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.     

An extended quark recombination model with valence quark annihilation compared to inclusive π+/π− ratios

Valence quark annihilation with subsequent recombination is considered as the dominant nonscaling process contributing to lowp _⊥ pion production in the proton fragmentation region at medium energies. With the aid of a Kuti-Weisskopf model for quark distribution functions the inclusive ratios π⁺/π^? have been calculated and compared to data forHp→π^± +anything withH=π^±,K ^?, \(\bar p\) . Each of these beam particles carries valence antiquarks. The dependence of the ratios on the Feynman variablex and their energy dependence is well reproduced.     

Charged multiplicity distributions and neutral particle production in 14.75 GeV/c pp interactions

From an exposure of the Brookhaven National Laboratory 80-inch hydrogen bubble chamber to a 14.75 GeV/s separated anti-proton beam we have determined an average charged particle multiplicity of 4.12±0.06. We have also studied the inclusive production of γ, K_S^o, and Λ^o particles. The correlations between π^± and π^o, K_S^o, or Λ^o are described and the strong correlation observed between π^± and π^o is contrasted to the apparent lack of correlation found in other hadron-hadron interactions at similar beam momenta. Invariant cross sections for γ, K_S^o, and Λ^o production are presented as a function of x.     

Quark-antiquark recombination in the fragmentation region

Meson production at low transverse momentum in the fragmentation region (x>0.5) in pp collisions is considered in the context of the parton model. It is shown that the quark decay process is unimportant compared to the quark-antiquark recombination process. The calculated results of the model agree very well with the experimental data on the longitudinal momentum distributions of π^± and K^± in both the shapes and the normalizations.     

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.     

Experimental comparison of Jψ production by π±, K±, p and p̄ beams at 39.5 GeV/c

Measurements have been made of relative production cross sections of the $\text{J}\text{ψ}$ by π^±, K^±, p and p? at 39.5 GeV/c incident on copper. $\text{J}\text{ψ}$ production rates from π^?, K^? and p? are similar. The $\text{J}\text{ψ}$ relative particle/anti-particle production cross sections for x>0 are $\text{σ(π}{}^{\mathrm{+}}\text{)}\text{σ(π}{}^{\mathrm{?}}\text{)=(0.87±0.14)}$, σ(K⁺)/σ(K^?)=(0.85±0.5) and $\text{σ(}\text{p}\text{)}\text{σ(}\text{p}\text{?}\text{)=(0.15 ±0.08)}$. The small p/p? cross section ratio disagrees with models of J/ψ production by gluon amalgamation.     

Single-spin asymmetry for charged hadrons produced in proton-nucleus collisions at 40 GeV for c.m. production angles in the range 40°–79°

The transverse single-spin asymmetry for charged hadrons (π ^±, K ^±, p, $\bar p$ ) produced in proton-nucleus collisions was measured for c.m. production angles in the range 40°–79°. The measurements were performed with the FODS-2 setup by using a 40-GeV polarized proton beam originating from the accelerator of the Institute for High Energy Physics (Protvino) and hitting carbon and copper nuclear targets. The data in question were obtained in the polarized-proton-fragmentation region (0.0 < x _F < 0.7, 0.6 < p T < 2.5 GeV/c). In agreement with data obtained at other energies, the single-spin asymmetry for π ^± mesons is significant at high x _F. For the first time, a sizable analyzing power, which changes sign at x _F = 0.43, is observed for protons. The dependence of the analyzing power on the target-nucleus mass is insignificant.     

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.     

Inclusive single-particle distributions in π±p reactions at 8 and 16 GeV/c

Invariant single-particle cross sections for pion and proton production in π^±p interactions at 8 and 16 GeV/c are presented in terms of integrated distributions as functions of x, reduced rapidity ζ and p_⊥², and also in terms of double differential cross sections E d²σ/(dx dp_⊥²) and dζ dp_⊥²). A comparison of π^± and π^? induced reactions is made and the energy dependence is discussed. It is shown that the single-particle structure function cannot be factorized in its dependece on transverse and longitudinal momentum. For the beam-unlike pion, there is an indication for factorizability in terms of rapidity and transverse momentum in a small central region.     

Observation of diffraction excitation in pp → (pπ+π−)+X at the CERN-ISR and tests of limiting fragmentation

In a single-arm magnetic spectrometer experiment at the CERN Intersecting Storage Rings (ISR), a prominent diffractive enhancement is observed for inclusive production of (pπ⁺π^?) systems near x ～ 1 at √s = 53 and 35 GeV. In testing limiting fragmentation and scaling for this system, inclusive pπ⁺π^? diffractive excitation into a fixed invariant mass range is found to possess a cross-section independent of s to within (3 ± 5)%. The main component in the (pπ⁺π^?) system is Δ(1236)π, with a charge structure compatible with the break-up of an isotopic spin $\text{1}\text{2}$ system.     

Observation of πK-atoms with DIRAC-II

We present evidence for the first observation of electromagnetically bound π ^± K ^???-pairs (πK-atoms) with the DIRAC-II experiment at the CERN-PS. The πK-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the dissociated π ^± and K ^???-mesons analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173±54 πK-atoms. The mean life of πK-atoms is related to the s-wave πK-scattering lengths. From these first data we derive a lower limit for the mean life of 1.5 fs at 84% confidence level.     

Hadron production at transverse momenta from 0.5 up to 2.2 GeV/c in proton-proton collisions at 70 GeV

The cross sections for π^±, K^±, p, and $\text{p}$ production in pp collisions have been measured at transverse momenta from 0.48 up to 2.21 GeV/c at 70 GeV. The data are compared with results obtained at lower and higher proton energies and also with the quantum chromodynamics parton model (QPM) calculations. Common behaviour of the cross sections of the form $\text{g(p}{}_{\mathrm{\perp }}\text{)?(x}{}_{\mathrm{\perp }}\text{)}$ in the energy range above 200 GeV does not take place at lower energies. Qualitatively QPM fits the data and the best agreement is for π⁺/π^? and K⁺/π⁺ ratios.     

Experimental results on J/ψ production by π±, K±, p and p incident on hydrogen at 39.5 GeV/c

J/ψ production at 40 GeV/c by π^±, K^±, p and $\text{p}$ incident on hydrogen has been studied and results compared with those obtained on tungsten in the same experiment. On hydrogen, J/ψ cross-section ratios relative to π^? have been measured to be (for $\text{x}{}_{\mathrm{<mtext>F</mtext>}}\text{> 0) σ(π}{}^{\mathrm{?}}\text{) : σ(π}{}^{\mathrm{+}}\text{) : σ(}\text{p}\text{) : σ(}\text{p}\text{) = 1 : (0.78 ± 0.09) : (0.83 ± 0.35) : (0.07 ± 0.04)}$. The suppression of the proton induced cross sections shows the importance of calence quark-antiquark fusiin J/ψ production at this energy (i.e. M_J²/_ψ/s=0.13).     

Inclusive reactions: A new parametrization

We have fitted the π^? spectra from the reactions π^±p → π^?+ anything using an expression which exhibits the differing forward-backward slopes of the x-distributions, the turnover near (but not exactly at) x = 0 and the correlations between P₁ and p²_T. The expression is a generalized Bose-Einstein distribution which is covariant with respect to Lorentz transformation along the incident beam direction.     

Evidence for Λc+ in inclusive pp → (Λ0π+π+π−) + X and pp → (K−π+p) + X at √s = 53 and 62 GeV

A search for the charmed baryon, Λ_c⁺, has been carried out in inclusively, measured Λ⁰π^±π⁺π^? and K^?π^±p final states with longitudinal x > 0.75 in an experiment at the CERN intersecting storage rings. An effect with invariant mass near 2.3 GeV is observed in Λ⁰π⁺π⁺π^? with cross section times branching ratio Bσ = (2.8±1.0) μb; similar effect is observed in K^?π⁺p with Bσ = (2.3 ± 0.3) μb. The effect is seen only in the positive charge state, in agreement with an interpretation as Λ_c⁺. However, it is pointed out that in the same experiment, the non-charmed hyperon state Σ(1385)⁺ also has a cross section much larger than its corresponding negative charge state Σ(1385)^?.     

Photoproduction of charmed F mesons at γ energies of 20–70 GeV

Evidence is presented for inclusive photoproduction of F^± mesons in three decay modes, ηπ^±, ηπ^±π⁺π^? and ηπ^±π⁺π⁺π^?π^?. The average mass of the F^± is found to be 2.020±0.010 GeV.     

Inclusive φ-meson production in 93 and 63 GeV hadron interactions

The inclusive reactions h+p→φ+X, (h=π^±,,K^±,p^±), are studied for 0?x_F?0.3 and p⊥ ? 1 GeV at 93 and and 63 GeV incident momentum. Differential cross sections dσ/dp_⊥² anddσ/dx_F are presented and are compared with predictions of the naive parton model.     

Study of the reaction ¯pd→p s π+2π−π0 at 5.5 GeV/c incident momentum

A study of a 150000-picture exposure of ¯pd at 5.5 GeV/c yielded 152 events satisfying the hypothesis ¯pd→p _s π⁺2π^?π⁰. For the events with proton spectator in the momentum range 100–280 MeV/c we obtained the cross section of 0.11±0.02 mb. Assuming the validity of the impulse approximation we estimate a cross section of 0.43±0.06 mb for the reaction ¯pn→ π⁺2π^?π⁰. The rate for single ? meson production and an upper limit for double ? production are given. A modified multiperipheral Regge model was used in order to describe the general features of the data.     

Absorption of stopped π− in 59Co, 75As, 197Au and 209Bi investigated by in-beam and activation γ-ray spectroscopy

In-beam pionic X-ray and γ-ray spectra and activation γ-ray spectra following π^? absorption at rest in ⁵⁹Co, ⁷⁵As, ¹⁹⁷Au and ²⁰⁹Bi have been measured. The isotopic yield distributions and thus the (π^?, xnγp) reaction yields were determined. The mean numbers of emitted neutrons and protons are, respectively, 4.5 ± 0.2 and 1.48 ± 0.16 for ⁵⁹Co, 5.1 ± 0.3 and 1.02 ± 0.14 for ⁷⁵As, 6.6 ± 0.4 and 0.32 ± 0.14 for ¹⁹⁷Au, and 6.8 ± 0.4 and 0.37 ± 0.16 for ²⁰⁹Bi. The experimental results are compared with a pre-equilibrium exciton model calculation and proton-induced spallation reactions. High spin states in the residual nuclei were observed. For pionic X-rays absolute intensities of various transitions are given.     

Spectroscopy of 7Li in stopped pion absorption reactions

The structure of excited levels in the ⁷Li isotope is studied via inclusive and correlation measurements in the stopped π^? meson absorption reactions ¹⁰B(π^?, t)X and ¹²C(π^?, dt)X, respectively. The experiment is conducted using a low-energy pion beam at the LAMPF meson factory. Analysis of the missing mass spectra reveals ⁷Li states with the resonance parameters (E _x , Γ) (4.7, 0.1), (6.6, 0.9), (7.3, 0.1), (9.1, 2.8), and (9.6, 0.4) MeV. A highly excited state with E _x ≈ 11.2 MeV (i.e., an isobar analog of ⁷He) is observed in the ¹⁰B(π^?,t)X reaction. An excited state with E _x = 10.3 ± 0.1 MeV and γ = 1.8 ± 0.4 Mev is observed for the first time in the ¹²C(π^?,dt)X reaction.