking parameters which are motivated by theoretical and experimental considerations. Here, we discuss some of the lesser-known theories of low-energy supersymmetry, and outline their phenomenological consequences. In some cases, these theories have more gauge symmetry or particle content than the Minimal Supersymmetric Standard Model. In other cases, the parameters of the Lagrangian are unusual compared to commonly accepted norms (e.g., Wino LSP, heavy gluino LSP, light gluino, etc.). The phenomenology of supersymmetry varies greatly between the different models. Correspondingly, particular aspects of the detectors assume greater or lesser importance. Detection of supersymmetry and the determination of all parameters may well depend upon having the widest possible view of supersymmetry phenomenology.
We present an outlook for possible discovery of supersymmetry with broken R-parity at Run II of the Tevatron. We first present a review of the literature and an update of the experimental bounds. In turn we then discuss the following processes: 1. Resonant slepton production followed by R-parity violating decay, (a) via $LQD^c$ and (b) via $LLE^c$. 2. How to distinguish resonant slepton production from $Z'$ or $W'$ production. 3. Resonant slepton production followed by the decay to neutralino LSP, which decays via $LQD^c$. 4. Resonant stop production followed by the decay to a chargino, which cascades to the neutralino LSP. 5. Gluino pair production followed by the cascade decay to charm squarks which decay directly via $L_1Q_2D^c_1$. 6. Squark pair production followed by the cascade decay to the neutralino LSP which decays via $L_1Q_2D^c_1$. 7. MSSM pair production followed by the cascade decay to the LSP which decays (a) via $LLE^c$, (b) via $LQD^c$, and (c) via $U^cD^cD^c$, respectively. 8. Top quark and top squark decays in spontaneous R-parity violation.
ISAJET is a Monte Carlo program which simulates $pp$, $\bar pp$ and $e^+e^-$ interactions at high energies. This document summarizes the physics underlying the program and describes how to use it. Version~7.48 includes several new features. Anomaly Mediated SUSY Breaking (AMSB) models and right-handed sneutrinos have been added; the latter play a role, e.g., in inverted hierarchy models. A new process generating $Z+\hbox{2 jets}$ based on the Helas library and MadGraph has been added. Another new process generating Kaluza-Klein gravitons in models with extra dimensions has been added.
ISAJET is a Monte Carlo program which simulates $pp, \bar pp$ and $e^+e^-$ interactions at high energies. This document summarizes the physics underlying the program and describes how to use it. New features of Version 7.40 include generation of $W+H$ and $Z+H$ events, non-minimal GMSB models, and use of the experimental $α_s(M_Z)$ by default.
We consider the possibility that the lightest supersymmetric particle is a heavy gluino. After discussing models in which this is the case, we demonstrate that the gluino-LSP could evade cosmological and other constraints by virtue of having a very small relic density. We then consider how neutral and charged hadrons containing a gluino will behave in a detector, demonstrating that there is generally substantial apparent missing momentum associated with a produced gluino-LSP. We next investigate limits on a (heavy) gluino-LSP deriving from LEP, LEP2 and RunI Tevatron experimental searches for excess events in the jets plus missing momentum channel and for stable heavily-ionizing charged particles. The range of gluino mass that can be excluded depends upon the path length of the gluino in the detector, the amount of energy it deposits in each hadronic collision, and the probability for the gluino to fragment to a pseudo-stable charged hadron after a given hadronic collision. We explore how the range of excluded gluino mass depends upon these ingredients, concluding that for non-extreme cases the range $3\gev\lsim\mgl\lsim 130-150\gev$ can be excluded at 95% CL based on currently available OPAL and CDF analyses. We find that RunII at the Tevatron can extend the excluded region (or discover the gluino) up to $\mgl\sim 160-180\gev$. For completeness, we also analyze the case where the gluino is the NLSP (as possible in gauge-mediated supersymmetry breaking) decaying via gluino -> g + gravitino. We find that the Tevatron RunI data excludes $\mgl\leq 240$ GeV. Finally, we discuss application of the procedures developed for the heavy gluino-LSP to searches for other stable strongly interacting particles, such as a stable heavy quark.
ISAJET is a Monte Carlo event generator for $pp$, $\bar pp$, and $e^+e^-$ interactions at high energies. This document summarizes the physics underlying the program and describes how to use it.
We provide a mini-guide to some of the possible manifestations of weak scale supersymmetry. For each of six scenarios we provide a brief description of the theoretical underpinnings, the adjustable parameters, a qualitative description of the associated phenomenology at future colliders, comments on how to simulate each scenario with existing event generators.
Review of Monte Carlo event generators for signals of new particles at LEP2. The areas covered include SUSY, HIGGS and Leptoquarks.
Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.
We summarize the current status and future prospects for low energy (weak scale) supersymmetry. In particular, we evaluate the capabilities of various $e^+e^-$, $p\bar p$ and $pp$ colliders to discover evidence for supersymmetric particles. Furthermore, assuming supersymmetry is discovered, we discuss capabilities of future facilities to dis-entangle the anticipated spectrum of super-particles, and, via precision measurements, to test mass and coupling parameters for comparison with various theoretical expectations. We comment upon the complementarity of proposed hadron and $e^+e^-$ machines for a comprehensive study of low energy supersymmetry.
We use ISAJET to perform a detailed study of the missing transverse energy $\eslt$ plus multi-jet signal expected from superparticle production at the CERN LHC. Our analysis is performed within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking. We delineate the region of parameter space where the $\eslt$ supersymmetry signal should be observable at the LHC and compare it to the regions explorable via searches for sleptons and for chargino/neutralino production. We confirm that, given a data sample of 10~$\fb^{-1}$, $m_{\tg}\sim 1300$ GeV can be explored if $m_{\tq}\gg m_{\tg}$, while $m_{\tg}\sim 2000$ GeV can be probed if $m_{\tq}\simeq m_{\tg}$. We further examine what information can be gleaned from scrutinizing this event sample. For instance, the multi-jet multiplicity yields information on whether squark production makes a significant contribution to the observed $\eslt$ sample. Furthermore, reconstructing hemispheric masses may yield a measure of $m_{\tg}$ to $\sim 15-25\%$. Finally, for favourable ranges of parameters, by reconstructing masses of tagged $b\bar{b}$ jet pairs, it may be possible to detect Higgs bosons produced via sparticle cascade decay chains.
We evaluate cross sections for $\eslt$, 1$\ell$ and various dilepton and multilepton event topologies that result from the simultaneous production of all sparticles at the Tevatron collider, both within the minimal model framework as well as in two different $R$-parity violating scenarios. Our analysis assumes that these $R$-violating couplings are small, and that their sole effect is to cause the lightest supersymmetric particle to decay inside the detector. We reassess future strategies for sparticle searches at the Tevatron, and quantify by how much the various signals for supersymmetry could differ from their minimal model expectations, if $R$-parity is not conserved due to either baryon number or lepton number violating operators. We also evaluate the Tevatron reach in $m_{\tg}$ for the various models, and find that rate-limited multilepton signals ultimately provide the largest reach for both $R$-parity conserving and $R$-parity violating cases.
We examine the phenomenology of minimal supergravity models, assuming only that the low energy theory has the minimal particle content, that electroweak symmetry is radiatively broken, and that R-parity is essentially conserved. After delineating regions of supergravity parameter space currently excluded by direct particle searches at LEP and the Tevatron, we quantify how this search region will be expanded when LEP~II and the Tevatron Main Injector upgrades become operational. We describe how various experimental analyses can be consistently combined within a single framework, resulting in a multi-channel search for supersymmetry, but note that this analysis is sensitive to specific assumptions about physics at the unification scale.
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 ISAJET 7.07 so that explicit signatures can be examined in detail. We find that, for some of the boundary condition choices, large regions of parameter space can be explored via same-sign dilepton and isolated trilepton signals. For other choices, the mass reach of Tevatron collider experiments is much more limited. We also compare mass reach of Tevatron experiments with the corresponding reach at LEP 200.