Evidence for a narrow width boson of mass 2.95 GeV

In a search for resonances coupled to the $\text{p}$pπ^? system, we have studied π^?p interactions at 16 GeV/c giving a forward antiproton, using the Omega spectrometer at CERN. In the final states involving a $\text{p}$, p and π^? we observe a 5.6 (6.3) standard deviation enhancement in the $\text{p}$pπ^? mass spectrum at (2.95 ± 0.01) GeV with a width consistent with the resolution (σ = 15 MeV). The production cross section × branching ratio is estimated to be of the order 1 μb. The data are consistent with a resonance decaying partly via intermediate $\text{p}$p final states.     

A study of high transverse momentum π0's at ISR energies

We present a study of the transverse momentum spectrum of π⁰'s produced at c.m. angles θ = 90° and 53° in pp collisions at √s = 23.6, 30.8, 45.1, 53.2, and 62.9 GeV. The experiment was performed with a lead-glass detector. The data can be described with the usual parametrization $\text{p}{}_{\mathrm{<mtext>T</mtext>}}{}^{\mathrm{?n}}\text{?;(x}{}_{\mathrm{<mtext>T</mtext>}}\text{, θ)}$, with n = 7.2 ± 0.2. Comparison between the 90° and 53° data further indicates no appreciable dependence on θ, at least for x_T < 0.3. Two-particle inclusive cross sections for π⁰'s produced alongside are also presented. They are observed to have a dependence upon the transverse momentum of the dipion similar to that of single-particle cross sections and with the same value of n. Two-photon decays of η mesons are observed between 3 and 4 GeV/c transverse momentum with a production cross section half of that of π⁰.     

Charged pion production in e+e− annihilation at 14, 22 and 34 GeV CM energy

The inclusive production of π^± mesons in e⁺e^? annihilation has been measured at c.m. energies of 14, 22 and 34 GeV for pion momenta between 0.3 ans 10 GeV/c. The fraction of pions among the charged hadrons is above 90% at 0.4 GeV/c and decreases to about 50% at high momenta. The scaled cross sections ($\text{s}\text{β}$) $\text{d}\text{σ}\text{d}\text{x}$ at 14, 22 and 34 GeV as well as the 5.2 GeV data from DASP have a rather similar x dependence. After integration over the x range from 0.2 to 0.6 the cross sections indicate a monotonic decrease with increasing centre-of-mass energy.     

Results on the production cross sections π−p → neutrals and π− p→ χ↳2γ0n at 3.8, 6, 8 and 12 GeV/c

The ratio between the cross sections for the reactions $\text{π}{}^{\mathrm{?}}\text{p→}\text{χ}\text{?}{}_{\mathrm{2\gamma }}{}^0\text{n}$ and π^?p → η_→2γ n has been measured to be (2.4 ± 0.9) × 10^?2, (2.1 ± 0.6) × 10^?2 and (2.8 ± 1.3) × 10^?2 at 3.8,6,8 and 12 GeV/c incident momentum respectively.At the same momenta the cross section for π^t- p → neutrals is (1.48 ± 0.09) mb, (0.86 ± 0.05) mb, (0.64 ± 0.04) mb and (0.42±0.03) mb.     

Experimental results on diffractive one-pion production at the CERN ISR

New experimental results are reported on diffractive dissociation of protons into (nπ⁺) in proton-proton collisions at a centre-of-mass energy of $\text{s}\text{= 45}\text{GeV}$. The data were obtained using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. We have searched for resonance contributions and found peaks at mass values of 1.5 GeV, 1.65 GeV, and 2.1 GeV. A dip in $\text{d}\text{σ}\text{d}\text{t}$ is observed at low t and low mass; it is most pronounced for events with neutrons emitted at 90° in the Gottfried-Jackson frame. The correlation between mass and slope depends strongly on θ_J. The cross section of the channel pp → pnπ⁺ is 400 ± 110 μb at $\text{s}\text{= 45}\text{GeV}$, giving an energy dependence of s^?0.30±0.07 for isospin exchange zero in this channel.     

Large angle production of stable particles heavier than the proton and a search for quarks at the CERN intersecting storage rings

Measurements have been performed on production of particles with mass 1.5 GeV/c² and charge $\text{?}\text{2}\text{3}$ for θ_lab = 62.5° and $\text{s}\text{= 53}\text{GeV}$. At p_T = 0.7 GeV/c the relative rate of production of antideuterons to π^? is (5 ± 1) × 10^?5. The deuteron to antideuteron ratio is 3.7 ± 1.2. No new stable particle has been amongst 0.7 × 10⁸ charged particles entering our detector.     

Search for long-lived particles in 200 GeV/c proton-nucleon collisions

A search for long-lived particles (τ ? 10^?8 sec), with changes $\text{±}\text{2}\text{3}\text{, ± 1, ±}\text{4}\text{3}\text{and}\text{± 2}$, produced in 200 GeV pN collisions was performed at the CERN-SPS in a secondary beam equipped with superconducting r.f. separators. Upper limits were obtained for the production of long-lived hadrons and leptons. For charge - 1 particles the limits are at the level of 10^?7 of the pions at a mass m = 0.2 GeV and reach the 10^?11 level from $\text{3}\text{to}\text{8}\text{GeV}$. The production of light antinuclei was measured. The cross sections for ³He production are (1.3 ± 0.3) and (1.9 ± 0.3) × 10^?34 cm²/sr · GeV/c at 21 and 47.4 GeV/c respectively; for t the cross section is (7.6 ± 0.9) × 10^?34 cm²/sr · GeV/c at 23.7 GeV/c.     

Production of γ by 194 GeV/c negative pions on tungsten

On the basis of 2000 ?, ?′ and ?″ events obtained in π^?-W interactions at 194 GeV/c we extract a value for the cross section times the branching ratio of B_μμσ = (0.96±0.04±0.17) pb nucleon^?1. The $\text{(?′ + ?″)}\text{?}$ ratio is found to be 0.53 ± 0.19. The observed differential x_F and P_T distributions are compared with those of the Drell-Yan continuum, and the cross section and the x_F distribution are compared with theoretical predictions.     

Semicoherent elastic pion-carbon scattering at 25 and 40 GeV/c

In the frame of a systematic study of hadron-nucleus interactions performed at the Serpukhov accelerator (CERN-IHEP 5th experiment), semicoherent elastic scattering on carbon $\text{π}{}^{\mathrm{?12}}\text{C}\text{a}\text{?}\text{π}{}^{\mathrm{?12}}\text{C}{}^1\text{(4.44}\text{MeV}\text{)}$ was investigated with 25 and 40 GeV/c incident pions.The experimental data were obtained with a counter technique, looking at the coincidence between the scattered pion and the 4.44 MeV photon from the J^P = 2⁺ carbon excited state detected by a NaI counter.The value obtained for the integrated cross section at 40 GeV/c in the 0.0032 ? |t| ? 0.27 (GeV/c)² four-momentum transfer range isσ = 1.16 ± 0.11 mb.According to the theoretical models, this t-range at 40 GeV/c covers more than 99% of the angular distribution, so the above value almost corresponds to the total semicoherent elastic cross section.     

Charged particle multiplicities in 100 GeV/cpp interactions

Results are presented on the topological cross sections obtained for antiproton-proton interactions from an exposure of the Fermilab 30-inch bubble chamber to a 100 GeV/c negative beam enriched in $\text{p}$'s. The $\text{p}$p inelastic cross section is found to be σ_inel = 34.6 ± 0.4 mb, and the average inelastic charged particle multiplicity to be 〈n〉 = 6.74 ± 0.05.     

On the particle multiplicity distributions at high energy

An experiment has been performed to study the inclusive photoproduction of π⁰ mesons. Photoproduced π⁰'s were detected in a hodoscope consisting of 14 lead glass Cerenkov counters. To obtain the cross sections at a photon energy of 6 GeV we used the photon-difference method. Data are presented in terms of the Feynman variable $\text{x = q}{}_6{}^1\text{(√s/2)}$ and the trnasverse momentum q⊥. We have measured four q⊥ distributions at x = 0.2, 0.4, 0.6 and 0.8. The results dhow that the π⁰ rate at small values of q⊥ is smaller than the π± rate. The data can be fitted smoothly by a form A exp (?Bq_⊥²) with a value about 3.5 GeV^?2 for the slope parameter B.     

Total cross sections νμ and ḡnμcharged-current interactions between 20 and 200 GeV

Exposures of the Ne/H₂ filled Big European Bubble Chamber (BEBC) to a dichromatic neutrino (antineutrino) beam produced by 400 GeV protons of the CERN SPS yielded ～ 3100 events with a negative, and ～ 1100 with a positive, muon. The neutrino flux is determined from the muon flux in the shielding. Assuming a linear energy dependence of the cross section, the values $\text{σ}\text{E}$ between 20 and 200 GeV are found to be 0.657 ± 0.012 (stat.) ± 0.027 (syst.) and 0.309 ± 0.009 (stat.) ± 0.013 (syst.) cm² (GeV nucleon)^?1, for neutrinos and antineutrinos, respectively. The scaling variable $\text{q}{}^2\text{E}$ decreases significantly with increasing energy both for neutrinos and antineutrinos.     

Inclusive K1±(892) production in pp and π+p interactions

A study is presented of the inclusive production cross sections of K^1±(892) vector mesons in pp interactions at 12 and 24 GeV/c and in π⁺p interactions at 16 GeV/c. The K^1± inclusive cross section is ～0.9 mb for both pp at 24 GeV/c and π⁺p interactions at 16 GeV/c. For pp interactions, $\text{σ(}\text{K}{}^{\mathrm{1+}}\text{)}$ and $\text{σ(}\text{K}{}^{\mathrm{1?}}\text{)}$ are seen to rise with energy, showing a threshold behaviour. In both pp and π⁺p interactions, $\text{σ(}\text{K}{}^{\mathrm{1+}}\text{)}$ largely exceeds $\text{σ(}\text{K}{}^{\mathrm{1?}}\text{)}$ at these energies and this excess is interpreted as K¹⁺ production by beam and target fragmentations. The decays of K^1±0 yield ～30% of the K⁰ observed in the final states. The p_T² dependence of both K¹⁺ and K^1? cross sections is described by an exponential with slope of ～3.3 (GeV/c)^?2. The longitudinal momentum spectra for K¹⁺ in 16 GeV/cπ⁺p and 24 GeV/c pp interactions are similar in shape in the target hemisphere. The K^1? spectra are similar over the whole kinematic region when viewed in the quark c.m.s. and point to a central production mechanism. Comparing K¹⁺ and ρ⁰ production, striking similarities are found.     

High transverse momentumη production in π− p, π+ p,andpp interactions at 280 GeV/c

The inclusive cross sections for η production by the interactions of 280 GeV/c momentum π^?, π⁺, and proton beams in hydrogen have been measured. The kinematical range covered is ?0.45<x _F <0.45, and 4.0<P _T <7.0 GeV/c for Feynmanx _F and transverse momentum respectively. The η to π⁰ cross section ratios are given for the three reactions. The ratio of π^? p to π⁺ p cross sections for η production in the above kinematic ranges is 1.22±0.08±0.11.     

Experimental results on J/ψ production by π±, K±, p and p incident on hydrogen at 39.5 GeV/c

J/ψ production at 40 GeV/c by π^±, K^±, p and $\text{p}$ incident on hydrogen has been studied and results compared with those obtained on tungsten in the same experiment. On hydrogen, J/ψ cross-section ratios relative to π^? have been measured to be (for $\text{x}{}_{\mathrm{<mtext>F</mtext>}}\text{> 0) σ(π}{}^{\mathrm{?}}\text{) : σ(π}{}^{\mathrm{+}}\text{) : σ(}\text{p}\text{) : σ(}\text{p}\text{) = 1 : (0.78 ± 0.09) : (0.83 ± 0.35) : (0.07 ± 0.04)}$. The suppression of the proton induced cross sections shows the importance of calence quark-antiquark fusiin J/ψ production at this energy (i.e. M_J²/_ψ/s=0.13).     

Inclusive π0 production at very large pT at the ISR

Inclusive π⁰ production at 90° has been studied at the ISR at $\text{s}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 52.7}\text{and}\text{62.4}\text{GeV}$ over the p_T range from 7 to 15 GeV/c. The two photons from π⁰ decay yielded overlapping electromagnetic showers in the liquid-argon-Pb plate calorimeter detector system. Any direct photon production is included in these measurements. For large values of p_T, the cross section is observed to decrease with p_T more slowly than the p_T^?8 behaviour which has been observed at lower values of p_T.     

Measurements of tau decay modes and a precise determination of the mass

The cross sections for e⁺e^? → e⁺(μ⁺ + non showering track + any photons have been measured for cm energies between 3.1 GeV and 5.2 GeV. We observe τ-pair production below the thresholdfor charm production and determine the τ mass to be 1.807 ± 0.020 GeV from a fit to the energy dependence of the cross section. The ration of the leptonic branching ratios B_μ/B_e = 0.92 ± 0.32 is consistent with eμ-universality. The following branching ratios are determined for a V-A coupling: $\text{B(τ → ν}{}_{\mathrm{\tau }}\text{e}\text{ν}\text{) = B(τ → ν}{}_{\mathrm{\tau }}\text{μ}\text{ν}\text{) = 0.182 + 0.028}$. B(τ → ν_τ + charged hadron + any photons) = 0.29 ± 0.11, B(τ → ν_τ + three or more charged hadrons + any photons) = 0.35 ± 0.11.     

Measurements of elastic scattering in alpha-alpha and alpha-proton collisions at the CERN intersecting storage rings

We measured the elastic scattering of $\text{αα}\text{at}\text{s}\text{= 126}\text{GeV}$ and of αp at $\text{s}\text{= 89}\text{GeV}$. For αα, the differential cross section dσ/dt has a diffractive pattern minima at |t| = 0.10 and 0.38 GeV². At small |t| = 0.05?0.07 GeV², this cross section behaves like exp[(100 ± 10) t]. Extrapolating a fit to the data to the optical point, we obtained for the total cross section α_tot(αα) = 250 ± 50 mb and an integrated elastic cross section σ_e1(αα) = 45 ± mb. Another method of estimating σ_tot(αα), based on measuring the interaction rate, yielded 295 ± 40 mb. For αp, dσ/dt has aminimum at |t| = 0.20 GeV², and for 0.05 < |t| < 0.18 GeV² behaves like exp[(41 ± 2) t]. Extrapolating this slope to |t| = 0, we found σ_tot(αp) = 130 ± 20 and σ_e1(αp) = 20 ± 4mb. Results on pp elastic scattering at $\text{s}\text{= 63}\text{GeV}$ agree with previous ISR experiments.     

Proton-proton inelastic scattering at 0.5 TeV

We have measured at 500 GeV the cross section $\text{d}{}^2\text{σ}\text{dt dM}{}_{\mathrm{X}}{}^2$ for the inclusive reaction p + p → + X. We determine the mass spectrum of the diffractive peak to be $\text{1}\text{M}{}^{\mathrm{3.8\pm 0.2}}$ and the scaling part of the cross section to be dσ/dM_X² = (15.7±1.1)/smb/GeV².     

Regeneration amplitude of KS0 from KL0 in carbon

We have measured the transmission regeneration amplitude for carbon. The invariant amplitude $\text{[?(0) ?}\text{?}\text{(0)]/P}$ varies from 5.909 ± 0.066 mb at 4.5 GeV/c to 3.933 ± 0.152 mb at 9.5 GeV/c. The results agree with optical model calculations using measured kaon-nucleon total cross sections. The data also provide a value for the ω trajectory intercept α_ω(0) = 0.42 ± 0.04.