Origin of trimuon events in high-energy neutrino interactions

The properties of 76 neutrino-initiated μ^?μ^?μ⁺ events observed in the CDHS detector in the 350 GeV and 400 GeV wide-band beams at the CERN SPS are discussed. For neutrino energies > 30 GeV and muon momenta ? 4.5 GeV, the average trimuon rate is (3.0±0.4)×10^?5 of the single-muon event rate. The data are in agreement with normal charged-current interactions with the additional production of a muon pair by both hadronic and radiative processes. No evidence is found for either heavy-lepton or heavy-quark cascades. Upper limits for these two possibilities are established.     

Direct muon production in proton-nuclear collisions at 70, 50 and 35 GeV

Direct muon yields (μ^±) in the transverse momentum range of 1.9–3.1 GeV/c on Cu and Be nuclei at the proton energies 70, 50 and 35 GeV have been measured. The yield of direct μ/π is shown to considerably decrease when proton energy varies from 70 to 35 GeV. The charge ratio of direct muon μ⁺/μ^? as well as the dependence of the yield of direct muons on the atomic number of the target have been measured.     

A study of trimuon events in 280 GeV muon interactions

In 280 GeV μ⁺ iron interactions the inelastic production of muon pairs has been observed in excess of QED processes. For energies greater than 20 GeV deposited in the target calorimeter the interactions are found to be mainly hadronic. Cross sections are presented for this process in the mass range 1?2.5 GeV/c² and in the kinematic regions covered by the apparatus acceptance. The data are in good agreement with a photon-gluon fusion model for charmed particle production.     

Muo-production of neutrino pairs and the number of generations

The cross section for production of neutrino pairs by high energy muons in the nuclear Coulomb field is calculated analytically. For right (left)-handedμ ^?(μ ⁺) helicity, the process is only mediated by neutral currents, which opens the possibility to look for the number of generations. Assuming three generations, the calculated cross section turns out to be 1.1×10^?40 cm² for⁵⁶Fe and 6.6×10^?40cm² for²⁰⁸Pb at an incident muon energy of 300 GeV. Some comments about the equivalent photon approximation are made.     

Study of the charge-exchange reactions\pi ^ - p \to (\pi ^0 ,\eta ,\eta \prime )n at 63 GeV

Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π⁰ production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ _e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10^?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions.     

Observation of ω → π0μ+μ− decay

The results of studying the mass spectrum of μ⁺μ^?γγ systems produced in π^?p collisions at 25 and 33 GeV/c presented. The wide-aperture magnetic spectrometer with a hodoscope γ-detector was used to identify muon pairs and photons. There is a clear peak in the mass spectrum which corresponds to the decay ω → π⁰μ⁺μ^? previously not observed. The branching ratio for the decay is estimated to be 9 × 10^?5 with a systematic error of 50%.     

Anomalous magnetic moment of the muon in the left-right model

The effect of Higgs bosons on the anomalous magnetic moment of the muon is considered within the model that is based on the SU(2)_L×SU(2)_R×U(1)_B–L gauge group and which involves a bidoublet and two triplets of Higgs fields (left-right model). For the Yukawa coupling constants and the masses of Higgs bosons, the regions are found where the model leads to agreement with experimental results obtained at the Brookhaven National Laboratory (BNL) for the anomalous magnetic moment of the muon. In order to explore corollaries from the constraints obtained for the parameters of the Higgs sector, the processes e⁺e^? → μ⁺μ^?, τ⁺τ^? and μ⁺μ^? → μ⁺μ^?, τ⁺τ^? are considered both within the left-right model and within the model involving two Higgs doublets (two-Higgs-doublet model). It is shown that, if the mass of the lightest neutral Higgs boson does indeed lie in the range 3.1–10 GeV, as is inferred from the condition requiring the consistency of the two-Higgs-doublet model with the data of the BNL experiment, this Higgs boson may be observed as a resonance peak at currently operating e⁺e^? colliders (VEPP-4M, CESR, KEKB, PEP-II, and SLC). In order to implement this program, however, it is necessary to reduce considerably the scatter of energy in the e⁺ and e^? beams used, since the decay width of the lightest neutral Higgs boson is extremely small at such mass values. It is demonstrated that, in the case of the left-right model, for which the mass of the lightest neutral Higgs boson is not less than 115 GeV, the resonance peak associated with it may be detected at a muon collider.     

Anomalous muon production in e+e− annihilations as evidence for heavy leptons

We have measured inclusive muon production in e⁺e^? annihilation for CMS energies between 3.6 and 5.0 GeV. Above 4 GeV the cross section cannot be explained by conventional sources like higher order QED processes or inclusive production of the $\text{J}\text{?}$ (3.1). It is, however, compatible with the pair production of heavy particles of a mass of about 1.9 GeV/c². Spin assignment and decay parameters are investigated.     

Lower limit for heavy muon mass obtained from the data of the CERN neutrino experiment

A lower limit for the heavy muon (heavy lepton omega′^? which can have the same lepton number as omega^? and ν_omega) mass M_μ′ > 1.8 GeV at 90% confidence level is obtained with the help of the bubble chamber “Gargamelle” data in the CERN neutrino experiment. This limit should not be confused with the known limit for an M⁺ (heavy lepton M⁺ which can have the same lepton number as μ^? and ν_μ).     

Monochromatic neutrinos from the annihilation of fourth-generation massive stable neutrinos in the Sun and in the Earth

The accumulation of relic fourth-generation heavy neutrinos (of mass 50 GeV) in the Earth and the Sun, which is followed by their annihilation, is considered. The most conservative estimates of the fluxes of monochromatic electron, muon, and tau neutrinos and antineutrinos of energy 50 GeV from the annihilation of heavy neutrinos are 4.1×10^?6 cm^?2 s^?1 from Earth’s core and 1.1×10^?7 cm^?2 s^?1 from Sun’s core, whence it follows that an analysis of data from underground neutrino observatories may furnish additional information about the existence of fourth-generation neutrinos. It is shown that, because of kinetic equilibrium between the arrival of cosmic neutrinos and their annihilation, the existence of new U(1) gauge interaction of fourth-generation neutrinos has virtually no effect on the estimates of the annihilation fluxes of electron, muon, and tau neutrinos.     

Interaction of high energy muons in association with EAS,with rock and lead

An investigation on the interaction of high energy muons, associated with EAS and having energies greater than several hundred GeV, has been carried out at Kolar Gold Fields. A visual detector consisting of neon flash tube hodoscope has been used together with a scintillator detector to observe the muons and accompanying showers at the underground level. It has been found that nearly 90% of the showers observed at the underground level are generated in course of pure electromagnetic interactions of the muons with the matter traversed by them. The observed number of the showers is found to be consistent with the expected number calculated using the cross-sections for knock-on, bremsstrahlung and direct pair production processes. Rest of the observed showers do not appear to fit in the pure electromagnetic interaction scheme. Various possible production processes for these events have been discussed. Considering these events to be due to photonuclear interaction of muons in the rock, the observed number leads to a production cross-sectionσ _μ (?25 GeV) ?(1.6±0.75)10^?29 cm²/nucl.     

Direct observations of the decay of beauty particles into charm particles

The associated production of a pair of beauty particles B^? and $\text{B}{}^0$ by a 350 GeV π^? interaction has been observed in an emulsion target inserted in an array of silicon microstrip detectors. Both beauty particles decay into charm particles, both of which are also observed to decay in the emulsion. Two negative muons were identified and their momenta measured in a large muon spectrometer. One muon has a p_T of 1.9 GeV/c and is associated with a beauty particle decay. The other, with a p_T of 0.45 GeV/c is associated with a charm particle decay. The flight times of the two beauty particles are respectively (0.8 ± 0.1) × 10^?13 s and (5⁺²_?1) × 10^?13 s. Alternative interpretations of this event have negligible probability.     

Are there “prompt” like-sign dimuons?

From exposures of the CDHS detector at the CERN SPS we have obtained 367μ ⁺ μ ^? events in neutrino beams and 73μ ⁺ μ ⁺ events in an antineutrino beam. The magnitude of a prompt like-sign signal has been controversial in the past and moreover could not be explained by known production mechanisms. A critical discussion of the experimental situation is given. We have tried to reduce the systematic uncertainties of previous experiments and to get more information on the dependence of the signal with energy and the muon momentum cut-off. This experiment yields a signal of 2.8σ (2.4σ) of prompt like-sign dimuon events in the case of neutrinos (antineutrinos). The rate to charged current events is of the order of 10^?4 forp _μ<9GeV andE>100 GeV. The prompt signal has all the properties expected from the production and decay of charm-anticharm events. The magnitude, however, is substantially higher then the prediction of perturbative QCD but lower than some other experiments.     

Experimental limits on the strength of weak neutral currents in lepton pair production at PETRA energies

The processes e⁺e^? → e⁺e^? and μ⁺μ^? have been studied at PETRA using the JADE detector. The data, which were collected at s-values of up to 1300 GeV² have been analysed in terms of an electro-weak extension of QED to obtain values for the weak vector and axial vector couplings in the lepton sector. The values obtained agree with the predictions of the standard Salam-Weinberg model and the data are further analysed in terms of this model to obtain the limits 0.10 < sin²?_w < 0.40 (68% CL). The mass of the neutral weak gauge boson is deduced to be greater than 51 GeV/c².     

Search for heavy quasistable leptons

Negative results of a search for heavy quasistable charged leptons at the IHEP accelerator are reported. For the selection of heavy leptons a system of scintillation and gas ?erenkov counters was used. The upper limit estimations of the differential cross sections for heavy lepton production in pN collisions at E_p = 70 GeV are, for example, d²σ/dpω (p = 30 GeV/c, θ = 2 mrad, 1 ? M_λ ? 4.8 GeV) = 4.10^?38 cm²/sr · GeV. The results of the present work, together with the data on muon pair production in nucleon-nucleon interactions, show that there are no heavy charged leptons with masses from 0.55 GeV (τ_λ > 7 · 10^?10 sec) up to 4.5 GeV (τ_λ > 3 · 10^?8 sec).     

Possible structures of the neutral current within a gauge theory framework

We examine a class of gauge theories based on U(1)×SU(2)×G allowing for an arbitrary number of gauge bosons, while retaining the lowq ² four fermion interaction of the standard model. Measurable consequences fore ⁺ e ^?→μ ⁺ μ ^? ande ⁺ e ^?→e ⁺ e ^? at presently available as well as LEP energies are presented. Implications of the recently determined QED cut-offΛ _? ? 100 GeV on gauge boson properties and the anomalous magnetic moment of the muon are pointed out.     

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.     

A study of wrong-sign single muon production inv μ-nucleon interaction

We report on a search forv _μ-induced events where the single emerging muon carries lepton number opposite that of the incident neutrino. The rate and kinematic quantities of the candidate events are compared with known backgrounds from \(\bar v_\mu \) -induced charged current interactions and ν-induced interactions that produce dileptons. We derive an upper limit on the rate of wrong-sign single muon production relative to the rate ofv _μ charged current interactions to be 1.6×10^?4 fory<0.5 and 3.1×10^?4 fory>0.5 (90% CL). These upper limits enable us to constrain exotic sources of wrong-sign muons such as the charm component of the nucleon sea, flavor changing neutral currents and lepton number violating processes. Finally, the rate and kinematic properties of these events are compared with those of the neutrino-induced opposite-sign dimuon events.     

A light neutral intermediate vector boson without large e+e−→ μ+μ− asymmetries

An effective SU(2)×U(1)×U(1)' electroweak theory is shown to permit the occurence of a pair of neutral intermediate vector bosons with masses 40 GeV?m_light?70 GeV, m^W.S._Z⁰<m_heavy?100 GeV. Neutrino neutral current interactions are shown to be the same as in the standard electroweak model, and e⁺e^?→μ⁺μ^? forward-backward asymmetries are within experimental bounds for m_light?40 GeV.