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1.
We present a dynamical study ofK + production in proton-nucleus collisions from 1.2 to 2.5 GeV bombarding energy. The evolution of the proton-nucleus collision is described by a transport equation of the Boltzmann-Uehling-Uhlenbeck type. We incorporate all known sources forK + production and study their momentum and angular distributions, and the excitation function. We show that at lower energies (E b<1.5 GeV) theNΔ andNN* channels dominate the kaon yield for light systems. At higher bombarding energies the directNN channel accounts for almost the whole cross section.  相似文献   

2.
We report on measurements of the reactionepenπ+ in the region of theD 13(1520) andF 15(1688) resonances. At an invariant four-momentum transferq 2=0.3 (GeV/c)2 the outgoing pion was detected in the forward and backward directions. The values of the helicity-1/2-partial wave amplitudesA 2?(D 13(1520)) andA 3?(F 15(1688)) are determined from these measurements. A comparison of the results with single quark transition models is made.  相似文献   

3.
We have studied the inclusive production of strange meson and baryon resonances in 360 GeV/cpp interactions. Cross sections forK *+(892) andK *?(892) are estimated to be 4.42±0.62 mb and 2.54±0.47 mb respectively and those for +(1385) and ?(1385) are 0.67±0.11 mb and 0.26±0.07 mb respectively. Longitudinal and transverse momentum distributions forK *(892) and Σ(1385) are presented, as well as for their decay productsK 0 and Λ. An estimation is given on theK *(1430) and *(1915) productions.  相似文献   

4.
A simpleππ, $\bar K$ K, andρρ(ωω) fully coupled channel model is proposed to predict the isoscalarS-wave phase shifts and inelasticities forππ scattering in the 1.0 to 2.0 GeV region. TheS- matrix is required to exhibit poles corresponding to the established isoscalarJ π=0+ resonancesf 0(975),f 0(1400), andf 0(1710). A dominant feature of the experimentalππ inelasticity is the clear opening of the $\bar K$ K channel near 1 GeV, and the opening of another channel in the 1.4–1.5 GeV region. The success of our model in predicting this observed dramatic energy dependence indicates that the effect of multipion channels is adequately described by theππ coupling to the $\bar K$ K channel, theρρ(4π) andωω(6π) channels.  相似文献   

5.
Total and semi-inclusive cross sections, longitudinal and transverse momentum distributions and spin density matrix elements of theK *+(892) andK *0(892) produced in the inclusive reactionsK + pK *+(892)+X andK + pK *0(892)+X at 32 GeV/c are studied in detail. The inclusive spectra of theK *(892) and their decay products are compared with pion and neutral kaon production. TheK *+(892) andK *+(892) are dominantly produced by kaon fragmentation processes. The dependence of average transverse momentum <p T> vs.x for resonances has been investigated for the first time.  相似文献   

6.
The one pion exchange contribution to the differentialπ ? pπ ? cross-section is calculated assuming that theππω amplitude associated with one of the vertices is described by the Veneziano formula, and that only a trivial dependence of the latter on the mass of the exchanged pion needs to be taken into account. The remaining unknown overall constant is then fixed by considering the decayω→3π. A rough comparison with preliminary data from a 16 GeV/cπ ? p experiment shows that the one pion exchange model could possibly describe the reactionπ ? pπ ? forπω masses above 1.4 GeV.  相似文献   

7.
The reactions π+ p→π++π+π-π-)p andppp+π+π-π-)p, where the (π+ π+ π- π-) system is centrally produced have been studied at 85 GeV/c. The π+π+π-π- mass spectrum shows evidence for thef 1 (1285) meson with a mass of 1278±2 MeV and width 41±12 MeV which decays mainly through ρ0(770)π+π-. Thef 1(1285) is also observed in the ηπ+π- channel. There is no significant evidence for ηππ or 4π decay modes of thef 1(1420). The ρ0ρ0 production is found to be small. A Dalitz plot analysis of the 3π system shows evidence fora 2 (1320) production and for a large contribution of theJ PC=1++ ρπ wave.  相似文献   

8.
Data are presented on Pomeron-Pomeron interactions which produce a centralπ + π ? system in proton-proton collisions at \(\sqrt s = 62 GeV\) at the CERN Intersecting Storage Rings. This process may favor the production of gluonic bound states. A partial-wave analysis of theπ + π ? system shows evidence for the production of the statesf 0(975),f 0(1400), andf 2(1270). The fitted mass for thef 2(1270) is about 50 MeV below the world average. In addition, the production mechanism for thef 2(1270) is uniquely different from that for the other final states in that there is a correlation between the outgoing protons. this is consistent with a picture of two-gluon exchange with thef 2(1270) produced by gluon fusion, and could indicate that thef 2(1270) has a glueball component.  相似文献   

9.
An experiment performed at Fermilab used double-arm calorimeter triggers to study di-jet production by 400 GeV protons and 200 GeVπ ? mesons incident on liquid hydrogen. The observed ratio of positive to negative leading particles in the jets was compared forpp andπp production using a tree level parton scattering model. The results are moderately sensitive to the form of the pion gluon distribution function and yieldx g(x)?(1?x)2.75±0.40±0.75.  相似文献   

10.
The rest-frame of secondaries frompp collisions determined by the covariant Boltzmann factor is found to be independent of the massm of the secondary. In this frame, the hadron production behaves like bremsstrahlung:n(m)W * (m)/m 2,W * (m) being the available energy. This multiplicity law fitsp+pm+? at 400 GeV/c of NA 27 Collaboration without free-parameters. Extended top-nucleus and heavy-ion collisions, assuming a mean-free-path of collision between the incident and the target nucleon to be ~2.80 fm and 1.63 fm respectively, it accounts forn(K ?) and \(n(\bar \Lambda )\) of CERN-SPS experiments and theK ?? ratio of BNL experiments.  相似文献   

11.
A study of \(\bar np\) annihilations with \(\bar n\) momentum between 0.5 and 0.8 GeV/c is presented. The search fors-channel resonances in \(\bar np\) annihilations reveal possibly two narrow structures in the odd pions final state. Inclusiveρ 0 andf 0 cross sections in \(\bar np\) annihilations have been estimated to be 9.0±0.6 mb and 3.4±0.6 mb respectively. Longitudinal and transverse momentum distributions for inclusiveρ 0 production have been presented. A study of resonance production in exclusive final state revealsρ 0 production to be dominant in the odd pion final states andρ +,ω 0 productions are most important for the even pion final states. Theπ + π ? effective mass spectra in the backward and the forward directions in the \(\bar np\) c.m. system have been examined for a possible ?-ω interference effect.  相似文献   

12.
Results from a partial wave analysis of theKππ system produced in the hypercharge exchange reaction π? p→(K +π?π0)Λ at 3.95 GeV/c are presented. SignificantQ 1 production is observed but no evidence is found forQ 2 production thus confirming the results obtained in a previous decay Dalitz plot analysis of the same reaction. The relative phase behaviour of the 1+(K?) partial waves obtained with the present analysis provides additional confirmation of the resonance interpretation of theQ 1 enhancement. Information is also obtained about its production properties and the role played by the Λ polarization in the hypercharge exchange reaction. This is compared with the results obtained in the reactionK ? p→(π+π?π0)Λ at 4 GeV/c.  相似文献   

13.
In a study of the reactionK ? pK -π?π+ p at 10 and 16 GeV/c the one-pion-exchange model was tested by attempting to extract on this basis the angular distributions for π+ p elastic scattering and comparing to real π+ p scattering. In thes-channel frame high order moments already appeared at relatively low mass. In general there are large discrepancies in both thes- andt-channel frames which remain after extrapolation to the pion pole and are related toQ ? production. The structure of the decay angular distribution of theK ? K - π- system produced in association with Δ++ is dominated by proton diffractive dissociation into Δ++π-.  相似文献   

14.
Identified π±,K ±, p and -p transverse momentum spectra at mid-rapidity in √sNN = 130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleonsN part similarly for all particle species. The multiplicity densities scale faster thanN part. TheK ± andp ±yields per participant increase faster than the π± yields. We combine the PHENIX neutral and charged pion measurement and find that in central collisions forp T >-2 GeV/c,-p andp yields are comparable to or even exceed the pion yields.  相似文献   

15.
We investigate the production of e + e ? pairs from p + Be and nucleus-nucleus collisions from 2 GeV/A to 200 GeV/A within a covariant transport approach and focus on the dilepton angular anisotropies as a function of the dilepton invariant mass. Whereas the low mass regime yields information about the Dalitz decays of the Δ, η and ω, above M ≈ 0.5 GeV the angular anisotropies provide additional information about the π + π ?ρ 0e + e ? channel in the medium. The anisotropy coefficient is found to change its sign for M > 0.5 GeV in case of nucleus-nucleus reactions when increasing the bombarding energy from 2 GeV/A to 200 GeV/A which sheds some light on the ππρ dynamics.  相似文献   

16.
17.
The reactionppp f (ηπ+π?)p s where the ηπ+π? system is centrally produced has been studied at 300 GeV/c incident momentum at the CERN Ω spectrometer. The ηπ± mass spectrum shows a strong δ/a 0(980) signal having a mass of 984±4 and Γ=95±14 MeV. The ηπ+π? mass spectrum shows η′ andf 1(1285) signals over little background. A spin-parity analysis of the ηπ+π? system shows evidence for aJ PC =1++ peak at thef 1(1285) mass but no evidence for the pseudoscalar states η(1270) andl/η(1440). No evidence is found for the ηππ decay of theE/f 1(1420) meson for which we set an upper limit BR(E/f 1(1420)→ηππ)<0.1 at 95% cl.  相似文献   

18.
The reconstructed experimental transverse momentum (p t ) distributions of Δ0(1232) resonances produced in p 12C and d 12C collisions at 4.2 A GeV/c and the corresponding spectra calculated using Modified FRITIOF model were analyzed in the framework of Hagedorn Thermodynamic Model. The spectral temperatures of Δ0(1232) resonances were extracted from fitting their p t spectra with one-temperature Hagedorn function. The extracted spectral temperatures of Δ0(1232) were compared with the corresponding temperatures of π ? mesons in p 12C and d 12C collisions at 4.2 A GeV/c obtained similarly from fitting the p t spectra of π ? by one-temperature Hagedorn function. The spectral temperatures of Δ0(1232) resonances agreed within uncertainties with the corresponding temperatures of π ? mesons produced in p 12C and d 12C collisions at 4.2 A GeV/c.  相似文献   

19.
Data one + e ?η/π 0 γ collected by the Neutral Detector at Novosibirsk in a c.m. energy range up to 1.04 GeV have been studied with a purpose to single out of the scattering amplitude the triangle anomaly contribution predicted byqcd, pcac and Chiral Theories. We show that the cross section fore + e ?π 0 γ exhibits no sensitivity to theπ 0 triangle anomaly; instead, the cross section fore + e ?ηγ shows a clear sensitivity to the value of theη triangle anomaly and the best fit corresponds to a value for theη width in good correspondence with the world average value. It is also shown that the value of theρηγ branching fraction is noticeably influenced by the existence of the anomaly. Finally, we give for the first time the absolute value for the hadronic phases of the vector mesons for the decay modesηγ andπ 0 γ.  相似文献   

20.
The production ofK + mesons in proton-nucleus and deuteron-nucleus collisions is analyzed with respect to one-step nucleon-nucleon (NN → N ΛK +),Δ- nucleon (ΔN → N Λ K+) and two-step pion-nucleon (πN → K + Λ) production channels on the basis of experimental ground state momentum distributions and free on-shell production processes. Whereas forK + production in proton-nucleus reactions the secondary channelπN clearly dominates at subthreshold energies, meson and nucleon induced channels are of similar magnitude in deuteron-nucleus reactions. Contrary to nucleus-nucleus collisions theΔ induced reaction channels are found to be of minor importance. The experimental differentiation of the underlying microscopic reaction channels appears possible via differential proton —K + coincidence measurements as shown in detail by the microscopic simulations including proton rescattering.  相似文献   

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