Dibaryon Resonances Research Articles

Cross section asymmetry ∑ for the reaction γd→dπ 0 in the energy range 0.5–0.9 GeV

The cross section asymmetry ∑ has been measured for the reaction γd→dπ 0 in the energy range of E γ =500–900 MeV and for pion CM angle 130°. The experimental data disagrees with the predictions of the impulse approximation. The account of the double scattering term, and the additional contribution of dibaryon resonances do not improve significantly the description of the data presented.

Measurement of t20 in pi +d elastic scattering.

Measurements of the tensor polarization t/sub 20/ in ..pi../sup +/d elastic scattering have been performed at theta/sub d//sup lab/ = 15/sup 0/ between T/sub ..pi../ = 116 and 145 MeV. Angular distributions at 133 and 140 MeV were also determined. These results resolve the discrepancy that has existed between the measurements made by other groups at SIN and at LAMPF, as our values are negative for all energies and angles investigated and consistent with the LAMPF data. Our results are also in good agreement with the corresponding measurements of analyzing powers. Lack of any significant oscillatory nature is in general agreement with theories at these kinematic regions and does not lend support to exotic effects such as dibaryon resonances.

Measurement of the cross section of the reaction pp ? pp ?0 in the region of dibaryon resonances

The energy dependence of the cross section of the neutral pion production is measured in the range 600÷900 MeV. No unambiguous evidences for the existence of broad isovector dibaryon resonances were obtained. The isoscalar cross section of the pion production does not reveal any structure, predicted by the theory with resonances.

Effects of six-quark bags on the1 D 2 NN partial wave and the question of dibaryon resonances

The coupled1D2(pp)−5S2 (ΔN) channels are studied in a relativized version of the Quark Compound Bag (QCB) model. The QCB short-range force is shown to reproduce an, energy dependence of the1D2 phase shift and inelasticity atT≳200MeV predicted by the energy-independent solution of the VPISU phase-shift analysis. At lower energy the effect of the long-range meson force is essential. The values of the QCB parameters found from the fit to the data are in good agreement with theoretical predictions for the MIT bag model.

Flavor-octet dibaryons in the quark model.

The possibility of flavor-SU(3)-octet dibaryon resonances is studied in the quark model. Because the color-magnetic gluon-exchange interaction is attractive for the flavor octets as well as the singlet, bound and/or resonance states are expected. The importance of two-baryon channel couplings and quark antisymmetrization is stressed for low-lying bound/resonance states. The dibaryon spectrum is studied by applying the quark cluster model to the J${=1}^{+}$ and ${2}^{+}$ six-quark states. Several J${=2}^{+}$ dibaryon resonances are predicted.

On fluctuations of cross sections of dibaryon resonances

An analysis of the distributions and energy correlation functions of the cross sections of production of dibaryon resonances shows that the peaks observed in effective-mass spectra of np- and pp-systems in the reactions np→pp π − and dp→ppn may be interpreted as fluctuations of the cross sections resulting from the overlap of a large number of dibaryon resonances.

Search for proton-proton dibaryon resonances in the dp → (pp)n reaction

The pp mass distribution in the dp → (pp)n reaction has been measured at the deuteron momentum from 1700 to 2280 MeV/ c. The results show no prominent peak which suggests the existence of dibaryon resonances in the mass range of 2000 to 2200 MeV/ c 2.

Recoil nucleon momentum distribution in hadron-nucleus collisions

A momentum distribution function of recoil nucleons in hadron-nucleus collisions is determined consistently in the framework of the multichain model. The resulting distribution depends on the parameter a characterising the leading cluster momentum distribution. The results for the multiplicity ratio show good agreement with experimental data without introducing other effects such as the dibaryon resonances.

Measurement of the spin correlation parameters All and Asl for the reaction pp-->d pi + in the energy region 500-800 MeV.

Angular distributions of the spin-correlation parameters A/sub s//sub l/ and A/sub l//sub l/ for the reaction pp..--> pi../sup +/d have been measured at pion center-of-mass angles 40/sup 0/less than or equal totheta/sub ..pi..//sub =//sup */less than or equal to130/sup 0/ at incident energies of 500, 650, and 800 MeV. Additional measurements of A/sub l//sub l/ were made at 600, 700, and 750 MeV. The results of the experiment are compared with the predictions of several unified coupled-channel calculations and partial-wave analyses. While the latest partial-wave analyses were found to fit the data reasonably well, all except one of the various model predictions not only do not fit the data well, but also tend to be in disagreement with each other. The data show no clear sign of a need for proposed dibaryon resonances.

Hyperon-nucleon interaction and the 2.13 GeV strange dibaryonic system in the P-matrix approach

A description is presented of the low-energy YN (Y = Λ,∑) interactions within the Jaffe-Low P -matrix formalism. Analysing the enhancement of the Λp invariant mass near the ∑ + n threshold we conclude that it should be identified as a P -matrix partner of the deuteron and not as a six-quark dibaryon resonance.

Strong energy dependence of the analysing power in the pp→d π+ reaction and the question of an isovector dibaryon resonance. II

Forward angular distributions of the analysing power for the pp→d π + reaction have been measured at six energies T p=1.2, 1.4, 1.6, 1.8, 2.0, 2.3 GeV. A strong energy dependence is observed for A y0 ( t=0) and A y0 ( θ CM π =90°). The data are compared with the backward angular distributions previously published and suggest the existence of a resonant state in the pp system at the approximate energy of 2.7 GeV.

Search for strange ( S = −1) dibaryons by means of the reaction pp → K +X

Recent Saturne experiment searching for strange dibaryon resonances between 2050 and 2170 MeV Is described. The reaction pp → K +X was studied with protons of Incident energy T = 2.3 GeV on a liquid hydrogen target detecting the kaons in the SPES IV spectrometer from 1.1 to 1.4 GeV/c. The detection system Including Cerenkov counters as a online particle trigger with an efficient pion and proton rejection Is described. The results for e K = 8° and 10° are presented, showing a strong final state Interaction Λp close to threshold and a small structure at the ΣN thresholds. Preliminary calculations In the one meson exchange model with final state interaction are presented.

Search for dibaryon resonances in photo-deuteron reactions

The present status of non-strange dibaryon resonances including two new data contributed to this conference is briefly surveyed. A new γd experiment using a spectrometer, TAGX, with an acceptance of π sr at the 1.3 GeV Tokyo Electron Synchrotron (ES) is desribed. Discussions on the search for some structures in the E γ dependence of the γd→ π −pp reaction and γd→ π −X missing mass spectra are presented on the basis of a preliminary analysis of the experiment.

Multi-quark effects in high energy nucleon-nucleon and nucleus-nucleus collisions

Recent data obtained in two experiments performed in the framework of the Bucharest-Dubna collaboration are presented i.e.: the observation of narrow dibaryonic resonances in neutron-proton interactions in 1m HBC at different momenta of incident neutrons in the range 1–5 GeV/c, and the cumulative production of negative pions in nucleus-nucleus interactions in SKM-200 streamer chamber at 4.5 GeV/c. The interpretation of these results in terms of multiquark states is discussed.

Target asymmetry measurement in gamma d-->

The polarized target asymmetry T(\ensuremath{\theta}) for the reaction \ensuremath{\gamma}d\ensuremath{\rightarrow}pn has been measured at proton c.m. angles of 70\ifmmode^\circ\else\textdegree\fi{}, 100\ifmmode^\circ\else\textdegree\fi{}, and 130\ifmmode^\circ\else\textdegree\fi{} in the photon energy region between 300 and 700 MeV. The observed asymmetry shows relatively small values. A phenomenological partial wave analysis is carried out by using the present T(\ensuremath{\theta}) data together with recent results on the differential cross section d\ensuremath{\sigma}/d\ensuremath{\Omega}, the recoil proton polarization P(\ensuremath{\theta}), and the polarized beam asymmetry \ensuremath{\Sigma}(\ensuremath{\theta}). The gross features of d\ensuremath{\sigma}/d\ensuremath{\Omega}, T(\ensuremath{\theta}), and \ensuremath{\Sigma}(\ensuremath{\theta}) are reproduced reasonably well without dibaryon resonances, but those of P(\ensuremath{\theta}) are not, even with arbitrary smooth backgrounds in the present scheme of analysis. Possible contributions of dibaryon resonances are studied.

The reactionpd ? ppn and the narrow dibaryon resonances

The effective mass spectra of two nucleons from the reactionpd →ppn were studied at four incident proton energies in the range 800–1000 MeV, one of nucleons being backward emitted. After selecting the events either with large nucleon momenta or with large opening angles between the nucleons several narrow peaks are observed in the effective mass spectra (M=1.95, 2.03, 2.08 and 2.14 GeV/c2) which can be considered as probable dibaryon resonances.

Analysis of coherent pion photoproduction on the deuteron at large angles.

The differential cross section for $^{2}\mathrm{H}$(\ensuremath{\gamma}, ${\ensuremath{\pi}}^{0}$${)\mathrm{}}^{2}$H for photon energies from 500 to 800 MeV is calculated based on elementary processes. A comparison between calculated results and the experimental data at large angles demonstrates that double scattering becomes dominant in this region and that dibaryon resonances make no contribution to within the experimental accuracy.

Polarized pion-deuteron breakup in the region of the 3,3 resonance.

The vector analyzing power iT/sub 11/ for pion-deuteron breakup has been calculated at three different energies in the region of the 3,3 resonance and compared with recent data. The calculations have been performed using the relativistic Faddeev theory proposed by the author. The relationship of this theory to other formalisms is discussed, as well as the implications of our results to the question of the existence or nonexistence of dibaryon resonances.

Measurement of the cross section for γd → π0d at 140° ⩽ θCM ⩽ 156°

The differential cross sections for the reactions γd → π 0d have been measured for photons from 500 to 1000 MeV. We discuss the effect of the double scattering term and suggest no indication for the dibaryon resonances of the mass around 2.5 GeV.

Strange dibaryons

Dibaryons in the bag model of hadrons are briefly discussed. First results of the AGS experiment searching for 3P J strangeness −1 dibaryon resonance are described. New experiments aiming at observation of the H-particle (6 quark sudsud bag) are presented.