Singularities in the energy distribution of a single lepton in the search for dark matter particles at the international linear Collider/Compact linear Collider: Source for measuring their masses

The measuring of model-independent singularities in the energy distribution of a single lepton in the cascade process e ⁺ e ^? ?? D ⁺ D ^? ?? DDW ⁺ W ^? ?? DD(q q?)??? will allow one to reliably determine the mass of a candidate for dark matter D and its charged partners D ^± in future experiments at the International Linear Collider/Compact Linear Collider (ILC/CLIC).     

Precise measuring mass and spin of dark matter particles at ILC via singularities in the single lepton energy spectrum

We consider models, in which stability of Dark Matter particles D is ensured by the conservation of the new quantum number, called D-parity here. Our models contain also charged D-odd particle D ^±. We propose method for precision measuring masses and spin of D-particles via the study of energy distribution of single lepton (e or μ) in the process e ⁺ e ^? → D ⁺ D ^? → DDW ⁺ W ^? with the observable state dijet + μ (or e) + nothing. It is shown that this distribution has kinematically determined singular points (upper edge and kinks or peak). Measuring of their positions allow to determine precisely masses of D and D ^±. After this, even a rough measuring of corresponding cross section allows to determine the spin of D particles.     

Observation of possible production and decay of short-living heavy neutral particles in the SKAT neutrino experiment

In the SKAT bubble chamber neutrino experiment production of a short-living neutral particle with mass (1.4?m?2.5) GeV/c² and lifetime τ≈6×10^?12 s has been detected. The event may be interpreted as production and decay of the heavy lepton M⁰→μ^?+e⁺+ν_e with mass (1.4?m_M⁰?2.1) GeV/c². It might also be the production of a charmed particle D⁰→e⁺+τ^?+ν_e (D⁰→e⁺+π^?+ν_e) with mass 1.4?m_D⁰?2.5) GeV/c² in a non-diagonal neutral current. The probability to interpret the event as other possible processes is very low.     

Exotic decays of the muon and heavy leptons in gauge theories

We have studied the decay ?₁ → ?₂ + γ for arbitrary like charged spin $\text{1}\text{2}$ leptons in a manner which is applicable to a large class of models. Our computations assume that this process is induced by one loop diagrams. When the leading effect is cancelled by a leptonic G.I.M. mechanism, we find an extremely large enhancement of O(M_W⁴/M_L⁴) in Λ(μ^?→e^?+e⁺e^?)/Λ(μ^?→e^?+γ) if the intermediate lepton is charged.     

Study of some rare decays of the K+ meson

In a search for very rare decays of the K⁺ meson we observed the K⁺→μ⁺νe⁺e^? and K⁺→e⁺ν e⁺e^? modes with branching ratios of (10±3) ×10^?7 and (2⁺²_?2)×10^?7 respectively. We also put new limits on a decay allowed by the alternate scheme of lepton conservation K⁺→π^?μ⁺e⁺, on a decay with double charged weak current K⁺→π^? e⁺e⁺ and on other forbidden decays K⁺→μ^?νe⁺e⁺ and K⁺→π⁺μ^±e^±.     

Measurement of e+e−→τ+τ− at high energy and properties of the τ lepton

The e⁺e^?→τ⁺τ^? process has been measured using the CELLO detector at a mean total centre of mass energy of 34.2 GeV using essentially all the decay channels of the τ lepton. The measured cross section yields R_τ=1.03±0.05 (stat)±0.07 (syst). Topological branching fraction are given for τ → 1, 3 or 5 charged tracks. The angular distribution shows a clear 1 + cos²θ dependance with a forward-backward asymmetry of -0.103 ± 0.052 corresponding to an axial-vector coupling a_τ of the τ to the weak neutral current given by a_τ=?1.12 ± 0.57.     

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 two types of new particles (heavy charged fermion, e.g. new sequential lepton or top quark; and supersymmetric scalar lepton, i.e. slepton), along with the (small) standard model “background”. The x-dependence of W_L provides a distinct signature of the identity of the new particle. Extensions of this approach are discussed.     

W ± + 4jet irreducible background events from QCD in top and Higgs searches at the Next Linear Collider

Irreducible background effects due to e ⁺ e ^? → W ^± + bbjj and e ⁺ e ^? → W ^± + jjjj events produced via QCD in top-antitop production and heavy Higgs searches in the bremsstrahlung channel are studied at the Next Linear Collider. Various distributions relevant to phenomenological analyses are given and compared to those expected from top and Higgs signals in the decay channel bb?W ⁺ W ^? → bb?W ^± jj. This analysis follows similar ones previously carried out for the case of the irreducible background proceeding via electroweak interactions     

Dynamics of η→3π0 decay

The η→3π⁰ decay was studied with the SND detector at the VEPP-2Me ⁺ e ^? collider. The parameter that describes deviation of the Dalitz plot of events from a uniform distribution was found to be α=?0.010±0.021±0.010.     

On the QCD perturbative predictions for the signal ofW± production in hadronic collisions

Evidence for the intermediate bosons in high energy pp and p?p collisions as signal in the cross section of large p_T charged lepton pp, $\text{p}\text{p}\text{→}\text{W}{}^{\mathrm{\pm }}\text{+}\text{X}$, W^±→?^±ν_? is considered for CM energy range $\text{s}\text{=100?800}\text{GeV}$. Besides the usual Drell-Yan term which gives a very sharp peak in the lepton p_T distribution, the first order QCD contribution is included thus producing the intermediate boson with transverse momentum and smearing the lepton distribution. Scaling violation of the structure functions is incorporated and compared with the case when it is absent.     

A measurement of σtot(e+e− → hadrons) for cm energies between 12.0 and 36.7 GeV

The ration R = σ(e⁺e^? → hadrons)σ_μμ was measured between 12.0 and 36.7 GeV c.m. energy W with a precision of typically ± 5.2%. R is found to be constant with an average R = 4.01 ± 0.03 (stat) ± (syst.) for W ? 14 GeV. Quarks are found to be point-like, the mass parameter describing a possible quark form-factor being larger than 186 GeV. Fits including QCD corrections and a weak neutral-current contribution are presented.     

Time-projection chamber for the PEN experiment

The PEN collaboration carries out a precision measurement of the ??⁺ ?? e ⁺?? decay branching ratio at the Paul Scherrer Institute (PSI, Switzerland). A special mini time-projection chamber (mTPC) has been developed for registration of particles in the pion beam. The chamber contains 14 × 10^?3 g/cm² of matter on the particle path. The chamber was successfully used during one-year-long run. Design and characteristics of the mTPC are described.     

Multihadronic decays and partial widths of the J/Ψ (3100) resonance produced in e+e− annihilation at adone

The reactions e⁺e^?→ hadrons and e⁺e⁺e^?→e⁺e^? have been studied at the J/gY (3100) resonance). The relative weights of the topological cross sections for fixed charged multiplicity are σ₂=(32±5)%, σ₄=(49±8)%, σ₆=(18±3)%, and σ₈=(1±0.6)%. The average pion multiplicities are 〈n_ch〉=3.8±0.3 and 〈n_{π^o〉=3.1±0.8}. The decay widths are Γ_e=(4.6±0.8) keV, Γ_h=(59±24) keV, and Γ=(68±26) keV.     

A determination of sin2θ w and the lepton and quark electroweak couplings frome + e − data

Published data on lepton pair and quark pair final states ine ⁺ e ^? annihilation have been analysed in a self consistent way to yield values for the lepton and quark weak vector and axial vector couplings. Generation universality has been tested for the leptons and under the assumption of the standard model of the weak interaction, the parameter sin²θ _w has been determined separately for the lepton and quark sector. In the renormalisation scheme α,G _μ and sin²θ _w , the result for the lepton final states is sin²θ _w = 0.212±0.014 and for the hadron final states, sin²θ _w = 0.236±0.015. The combined result for this single parameter in the model is sin²θ _w = 0.223±0.011±0.007, corresponding tom _Z =93.0 _?1.8 ^+2.0 GeV.     

Leptonic polarization asymmetries ate + e − colliders inE 6 theories

We examine the left-right and azimuthal polarization asymmetries of lepton pairs produced ine ⁺ e ^? ande ^? e ^? interactions as probes of new physics resulting fromE ₆ theories. The asymmetries are calculated and compared for the processese ⁺ e ^?→µ ⁺ µ ^?,e ⁺ e ^?→e ⁺ e ^?,e ^? e ^?→e ^? e ^?, ande ⁺ e ^?→L ⁺ L ^? whereL is either anE ₆ exotic, mirror, or fourth generation heavy lepton. Our results show that lepton polarization asymmetries can be used to easily distinguish differentE ₆ models and can be used to distinguish among possible new heavy leptonsL.     

Measurement of e+e− → e+e− and e+e− → λλ at energies up to 36.7 GeV

The differential cross sections of the reactions e⁺e^? → e⁺e^? and e⁺e^? → λλ are measured at energies between 33.0 and 36.7 GeV. The results agree with the predictions of quantum electrodynamics. A comparison with the standard model of electroweak interaction yields sin²θ_W = 0.25 ± 0.13.     

Study of the process e + e − → π+π− in the energy region 400 < \sqrt s < 1000 MeV^\P

The cross section of the process e ⁺ e ^? → π⁺π^? was measured in the spherical neutral detector experiment at the VEPP-2M collider in the energy region $400 < \sqrt s < 1000 MeV$ . This measurement was based on about 12.4 × 10⁶ selected collinear events, which include 7.4 × 10⁶ e ⁺ e ^? → e ⁺ e ^?, 4.5 × 10⁶ e ⁺ e ^? → π⁺π^?, and 0.5 × 10⁶ e ⁺ e ^? → μ⁺μ^? selected events. The systematic uncertainty of cross section determination is 1.3%. The ρ-meson parameters were determined as m _ρ = 774.9±0.4±0.5 MeV, Γ _ρ = 146.5±0.8±1.5 MeV, and σ(ρ → π⁺π^?) = 1220 ± 7 ± 16 nb and the parameters of the G-parity suppressed decay ω → π⁺π^? as σ(ω → π⁺π^?) = 29.9 ± 1.4 ± 1.0 nb and φ_ρω = 113.5±1.3±1.7°.     

Nonminimal Higgs models,dark matter,and evolution of the universe

The set of sum rules for a wide class of nonminimal Higgs models has been obtained. Difficulties and ways for revealing the possibilities of studying extended Higgs models at colliders have been revealed with the use of these sum rules and recent LHC results. New methods of studying multidoublet Higgs models with various symmetry groups have been applied to solve problems of classification of these groups, breaking of symmetries in vacuum, etc. A method for the determination of masses and spins of dark-matter particles D and their partners via the energy spectrum of a lepton in the e ⁺ e ^? → DDW ⁺ W ^? process has been proposed. The possibility of the existence of strongly interacting dark matter has been revealed. Variants of the evolution of the phase states of the Universe have been analyzed within the inert doublet model.     

SU(2)×U(1) effects in e+e− annihilation: Generalized charge asymmetry

The observability of the SU(2)×U(1) electroweak charge asymmetry effects in e⁺e^? annihilation at $\text{s}\text{=29}\text{GeV}$ is addressed in the context of a Feynman-Field type fragmentation model. We assume three colors of five flavored quarks and one heavy lepton τ. We neglect, at this time, the hard gluon bremsstrahlung events. We take b→c+X as the b-decay mode and we assume all τ's and heavy hadrons decay within the resolution of the detector so thatonly light hadrons and leptons are detected. Allowing all these decays to occur, we then compute the expected front-back asymmetry of negatively charged particles weighted with zⁿ for z?0.0175, where n = 0.5, 1…, 7, 10, and z is the light-cone momentum fraction. We find, for example, that such an asymmetry is ≈5% for n=2for sin²θ_w=0.236 and Λ_{QCD=0.34 GeV}. In other words, due to the large number of charge particles produced per event, this SU(2)×U(1) charge asymmetry may be accessible experimentally in e⁺e^? → X already at PEP and PETRA energies.