Dibaryon Signals in NN Scattering data and high strangeness dibaryon sesarch at RHIC Fan Wang Dept. of Physics, Nanjing Univ. Joint Center for Particle-Nuclear Physics and Cosmology (CPNPC) of NJU and PMO J.L.Ping, H.X.Huang C.L.Chen, H.R.Pang C.W.Wong, UCLA Arxiv: [nucl-th]

Outline I. Introduction II. Dibaryons in NN scattering data III. QCD models calculation IV. High strangeness dibaryon search at RHIC

I.Introduction NN scattetering and reaction data show evidences of dibaryon resonances: NN scattering has been measured for more than 70 years and vast data existed; Phase shift analysis showed evidences of dibaryon resonances, which had been there about 15 years! R.A.Arndt et al, Phys.Rev.D45,3995(1992); C50,2731(1994)

No reliable theory to calculate multi- quark resonance : The present lattice QCD is impossible to calculate the broad resonance; Chiral perturbation is hard to extend to resonance energy region; The phenomenological meson exchange model needs new parameters ofπNΔ,πΔΔ coupling to deal with NΔ,ΔΔ channels coupling and so almost no predictive power in calculating NΔand ΔΔ dibaryon resonances. The strangeness channels are even harder.

The advantage of quark model (chiral quark model, quark delocalization and color screening model, etc.) is the model parameters can be fixed by hadron spectroscopy, at most the NN scattering and then the dibaryon resonances can be “predicted” in detail; The disadvantage is it is just a model and the predictive power is limited.

II.Dibaryons in NN Scattering Data Partial wave analysis (PWA) pp↔d

Dibaryon resonances parameters from PWA

CELSIUS-WASA

This results were observed recently by SELSIUS-WASA collaboration through pn->d and d doubleπproduction reaction. The total and differential cross sections can be fitted by assuming a ΔΔ resonance with

III.QCD models calculation Two quark models have been employed to do NN, NΔ,ΔΔ channels coupling calculation to study the NΔ,ΔΔ dibaryon resonances appearing in NN scattering data: 1.Chiral quark model, Salamanca version; 2.Quark delocalization color screening model (QDCSM).

Salamanca chiral quark model

QDCSM

Quark models fitted the NN scattering data well (even though not as well as meson exchange models) with much less adjustable parameters might mean there is right physics there. QDCSM with the fewest adjustable parameters; it is the unique one which explained the long standing fact that the molecular and nuclear force are similar.

Quark models are less repulsive for partial waves in the higher scattering energy region, some kind short range repulsion might be missing. The P-wave phase shifts have not been fitted well, both the central and spin-orbit P-wave interactions have not enough attraction.

NΔ,ΔΔdibaryon resonances in quark models Channel coupling calculations including NN, NΔ,ΔΔ and even hidden color channels with two quark models have been done to study the standard Feshbach resonances due to the coupling between closed channels NΔ,ΔΔ and the open channel NN. NΔ↔ and dibaryon resonances obtained.

Quark models explained the resonance discovered in PWA is an NΔ resonance. The ΔΔ isoscalar resonance discovered (if confirmed) by CELSIUS-WASA group is a ΔΔ resonance. Quark model could not obtain the and isoscalar resonances discovered in PWA.

These calculations show that the low energy NN scattering data can not fix the BB Interaction in the resonance energy region. They also show that the bare quark model prediction on the dibaryon resonances might be far from reality, the open channel coupling might shift the resonance energy few hundred MeV. The bare quark model calculated hadron spectroscopy has the same uncertainty.

There should be dibaryon resonances contributing to these broad structure of the NN scattering in the resonance energy region.

IV.High Strangeness dibaryon search at RHIC Quark model predicted there should be strong attraction for some decuplet-decuplet BB channels and mild attraction for some decuplet-octet BB channels; The octet-octet channels will have repulsive core and weak attraction. The N-Delta and di-Delta resonance (if confirmed) support this prediction.

The relativistic heavy ion reaction should be an oven to produce the multiquark systems, to search NΔandΔΔresonance there might be hard but our model predict another interesting dibaryon resonance, SI = -3. It is almost a NΩ dibaryon, which mainly decay to ΛΞ with an estimated width ~ keV, so it can be searched through the reconstuction of theΛΞ invariant mass with the data stored in STAR and other detectors.

N  I=1/2,J p =2 +,S=-3 Wang Zhang Others Threshold M(MeV) deeply bound to unbound (2590)  (keV) Decay mode N  -->  1 D 2, 3 D 2. D-wave decay, no strong πtensor interaction in N  channel, one quark must be exchanged to form  from N . These factors all suppress the decay rate and make N  quite possible a narrow resonance. (Wang:PRL 59(87)627, 69(92)2901, PRC 51(95)3411, 62(00)054007, 65(02)044003, 69(04)065207; Zhang:PRC 52(95)3393, 61(00)065204, NPA 683(01)487.)

IV.Further measurements at CSR The NN scattering, pp and pd, in the resonance region should be measured further. The dibaryon production cross section is in the order of μb and the total pp cross section in the resonance energy region is about 50 mb, a big challenge to the scattering cross section measurement. The pp->d should be measured again. It is a good channel to study the isovector dibaryon resonances. The pd->pd should be checked. WASA group proposed to do further measurement at COSY, CSR is almost a unique machine to do an independent check.

Few words about γd γd->dπ, dππ, NNπ, NNππ not only provide N resonances information but also dibaryon resonance information, especially di-Δ or the d* resonance information. The production cross section is about 10 nb. It should be a good check of CELSIUS -WASA di-Δ resonance signal, the γ Energy should be around 500 MeV.

Advertisement about nucleon spin structure PRL100,232002(2008); Arxiv: [hep-ph];

New decomposition

Esential task:to define properly the pure gauge field and physical one

II.Color confinement Color structure of nucleon obtained from lattice QCD

Simplified version of the color structure, color string nucleon meson

Color structure of multi-quark systems Hadron phase Multi- quark phase Five quarkSix quark

QCD quark benzene QCD interaction should be able to form a quark benzene consisted of six quarks

Lattice QCD results of the quark interaction PRL 86(2001)18,90(2003)182001,hep-lat/ Suppose these lattice QCD results are qualitatively correct, then multi-quark system is a many body interaction multi-channel coupling problem.

Two hadrons collide each other, if they are close enough there should be a possibility that two hadrons rearrange there internal color structure to transform from hadron phase to multi-quark phase. Once the multi-quark is formed, especially if the scattering energy is around the hidden color states it should be a mixture of various color structure and colorless hadronic molecular is only one of them. All hidden color component cannot decay directly. It must transform to color singlet hadronic phase first then decay, so there must be resonance related to these genuine multi-quark system similar to compound nucleus.

The product cross section and the decay width of multi-quark system are determined by the transition interaction between color singlet hadrons and genuine color multi-quark systems. Up to now we don’t have any reliable information about this transition interaction. One possibility is that such a transition from color singlet hadrons to genuine color multi-quark system only takes place at short distances, i.e. through violent high energy processes only. The color singlet hadrons like the inertial elements.

Quark delocalization, color screening model (QDCSM) Based on the above understanding, we take Isgur model as our starting point, but modify it for multi quark systems by two new ingredients: 1. The confinement interaction is re-parameterized aimed to take into account the effect of multi channel coupling, especially the genuine color channels coupling; 2. The quark delocalization, similar to the electron delocalization in molecule, is introduced to describe the effect of mutual distortion.

Color screening ： qq interaction: intra baryon inter baryon different the color configuration mixing and channel coupling have been taken into account to some extent. three gluons exchange 0 (intra baryon) = 0 (inter baryons), etc.

Quark delocalization: the parameter εis determined variationally by the dynamics of the quark systems. of quark distribution and gluon distribution has been taken into account to some extent. the self-consistency

Parameters of QDCSM m u =m d =313 MeV m s =560 MeV α=1.54 b=0.603 fm a=25.13 MeV/fm 2 μ=1.0 fm -2 Almost the same as Isgur model except the color screening

This model, without invoking meson exchange except pion, with only one additional adjustable parameter-the color screening constant μ reproduce the deuteron properties, the NN, NΛ, NΣ scattering data. Moreover it explains the long standing facts: 1. The molecular force is similar to nuclear force except the energy and length scale; 2. The nucleus can be approximated as a nucleon system.

Thanks

QDCSM predicted another six quark state M(MeV) threshold 2611  (keV) Decay mode N  -->  1 D 2, 3 D 2. D-wave decay, no strong πtensor interaction in N  channel, one quark must be exchanged to form  from N . These factors all suppress the decay rate and make N  quite a narrow resonance. This state might be created in RHIC and detected by STAR through the reconstruction of  decay product. (Wang:PRL 59(87)627, 69(92)2901, PRC 51(95)3411, 62(00)054007, 65(02)044003, 69(04)065207; Zhang:PRC 52(95)3393, 61(00)065204, NPA 683(01)487.) N  I=1/2,J p =2 +,S=-3