Measurement of Tensor Analyzing Power Components of the γd→pnπ0 Reaction

Russian Physics Journal - The results of measurements of three tensor analyzing power components of the reaction of incoherent photoproduction of a π0-meson on a deuteron in the ranges of...     

Evidence for directp p interactions in the fragmentation channelp +α →p + pX at √s=88 GeV

We have investigated kinematical correlations between the outgoing beam proton and the proton emerging from the fragmentingα-particle inpα collisions at \(\sqrt {s_{p\alpha } } = 88GeV\) . Strong correlations are seen, indicating the dominance of quasi-elasticpp scattering in the fragmentation channelp+α→p+pX, for the ¦t¦ range 0.05–1.00 (GeV/c)². A Monte Carlo simulation of this process can explain the observed correlation spectra assuming an admixture of about 16% spectator protons.     

Investigation of the diffractive reaction p + N → [∑+ K 0] + N at the proton energy of E p =70 GeV and observation of the decay process X(2000) → ∑+ K 0

The diffractive reaction p + N → [∑⁺ K ⁰] + N induced by 70-GeV protons is investigated at the SPHINX facility. The measured mass spectrum of the ∑⁺ K ⁰ system originating from this reaction shows a resonance structure with a mass of M=1995±18 MeV and a width of Γ=90±32 MeV. The cross section for the formation of this structure is found to be σ=182±38 nb per target nucleon. These data comply well with the results that we obtained previously in studying the reaction p + N → [∑⁰ K ⁺] + N, where we observed the formation of the X(2000) → ∑⁰ K ⁺ state, a candidate for an exotic baryon with hidden strangeness. The measured ratio R of the two branching fractions, R = Br[X(2000) → ∑⁺ K ⁰]/Br[X(2000) → ∑⁰ K ⁺] = 1.91 ± 0.38, is consistent with the value of R=2 expected for an isospin-1/2 baryon.     

Scaling in the mean of the p+p→π0+X inclusive reaction data and the energy dependence of Feynman variable

We have studied the p+p⁰+X inclusive reaction data of Carey et al. in the framework of the scaling in the mean hypothesis first proposed by Dao et al. These data have been used to obtain the gamma ray spectrum in terms of the average value of the Feynman variablex, written as x.A comparison with the observed gamma ray spectrum at Mt. Chacaltaya by the Japanese and Brazilian Group gives the energy dependence of x at very high energy.     

Measurement of the single-spin asymmetry in the reaction π − d ↑ → π 0 X in the beam-fragmentation region at 40 GeV and p T of up to 2 GeV/c

The single-spin asymmetry A _N in the reaction π ^? + d _↑ → π ⁰ + X in the beam-fragmentation region at the energy of 40 GeV was investigated by using the PROZA setup installed at the U-70 accelerator of the Institute for High Energy Physics (IHEP, Protvino). It was measured to be A _N = (13.6 ± 2.6(stat.) ± 2.0(syst.))% in the intervals 0.7 < x _F < 1.0 and 1.0 < p _T < 1.8 GeV/c. The results agree with the asymmetry of π ⁰ mesons in the charge-exchange reaction π ^? + p _↑ → π ⁰ + n at the same values of the transverse momentum and beam energy. The asymmetry in the reaction K ^? + d _↑ → π ⁰ + X was simultaneously measured and found to be A _N = (11 ± 14)% for p _T > 1.2 GeV/c.     

Measurement of γp→K + Λ and γp→K + Σ 0 at photon energies up to 1.47 GeV

The reactions pK ⁺ and pK ^{+ 0} have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the ⁰ polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and ⁰ is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I     

Deuteron fragmentationd+p→p+p+n at 9 GeV/c

Gamma-ray energy correlations have been measured for several reactions leading to light-mass Hf isotopes with 160 ?A?166. The correlation spectra show ridge-valley structures up to high rotational frequencies from which a drop in J _c ⁽²⁾ is deduced at high frequencies. This drop suggests that a large portion of the angular momentum is generated by aligning particles. It may also be explained by the theoretically predicted triaxial states with large deformation.     

Measurement of the cross section for the e + e ? → ωπ0 → π0π0γ process in the energy range of 1.1–1.9 GeV

The cross section for the e ⁺ e ^? ?? ???⁰ ?? ??⁰??⁰?? process has been measured in the energy range of 1.1?C1.9 GeV. The measurement has been made with the Spherical Neutral Detector at the VEPP-2000 e ⁺ e ^? collider. The data in the energy range of 1.1?C1.4 GeV are in agreement with the earlier measurements with the SND and CMD-2 detectors. The cross section has also been measured above 1.4 GeV.     

Investigation of charged-hadron production in proton–nucleus interactions at the energy of 50 GeV

Cross sections for the production of high-transverse-momentum charged hadrons in proton–nucleus interactions at the incident-proton energy of 50 GeV were measured with the aid of the FODS double-arm spectrometer. Single hadrons (charged pions and protons) emitted at a c.m. angle of about 90° and high-effective-mass pairs of hadrons flying apart at a c.m. angle of 180° were detected simultaneously. Results on the production of single hadrons are presented.     

Measurement of the yields of positively charged particles at an angle of 35° in proton interactions with nuclear targets at an energy of 50 GeV

Momentum spectra of cumulative particles in the region of high transverse momenta (P _T ) in pA → h ⁺ + X reactions were obtained for the first time. The experiment in which this was done was performed at the SPIN setup (Institute for High Energy Physics, Protvino) in a beam of 50-GeV protons interacting with C, Al, Cu, and W nuclei. Positively charged particles were detected at a laboratory angle of 35° and in the transverse-momentum range between 0.6 and 3.7 GeV/c. A strong dependence of the particle-production cross section on the atomic number was observed. A comparison with the results of calculations based on the HIJING and UrQMD models was performed in the subcumulative region.     

Study of the mechanism of the 3He + p → p + p + d reaction at a 3He momentum of 5 GeV/c

The mechanism of the reaction ³He + p → p + p + d is studied by making use of the ITEP 80 cm liquid-hydrogen bubble chamber exposed to a beam of 5 GeV/c ³He nuclei. The reaction cross section is equal to 20.6 ± 0.3 mb. The phase-space regions associated with quasifree scattering (QFS) and final-state interactions (FSI) are selected. Angular, mass and momentum distributions of the reaction products are obtained in the entire kinematically allowed range. The experimental data in the QFS region are compared with theoretical calculations based on the simplest pole-diagram approximation. The ³He and deuteron wave functions (WF) correspond to the realistic RSC potential. The D-wave components of these WF are taken into account. The absolute value of the cross section and shape of the distributions are described as a whole reasonably well within the frame of the model considered in the kinematical region where FSI may be neglected. But at large spectator momenta there is an essential disagreement. The possible reasons for this are discussed.     

The reaction e+e-→ωπ0 in the cm energy range from 1.0 to 1.4 GeV

The reaction e⁺e^-→ωπ⁰→π⁰π⁰γ has been studied with the Neutral Detector at the VEPP-2M collider. The cross section values differ from the predictions of the vector dominance model with one ϱ(770) meson, and are consistent with the contributions of ϱ(770) and ϱ(1600). ϱ(1250) has not been observed.     

A quark model of the meson fragmentation region in πp collisions

A model is explored in which the fragmentation region is populated by the hadronization of a string which stretches from a fast forward quark to a quark in the backward hemisphere of the p collision. This model is a part of more complicated models which have been studied elsewhere. It successfully fits observed inclusive production of ⁰-mesons, ⁰-mesons and -mesons, and agrees with the result that their production in p collisions is harder than in electron-position annihilation if: (a) the forward quark has an initial momentum which is at least 0·9 of that of the ⁰-mesons (b) gluon radiation is weaker than in electron-positron annihilation.     

Measurement of the reaction γp → K0Σat photon energies up to 2.6 GeV⋆

The reaction p K⁰⁺ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross-section and the polarization of the ⁺ as a function of the kaon production angle in the centre-of-mass system, cos^c.m._K, and the photon energy. The cross-section is lower and varies less with photon energy and kaon production angle than that of p K⁺⁰. The ⁺ is polarized predominantly at cos^c.m._K 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.     

Study of the process e+e-→π+π-π0π0 at energies √s< 1 GeV

In an experiment with the Spherical Neutral Detector at VEPP-2M collider the cross section of the process e+e-→π+π-π0π0 was measured. At energies √s < 920 MeV this cross section was measured for the first time. The energy dependence of the cross section is well discribed by the vector dominance model with contributions from ρ, ρ' ρ", mesons. The decay probability ρ→π+π-π0π0was found to be Bρ = (1.60±0.74±0.18)×10-5. The upper limit for the decay ω→π+π-π0π0 was improved by two orders of magnitude compared to the previous measurements and is Bω < 2 × 10-4 at 90% confidence level.