The production of a Λ+c charmed baryon has been observed in pp collisions at the CERN ISR. A sharp peak at 2.26 GeV/c2 was found in the decay mode Λ+c → p in events triggered with a forward K? meson. Also the decay mode Λ+c → K? Δ++ seems to be present. The estimation of the total cross section for Λ+c production is given. However, the resulting value depends on the assumed form of the differential cross section. In addition, Λ+c production in events triggered by the presence of a direct electron is discussed. 相似文献
The mass, width and branching fractions of the Λ(1520) into have been determined using a Λ(1520) sample produced in the reaction K?d→Λ(1520)π?ps at K? -neutron centre-of-mass energies between 1.9 and 2.2 GeV. A Dalitz plot analysis of the Λ0π+π? decay mode shows that there is a substantial Σ(1385)π component. The SU(3) octet-singlet mixing angle for the baryons calculated from the partial widths for the s-wave σ(1385)π decay of the Λ(1520) and Λ(1690) is found to be consistent with that obtained from the d-wave decays of the singlet and octet members, within experimental limits. 相似文献
Results are presented for p → (ΛK+) dissociation in the reactions K?p → ΛK+K? and and π±p → ΛK+π±at 10 and 16 GeV/c. The cross sections for the low-mass ΛK+ enhancement are compatible with the energy dependence σ ∝ plab?0.3. The t′ spectra or the (ΛK+) threshold enhancement are exponential in shape. Its decay angular distribution reveals neither s-channel nor t-channel helicity conservation. The relative probabilities of the processes dissociation are in the ratios 100 : 10 : 0.2, independent of the nature of the incident particle. 相似文献
We observe a threshold ΛK+ enhancement in the reaction π+p → ΛK+π+ at 10.3 GeV/c. The production characteristics are very similar to those of the diffractive ΛK+ enhancement observed at the CERN ISR. The ΣKπ channels show no similar (ΣK)+ enhancement, as predicted by SU(6). 相似文献
The reactions (1) K?p → K+K?Λ and (2) have been studied on samples of 109 and 64 events, respectively, at 10 GeV/c and 125 and 69 events at 16 GeV/c, reasonably free from contaminations. The investigation of the first reaction uses also 84 events of the final state at 10 GeV/c. Analysis of the Van Hove plots indicates that the K+K?Λ and final states are produced by two main mechanisms: (i) a ΔQ = 0 process, with a strong diffractive component near threshold, involving the dissociations p → K+Λ in reaction (1) and in reaction (2) and (ii) a ΔQ = 1 process involving hypercharge exchange, and producing K+K? and systems in reactions (1) and (2), respectively, recoiling off the Λ. With increasing energy, this hypercharge exchange process decreases slowly when K+K? is produced, but fast where the production of , violating the Zweig rule, occurs. 相似文献
Lambda production is studied in K?p interactions at 32 GeV/c. The total Λ cross section is 2.31±0.03 mb. Using the measured Λγ combinations we find that (31±4)% of all Λ's are produced via the Σ0→Λγ decay. About 60% of the Λ's are associated with either a pair; about 40% of the Λ's are produced through the hypercharge annihiltion reaction K?p→Λ+π'a. The two-peak structure of the invariant x distribution can be related to fragmentation processes. The Λ is found to be unpolarized in the target fragmentation region, whereas a transverse polarization is observed for forward produced Λ's. As a function of p⊥, a polarization effect is measured at medium p⊥. 相似文献
Cross sections for various channels in 3 prong + V0 final states of K?n interactions are obtained at 8.25 GeV/c. An energy dependence study of the quasi two-body reactions Σ?(1385) + vector meson and ΛB? seem to imply the presence of cuts in the Regge exchange formalism, whereas the reaction Δ(1236) 1 (890) does not require such cuts. Upper limits of 1 and 2 μb are found for the reactions K?n → ΛA1 and K?n → ΛA2. 相似文献
Λp interactions have been studied at momenta up to 24 GeV/c using a new bubble chamber technique. We find that the Λp elastic cross section has fallen to approximately 6 mb at the highest momentum. Results are presented on Λp→Λpπ+π? for the first time above 5 . 相似文献
We have performed an energy-independent phase-shift analysis of πN → KΣ by analyzing differential cross-section and polarization data for the reactions π+p → K+∑+ and at fifteen energies from threshold to 2137 MeV invariant mass. The single-energy solutions were linked by shortest-path methods with and without constraints implied by the Odorico zeros for the reaction π?p → K+Σ?. Similar to π?p → KΛ it has been found that both isostates are dominated below 1900 MeV by resonances in the spin waves. The F37 resonance couples to KΣ with √xπNxKΣ= 0.04. 相似文献
Three- and four-body final states with strange particles are studied in π+p and π?p interactions at 16 GeV/c. We present cross sections and investigate their energy dependence. Production mechanism, resonance production and quantum number transfer are discussed. Strong Y1(1385) production is found in the reaction π+p → ΛK+π+, while the corresponding π?p reaction is dominated by production of K1(890). In the channels, the K and are produced mainly at the same vertex, i.e. non-strangeness exchange ΔS = 0 is dominant (about 75% of the cases), whereas in the ΛKππ channels, the Λ and K are more frequently produced at opposite vertices, i.e. |ΔS| = 1 exchange is important (about 60% of the cases). Results on the polarization of the lambdas produced in the π+p reactions are given. 相似文献
In the presence of right-handed currents including , it is emphasized that the dominant parity-violating (-conserving) Hamiltonian for nonleptonic decays of charmed hadrons transforms like of SU(4), and leads to distinctive results especially in D+ → KSπ+, F+ → μ+νμ and D0 → K?e+νe, etc. 相似文献
The production of is measured in π+p reactions at 16 GeV/c. The total strange particle cross section is found to be 4.0 ± 0.3 mb, about 20% of the inelastic cross section. Cross sections for single strange particles and for strange particle pairs are determined, both inclusively and as functions of the charged multiplicity. Relative production rates for different strange particle combinations are compared with the prediction of the isospin statistical model. Inclusive spectra for single particles are studied and it is found the KS0 are produced mostly in the forward hemisphere, most probably by fragmentation of the incident pion into . The Λ are mostly backwards, probably deriving from fragmentation of the proton into ΛK pairs. The tend to be produced forwards, but evidence is found for central production. Distributions in rapidity of the Λ particles from π+p interactions are compared in terms of the factorisation hypothesis. Results are given on the Λ transversal polarisation. 相似文献
We have analysed about 85 000 fast Λ0 events, obtained in a fast proton triggered experiment performed at the CERN-Ω spectrometer at 9 and 12 GeV/c incident π? beam. Nearly 2500 Λ0K+π? events have been isolated. We find strong production of quasi-two-body processes and consistent with u-channel hyperon exchange. Results on Λ0 polarization, K10 decay parameters and differential cross sections are given for and final states. A comparison is made with the associated backward production seen in the four-prong reaction π?p→pK?K+π? obtained in the same experiment. 相似文献
A study of the inclusive and semi-inclusive Λ and production in K+p interactions at 32 GeV/c is presented. The inclusive cross sections for Λ and amount to 0.78 ± 0.05 and 0.42 ± 0.04 mb thus showing a remarkable growth between 16 and 32 GeV/c with a factor of 1.7 for Λ and 2.8 for . Target and beam fragmentation processes are found to be dominant for Λ and production respectively with the following lower limits for the corresponding cross sections: and . Although the early scaling conditions are fulfilled for the Λ production in the target fragmentation region, and production in the beam fragmentation region, scaling is not observed between 16 and 32 GeV/c in the x and pT2 Feynman variables. The Λ production is found to be very similar in the K+p inclusive reaction at 32 GeV/c and in the semi-inclusive reaction at the same energy. The pair production cross section increases significantly in K+p interactions from 16 to 32 GeV/c where it reaches the value . The cross sections for Λ or produced in association with an identified proton are also given and discussed. 相似文献
We present measurements from a spark chamber experiment of the differential cross-sections for p → π?π+, K?K+ at 20 momenta in the range 0.8–2.4 GeV/c (c.m. energy 2.02 to 2.57 GeV). The c.m. angular range was . There are about 2000π?π+ events and about 300 K?K+ events at each momentum. 相似文献
In a high statistics bubble chamber experiment on K?p interactions at 8.25 , the study of the reaction K?p → KKΛ provides evidence for an enhancement in the KK system with a mass of (1850 ± 10) MeV and a width of (80?30+40) MeV. Its possible identification with the missing isosinglet of the 3? nonet is discussed. A K1 decay mode is also observed. 相似文献
A partial-wave analysis of the (3π)0 system produced peripherally in the reaction K?p → π+π?π0Λ at 4.2 GeV/c is presented. The observation of the weak Λ decay allows a determination of all the transversity production amplitudes except for two phases. The production of known resonances having decay modes other than 3π is used to test the isobar model ansatz. Significant ω(783), φ(1020) and A2(1310) production is observed. The spin parity of the is established as 3?. No evidence for production of other resonances, such as axial vector-mesons, is found. 相似文献
Topological cross sections are presented for K+p, K?p and interations at 32 GeV/c and for π+p and π?p interactions at 50 GeV/c observed in the 4.5 m Mirabelle hydrogen bubble chamber at Serpukhov. Parameters characterizing the behaviour of the multiplicity distributions, namely 〈nc〉, D and f2 and the normalized moments are given. The dependence of these parameters on the energy and the nature of the beam particle is discussed. The multiplicity distributions obtained cannot be described by a single function in the KNO variables. 相似文献
The exclusive reaction pp→Λ°K+p has been studied at 0.1<?tpp<0.6 GeV2 and energies √s=45 GeV and 53 GeV at the CERN ISR. Diffractive excitation p→Λ°K+ occurs predominantly in the mass range M(Λ°K+)≈2.1 GeV and peaks at 1.7 GeV. The cross section for pp→Λ°K+p is 10±3μb for M(Λ°K+)<2.5 GeV, and the tpp dependence is exp (bt) with b=7.0±0.5 GeV?2. 相似文献
The production of a strange dibaryonic system called H+1 (M = 2.13 GeV/c2, S = ?1), has been studied with a missing mass spectrometer, at the CERN Proton Synchrotron, in the reaction K?d → π?H+1 and in the line-reversed reaction π+d → K+H+1 between 0.9 and 1.4 GeV/c.The reactions , ,have been studied in a missing mass spectrometer at CERN. The experiment (PS159) is well adapted to search for a signal in the missing mass X+ (B = 2, S = ?1) produced in the backward c.m.s. direction, between 2.0 and 2.3 GeV/c2. The two reactions have been analysed at three different beam settings: 1.4, 1.06 and 0.92 GeV/c for reaction (1) and 1.4, 1.2 and 1.06 GeV/c for reaction (2). 相似文献