Diffraction dissociation of neutrons in the reaction dp → pppπ− at 25 GeV/c

We observe the reaction dp → p_spec (pπ^?)p in a bubble chamber exposure at 25 GeV/c incident deuteron momentum. The (pπ^?) system with invariant mass below 2.0 GeV is interpreted as neutron diffraction dissociation. The (pπ^?) mass spectra show little if any direct evidence of N¹ production. The decay angular distributions and the momentum transfer distributions of the (pπ^?) system suggest a smooth increase in contributions from higher partial waves $\text{(J ?}\text{3}\text{2}\text{)}$ with increased mass or momentum transfer. A simple partial-wave analysis shows a P₁₁ contribution below 1.3 GeV for small ?t′ and a dominant D₁₃ contribution elsewhere. Both the P₁₁ and D₁₃ amplitudes peak far below the N¹(1470) and N¹(1520) resonances. We also find evidence for the charge-exchange reaction np → p(pπ^?). In this process the (pπ^?) system shows evidence for Δ^o(1236) and N¹(1520) production.     

Multiquark clusters in nuclei. distributions ofu- andd-quarks

Effects related to the possible admixture of multiquark (mainly 12q) clusters (bags) in nuclei are discussed. In particular the differencies in theu- andd-quark distributions inN≠Znuclei are considered. The quark distribution function is assumed to consist of two components: the nucleon component and the bag one (mainly the 12q-bag). The yields ofπ-mesons and nucleons into the backward hemisphere are governed mainly by the contribution of the bag component. It comes from the available data on theπ ⁺/π ^? andn/p ratios that thed-quarks in the bag component of nuclei withN>Z are “more soft” than theu-quarks in contrast to the situation in the nucleon component. The manifestation of the latter effect in theA-dependence of the ratio of structure functionsR=F _2A(x)/F _2D(x) is also discussed.     

Impact parameter analysis of the reaction π−p→pπ+π−π− at 9 and 12 GeV/c with very fast secondary proton

The results on the impact parameter for the reactions π^?p→pπ⁺π^?π^?, pK⁺K^?π^?, with a fast secondary forward proton are given at 9 and 12 GeV/c. For the reaction π^?p→pπ⁺π^?π^? our results corresponding to the small |u| region (|u| < 1 GeV²) are compared to the existing data for the small |t| region. We show that small |u| events are more central than small |t| events.     

Higher-twist effects in deep-inelastic scattering

Non-scaling, non-factorizing 1/Q² contributions to cross sections are derived for semi-inclusive deep-inelastic scattering, ?N → ?′πX. These higher twist terms are dominant at large z = p_π · p_N/Q · p_N. They provide unusual (1 ? y) terms in the cross section. as well as asymmetries in the azimuthal angle dependence. Calculations are also presented for the quark to pion fragmentation function D_π(z, Q²).     

Production and loss of N2 + ions during the decay period of plasmas produced in helium-nitrogen mixtures

The time dependence of the number density of N₂ ⁺ ions during the decay period of plasmas produced in helium containing 0.05, 0.17 and 0.5 percent nitrogen was studied in the pressure range from about 0.3 to 7 Torr by means of mass spectrometer techniques. During the early part of the afterglow period the time dependence of N₂ ⁺ is controlled by ambipolar diffusion loss towards the plasma container walls. The product of the ambipolar diffusion coefficientD _a and the reduced pressurep ₀ wasD _ap₀=900± 50 cm² Torr/sec. The production of N₂ ⁺ by collisions between metastable nitrogen molecules determines the temporal behavior of the N₂ ⁺ density during the late afterglow for extremely pure discharge conditions. From the data it follows that the metastable molecules involved are de-excited by collisions with ground state helium atoms with a rate constant of 3.4 × 10^?15 cm³ sec^?1, while the radiative lifetime of these metastable molecules is at least 20 msec. The surface catalytic efficiency for de-excitation upon striking the molybdenum covered plasma container walls was estimated to be smaller than 10^?3. Energy and radiative lifetime requirements suggest that N₂ ⁺ is produced during the plasma decay period by the process N₂ (a′¹ Σ _u ^? )+N₂ (a′¹σ _u ^? →N₂ ⁺ (X²Σ _u ⁺ )+N₂(X)+e.     

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.     

Study of the centrally produced ωρ0 and ωω systems inpp interactions at 300 GeV/c

We have performed a search for vector-vector final states centrally produced in proton proton interactions at 300 GeV/c using the CERN Ω spectrometer. Evidence is found for ωρ⁰ production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s and for ωω production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s . However no evidence is found for ωø production in the reactionpp→p _f (K ⁺ K ^?π⁺π^?π⁰)p _s .     

Line reversal in baryon exchange reactions and the energy dependence of dip locations

An empirical investigation of $\text{p}\text{p}\text{→ππ}\text{and}\text{π}\text{p}\text{→π}\text{p}$ data provides evidence for a dynamical variable connected with the boundary of the physical region. Absence of a fixed u = ?0.2 dip in recent $\text{p}\text{p}\text{→π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$ high-energy data disagrees with nucleon-exchange (N) line-reversal expectations from π⁺p→pπ⁺ backward scattering. We notice however that the π⁺p→pπ⁺ dip is not located at fixed u but remains with a surprising accuracy at a fixed distance u' = u ? u_min from the physical boundary. Conjecturing that dips associated with particle exchanges occur at fixed u', we predict that the N-exchange dip in $\text{p}\text{p}\text{→π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$ will be considerably displaced at non-asymptotic energies. Our conjecture places the fixed u' = ?0.2 dip near $\text{u ? ?0.4}\text{in}\text{p}\text{p}\text{→π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$ for momenta around 2 GeV/c. Folded $\text{p}\text{p}\text{→ ππ}$ distributions exhibit a dip structure at this location. These observations suggest that the failure of line reversal at low energies is due to direct-channel effects, since fixed u' dips occur naturally in geometrical and direct-channel models.     

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.     

Backward production of the B meson in K−p interactions at 4.2 GeVc

The backward production of the B(1235) meson is studied in the reaction K^?p→Σ^?π⁺ω. This reaction is observed in the final state Σ^?π⁺π⁺π^?π⁰. A π⁺ω mass enhancement is visible in the region of the B meson for events with small |u|K^? →Σ^?) squared four-momentum transfer. The properties of the enhancement agree with those of the B meson. The cross section for K^?p→Σ^?B⁺ at $\text{4.15}\text{GeV}\text{c}$ incident K^? momentum is (3.2 ± 0.5) μb. The backward production of the B meson is compared with similar baryon exchange productions of the A₁ and C(Q₁) axial vector mesons observed in the same experiment.     

The reactions π±p→pπ±π+π− at 18.5 GeV/c

Studies have been made of the reactions π⁺p→pπ⁺π⁺π^? and π^?p→pπ⁺π^?π^?, both at an incident pion momentum of 18.5 GeV/c. The two-body (primarily Δ⁺⁺ and ?^o and three-body (low-mass A enhancement, A₃, N¹ (1400), and N¹ (1700)) subsystems are discussed. Cross sections for all significant channels of the reactions are given.     

Study of longitudinal distributions in the fragmentation regions,using the quark-parton model,in K−p interactions at 70 GeV/c

The study of π^±, π⁰, K⁰ and Λ production in the fragmentation regions (|x|0.2) of K^?p interactions at 70 GeV/c shows that the x-dependence of each invariant cross section is well described by the power law (1?|x|)ⁿ suggested by the dimensional counting rule. Furthermore, pion production is found, both in K^? and proton fragmentation regions, to be very similar to their production in $\text{ν(}\text{ν}\text{)}\text{p}$ interactions as expected from quark-parton models. The quark and diquark fragmentation functions D_u^π, D_uu^π and D_ud^π are extracted from our data.     

Production of exotic Λ hypernuclei via mesonic beams

We study the production of neutron-rich hypernuclei _Λ ¹² Be, _Λ ¹⁶ C, and _Λ ¹⁰ Li by the (π^?, K⁺) and (K^?, π⁺) reactions in flight and treat two different mechanisms of production. The first mechanism is a two-step process with meson charge exchange (e.g., π^?p → π⁰n, π⁰p → K⁺Λ). The other mechanism is one-step production (π^?p → K⁺Σ^?) proceeding via a small Σ^? component, arising in Λ hypernuclei due to ΛN–ΣN coupling, as a doorway state. Typically, the two-step mechanism is more productive. The forward differential cross section of the ¹⁰B(π^?,K⁺) reaction is about 70 nb/sr at an incident momentum of 1.05 GeV/c. On the other hand, the one-step process can serve as a direct measurement of the Σ admixture if the two-step contribution is suppressed by a suitable choice of the reaction kinematics.     

Production properties ofD 0,D +,D *+ andD s + in 230 GeV/cπ − andK −-Cu interactions

We have studied the hadronic production of charmed mesons in the NA 32 experiment at CERN. A special trigger together with a high resolution vertex detector consisting of charge coupled devices and silicon microstrip detectors allowed the selection of very clean samples of charmed mesons. We have collected 852 fully reconstructed decays: 60D _s ⁺ →K ⁺ K ^?π⁺, 543D°→K ^?π⁺ andK ^?π⁺π^?π⁺ as well as 249D ⁺→K ^?π⁺π⁺ (or charge conjugate). 147 mesons out of our \({{D^0 } \mathord{\left/ {\vphantom {{D^0 } {\bar D^0 }}} \right. \kern-0em} {\bar D^0 }}\) sample were produced via chargedD ^* state. For all charmed mesons we determine the total production cross-section and study thex _F andp _t ² distributions.     

Large-pT direct photon production and opposite-side photon-hadron correlations in QCD

Direct photon production in p-p, π-p and $\text{p}\text{-}\text{p}$ collisions at large transverse momenta (p_T) is studied in QCD and compared with existing data. Apart from the quark-gluon and quark-antiquark contributions, corrections due to bremsstrahlung of photons (q+q→q+q+γ) and to partons' intrinsic transverse momenta are taken into account. It is shown that p+p→γ+X provides one of the best determinations of the gluon distribution in the proton. Hadron production with an opposite-side large-p_T photon trigger is also studied. It is shown that the difference between the momentum sharing (x_e) distributions of π^?+p→γ+π^±+X and π⁺+p →γ+π^±+X (or of $\text{p}\text{+}\text{p}\text{→γ+π}{}^{\mathrm{\pm }}\text{+}\text{X}$ and p+p→γ+π^±+X) provides a good determinati on of the gluon fragmentation to a pion.     

Pair production of pions with symmetric momenta in the range 0.5⩽pT⩽2.0 GeV/c In 70 GeV p-p collisions

The invariant cross-section slope of the pp→π⁺π^?+X process as a function of p_T is found to have a break near 1 GeV/c. Fitting the cross section by a sum of two exponents gives the values of powers (12.3±0.9)(GeV/c)^?1 and (8.7±0.6)(GeV/c)^?1. The experimental points at p_T?1 GeV/c are significantly higher than predictions based on hard scattering models such as QCD and CIM.     

A study of the centrally produced π+π−π0 system formed in the reactionpp→p f (π+π−π0)p s at 300 GeV/c

The reactionpp→p _f (π⁺π^?π⁰)p _s , where the π⁺π^?π⁰ system is centrally produced, has been studied at 300 GeV/c. The π⁺π^?π⁰ mass spectrum shows evidence for the η, ω anda ₂ (1320) as well as an enhancement in thea ₁ (1260) region. A Dalitz plot analysis of the π⁺π^?π⁰ system has been performed. Thea ₁ (1260) parameters coming from the fit of the 1⁺ S wave arem=1208±15 MeV and Γ=430±50 MeV. No evidence is found for theh ₁(1170) orh ₁(1380).     

A partial wave analysis of the (Kππ) system in the reaction π− p→(K +π−π0)Λ at 3.95 GeV/c

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.     

Probing the mesonic structure of the nucleon by means of exclusive quasielastic pion knockout in (e, e′π) reactions at high energies

By including the Z diagram in an analysis performed in the laboratory frame (instantaneous form of dynamics), the notion of quasielastic pion knockout by protons and electrons [(p, 2p) and (e, e′p) reactions treated in terms of the relevant pole diagrams] is generalized to the relativistic case where a meson is quasielastically knocked out of a nucleon by an electron having an energy of a few GeV. The concept of the wave function is introduced for the pion (and for other mesons), and its relation to the vertex constant G _πNN and the vertex function g _πNN(k ²) is indicated. The spectroscopic factor S _N ^B? is defined as the normalization of the wave function for the meson ?. It is shown by two methods that, under the kinematical conditions of quasielastic knockout that include the condition E _π?m _π (E _π is the energy of the knock-on pion) and the condition that the square Q ² of the virtual pion mass is large, the competing tree diagram is suppressed in relation to the pole diagram (this is not so in the case of pion photoproduction). From data of a p(e, e′π ⁺)n experiment involving longitudinal virtual photons γ _L ^* , the momentum distribution |Ψ _p ^nπ (k)|² of pions in the nucleon is extracted for the first time over the entire range of significant momenta k, and this result is used to determine the cutoff constant Λ_π and the value of S _p ^nπ ≈0.2. The momentum distribution of positive rho mesons in the soft section of the spectrum is determined from experimental data on the process p(e, e′π ⁺)n proceeding through the mechanism ρ ⁺+γ _T ^* → π ⁺ involving transverse photons. A way to determine the momentum distribution of omega mesons through data on the process p(e, e′π ⁰)p is indicated. Two forms of dynamics—instantaneous form and that of light-front dynamics (the latter does not involve the Z diagram)—are compared for the example where the calculations are performed for the spectroscopic factor S _N ^B? .     

Investigation of the double diffraction dissociation reaction pp → (pπ+π−) (pπ+π−) at 24 GeV/c

Data from a high-statistics bubble chamber experiment at 24 GeV/c are used to study the double diffraction dissociation reaction pp→(pπ⁺π^?) (pπ⁺π^?) where both protons of the initial state dissociate into pπ⁺π^? systems. Cross section, mass spectra and dσ/dt' distributions have been determined and are compared with the results found for the single diffraction dissociation reaction pp → p(pπ⁺π^?), which have been obtained from the same experiment. All our findings agree well with what is expected from the factorization hypothesis.