A measurement of the branching ratios of the A2− meson produced in 3.9 GeV/cπ−ϱ interactions

We have measured the branching fractions of the A₂^? meson, produced in the reaction π^?p → pA₂^? at 3.9 GeV/c incident momentum. The rates for the ηπ and K$\text{K}$ modes relative to ?π are 0.211 ± 0.044 and 0.056 ± 0.014, respectively. The upper limit for the η′π mode is 0.056 at the 90% confidence level. We have also looked for an ωππ decay of the A₂^? and our data are consistent with a rate of 0.10 ± 0.05, relative to ?π.     

Eine PrÄzisionsmessung des VerhÄltnisses der Spinresonanzfrequenz von Protonen zur Zyklotronfrequenz freier Elektronen im gleichen Magnetfeld

A new precision measurement of the ratio of the proton NMR frequency to the cyclotron frequency of free electrons in the same magnetic field, Ω _p /Ω_e=γ _p mc/e, has been performed. A cyclotron resonance linewidth of 5 ppm only and a reduction of the large space charge shifts, amounting up to the order of 50 ppm in earlier published measurements, enabled a high accuracy. The final result is Ω _p /Ω _e =1.5209945×10^?3±0.5 ppm, where the NMR is referred to a long cylindrical sample of H₂O, 0.2 m CuSO₄. Corrected to the free proton, we get Ω _p /Ω _e =1.5210329×10^?3±0.6 ppm. Combination of our result with an EPR-measurement ofLambe yields a free electrong-factor ofg=2(1+(α/2π)?(0.30±0.09) (α/π)²) in good agreement with the theoretical valueg=2(1+(α/2π)?0.328(α/π)²±...).     

A two-component model definition of two-body nucleon diffraction dissociation in πp → π(Nπ)reactions at 3.9 GeV/c and comparison with other experiments

Four low-mass “diffractive like” reactions π^±p → π^±(pπ⁰) and π^±p → π^±(nπ⁺) have been studied at 3.9 GeV/c incident pion momentum. These channels have been studied in the framework of a two-component model and we have proposed a definition of the diffraction dissociation amplitude. The following three features of the data are discussed: (1) an apparent violation of the predictions of isospin invariance for the cross section ratios, (2) the marked anisotropy of the s-channel helicity distributions and (3) the absence of the cross-over effect in the differential cross sections. The predictions of a two-component model previously used to explain the low mass $\text{I =}\text{1}\text{2}\text{(}\text{N}\text{π)}$ enhancement [1] and s- and t-channel helicity non-conservation [2] are seen to be in agreement with these observations. Predictions are also made for higher energy incident pions and incident K, p, and $\text{p}$ projectiles. These predictions are compared with available data including recent results at Fermilab and ISR energies.     

Photoproduction of charmed F mesons at γ energies of 20–70 GeV

Evidence is presented for inclusive photoproduction of F^± mesons in three decay modes, ηπ^±, ηπ^±π⁺π^? and ηπ^±π⁺π⁺π^?π^?. The average mass of the F^± is found to be 2.020±0.010 GeV.     

Measurement of particle and antiparticle elastic scattering on protons between 6 and 14 GeV

Differential cross sections in the t-range between 0.02 and 1.5 GeV² have been measured for the elastic scattering of particles and antiparticles on protons at 6.4, 10.4 and 14 GeV for K^±p and 10.4 GeV for π^±p and p^±p. Large statistics have been achieved and systematic uncertainties have been minimized. The relative systematic uncertainty between particle and antiparticle data is less than 0.5%. Accurate measurements of the position of the first crossover between particle and antiparticle differential cross sections have been performed. As the energy increases from 6.4 to 14 GeV the K^±p crossover moves to smaller values by 0.010 GeV² with a statistical error of 0.006 GeV² and a systematic uncertainty of 0.005 GeV². The crossover positions at 10.4 GeV for π^±, K^± and p^± scale approximately with the interaction radii.     

Measurement of the J/ψ radiative decay into f0(1270)γ

The J/ψ decay modes f⁰(1270)γ and ρπ have been studied in e⁺e^? collision at 3.1 GeV center of mass energy leading to the π⁺π^?γ and π⁺π^?π⁰ final states. The f⁰γ decay branching ratio is measured to be (0.20 ± 0.07) × 10^?2, a value comparable to the J/ψ radiative decay rates into the ηγ and η′γ channels. The J/ψ decay branching ratio into ?π is measured to be (1.6 ± 0.4) × 10^?2.     

Cluster Model Analysis of Pion Elastic and Inelastic Scattering from 12C

Angular distributions of differential cross sections for the ¹²C(π ^±, π ^±)¹²C and ¹²C(π ^±, π ^±)¹²C^* reactions at pion kinetic energy ranging from 50 to 260 MeV have been analyzed with the 3α-particle model of ¹²C. The model provides good fits to a wide range of data. Differential cross sections for inelastic transitions to the (2^?+?; 4.44 MeV) and (3^???; 9.64 MeV) states in ¹²C are computed and the deformation lengths δ ₂ and δ ₃ are extracted. It is found that the extracted deformation lengths are sensitive to the nuclear model used and similar to the corresponding values found with other probes and nuclear models.     

Direct measurement of the lifetime of the neutral pion

The lifetime of the neutral pion (π⁰) has been directly measured. The lifetime has been found to be τ_π⁰ = (0.897±0.022±0.017) × 10^?16 s. The systematic error results from uncertainties in the momentum spectrum of the π⁰ used for the measurement. This measurement yields a decay width of the π⁰ of (7.34±0.18±0.11) eV. An axial anomaly calculation, which neglects the finite mass of the π⁰, predicts a value of 7.87 eV.     

Cross section determination for the reaction K+p → K+pπ+π−π0 and K+π+π+π−n at 8.2 and 16 GeV/c

The cross sections for the reactions: (a) K⁺p → K⁺pπ⁺π^?π⁺ and (b) K⁺p → K⁺π⁺π⁺π^?n have been determined at 8.2 and 16 GeV/c with the following results:at 8.2 GeV/c: (a) 0.99 ± 0.07 mb, (b) 0.41 ± 0.04 mb;at 16 GeV/c: (a) 0.72 ± 0.05 mb, (b) 0.28 ± 0.05 mb.Using the available data at other energies, the cross-section dependence of these reactions on the incident momentum is discussed.     

Systematics of exclusive diffraction dissociation modes inK ± p interactions at 32 GeV/c

We present results of an investigation of diffraction dissociation in exclusive channels inK ^± p interactions at 32 GeV/c. Total cross sections are determined forK ^±→K ^±π⁺π^?,K ^±2π⁺2π^?,K ⁰π^±π^± K ^±2π⁺π^?,K ^± K ⁺ K ^?,K ^±p \(\bar p\) , \(\bar \Lambda \) p, andp→pπ ⁺π^?,p2π⁺2π^?,pK ⁺K^?,ΛK ⁺,ΛK ⁺π⁺π^? dissociation modes, ranging from a high of ? 300 μb to ～ 3 μb. Thedσ/dt′ differential cross sections of most of the systems studied exhibit structure, with breaks of slope att′ ～ 0.2 to 0.5 GeV²; some modes have a sharp forward spike with a slope exceeding 10 GeV^?2. A systematic investigation of two-body dissociation modesK→A+B andp→A′+B′ shows that these cross sections decrease with increasing threshold massM _A+M _B, that they are comparable for kaon and proton dissociations at similar diffractive excitation masses and are systematically suppressed by a factor 3–4 for dissociations requiring an \(s\bar s\) quark pair creation when compared to \(u\bar u\) pair creation indicating a breakdown ofSU ₃ symmetry for the \(q\bar q\) sea.     

Measurement of the pion axial form factor from radiative decay

The decay π⁺→e⁺νγ has been measured by detecting the positron with a magnetic spectrometer and the photon with an array of NaI scintillators. Using CVC to compute the vector form factor from the π⁰ lifetime we use our data to determine the ratio γ of the axial-vector form factor to the vector form factor. With the best present value for the π⁰ lifetime (0.897±0.022±0.017)×10⁻¹⁶ s and F_V=(2.55 ±0.05)×10⁻² we obtain two solutions: γ=0.52 ±0.06, favored by a likelihood ratio greater than 8.5 against γ=−2.48±0.06.     

The real part of the forward scattering amplitude in π±p elastic scattering below 2 GeV/c

The differential cross section for π^±p elastic scattering below 2 GeV/c has been measured at small forward pion angles by an electronics experiment. The interference effects observed between the Coulomb and the nuclear interaction have been used to determine the magnitude and sign of the real parts of the π^±p forward scattering amplitude. The latter are compared to the values predicted by the dispersion relations.     

Differential cross section for elastic π± helium isotopes scattering from 25 to 65 MeV

Measurements of absolute elastic-scattering differential cross sections for π^±He at T^lab_π = 30.2 MeV, 45.1 MeV and 65.0 MeV and for π^±-⁴?⁴He at T^lab_π = 25.1 MeV and 51.1 MeV have been made in the angular range 40° to 145°. An overall accuracy of about ±5% was achieved. The results are compared with available theoretical calculations.     

Backward πd scattering between 140 and 260 MeV

Differential cross sections for elastic scattering of pions by deuterons have been measured for centre-of-mass angles between 130° and 175°, and at laboratory energies 141, 177, and 260 MeV for π⁺, and at 151, 185, and 189 MeV for π^?. At 177 and 260 MeV the cross sections are a factor of 2 lower than the predictions of three-body theories.     

Charged-pion photoproduction measurement on deuterium in the Δ(1236) region using a quasi-monochromatic photon beam

Charged-pion photoproduction spectra on hydrogen and deuterium have been measured using an in-flight positron annihilation photon beam. Pions were detected in magnetic spectrometers. The experiment consisted of π^± angular distributions at 300 MeV, and fixed-angle excitation curves at 20° (π^±) and 55° (π^±) in the photon energy range 300–460 MeV. Experimental data are compared to a calculation by Laget which includes final-state nucleon-nucleon interaction and Pauli correlations. The overall agreement is satisfactory; however, the model slightly overestimates the nucleon-nucleon rescattering contribution.     

Measurement of the π−n→π−π−p cross section near threshold

The cross section for the reaction π^?n→π^?π^?p has been measured in a deuterium bubble chamber. The cross section at E_π,lab = 226, 250 and 312 MeV was found to be equal to 9.4 ± 2.3, 25.0 ± 5.3 and 57 ± 10 μb, respectively.     

Measurement of the slope of the π0-electromagnetic form factor

Using a magnetic spectrometer, we have studied 30 000 π⁰ → e⁺e^?γ events coming from K_π2⁺ decays in flight. We find a positive value for the slope of the neutral-pion electromagnetic form factor: a = +0.10 ± 0.03 (or a = +0.05 ± 0.03 without radiative corrections). This value is higher than the predictions of vector meson models.     

Measurement of mass and lifetime of hadronically produced charmed F mesons

We have observed three unique decays of F mesons into KKπ and five unique decays of D mesons into KKπ using the NA11 spectrometer together with a telescope of high-resolution silicon microstrip detectors. The mass value obtained for the F meson is (1975 ± 4) MeV, the lifetime (3.2±_1.3^3..0)×10^?13 s.     

Study of the reaction ¯pd→p s π+2π−π0 at 5.5 GeV/c incident momentum

A study of a 150000-picture exposure of ¯pd at 5.5 GeV/c yielded 152 events satisfying the hypothesis ¯pd→p _s π⁺2π^?π⁰. For the events with proton spectator in the momentum range 100–280 MeV/c we obtained the cross section of 0.11±0.02 mb. Assuming the validity of the impulse approximation we estimate a cross section of 0.43±0.06 mb for the reaction ¯pn→ π⁺2π^?π⁰. The rate for single ? meson production and an upper limit for double ? production are given. A modified multiperipheral Regge model was used in order to describe the general features of the data.     

Photoproduction of ϱ0 and ω on hydrogen at photon energies of 20 to 70 GeV

We present results on photoproduction of ?⁰ and ω in the reactions γp→π⁺π^?p and γp→π⁺π^?π⁰p by tagged photons in the energy ranges 20 to 70 GeV and 20 to 45 GeV, respectively. The production of the ?⁰ shows dominantly the characteristics of a diffractive process with respect to the E_γ and t dependence of the cross section and the spin density matrix. The ?⁰ photoproduction yields on average over the photon energy range a total cross section of σ(γp→?⁰p) = 9.4±0.1 μb with an additional systematic error of ±1 μb, and average slope parameters of the t distribution dσ/dt≈exp(?b|t| + ct²), of b=9.1±0.1 GeV^?2 and c = 3.1 ±±0.2 GeV^?4. The shape of the ?⁰ peak in the π⁺π^? invariant spectra shows a skewing similar to that observed at lower energies. The photoproduction of ω is also consistent with a diffractive process and has a cross section of σ(γp→ωp) = 1.2± 0.1 μb with an additional systematic error of ±0.2 μb. The average slope parameters of the t distribution are b=8.3 ± 1.3 GeV^?2 and c = 3.4±2.6 GeV^?4.