GLUEBALL CANDIDATES

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Submitted on 1 Jan 1982

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GLUEBALL CANDIDATES

J. Donoghue

To cite this version:

J. Donoghue. GLUEBALL CANDIDATES. Journal de Physique Colloques, 1982, 43 (C3), pp.C3-89-

C3-91. �10.1051/jphyscol:1982320�. �jpa-00221873�

JOURNAL DE PHYSIQUE

CoZloque C3, supple'ment au n o 22, Tome 43, de'cembre 1982 page C3-89

GLUEBALL CANDIDATES

J.F. Donoghue

Department of Physics and Astronomy, UMiversity of Massachusetts, Amherst, Massachusetts 01003, U. S . A.

At present, the main theoretical activity related to glueballs is the lattice Monte Carlo studiescl) which are predicting that glueballs are fairly light (i.e.

in the 1 + 2 range), in agreement with most earlier predictions. However, theory is not yet adequate to make detailed predictions of the behavior of glueballs.

Hope for more progress centers on experiments. In this talk I briefly summarize portions of the experimental situation.

One glueball candidate is the 1(1440), a .JPC = 0-+ state clearly seen in J/$

radiative decays, (2) and possibly seen elsewhere. It is located close to states which have been identified with the radially excited 0-+ nonet (3) (V' (1270),

5(1274), K'(1400)). As there is one member of this nonet missing, it would be natural to assign the I to the missing slot. There are four objections to such an assignment:

1) The mass is not what one would expect. (4)

2) If the assignment were made, we would also expect to see the C(1275) produced in $ radiative decays, at roughly twice the strength of the l(1440). ( 4 ) Experimenters have not quoted a limit for this, but my es- timate of it from the recent 1]nT data is less than one quarter of the strength of the I. Points (1) and (2) are based on a general mixing scheme relating particular masses to their octet singlet mixing.

3) If the octet-singlet mixing were adjusted, by fiat, to remove point (2), then the I should have been strongly produced in the experiment which saw the c(1275). (5)

f) It is hard to account for the strength of the production rate of I if it is a radial excitation. (5)

Theoretically these arguments are strong. It has been pointed out that a possible weakness lies in use of data on the radial 0-+ nonet. In particular the existence of the G(1275) is crucial for I), 2), and 3), and only one experiment has seen this state. Its confirmation woul dd strength to the arguments. The ~'(1270) (which has recently been confirmedf68) and the K'(l400) are less central. A11 that is required is that they not be lighter than the presently quoted masses.

A suggestion to alleviate problem (4) by mixing with the ground state(7) is ruled out by the mass spectrum and by point (2).

The other natural interpretation of the t is as a glueball. The only problem that I see with this is the lack of an QTT signal(8) due to the I . This has two aspects. One is purely an experimental problem in that experimgnt shows that

I-+& is dominant, and 6 is kgown to decay to 1]n as often as KK, so that I+1]TT

should occur as often as I + K K ~ . The present 90% C.L bound is 50% of KKT. Per- haps the weak point here is 67r dominance. This also has bearing on the theoret- ical interpretation. An SU(3) singlet (like a glu~ball) would be predicted by SU(3) to decay into 1]nn at one third the rate of KKn, times a phase space factor which depends on the shape of the Dalitz plot, but which will favor WTr. However,

SU(3) invariance may not be very accurate for these decays. Signs of SU(3) break- ing in models are seen(9) decreasing qrn, mixings with qq states need to be-in- cluded, and possible "helicity suppression" of the decays(lO) would favor KKIT over r)m. If the experimental limit were to be pushed much lower, this could be a problem, but at present I don't feel that it is very strong.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982320

C3-90 JOURNAL DE PHYSIQUE

My conclusion is that the glueball interpretation is favored over that of a q< state. This should be encouraging for the lattice Monte Carlo studies, which predict a 0-+ glueball at 1.4 GeV (with sizable errors). Many experiments are on- going which will provide data on states in this region. Hopefully, the status of these particles will become more convincing in the near future.

A second glueball candidate is the 0(1640),(11) with J~~ = 2*. Again lattice studies predict such a sLate near this mass, while the bag model(12) puts it some- what lighter. The 2* qq states in this region have all been identified, so that the 8 must be something else. Again SU(3) invariance of the decays enters the phenomenology, this time more strongly. ~charre(l3) has noted that a glueball would decay 12 times as strongly into TIT vs

nn

(using SU(3) plus phase space), while the experimental limit is a factor of 20 below the prediction. This much violation of SU(3) would look bad for a glueball interpretation. ~chnitzer(l4) has a model of f, f', glueball mixing which can be adjusted to suppress nn for both the f' and the 8. I do not favor such a model because it requires rather arbitrary fine tuning, and some aspects of the model are now in conflict with f' and f production by two photons,(15) but it remains 2 logical possibility.

Other possible interpretations are as a

qqqq

state or qq plus a gluon, with some of the quarks being ss in order to explain the lack of an decays. All choices are consistent with the recent 6

+ g

results, which did, however, rule out a pro- posal that the 0 was simply an interference effect.(7)

0 0

An open question is whether the signal in J/++yp p is associated with the 0 or is a threshold effect. If it is the 8, the various interpretations using strange quarks are probably ruled out. A test of this is upcoming when the signal for J/+ +

~K*K*

is looked for. This has a different threshold and could sort out the origin of the signal.

There has also been the suggestion, (12*16) based on a variety of motives, that a 2* glueball could exist hidden near the broad f (1270) resonance. Some hints of such a state do exist. The 1980 Particle Data Tables list under

X(1410-1440) eight fairly low statistics experiments which have seen possible evi- dence for a state near 1.4 GeV. Since then this structure may have been seen in more experiments. A high statistics experiment(l7) measuring + mom0 finds that adding a 2* state at 1.4 GeV significantly improves the comparison with theory, although they refrain from strong claims about it. Likewise a good statistics experiment(l8) on IT p +K+K-n claims they can only obtain a good fit by introducing a tensor meson at 1.422

+

.009 GeV with

r

⁼ 80 f 42 MeV. The signal becomes more prominent at higher p,

.

Finally if one studies plots of $+yn+n-

(Mark 11) and ++ynono (Crystal Ball) one sees low statistics signals of inter- ference with the f(1270) at this mass value. My feeling is that these hints need to be taken seriously and that it is important to clear up the experimental sit- uation in this channel.

Other suggestions for glueball candidates include the overpopulated isoscalar J~~ = O* states(19) and the new evidence for resonances in the @$I final state.(20) I find the recent activity in meson spectroscopy encouraging because there appears to be hope that, through time and effort, we will be able to further unravel the origins of the hadron spectrum.

References

(1) SCHIERHOLZ G., invited talk at this conference (Session on lattice gauge theories).

(2) EDWARDS C. et al, Phys. Rev. Lett.

9

(1982) 259.

(3) CHANOWITZ M., Proc. of 1981 SLAC Summer Institute, Stanford 1981.

(4) DONOGHUE J.F. and H. GOMM, Phys. Lett. (1982) 409.

(5) CHANOWITZ M., Proc. of Particles and Fields-1981: Testing the Standard Model, Santa Cruz, 1981, ed. by C. Heusch and W. Kirk, p. 85.

(6) BELLINI G. et al., Phys. Rev. Lett.

48

(1982) 1697.

(7) COHEN I., N. Isgur and H. Lipkin, Phys. Rev. Lett.

48

(1982) 1074.

J. F. Donoghue

(8) HOLMES C., invited talk at this conference

(9) ROSENZWEIG C., A. Salomone and J. Schecter, to be published in Nuclear Physics.

(10) CARLSON C., J. J. Coyne, P. Fishbane, F. Gross and S. Meshkov, Phys. Lett.

99B (1981) 353.

(11)

EDWARDS

C. et al., Phys. Rev. Lett.

48

(1982) 458.

(12) JAFFE R. L. and K. !Johnson, Phys. Lett.

3

(1976) 1645;

DONOGHUE J. F., K. Johnson and B. A. Li, Phys. Lett. (1981) 416.

(13) SCURRE D., invited talk at Orbis Scientiae-1982, Coral Gables, to be pub- lished in the Proceedings.

(14) SCHNITZER H., Brandeis preprint.

(15) BURKE D.. invited talk at this conference (16) ROSNER J., Phys. Rev.

D24

(1981) 1347.

(17) CASON N. et al., Phys. Rev. Lett. g(1982) 1316.

(18) CHABAYD V. et al., Acta Phys. Pol.

B12

(1981) 575.

(19) ETKINS E. et al., Phys. Rev.

2

(1982) 2446.

(20) LINDENBAUM S., invited talk at this conference