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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
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DOE OSTI2011

Correlation between flavor-violating decay of long-lived slepton and tau in the coannihilation scenario with the seesaw mechanism

We investigate flavor violating decays of the long-lived lightest slepton and the tau lepton in the coannihilation region of the minimal supersymmetric standard model with a seesaw mechanism to generate neutrino masses. We consider a situation where the mass difference between the lightest neutralino, as the lightest supersymmetric particle, and the lightest slepton, as the next-to-lightest supersymmetric particle, is smaller than the mass of tau lepton. In this situation, the lifetime of the lightest slepton is very long and it is determined by lepton flavor violating (LFV) couplings because the slepton mainly consists of the lighter stau and the flavor conserving 2-body decay is kinematically forbidden. We show that the lifetime can change many orders of magnitude by varying the Yukawa couplings entering the seesaw mechanism. We also show that the branching ratios of LFV tau decays are strongly correlated with the lightest slepton lifetime. Therefore the branching ratios of LFV tau decays can be determined or constrained by measuring the slepton lifetime at the LHC experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Comment on 'Amplification of endpoint structure for new particle mass measurement at the LHC'

We present a comment on the kinematic variable m{sub CT2} recently proposed in Won Sang Cho, Jihn E. Kim, and Ji-Hun Kim, Phys. Rev. D 81, 095010 (2010). The variable is designed to be applied to models such as R-parity conserving supersymmetry (SUSY) when there is pair production of new heavy particles each of which decays to a single massless visible and a massive invisible component. It was proposed by Cho, Kim, and Kim that a measurement of the peak of the m{sub CT2} distribution could be used to precisely constrain the masses of the SUSY particles. We show that, for the an example characterized by direct squark decays, when standard model backgrounds are included in simulations, the sensitivity of the m{sub CT2} variable to the SUSY particle masses is more seriously impacted for m{sub CT2} than for other previously proposed variables.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Squark contributions to photon structure functions and positivity constraints

Photon structure functions in supersymmetric QCD are investigated in terms of the parton model where squark contributions are evaluated. We calculate the eight virtual photon structure functions by taking the discontinuity of the squark massive one-loop diagrams of the photon-photon forward amplitude. The model-independent positivity constraints derived from the Cauchy-Schwarz inequalities are satisfied by the squark parton model calculation and actually the two equality relations hold for the squark contribution. We also show that our polarized photon structure function g{sub 1}{sup {gamma}} for the real photon leads to the vanishing first moment sum rule, and the constraint |g{sub 1}{sup {gamma}}|{<=}F{sub 1}{sup {gamma}} is satisfied by the real photon. We also discuss a squark signature in the structure function W{sub TT}{sup {tau}}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Sneutrino-antisneutrino oscillation at the Tevatron

Sneutrino-antisneutrino oscillation can be a very useful probe to look for signatures of lepton number violation ({Delta}L=2) at the Tevatron. Here, we discuss a scenario where the total decay width of the sneutrino is very small, producing interesting signals at the Tevatron for a mass splitting {Delta}m as small as 10{sup -14} GeV between the sneutrino mass eigenstates.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Can flavor physics hint at distinctive signals for R-parity violation at the LHC?

Observation of some low-energy processes in the flavor physics regime may require the existence of supersymmetry with two relatively large R-parity-violating couplings of the {lambda}{sup '}-type, together with reasonably light superparticles. At the LHC, such interactions would be expected to give rise to clear signals with convenient leptonic triggers, including some multileptons of the same sign. We undertake a detailed investigation of these signals taking care to correlate with low-energy requirements and taking proper account of the standard model backgrounds as well as the R-parity-conserving sector of the supersymmetric model. We find clear indications that R-parity violation as envisaged in this scenario can be detected at the LHC - even, perhaps, in the early runs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Gauge mediation to effective supersymmetry through U(1)s with a dynamical supersymmetry breaking, and string compactification

We investigate the possibility of U(1){sup '} mediation, leading to an effective SUSY where the first two family sfermions are above 100 TeV but the third family sfermions and the Higgs doublets are in the TeV region (or the light stop (t-tilde{sub l}) case). The U(1)' gaugino, Zprimino (Z'-ino), needs not to be at a TeV scale, but needs to be somewhat lighter than the messenger scale. We consider two cases, one the mediation is only through U(1){sup '} and the other through U(1)' and the electroweak hypercharge U(1){sub Y}. In the SUSY field theory framework, we calculate the superpartner mass spectra for these two cases. We also point out that the particle species needed for these mechanisms are already obtained from a Z{sub 12-I} orbifold compactification.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Stop as a next-to-lightest supersymmetric particle in constrained MSSM

So far the squarks have not been detected at the LHC indicating that they are heavier than a few hundred GeVs, if they exist. The lighter stop can be considerably lighter than the other squarks. We study the possibility that a supersymmetric partner of the top quark, stop, is the next-to-lightest supersymmetric particle in the constrained supersymmetric standard model. Various constraints, on top of the mass limits, are taken into an account, and the allowed parameter space for this scenario is determined. Observing stop which is the next-to-lightest supersymmetric particle at the LHC may be difficult.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Impact of squark flavor violation on neutralino dark matter

We discuss the possibility of new sources of flavor violation in the squark sector of supersymmetric models in the context of the dark matter relic density. We show that the corresponding nonminimal flavor violation terms in the squark mass matrices can have an important impact on the thermally averaged (co)annihilation cross section of the neutralino, and in consequence can modify its predicted relic density. We discuss in detail the relevant effects and present a numerical study of neutralino annihilation and coannihilation in this context. We also comment on the LHC phenomenology of the corresponding scenarios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Astrophysical limits on light NMSSM neutralinos

It was recently shown that light LSP neutralinos could be found in the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). These candidates would escape known particle physics constraints even though they are relatively light. We now investigate the astrophysical limits which can be set on these particles. We show, in particular, that the Fermi observation of dwarf spheroidal galaxies enable to constrain the parameter space associated with these candidates. Combined with the XENON100 experimental limits, our results illustrate the complementarity between direct and indirect searches for dark matter. Yet, our findings also suggest that probing light neutralinos in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) scenario will be very difficult because the sensitivity of both dark matter direct and indirect detection experiments would have to be improved by at least six orders of magnitude compared to present values in order to explore the entire parameter space. Finally, we show that the parameter space compatible with the CoGeNT signal (albeit disfavored by the XENON100 limit) is not excluded by gamma nor radio observations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Revisiting light neutralino scenarios in the MSSM

We revisit the case of a light neutralino lightest supersymmetric particle in the framework of the minimal supersymmetric standard model. We consider a model with 11 free parameters. We show that all scenarios where the annihilation of light neutralinos rely mainly on the exchange of a light pseudoscalar are excluded by direct detection searches and by Fermi measurements of the {gamma}-flux from dwarf spheroidal galaxies. On the other hand, we find scenarios with light sleptons that satisfy all collider and astroparticle physics constraints. In this case, the lower limit on the lightest supersymmetric particle mass is 12.6 GeV. We discuss briefly how the parameter space of the model could be further probed at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Search for new phenomena in events with two Z bosons and missing transverse momentum in pp̄ collisions at √s=1.96 TeV

We present a search for new phenomena in events with two reconstructed Z bosons and large missing transverse momentum, sensitive to processes pp̄→X₂X₂→ZZX₁X₁, where X₂ is an unstable particle decaying as X₂→ZX₁ and X₁ is undetected. The particles X₁ and X₂ may be, among other possibilities, fourth-generation neutrinos or supersymmetric particles. We study the final state in which one Z boson decays to two charged leptons and the second decays hadronically. In data corresponding to an integrated luminosity of 4.2 fb⁻¹ from proton-antiproton collisions recorded by the CDF II detector at the Tevatron, with center-of-mass energy of 1.96 TeV, we find agreement between data and standard-model backgrounds. We calculate 95% confidence level upper limits on the cross section of the process pp̄→X₂X₂→ZZX₁X₁ ranging from 50 fb to 1 pb, depending on the masses of X₁ and X₂.

Aaltonen, T.↗
DOE OSTI2019

Search for pair production of first-generation scalar leptoquarks at s =13 TeV

A search for the pair production of first-generation scalar leptoquarks is performed using proton-proton collision data recorded at 13 TeV center-of-mass energy with the CMS detector at the LHC. The data correspond to an integrated luminosity of 35.9 fb-1. The leptoquarks are assumed to decay promptly to a quark and either an electron or a neutrino, with branching fractions β and 1-β, respectively. The search targets the decay final states comprising two electrons, or one electron and large missing transverse momentum, along with two quarks that are detected as hadronic jets. First-generation scalar leptoquarks with masses below 1435 (1270) GeV are excluded for β=1.0(0.5). These are the most stringent limits on the mass of first-generation scalar leptoquarks to date. The data are also interpreted to set exclusion limits in the context of an R-parity violating supersymmetric model, predicting promptly decaying top squarks with a similar dielectron final state. © 2019 2019 CERN, for the CMS Collaboration.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

Search for Supersymmetry in pp Collisions at {radical}(s)=7 TeV in Events with Two Photons and Missing Transverse Energy

A search for supersymmetry in the context of general gauge-mediated breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is presented. The data sample corresponds to an integrated luminosity of 36 pb{sup -1} recorded by the CMS experiment at the LHC. The search is performed by using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for general gauge-mediated supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squark, gluino, and neutralino masses, excluding supersymmetry parameter space that was inaccessible to previous experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

First Search for Multijet Resonances in $\sqrt{s} = 1.96$ TeV $ p\bar{p}$ Collisions

We present the first model independent search for three-jet hadronic resonances within multijet events in $\sqrt{s} = 1.96$ TeV $ p\bar{p}$ collisions at the Fermilab Tevatron using the CDF II detector. Pair production of supersymmetric gluinos and squarks with hadronic R-parity violating decays is employed as an example of a new physics benchmark for this signature. Selection criteria based on the kinetmatic properties of an ensemble of jet combinations within each event help to extract signal from copious QCD background. Our background estimates include all-hadronic t{anti t} decays that have a signature similar to the signal. No significant excess outside the top quark mass window is observed in data with an integrated luminosity of 3.2 fb{sup -1}. We place 95% confidence level limits on the production cross section {sigma}(p{anti p} {yields} X X&#x27;) x BR ((tilde gg) {yields} 3 jet + 3 jet) where X, X&#x27; = {tilde g}, {tilde q}, or {tilde {anti q}}, with {tilde q}, {tilde {anti q}} {yields} {tilde g} + jet, as a function of gluino mass, in the range of 77 GeV/c{sup 2} to 240 GeV/c{sup 2}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗