5,936 research outputs found

    Trileptons from Chargino-Neutralino Production at the CERN Large Hadron Collider

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    We study direct production of charginos and neutralinos at the CERN Large Hadron Collider. We simulate all channels of chargino and neutralino production using ISAJET 7.07. The best mode for observing such processes appears to be pp\to\tw_1\tz_2\to 3\ell +\eslt. We evaluate signal expectations and background levels, and suggest cuts to optimize the signal. The trilepton mode should be viable provided m_{\tg}\alt 500-600~GeV; above this mass, the decay modes \tz_2\to\tz_1 Z and \tz_2\to H_{\ell}\tz_1 become dominant, spoiling the signal. In the first case, the leptonic branching fraction for ZZ decay is small and additional background from WZWZ is present, while in the second case, the trilepton signal is essentially absent. For smaller values of mtgm_{\tg}, the trilepton signal should be visible above background, especially if μmtg|\mu|\simeq m_{\tg} and m_{\tell}\ll m_{\tq}, in which case the leptonic decays of \tz_2 are enhanced. Distributions in dilepton mass m(ˉ)m(\ell\bar{\ell}) can yield direct information on neutralino masses due to the distribution cutoff at m_{\tz_2}-m_{\tz_1}. Other distributions that may lead to an additional constraint amongst the chargino and neutralino masses are also examined.Comment: preprint nos. FSU-HEP-940310 and UH-511-786-94, 13 pages (REVTEX) plus 7 uuencoded figures attache

    Assessment of flywheel energy storage for spacecraft power systems

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    The feasibility of inertial energy storage in a spacecraft power system is evaluated on the basis of a conceptual integrated design that encompasses a composite rotor, magnetic suspension, and a permanent magnet (PM) motor/generator for a 3-kW orbital average payload at a bus distribution voltage of 250 volts dc. The conceptual design, which evolved at the Goddard Space Flight Center (GSFC), is referred to as a Mechanical Capacitor. The baseline power system configuration selected is a series system employing peak-power-tracking for a Low Earth-Orbiting application. Power processing, required in the motor/generator, provides a potential alternative configurations that can only be achieved in systems with electrochemical energy storage by the addition of power processing components. One such alternative configuration provides for peak-power-tracking of the solar array and still maintains a regulated bus, without the expense of additional power processing components. Precise speed control of the two counterrotating wheels is required to reduce interaction with the attitude control system (ACS) or alternatively, used to perform attitude control functions. Critical technologies identified are those pertaining to the energy storage element and are prioritized as composite wheel development, magnetic suspension, motor/generator, containment, and momentum control. Comparison with a 3-kW, 250-Vdc power system using either NiCd or NiH2 for energy storage results in a system in which inertial energy storage offers potential advantages in lifetime, operating temperature, voltage regulation, energy density, charge control, and overall system weight reduction

    SUPERSYMMETRY REACH OF AN UPGRADED TEVATRON COLLIDER

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    We examine the capability of a s=2\sqrt{s}=2 TeV Tevatron ppˉp\bar p collider to discover supersymmetry, given a luminosity upgrade to amass 25 fb125\ fb^{-1} of data. We compare with the corresponding reach of the Tevatron Main Injector (1 fb11\ fb^{-1} of data). Working within the framework of minimal supergravity with gauge coupling unification and radiative electroweak symmetry breaking, we first calculate the regions of parameter space accessible via the clean trilepton signal from \tw_1\tz_2\to 3\ell +\eslt production, with detailed event generation of both signal and major physics backgrounds. The trilepton signal can allow equivalent gluino masses of up to mtg600700m_{\tg}\sim 600-700 GeV to be probed if m0m_0 is small. If m0m_0 is large, then mtg500m_{\tg}\sim 500 GeV can be probed for μ0\mu 0 and large values of m0m_0, the rate for \tz_2\to\tz_1\ell\bar{\ell} is suppressed by interference effects, and there is {\it no} reach in this channel. We also examine regions where the signal from \tw_1\overline{\tw_1}\to \ell\bar{\ell}+\eslt is detectable. Although this signal is background limited, it is observable in some regions where the clean trilepton signal is too small. Finally, the signal \tw_1\tz_2\to jets+\ell\bar{\ell} +\eslt can confirm the clean trilepton signal in a substantial subset of the parameter space where the trilepton signal can be seen. We note that although the clean trilepton signal may allow Tevatron experiments to identify signals in regions of parameter space beyond the reach of LEP II, the dilepton channels generally probe much the same region as LEP II.Comment: 19 page REVTEX file; a uuencoded PS file with PS figures is available via anonymous ftp at ftp://hep.fsu.edu/preprints/baer/FSUHEP950301.u

    Mixed Higgsino Dark Matter from a Large SU(2) Gaugino Mass

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    We observe that in SUSY models with non-universal GUT scale gaugino mass parameters, raising the GUT scale SU(2) gaugino mass |M_2| from its unified value results in a smaller value of -m_{H_u}^2 at the weak scale. By the electroweak symmetry breaking conditions, this implies a reduced value of \mu^2 {\it vis \`a vis} models with gaugino mass unification. The lightest neutralino can then be mixed Higgsino dark matter with a relic density in agreement with the measured abundance of cold dark matter (DM). We explore the phenomenology of this high |M_2| DM model. The spectrum is characterized by a very large wino mass and a concomitantly large splitting between left- and right- sfermion masses. In addition, the lighter chargino and three light neutralinos are relatively light with substantial higgsino components. The higgsino content of the LSP implies large rates for direct detection of neutralino dark matter, and enhanced rates for its indirect detection relative to mSUGRA. We find that experiments at the LHC should be able to discover SUSY over the portion of parameter space where m_{\tg} \alt 2350-2750 ~GeV, depending on the squark mass, while a 1 TeV electron-positron collider has a reach comparable to that of the LHC. The dilepton mass spectrum in multi-jet + \ell^+\ell^- + \eslt events at the LHC will likely show more than one mass edge, while its shape should provide indirect evidence for the large higgsino content of the decaying neutralinos.Comment: 36 pages with 26 eps figure

    Testing the gaugino AMSB model at the Tevatron via slepton pair production

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    Gaugino AMSB models-- wherein scalar and trilinear soft SUSY breaking terms are suppressed at the GUT scale while gaugino masses adopt the AMSB form-- yield a characteristic SUSY particle mass spectrum with light sleptons along with a nearly degenerate wino-like lightest neutralino and quasi-stable chargino. The left- sleptons and sneutrinos can be pair produced at sufficiently high rates to yield observable signals at the Fermilab Tevatron. We calculate the rate for isolated single and dilepton plus missing energy signals, along with the presence of one or two highly ionizing chargino tracks. We find that Tevatron experiments should be able to probe gravitino masses into the ~55 TeV range for inoAMSB models, which corresponds to a reach in gluino mass of over 1100 GeV.Comment: 14 pages including 6 .eps figure

    Hidden SUSY at the LHC: the light higgsino-world scenario and the role of a lepton collider

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    While the SUSY flavor, CP and gravitino problems seem to favor a very heavy spectrum of matter scalars, fine-tuning in the electroweak sector prefers low values of superpotential mass \mu. In the limit of low \mu, the two lightest neutralinos and light chargino are higgsino-like. The light charginos and neutralinos may have large production cross sections at LHC, but since they are nearly mass degenerate, there is only small energy release in three-body sparticle decays. Possible dilepton and trilepton signatures are difficult to observe after mild cuts due to the very soft p_T spectrum of the final state isolated leptons. Thus, the higgsino-world scenario can easily elude standard SUSY searches at the LHC. It should motivate experimental searches to focus on dimuon and trimuon production at the very lowest p_T(\mu) values possible. If the neutralino relic abundance is enhanced via non-standard cosmological dark matter production, then there exist excellent prospects for direct or indirect detection of higgsino-like WIMPs. While the higgsino-world scenario may easily hide from LHC SUSY searches, a linear e^+e^- collider or a muon collider operating in the \sqrt{s}\sim 0.5-1 TeV range would be able to easily access the chargino and neutralino pair production reactions.Comment: 20 pages including 12 .eps figure

    SIGNALS FOR MINIMAL SUPERGRAVITY AT THE CERN LARGE HADRON COLLIDER: MULTI-JET PLUS MISSING ENERGY CHANNEL,

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    We use ISAJET to perform a detailed study of the missing transverse energy \eslt plus multi-jet signal expected from superparticle production at the CERN LHC. Our analysis is performed within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking. We delineate the region of parameter space where the \eslt supersymmetry signal should be observable at the LHC and compare it to the regions explorable via searches for sleptons and for chargino/neutralino production. We confirm that, given a data sample of 10~\fb^{-1}, mtg1300m_{\tg}\sim 1300 GeV can be explored if m_{\tq}\gg m_{\tg}, while mtg2000m_{\tg}\sim 2000 GeV can be probed if m_{\tq}\simeq m_{\tg}. We further examine what information can be gleaned from scrutinizing this event sample. For instance, the multi-jet multiplicity yields information on whether squark production makes a significant contribution to the observed \eslt sample. Furthermore, reconstructing hemispheric masses may yield a measure of mtgm_{\tg} to 1525%\sim 15-25\%. Finally, for favourable ranges of parameters, by reconstructing masses of tagged bbˉb\bar{b} jet pairs, it may be possible to detect Higgs bosons produced via sparticle cascade decay chains.Comment: 22 pages (REVTEX); a PS text file (etmiss.ps) and 12 figures (etlhc.uu or etlhc.ps) can be obtained via anonymous ftp at ftp://hep.fsu.edu/anonymous.bae

    Probing Minimal Supergravity at the CERN LHC for Large tanβ\tan\beta

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    For large values of the minimal supergravity model parameter tanβ\tan\beta, the tau lepton and the bottom quark Yukawa couplings become large, leading to reduced masses of τ\tau-sleptons and bb-squarks relative to their first and second generation counterparts, and to enhanced decays of charginos and neutralinos to τ\tau-leptons and bb-quarks. We evaluate the reach of the CERN LHC pppp collider for supersymmetry in the mSUGRA model parameter space. We find that values of mtg15002000m_{\tg}\sim 1500-2000 GeV can be probed with just 10 fb1^{-1} of integrated luminosity for tanβ\tan\beta values as high as 45, so that mSUGRA cannot escape the scrutiny of LHC experiments by virtue of having a large value of tanβ\tan\beta. We also perform a case study of an mSUGRA model at tanβ=45\tan\beta =45 where \tz_2\to \tau\ttau_1 and \tw_1\to \ttau_1\nu_\tau with 100\sim 100% branching fraction. In this case, at least within our simplistic study, we show that a di-tau mass edge, which determines the value of m_{\tz_2}-m_{\tz_1}, can still be reconstructed. This information can be used as a starting point for reconstructing SUSY cascade decays on an event-by-event basis, and can provide a strong constraint in determining the underlying model parameters. Finally, we show that for large tanβ\tan\beta there can be an observable excess of τ\tau leptons, and argue that τ\tau signals might serve to provide new information about the underlying model framework.Comment: 22 page REVTEX file including 8 figure
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