S. Ambrosanio

Search for supersymmetry with a light gravitino at the Fermilab Tevatron and CERN LEP colliders

We analyze the prospects for discovering supersymmetry at the Fermilab Tevatron and CERN LEP colliders in the scenario that the lightest supersymmetric particle is a gravitino of mass {approx_lt}1 keV. We consider in particular the case that the lightest neutralino has a nearly 100{percent} branching fraction into gravitino+photon within the detector. This implies that supersymmetric events should contain both missing (transverse) energy and two energetic photons. Therefore, one can search for supersymmetry simply through inclusive production of superpartners. We consider the exclusion and reach capabilities of the Tevatron in exploring the supersymmetric parameter space, and study the efficiencies which can be achieved in this search. We also consider the discovery reach and backgrounds at LEP with {radical}{ital s}=160, 175, and 190 GeV. {copyright} {ital 1996 The American Physical Society.}

Supersymmetric analysis and predictions based on the CDF e e gamma gamma + missing transverse energy event

We have analyzed the Collider Detector at Fermilab {ital ee}{gamma}{gamma}+ missing energy event. Its kinematics and expected rate are consistent with selectron pair production. We consider two classes of general low-energy supersymmetric theories where the lightest neutralino or the gravitino is the lightest supersymmetric particle. The supersymmetric Lagrangian is tightly constrained by the production and decay of the selectron and other data. We discuss other processes at the Fermilab Tevatron and at LEP that could confirm or exclude a supersymmetric explanation of the event. {copyright} {ital 1996 The American Physical Society.}

Signals for gauge-mediated supersymmetry-breaking models at the CERN LEP 2 collider

We consider a general class of models with gauge-mediated supersymmetry breaking in which the gravitino is the lightest supersymmetric particle. Several qualitatively different scenarios arise for the phenomenology of such models, depending on which superpartner(s) decay dominantly to the gravitino. At LEP2, neutralino pair production and slepton pair production can lead to a variety of promising discovery signals, which we systematically study. We investigate the impact of backgrounds for these signals and show how they can be reduced, and outline the effects of model parameter variations on the discovery potential.

Three-body decays of selectrons and smuons in low-energy supersymmetry breaking models

Abstract In models with low-energy supersymmetry breaking, it is well known that charged sleptons can be significantly lighter than the lightest neutralino, with the gravitino and lighter stau being the lightest and next-to-lightest supersymmetric particles respectively. We give analytical formulas for the three-body decays of right-handed selectrons and smuons into final states involving a tau, a stau, and an electron or muon, which are relevant in this scenario. We find that the three-body decays dominate over much of the parameter space, but the two-body decays into a lepton and a gravitino can compete if the three-body phase space is small and the supersymmetry breaking scale (governing the two-body channel) is fairly low. We study this situation quantitatively for typical gauge-mediated supersymmetry breaking model parameters. The three-body decay lengths are possibly macroscopic, leading to new unusual signals. We also analyze the final-state energy distributions, and briefly assess the prospects for detecting these decays at CERN LEP2 and other colliders.

Low energy supersymmetry with a neutralino LSP and the CDF ee{gamma}{gamma}+E/{sub T} event

We present a refined and expanded analysis of the CDF ee{gamma}{gamma}+E/{sub T} event as superpartner production, assuming the lightest neutralino is the lightest supersymmetric particle. A general low energy Lagrangian is constrained by a minimum cross section times branching ratio into two electrons and two photons, kinematics consistent with the event, and LEP 1{endash}LEP 130 data. We examine how the supersymmetric parameters depend on the kinematics, branching ratios, and experimental predictions with a selectron interpretation of the event, and discuss to what extent these are modified by other interpretations. Predictions for imminent CERN LEP upgrades and the present and future Fermilab Tevatron are presented. Finally, we briefly discuss the possible connection to other phenomena including a light top squark, the neutralino relic density, the shift in R{sub b}, and the associated shift in {alpha}{sub s}, and implications for the form of the theory. {copyright} {ital 1997} {ital The American Physical Society}

New multi-scale supersymmetric models with flavor changing neutral current suppression

Abstract 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.

Supersymmetric analysis and predictions based on the CDF ee\gamma\gamma + missing E_T event

We have analyzed the Collider Detector at Fermilab {ital ee}{gamma}{gamma}+ missing energy event. Its kinematics and expected rate are consistent with selectron pair production. We consider two classes of general low-energy supersymmetric theories where the lightest neutralino or the gravitino is the lightest supersymmetric particle. The supersymmetric Lagrangian is tightly constrained by the production and decay of the selectron and other data. We discuss other processes at the Fermilab Tevatron and at LEP that could confirm or exclude a supersymmetric explanation of the event. {copyright} {ital 1996 The American Physical Society.}

Supersymmetric analysis and predictions based on the collider detector at Fermilab {ital ee}{bold {gamma}}{bold {gamma}}{bold +} missing energy event

We have analyzed the Collider Detector at Fermilab {ital ee}{gamma}{gamma}+ missing energy event. Its kinematics and expected rate are consistent with selectron pair production. We consider two classes of general low-energy supersymmetric theories where the lightest neutralino or the gravitino is the lightest supersymmetric particle. The supersymmetric Lagrangian is tightly constrained by the production and decay of the selectron and other data. We discuss other processes at the Fermilab Tevatron and at LEP that could confirm or exclude a supersymmetric explanation of the event. {copyright} {ital 1996 The American Physical Society.}

Supersymmetric analysis and predictions based on the CDF ee{gamma gamma} + missing transverse energy.

We have analyzed the Collider Detector at Fermilab {ital ee}{gamma}{gamma}+ missing energy event. Its kinematics and expected rate are consistent with selectron pair production. We consider two classes of general low-energy supersymmetric theories where the lightest neutralino or the gravitino is the lightest supersymmetric particle. The supersymmetric Lagrangian is tightly constrained by the production and decay of the selectron and other data. We discuss other processes at the Fermilab Tevatron and at LEP that could confirm or exclude a supersymmetric explanation of the event. {copyright} {ital 1996 The American Physical Society.}