118642770
Low scale and gauge mediated supersymmetry breaking at the Fermilab Tevatron Run II
The prospects for discovering and studying signals of low-scale supersymmetry breaking models at the Tevatron Run II and beyond are explored. These models include gauge-mediated supersymmetry breaking as the most compelling and concrete realization, but more generally are distinguished by the presence of a nearly massless Goldstino as the lightest supersymmetric particle. The next-lightest supersymmetric particle(s) (NLSP) decays to its partner and the Goldstino. Depending on the supersymmetry breaking scale, these decays can occur promptly or on a scale comparable to or larger than the size of a detector. A systematic analysis based on a classification in terms of the identity of the NLSP and its decay length is presented. The various scenarios are discussed in terms of signatures and possible event selection criteria. The Run II and beyond discovery and exclusion reaches, including the effects of background, are detailed for the most compelling cases. In addition to standard event selection criteria based on missing energy and photons, leptons, jets, taus, tagged b-jets, or reconstructed Z-bosons, more exotic signals of metastable NLSPs such as displaced photons, large negative impact parameter tracks, kink tracks, both opposite and same-sign highly ionizing tracks, time of flight measurements, charge-changing tracks, charge-exchange tracks, and same-signmore » di-top events are investigated. The interesting possibility of observing a Higgs boson signal in events that are efficiently ''tagged'' by the unique signatures of low-scale supersymmetry breaking is also considered.« less
16884548
The Reach of Tevatron upgrades in gauge mediated supersymmetry breaking models
We examine signals for sparticle production at the Fermilab 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 supersymmetry 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 minimal supergravity framework. For two of these model lines, we find that the ability to identify {ital b}-quarks and {tau}-leptons with high efficiency and purity is essential for the detection of the signal. {copyright} {ital 1999} {ital The American Physical Society}
16924543
Reach of the CERN Large Hadron Collider for gauge-mediated supersymmetry breaking models
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 ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}},$ 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 ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}g~3$ TeV, assuming 10 ${\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity.
17823222
LHC reach for gauge mediated supersymmetry breaking models via prompt photon channels
Abstract We evaluate the supersymmetry reach of the Large Hadron Collider within the gauge-mediated low energy supersymmetry breaking framework, assuming that a neutralino is the second lightest sparticle and that it decays promptly into a gravitino which escapes detection. We find that the maximum reach is obtained via a search for inclusive γγ+ E / T events coming dominantly from chargino and neutralino production. Assuming an integrated luminosity of 10 fb −1 , we find that LHC experiments will be able to probe values of the model parameter Λ ≲400 TeV, corresponding to m g ≤2.8 TeV. A measure of the model parameter Λ may be possible from the photon p T spectrum.
126247646
Yields and elliptic flow of d(anti-d) and He-3(anti-He-3) in Au + Au collisions at s(NN)**(1/2) = 200- GeV
118168382
First observation of the isospin violating decay $J/\psi\rightarrow \Lambda\bar{\Sigma}^{0}+c.c.$
Using a sample of $(225.2\pm 2.8)\times 10^6$ $J/\psi$ events collected with the BESIII detector, we present results of a study of $J/\psi\rightarrow \gamma\Lambda\bar{\Lambda}$ and report the first observation of the isospin violating decay $J/\psi\rightarrow\Lambda\bar{\Sigma}^{0}+c.c.$, in which $\bar{\Sigma}^{0}$ decays to $\gamma \bar{\Lambda}$. The measured branching fractions are $\mathcal{B}(J/\psi\rightarrow\bar{\Lambda}\Sigma^{0}$) = $(1.46\pm0.11\pm0.12) \times10^{-5}$ and $\mathcal{B}(J/\psi\rightarrow\Lambda\bar{\Sigma^{0}}$) = $(1.37\pm0.12\pm0.11) \times10^{-5}$. We search for $\Lambda(1520) \rightarrow \gamma \Lambda$ decay, and find no evident signal, and an upper limit for the product branching fraction $\mathcal{B}(J/\psi\rightarrow\Lambda\bar{\Lambda}(1520)+c.c.)\times \mathcal{B}(\Lambda(1520)\rightarrow\gamma\Lambda)<4.1 \times10^{-6}$ is set at the 90% confidence level. We also report the observation of $\eta_{c}\rightarrow\Lambda\bar{\Lambda}$ in $J/\psi \rightarrow \gamma \eta_{c}$, $\eta_{c}\rightarrow\Lambda\bar{\Lambda}$ and measure the branching fraction $\mathcal{B}(\eta_{c}\rightarrow\Lambda\bar{\Lambda}) =(1.16\pm0.12 (stat)\pm0.19(syst)\pm0.28(PDG))\times10^{-3}$.
119295809
Toward the Natural and Realistic NMSSM with and without $R$-Parity
From the current ATLAS and CMS results on Higgs boson mass and decay rates, the NMSSM is obviously better than the MSSM. To explain the fine-tuning problems such as gauge hiearchy problem and strong CP problem in the SM, we point out that supersymmetry does not need to provide a dark matter candidate, i.e., R-parity can be violated. Thus, we consider three kinds of the NMSSM scenarios: in Scenarios I and II R-parity is conserved and the lightest neutralino relic density is respectively around and smaller than the observed value, while in Scenario III R-parity is violated. To fit all the experimental data, we consider the \chi^2 analyses, and find that the Higgs boson mass and decay rates can be explained very well in these Scenarios. Considering the small \chi^2 values and fine-tuning around 2-3.7% (or 1-2%), we obtain the viable parameter space with light (or relatively heavy) supersymmetric particle spectra only in Scenario III (or in Scenarios I and II). Because the singlino, Higgsinos, and light stop are relatively light in general, we can relax the LHC supersymmetry search constraints but the XENON100 experiment gives a strong constraint in Scenarios I and II. In all the viable parameter space, the anomalous magnetic moment of the muon (g_{\mu} - 2)/2 are generically small. With R-parity violation, we can increase (g_{\mu} - 2)/2, and avoid the contraints from the LHC supersymmetry searches and XENON100 experiment. Therefore, Scenario III with R-parity violation is more natural and realistic than Scenarios I and II.
5692175
Effects of correlation between merging steps on the global halo formation
The excursion set theory of halo formation is modified by adopting the fractional Brownian motion, to account for possible correlation between merging steps. We worked out analytically the conditional mass function, halo merging rate and formation time distribution in the spherical collapse model. We also developed an approximation for the ellipsoidal collapse model and applied it to the calculation of the conditional mass function and the halo formation time distribution. For models in which the steps are positively correlated, the halo merger rate is enhanced when the accreted mass is less than similar to 25M*, while for the negatively correlated case this rate is reduced. Compared with the standard model in which the steps are uncorrelated, the models with positively correlated steps produce more aged population in small mass haloes and more younger population in large mass haloes, while for the models with negatively correlated steps the opposite is true. An examination of simulation results shows that a weakly positive correlation between successive merging steps appears to fit best. We have also found a systematic effect in the measured mass function due to the finite volume of simulations. In future work, this will be included in the halo model to accurately predict the three-point correlation function estimated from simulations.
118712522
EXPLORING THE COSMIC REIONIZATION EPOCH IN FREQUENCY SPACE: AN IMPROVED APPROACH TO REMOVE THE FOREGROUND IN 21 cm TOMOGRAPHY
With the intent of correctly restoring the redshifted 21 cm signals emitted by neutral hydrogen during the cosmic reionization processes, we re-examine the separation approaches based on the quadratic polynomial fitting technique in frequency space in order to investigate whether they work satisfactorily with complex foreground by quantitatively evaluating the quality of restored 21 cm signals in terms of sample statistics. We construct the foreground model to characterize both spatial and spectral substructures of the real sky, and use it to simulate the observed radio spectra. By comparing between different separation approaches through statistical analysis of restored 21 cm spectra and corresponding power spectra, as well as their constraints on the mean halo bias b and average ionization fraction x(e) of the reionization processes, at z = 8 and the noise level of 60 mK we find that although the complex foreground can be well approximated with quadratic polynomial expansion, a significant part of the Mpc-scale components of the 21 cm signals (75% for greater than or similar to 6 h(-1) Mpc scales and 34% for greater than or similar to 1 h(-1) Mpc scales) is lost because it tends to be misidentified as part of the foreground when the single-narrow-segment separation approach is applied. The best restoration of the 21 cm signals and the tightest determination of b and xe can be obtained with the three-narrow-segment fitting technique as proposed in this paper. Similar results can be obtained at other redshifts.