Dibaryon States Research Articles

Is there a Di-Ω State?**The project partly supported by the Foundation of the Heavy Ion Research Facility Laboratory, National Natural Science Foundation of China, and the Foundation of the Education Ministry of China

Resonating-group method has been applied to calculate the dibaryon state in the framework of the extended quark-delocalization color-screening model. The mass of the di-Ω is predicted to be about 45 MeV lower than the threshold. The effect of channel coupling due to the tensor force and sensitivity to meson exchange short-range cutoff radius, have also been studied.

Di-Ω in the extended quark delocalization, color screening model

The \ensuremath{\Omega}\ensuremath{\Omega} $(SIJ=\ensuremath{-}6,0,0)$ dibaryon state is studied with the extended quark-delocalization color-screening model including a \ensuremath{\pi}-meson exchange tail, which reproduces the properties of the deuteron quantitatively. We find the mass of the di-\ensuremath{\Omega} to be about 45 MeV lower than the \ensuremath{\Omega}-\ensuremath{\Omega} threshold. The effect of channel coupling due to the tensor force has been calculated and found to be small in this case. We have also studied the effect of other pseudoscalar meson exchanges and sensitivity to the short-range cutoff radius ${r}_{0}$ for the meson exchanges.

Exact wave functions of a four-body system

In this Letter the exact wave functions of a model four-quark system in SU (2) color are calculated for spinless but isospinor quarks in Schrödinger equation as an analogue to the actual six-quark problem in SU (3) color which arises naturally in the study of dibaryon states. This model four-quark problem is shown to be exactly soluble for the admissible states of isospin I =2 provided that the pairwise interactions between the quarks are supplemented by some four-body counter terms (interpreted as four-body forces). This model correctly simulates the color with orbital structure expected of the corresponding fermionic 4 N problem. Further the possible exact solutions such as these can prove to be useful as test cases for the study of the full q 6 problem in SU (3) color with spin-dependent forces.

Characteristic predictions of topological soliton models

The characteristic predictions of chiral soliton models - the Skyrme model and its extentions - are discussed. The chiral soliton models prediction of dibaryon states with masses below NN-pion threshold is in qualitative agreement with recent evidence for the existence of narrow dibaryons in reactions of inelastic proton scattering on deuterons and two-photon radiation in proton-proton scattering. The connection between isovector magnetic momentum operator and mixed tensor of inertia of multiskyrmion, as well as between isoscalar magnetic momentum and orbital tensor of inertia valid for skyrmions with any B-numbers allows to estimate the electromagnetic decay widths of some states of interest. Another kind of predictions are multibaryons with nontrivial flavour - strangeness, charm or bottom, which can be found, in particular, in high energy heavy ions collisions. It is shown that the large B multiskyrmions given by rational map ansaetze can be described reasonably well within the domain wall approximation, or as spherical bubble with energy and baryon number density concentrated at its boundary. A simple formula is obtained describing the masses of known RM multiskyrmions with good accuracy.

Electroproduction of kaons and light hypernuclei

A detailed investigation of the basic hyperon-nucleon interactions in nuclei is one of the aims of Experiment 91-016, approved with high priority at CEBAF, to study the electroproduction of kaons on targets of deuterium, {sup 3}He, and {sup 4}He. Inasmuch as both the electron and K{sup +} are particles that interact relatively weakly with nucleons, electroproduction of light hypernuclei provides a low-distortion method for investigating the fundamental interactions between nucleons, {Alpha}`s, and {Epsilon}`s in few-body systems. In particular, the (e,e`K{sup +}) reactions on cryogenic targets of D, {sup 3}He, and {sup 4}He will be studied at incident electron energies near 3 GeV with coincident detection of the emergent e and K{sup +} in the HMS and SOS magnetic spectrometers in Hall C. Construction of the He target, operating at {approximately}10 atm, {approximately}50 K and capable of dissipating {approximately}30 W, is expected to be complete prior to commencement of production runs in Hall C. The first data runs for E91-016, expected to begin late in FY 1995, will also be the basis for a doctoral thesis at Hampton University. In addition to providing new information on the phases of hyperon-nucleon interactions, measurements of cross sections for hypernuclear formation, and interference phenomena,more » the data may provide evidence for the presence of bound {Epsilon}`s and strange di-baryonic states that are the subject of considerable theoretical discussion.« less

Dibaryon systems in chiral [formula omitted] quark model

The possible candidates of S-wave dibaryons with various strange numbers are studied under the chiral SU(3) quark model. It is shown that there are three types of baryon–baryon bound states. The states of the first type are called deuteron-like states. If chiral fields can provide enough attraction between interacting baryons, these systems, such as [ΞΩ−Ξ∗Ω](1,1/2), [ΞΞ](0,1), [NΩ](2,1/2) would be weakly bound. The states of the second type such as [Σ∗Δ](0,5/2), [Σ∗Δ](3,1/2), [ΔΔ](0,3) and [ΔΔ](3,0) are named as ΔΔ-like states. Due to the highly symmetric character in orbital space, these systems could be relatively deeply bound, but the strong decay modes of composed baryons cause the widths of the states much broader. The states of the third type are entitled as ΩΩ-like states. Due to the same symmetry character shown in the systems of the second type and the only weak decay mode of composed baryons, for instance in [ΩΩ](0,0), or at most one strong decay mode of composed baryons, for example in [Ξ∗Ω](0,1/2), these states are deeply bound states with narrow widths. The states of latter two types are most interesting new dibaryon states and should be carefully investigated both theoretically and experimentally.

Can doubly strange dibaryon resonances be discovered at RHIC?

The baryon-baryon continuum invariant mass spectrum generated from relativistic nucleus + nucleus collision data may reveal the existence of doubly-strange dibaryons not stable against strong decay if they lie within a few MeV of threshold. Furthermore, since the dominant component of these states is a superposition of two color-octet clusters which can be produced intermediately in a color-deconfined quark-gluon plasma (QGP), an enhanced production of dibaryon resonances could be a signal of QGP formation. A total of eight, doubly-strange dibaryon states are considered for experimental search using the STAR detector (Solenoidal Tracker at RHIC) at the new Relativistic Heavy Ion Collider (RHIC). These states may decay to Lambda-Lambda and/or proton-Cascade-minus, depending on the resonance energy. STAR's large acceptance, precision tracking and vertex reconstruction capabilities, and large data volume capacity, make it an ideal instrument to use for such a search. Detector performance and analysis sensitivity are studied as a function of resonance production rate and width for one particular dibaryon which can directly strong decay to proton-Cascade-minus but not Lambda-Lambda. Results indicate that such resonances may be discovered using STAR if the resonance production rates are comparable to coalescence model predictions for dibaryon bound states.

Dibaryons with strangeness: their weak nonleptonic decay using SU(3) symmetry and how to find them in relativistic heavy-Ion collisions

Weak SU(3) symmetry is successfully applied to the weak hadronic decay amplitudes of octet hyperons. Weak nonmesonic and mesonic decays of various dibaryons with strangeness, their dominant decay modes, and lifetimes are calculated. Production estimates for the Brookhaven Relativistic Heavy Ion Collider are presented employing wave-function coalescence. Signals for detecting strange dibaryon states in heavy-ion collisions and revealing information about the unknown hyperon-hyperon interactions are outlined.

A study of six quark cluster states in chiral SU(3) quark model

The energies of the (0 S) 6 six quark cluster states are calculated in the chiral SU(3) quark model. The results show that some states with high strangeness have more attraction from the chiral SU(3) coupling, and this feature is interesting in discussing if there exists some new narrow width six quark states. Further, we did a RGM calculation to study some multi-strangeness dibaryon states. We found that ΩΩ dibaryon is a deeply bound state and ΞΩ dibaryon is slightly bound.

Search for the weak decay of a lightly bound H0 dibaryon

We present results of a search for a new form of hadronic matter, a six-quark, dibaryon state called the H0, a state predicted to exist in several theoretical models. Analyzing data collected by experiment E799-II at Fermilab, we searched for the decay H0-->Lambdappi(-) and found no candidate events. We place an upper limit on [B(H0-->Lambdappi(-))dsigma(H)/dOmega]/(dsigma(Xi)/dOmega) and, in the context of published models, exclude the region of lightly bound mass states just below the LambdaLambda mass threshold, 2.194<M(H)<2.231 GeV/c(2), with lifetimes from approximately 5x10(-10) sec to approximately 1x10(-3) sec.

Pion correlations and two-particle bound states

A method to investigate possible loosely bound dibaryon states is suggested. The momentum dependence of a two-pion correlation function is shown to depend on the (non)existence of a bound state.

Study of Dibaryon States Containing Three Different Types of Quarks

Previously we have shown, in a simple chromomagnetic model, that including heavy quarks in the dibaryon sector can lead to favorable configurations for stability against decay into two baryons. In this study we investigate a reduced set of favorable candidates that have emerged from our previous works. We use a non-relativistic quark model with quarks interacting through a QCD-inspired potential, which has been tested previously in meson and baryon spectroscopy. A variational procedure is performed using a great number of Gaussian functions containing all the possibilities for colour, isospin, and spin components.

SYSTEMATIC THEORETICAL SEARCH FOR DIBARYONS IN A RELATIVISTIC MODEL

A relativistic quark potential model is used to do a systematic search for quasi-stable dibaryon states in the u, d and s three-flavor world. Flavor symmetry breaking and channel coupling effects are included and an adiabatic method and fractional parentage expansion technique are used in the calculations. The relativistic model predicts dibaryon candidates completely consistent with the nonrelativistic model.

Can only flavor-nonsinglet H dibaryons be stable against strong decays?

Using the QCD sum-rule approach, we show that the flavor-nonsinglet H dibaryon states with J{sup {pi}}=1{sup +}, J{sup {pi}}=0{sup +}, I=1 (27 plet) are nearly degenerate with the J{sup {pi}}=0{sup +}, I=0 singlet H{sub 0} dibaryon, which has been predicted to be stable against strong decay, but has not been observed. Our calculation, which does not require an instanton correction, suggests that the H{sub 0} is slightly heavier than these flavor-nonsinglet H{close_quote}s over a wide range of the parameter space. If the singlet H{sub 0} mass lies above the {Lambda}{Lambda} threshold (2231 MeV), then the strong interaction breakup to {Lambda}{Lambda} would produce a very broad resonance in the {Lambda}{Lambda} invariant mass spectrum which would be very difficult to observe. On the other hand, if these flavor-nonsinglet J=0 and 1 H dibaryons are also above the {Lambda}{Lambda} threshold, but below the {Xi}{sup 0}n breakup threshold (2254 MeV), then because the direct, strong interaction decay to the {Lambda}{Lambda} channel is forbidden, these flavor-nonsinglet states might be more amenable to experimental observation. The present results allow a possible reconciliation between the reported observation of {Lambda}{Lambda} hypernuclei, which argue against a stable H{sub 0}, and the possible existence of H dibaryons in general. {copyright}more » {ital 1997} {ital The American Physical Society}« less

Constant-cutoff approach toSU(3)-symmetry breaking for strange dibaryon states

We suggest a quantum stabilization method for theSU(2)σ-model, based on the constant-cutoff limit of the cutoff quantization method developed by Balakrishnaet al., which avoids the difficulties with the usual soliton boundary conditions pointed out by Iwasaki and Ohyama. We investigate the baryon numberB = 1 sector of the model and show that after the collective coordinate quantization it admits a stable soliton solution which depends on a single dimensional arbitrary constant. We then show that the approach toSU(3)-symmetry breaking for strange dibaryon states proposed by Kopeliovichet al. can be simplified by omitting the Skyrme stabilizing term and using the constant-cutoff stabilization method. We derive the results for spectra of some strange and nonstrange dibaryon states and obtain the numerical results for the absolute masses of these states, in reasonable agreement with the values obtained, using the complete Skyrme model, by Kopeliovichet al.

Dibaryon states containing two different types of heavy quarks.

In a recent series of papers we have shown that including heavy quarks in the dibaryon sector can lead to configurations stable against decay into two baryons. In this study we extend our previous work by a study of all the physical ${\mathit{Q}}^{2}$${\mathit{q}}^{4}$ [Q denotes a heavy quark and q denotes a member of the SU(3${)}_{\mathit{F}}$ triplet representation] systems in a solvable chromomagnetic model. We propose a number of new heavy states which could be stable under strong interactions.

Probing nuclear properties beyond the mean field

Three experimental activities related to the question of short-range correlations (SRCs) in nuclei are reported. The shell-model occupancy of 3s protons in 208Pb has been determined by the CERES method to be (77 ± 9)%. The depletion exceeds that predicted from long-range correlations alone, but is weaker than predicted from some models accounting for SRCs. More direct evidence for SRCs is expected from (γ, 2 N ) experiments with 100 ≲ E γ ≤ 500 MeV performed at MAMI-B. As a very promising first result we are able to present 6Li(γ,pn) cross sections whose energy dependence for transitions from the 1p and 1s shells, respectively, differ remarkably. Finally, in studying pionic double-charge-exchange reactions which are known to depend on nucleon-nucleon correlations in nuclei, we discovered a candidate for a narrow πNN resonance called d′ with I( J P ) = 0(0 −) at 2.06 GeV. The various experiments persued in the hunt for this dibaryon state are described.

Orbitally excited hadrons

This review is devoted to the description of high-spin hadrons. A relativistic QCD-string model that reproduces the principal feature of the spectra of orbitally excited hadrons, namely, the linearity of Regge trajectories, is employed. Particular emphasis is placed on the inclusion of spin effects. For large orbital excitations, these effects appear as the spin-orbit interaction whose sign and magnitude are determined by confinement properties. Arguments are presented in support of the proposition that, for large orbital excitations, the spin-orbit interaction of quarks in the string model is largely due to the Thomas effect. The consequences of this hypothesis are analyzed phenomenologically, and the results are compared with experimental data. Specific predictions are obtained and await experimental verification. Orbital excitations of four-quark and dibaryon states are predicted.

New particle searches and exotic phenomena — part 2

In the second part of Session XVI papers on top quarks, light Higgs bosons, dibaryonic states, magnetic monopoles, neutron-antineutron oscillations and electric charge conservation have been presented; they are summarized in the following.

Instanton induced interaction and the strange dibaryons

We study the effective quark-quark interaction induced by the coupling of nonperturbative gauge field configurations, i.e., instantons. Three flavors of light quarks are included and, therefore, the coupling induces a three-body effective interaction. The effective interaction obtained is applied to the valence quark model in order to estimate its contribution. The spectrum of strange 6-quark systems, especially the H dibaryon state, is studied in detail. The three-body interaction is found strongly repulsive, and a quark cluster model calculation suggests that the strange dibaryon states can be totally eliminated.