Flavor changing neutral currents and multileptons in e+e- and vμN,vμN

New quarks and new flavor-changing neutral currents give multiple lepton plus hadron final states in e⁺e^-, $\text{v}{}_{\mathrm{\mu }}\text{N,}\text{v}{}_{\mathrm{\mu }}\text{N}$. We observe that (i) e⁺e^- is a favored place to search for their effects through inclusive ratios σ(e⁺e^-+x:σ (μ⁺μ^- +x): σ(e±μ±+x) and same sign leptons e±e±+x, μ±μ±+x,e±μ±+x. Above a new flavor threshold four charged lrpton final states may become important. (ii) Trilepton final states in $\text{v}{}_{\mathrm{\mu }}\text{N,}\text{v}{}_{\mathrm{\mu }}\text{N}$ are not sensitive to the presence of flavor-changing neutral currents. Much more sensitive are the processes $\text{v}{}_{\mathrm{\mu }}\text{N}$ are ⁺e^-+βand (for charm changing neutral currents) $\text{v}{}_{\mathrm{\mu }}\text{N→e}{}^{\mathrm{+}}\text{β}$.     

Investigation of like-sign dimuon production in neutrino and antineutrino reactions

290 events of the type νFe→μ^?μ^?X and 53 events from the reaction $\text{ν}\text{Fe→μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{+}}\text{X with}\text{E}{}_{\mathrm{\nu }}\text{>30}\text{GeV}$ and muon momenta p_μ>6.5GeV/c have been observed in the CDHS detector. After subtracting the background from charged-current processes with one π or K meson of the hadronic shower decaying into $\text{μ}{}^{\mathrm{?}}\text{ν}\text{(or μ}{}^{\mathrm{+}}\text{μ)}$, we obtain for neutrinos a rate of prompt like- sign dimuon production of (3.4±1.8)×10^?5 relative to the rate of charged-current events with the same cuts, or (4.1 ± 2.2)% relative to the prompt μ^?μ⁺ rate, and for antineutrinos the corresponding relative rates (4.3±2.3)×10^?5 and (4.2 ± 2.3)%. A possible explanation for the events is charm pair production at a level of 10^?3 relative to all charged-current reactions.     

Observation of wrong-sign tri-muon events in 250 GeV muon-nucleon interactions

Two trimuon events of the type μ⁺N→μ⁺μ⁺μ⁺X and one μ⁺N→μ⁺μ^?μ^?X have been observed in 250 GeV μ⁺ -iron interactions. The expected rate from the decay of hadrons (charm, π, K) is about one event. Other processes that may contribute are both beauty production and charm production with $\text{D}{}^0\text{?}\text{D}{}^0$ mixing. The data give upper limits of 12×10^?36 cm² for the cross section of beauty pair production by muons, and 20% for $\text{D}{}^0\text{?}\text{D}{}^0$ transitions due to mixing, both at 90% confidence level.     

Positron production by muon neutrinos BEBC filled with a neon-hydrogen mixture

For e⁺ energy > 0.3 GeV and 10 GeV < visible energy < 100 GeV we find that: (i) $\text{? = (v}{}_{\mathrm{\mu }}\text{+}\text{Ne}\text{→ μ}{}^{\mathrm{?}}\text{e}{}^{\mathrm{+}}\text{)/(v}{}_{\mathrm{\mu }}\text{+}\text{Ne}\text{→ μ}{}^{\mathrm{?}}\text{) = (0.41 ± 0.15)\%}$; (ii) 1.2 ± 0.5 neutral strange particles are produced per μ^?e⁺ event; (iii) the lifetime of possible positron-parent particles is < 3 × 10^?10 s (90% C.L.); (iv) the cross section for direct e⁺ production via the neutral current is < 0.2 times that via the charged current (90% C.L.); (v) the cross section for producing heavy leptons, L⁺, decaying into e⁺ … is < 0.7 × 10^?3 times that for μ^?production, implying M(L⁺) > 10 GeV.     

Charm production by weak neutral currents

We discuss quantitatively the production of charm in $\text{v}\text{N and}\text{v}\text{N}$ neutral current interactions, and the anomalous lepton events that follow from semi-leptonic charm decay. Diagonal neutral currents, in the Weinberg-Salam model and similar models, predict associated charm production with small cross sections: e.g. $\text{σ(v}\text{N}\text{→ vcc}{}^{\mathrm{?}}\text{X}\text{)/σ(v}\text{N}\text{→ μ}{}^{\mathrm{?}}\text{X}\text{) ? 10}{}^{\mathrm{?2}}$ at high energy. The meagre data on vN → ve⁺X are consistent with a rate of this order. Non-diagonal neutral currents, if present, could give larger cross sections via valence p → c transitions. It should be possible to distinguish diagonal from non-diagonal contributions by their x- or u-dependences, where u = x(1 ? y). We calculate the expected energy distributions of the leptons in characteristic vN → v?⁺X and vN → v?⁺?^?X charm decay events using simple models, and discuss some practical problems in neutral current measurements.     

A measurement of the K+ → e+v)(K+ → μ+v) branching ratio

The branching ratio $\text{R =}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{v)}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→ μ}{}^{\mathrm{+}}\text{v)}$ has been measured on the basis of 534 observed K⁺ → e⁺v decays. The K⁺ decay at rest; the momenta of the e⁺ and μ⁺ are measured in a magnetic spectrometer using multiwire driftchambers, and the electrons are identified in a gas Cerenkov counter. The result is R = (2.37 ± 0.17_× 10^?5. The value predicted for pure axial-vector interaction and μ-e-universality is R = 2.57 × 10^?5.     

Heavy flavour contributions to massive lepton pair production

Massive lepton pair production in hadronic collisions, A + B → μ⁺μ^? X, is usually assumed to proceed via ann intermediate virtual photon, $\text{ψ}{}^1\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}$, the Drell-Yan process. We examine other contributions arising from heavy flavour production, $\text{A}\text{+}\text{B}\text{→}\text{Q}\text{Q}\text{X}\text{;}\text{Q}\text{→ μν}\text{X}$. We find that this background is comporable to the Drell-Yan signal at small values of $\text{M}{}_{\mathrm{<mtext>\mu </mtext><mtext>\mu </mtext>}}{}^2\text{/s}$ but negligible at large values. Characteristic siggnatures are described that distinguish the background from the signal.     

O(18) revived: Splitting the spinor

We propose an O(18) theory which is perturbatively unifiable and which accounts for the absence of right-handed families in the low-energy world. The theory predicts a fourth left-handed family as well as four right-handed families at energies near the weak scale. It also implies the existence of eight light neutrinos, all of which contribute to the width of the Z⁰. Cosmological arguments suggest that four of these neutrinos should have masses between 2 and 35 GeV, and that the other four should be much lighter. They also suggest the existence of a doubly charged scalar φ⁺⁺ and a singly charged scalar φ⁺. Dramatic signatures include the production of four right-handed charged leptons and eight right-handed quarks, $\text{Z}{}^0\text{→ v′}{}_{\mathrm{<mtext>R</mtext>}}\text{+}\text{v}\text{′}{}_{\mathrm{<mtext>R</mtext>}}\text{→ v}{}_{\mathrm{<mtext>R</mtext>}}\text{γ +\_}\text{v}{}_{\mathrm{<mtext>R</mtext>}}\text{γ}$, and e⁺e^? → φ⁺⁺ + φ^??. The lightest right-handed charged quark should be surprinsingly long-lived $\text{(τ?10}{}^{\mathrm{?2}}\text{sec}\text{)}$ for a particle of mass ? 100 GeV.     

Electromagnetic effects in the production of dimuons at large transverse momentum

The effects of single-photon corrections to the simple Drell-Yan mechanism $\text{(}\text{q}\text{q}\text{→ γ}{}^1\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{)}$ are studied for massive dimuons at large transverse momentum in the processes $\text{π}{}^{\mathrm{?}}\text{p}\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{X and}\text{p}\text{p}\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{X}$. It is found that single-photon emission by the muons constitutes an important correction to the effects of single-gluon emission by the quarks for very massive (M_μμ² ? m_μ²) muon pairs.Interference of the amplitude for photon emission from the muons with that for radiation from the quarks generates an asymmetry in the muon angular distribution. The forward-backward asymmetry is studied in detail as a function of pair mass and transverse momentum.     

Strange particle production by antineutrinos

Cross sections are presented for antineutrino production of Λ, Σ⁰ and K⁰ in strangeness changing reactions. Associated production reactions (ΔS = 0) have been observed in the charged and the neutral current channels. For the elastic reaction $\text{v}\text{p}\text{→ μ}{}^{\mathrm{+}}\text{Λ}$, estimates have been made of the axial transition form factor.     

New upper limit for μ− → e+ conversion

An upper limit for μ^? → e⁺ conversion has been established by searching for specific decay properties of the expected final state nucleus. We obtain $\text{R}{}_{\mathrm{<mtext>coh</mtext>}}\text{= (μ}{}^{\mathrm{?}}\text{+}{}^{127}\text{I →}\text{e}{}^{\mathrm{+}}{}^{127}\text{Sb}{}^1\text{)/(μ}{}^{\mathrm{?}}\text{→ v}{}_{\mathrm{\mu }}\text{) < 3 × 10}{}^{\mathrm{?10}}$ with 90% c.l.     

Upper limits on D0-D0 mixing and BB production from muon-nucleon scattering

In deep inelastic interactions of 200 GeV muons with a carbon target, we have found 17 events of the type μ^±N→μ^±μ^?μ^?X (“wrong-sign” dimuons). We derive upper limits of 1.2% (90% CL) on $\text{D}{}^0\text{-}\text{D}{}^0$ transitions (mixing) or, alternatively, of 9 pb (90% CL) cross section for $\text{B}\text{B}$ pair production as possible sources of such events.     

Calculation of the γγ → ϱ0ϱ0 cross section at high energies

The processes with the cross sections not decreasing with energy become important at high energies. The simplest processes of this kind are γγ → V_i⁰V_j⁰ where V⁰ = ?⁰, ω, ?, ….. We calculate their cross sections in the high-energy small angle region s ? |t| ? μ². The cross section γγ → ?⁰?⁰ at high energies (s ? 10 GeV²) exceeds those of γγ → ππ, ?⁺?^? considerably. At $\text{s ? 10}{}^4\text{GeV}{}^2$ (this is the characteristic energy for the VLEPP and SLC colliders) and $\text{|t| ? 2}\text{GeV}{}^2$, the ratio $\text{(}\text{d}\text{σ/}\text{d}\text{t)(γγ → ?}{}^0\text{?}{}^0\text{)/(}\text{d}\text{σ/}\text{d}\text{t)(γγ → μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{) ? 70}$.     

Production and signature of intermediate vector bosons

The front-back asymmetry of outgoing muons in the inclusive reaction $\text{p}\text{p}\text{→ Z(→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{)+}$ anything is calculated in the framework of the Drell-Yan model. We get very general expressions for the front-back asymmetry and the differential cross section in terms of the weak coupling constants and the parton distributions. Results for W^± production and proton-proton collisions are also given. Numerical estimates are made using various parton distributions and the Weinberg-Salam model for definiteness. We comment on the predictions of gauge theories that accommodate the absence of parity violating effects in atomic physics. We also give a new estimate of the inclusive cross sections $\text{p}\text{p}$ or pp → Z(→ μ⁺μ^?) or W^±(→ μ^±ν_μ) + anything. The effects of asymptotic freedom in the frontback asymmetries and the total cross sectons are investigated. We reanalyze results for the purely leptonic reaction e⁺e^? → γ, Z → μ⁺μ^?.     

Perhaps scalar neutrinos are the lightest supersymmetric partners

We consider the possibility that the scalar partners of the neutrinos $\text{(}\text{v}\text{)}$ are the least massive supersymmetric partners, and show that this alternative is compatible with cosmological constraints, which put a significant lower bound on photino masses but not on $\text{v}$ masses. Various consequences are examined: the photon counting rate for $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{-}}\text{→γ}\text{v}$$\text{v}\text{?}\text{?}$ may be large; the rate for $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{-}}\text{→}\text{W}{}^{\mathrm{+}}\text{a}\text{W}{}^{\mathrm{-}}$ by $\text{v}$ exchange is enhaced; Z⁰→ increases Γ(Z⁰) by about 0.25 GeV; $\text{W}{}^{\mathrm{\pm }}\text{→}\text{?}{}^{\mathrm{+-}}\text{v}$ may be enhanced; the decay $\text{τ→}\text{v}{}_{\mathrm{\tau }}\text{?}{}_{\mathrm{?}}$$\text{v}\text{?}\text{?}$ may be detectable; there can be additional contributions to the rare decay $\text{K}{}^{\mathrm{+}}\text{→π}{}^{\mathrm{+}}\text{v}$$\text{v}\text{?}\text{?}$; restrictions on gluino masses, which depend on photinos interacting before they decay, have to be re-examined; scalar neutrinos have suitable characteristics as candidates for dark matter in the universe. We discuss one currently fashionable class of models that can predicr a light $\text{v}$.     

A new measurement of the (K+ → e+v)(K+ → μ +v) branching ratio

The branching ratio $\text{R = Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{v)}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→ μ}{}^{\mathrm{+}}\text{v)}$ has been measured with an improved version of the apparatus described elsewhere. From 404 observed K⁺ → e⁺v decays, R = (2.51 ± 0.15) × 10^?5 was obtained, to be compared with the value predicted for pure axialvector interaction and μ-e-universality, R_theor = 2.57 × 10^?5.     

On the semileptonic decay of charmed hadrons

The semileptonic and leptonic decay modes of charmed hadrons produced in e⁺e^? collisions above 4 GeV in the cm have been investigated by selecting events with a single electron plus at least two charged tracks. The electron momentum spectrum peaks near 0.5 GeV/c with few events above 0.7 GeV/c. The spectrum excludes large rates for the decays $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}$ and $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{π}$, but is compatible with $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{K}{}^1\text{(892)}$, $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{K}$ or a mixture of both. The semileptonic branching ratio is obtained both by comparing the inclusive electron cross section with the total cross section attributable to charm, and by studying the fraction of events containing a second electron. The semileptonic charm branching ratios obtained are 0.11 ± 0.03 and 0.16 ± 0.06 respectively. A single event with three electrons and hadrons is found, consistent with the estimated background. The 90% confidence upper limit for σ(e⁺e^? → 3e + hadrons) is 0.1 nb.     

Parity violating effects in dilepton production using polarized targets

Parity violating effects in PP → μ⁺μ^?X and $\text{P}\text{P}\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{X}$ with the polarized targets have been calculated in the parton picture. The weak neutral currents used are based on an SU(2)_L × SU(2)_R × U(1) model. The result for the Weinbergy-Salam model occurs as a special case.     

Ω− produced in K−p reactions at 4.2 GeV/c

Forty $\text{Ω}{}^{\mathrm{?}}$ events have been observed in a large (133 events/βb) experiment at 4.2 GeV/c incident K^? momentum. Thirty nine of the events come from the three-body reaction $\text{K}{}^{\mathrm{?}}\text{p}\text{→Ω}{}^{\mathrm{?}}\text{K}{}^{\mathrm{+}}\text{K}{}^0$. The $\text{Ω}{}^{\mathrm{?}}$ is mainly produced in the forward hemisphere (direction of the incident K^?). The lifetime is measured to be τ = (0.75 _+0.14?0.11 × 10^?10 sec substantially less than the Particle Data Group value of (1.3 _?0.3^+0.2) × 10^?10 sec. The mass is determined to be 1671.7 ± 0.6 MeV, in good agreement with other determinations. The decay asymmetry parameter α (for the decay mode $\text{Ω}{}^{\mathrm{?}}\text{→ Λ}\text{K}{}^{\mathrm{?}}$) is found to be ?0.2 ± 0.4.     

Study of the lepton-violating (μ−, e+) reaction in modern gauge theories

The lepton-violating (μ^?, e⁺) reaction has been studiedin the context of modern gauge theories. Both left-handed and right-left symmetric models have been examined. Special attention has been paid to the following mechanisms: (i) those mediated by massive neutrinos (light or heavy); (ii) those accompanied by massless or light physical Higgs particles (majoron); (iii) those involving more intermediate Higgs particles, e.g. singly charged isosinglets (Zee model) and doubly charged isotriplets; (iv) right-handed currents. The formalism has been applied to the experimentally interesting process $\text{μ}{}^{\mathrm{?}}\text{+}{}^{58}\text{Ni}\text{→}{}^{58}\text{Fe(gs)}\text{+}\text{e}{}^{\mathrm{+}}$. The branching ratio is computed using realistic nuclear wave functions. It is found to be ?10^?27 in all models, i.e. too small to be measurable in the foreseeable future. The branching ratio for the (μ^?, e⁺) reaction to all nuclear states is estimated to be ?10^?20, i.e. beyond the goals of planned experiments.