Scalar Leptons Research Articles

Search for supersymmetric particles in e +e − collisions at centre-of-mass energies of 130 and 136 GeV

Searches for supersymmetric particles produced in e +e − collisions at centre-of-mass energies of 130 and 136 GeV have been performed in a data sample of 5.7 pb −1 collected in the autumn of 1995 by the ALEPH detector at LEP. No candidate events were found, allowing limits to be set on the masses and production cross-sections of scalar leptons, scalar tops, charginos and neutralinos. The domains previously excluded at LEP1 are substantially extended. For instance, masses of gaugino-like charginos smaller than 67.8 GeV/ c 2 are excluded at the 95% C.L. for scalar neutrino masses larger than 200 GeV/ c 2.

Precision Study of MSSM at Futuree+e-Linear Colliders

The lighter scalar tau lepton $\sti$ may be the lightest scalar lepton and therefore would be found earlier in future collider experiments. We point out the impact of the measurement of the mass and the mixing angle of $\st$ to discriminate the models of SUSY breaking. Furthermore, the measurement of the polarization of $\tau$ lepton($P_{\tau}$) from the decaying $\sti$ helps to determine the Yukawa sector of minimal supersymmetric standard model. We present our MC study of the production and the decay of $\sti$ lepton at a future linear collider at $\sqrt{s}=500$ GeV. The mass, mixing angle of $\sti$ and $P_{\tau}(\sti\rightarrow\tau \chi_1^0)$ would be measured precisely at the future LC. ( talks given at Yukawa International Seminar(YIKS) '95 on some very hot and humid day in August, and also at Workshop on {\it Physics and Experiments with Linear $e^+e^-$ Colliders} Appi, Iwate Japan Sep.8-12 1995.)

Cosmological baryon asymmetry in supersymmetric standard models and heavy particle effects

Cosmological baryon asymmetry B is studied in supersymmetric standard models, assuming the electroweak reprocessing of B and L. Only when the soft supersymmetry breaking is taken into account, B is proportional to the primordial B − L in the supersymmetric standard models. The ratio B/( B − L) is found to be about one percent less than the nonsupersymmetric case. Even if the primordial B − L vanishes, scalar-leptons can be more efficient than leptons to generate B provided that mixing angles θ among scalar leptons satisfy ¦θ¦ < 10 −8( T/GeV) 1 12 .

Polarization effects in scalar lepton production at high energy γγ colliders

We investigate the charged scalar lepton production processes γγ → ℓ + ℓ − at high energy γγ colliders in the framework of the minimal supersymmetric standard model (MSSM). Here the high energy γ beams are obtained by the backward Compton scattering of the laser flush by the electron in the basic linear TeV ee colliders. We consider the polarization of the laser photons as well as the electron beams. Appropriate beam polarization could be effective to enhance the cross section and to extract the signal from the dominant background γγ → W + W −.

Nature of production of the supersymmetric particles gravitino, photino and light scalar leptons in Z0-decay and their experimental searches

This paper investigates the behaviors of production of gravitino\(\left( {\tilde G} \right)\), photino\(\left( {\tilde \gamma } \right)\) and the light scalar leptons like scalar electron\(\left( {\tilde e} \right)\) and scalar electronneutrino\(\left( {\tilde \nu _e } \right)\) via Z0-decay with the help of the dimensionality-based decay selection rule, namely the pseudodimension rule. It has been shown that\(\tilde G\) and\({\tilde \gamma }\) may be freely produced in the decays\(Z^0 \to \tilde G\tilde \bar \gamma /\tilde \bar G\tilde \bar \gamma ,\tilde \gamma \tilde \bar \gamma \) which are allowed by the above-mentioned decay selection rule. In contrast to this, suppression must the witnessed in production of\(\tilde e\) and\(\tilde \nu _e \) through the decays\(Z^0 \to \tilde e\tilde \bar e,\tilde \nu _e \tilde \bar \nu _e \) which are forbidden by the same selection rule. These facts have the obvious implication that Z0-decay may turn out to be a convenient platform for experimental searches of gravitino and photino but definitely not so for the light scalar leptons\(\tilde e\),\(\tilde \nu _e \) as highlighted in this paper.

A model for spontaneous R parity breaking

We suggest a model for spontaneous R parity breaking in the standard SU (2) ⊗ U (1) supersymmetric model induced by non-zero vacuum expectation values (VEVs) for isosinglet scalar leptons. R parity breaking occurs at the electroweak scale with no fine-tuning required in order to suppress stellar energy loss due to majoron emission and no contribution of scalars to the invisible Z decay width. The τ neutrino may be very heavy and there may be experimentally observable rates for flavour-violating processes.

Direct search for pair production of heavy stable charged particles in Z decays.

A search for pair production of stable charged particles from Z decay has been performed with the Mark II detector at the SLAC Linear Collider. Particle masses are determined from momentum, ionization energy loss, and time-of-flight measurements. A limit excluding pair production of stable fourth-generation charged leptons and stable mirror fermions with masses between the muon mass and 36.3 GeV/c2 is set at the 95% confidence level. Pair production of stable supersymmetric scalar leptons with masses between the muon mass and 32.6 GeV/c2 is also excluded.Received 5 March 1990DOI:https://doi.org/10.1103/PhysRevLett.64.2980©1990 American Physical Society

Neutrino magnetic moment inN=1 minimal supergravity

The complete one-loop supersymmetric (SUSY) correction to the magnetic moment (NMM) of a Dirac neutrino is calculated with allowance for mixing between the scalar leptons and for mixing between theW-gaugino and Higgs fermions. The contribution from the charged Higgs loop is negligible for all practical purpose. We thoroughly study the dependence of NMM on the SUSY parameters. The SUSY contribution to the NMM can be a few times less than or comparable to the value of the standard model (with a right-handed neutrino singlet added). The SUSY correction to the NMM increases with decreasing β value (tan β=〈H2〉/〈H1〉), and is not very sensitive to the charged scalar lepton mass.

A search for acoplanar pairs of leptons or jets in Z 0 decays. Mass limits on supersymmetric particles

We have searched for Z 0 decays into acoplanar pairs of leptons or jets. The data were recorded with the OPAL detector during an energy scan around the Z 0 peak and correspond to about 17000 produced Z 0,s. We have determined model independent limits on branching ratios for the Z 0 to decay into pairs of heavy particles with subsequent decays leading to the above topologies. In the context of supersymmetric models, mass bounds close to the kinematic limit were obtained for the scalar leptons, ẽ, g̃m, g̃t, and for the chargino, X̃ ±.

Search for susy partners of charged leptons in e +e − collisions with [formula omitted] up to 60.8 GeV

Supersymmetric partners of charged leptons, scalar leptons were searched for in e +e − collisions at TRISTAN with center-of-mass energies up to 60.8 GeV. The pair production of unstable scalar leptons were searched for among identified lepton-pair events, and stable ones among collinear two-track events. No evidence was found for them. Mass limits are presented for both large-splitting and degenerate cases.

Beam-polarization phenomena in high-energy e+e- collider physics.

We consider the possible effects of a nontrivial initial-beam polarization in high-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider physics. Specifically, we address initial-beam-polarized production of possible new scalars and fermions. For definiteness, we take scalar leptons and scalar quarks as our typical new scalars and we take supersymmetric gauge-Higgs fermions as our typical fermions. In this way, we arrive at formulas which can be applied to any scalar and any fermion pair produced in lowest order in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}A$, ${Z}^{0}\ensuremath{\rightarrow}X$. We have in mind that our formulas will be used first at the SLAC Linear Collider (SLC) and the CERN collider LEP. Thus, we illustrate them in the SLC-LEP-type energy regime. Applications to the TeV Linear Collider and CERN Linear Collider are immediate and will be taken up elsewhere.

Lepton number nonconservation in supersymmetric theories

We consider a class of supersymmetric models lepton number nonconservation due to mixing of scalar leptons. It is shown that a range of parameters exists such that the processes μ→eγ, μ→eγγ, μ→3e, μ+e−→μ−e+ are strongly suppressed, whereas the decay\(\mu \to e\tilde \gamma \tilde \gamma \) can proceed with a rate\(BR(\mu \to e\tilde \gamma \tilde \gamma ) \lesssim 0.01\). The signatures of such decay can be the production of right-handed electrons with the energy aroundmμ/3 and modification of the energy spectrum of the electrons in that region as compared with the standard model prediction.

Nonconservation of lepton number in supersymmetric theories

We consider a class of supersymmetric models with lepton number violation due to mixing of scalar leptons. It is shown that a range of parameters exists such that the processes μ→e γ, μ→ ge, μ→e γγ, μ +e −→ μ −e + are strongly suppressed, whereas the decay μ→ e γ ̃ γ ̃ can proceed with a rate which can be experimentally interesting. The signatures of such decay can be the production of right-handed electrons with the energy around 1 3 ω ν and modification of the energy spectrum of the electrons in that region as compared with the standard model prediction.

T-ODD ASYMMETRY IN TRILEPTONIC DECAY OF SCALAR LEPTON

The complex mass matrix for neutralinos could lead to T-violation in the neutralino decay. We analyze the successive decay of the scalar lepton into three leptons and the lightest neutralino, which is mediated by a heavier neutralino. If the magnitude of CP-violation is not small, T-odd asymmetry will be observed in the angular distribution of the three leptons.

SupersymmetricZ 0 decay into lepton-antilepton and two photinos

Working in a softly broken supersymmetricSU(2)×U(1) standard model with the photino as lightest SUSY-particle $$(m_{\bar \gamma } \leqq 10GeV)$$ differential and total rates for the decay $$Z^0 \to l^ + l^ - \tilde \gamma \tilde \gamma $$ as functions of various parameters of the model are presented. The decay involves intermediate scalar leptons and the total rate strongly depends on their masses. The results indicate that for a scalar lepton mass less than 70GeV this process might still be seen at SLC and CERN LEP I.

Search for sleptons at the Z 0 peak in e −e + collider (I)

We investigate the single scalar lepton production process e − e + → Z 0 → ℓ ∓ γℓ +- at the Z 0 peak. We find: (i) that for 5 ∼ m γ ∼ 25 GeV (0 ∼ m γ ∼ 25 GeV) a sizable event rate for e γ e ( μ γμ ) events passing the cuts introduced to eliminate all possible backgrounds should be obtained at the SLC and LEP-I colliders even if the slepton masses substantially exceed the beam energy E = m Z/2 ≅ 46 GeV; and (ii) that considerably higher slepton masses can be reached with this experiment at these e −e + colliders than with slepton searches at the S p pS and TEVATRON p p colliders. Encouraged by this observation we evaluate the angular-energy distributions and the angular-spin asymmetries for the detected leptons in this process; the information these can provide would be valuable in identifying this proposed production mechanism and the new particles responsible for it, including their spins, masses and couplings.

Lepton inclusive distributions and asymmetries from the decay of scalar lepton pairs in e+e− collisions with polarized beams

We present a detailed analysis of the inclusive spectral and angular distributions of a lepton coming from the decay of a scalar lepton pair—produced in electron-positron collisions with polarized beams, in a simple softly broken supersymmetric model of electroweak interactions. We analyse in detail also the longitudinal and transverse polarization asymmetries in various cases (degenerate or not degenerate sleptons, massive or massless photino) pointing out the corresponding signatures.

Distinctive signatures for new particles in e +e − annihilation and Z-decay

New particles and new interactions reveal themselves most clearly where standard model contributions are negligibly small. A prominent example with this advantage is the one-lepton inclusive longitudinal structure function ( W L) in e +e − annihilation and Z-decay. We discuss general features of this approach and present structure functions for four types of new particles: heavy charged fermion (a new sequential lepton and the top quark), neutral heavy lepton (Dirac-a and Majorana-neutrino), supersymmetric scalar lepton (slepton), and Higgs particles. We also discuss the (small) standard model “background”, especially the QCD correction. The x-dependence of W L provides a distinct signature of the identity of the new particle, and it also distinguishes the background from the new particle signal. Extensions of this approach are discussed.

Electroproduction of supersymmetric particles and gauge bosons

The electroproduction of scalar leptons and gauginos at HERA and at supercollider energies is studied. In particular, the channel ep → e(→ e + γ)γX is analyzed in full detail. The exa analytic expressions for the cross section and the spectrum of the final electron are derived and evaluated for √s ⋍ 0.15−3 TeV and different values of the scalar electron and photino masses. Since the exact formulae are relatively complicated, simplified expressions in the Weizsacker-Williams approximation are also given and their accuracy is discussed by comparison with the exact formulae. The standard processes ep → Z(→ vv)eX and ep → W(→ ev)vX which also lead to one final electron and two invisible particles are considered in parallel. The corresponding cross sections and distributions are discussed in comparison with the supersymmetric signal. The Z0 cross section is found to be quite smaller than was reported previously. To clarify this point the Z0 production at the leptonic vertex was computed both exactly and in the Weizsacker-Williams approximation with quite consistent results.

Nucleon decay in supergravity unified theories.

A general analysis of nucleon decay in supergravity unified models is given including the full set of W-gaugino, gluino, and Z-gaugino dressing diagrams (with gauge as well as Yukawa interactions at vertices) of LLLL and RRRR dimension-five operators generated by Higgs-triplet exchange. The analysis is carried out within the framework of a model-independent formalism of SU(2)\ifmmode\times\else\texttimes\fi{}U(1) breaking in supergravity models. Full symmetry-breaking effects on the vertices as well as all the allowed mass splittings of the supersymmetric particles that enter the dressing diagrams (i.e., W gauginos, Z gauginos, scalar quarks, and scalar leptons) are included. L-R mixing effects on scalar-quark--scalar-lepton masses, which are quite significant for the third generation for a heavy top quark, are also taken into account. Applications of the general analysis are made and it is shown that modification of supersymmetry predictions of nucleon decay can arise due to the inclusion of the new effects. It is shown specifically that \ensuremath{\nu}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\pi} modes dominate nucleon decay in certain domains of the parameter space rather than \ensuremath{\nu}\ifmmode\bar\else\textasciimacron\fi{}K modes as is conventionally the case.