Is there a narrow ε under the ϱ?

The possibility that a narrow ? resonance exists, approximately degenerate in mass and width with the ?, is considered. It is shown that data on π⁺π^? production near the ? mass, including the full set of joint moments in π⁺p → π⁺π^?Δ⁺⁺ as well as the moments obtained with a polarized target in π^?p → π^?π⁺n, are consistent with the existence of such a resonance. Our method, which involves a compromise two-parameter fit to the mass dependence of some moments and the mass-averaged values of all moments, indicates that a broad ? with a slowly varying phase shift and a rather low mass, 600 MeV, also fits the data. However, the two solutions could be distinguished by accurate measurements of the mass dependence of some moments, using existing data on π⁺p → π⁺π^?Δ⁺⁺, and the existence (or non-existence) of a narrow ? clearly demonstrated.     

Search for the ϕ → π+π−γγ and ϕ → π+π−η decays with the CMD-2 detector

The ? → π⁺π^?γγ and ? → π⁺π^?η decays are sought in the experimental data obtained with the CMD-2 detector in the region of the ?-meson resonance. Upper limits ?(? → ππγγ)< 1.2 × 10^?4 and ?(? → ππη) < 6.1 × 10^?5 (both at a C.L. of 90%) are determined for the branching ratios of these decays.     

Contributions of exclusive pion electroproduction reactions to inclusive structure functions

The contributions of exclusive π⁺n, π⁰p, and π^?π⁺p channels to the inclusive structure function F ₂(x, Q ²) are determined from the CLAS collaboration data analysis. Reliability of the CLAS data on the inclusive structure function and single-pion electroproduction channels is verified. The total contribution of the uninvestigated π⁺π⁰n and π⁰p channels to this function and the integrated cross sections of these channels at photon virtualities Q ² = 0.4 and 0.5 GeV² are predicted.     

D meson production and decay in e+e− annihilation at 4.03 and 4 GeV c.m. energy

Decay modes of the charmed mesons, D⁰ and D⁺, are studied in e⁺e^? annihilation data at 4.03 and 4.41 GeV c.m. energy. The products of cross section times branching ratio are measured for the K^?π⁺, K^?π⁺π⁺π^?, K_Sπ⁺π^? and K^?π⁺π⁺ final states. Upper limits are established for the Cabibbo forbidden decays via π⁺π^?, K⁺K^?, K⁺K^? π⁺, K⁺π⁺π^? and π⁺π^?π⁺. The K^?π⁺π⁺π^? final state is shown to be dominated by K^?π⁺ρ⁰.     

Study of process e + e − → π+π−π0π0 at energies √s < 1 GeV with the spherical neutral detector

The cross section for the process e ⁺ e ^? → π⁺π^?π⁰π⁰ has been measured in an experiment with a spherical neutral detector, with the cross section at energies √s < 920 MeV having been measured for the first time. The model of vector dominance describes well the data obtained if the ρ, ρ′, and ρ″ resonances are taken into account. The probability of the decay ρ → π⁺π^?π⁰π⁰ is B(ρ → π⁺π^?π⁰π⁰) = (1.60 ± 0.74 ± 0.18) × 10^?5. The upper limit for the decay ω → π⁺π^?π⁰π⁰ has been improved by two orders of magnitude compared to previous measurements and is B(ω → π⁺π^?π⁰π⁰) < 2 × 10^?4 at a 90% confidence level.     

Observation of the (π−, π−n) and (π+, π+p) reactions at 165 MeV

The (π^?, π^?n) and the (π⁺, π⁺p) reactions were studied on C, Fe, and Bi at 165 MeV by coincidence measurement o outgoing particles. The nucleon-knockout reaction is the dominant inelastic process at backward pion-scattering angles at this energy. The quasifree (π^?, π^?n) and (π⁺, π⁺p) cross sections were determined from the π-N an correlations. Their σ_qf(π^?, π^?n)/σ_qf(π⁺, π⁺p) ratio is consistent with unity for C and is larger than the N/Z ratio for the heavier nuclei.     

A new Coulomb correction method for Bose-Einstein correlations,based on the π+π− correlation measurements

We present the measured correlation functions for π⁺π^?, π^?π^? and π⁺π⁺ pairs in central S+Ag collisions at 200 GeV per nucleon. The Gamov function, which has been traditionally used to correct the correlation functions of charged pions for the Coulomb interaction, is found to be inconsistent with all measured correlation functions. Certain problems which have been dominating the systematic uncertainty of the correlation analysis are related to this inconsistency. It is demonstrated that a new Coulomb correction method, based exclusively on the measured correlation function for π⁺π^? pairs, may solve the problem.     

On the possible existence of a vector meson ϱ' (1250)

By combining new results obtained at C.M. energies of 1.2 and 1.3 GeV with previous data obtained at lower energies from the e⁺e^? annihilation process e⁺e^? → π⁺π^?π^oπ^o, we get an indication in favour of the existence of a new vector meson of the ? type, ?' (1250), the first daughter of the ? in the predictions of the Veneziano model. Further results on the annihilation process e⁺e^? → π (1600) → π⁺π^?π⁺π^? are also presented.     

Pion-pair production on a proton by photons in the energy region of nucleon-resonance excitation

A model is proposed for describing the production of π⁺π^? pairs by real and virtual photons on protons in the energy region of nucleon-resonance excitation. The invariant-mass distributions of the π⁺π^? and π⁺ p systems at the photon point are calculated. The results are compared with available experimental data.     

Multipion production below 1.1 GeV by e+e− annihilation

The production of multipion events by e⁺e^? annihilation has been measured at centre of mass energies 915,990 and 1076 MeV. Both channels e⁺e^?→π⁺π^?π^o and e⁺e^?→π⁺π^?π⁺π^? have been analysed. An energy threshold effect analysed. An energy threshold effect around 919 MeV (m_ω + m_π^o) has been evidenced for the π⁺π^?π^oπ^o channel and the cross section is consistent with the quasi two-body process e⁺e^?→ωπ^o. The cross section for π⁺π^?π⁺π^? is lower by an order of magnitude and increases with the energy.     

Energy dependence of the cross sections for the e<Superscript>+</Superscript>e<Superscript>–</Superscript> → hadrons process near the production threshold for the <Emphasis Type="Italic">N</Emphasis><Emphasis Type="Italic">N̄</Emphasis> pair

The energy dependence of the cross sections for the processes e⁺e^? → π⁺π^?π⁰, K⁺K^?, ηπ⁺π^?, ωπ₀, and K⁺K^?π⁺π^? is studied near the production threshold for a nucleon–antinucleon pair. It is shown that, within the measurement errors, the cross sections in question behave smoothly in this energy region.     

The ω(782)→5π decay

The partial widths of the decays ω→2π⁺2π^?π⁰ and π⁺π^?3π⁰ are evaluated and their excitation curves in e ⁺ e ^? annihilation are obtained.     

π+/π− Ratio and two particle production in Proton's fragmentation region by Monte Carlo simulation

Hadron jet at lowp _T is generated by Monte Carlo method using several models including our quark cascade model in which the recombination mechanism is taken into account. The predicted results from those models on π⁺/π^? ratio,K ⁺ /K ^? ratio, π^± meson spectra and π⁺/π^? ratio under π^± meson and Λ particle trigger, ratio between invariant two particle cross-section (p→π ⁺ /π ^? )/(p→π ^? /π ^? are compared with the experimental data. The effects of the asymmetric initialu- andd-quark distributions the scaling and its violation of particle spectra and particle ratios under the other particle trigger are discussed. Predictions from our recombination model fit to the experimental data fairly well.     

Evidence forf 2 (1720) production in the reaction pomeron-pomeron→π+π−π+π−

Data are presented on pomeron-pomeron interactions which produce a central π⁺π^?π⁺π^? system in proton-proton collisions at √s=62 GeV at the CERN Intersecting Storage Rings. A spin-parity analysis of the π⁺π^?π⁺π^? system shows evidence for the production of the statef ₂ (1720) with decay to ρ⁰π⁺π^?. Since pomeron-pomeron interactions are expected to favor the production of gluonic bound states, observation of thef ₂ (1720) supports earlier interpretations of it as a glueball. In addition, enhancements near threshold give indication of the statef ₂ (1270) decaying to ρ⁰ρ⁰ and the statef ₀ (1400) decaying to ρ⁰π⁺π^?.     

Study of the δ− → π +π−π− Decay Mode

No enhancement in δ^? → π ⁺π^?π^? decay mode appeared at mass 962 MeV or at 996 MeV produced in π^?p → δ^?p interaction near its production threshold in a missing mass counter experiment. This finding fully supports the fact that the δ^? → π ⁺π^?π^? decay mode is not allowed by the conservations of the angular momentum and the parity.     

Measurement of the relative probability of φ →ηγ decay in the η → π +π−π0 channel

The relative decay probability B(φ → ηγ) = (1.259 ± 0.030 ± 0.059)% in the decay channel η → π⁺π^?π⁰ has been measured in an experiment using a spherical neutral detector in the VEPP-2M electron-positron storage ring. The result agrees with the tabulated value and with measurements of this probability using the spherical neutral detector in other η-meson decay channels.     

The process e + e − → ωπ0 near the Φ resonance

The reaction e ⁺ e ^?→ωπ⁰ near a Φ resonance was studied with a spherical neutral detector at VEPP-2M e ⁺ e ^? collider. Both main modes of decay of a ω meson were investigated: ω→π⁺π^?π⁰ and ω→π ⁰γ. The probability of decay Φ→ωπ⁰ was obtained from the magnitude of the interference wave in the cross section for the reaction e ⁺ e ^?→ωπ⁰→ π⁺π^?π⁰π⁰: B(Φ→ωπ⁰) = (5.5 _?1.4 ^+1.6 ±0.3) ×10^?5. The ratio of the partial widths of the ω meson was obtained from the ratio of the cross sections for the two modes: Γ(ω→π⁰γ )/Γ(ω→π⁺π^?π⁰) = 0.0994 ± 0.0036 ± 0.0038.