dibaryon signals in nn scattering data and high strangeness dibaryon sesarch at rhic fan wang dept....

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 PMOJ.L.Ping, H.X.HuangC.L.Chen, H.R.Pang

C.W.Wong, UCLAArxiv:0806.0458[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 calculatethe broad resonance; Chiral perturbation is hard to extend to resonance energy region; The phenomenological meson exchange modelneeds new parameters ofπNΔ,πΔΔ couplingto deal with NΔ,ΔΔ channels coupling and soalmost no predictive power in calculating NΔandΔΔ dibaryon resonances. The strangenesschannels are even harder.

The advantage of quark model (chiral quarkmodel, quark delocalization and color screening model, etc.) is the model parameters can be fixed by hadron spectroscopy, at most the NN scattering andthen 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

0 0

2.41rE GeV 100r MeV

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.

1 30 1,S S

NΔ,ΔΔdibaryon resonancesin 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.5

2S 12D NN 7 3

3 3S D NN

• 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.

12NN D

52S

73S

3 32 2P F

33F

• 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 b

e 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 ~12-22 keV, so it can be searched through the reconstuction of theΛΞ invariant mass with the data stored in STAR and other detectors.

pJ 12 2

N I=1/2,Jp=2+,S=-3

Wang Zhang Others ThresholdM(MeV) 2549 2561 deeply bound 2611 2557 2607 to unbound (2590)(keV) 12-22

Decay mode N--> 1D2,3D2. D-wave decay, no strongπtensor interaction in N channel, one quark must be exch

angedto form from N. These factors all suppress the decay r

ate andmake 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.

0 0,

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.

*N

Advertisement about nucleon spin structure

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Arxiv:0806.3166[hep-ph];

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New decomposition''''''

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

purephy AigD a

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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 quark Six 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/0407001

min

3 3 3 min 3

5 5 min 5

min

1

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qqqq qq qq

q q q qi j i j

i jsq q q

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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 closeenough there should be a possibility that twohadrons rearrange there internal color structure totransform from hadron phase to multi-quark phase.• Once the multi-quark is formed, especially if thescattering energy is around the hidden color states itshould be a mixture of various color structure andcolorless hadronic molecular is only one of them.• All hidden color component cannot decay directly. Itmust transform to color singlet hadronic phase firstthen decay, so there must be resonance related tothese genuine multi-quark system similar to compoundnucleus.

• 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 d

elocalization 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.

2

2

6

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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

2

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br

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Parameters of QDCSM mu=md=313 MeV

ms=560 MeV

α=1.54

b=0.603 fm

a=25.13 MeV/fm2

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 stateM(MeV) 2549-2557 threshold 2611 (keV) 12-22Decay mode N--> 1D2,3D2. D-wave decay, no strongπtensor interaction in N channel, one quark must beexchanged to form from N. These factors all suppressthe 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,Jp=2+,S=-3