Search for photinos in e+e− annihilation

Physics Letters B, 1997

A search for pair-production of long-lived, heavy, singly-charged particles has been performed with data collected by the ALEPH detector at a centre-of-mass energy of 172 GeV. Data at p s = 161, 136, and 130 GeV are also included to improve the sensitivity to lower masses. No candidate is found in the data. A model-independent 95% condence level upper limit on the production cross section at 172 GeV of 0.2{0.4 pb is derived for masses between 45 and 86 GeV/c 2 . This cross section limit implies, assuming the MSSM, a l o w er limit of 67 (69) GeV/c 2 on the mass of right-(left-) handed long-lived scalar taus or scalar muons and of 86 GeV/c 2 on the mass of long-lived charginos.

European Physical Journal C, 1999

The events with two photons and missing (transverse) energy collected by the DELPHI detector at centre-of-mass energies between 130 GeV and 183 GeV have been studied to search for processes of the type e+e- → YY with the subsequent decay Y → X7, where X is an undetectable neutral particle. Reactions of this kind are expected in supersymmetric models, where the Y particle can be either the lightest neutralino, decaying to a photon and a gravitino, or the next-to-lightest neutralino, decaying to a photon and the lightest neutralino. To study the case of long-lived Y particles, a search for single-photon events with the reconstructed photon axis pointing far from the beam interaction region has also been performed. No evidence for a deviation from Standard Model expectations has been observed in the data and upper limits have been derived on the signal cross-section as a function of the the X and Y masses and of the Y mean decay path.

The European Physical Journal C, 2002

In the context of the Minimal Supersymmetric extension of the Standard Model, we analyze the production at future high-energy e + e − colliders of second and third generation scalar leptons as well as scalar quarks in association with neutralinos and charginos, e + e − → ff χ. In the case of third generation squarks, we also discuss the associated production with gluinos. We show that the cross sections for some of these three-body final state processes could be significant enough to allow for the detection of scalar fermions with masses above the kinematical two-body threshold, √ s = 2mf. We then discuss, taking as a reference example the case of scalar muons, the production cross sections in various approximations and make a comparison with the full four-body production process, e + e − → ff χχ, in particular around the two-sfermion threshold.

Physical Review D, 1996

In a class of low-energy supersymmetry models the photino is a natural dark matter candidate. We investigate the effects of post-freeze-out photino annihilations which can generate electromognetic cascades and lead to photo-destruction of 4 He and subsequent overproduction of D and 3 He.

Physics Letters B, 1982

…, 1976

We present the properties of 103 events of the form e+ + -t-e--+e-+p + missing energy, in which no other charged particles or photons are detected.

Nuclear Physics B, 1995

We study the production and decay of heavy selectrons in the e − γ mode of a linear collider of the next generation. The standard model backgrounds can be substantially reduced by appropriate kinematical cuts. As a consequence, selectrons far heavier than the kinematical threshold for pair production are shown to be easily discoverable for large portions of the supersymmetry parameter space. We also describe a model-independent kinematical measurement of the mass of the lightest neutralino.

The European Physical Journal C - Particles and Fields, 2002

We investigate selectron pair production and decay in e − e − scattering and e + e − annihilation with polarized beams taking into account neutralino mixing as well as ISR and beamstrahlung corrections. One of the main advantages of having both modes at disposal is their complementarity concerning the threshold behaviour of selectron pair production. In e − e − the cross sections at threshold forẽ RẽR andẽ LẽL rise proportional to the momentum of the selectron and in e + e − that forẽ RẽL. Measurements at threshold with polarized beams can be used to determine the selectron masses mẽ L/R precisely. Moreover we discuss how polarized electron and positron beams can be used to establish directly the weak quantum numbers of the selectrons. We also use selectron pair production to determine the gaugino mass parameter M 1. This is of particular interest for scenarios with non-universal gaugino masses at a high scale resulting in |M 1 | |M 2 | at the electroweak scale. Moreover, we consider also the case of a nonvanishing selectron mixing and demonstrate that it leads to a significant change in the phenomenology of selectrons.

Nuclear Physics B, 1978

We have observed events of the form e + + e---, e + + e-and e + + e-~ ~+ + #-in which there are no other detected particles and there is substantial missing energy; and which cannot be explained by conventional electromagnetic interactions. We show that these events can be explained as the decay products from the pair production, e + + e---* r + + r-, of a new charged lepton, r -+, of mass ~1800 MeV/c 2. Some properties of these events are presented. In particular, this production cross section is inconsistent with the r being an electron-related paralepton.

The European Physical Journal C, 1999

The events with two photons and missing (transverse) energy collected by the DELPHI detector at centre-of-mass energies between 130 GeV and 183 GeV have been studied to search for processes of the type e + e ! YY with the subsequent decay Y ! X , where X is an undetectable neutral particle. Reactions

Physical Review D, 2004

We study two CP sensitive triple-product asymmetries for neutralino production e + e − →χ 0 iχ 0 j and the subsequent leptonic two-body decayχ 0 i →l ℓ,l →χ 0 1 ℓ, for ℓ = e, µ, τ . We calculate the asymmetries, cross sections and branching ratios in the Minimal Supersymmetric Standard Model with complex parameters µ and M 1 . We present numerical results for the asymmetries to be expected at a linear electronpositron collider in the 500 GeV range. The asymmetries can go up to 25%. We estimate the event rates which are necessary to observe the asymmetries. Polarized electron and positron beams can significantly enhance the asymmetries and cross sections. In addition, we show how the two decay leptons can be distinguished by making use of their energy distributions. *

Physical Review Letters, 2005

Physics Letters B, 1976

We present the properties of 103 events of the form e+ + -t-e--+e-+p + missing energy, in which no other charged particles or photons are detected.

1998

For the process e+e-+ p+p-(n) , the cross section and forward-backward charge asymmetry are measured at the highest ever center of mass energies which ranged from 130 to 183GeV. The data originates from 85pb-1 of integrated luminosity collected with the L3 detector at LEP. The measured muon pair cross section and forward-backward asymmetry agree with the Standard Model prediction with a XMI /N = .61 with 10 degrees of freedom. A mass limit on an additional heavy, neutral gauge boson of Mz, > 315GeV is set using muon pair production alone, rising to Mz, > 805GeV when all final states are considered. A search for an excited lepton decaying via p*-+ fy excludes such objects with electromagnetic coupling up to 183GeV.

Physics Letters B, 1993

We have studied the production of charged D* mesons m e+e -annxhflaUon at an average center-of-mass energy of 58.0 GeV. Charged D* mesons were identified using two independent methods; the mass-difference method and the detection of the low transverse-momentum plon The forward-backward asymmetry of the charm quark producUon was measured to be Ac= -0 61 +_0.13(stat )+0 08(syst.). The cross section of reclusive D* production was found to be e(e+e---,D*+-+X)=24.5+ 5.3 (star) + 3.0 (syst.) pb. If we assume the standard model prediction for the charm quark production, we obtain the branching ratio for the charm quark to produce a charged D* meson to be Br(c-.D °÷ + X) = (22 + 5 (stat) + 3 (syst.) )%.