EXOTIC STRUCTURES OF THE NUCLEON-NUCLEON SYSTEM IN THE 2.6 - 3.0 GeV / C2 MASS REGION

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EXOTIC STRUCTURES OF THE

NUCLEON-NUCLEON SYSTEM IN THE 2.6 - 3.0 GeV / C2 MASS REGION

E. Lomon

To cite this version:

E. Lomon. EXOTIC STRUCTURES OF THE NUCLEON-NUCLEON SYSTEM IN THE 2.6 - 3.0 GeV / C2 MASS REGION. Journal de Physique Colloques, 1990, 51 (C6), pp.C6-363-C6-365.

�10.1051/jphyscol:1990629�. �jpa-00230896�

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COLLOQUE D E PHYSIQUE

C o l l o q u e C6, s u p p l 6 m e n t a u n022, Tome 5 1 , 1 5 novembre 1990

EXOTIC STRUCTURES OF THE NUCLEON-NUCLEON SYSTEM IN THE 2.6

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^3.0G ~ V / C ~ MASS REGION' )

E.L. LOMON

C e n t e r f o r T h e o r e t i c a l P h y s i c s a n d L a b o r a t o r y f o r N u c l e a r S c i e n c e , M a s s a c h u s e t t s I n s t i t u t e of r e c h n o l o y y , C a m b r i d g e , M a s s a c h u s e t t s 02139, U.S.A.

Une ancienne prediction d ' e t a t s exotiques nucl6on-nucleon de p a r i t 6 p a i r e c o n s t r u i t s s u r des 6 t a t s ^B6 quarks ( l ~ ~ / , ) ~ par une m6thode de matrice R a 6 t 6 Btendue B l a configuration impaire (Is1 / ) ( l p l / )

.

^{L a}s t r u c t u r e des donn6es de A aL(pp) correspond t r b s bien aux predictions de p a r i t 6 paire. La masse l a plus basse pr6vue en p a r i t 6 impaire p o u r r a i t corespondre B une s t r u c t u r e B t r o i t e observ6e &n Ay(pp) 2.77 G ~ V / C ~ .

ABSTRACT

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An earlier R-matrix method prediction of even parity nucleon-nucleon exotics induced by the (ls1/2)6 quark configuration has been extended to the odd parity exotics of the ( 1 5 ~ / ~ ) 5 (lpll2) configuration. Structure in A a ~ ( p p ) data corresponds well to the even parity predictions. The lowest mass odd parity exotic may corresponcl to a narrow structure recently observed in A,(pp) a t 2.77 GeV/c2.

1 - INTRODUCTION

In QCD perturbative behavior is dominant in the short range asymptotically free region, while hadronic degrees of freedom are believed to dominate at long range in the region of full or near confinement. In the absence of feasible exact calculations this necessitates a hybrid approach to two-hadron reactions. The R-matrix method connects short range quark degrees of freedom to the long range hadronic wave function predicted by a hadron-exchange, hadroll and isobar coupled-channels model.

The R-matrix method is used in its f-matrix form/l/ corresponding to the vanishing of the valence quark wave functions a t a separation radius, ro, of the two hadroilic clusters of quarks.

with

given by the energies VVz of the internal quarlc states and by the fractional parentage coefficients of the hadronic states cv and

P

in the quark configuration i. The assumption of asymptotic freedom within ro requires that it be less than the radius of transition to non-perturbative behavior. For bag models this means less than the equilibriuin bag radius. This restriction on ro must be consistent with the fitting of low energy data and the requirement of Ecl. (1) that

The MIT Bag model is unsuccessful in meeting these combined criteria, so it is inadequate for the two- hadron sector. The Cloudy Bag model meets the criteria wit.11 an ro = 1.035 fm for the lowest energy q u u k configuration

IS^,^)

6 (R,,, = 1.13 fin).

CA This work is supported in part by funds provided by t,he U.S Department of Energy (D.O.E.) under contract #DE-AC03-76ER03069.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990629

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COLLOQUE DE PHYSIQUE

2

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PREVIOUS RESULTS

This hybrid model agrees with NN phase parameters for

zab ^<

1 GeV/2/ and with selected observables at higher energies/3/. The internal ( l ~ l , ~ ) 6 quark states are split by one-gluon exchange, requiring the evaluation of the a1 0 2 XI

.

X2 operator for each state of the configuration. This predicts an exotic multiplet (see Fig. 1) of a 3 S ~ ( I = 0) at 2.63 GeV/c2, a lSo(I = 1) at 2.70 GeV/c2, and a ' D 2 ( I = 1) with a 3D3(I = 0) at 2.84 GeV/c2 masses/3,4/. Data for A u ~ ( p p ) shows structure that supports the existence of both the I = 1 exotics with the predicted masses and widths/5/. Indeed a phase shift analysis/6/ identifies the first I = 1 structure as the predicted 'So state. Suitable I = 0 data is not available. The first I = 2 states are predicted to be above 3 CeV/c2.

Fig. 1: Nucleon-nucleon exotic states. The masses of even parity states are displayed in the left column and those of odd parity states on the right by solid lines. Two baryon thresholds are denoted by centered dashed lines. Masses are given in units of GeV/c2.

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3 - NEW RESULTS

Recent A,(pp) data171 shows a narrow structure a t 2.77 GeV/c2. This triplet spin structure must be associated with an odd parity state. Ay(pp + d ~ + ) data181 also shows narrow structure near this energy.

An investigation of the ( 1 ~(lpll2) quark configuration has been undertaken to determine possible low ~ ~ ~ ) ~ lying odd parity exotics predicted by'this hybrid model. The increased kinetic energy of the quark p112 state is partly compensated by the presence of flavor configurations of lower gluon exchange energy coupled with the new orbital symmetry, and by a decreased overlap of the sp pairs. For the ( 1 ~ ~ 1 ~ ) ~ configuration only the [6Iorb [33ITS Young symmetry is coupled to the antisymmetric color symmetry/g/. For the ( 1 . ~ 1 ~ 2 ) ~ ( 1 ~ 1 ~ 2 )

configuration there is, in addition, the [51Iorb [ 4 2 ] ~ s symmetry.

In the [6Iorb [ 3 3 ] ~ ~ symmetry the ( 1 . ~ ~ ~ ~ ) ~ (lpll2) states are raised by 150 - 260 MeV above their

IS,!^)^

analogs. The extra kinetic energy increases Re.,, leading to ro = 1.1 fm. This results in (as shown in Fig. 1) the odd parity states IP1(I = 0) at 2.89 GeV/c2, 3 P o ( I = 1) at 2.93 GeV/c2, and the 3 P z ( I = 1) and 'F3(I = 0) at 2.99 GeV/c2. However the new [S, l]orb [42ITs states are lower: 3 P l ( I = 1) at 2.84 and 2.94 GeV/c2, 3P2(I = 1) at 2.93 GeV/c2 and 3F3(I = 1) at 2.97 GeV/c2. The mass of the lighter 3Pl state is close to that of the experimental A,(pp) structure, and a small increase of ro would bring it into agreement.

Exotic states caused by the ( 1 ~ ~ ~quark configuration are expected to be in the same mass ~ ) ~ range as that of the two configurations already discussed, because the lp3/2 Dirac particle has a kinetic energy between those of the 1sl/2 and lpl12 particles (3.2 vs. 2.0 and 3.8 for massless particles, in units of 1/R). These orbitals require investigation of a more complicated orbital symmetry and also a non- isotropic boundary condition. The lowest of the exotic states induced by this configuration may represent the experimentally observed A, (pp) structure,rather than the Pl

(isll2)

(lPll2) state described above.

The widths of the exotics depend on the fractional parentage coefficients (see Eq. l ) , the phase space of the reaction, and on the coupling of the observed nucleon-nucleon state to the hadronic states within the quark configuration (the coupling is the result of the long range meson exchange interaction). Table 11 of Ref. [g] provides the fractional parentage coefficients, which are not very different in magnitude for the even and odd parity baryon-baryon states. But the odd parity quark states overlap only with B B * pairs (we use B for a baryon with the parity of a nucleon and B* for baryons with opposite parity). As the B*'s are higher in mass than the B's the phase space is reduced. One may also expect the meson exchange coupling of NAT pairs to BB* pairs to be weaker than the coupling to N and A pairs. These effects would reduce the width of the odd parity states as compared to that of the even parity states, which could explain the narrow width of the A,(pp) structure/7/compared to those of A a ~ ( p p ) / 5 / . The investigation of this aspect is in progress.

3 - CONCLUSIONS

The energies of the ( 1 ~ ~ 1 ~ ) ~ (lpll2) quark configuration have been investigated and found to be only a little higher than those of the (. 1, ,~configuration. Thus the lowest of the former, or perhaps a state of ~ ~ ~ ) ~ the ( 1 ~(lp3l2) ~ ~configuration, may be the source of the narrow odd parity state seen in A,(pp). The ~ ) ~ three quark configurations discussed indicate the possibilty of observing four I = 0 and six more I = 1 exotic structures, in addition to the three that may have already been observed. They are all expected to be in the range of 2.6 - 3.1 GeV/c2 mass, corresponding to proton or neutron beams of 1.8

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3.2 GeV energy. These states may also be excited by absorption of photons or pions in the 1 GeV region.

REFERENCES

/ l / Lomon, E. L., Journal de Phys. 46 (1985) C2-329; Nucl. Phys. A434 (1985) 139c.

/2/ Gonzblez. P. and Lomon, E. L., Phys. Rev. D34 (1986) 1351.

/3/ Gonzblez, P., LaFrance, P. and Lomon, E. L., Phys. Rev. D35 (1987) 2142.

/4/ LaFrance, P. and Lomon, E. L., Phys. Rev. D34 (1986) 1341.

/5/ Auer, I. P., et al., Phys. Rev. Lett. 62 (1989) 2649.

/6/ Hoshizaki, N., et al., in Pro~eedings of the Workshop on Experiments by KEK Polarized Proton and Electron Beams (ICEIC, Ibaraki, Japan, October 1988).

/7/ de Lesquen, A., AIP Conference Proceedings 187, Sth International Symposium on High Energy Spin Physics, ICJ. Heller, ed. (Minnesota, 1988).

/S/ Bertini, R., et al., Phys. Lett. 203 (1988) 18.