Tau decays into kaons

Predictions for semi-leptonic decay rates of theτ lepton into two meson final statesK ^?π⁰ v _τ, $\overline {K^0 } \pi - v_\tau $ ,K ⁰ K ^? v _τ, and three meson final statesK ^?π^? K ⁺ v _τ, $K^0 \pi ^ - \overline {K^0 } v_\tau $ ,K _sπ^? K _s v _τ,K _sπ^? K _L v _τ,K _Lπ^? K _L v _τ,K ^?π⁰ K ⁰ v _τ, π⁰π⁰ K ^? v _τ,K ^?π^?π⁺ v _τ, π^? K ⁰π⁰ v _τ are derived. The hadronic matrix elements are expressed in terms of form factors, which can be predicted by chiral Lagrangians supplemented by informations about all possible low-lying resonances in the different channels. Isospin symmetry relations among the different final states are carefully taken into account. The calculated branching ratios are compared with measured decay rates where data are available.     

Multipion and strange particle photoproduction off neutrons up to 5.3 GeV

In a study of photoproduction at photon energies up to 5.3 GeV in a deuterium bubble chamber the reactions γn→pπ⁺π^?π^? and γn→pπ⁺π^?π^?π⁰ were analyzed. In these reactions production of the resonances Δ⁺⁺, Δ⁰, ?⁰, ω and A₂^? was observed. Photoproduction of strange particles was investigated and cross sections for the reactions γn→ΛK⁺π^?, Σ^?K⁰π⁺, pK^?K⁰, ΛK⁰π⁺π^? and ΛK⁺π^?π⁰ are presented. Production of Σ^?(1385) and K¹⁰(890) was observed.     

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.     

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.     

A spin-parity analysis of the K+K+K− system produced in the reaction K+p → K+K+K−p

We present the first spin-parity analysis of the K⁺K⁺K^?) system produced in the reaction K⁺p → K⁺K⁺K^?p, and show that the general features of this system resemble those of the (ππ⁺π^?) and Kπ⁺π^?) systems produced in the reactions π(K)p → π(K)π⁺π^?p. There is a low mass enhancement, (47 ± 11)% of which corresponds to 1⁺ states decaying to Kø. At higher (K⁺K⁺K^?) masses 2^? → Kf′ becomes increasingly significant and at all masses there is a 0^? contribution of roughly 30%.     

Production ofD,D * andD s mesons in 200 GeV/c π− K − andp-Si interactions

The NA 32 experiment at the CERN SPS has collected 38 million hadronic interactions with incident 200 GeV/c π^?,K ^? andp beam. Using a segmented silicon active target and a telescope of high resolution silicon microstrip counters we have selected fully reconstructedD ⁰→K ^?π⁺,D ⁰→K ^?π⁺π⁺π^?,D ⁺→K ^?π⁺π⁺,D _s ⁺ →K ^? K ⁺π⁺π⁺ and charge conjugate decays. The integrated cross-sections forD ^o,D ⁺ D ^*+ andD _s ⁺ meson production and the dependence of the cross-section on longitudinal and transverse momentum of theD are presented.     

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.     

Sum rules for recoilless lambda production in nuclei

Simple sum rules for the (K ^?,π ^?) reaction on nuclei are derived by analogy with the Mössbauer effect. The relative contribution of the recoilless and quasi-freeδ production in the (K ^?,π ^?) reaction in nuclei is estimated.     

A study of K−p interactions in deuterium in the c.m. energy range from 1.60 to 1.74 GeV

We present results of a K^?d bubble-chamber experiment at four K^? momenta between 680 and 840 MeV/c. The validity of the spectator model for the analysisof KN interactions in deuterium is discussed. Cross sections are determined for the reactions K^?p → Σ^?π⁺, K^?p → Σ⁺π^? and K^?p → Λπ⁺π^? and are compared to those obtain ed on free protons.     

Two-nucleon production of hyperons and the search for strange dibaryons

The double charge exchange reaction³He(K^?,π ⁺)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c²), events were detected which can be attributed to the two-nucleon process pp(K^?,π ⁺)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (¹ P₁) spin-singlet dibaryon D_s suggested as the lowest massS=?1 dibaryon in the MIT Bag Model. Although the existence of the D_s is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K^?p→π ⁰λ,π ⁰p →π ⁺n. We also offer an interpretation of the recent (K^?,K⁺) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K⁺ momentum of 600 MeV/c. We find that the two-nucleon mechanism K^?N →πY,πN→K⁺Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K^?p →Φλ, followed by the decayΦ → K⁺K^?, accounts for the data.     

Contribution of the inelastic channels K − p → Yπ to the shift of the ground-state energy level of kaonic hydrogen

The contribution of the inelastic channels K ^? p → Yπ, where Yπ = Σ^? π ⁺, Σ ⁺ π ^?, Σ ⁰ π ⁰, or λ⁰ π ⁰, kinematically allowed at the K ^? p threshold to the S-wave scattering length of elastic K ^? p scattering, as well as the shift of the ground-state energy of kaonic hydrogen, is calculated. The result, δa ₀ ^K?p = ?0.037 ± 0.010 fm and δε _1s = 15 ± 4 eV, will be important for the theoretical analysis of the expected data from the experiments scheduled by the DEAR and SIDDHARTA Collaborations at the end of 2006.     

Spin parity structure of the Q and L enhancements in K−p → (K−π−π+)p at 10 and 16 GeV/c

A parital wave analysis of the (Kππ) system produced in K^?p → (K^?π^?π⁺)p at 10 and 16 GeV/c has been performed. It is found that in 88% of the cases the Kππ) system is in unnatural spin-parity (J^P) states 0^?, 1⁺, 2^? …, with contributions from many decay modes, $\text{κπ,}\text{K}{}^1\text{(890)π,}\text{K}{}^1\text{(1420)π,}\text{K}\text{?,}\text{K}\text{?}\text{and Kf}$. More than one decay m and J^P state are required to describe the Q and L enhancements, suggesting a composite structure of these enhancements. The (Kππ) system is produced dominantly (～95%) by natural parity exchange. Overall, the production mechanism of the (Kππ) system is remarkably similar to that of the 3π system in π^?p → (π^?π^?π⁺)p, even i detailed spin-parity structure.     

Measurement of the KS0 → π+π−γ decay rate

From a study of 70 000 K° decays in the CERN 2m hydrogen bubble chamber, we have estimated the rate for K_S⁰ → π⁺π^?γ for different cuts in the γ momentum. The results are in good agreement with inner bremsstrahlung on K_S⁰ → π⁺π^?. For γ momentum in the K° c.m. greater than 50 MeV/c, we obtain the branching ratio: Γ(K_S → π⁺π^?γ, k>50 MeV/c)/Γ(K_S→π⁺π^?)=(2.8. ± 0.6)×10^?3. This leads to an estimate for the direct γ emission process: Γ(K_S→π⁺π^?γ direct)/Γ(K_S → π⁺π^?)=(0.3 ± 0.6) × 10^?3.     

Test of the Zweig rule in π−p interactions at 19 GeV/c

We have observed φ production in π^?p interactions at 19 GeV/c with (44±10) events in the final state φπ⁺π^?π^?p and (45±9) events in φK⁺K^?π^?p. The production ratios φπ⁺π^?π^?p/ωπ⁺π^?π^?p ≈ 0.005 and φK⁺K^?π^?p/?°K⁺K^?π^?p ≈ 0.45 agree with Zweig-rule expectations.     

Strangeness at J-PARC

Strangeness nuclear physics is one of the main fields to be explored at the J-PARC Hadron Hall. The K ^?? and π ^± beams at the K1.8 beam line will be used mostly for hypernuclear experiments. The γ-spectroscopy of Λ hypernuclei using the K ^??,π ^?? reaction and the spectroscopy of neutron-rich hypernuclei via the π ^??,K ^?+? reaction are planned to be studied. As for Strangeness =???2 systems, experiments for Ξ hypernuclear spectroscopy via the K ^??,K ^?+? reaction, double Λ hypernuclei by the hybrid emulsion method, and Ξ^?-atomic X rays will be carried out.     

The theoretical basis and phenomenology of the OZI rule

No reliable theoretical recipe exists for predicting strengths of OZI-forbidden transitions proceeding via two OZI-allowed transitions like φ→K⁺K^?→?π, π^?p→K⁺K^?n→φφn or π^?p→ηn→φφn. Nonet symmetry, exchange degeneracy and duality suppress such transitions by cancellations between different diagrams. Unpredictable OZI violations are introduced by breaking of these symmetries. Phenomenological analyses of charmonium decays and meson photoproduction establish an emperical topological criterion for classifying some processes as less forbidden and suggest that π^?p→φφn should not be suppressed by a factor of more than three in amplitude. Its observation is not conclusive evidence for new exotic particles.     

Measurement of pp annihilation cross sections into charged particles in the momentum range 374–680 MeV/c

$\text{p}\text{p}$ annihilation cross sections into 2-, 4- and 6-prong topologies, and the exclusive annihilation cross sections for the π⁺π^?, K⁺K^?, π⁺π^?π⁰, π⁺π⁺π^?π^?, π⁺π⁺π^?π^?π⁰, π⁺π⁺π⁺π^?π^?π^?, and π⁺π⁺π⁺π^?π^?π^?π⁰ channels in the momentum range 374–680 MeV/c were measured. No prominent structure was observed in the momentum dependence of any of the above cross sections, but a small enhancement in the cross section was observed at 490 MeV/c corresponding to the S meson mass in the topological, and π⁺π^?π⁰ and π⁺π⁺π^?π^?π⁰ cross sections. If the extensive of the S meson with a mass and width of 1935.5 and 2.8 MeV/c² is assumed, our measurement gives a total resonant annihilation cross section into charged particles of 10.0±3.0 mb.     

Analysis of K−K+ and π−π+ final states in 13 GeV K−p interactions

The differential cross sections and density matrix elements for the φ and ?⁰ mesons have been measured in the reactions K^?p → K^?K⁺ (Λ, Σ⁰) and K^?p → π^?π⁺ (Λ, Σ⁰) at 13 GeV using a wire chamber spectrometer. The analysis shows that while the vector meson production is dominated by the natural parity exchange amplitude, some unnatural parity exchange is also required. Furthermore the φ and ? natural exchange cross sections are identical in shape and have the 2:1 relative strength expected in the quark model with K¹ and K⁷ exchange degeneracy. The analysis of the clear peak-dip ?^0?ω interference pattern observed in the π^?π⁺ data indicates that the ω production is in phase with the ? and of similar magnitude. Both the S¹ and f′ meson are clearly observed in this experiment. The S¹ data are found to be consistent with S¹ parameters deduced from ππ scattering analyses. The f′ density matrix elements and a new limit of the f′ → π^?π⁺ branching ratio are presented.     

A study of multiparticle fragmentation inK + p interactions at 32 GeV/c

Results are presented on inclusive production of resonant and non-resonant particle systems produced inK ⁺ p interactions at 32 GeV/c. We compareK ^*+(892), \(\bar \Sigma ^{ * - } \) (1385), Σ^*±(1385), and ?⁰ inclusivex-spectra with the ones of non-resonantK _s ⁰ π^±, \(\bar \Lambda \pi ^ - \) , Λπ^± and π⁺π^? pairs at the same effective mass. Resonance-particle pairsK ^*+π^±, Σ^*+π^?, and \(\bar \Sigma ^{ * - } \pi ^ - \) are also studied together with non-resonant tripletsK _s ⁰ π^±, Λπ⁺π^?, \(\bar \Lambda \pi ^ - \pi ^ - \) . The invariantx-spectra of resonant particle pairs decrease less rapidly withx then the corresponding non-resonant pairs. Comparison with quark-recombination predictions indicates that the particles, resonances and multiparticle systems are probably created off a single valence quark or diquark instead of carrying all possible valence-quarks.     

Excitation and structure of hypernuclear resonances in (K −,π ¯0)-reactions on 1p-shell nuclei

The available experimental data on the excitation functions (EF) of the 1p-shellΛ-hy-pernuclei in (K ^?, π^?) reactions atθ _π = 0^° has been analysed in terms of shell model and weak coupling scheme. It is substantiated by the experimental data on the neutron spectroscopic factors and on the fragmentation of nuclear hole excitations. The pronounced nuclear spectroscopic characteristics in the hypernuclear spectra are indicative of a weak coupling ofΛ-hyperon with nuclear subsystem. The analysis has made it possible to determine the difference is single-particle energies ofΛ-hyperon in the 1p- and 1s-states and to obtain additional evidence for the smallness of theΛ-nucleus spin-orbit interaction. The resonance structure of EF of hypernuclei, which were not studied in (K ^?,π ₀ ^? ) reactions, is predicted. The interrelated aspects of the studies of the (K ^?,π ₀ ^? ), (K ^?,π ₀ ^? β^′), and (K ^?, π⁺) reactions which are of interest to spectroscopy ofΛ-andΣ-hypernuclei are discussed.