Extracting GMSB Parameters at a Linear Collider

Assuming gauge-mediated supersymmetry breaking, we simulate precision measurements of fundamental parameters at a 500 GeV e+e- linear collider in the scenario where a neutralino is the next-to-lightest supersymmetric particle. Information on the supersymmetry breaking and the messenger sectors of the theory is extracted from realistic fits to the measured mass spectrum of the Minimal Supersymmetric Model particles and the next-to-lightest supersymmetric particle lifetime.Comment: 6 pages, LaTeX + epsf.sty, 3 figure

Precision GMSB at a Linear Collider

We simulate precision measurements of gauge-mediated supersymmetry breaking (GMSB) parameters at a 500 GeV e+e- linear collider in the scenario where a neutralino is the next-to-lightest supersymmetric particle. Information on the supersymmetry breaking and the messenger sectors of the theory is extracted from the measured sparticle mass spectrum and neutralino lifetime.Comment: LaTeX + sprocl.sty + epsf.sty, 6 pages, 3 figures (5 eps files

Measuring Gauge-Mediated SuperSymmetry Breaking Parameters at a 500 GeV e+e- Linear Collider

We consider the phenomenology of a class of gauge-mediated supersymmetry (SUSY) breaking (GMSB) models at a e+e- Linear Collider (LC) with c.o.m. energy up to 500 GeV. In particular, we refer to a high-luminosity (L ~ 3 x 10^34 cm^-2 s^-1) machine, and use detailed simulation tools for a proposed detector. Among the GMSB-model building options, we define a simple framework and outline its predictions at the LC, under the assumption that no SUSY signal is detected at LEP or Tevatron. Our focus is on the case where a neutralino (N1) is the next-to-lightest SUSY particle (NLSP), for which we determine the relevant regions of the GMSB parameter space. Many observables are calculated and discussed, including production cross sections, NLSP decay widths, branching ratios and distributions, for dominant and rare channels. We sketch how to extract the messenger and electroweak scale model parameters from a spectrum measured via, e.g. threshold-scanning techniques. Several experimental methods to measure the NLSP mass and lifetime are proposed and simulated in detail. We show that these methods can cover most of the lifetime range allowed by perturbativity requirements and suggested by cosmology in GMSB models. Also, they are relevant for any general low-energy SUSY breaking scenario. Values of c*tau_N1 as short as 10's of microns and as long as 10's of metres can be measured with errors at the level of 10% or better after one year of LC running with high luminosity. We discuss how to determine a narrow range (<~ 5%) for the fundamental SUSY breaking scale sqrt(F), based on the measured m_N1, c*tau_N1. Finally, we suggest how to optimise the LC detector performance for this purpose.Comment: 56 pages, 32 figures (48 eps files), LaTeX + epsf.sty + colordvi.sty. Revision v2: minor changes/additions, version to be published in EPJ

Superheavy Supersymmetry

One way to suppress flavor changing neutral currents or CP violating processes in supersymmetry is to make at least some of the first two generations' scalars superheavy (above ~20 TeV). We summarize the motivations and challenges, theoretically and phenomenologically, for superheavy supersymmetry. We then argue for more viable alternatives on the superheavy theme and are led to models where the heavy spectrum follows a pattern of masses similar to what arises from gauge-mediation or with a "hybrid" spectrum of light and heavy masses based on each particle's transformation under a global SU(5). In the end, despite the differences between the competing ideas, a self-consistent natural theory with superheavy masses seems to prefer low-energy supersymmetry breaking with possible correlations among the light sparticle masses. The resulting light gravitino and its couplings to matter could also impact the discovery capabilities and analyses of these models at colliders. In addition, we comment on how the presence of superheavy states may influence the light spectrum, and how this may help efforts to distinguish between theories post-discovery.Comment: LaTeX, 8 page

New Multi-Scale Supersymmetric Models with Flavor Changing Neutral Current Suppression

We discuss the phenomenology of a class of supersymmetric models in which some of the quark and lepton superfields are an integral part of a dynamical supersymmetry breaking sector. The corresponding squarks and sleptons are much heavier than any other superpartners, and could naturally have masses as high as ~ 40 TeV. We discuss a general set of conditions for acceptable flavor-changing neutral currents and natural electroweak symmetry breaking, and identify two particularly interesting new classes of theories. We discuss how phenomenological signatures of such multi-scale models at the CERN LEP II and Fermilab Tevatron colliders could significantly differ from previously considered scenarios. In particular, we give experimental signals which could be present if the left-handed selectron is much lighter than the right-handed one.Comment: 10 pages, LaTeX file + 2 figures embedded using epsf.sty. Source and ps files are also available at http://feynman.physics.lsa.umich.edu/~ambros/Physics.html#1

Supersymmetric Scenarios with Dominant Radiative Neutralino Decay

The radiative decay of the next-to-lightest neutralino into a lightest neutralino and a photon is analyzed in the MSSM. We find that significant regions of the supersymmetric parameter space with large radiative BR's (up to about 100%) do exist. The radiative channel turns out to be enhanced when the neutralino tree-level decays are suppressed either "kinematically" or "dynamically". In general, in the regions allowed by LEP data and not characterized by asymptotic values of the SuSy parameters, the radiative enhancement requires tan beta ~= 1 and/or M_1 ~= M_2, and negative values of \mu. We present typical specific scenarios where these "necessary" conditions are fulfilled, relaxing the usual relation M_1=(5/3)*tan^2(th_W)*M_2. The influence of varying the stop masses and mixing angle when the radiative decay is enhanced is also considered. Some phenomenological consequences of the above picture are discussed.Comment: 32 pages, LaTeX file + 23 figures embedded with epsf.sty. In this revised version, Eq.(3) plus some related notations and text passages have been changed. Minor error corrected in Fig.12(a). The numerical analysis and the conclusions of the paper are not affected. (Includes the erratum to appear in Phys. Rev. D.) Source and ps files are also available at ftp://hpteo.roma1.infn.it/pub/preprints/ambr-mele/Rome1-1148/ or at http://feynman.physics.lsa.umich.edu/~ambros/Physics.html#1

Neutralino Decays in the Minimal Supersymmetric Standard Model

A complete phenomenological study of the next-to-lightest neutralino decays is performed in the MSSM. The widths and branching ratios for all the possible decay channels (including the radiative decay X0(2) --> X0(1) gamma and the decay into a light Higgs X0(2) --> X0(1) h0) are studied in detail as functions of all the SuSy parameters of the model. Particular attention is paid to situations that are interesting for LEP2 searches. Non-trivial decay patterns are found that critically depend on the region of the parameter space considered.Comment: 29 pages, no figures, REVTeX. A gzipped postscript file of the complete paper (50 pages, 31 figs) is available via anonymous ftp at ftp://hpteo.roma1.infn.it/pub/preprints/ambr-mele/Rome1-1095.ps.gz (1 Mb --> 5.6 Mb

Extracting GMSB parameters at a linear collider

Assuming gauge-mediated supersymmetry breaking, we simulate precision measurements of fundamental parameters at a 500 GeV $e^+e^-$ linear collider in the scenario where a neutralino is the next-to-lightest supersymmetric particle. Information on the supersymmetry breaking and the messenger sectors of the theory is extracted from realistic fits to the measured mass spectrum of the Minimal Supersymmetric Model particles and the next-to-lightest supersymmetric particle lifetime