arXiv subjects
Publications and source records attributed to G. L. Kane.
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.
We describe a method to help the search for a light stop squark [M(stop) + M(LSP) < M(top)] at the Fermilab Tevatron. Traditional search methods rely upon a series of stringent background-reducing cuts which, unfortunately, leave very few signal events given the present data set. To avoid this difficulty, we instead suggest using a milder set of cuts, combined with a "superweight," whose purpose is to discriminate between signal and background events. The superweight consists of a sum of terms, each of which are either zero or one. The terms are assigned event-by-event depending upon the values of various observables. We suggest a method for choosing the observables as well as the criteria used to assign the values such that the superweight is "large" for the supersymmetric signal and "small" for the standard model background. For illustration, we mainly consider the detection of stops coming from top decay, making our analysis especially relevant to the W+2 jets top sample.
We present a refined and expanded analysis of the CDF $eeγγ+ \Et$ 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 LEP1-LEP130 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 stop, the neutralino relic density, the shift in $R_b$ and the associated shift in $α_s$, and implications for the form of the theory.
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 < 1 keV. We consider in particular the case that the lightest neutralino has a nearly 100% 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 $\sqrt{s} =$ 160, 175, and 190 GeV.
We argue that it is possible to make a consistent picture of FNAL data including the production and decay of gluinos and squarks. The additional cross section is several pb, about the size of that for Standard Model (SM) top quark pair production. If the stop squark mass is small enough, about half of the top quarks decay to stop squarks, and the loss of SM top quark pair production rate is compensated by the supersymmetric processes. This behavior is consistent with the reported top quark decay rates in various modes and other aspects of the data, and suggests several other possible decay signatures. This picture can be tested easily with more data, perhaps even with the data in hand, and demonstrates the potential power of a hadron collider to determine supersymmetric parameters. It also has implications for the top mass measurement and the interpretation of the LEP $R_b$ excess.
Motivated by the supersymmetric interpretation of the CDF eeγγplus missing energy event and the reported Z->bb excess at LEP, we analyze the Higgsino as a cold dark matter candidate. We examine the constraints as implied by the collider experiments, and then calculate its relic density. We find that this Higgsino-like lightest supersymmetric particle is a viable cold dark matter candidate (0.05 < Omega h^2 < 1), and we discuss its favorable prospects for laboratory detection.
We have analyzed the single $\eegg + \slashchar{E}_T$ event at CDF and found that the expected rate and kinematics are consistent with selectron pair production. We consider two classes of general low-energy supersymmetric theories, where either the lightest neutralino (``neutralino LSP'' scenario) or the gravitino (``light gravitino'' scenario) is the lightest supersymmetric particle. The parameter space of the supersymmetric Lagrangian is tightly constrained by the kinematics of the event and the branching ratios for the necessary decay chain of the selectron. We identify a region of the parameter space satisfying all low-energy constraints, and consistent with the selectron interpretation of the $eeγγ+ \Et$ event. We discuss other supersymmetric processes at Fermilab Tevatron and at CERN LEP in both scenarios that could confirm or exclude a supersymmetric explanation of the event, and that could distinguish between the neutralino LSP and the light gravitino scenarios.
If the reported excess (over the standard model prediction) for Z->bb from LEP persists, and is explained by supersymmetric particles in loops, then we show that (1) a superpartner (chargino and/or stop) will be detected at LEP2, and probably at LEP1.5 in 1995, (2) the basic parameter tan(beta) is at its lower perturbative limit, (3) BR(t->t1+chi0) is at or above 0.4, (4) the upper limit on m_h is considerably reduced, and (5) several important consequences arise for the form of a unified supersymmetric theory. Our analysis is done in terms of a general weak scale Lagrangian and does not depend on assumptions about SUSY breaking.
We discuss the production and two-photon decay of the lightest Higgs boson (h) of the minimal supersymmetric standard model at the CERN Large Hadron Collider. Since the observability of the signal is quite model dependent, we conduct a thorough scan of the parameter space of minimal supersymmetry, including experimental and theoretical constraints. If kinematically allowed, supersymmetric decay modes of h may be important, and can even dominate all others. The coupling of h to $b\overline b$ can be different from that of a standard model Higgs boson; this can diminish (or enhance, but only if tan$β$ is very large) the h -> $γγ$ signal. We emphasize the importance of a full treatment of radiative corrections in the Higgs sector for obtaining the h $b\overline b$ coupling. If supersymmetric particles are not too heavy, their contributions in loops can either enhance or suppress both the production cross-section and the h -> $γγ$ branching fraction. We discuss the relative importance of these factors in the context of various scenarios for the discovery of supersymmetry. Even if h is not detected at the LHC, h may still exist in its expected mass region.
We study the most promising signals of Constrained Minimal Supersymmetry detectable at a luminosity upgraded 2 TeV Fermilab Tevatron collider. Using a full event-level Monte Carlo based on Pythia/Jetset, we simulate the trilepton signal examining in detail the effect of constraints on the parameter space. We also simulate the monolepton and dilepton signals, the missing E_T + jets signal, and the signals of stop production in supersymmetry all with full Standard Model backgrounds with realistic detector cuts. We find that large fractions of parameter space can be probed (or eliminated if no signal is found), but mass limits on charginos and neutralinos are not possible based solely on the trilepton signal. Detection efficiencies depend strongly on supersymmetry parameters beyond simply the neutralino and chargino masses; analyses (experimental or theoretical) that do not include this will draw misleading conclusions. Finally, we comment on how searches at LEP II will complement searches at Fermilab.
We find that re-analyzing the LEP/SLC data with light superpartners and low $α_s(\mz^2)\simeq 0.112$ yields a better fit to the data than the Standard Model, giving a satisfactory description of the $R_b$ measurement, and a better fit to $A_{LR}$. A large body of low energy ($q^2 \ll \mz^2$) data and analyses provide compelling evidence for $α_s(\mz^2)\simeq 0.112$. Global fits to LEP/SLC data in the Standard Model, however, converge on a value of $α_s(\mz^2)\simeq 0.126$. Recently it has become increasingly clear that these should be viewed as incompatible rather than values that can be averaged. We investigate the possibility that new physics is causing the LEP high value. To this end we have conducted a global analysis of LEP/SLC data in the Standard Model and also in the Minimal Supersymmetric Standard Model. Several predictions could confirm (or rule out) the results of this paper: light chargino and stop, top decays into stop and neutralino, large $R_b$, large $A_{LR}$, and a higher $M_W$. We briefly discuss the implications of low $α_s$ for more fundamental high-scale supersymmetric theories.
Assuming that the actual values of the top quark mass at FNAL and of the ratio of partial widths Z->bb/Z->hadrons at LEP are within their current one-sigma reported ranges, we present a No-Lose Theorem for superpartner searches at LEP II and an upgraded Tevatron. We impose only two theoretical assumptions: the Lagrangian is that of the Minimal Supersymmetric Standard Model with arbitrary soft-breaking terms, and all couplings remain perturbative up to scales of order 10^16 GeV; there are no assumptions about the soft SUSY breaking parameters, proton decay, cosmology, etc. In particular, if the LEP and FNAL values hold up and supersymmetry is responsible for the discrepancy with the SM prediction of the partial width of Z->bb, then we must have charginos and/or top squarks observable at the upgraded machines. Furthermore, little deviation from the SM is predicted within "super-unified" SUSY. Finally, it appears to be extremely difficult to find any unified MSSM model, regardless of the form of soft SUSY breaking, that can explain the partial width for large tan(beta); in particular, no model with top-bottom-tau Yukawa coupling unification appears to be consistent with the experiments.
We have examined how a Standard Model or Supersymmetric Higgs boson h might be detected at possible hadron colliders. The channels W(to ell nu)h(to b b~), Z(to ell ell~)h(to b b~) and W/Z(to jets)h(to tau+ tau-) are most useful. The results imply that h with mass M_h can be detected or excluded for M_h between about 80--130 GeV at any hadron collider with energy greater or similar to 2 TeV and an integrated luminosity greater or similar to 10 fb^{-1}; high luminosity is the essential requirement. We comment on measuring $h$ couplings and branching ratios.
In constrained minimal supersymmetry the lightest neutralino of bino-type is the only neutral candidate for dark matter. As a result, one is typically able to restrict all the supersymmetric mass spectra below roughly 1-2\tev\ {\em without} imposing an ill-defined fine-tuning constraint.
In the constrained MSSM one is typically able to restrict the supersymmetric mass spectra below roughly 1-2\tev\ {\em without} resorting to the ambiguous fine-tuning constraint.
We examine the Constrained Minimal Supersymmetric Standard Model (CMSSM) with an additional requirement of strict b - tau unification in the region of small tan(beta). We find that the parameter space becomes completely limited below about 1 TeV by physical constraints alone, without a fine-tuning constraint. We study the resulting phenomenological consequences, and point out several ways of falsifying the adopted b - tau unification assumption. We also comment on the effect of a constraint from the non-observation of proton decay.
Taking seriously phenomenological indications for supersymmetry, we have made a detailed study of unified minimal SUSY, including effects at the few percent level in a consistent fashion. We report here a general analysis without choosing a particular unification gauge group. We find that the encouraging SUSY unification results of recent years do survive the challenge of a more complete and accurate analysis. Taking into account effects at the 5-10% level leads to several improvements of previous results, and allows us to sharpen our predictions for SUSY in the light of unification. We perform a thorough study of the parameter space. The results form a well-defined basis for comparing the physics potential of different facilities. Very little of the acceptable parameter space has been excluded by LEP or FNAL so far, but a significant fraction can be covered when these accelerators are upgraded. A number of initial applications to the understanding of the SUSY spectrum, detectability of SUSY at LEP II or FNAL, BR($b\to sγ$), Width($Z\to b\bar b$), dark matter, etc, are included in a separate section. We formulate an approach to extracting SUSY parameters from data when superpartners are detected. For small tan(beta) or large $m_top$ both $M_half$ and $M_0$ are entirely bounded from above at O(1 tev) without having to use a fine-tuning constraint.
The top group studied discovery issues as well as measurements to be made at the Tevatron, the LHC and the SSC.