We show that the QCD van der Waals attractive potential is strong enough to bind a φ meson onto a nucleon inside a nucleus to form a bound state. The direct experimental signature for such an exotic state is proposed in the case of subthreshold φ meson photoproduction from nuclear targets. The production rate is estimated and such an experiment is found to be feasible at the Jefferson Laboratory. 25.20.-x, 24.85.+p It has been suggested [1] that the QCD van der Waals interaction, mediated by multi-gluon exchanges, is dominant when the interacting two color singlet hadrons have no common quarks. In fact, the QCD van der Waals interaction is ehanced at low velocity as has been shown by Luke, Manohar, and Savage [2]. This finding supports the prediction that a nuclear-bound quarkonium can be produced in charm production reactions at threshold, and the interpretation that the structures seen in s 10 dσ/dt(pp → pp) and the A N N spin correlation at √ s ∼ 5 GeV and large cm angles [3] can be attributed to ccuuduud resonant states [4]. If these interpretations are correct, then analogous effects could also be expected at the strangeness threshold. The objective of this work is to explore this possibility.We are motivated by the investigation of the nuclearbound quarkonium by Brodsky, Schmidt, and de Téramond [1]. They used a non-relativistic Yukawa type attractive potential V (QQ)A = −αe −µr /r characterizing the QCD van der Waals interaction. They determined the α and µ constants using the phenomenological model of high-energy Pomeron interactions developed by Donnachie and Landshoff [5]. Using a variational wave function Ψ(r) = (γ 3 /π) 1/2 e −γr , they predicted bound states of η c with 3 He and heavier nuclei. Their prediction was confirmed by Wasson [6] using a more realistic V (QQ)A potential taking into account the nucleon distribution inside the nucleus.Similarly, one expects the attractive QCD van der Waals force dominates the φ-N interaction since the φ meson is almost a pure ss state. It is possible that a φ-N bound state or resonant state can be formed in some reactions. In photoproduction of φ meson from a proton target above threshold, the formation of a bound φ-N state is not likely because of the momentum mismatch between the φ and the recoil proton. As such, no experimental evidence exists on the formation of the φ-N bound state up to now. On the other hand, such a φ-N bound state could be formed inside a nucleus. In this paper, we will verify this possibility and make predictions for future experimental tests.Using the variational method and following Ref.[1] to assume V (ss),N = −αe µr /r, we find that a bound state of φ-N is possible with α = 1.25 and µ = 0.6 GeV. The binding energy obtained is 1.8 MeV. Our results should be compared with α = 0.6 and µ = 0.6 GeV determined by Brodsky, Schmidt, and de Téramond [1] for the cc quarkonium. The interaction is expected to be enhanced by (m c /m s ) 3 , i.e., qq separation cubed, from cc to ss. Since the radius of the φ meson is (0.4 fm [7]) twice the ...
The role of the nucleon resonances in the double polarization observables of pion photoproduction is investigated by using the resonance parameters predicted by Capstick and Roberts. As an example, we show that the not-well-determined two-star resonance N 3/2 Ϫ (1960) can be examined by performing experiments on beam-recoil polarization at large angles.
To facilitate the relativistic heavy-ion calculations based on transport equations, the binary collisions involving a ∆ resonance in either the entrance channel or the exit channel are investigated within a Hamiltonian formulation of πN N interactions. An averaging procedure is developed to define a quasi-particle ∆ * and to express the experimentally measured N N → πN N cross section in terms of an effective N N → N ∆ * cross section. In contrast to previous works, the main feature of the present approach is that the mass The ∆ potential in nuclear matter has been calculated by using a BrucknerHartree-Fock approximation. By including the mean-field effects on the ∆ propagation, the effective cross sections of the N N → N ∆ * , N ∆ * → N N and N ∆ * → N ∆ * reactions in nuclear matter are predicted. It is demonstrated that the density dependence is most dramatic in the energy region close to the pion production threshold.
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