... [6] JF Gunion, GL Kane and J. Wudka, UCD-87-28. [7] RJ Dewitt, LM Jones, JD Sullivan, DE Will... more ... [6] JF Gunion, GL Kane and J. Wudka, UCD-87-28. [7] RJ Dewitt, LM Jones, JD Sullivan, DE Williams and HD Wyld Jr., Phys. Rev. D 19 (1979) 2046; D 20 (1979 ) 1751(E); K. Koller, TF Walsh and PM Zerwas, Z. Phys. C 2 (1979 ) 197. [ 8 ] JF Owens, Rev. Mod. Phys. ...
Zeitschrift f�r Physik C Particles and Fields, 1989
... should result in a clearly visible W signal in the dijet invariant mass spectra both for dije... more ... should result in a clearly visible W signal in the dijet invariant mass spectra both for dijet and for three-jet events at HERA. ... 1. See eg, G. Wolf: Proceedings of the 1986 Lake Louise Winter Institute, New Frontiers in Particle Physics, J. Cameron, B. Campbell, A. Kamal, F. Khanna p ...
Simple supersymmetric grand unified models based on the gauge group SO(10) require-in addition to... more Simple supersymmetric grand unified models based on the gauge group SO(10) require-in addition to gauge and matter unification-the unification of t-b-τ Yukawa couplings. Owing to sparticle contributions to fermion self-energy diagrams, the Yukawa unification however only occurs for very special values of the soft SUSY breaking parameters. We perform a search using a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also require the relic density of neutralino dark matter to saturate the WMAPmeasured abundance. For Yukawa unified models with µ > 0, the spectrum is characterizd by three mass scales: first and second generation scalars in the multi-TeV range, third generation scalars in the TeV range, and gauginos in the ∼ 100 GeV range. Most solutions give far too high a relic abundance of neutralino dark matter. The dark matter discrepancy can be rectified by i). allowing for neutralino decay to axino plus photon, ii). imposing gaugino mass non-universality or iii). imposing generational non-universality. In addition, the MCMC approach finds a compromise solution where scalar masses are not too heavy, and where neutralino annihilation occurs via the light Higgs h resonance. By imposing weak scale Higgs soft term boundary conditions, we are also able to generate low µ, m A solutions with neutralino annihilation via a light A resonance, though these solutions seem to be excluded by CDF/D0 measurements of the B s → µ + µ − branching fraction. Based on the dual requirements of Yukawa coupling unification and dark matter relic density, we predict new physics signals at the LHC from pair production of 350-450 GeV gluinos. The events are characterized by very high b-jet multiplicity and a dilepton mass edge around mχ0 2 − mχ0 1 ∼ 50-75 GeV.
We survey a variety of proposals for new physics at high scales that serve to relate the multitud... more We survey a variety of proposals for new physics at high scales that serve to relate the multitude of soft supersymmetry breaking parameters of the MSSM. We focus on models where the new physics results in non-universal soft parameters, in sharp contrast with the usually assumed mSUGRA framework. These include i) SU (5) and SO(10) grand unified (GUT) models, ii) the MSSM plus a right-handed neutrino, iii) models with effective supersymmetry, iv) models with anomaly-mediated SUSY breaking and gaugino mediated SUSY breaking, v) models with non-universal soft terms due to string dynamics, and vi) models based on M-theory. We outline the physics behind these models, point out some distinctive features of the weak scale sparticle spectrum, and allude to implications for collider experiments. To facilitate future studies, for each of these scenarios, we describe how collider events can be generated using the program ISAJET. Our hope is that detailed studies of a variety of alternatives will help point to the physics underlying SUSY breaking and how this is mediated to the observable sector, once sparticles are discovered and their properties measured.
Supersymmetric grand unified models based on the gauge group SO(10) are especially attractive in ... more Supersymmetric grand unified models based on the gauge group SO(10) are especially attractive in light of recent data on neutrino masses. The simplest SO(10) SUSY GUT models predict unification of third generation Yukawa couplings in addition to the usual gauge coupling unification. Recent surveys of Yukawa unified SUSY GUT models predict an inverted scalar mass hierarchy in the spectrum of sparticle masses if the superpotential µ term is positive. In general, such models tend to predict an overabundance of dark matter in the universe. We survey several solutions to the dark matter problem in Yukawa unified supersymmetric models. One solution-lowering the GUT scale mass value of first and second generation scalars-leads toũ R andc R squark masses in the 90−120 GeV regime, which should be accessible to Fermilab Tevatron experiments. We also examine relaxing gaugino mass universality which may solve the relic density problem by having neutralino annihilations via the Z or h resonances, or by having a wino-like LSP.
We extend our earlier results delineating the supersymmetry (SUSY) reach of the CERN Large Hadron... more We extend our earlier results delineating the supersymmetry (SUSY) reach of the CERN Large Hadron Collider operating at a centre-of-mass energy √ s = 7 TeV to integrated luminosities in the range 5-30 fb −1. Our results are presented within the paradigm minimal supergravity model (mSUGRA or CMSSM). Using a 6-dimensional grid of cuts for the optimization of signal to background ratio-including missing E T-we find for mg ∼ mq an LHC 5σ SUSY discovery reach of mg ∼ 1.3, 1.4, 1.5 and 1.6 TeV for 5, 10, 20 and 30 fb −1 , respectively. For mq ≫ mg, the corresponding reach is instead mg ∼ 0.8, 0.9, 1.0 and 1.05 TeV, for the same integrated luminosities.
Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first and second generation... more Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first and second generation matter scalars, and sub-TeV third generation and Higgs scalars) have been proposed to ameliorate phenomenological problems arising from flavor changing neutral currents (FCNCs) and CP violating processes, while satisfying conditions of naturalness. Models with an IMH already in place at the GUT scale have been shown to be constrained in that for many model parameter choices, the top squark squared mass is driven to negative values. We delineate regions of parameter space where viable models with a GUT scale IMH can be generated. We find that larger values of GUT scale first and second generation scalar masses act to suppress third generation scalars, leading to acceptable solutions if GUT scale gaugino masses are large enough. We show examples of viable models and comment on their characteristic features. For example, in these models the gluino mass is bounded from below, and effectively decouples, whilst third generation scalars remain at sub-TeV levels. While possibly fulfilling criteria of naturalness, these models present challenges for detection at future pp and e + e − collider experiments.
A promising way to reconcile naturalness with a decoupling solution to the SUSY flavor and CP pro... more A promising way to reconcile naturalness with a decoupling solution to the SUSY flavor and CP problems is suggested by models with a radiatively driven inverted mass hierarchy (RIMH). The RIMH models arise naturally within the context of SUSY SO(10) grand unified theories. In their original form, RIMH models suffer from two problems: 1.) obtaining the radiative breakdown of electroweak symmetry, and 2.) generating the correct masses for third generation fermions. The first problem can be solved by the introduction of SO(10) D-term contributions to scalar masses. We show that correct fermion masses can indeed be obtained, but at the cost of limiting the magnitude of the hierarchy that can be generated. We go on to compute predictions for the neutralino relic density as well as for the rate for the decay b → sγ, and show that these yield significant constraints on model parameter space. We show that only a tiny corner of model parameter space is accessible to Fermilab Tevatron searches, assuming an integrated luminosity of 25 f b −1. We also quantify the reach of the CERN LHC collider for this class of models, and find values of mg ∼ 1600 GeV to be accessible assuming just 10 fb −1 of integrated luminosity. In an Appendix, we list the two loop renormalization group equations for the MSSM plus right handed neutrino model that we have used in our analysis.
We consider the possibility that the lightest supersymmetric particle is a heavy gluino. After di... more 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 g-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 g-LSP. We next investigate limits on the g-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 m g that can be excluded depends upon the path length of the g in the detector, the amount of energy it deposits in each hadronic collision, and the probability for the g to fragment to a pseudo-stable charged hadron after a given hadronic collision. We explore how the range of excluded m g depends upon these ingredients, concluding that for non-extreme cases the range 3 GeV < ∼ m g < ∼ 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 g) up to m g ∼ 160 − 180 GeV. For completeness, we also analyze the case where the g is the NLSP (as possible in gauge-mediated supersymmetry breaking) decaying via g → g + gravitino. We find that the Tevatron RunI data excludes m g ≤ 240 GeV. Finally, we discuss application of the procedures developed for the heavy g-LSP to searches for other stable strongly interacting particles, such as a stable heavy quark.
We study the predictions of the simplest SU(5) grand unified model within the framework of minima... more We study the predictions of the simplest SU(5) grand unified model within the framework of minimal supergravity, including constraints from the radiative breaking of electroweak symmetry. As a consequence of the unification of the b-quark and τ-lepton Yukawa couplings, the top quark mass is predicted to be close to its fixed point value. We delineate the regions of the supergravity parameter space allowed by constraints from the non-observation of proton decay and from the requirement that the LSP does not overclose the universe. These constraints lead to a definite pattern of sparticle masses: the feature unique to Yukawa unified models is that some of the third generation squarks are much lighter than those of the first two generations. Despite the fact that all sparticle masses and mixings are determined by just four SUSY parameters at the GUT scale (in addition to m t), we find that the signals for sparticle production can vary substantially over the allowed parameter space. We identify six representative scenarios and study the signals from sparticle production at the LHC. We find that by studying the signal in various channels, these scenarios may be distinguished from one another, and also from usually studied "minimal models" where squarks and sleptons are taken to be degenerate. In particular, our studies allow us to infer that some third generation squarks are lighter than other squarks-a feature that could provide the first direct evidence of supergravity grand unification.
We set up a formalism for calculating the O(o.,) corrections to the process pp-+ W X~rv A with sp... more We set up a formalism for calculating the O(o.,) corrections to the process pp-+ W X~rv A with spin-correlated w decays to leptons and mesons. Our results are applicable to Monte Carlo integration, which allows easy construction of any desired observable at next-to-leading-log level, and the possibility to include experimental cuts. Our results are applied explicitly to the decay modes-+ v ev"w-+ v sr+, and r~v sr+~; other decay modes may be included in a straightforward fashion. We show results for transverse momentum and rapidity variables in leading-log and nextto-leading-log approximations; the leptonic observables are compared to similar observables from direct W~ev, .
We examine signals for sparticle production at the Tevatron within the framework of gauge mediate... more We examine signals for sparticle production at the Tevatron within the framework of gauge mediated supersymmetry breaking models for four different model lines, each of which leads to qualitatively different signatures. We identify cuts to enhance the signal above Standard Model backgrounds, and use ISAJET to evaluate the SUSY reach of experiments at the Fermilab Main Injector and at the proposed TeV33. For the model lines that we have examined, we find that the reach is at least as large, and frequently larger, than in the mSUGRA framework. For two of these model lines, we find that the ability to identify b-quarks and τ-leptons with high efficiency and purity is essential for the detection of the signal.
We examine signals for sparticle production at the CERN Large Hadron Collider (LHC) within the fr... more We examine signals for sparticle production at the CERN Large Hadron Collider (LHC) within the framework of gauge mediated supersymmetry breaking models with a low SUSY breaking scale for four different model lines, each of which leads to qualitatively different signatures. We first examine the reach of the LHC via the canonical E T and multilepton channels that have been advocated within the mSUGRA framework. Next, we examine special features of each of these model lines that could serve to further enhance the SUSY signal over Standard Model backgrounds. We use ISAJET to evaluate the SUSY reach of experiments at the LHC. We find that the SUSY reach, measured in terms of mg, is at least as large, and sometimes larger, than in the mSUGRA framework. In the best case of the co-NLSP scenario, the reach extends to mg ≥ 3 TeV, assuming 10 f b −1 of integrated luminosity.
Physics at the Large Hadron Collider (LHC) and the International e + e − Linear Collider (ILC) wi... more Physics at the Large Hadron Collider (LHC) and the International e + e − Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC / LC Study Group so far is summarised in this report. Possible topics for future studies are outlined.
Recent comparisons of minimal supergravity (mSUGRA) model predictions with WMAP measurements of t... more Recent comparisons of minimal supergravity (mSUGRA) model predictions with WMAP measurements of the neutralino relic density point to preferred regions of model parameter space. We investigate the reach of linear colliders (LC) with √ s = 0.5 and 1 TeV for SUSY in the framework of the mSUGRA model. We find that LCs can cover the entire stau co-annihilation region provided tan β < ∼ 30. In the hyperbolic branch/focus point (HB/FP) region of parameter space, specialized cuts are suggested to increase the reach in this important "dark matter allowed" area. In the case of the HB/FP region, the reach of a LC extends well past the reach of the CERN LHC. We examine a case study in the HB/FP region, and show that the MSSM parameters µ and M 2 can be sufficiently well-measured to demonstrate that one would indeed be in the HB/FP region, where the lightest chargino and neutralino have a substantial higgsino component.
The observation of the Egret experiment of an excess of diffuse gamma rays with energies above E ... more The observation of the Egret experiment of an excess of diffuse gamma rays with energies above E γ = 1 GeV has previously been interpreted in the context of the minimal supergravity model (mSUGRA) as coming from neutralino annihilation into mainly bquarks in the galactic halo, with neutralino mass in the vicinity of 50-70 GeV. We observe that in order to obtain the correct relic abundance of neutralinos in accord with WMAP measurements, the corresponding neutralino-proton direct detection (DD) rates should be in excess of recent limits from the Xenon-10 collaboration. While it does not appear possible to satisfy the Egret, WMAP and Xenon-10 constraints simultaneously within the mSUGRA model, we find that it is easily possible in models with non-universal Higgs soft masses (NUHM). In either case, gluino pair production from mg ∼ 400 − 500 GeV should occur at large rates at the CERN LHC, and a gluino pair production signal should be visible with just 0.1 fb −1 of integrated luminosity. The NUHM interpretation predicts a rather light spectrum of heavy Higgs bosons with m A ∼ 140 − 200 GeV over the whole parameter space which would interpret Egret data. Spin-independent DD rates are predicted to be just above 10 −8 pb, within range of the next round of direct dark matter detection experiments.
Recent experimental and theoretical determinations of (g − 2) µ , Ω CDM h 2 and BF (b → sγ) place... more Recent experimental and theoretical determinations of (g − 2) µ , Ω CDM h 2 and BF (b → sγ) place exceedingly tight constraints on the minimal supergravity (mSUGRA) model. We advocate relaxing the generational universality of mSUGRA, so that GUT scale third generation scalar masses are greater than the (degenerate) first and second generation scalar masses (a normal scalar mass hierarchy (NMH)). The non-degeneracy allows for a reconciliation of all the above constraints, and also respects FCNC limits from B d − B d mixing and b → sγ. The NMH SUGRA model leads to the prediction of relatively light first and second generation sleptons. This yields large rates for multilepton collider signatures at the CERN LHC and also possibly at the Fermilab Tevatron. The spectrum of light sleptons should be accessible to a √ s = 0.5 − 1 TeV linear e + e − collider.
... [6] JF Gunion, GL Kane and J. Wudka, UCD-87-28. [7] RJ Dewitt, LM Jones, JD Sullivan, DE Will... more ... [6] JF Gunion, GL Kane and J. Wudka, UCD-87-28. [7] RJ Dewitt, LM Jones, JD Sullivan, DE Williams and HD Wyld Jr., Phys. Rev. D 19 (1979) 2046; D 20 (1979 ) 1751(E); K. Koller, TF Walsh and PM Zerwas, Z. Phys. C 2 (1979 ) 197. [ 8 ] JF Owens, Rev. Mod. Phys. ...
Zeitschrift f�r Physik C Particles and Fields, 1989
... should result in a clearly visible W signal in the dijet invariant mass spectra both for dije... more ... should result in a clearly visible W signal in the dijet invariant mass spectra both for dijet and for three-jet events at HERA. ... 1. See eg, G. Wolf: Proceedings of the 1986 Lake Louise Winter Institute, New Frontiers in Particle Physics, J. Cameron, B. Campbell, A. Kamal, F. Khanna p ...
Simple supersymmetric grand unified models based on the gauge group SO(10) require-in addition to... more Simple supersymmetric grand unified models based on the gauge group SO(10) require-in addition to gauge and matter unification-the unification of t-b-τ Yukawa couplings. Owing to sparticle contributions to fermion self-energy diagrams, the Yukawa unification however only occurs for very special values of the soft SUSY breaking parameters. We perform a search using a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also require the relic density of neutralino dark matter to saturate the WMAPmeasured abundance. For Yukawa unified models with µ > 0, the spectrum is characterizd by three mass scales: first and second generation scalars in the multi-TeV range, third generation scalars in the TeV range, and gauginos in the ∼ 100 GeV range. Most solutions give far too high a relic abundance of neutralino dark matter. The dark matter discrepancy can be rectified by i). allowing for neutralino decay to axino plus photon, ii). imposing gaugino mass non-universality or iii). imposing generational non-universality. In addition, the MCMC approach finds a compromise solution where scalar masses are not too heavy, and where neutralino annihilation occurs via the light Higgs h resonance. By imposing weak scale Higgs soft term boundary conditions, we are also able to generate low µ, m A solutions with neutralino annihilation via a light A resonance, though these solutions seem to be excluded by CDF/D0 measurements of the B s → µ + µ − branching fraction. Based on the dual requirements of Yukawa coupling unification and dark matter relic density, we predict new physics signals at the LHC from pair production of 350-450 GeV gluinos. The events are characterized by very high b-jet multiplicity and a dilepton mass edge around mχ0 2 − mχ0 1 ∼ 50-75 GeV.
We survey a variety of proposals for new physics at high scales that serve to relate the multitud... more We survey a variety of proposals for new physics at high scales that serve to relate the multitude of soft supersymmetry breaking parameters of the MSSM. We focus on models where the new physics results in non-universal soft parameters, in sharp contrast with the usually assumed mSUGRA framework. These include i) SU (5) and SO(10) grand unified (GUT) models, ii) the MSSM plus a right-handed neutrino, iii) models with effective supersymmetry, iv) models with anomaly-mediated SUSY breaking and gaugino mediated SUSY breaking, v) models with non-universal soft terms due to string dynamics, and vi) models based on M-theory. We outline the physics behind these models, point out some distinctive features of the weak scale sparticle spectrum, and allude to implications for collider experiments. To facilitate future studies, for each of these scenarios, we describe how collider events can be generated using the program ISAJET. Our hope is that detailed studies of a variety of alternatives will help point to the physics underlying SUSY breaking and how this is mediated to the observable sector, once sparticles are discovered and their properties measured.
Supersymmetric grand unified models based on the gauge group SO(10) are especially attractive in ... more Supersymmetric grand unified models based on the gauge group SO(10) are especially attractive in light of recent data on neutrino masses. The simplest SO(10) SUSY GUT models predict unification of third generation Yukawa couplings in addition to the usual gauge coupling unification. Recent surveys of Yukawa unified SUSY GUT models predict an inverted scalar mass hierarchy in the spectrum of sparticle masses if the superpotential µ term is positive. In general, such models tend to predict an overabundance of dark matter in the universe. We survey several solutions to the dark matter problem in Yukawa unified supersymmetric models. One solution-lowering the GUT scale mass value of first and second generation scalars-leads toũ R andc R squark masses in the 90−120 GeV regime, which should be accessible to Fermilab Tevatron experiments. We also examine relaxing gaugino mass universality which may solve the relic density problem by having neutralino annihilations via the Z or h resonances, or by having a wino-like LSP.
We extend our earlier results delineating the supersymmetry (SUSY) reach of the CERN Large Hadron... more We extend our earlier results delineating the supersymmetry (SUSY) reach of the CERN Large Hadron Collider operating at a centre-of-mass energy √ s = 7 TeV to integrated luminosities in the range 5-30 fb −1. Our results are presented within the paradigm minimal supergravity model (mSUGRA or CMSSM). Using a 6-dimensional grid of cuts for the optimization of signal to background ratio-including missing E T-we find for mg ∼ mq an LHC 5σ SUSY discovery reach of mg ∼ 1.3, 1.4, 1.5 and 1.6 TeV for 5, 10, 20 and 30 fb −1 , respectively. For mq ≫ mg, the corresponding reach is instead mg ∼ 0.8, 0.9, 1.0 and 1.05 TeV, for the same integrated luminosities.
Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first and second generation... more Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first and second generation matter scalars, and sub-TeV third generation and Higgs scalars) have been proposed to ameliorate phenomenological problems arising from flavor changing neutral currents (FCNCs) and CP violating processes, while satisfying conditions of naturalness. Models with an IMH already in place at the GUT scale have been shown to be constrained in that for many model parameter choices, the top squark squared mass is driven to negative values. We delineate regions of parameter space where viable models with a GUT scale IMH can be generated. We find that larger values of GUT scale first and second generation scalar masses act to suppress third generation scalars, leading to acceptable solutions if GUT scale gaugino masses are large enough. We show examples of viable models and comment on their characteristic features. For example, in these models the gluino mass is bounded from below, and effectively decouples, whilst third generation scalars remain at sub-TeV levels. While possibly fulfilling criteria of naturalness, these models present challenges for detection at future pp and e + e − collider experiments.
A promising way to reconcile naturalness with a decoupling solution to the SUSY flavor and CP pro... more A promising way to reconcile naturalness with a decoupling solution to the SUSY flavor and CP problems is suggested by models with a radiatively driven inverted mass hierarchy (RIMH). The RIMH models arise naturally within the context of SUSY SO(10) grand unified theories. In their original form, RIMH models suffer from two problems: 1.) obtaining the radiative breakdown of electroweak symmetry, and 2.) generating the correct masses for third generation fermions. The first problem can be solved by the introduction of SO(10) D-term contributions to scalar masses. We show that correct fermion masses can indeed be obtained, but at the cost of limiting the magnitude of the hierarchy that can be generated. We go on to compute predictions for the neutralino relic density as well as for the rate for the decay b → sγ, and show that these yield significant constraints on model parameter space. We show that only a tiny corner of model parameter space is accessible to Fermilab Tevatron searches, assuming an integrated luminosity of 25 f b −1. We also quantify the reach of the CERN LHC collider for this class of models, and find values of mg ∼ 1600 GeV to be accessible assuming just 10 fb −1 of integrated luminosity. In an Appendix, we list the two loop renormalization group equations for the MSSM plus right handed neutrino model that we have used in our analysis.
We consider the possibility that the lightest supersymmetric particle is a heavy gluino. After di... more 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 g-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 g-LSP. We next investigate limits on the g-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 m g that can be excluded depends upon the path length of the g in the detector, the amount of energy it deposits in each hadronic collision, and the probability for the g to fragment to a pseudo-stable charged hadron after a given hadronic collision. We explore how the range of excluded m g depends upon these ingredients, concluding that for non-extreme cases the range 3 GeV < ∼ m g < ∼ 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 g) up to m g ∼ 160 − 180 GeV. For completeness, we also analyze the case where the g is the NLSP (as possible in gauge-mediated supersymmetry breaking) decaying via g → g + gravitino. We find that the Tevatron RunI data excludes m g ≤ 240 GeV. Finally, we discuss application of the procedures developed for the heavy g-LSP to searches for other stable strongly interacting particles, such as a stable heavy quark.
We study the predictions of the simplest SU(5) grand unified model within the framework of minima... more We study the predictions of the simplest SU(5) grand unified model within the framework of minimal supergravity, including constraints from the radiative breaking of electroweak symmetry. As a consequence of the unification of the b-quark and τ-lepton Yukawa couplings, the top quark mass is predicted to be close to its fixed point value. We delineate the regions of the supergravity parameter space allowed by constraints from the non-observation of proton decay and from the requirement that the LSP does not overclose the universe. These constraints lead to a definite pattern of sparticle masses: the feature unique to Yukawa unified models is that some of the third generation squarks are much lighter than those of the first two generations. Despite the fact that all sparticle masses and mixings are determined by just four SUSY parameters at the GUT scale (in addition to m t), we find that the signals for sparticle production can vary substantially over the allowed parameter space. We identify six representative scenarios and study the signals from sparticle production at the LHC. We find that by studying the signal in various channels, these scenarios may be distinguished from one another, and also from usually studied "minimal models" where squarks and sleptons are taken to be degenerate. In particular, our studies allow us to infer that some third generation squarks are lighter than other squarks-a feature that could provide the first direct evidence of supergravity grand unification.
We set up a formalism for calculating the O(o.,) corrections to the process pp-+ W X~rv A with sp... more We set up a formalism for calculating the O(o.,) corrections to the process pp-+ W X~rv A with spin-correlated w decays to leptons and mesons. Our results are applicable to Monte Carlo integration, which allows easy construction of any desired observable at next-to-leading-log level, and the possibility to include experimental cuts. Our results are applied explicitly to the decay modes-+ v ev"w-+ v sr+, and r~v sr+~; other decay modes may be included in a straightforward fashion. We show results for transverse momentum and rapidity variables in leading-log and nextto-leading-log approximations; the leptonic observables are compared to similar observables from direct W~ev, .
We examine signals for sparticle production at the Tevatron within the framework of gauge mediate... more We examine signals for sparticle production at the Tevatron within the framework of gauge mediated supersymmetry breaking models for four different model lines, each of which leads to qualitatively different signatures. We identify cuts to enhance the signal above Standard Model backgrounds, and use ISAJET to evaluate the SUSY reach of experiments at the Fermilab Main Injector and at the proposed TeV33. For the model lines that we have examined, we find that the reach is at least as large, and frequently larger, than in the mSUGRA framework. For two of these model lines, we find that the ability to identify b-quarks and τ-leptons with high efficiency and purity is essential for the detection of the signal.
We examine signals for sparticle production at the CERN Large Hadron Collider (LHC) within the fr... more We examine signals for sparticle production at the CERN Large Hadron Collider (LHC) within the framework of gauge mediated supersymmetry breaking models with a low SUSY breaking scale for four different model lines, each of which leads to qualitatively different signatures. We first examine the reach of the LHC via the canonical E T and multilepton channels that have been advocated within the mSUGRA framework. Next, we examine special features of each of these model lines that could serve to further enhance the SUSY signal over Standard Model backgrounds. We use ISAJET to evaluate the SUSY reach of experiments at the LHC. We find that the SUSY reach, measured in terms of mg, is at least as large, and sometimes larger, than in the mSUGRA framework. In the best case of the co-NLSP scenario, the reach extends to mg ≥ 3 TeV, assuming 10 f b −1 of integrated luminosity.
Physics at the Large Hadron Collider (LHC) and the International e + e − Linear Collider (ILC) wi... more Physics at the Large Hadron Collider (LHC) and the International e + e − Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC / LC Study Group so far is summarised in this report. Possible topics for future studies are outlined.
Recent comparisons of minimal supergravity (mSUGRA) model predictions with WMAP measurements of t... more Recent comparisons of minimal supergravity (mSUGRA) model predictions with WMAP measurements of the neutralino relic density point to preferred regions of model parameter space. We investigate the reach of linear colliders (LC) with √ s = 0.5 and 1 TeV for SUSY in the framework of the mSUGRA model. We find that LCs can cover the entire stau co-annihilation region provided tan β < ∼ 30. In the hyperbolic branch/focus point (HB/FP) region of parameter space, specialized cuts are suggested to increase the reach in this important "dark matter allowed" area. In the case of the HB/FP region, the reach of a LC extends well past the reach of the CERN LHC. We examine a case study in the HB/FP region, and show that the MSSM parameters µ and M 2 can be sufficiently well-measured to demonstrate that one would indeed be in the HB/FP region, where the lightest chargino and neutralino have a substantial higgsino component.
The observation of the Egret experiment of an excess of diffuse gamma rays with energies above E ... more The observation of the Egret experiment of an excess of diffuse gamma rays with energies above E γ = 1 GeV has previously been interpreted in the context of the minimal supergravity model (mSUGRA) as coming from neutralino annihilation into mainly bquarks in the galactic halo, with neutralino mass in the vicinity of 50-70 GeV. We observe that in order to obtain the correct relic abundance of neutralinos in accord with WMAP measurements, the corresponding neutralino-proton direct detection (DD) rates should be in excess of recent limits from the Xenon-10 collaboration. While it does not appear possible to satisfy the Egret, WMAP and Xenon-10 constraints simultaneously within the mSUGRA model, we find that it is easily possible in models with non-universal Higgs soft masses (NUHM). In either case, gluino pair production from mg ∼ 400 − 500 GeV should occur at large rates at the CERN LHC, and a gluino pair production signal should be visible with just 0.1 fb −1 of integrated luminosity. The NUHM interpretation predicts a rather light spectrum of heavy Higgs bosons with m A ∼ 140 − 200 GeV over the whole parameter space which would interpret Egret data. Spin-independent DD rates are predicted to be just above 10 −8 pb, within range of the next round of direct dark matter detection experiments.
Recent experimental and theoretical determinations of (g − 2) µ , Ω CDM h 2 and BF (b → sγ) place... more Recent experimental and theoretical determinations of (g − 2) µ , Ω CDM h 2 and BF (b → sγ) place exceedingly tight constraints on the minimal supergravity (mSUGRA) model. We advocate relaxing the generational universality of mSUGRA, so that GUT scale third generation scalar masses are greater than the (degenerate) first and second generation scalar masses (a normal scalar mass hierarchy (NMH)). The non-degeneracy allows for a reconciliation of all the above constraints, and also respects FCNC limits from B d − B d mixing and b → sγ. The NMH SUGRA model leads to the prediction of relatively light first and second generation sleptons. This yields large rates for multilepton collider signatures at the CERN LHC and also possibly at the Fermilab Tevatron. The spectrum of light sleptons should be accessible to a √ s = 0.5 − 1 TeV linear e + e − collider.
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Papers by H. Baer