Baryon-antibaryon System Research Articles

Possible Σc*Σ¯ molecular states

We investigate the possibility of deuteronlike Σc*Σ¯ bound states within the one-boson-exchange model and systematically analyze the effects of the contact range δ3(r→) potential, the tensor term from the vector-meson exchange, and nonlocal potentials due to the dependence on the sum of the initial and final state center-of-mass momenta. We find that the pion-exchange potential including the δ3(r→) term and the tensor term of the ρ-exchange potential exhibit comparable magnitudes but opposite signs for any S-wave baryon-antibaryon systems. For the Σc*Σ¯ system, it is most likely to form bound states with mass around 3.7 GeV in the I(JP)=0(2−) and 1(2−) channels. Published by the American Physical Society 2024

Deuteron-like states composed of two doubly charmed baryons

We present a systematic investigation of the possible molecular states composed of a pair of doubly charmed baryons ($\Xi_{cc}\Xi_{cc}$) or one doubly charmed baryon and one doubly charmed antibaryon $(\Xi_{cc}\bar{\Xi}_{cc})$ within the framework of the one-boson-exchange-potential model. For the spin-triplet systems, we take into account the mixing between the ${}^3S_1$ and ${}^3D_1$ channels. For the baryon-baryon system $\Xi_{cc}\Xi_{cc}$ with $(R,I) = (\bar{3}, 1/2)$ and $(\bar{3}, 0)$, where $R$ and $I$ represent the group representation and the isospin of the system, respectively, there exist loosely bound molecular states. For the baryon-antibaryon system $\Xi_{cc}\bar{\Xi}_{cc}$ with $(R,I) = (8, 1)$, $(8, 1/2)$ and $(8,0)$, there also exist deuteron-like molecules. The $B_{cc}\bar{B}_{cc}$ molecular states may be produced at LHC. The proximity of their masses to the threshold of two doubly charmed baryons provides a clean clue to identify them.

Correlated leading baryon-antibaryon production ine+e−→cc¯→Λc+Λ¯c−X

We present a study of 649 \pm 35 e+e- --> ccbar events produced at sqrt{s}~10.6 GeV containing both a Lambda_c baryon and a Lambda_c antibaryon. The number observed is roughly four times that expected if the leading charmed hadron types are uncorrelated, confirming an observation by the CLEO Collaboration. We find a 2-jet topology in these events but very few additional baryons, demonstrating that the primary c and cbar are predominantly contained in a correlated baryon-antibaryon system. In addition to the charmed baryons we observe on average 2.6 \pm 0.2 charged intermediate mesons, predominantly pions, carrying 65% of the remaining energy.

Study ofB+→pΛ¯γ,pΛ¯π0andB0→pΛ¯π−

We study the charmless baryonic three-body decays of B mesons: B+ to p Lambdabar gamma, B+ to p Lambdabar pi0 and B0 to p Lambdabar pi-. The partial branching fractions as a function of the baryon-antibaryon mass and the polar angle distributions of the proton in the baryon-antibaryon system are presented. This study includes the first observation of B+ to p Lambdabar pi0, which is measured to have a branching fraction of (3.00^{+0.61}_{-0.53}\pm 0.33) times 10^{-6}. We also set upper limits on branching fractions of the two-body decays B0 to p Sigmabar^{*-}, B0 to Delta^0 Lambdabar, B+ to p Sigmabar^{*0}, and B+ to Delta^+ Lambdabar at the 90% confidence level. These results are obtained from a 414fb^{-1} data sample collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider.

Towards the resolution of the e+ e− → N puzzle

We discuss the puzzling experimental results on baryon-antibaryon production in e+e- annihilation close to the threshold, in particular the fact that sigma(e+e- --> nbar n) is somewhat greater than sigma(e+e- --> pbar p). We discuss an interpretation in terms of a two-step process, via an intermediate coherent isovector state serving as an intermediary between e+e- and the baryon-antibaryon system. We provide evidence that the isovector channel dominates both e+e- --> pions and from Nbar N annihilation at rest, and show that the observed ratio of sigma(e+e- --> nbar n)/sigma(e+e- --> pbar p) can be understood quantitatively in this picture.

On electron-positron annihilationinto nucleon-antinucleon pairs

We discuss the puzzling experimental results onbaryon-antibaryon production in e+e- annihilation close tothe threshold, in particular the fact that ≳ . We discuss aninterpretation in terms of a two-step process, via anintermediate coherent isovector state serving as an intermediarybetween e+e- and the baryon-antibaryon system. We provideevidence that the isovector channel dominates both e+e- → pions and from annihilation at rest, and showthat the observed ratio of to can be understood quantitatively inthis picture.

A study of the centrally produced baryon-antibaryon systems in pp interactions at 450 GeV/c

A study of the centrally produced p p , p pπ 0 , p pπ +π − and Λ Λ channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. No significant new structures are observed in the mass spectra, however, important new information on the production dynamics is obtained. A systematic study of the production properties of these systems has been performed and it is found that these systems are not produced dominantly by double Pomeron exchange.

NEARTHRESHOLD PHENOMENA IN LOW ENERGY ANTIPROTON PHYSICS

The experimental data on low energy [Formula: see text] elastic scattering and annihilation, and on the [Formula: see text] reaction near threshold are well-described in the framework of a simple unitary coupled channel model. Large P-wave enhancement observed in these experiments is shown to be a result of the existence of the nearthreshold bound and resonant P-states of quasinuclear nature in baryon-antibaryon systems. Other possible manifestations of such [Formula: see text] states in the experiments with low energy antiprotons are considered.

Internal meson dominance for pp-bar annihilation.

The previously considered $^{3}\mathrm{S}_{1}$ internal fusion model of pp\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}YY\ifmmode\bar\else\textasciimacron\fi{}, YY\ifmmode\bar\else\textasciimacron\fi{} $^{\mathrm{*}}$, and ${Y}^{\mathrm{*}}$Y${\ifmmode\bar\else\textasciimacron\fi{}}^{*}$ (Y denotes hyperon) at low energies is modified and thereby extended to also include pp\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}nn\ifmmode\bar\else\textasciimacron\fi{} and ${\ensuremath{\Delta}}^{++}$\ensuremath{\Delta}${\ifmmode\bar\else\textasciimacron\fi{}}^{\ensuremath{-}\ensuremath{-}}$. It is assumed that the same nonperturbative mechanism that mixes the different qq\ifmmode\bar\else\textasciimacron\fi{} pairs within the neutral, nonstrange mesons is also responsible for the scattering, annihilation, and creation of qq\ifmmode\bar\else\textasciimacron\fi{} pairs within the baryon-antibaryon system. More specifically, we assume that processes qq\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}QQ\ifmmode\bar\else\textasciimacron\fi{} within the baryon-antibaryon system with q=d or u and Q=d, u, or s quarks is mediated by fusion of the qq\ifmmode\bar\else\textasciimacron\fi{} to a pseudoscalar or vector meson that also within the system decays into QQ\ifmmode\bar\else\textasciimacron\fi{}. The $^{1}\mathrm{S}_{0}$ pseudoscalar-meson model disagrees with experiment whereas the $^{3}\mathrm{S}_{1}$ vector-meson fusion model is in reasonable agreement with it. As compared to the previously considered $^{3}\mathrm{S}_{1}$ internal fusion model the main change is an extension of the approximate agreement to the nonstrange final-state baryons. This is achieved since strange baryons in the model are only produced via the small \ensuremath{\omega}-\ensuremath{\varphi} mixing.

A molecular model for baryonium

In analogy with the diatomic molecules, a model for the baryon-antibaryon system is proposed. In this model, the states below threshold are described as the vibrational states, whereas the states above threshold are attributed to the quark excitations in a quark-diquark picture of the baryon. The agreement with experiments is found to be satisfactory. It is expected that this model would simulate the spirit of both the potential and quark model approaches used in recent times to analyse the observed baryonium states.

Study of [formula omitted] and [formula omitted] production in π±p reactions at 18.5 GeV/ c

Studies have been made of the rare reactions π + p → π + pp p and Λ + Λ + anything , and of π − p → π − pp p and Λ + Λ + anything , with cross sections of 18.5 ± 5.5, 10.7 ± 3.0, 12.0 ± 5.0, and 19.7 ± 4.8 μb, respectively. Production characteristics of these reactions are examined and effective-mass spectra are presented. There is no significant evidence in the data for production of Ψ(3095) in the baryon-antibaryon system, or for any other high-mass resonances.

Are There NarrowD-Wave Baryon-Antibaryon Resonances?

The conjecture of a possible narrow $D$-wave resonance of the $\ensuremath{\Omega}\overline{\ensuremath{\Omega}}$ system is extended to general baryon-antibaryon systems. On the basis of the well-known $\mathrm{NN}$ forces one finds that $B\overline{B}$ systems bound by pion forces are more likely to produce narrow resonances. In particular one may expect narrow resonances below the $N\overline{N}$, $\ensuremath{\Lambda}\overline{\ensuremath{\Lambda}}$, and perhaps even the $\ensuremath{\Xi}\overline{\ensuremath{\Xi}}$ thresholds. A narrow $B\overline{B}$ resonance may serve in a second step (similar to the $\ensuremath{\alpha}$ particle) to explain the narrow $\ensuremath{\psi}$ and ${\ensuremath{\psi}}^{\ensuremath{'}}$.

Experimental Tests for Exotic States in the Baryon-Antibaryon System

New experiments are proposed in which negative as well as positive results are significant. A new finite-energy sum rule based on dominance of $\ensuremath{\rho}$ and $\ensuremath{\omega}$ exchange for high-energy odd-signature amplitudes gives quantitative estimates for production of doubly charged exotic meson resonances via $\ensuremath{\Delta}$ exchange in nucleon-antinucleon and pion-nucleon reactions. Absence of exotic resonances with predicted cross sections would indicate serious disagreement with two-component duality.

Compulsory Resonance Formation

It is noted that if two mesons are allowed by the quark model to resonate, they do so for ${p}^{*}\ensuremath{\le}{p}_{0}^{\mathrm{MM}}\ensuremath{\equiv}350$ MeV/c, where ${p}^{*}$ is the c.m. momentum. The corresponding value for mesonbaryon systems is ${p}_{0}^{\mathrm{MB}}\ensuremath{\equiv}250$ MeV/c, suggesting (in an optical picture) that the baryon is indeed bigger than the meson. Crucial tests of the rule are provided by exotic baryon-antibaryon systems, for which one expects ${p}_{0}^{\mathrm{BB}}\ensuremath{\cong}200$ MeV/c, and by other specific two-body modes which are predicted to resonate not far above threshold.

Quark model selection rules for Hadron couplings

Quark model selection rules are derived which apply to the couplings of hadrons composed of any number of quarks. These reduce to well-known and experimentally verified rules in the simplest cases, provide a necessary selection rule in the application of duality to baryon-antibaryon systems, and could explain the apparent difficulty of producing free quarks. Some experimental consequences of the rules are discussed.

Energy dependence of total cross-sections in the CHKN model

The fit to high-energy cross-sections made by Cabibbo, Horwitz, Kokkedee and Ne’eman is used to predict various meson-meson, meson-baryon, baryon-baryon and baryon-antibaryon total cross-sections. By correlating the energy dependence of these cross-sections with theSU3 representations allowed in the direct channel, we find that: i) In all channels in which resonances are expected, total cross-sections decrease at least as rapidly as in channels where resonances are not expected. ii) In baryon-antibaryon systems forming10+27, total cross-sections decrease more rapidly than in those forming27 alone. iii) Baryon-baryon total cross-sections involving1, 8 or10 direct-channel contributions are essentially constant or increasing, while those involving only or27 contributions are decreasing. In particular,σT(Σ−p) andσT(Ξ−p) are predicted to rise by 13% and 20% respectively, in the range 5 GeV⩽ ⩽plab⩽20 GeV/c.