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Extended gauge models and e{sup -}e{sup -} {r_arrow} W{sup -}W{sup -} at the NLC

Description: We briefly discuss two possible manifestations of the lepton number violating reaction e{sup -}e{sup -} {r_arrow} W{sub i}{sup -}W{sub j}{sup -}, which probes the masses and mixings of heavy Majorana neutrinos, at the Next Linear Collider (NLC). Cross sections for this process are shown to be potentially quite large at center of mass energies of order 1-1.5 TeV.
Date: October 1, 1995
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Like-sign charged Higgs boson production in e{sup -}e{sup -} collisions at the NLC

Description: We consider the production of a pair of like-sign charged Higgs bosons in e{sup -} e{sup -} collisions at the NLC within the context of several electroweak models with extended symmetry breaking sectors. We find that the rate for this process, which proceeds through W{sup -}W{sup -} fusion, is a very sensitive probe of the nature of these extended Higgs sectors and that the corresponding cross sections can vary by as much as several orders of magnitude at NLC energies.
Date: October 1, 1995
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Extended gauge sectors at future colliders: Report of the New Gauge Boson Subgroup

Description: The author summarizes the results of the New Gauge Boson Subgroup on the physics of extended gauge sectors at future colliders as presented at the 1996 Snowmass workshop. He discusses the direct and indirect search reaches for new gauge bosons at both hadron and lepton colliders as well as the ability of such machines to extract detailed information on the couplings of these particles to the fermions and gauge bosons of the Standard Model. 41 refs., 18 figs., 5 tabs.
Date: December 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Searches for scalar and vector leptoquarks at future hadron colliders

Description: The search reaches for both scalar(S) and vector(V) leptoquarks at future hadron colliders are summarized. In particular the authors evaluate the production cross sections of both leptoquark types at TeV33 and LHC as well as the proposed 60 and 200 TeV colliders through both quark-antiquark annihilation and gluon-gluon fusion: q{anti q},gg {r_arrow} SS,VV. Experiments at these machines should easily discover such particles if their masses are not in excess of the few TeV range.
Date: September 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

The polarization asymmetry in {gamma}e collisions at the NLC and triple gauge Boson couplings

Description: The capability of the NLC in the {gamma}e collider mode to probe the CP-conserving {gamma}WW and {gamma}ZZ anomalous couplings through the use of the polarization asymmetry is examined. When combined with other measurements, very strong constraints on both varieties of anomalous couplings can be obtained. The author shows that these bounds are complementary to those that can be extracted from data taken at the LHC.
Date: September 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Using final state gluons as probes of anomalous top quark couplings at the NLC

Description: The rate and corresponding gluon jet energy distribution for the process e{sup +}e{sup {minus}} {r_arrow} t{anti t}g are sensitive to the presence of anomalous dipole-like couplings of the top to the photon and Z at the production vertex as well as to the gluon itself. For sizeable anomalous couplings substantial derivations in the shape and magnitude of the gluon spectrum from the expectations of the Standard Model are anticipated. The authors explore the capability of the Next Linear Collider to either discover or place bounds on these types of top quark couplings through measurements of the gluon energy distribution. The resulting constraints are found to be quite complementary to those obtained using other techniques.
Date: October 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

b {r_arrow} sl{sup +}l{sup {minus}} in the left-right symmetric model

Description: We begin to analyze and contrast the predictions for the decay b {r_arrow} sl{sup +}l{sup {minus}} in the Left-Right Symmetric Model (LMR) with those of the Standard Model (SM). In particular, we show that the forward-backward asymmetry of the lepton spectrum can be used to distinguish the SM from the simplest manifestation of the LRM.
Date: May 1, 1997
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Constraints on anomalous top quark couplings at the LHC

Description: Measurements of distributions associated with the pair production of top quarks at the LHC can be used to constrain (or observe) the anomalous chromomagnetic dipole moment(k) of the top. For example, using either the tt(bar) invariant mass or the Pt distribution of top we find that sensitivities to ; k; of order 0.05 are obtainable with 100 /fb of integrated luminosity. This is similar in magnitude to what can be obtained at a 500 GeV NLC with an integrated luminosity of 50 /fb through an examination of the e(+)e(-) right arrow tt(bar)g process.
Date: September 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Searches for new gauge bosons at future colliders

Description: The search reaches for new gauge bosons at future hadron and lepton colliders are summarized for a variety of extended gauge models. Experiments at these energies will vastly improve over present limits and will easily discover a Z` and/or W` in the multi-TeV range.
Date: September 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Constraints on q{bar q}{gamma}{gamma} contact interactions at future hadron colliders

Description: The author explores the capability of the Tevatron and LHC as well as other future hadron colliders to place limits on the possible existence of flavor-independent q{bar q}{gamma}{gamma} contact interactions which can lead to an excess of high p{sub t} diphoton events with large invariant masses. Constraints on the corresponding e{sup +}e{sup {minus}}{gamma}{gamma} contact interaction already exist from LEP. In the case of hadron colliders, strong constraints on the scale associated with such interactions are achievable in all cases, e.g., of order 0.9(3) TeV at TeV33(LHC).
Date: September 1, 1996
Creator: Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Dissecting the Wjj Anomaly: Diagnostic Tests of a Leptophobic Z'

Description: We examine the scenario where a leptophobic Z{prime} boson accounts for the excess of events in the Wjj channel as observed by CDF. We assume generation independent couplings for the Z{prime} and obtain allowed regions for the four hadronic couplings using the measured cross section as well as constraints from dijet production at UA2. These coupling regions translate into well-determined rates for the associated production of Z/{gamma} + Z{prime} at the Tevatron and LHC, as well as W + Z{prime} at the LHC,that are directly correlated with the Wjj rate observed at the Tevatron. The Wjj rate at the LHC is large and this channel should be observed soon once the SM backgrounds are under control. The rates for Z/{gamma} + Z{prime} associated production are smaller, and these processes should not yet have been observed at the Tevatron given the expected SM backgrounds. In addition, we show that more coupling information is obtainable from the M{sub WZ{prime}} distribution. Once detected, these processes will provide further valuable information on the Z{prime} boson couplings.
Date: August 15, 2011
Creator: Hewett, J. L. & Rizzo, T. G.
Partner: UNT Libraries Government Documents Department

SUSY Without Prejudice

Description: We begin an exploration of the physics associated with the general CP-conserving MSSM with Minimal Flavor Violation, the pMSSM. The 19 soft SUSY breaking parameters in this scenario are chosen so as to satisfy all existing experimental and theoretical constraints assuming that the WIMP is a thermal relic, i.e., the lightest neutralino. We scan this parameter space twice using both flat and log priors for the soft SUSY breaking mass parameters and compare the results which yield similar conclusions. Detailed constraints from both LEP and the Tevatron searches play a particularly important role in obtaining our final model samples. We find that the pMSSM leads to a much broader set of predictions for the properties of the SUSY partners as well as for a number of experimental observables than those found in any of the conventional SUSY breaking scenarios such as mSUGRA. This set of models can easily lead to atypical expectations for SUSY signals at the LHC.
Date: December 11, 2008
Creator: Berger, C.F.; Gainer, J.S.; Hewett, J.L. & Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Probing the Universal Randall-Sundrum Model at the ILC

Description: The Randall-Sundrum model with all Standard Model (SM) fields in the bulk, including the Higgs, can be probed by precision measurements at the ILC. In particular, the couplings of the Higgs to the gauge bosons of the SM can be determined with high accuracy at the ILC. Here we examine the deviations in these couplings from their SM values within the framework of the Universal Randall-Sundrum Model (URSM) as well as the corresponding couplings of the first Higgs Kaluza-Klein excitation.
Date: December 14, 2005
Creator: Davoudiasl, H.; /Wisconsin U., Madison; Lillie, B.; Rizzo, T.G. & /SLAC
Partner: UNT Libraries Government Documents Department

The LHC Inverse Problem, Supersymmetry and the ILC

Description: We address the question whether the ILC can resolve the LHC Inverse Problem within the framework of the MSSM. We examine 242 points in the MSSM parameter space which were generated at random and were found to give indistinguishable signatures at the LHC. After a realistic simulation including full Standard Model backgrounds and a fast detector simulation, we find that roughly only one third of these scenarios lead to visible signatures of some kind with a significance {ge} 5 at the ILC with {radical}s = 500 GeV. Furthermore, we examine these points in parameter space pairwise and find that only one third of the pairs are distinguishable at the ILC at 5{sigma}.
Date: November 12, 2007
Creator: Berger, C.F.; Gainer, J.S.; Hewett, J.L.; Lillie, B. & Rizzo, T.G.
Partner: UNT Libraries Government Documents Department

Higgs Properties in the Fourth Generation MSSM: Boosted Signals Over the 3G Plan

Description: The generalization of the MSSM to the case of four chiral fermion generations (4GMSSM) can lead to significant changes in the phenomenology of the otherwise familiar Higgs sector. In most of the 3GMSSM parameter space, the lighter CP-even h is {approx} 115-125 GeV and mostly Standard Model-like while H,A,H{sup {+-}} are all relatively heavy. Furthermore, the ratio of Higgs vevs, tan {beta}, is relatively unconstrained. In contrast to this, in the 4GMSSM, heavy fourth generation fermion loops drive the masses of h,H,H{sup {+-}} to large values while the CP-odd boson, A, can remain relatively light and tan {beta} is restricted to the range 1/2 {approx}< tan {beta} {approx}< 2 due to perturbativity requirements on Yukawa couplings. We explore this scenario in some detail, concentrating on the collider signatures of the light CP-odd Higgs at both the Tevatron and LHC. We find that while gg {yields} A may lead to a potential signal in the {tau}{sup +}{tau}{sup -} channel at the LHC, A may first be observed in the {gamma}{gamma} channel due to a highly loop-enhanced cross section that can be more than an order of magnitude greater than that of a SM Higgs for A masses of {approx} 115-120 and tan {beta} < 1. We find that the CP-even states h,H are highly mixed and can have atypical branching fractions. Precision electroweak constraints, particularly for the light A parameter space region, are examined in detail.
Date: August 15, 2011
Creator: Cotta, R.C.; Hewett, J.L.; Ismail, A.; Le, M.-P.; Rizzo, T.G. & /SLAC
Partner: UNT Libraries Government Documents Department

Dark Matter in the MSSM

Description: We have recently examined a large number of points in the parameter space of the phenomenological MSSM, the 19-dimensional parameter space of the CP-conserving MSSM with Minimal Flavor Violation. We determined whether each of these points satisfied existing experimental and theoretical constraints. This analysis provides insight into general features of the MSSM without reference to a particular SUSY breaking scenario or any other assumptions at the GUT scale. This study opens up new possibilities for SUSY phenomenology both in colliders and in astrophysical experiments. Here we shall discuss the implications of this analysis relevant to the study of dark matter.
Date: April 7, 2009
Creator: Cotta, R.C.; Gainer, J.S.; Hewett, J.L.; Rizzo, T.G. & /SLAC
Partner: UNT Libraries Government Documents Department

No Prejudice in Space

Description: We present a summary of recent results obtained from a scan of the 19-dimensional parameter space of the pMSSM and its implications for dark matter searches. We have generated a large set of points in parameter space (which we call 'models') for the 19-parameter CP-conserving pMSSM, where MFV has been assumed. We subjected these models to numerous experimental and theoretical constraints to obtain a set of {approx}68 K models which are consistent with existing data. We attempted to be somewhat conservative in our implementation of these constraints; in particular we only demanded that the relic density of the LSP not be greater than the measured value of {Omega}H{sup 2} for non-baryonic dark matter, rather than assuming that the LSP must account for the entire observed relic density. Examining the properties of the neutralinos in these models, we find that many are relatively pure gauge eigenstates with Higgsinos being the most common, followed by Winos. The relative prevalence of Higgsino and Wino LSPs leads many of our models to have a chargino as nLSP, often with a relatively small mass splitting between this nLSP and the LSP; this has important consequences in both collider and astroparticle phenomenology. We find that, in general, the LSP in our models provides a relatively small ({approx} 4%) contribution to the dark matter, however there is a long tail to this distribution and a substantial number of models for which the LSP makes up all or most of the dark matter. Typically these neutralinos are mostly Binos. Examining the signatures of our models in direct and indirect dark matter detection experiments, we find a wide range of signatures for both cases. In particular, we find a much larger range of WIMP-nucleon cross sections than is found in any particular model of SUSY-breaking. As these cross sections ...
Date: August 26, 2010
Creator: Cotta, R.C.; Gainer, J.S.; Hewett, J.L.; Rizzo, T.G. & /SLAC
Partner: UNT Libraries Government Documents Department

Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies

Description: We examine the ability for the Large Area Telescope (LAT) to constrain Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest Supersymmetric Particles (LSPs) for a set of {approx}71k experimentally valid supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find that none of these models can be excluded at 95% confidence by the current analysis; nevertheless, many lie within the predicted reach of future LAT analyses. With two years of data, we find that the LAT is currently most sensitive to light LSPs (mLSP < 50 GeV) annihilating into {tau}-pairs and heavier LSPs annihilating into b{bar b}. Additionally, we find that future LAT analyses will be able to probe some LSPs that form a sub-dominant component of dark matter. We directly compare the LAT results to direct detection experiments and show the complementarity of these search methods.
Date: March 15, 2012
Creator: Cotta, R.C.; /SLAC; Drlica-Wagner, A.; Murgia, S.; /SLAC /KIPAC, Menlo Park; Bloom, E.D. et al.
Partner: UNT Libraries Government Documents Department

pMSSM Dark Matter Searches on Ice

Description: We explore the capability of the IceCube/Deepcore array to discover signal neutrinos resulting from the annihilations of Supersymmetric WIMPS that may be captured in the solar core. In this analysis, we use a previously generated set of {approx} 70k model points in the 19-dimensional parameter space of the pMSSM which satisfy existing experimental and theoretical constraints. Our calculations employ a realistic estimate of the IceCube/DeepCore effective area that has been modeled by the IceCube collaboration. We find that a large fraction of the pMSSM models are shown to have significant signal rates in the anticipated IceCube/DeepCore 1825 day dataset, including some prospects for an early discovery. Many models where the LSP only constitutes a small fraction of the total dark matter relic density are found to have observable rates. We investigate in detail the dependence of the signal neutrino fluxes on the LSP mass, weak eigenstate composition, annihilation products and thermal relic density, as well as on the spin-independent and spin-dependent scattering cross sections. Lastly, We compare the model coverage of IceCube/DeepCore to that obtainable in near-future direct detection experiments and to pMSSM searches at the 7 TeV LHC.
Date: August 12, 2011
Creator: Cotta, R.C.; /SLAC; Howe, K.T.K.; /SLAC /Stanford U., Phys. Dept.; Hewett, J.L.; Rizzo, T.G. et al.
Partner: UNT Libraries Government Documents Department

Cosmic Ray Anomalies from the MSSM?

Description: The recent positron excess in cosmic rays (CR) observed by the PAMELA satellite may be a signal for dark matter (DM) annihilation. When these measurements are combined with those from FERMI on the total (e{sup +} + e{sup -}) ux and from PAMELA itself on the {anti p}p ratio, these and other results are difficult to reconcile with traditional models of DM, including the conventional minimal Supergravity (mSUGRA) version of Supersymmetry even if boosts as large as 10{sup 3-4} are allowed. In this paper, we combine the results of a previously obtained scan over a more general 19-parameter subspace of the Minimal Supersymmetric Standard Model (MSSM) with a corresponding scan over astrophysical parameters that describe the propagation of CR. We then ascertain whether or not a good fit to this CR data can be obtained with relatively small boost factors while simultaneously satisfying the additional constraints arising from gamma ray data. We find that a specific subclass of MSSM models where the Lightest Supersymmetric Particle (LSP) is mostly pure bino and annihilates almost exclusively into {tau} pairs comes very close to satisfying these requirements. The lightest in this set of models is found to be relatively close in mass to the LSP and is in some cases the nLSP. These models lead to a significant improvement in the overall fit to the data by {approx}1 unit of {chi}{sup 2}/dof in comparison to the best fit without Supersymmetry while employing boosts in the range {approx}100-200. The implications of these models for future experiments are discussed.
Date: August 11, 2011
Creator: Cotta, R.C.; /SLAC; Conley, J.A.; U., /Bonn; Gainer, J.S.; U., /Argonne /Northwestern et al.
Partner: UNT Libraries Government Documents Department