Production of strange particles in antineutrino interactions at the CERN PS

We have studied neutral strange particle production in the bubble chamber Gargamelle filled with propane and exposed to antineutrinos from the CERN PS. Cross sections are presented for Λ, Σ⁰ and K⁰ production. Associated production reactions (ΔS = 0) have been observed in the charged and the neutral current channels. From 45 candidates for the quasi-elastic reaction $\text{ν}\text{p}\text{→ μ}{}^{\mathrm{+}}\text{Λ}$, on bound and free protons, estimates of the axial transition form factor M_A have been made using the total cross section and the t distribution. The weighted average from the two methods is M_A = 862 ± 190 MeV. From a subsample of 15 candidates for $\text{ν}$ interactions on free protons in propane, with (28±6)% background from $\text{ν}$ interactions on bound protons, we obtain M_A = 883 ± 243 MeV. The polarization of the Λ hyperons has been studied for the quasi-elastic reaction. We observe a significant Λ polarization in the production plane, normal to the Λ line of flight. The observed polarizations agree well with the predicted theoretical polarizations without any contribution from second-class axial coupling.     

Study of the reaction e+e− → K+K− in the total energy range 1400–2060 MeV

The e⁺e^? → K⁺K^? cross section has been measured between 1400 and 2060 MeV. About 500 K⁺K^? events were detected in the magnetic detector DM1 at the Orsay storage rings DCI. The charged kaon form factor is appreciably higher than predicted by only the ?, ω, ø tails, suggesting contributions from higher vector mesons.     

Energy dependence of the reactions KLop→KSop,π+Λ, π+Σo from 1540 to 1610 MeV

The reactions K_L^op→K_S^op, π⁺Λ, π⁺Σ^o have been measured for center-of-mass energies from 1540 to 1610 MeV. Channel cross sections and coefficients of the Legendre polynomial expansion of the differential cross sections and hyperon polarizations are presented. We see no evidence in the πΛ channel for the suggested $\text{3}\text{2}{}^{\mathrm{?}}$ resonance at 1580 MeV. The cross section for the K_S^op channel shows an energy dependence which is not predicted by the existing phase shift solutions based on charged kaon data.     

Inclusive neutral kaon production in 70 GeV/c K+p interactions

The inclusive production of neutral kaons in 70 GeV/c K⁺p interactions is studied with the CERN BEBC bubble chamber. The (semi-)inclusive cross sections are interpreted in terms of the various strangeness channels leading to neutral kaon production. The invariant inclusive cross section for kaon production is studied as a function of p_t² and the Feynman variable x. The latter distributions are considered both “raw” and corrected for the presence of K⁰'s resulting from K¹ decay. They are compared with the predictions expected from the Regge-Mueller formalism, the recombination model and fragmentation models.     

K*0Σ+ Photoproduction from Threshold to 3.0 GeV

The CLAS collaboration and the CBELSA/TAPS collaboration reported the differential cross section data for K*⁰ photoproduction, and found that the t-channel K exchange dominates the production amplitudes at small scattering angles. The measurement of forward-angle parity spin asymmetry for the γ p → K*⁰Σ⁺ reaction, where the theoretical calculations show an unambiguous signal, would establish the role of the κ(800). The γ p → K*⁰Σ⁺ reaction, where the Σ⁺ was identified through missing mass, on a liquid hydrogen target was measured at the LEPS detector in the energy from threshold to 3.0 GeV by using a linearly polarized photon beam at SPring-8. Decay angular distributions in the rest frame of the K ⁺ π ^? system were fit to extract spin-density matrix elements of the K*⁰ decay.     

A precise determination of the τ-mass

The energy dependence of the cross sections for e⁺e^? → e^±(μ^±) + 1 charged track has been measured for centre of mass energies between 3.60 and 4.40 GeV. The pair production of the τ-lepton is observed at all energies and the τ-mass is determined to be 1.787_?0.018^+0.010 GeV from a fit to the energy dependence of the cross section.     

K−π− elastic scattering cross section measured in 14.3 GeV/c K−p interactions

Results are presented on a measurement of the I = 3/2 Kπ elastic scattering cross section by applying the Chew-Low extrapolation method in the reaction K^?p → K^?π^?Δ⁺⁺at14.3GeV/c. The magnitude of σ(K^?π^? → K^?π^?) is found to be about 3 mb at threshold and slowly falling with energy to about 1.5 mb at 2.8 GeV. The off-mass-shell moments of the differential elastic cross section are given. The absolute value of δ₃⁰ is found to be increasing slowly from 0° to 20° between threshold and 1.2 GeV.     

Neutral strange particle production in charged current νA-interactions in the energy range 3≦E ν≦30 GeV

For charged current neutrino nucleus interactions at energies below 30 GeV, resulting from an experiment with the freon filled bubble chamber SKAT,K ⁰ and Λ production is investigated. An estimation of the total strange and charm production cross section is made.K ⁰ and Λ production rates are given in dependence on different inclusive variables. The production properties forK ⁰′s and Λ′s are discussed in terms of the Quark-Parton-Model. Comparisons with other ν-experiments at higher energies are performed.     

Inclusive single and double diffractive dissociations inK + p interactions at 32 GeV/c

We study single and double inclusive diffractive production in a 32 GeV/c K ⁺ p experiment in MIRABELLE at the Serpukhov accelerator. From reactionsK ⁺ p→K ⁺+X ⁺ andK ⁺ p→X ⁺+p we determine the total proton and kaon single diffractive dissociation cross sections \(\sigma (p\xrightarrow{{K^ + }}p_D ) = 0.90 \pm 0.12 mb\) and \(\sigma (K^ + \xrightarrow{p}K_D^ + ) = 0\) . 90±0.17 mb, respectively. In either case the only notable contributions come from dissociations into 1 and 3 charged particles. Kaon dissociation exhibits a pronounced slope-mass correlation. The search for double diffractive production in reactionsK ⁺ p→(K ⁺π^?π⁺)+X ⁺ andK ⁺ p→(pπ ⁺ π ^?)+X ⁺ leads in either case to an estimated total double diffractive cross section σ(K ⁺p→K _D ⁺ p_D) of ?220 μb. The double dissociation differential cross section exhibits a large slope of ?10GeV^?2 in the nearthreshold mass region, rapidly decreasing to ?4 GeV^?2 with increasing excitation mass. At our c.m. energy \((\sqrt s \simeq 8 GeV)\) the ratio σ_{inel dif}/σ_el is 0.85±0.10, the total diffractive cross section σ_dif≡σ_el+σ_{inel dif}=4.41±0.24 mb and the fraction σ_dif(K ⁺ p)/σ_tot(K ⁺ p) is 25±2%. TheK ⁺ andK ^? diffractive excitation mass spectra, differential cross sections and total diffractive cross sections are very similar for both single and double dissociations.     

Measurement of e+e−→τ+τ− at high energy and properties of the τ lepton

The e⁺e^?→τ⁺τ^? process has been measured using the CELLO detector at a mean total centre of mass energy of 34.2 GeV using essentially all the decay channels of the τ lepton. The measured cross section yields R_τ=1.03±0.05 (stat)±0.07 (syst). Topological branching fraction are given for τ → 1, 3 or 5 charged tracks. The angular distribution shows a clear 1 + cos²θ dependance with a forward-backward asymmetry of -0.103 ± 0.052 corresponding to an axial-vector coupling a_τ of the τ to the weak neutral current given by a_τ=?1.12 ± 0.57.     

Inclusive neutral kaon and lambda production in 69 GeV pp interactions

From a study of 180 neutral vees in the hydrogen bubble chamber Mirabell, we have obtained respectively, for the cross sections of the inclusive reactions pp → K⁰X and pp → λX, 8.4 ± 1.1 and 3.6 ± 0.5 mb. Data presented for the neutral kaons and λ in terms of the invariant cross sections F(x, p_⊥, s) show, when compared with lower and higher energy results, that scaling is approximately valid at our energy for K^o and λ production.     

Multihadron production in e+e− collisions up to 3 GeV total C.M. energy

New results on the multihadron production by electron and positron beams colliding with a total energy of up to 3 GeV are reported. Disregarding possible kaon final states, the ratio σ_mh/σ_μμ of the total multihadron cross-section to the point-like cross section for process e⁺e^?→μ⁺μ^? has an average value of 1.58 ± 0.25 in the energy interval 2.6–3.0 GeV. The average charged multiplicity over this energy range is 〈n_c〉 = 2.9 ± 0.3.     

Kaon production in hadronic matter

Subthreshold kaon production has been studied in symmetric nucleus-nucleus collisions as a function of the nucleus mass, beam energy and centrality. In Au+Au collsions at 1 AGeV theK ⁺ multiplicity increases more than linearly with increasing number of participating nucleons. Transport calculations have to assume a soft equation of state in order to reproduce the data. The in-mediumK ^? cross section measured in Ni+Ni collisions is enhanced by about a factor of 7 as compared to the free cross section when using theK ⁺ cross section at equivalent beam energies as a normalization.     

Neutral kaon production in K+p interactions at 32 GeV/c

The production of neutral kaons in the reaction K⁺p → Kⁿ + X is studied at the incident momentum of 32 GeV/c. Inclusive cross sections and single-particle distributions are presented and compared with the data at lower energies. The total inclusive cross section amounts to 7.9 ± 0.3 mb at 32 GeV/c and is significantly higher than at lower energies due to the rapid rise of multikaon production. The fraction of Kⁿ's coming from the decay of the K¹ resonances stays roughly constant with energy between 8.2 and 32 GeV/c. In the central and beam fragmentation regions the single-particle distributions reveal no energy dependence between the 16 and 32 GeV/c data in contrast with the behaviour at lower energies, while in the proton fragmentation region the data are compatible with the trend observed at lower energies and with theoretical expectations.     

Kaon production in S+nucleus and Pb+Pb collisions at CERN SPS

Charged and neutral kaon production in S-nucleus and Pb-Pb collisions has been measured at CERN in the NA35 and NA49 experiments, close to mid-rapidity. The production ofK ^± in S+S, Ag, Au at 200 GeV/nucleon was measured via their one-prong (kink) topology inside a Time Projection Chamber (TPC). The resulting charged kaon yields are in agreement with other measurements done in the same experiment. TheK ⁺/K ^? ratio was found to be 1.30±0.15 in central S+Au interactions. The production ofK _S ⁰ in Pb+Pb collisions was measured using the NA49’s large (Main) TPCs outside the magnetic field. The resulting yields are compatible with other measurements performed in the same experiment, within the quoted systematic errors. The preliminary rapidity distribution in Pb+Pb scales with the number of participants if compared to S+S collisions. From this we conclude that no further strangeness enhancement (relative to nucleon-nucleon collisions) is observed in going from S+S to Pb+Pb.     

Direct Measurement of 12C+4He Fusion Cross Section at E cm = 1.5 MeV at KUTL

¹²C+⁴He fusion reaction at E _cm  = 0.3 MeV is one of the main reaction in ⁴He-burning in stars, and is very important in nuclear synthesis. However the fusion cross section has not been determined yet in spite of 40 years efforts in the world. Recently we succeeded in the measurement at 1.5 MeV. We have a plan to make direct measurement of the total fusion cross section down to 0.7 MeV at Kyushu University Tandem accelerator Laboratory (KUTL), and to determine the cross section at 0.3 MeV by extrapolation.     

Neutral charm production in 400 GeV proton-emulsion interactions

A search has been carried out for neutral charm production in 5,108 proton-emulsion interactions at 400 GeV/c. Nine charm candidates have been observed in our fiducial volume which extends from 100 μm-1,000 μm in the forward cone. One of these is a 4-prong and the others are 2-prong events with opening angle>10 mrad and momenta of both decay tracks>150 MeV/c. Search for associated charm decays was made in an extended fiducial volume around the primary stars of these nine candidates. This yielded two neutral 2-prong events, one associated with the 4-prong and the other with a 2-prong candidate. All unassociated candidates are consistent with being backgrounds due toK _s , Λ decays, neutral interactions and γ conversions whereas the background to associated events is negligible. Based on the two associated decays the inclusive cross section forD ^{0, ?0} production is determined as 27±20 μb/nucleon. Detailed measurements on the 4-prong candidate lead to the identification of one decay track as an electron and another as a kaon. This is interpreted as a semi-leptonic, Cabbibo favouredD ⁰/D ^?0 decay.     

Properties of K0 and Λ inclusive production in charged-current antineutrino-nucleon interactions

In this paper we discuss inclusive spectra of K⁰'s and Λ's produced in charged in charged-current $\text{ν}{}_{\mathrm{\mu }}\text{N}$ interactions in the Fermilab 15 ft bubble chamber filled with a 64% Ne-H₂ mixture. Data presented in terms of the invariant cross section show, when compared with results from experiments with other incident beams, that the behavior of these distributions is approximately the same. The K⁰ and Λ fragmentation functions are presented and the shape of the K⁰ fragmentation function is found to be consistent with the parametrization of Field and Feynman.The average K⁰ and Λ transverse momentum squared as a function of Q², W², x and z is presented. Comparisons for the K⁰'s produced in the current fragmentation region are in qualitative agreement with QCD predictions. The value of the Λ polarization is measured and a positive normal polarization P_N = 0.34±0.18 is found.     

Two-state curve crossing processes involving rotational coupling in the Na 2 + molecular ion

We examine the relative utility of the Landau-Zener, phase integral, and semiclassical Magnus approximations for processes involving a real crossing of two potential curves. As an example we consider rotational coupling in Na ₂ ⁺ . Numerical calculations for the ¦3p〉→¦3s〉 quenching process and for ¦3p〉→¦3d〉 excitation agree well with recent experiments in the energy range 20 eV≦E_K≦50 eV. Simple expressions forS-matrix elements, differential and total cross sections in these approximations depend only on accurate evaluation of a few JWKB phases. For the total cross section further simplification of the Magnus results yields a useful semiempirical formula.     

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.