Neutralino Pair Production Research Articles

Search for R-parity violating decays of supersymmetric particles in $\mathrm{e^+e^-}$ collisions at $\sqrt{s}=$ 189 GeV

A search for chargino, neutralino and scalar lepton pair-production in e+e- collisions at the centre-of-mass energy of 189 GeV is performed under the assumptions that R-parity is not conserved in decays and only one of the coupling constants lambda_ijk, lambda'_ijk or lambda''_ijk is non-negligible. No signal is found in a data sample corresponding to an integrated luminosity of 176.4 pb-1. Limits on the production cross sections, on the Minimal Supersymmetric Standard Model parameters and on the masses of the supersymmetric particles are derived.

Search for supersymmetric particles in e +e − collisions at [formula omitted] up to 202 GeV and mass limit for the lightest neutralino

Searches for pair production of squarks, sleptons, charginos and neutralinos are performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies from 188.6 to 201.6 GeV. No evidence for any such signals is observed in a total integrated luminosity of about 410 pb −1. The negative results of the searches are translated into exclusion domains in the space of the relevant MSSM parameters, which improve significantly on the constraints set previously. Under the assumptions of gaugino and sfermion mass unification, these results allow a 95% C.L. lower limit of 37 GeV/ c 2 to be set on the mass of the lightest neutralino for any tan β and sfermion mass. Additional constraints in the MSSM parameter space are derived from the negative results of ALEPH searches for Higgs bosons. The results are also interpreted in the framework of minimal supergravity.

Search for neutralino pair production at $\sqrt{s}$ = 189 GeV

A search for pair-production of neutralinos at a LEP centre-of-mass energy of 189 GeV gave no evidence for a signal. This limits the neutralino production cross-section and excludes regions in the parameter space of the Minimal Supersymmetric Standard Model (MSSM).

Pair production of neutralinos via photon-photon collisions

We investigate the production of neutralino pairs via photon-photon collisions in the minimal supersymmetric model at future linear colliders. The numerical analysis of their production rates is carried out in the minimal supergravity scenario. The results show that this cross section can reach about 18 fb for ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}$ pair production and 9 fb barn for ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}$ pair production with our chosen input parameters.

Search for SUSY with R-parity violating [formula omitted] couplings at [formula omitted] GeV

Searches for pair production of supersymmetric particles under the assumption that R-parity is not conserved are presented, based on data recorded by the DELPHI detector in 1998 from e +e − collisions at a centre-of-mass energy of 189 GeV. Only one R-parity violating LL E ̄ term (i.e. one λ coupling), which couples scalar leptons to leptons, is considered to be dominant at a time. Moreover, it is assumed that the strength of the R-parity violating couplings is such that the lifetimes can be neglected. The search for pair production of neutralinos, charginos and sleptons has been performed for both direct R-parity violating decays and indirect cascade decays. The results are in agreement with Standard Model expectations, and are used to update the constraints on the MSSM parameter values and the mass limits previously derived at s =183 GeV. The present 95% C.L. limits on supersymmetric particle masses are: • m χ ̃ 0 > 30 GeV/ c 2 and m χ ̃ ± > 94 GeV/ c 2; • m ν ̃ > 76.5 GeV/ c 2 (direct and indirect decays); • m ℓ ̃ R > 83 GeV/ c 2 (indirect decay only).

Neutralino Pair Production at Proton-Proton Collider**The project supported in part by National Natural Science Foundation of China (Nos 19675033 and 19875049), the Youth Science Foundation of the University of Science and Technology of China and a grant from the State Commission of Science and Technology of China

We investigated the Drell-Yan process of the light neutralino pair productions at hadron colliders. We studied the dependence of the coupling properties of two light neutralinos on, three SUSY Lagrangian parameters , and , and find that the production rate of pair will be dominated by the Higgsino-like couplings under the conditions and , while the productions of and pairs will be enhanced by the gaugino-like couplings under . For the Higgsino-like neutralinos, the cross section of production at the LHC can reach 100 fb.

Search for R-parity violating chargino and neutralino decays in e+e− collisions up to [formula omitted] GeV

A search for chargino and neutralino pair production in e+e− collisions at center-of-mass energies between 161GeV and 183GeV is performed under the assumptions that R-parity is not conserved and that only purely leptonic or hadronic R-parity violating decays are allowed. No signal is found in the data. Limits on the production cross sections, on the Minimal Supersymmetric Standard Model parameters and on the masses of the supersymmetric particles are derived.

Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP

Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP

Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP

Molecular dynamics simulations were carried out to investigate the adsorption of a low-energy C20 on a reconstructed silicon (001)-(\(\)) surface. The impact energies of the C20 fullerene range from 1 eV/atom to 5 eV/atom. After impacting, the C20 molecule is found to move along (011) direction and resides either in the trough or on the dimer at the end of our simulations. The lateral motion of C20 on the surface is dependent on its incident energy. Chemical bonds are formed between C20 and the surface. By the force field analysis, we show that the anisotropic molecule-surface interaction plays the leading role in the lateral motion of C20 as well as its preferable adsorption sites on the dimerized Si surface. These findings are consistent with experimental observations of C60 on Si (001) surface and small carbon clusters on solid surfaces.

Search for chargino and neutralino production at

A search for charginos and neutralinos, predicted by supersymmetric theories, has been performed using a data sample of 57 pb $^{-1}$ at centre-of-mass energies of 181–184 GeV taken with the OPAL detector at LEP. No evidence for chargino or neutralino production has been found. Upper limits on chargino and neutralino pair production ( $\tilde\chi^+_1 \tilde\chi^-_1$ , $\tilde\chi^0_1 \tilde\chi^0_2$ ) cross-sections are obtained as a function of the chargino mass ( $m_{\tilde\chi^\pm_1}$ ), the lightest neutralino mass ( $m_{\tilde\chi^0_1}$ ) and the second lightest neutralino mass ( $m_{\tilde\chi^0_2}$ ). For large chargino masses the limits have been improved with respect to the previous analyses at lower centre-of-mass energies. Exclusion regions at 95% confidence level (C.L.) of parameters of the Constrained Minimal Supersymmetric Standard Model are determined for the case of a large universal scalar mass, $m_0$ , implying heavy scalar fermions, and for the case of a small $m_0$ resulting in light scalar fermions and giving the worst-case limits. Within this framework and for $m_{\tilde\chi^\pm_1} - m_{\tilde\chi^0_1} \geq 5$ GeV the 95% C.L. lower limits on $m_{\tilde\chi^\pm_1}$ for $m_0=500$ GeV are 90.0 and 90.2 GeV for $\tan \beta = 1.5$ and 35 respectively. These limits for all $m_0$ (the worst-case) are 69.1 and 65.2 GeV for $\tan \beta = 1.5$ and 35 respectively. Exclusion regions are also presented for neutralino masses, including an absolute lower limit at 95% C.L. for the mass of the lightest neutralino of 30.1 GeV for $m_0 = 500$ GeV (24.2 GeV for all $m_0$ ), with implications for experimental searches for the lightest neutralino as a dark matter candidate.

Multilepton signatures of gauge mediated SUSY breaking at CERN LEP II

In the framework of gauge-mediated supersymmetry breaking models pair production of the lightest neutralinos, scalar leptons, or charginos at LEPII gives rise to interesting signals involving multilepton final states and missing energy. In the parameter space where the scalar tau, $\tilde{\tau}_1$, is the next-to-lightest supersymmetric particle, we identify three interesting regions, which give rise to distinctly different final states: (i) 2 $\tau$-leptons plus missing energy, (ii) 4 charged leptons plus missing energy where in some regions all four are $\tau$-leptons, or (iii) six charged leptons, of which four are $\tau$-leptons and the other two are electrons or muons, plus missing energy. We study in detail the size of these regions in the parameter space of gauge-mediated models and give cross section contours in these regions for various LEPII energies. We also discuss the possibility of chargino-pair production at LEPII.

Search for chargino and neutralino production at $\sqrt{s} = 170$ and 172 GeV at LEP

A search for charginos and neutralinos, predicted by supersymmetric theories, is performed using a data sample of 182.1 pb-1 taken at a centre-of-mass energy of 189 GeV with the OPAL detector at LEP. No evidence for chargino or neutralino production is found. Upper limits on chargino and neutralino pair production (X1+X1-, X10X20) cross-sections are obtained as a function of the chargino mass (mX1±), the lightest neutralino mass (mX10) and the second lightest neutralino mass (mX20). Within the Constrained Minimal Supersymmetric Standard Model framework, and for mX1± - mX10 ≥ 5 GeV, the 95% confidence level lower limits on mX1± are 93.6 GeV for tan β = 1.5 and 94.1 GeV for tan β = 35. These limits are obtained assuming a universal scalar mass m0 ≥ 500 GeV. The corresponding limits for all m0 are 78.0 and 71.7 GeV. The 95% confidence level lower limits on the lightest neutralino mass, valid for any value of tan β are 32.8 GeV for m0 ≥ 500 GeV and 31.6 GeV for all m0.

Gauge-mediated supersymmetry breaking signals at LEP2

We consider the experimental signals that can arise in a general class of models with gauge-mediated supersymmetry breaking in which the gravitino is the lightest supersymmetric particle. Depending on which superpartners decay dominantly to the gravitino, several qualitatively different possibilities arise for the phenomenology of such models. At LEP2, neutralino pair production and/or slepton pair production can lead to a variety of promising discovery signals. We investigate the impact of backgrounds for these signals and show how they can be reduced. (Work done in collaboration with S. Ambrosanio and G.D. Kribs. [1])

Experimental Search for Chargino and Neutralino Production in Supersymmetry Models with a Light Gravitino

We search for inclusive high $E_T$ diphoton events with large missing transverse energy in $p\bar{p}$ collisions at $\sqrt{s}$=1.8 TeV. Such events are expected from pair production of charginos and neutralinos within the framework of the minimal supersymmetric standard model with a light gravitino. No excess of events is observed. In that model, and assuming gaugino mass unification at the GUT scale, we obtain a 95% CL exclusion region in the supersymmetry parameter space and lower mass bounds of 150 GeV/c$^2$ for the lightest chargino and 75 GeV/c$^2$ for the lightest neutralino.

Testing gauge-gravitino coupling in gauge-mediated supersymmetry breaking through single photon events

We show that the process $e^+e^- \to \gamma+$ missing energy, arising from the pair production of neutralinos, can probe the $\gamma-\tilde\gamma- \gravitino$ as well as the $Z-\tilde Z-\gravitino$ couplings in Gauge Mediated Supersymmetry Breaking models. This enables one to study the mutual relationship of the Goldstino couplings of the different gauginos, a feature whose testability has not been emphasized so far. The Standard Model backgrounds get suppresed with the use of a right polarized electron beam. The energy and angular distribution of the emitted photon can distinguish such models from the minimal supersymmetric theory and its variants.

Search for charginos, neutralinos and gravitinos at LEP

An update of the searches for charginos and neutralinos in DELPHI is presented, based mainly on recent data collected at centre-of-mass energies of 161 GeV and 172 GeV. No signal is found. For a sneutrino with mass above 300 GeV/c 2 and a mass difference between the chargino and the lightest neutralino above 10 GeV/c 2, the lower limit at 95% confidence level on the chargino mass ranges from 84.3 GeV/c 2 to the kinematical limit (86.0 GeV/c 2), depending on the mixing parameters. The limit decreases for lower chargino-neutralino mass differences. The limit in the case of a light sneutrino is 67.6 GeV/c 2, provided that that there is no light sneutrino with a mass within 10 GeV/c 2 below the chargino mass. Upper limits on neutralino pair production cross-sections of about a picobarn are derived. The (μ,M 2) domain excluded in the MSSM-GUT scenario is determined by combining the neutralino and chargino searches. These results imply a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 24.9 GeV/c 2 for tanß >- 1. The search has also been extended to the case where the lightest neutralino is unstable and decays into a photon and a gravitino. imply a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 24.9 GeV/c 2 for tanß >- 1. The search has also been extended to the case where the lightest neutralino is unstable and decays into a photon and a gravitino.

Signals for gauge-mediated supersymmetry-breaking models at the CERN LEP 2 collider

We consider a general class of models with gauge-mediated supersymmetry breaking in which the gravitino is the lightest supersymmetric particle. Several qualitatively different scenarios arise for the phenomenology of such models, depending on which superpartner(s) decay dominantly to the gravitino. At LEP2, neutralino pair production and slepton pair production can lead to a variety of promising discovery signals, which we systematically study. We investigate the impact of backgrounds for these signals and show how they can be reduced, and outline the effects of model parameter variations on the discovery potential.

Single-photon signals at CERN LEP in supersymmetric models with a light gravitino

We study the single-photon signals expected at CERN LEP in models with a very light gravitino ${(m}_{\mathrm{G\ifmmode \tilde{}\else \~{}\fi{}}}\ensuremath{\lesssim}{10}^{\ensuremath{-}3}\mathrm{eV})$. The dominant process is neutralino-gravitino production ${(e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\chi}\mathrm{G\ifmmode \tilde{}\else \~{}\fi{}})$ with subsequent neutralino decay via $\ensuremath{\chi}\ensuremath{\rightarrow}\ensuremath{\gamma}\mathrm{G\ifmmode \tilde{}\else \~{}\fi{}}$, giving a $\ensuremath{\gamma}+{\mathrm{E}}_{\mathrm{miss}}$ signal. We first calculate the cross section at arbitrary center-of-mass energies and provide new analytic expressions for the differential cross section valid for general neutralino compositions. We then consider the constraints on the gravitino mass from LEP 1 and LEP 161 single-photon searches, and possible such searches at the Fermilab Tevatron. We show that it is possible to evade the stringent LEP 1 limits and still obtain an observable rate at LEP 2, in particular, in the region of parameter space that may explain the CDF $\mathrm{ee}\ensuremath{\gamma}\ensuremath{\gamma}{+E}_{T,\mathrm{miss}}$ event. As diphoton events from neutralino pair production would not be kinematically accessible in this scenario, the observation of whichever photonic signal will discriminate among the various light-gravitino scenarios in the literature. We also perform a Monte Carlo simulation of the expected energy and angular distributions of the emitted photon, and of the missing invariant mass expected in the events. Finally we specialize the results to the case of a recently proposed one-parameter no-scale supergravity model.

Signals of left-right supersymmetry in e + e - collisions

We study chargino and neutralino pair production at the Next Linear e+ e− Collider in a supersymmetric left-right model. We investigate on- and off-resonance signals via the processes: $e^{+}e^{-}⌝ghtarrow {⇔lde chi}_{1}^{+}{⇔lde chi}_{1}^{-} ⌝ghtarrow e^{+}e^{-}+{⤪ p}_{⤪ miss}$ and $e^{+}e^{-}⌝ghtarrow {⇔lde chi}_{2}^{0}{⇔lde chi}_{1}^{0} ⌝ghtarrow e^{+}e^{-}+{⤪ p}_{⤪ miss}$. These reactions could lead to observable signals as they compare with the background signal from W± -pair production.

Prospects for supersymmetry at CERN LEP 2.

Working within the framework of the mininal supergravity (SUGRA) model with gauge coupling unification and radiative electroweak symmetry breaking we map out regions of parameter space explorable by experiments at CERN LEP 2, for center-of-mass energy options of \ensuremath{\surd}s =150, 175, 190, and 205 GeV. We compute signals from all accessible 2\ensuremath{\rightarrow}2 supersymmetry (SUSY) pair production processes using the isaget simulation program, and devise cuts that enhance the signal relative to standard model backgrounds, and which also serve to differentiate various supersymmetric processes from one another. We delineate regions of SUGRA parameter space where production of neutralino pairs, chargino pairs, slepton pairs, and the production of the light Higgs scalar of SUSY is detectable above standard model backgrounds and distinguishable from other SUSY processes. In addition, we find small regions of SUGRA parameter space where e\ifmmode \tilde{}\else \~{}\fi{} e\ifmmode \tilde{}\else \~{}\fi{}, Z${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{2}$Z${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{2}$, and \ensuremath{\nu}${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{\mathit{L}}$\ensuremath{\nu}${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{\mathit{L}}$ production yields spectacular events with up to four isolated leptons. The combined regions of parameter space explorable by LEP 2 are compared with the reach of Fermilab Tevatron Main Injector era experiments. Finally, we comment on how the reach via the neutralino pair channel is altered when the radiative electroweak symmetry breaking constraint is relaxed.