ss Spectroscopy from the lass spectrometer

32

Nuclear Phy.slcs B (}'roe Suppl ) ~ (19S9) :12 :~'1 North-l|olland Amat~'rdam

s~ SPECTROSCOPY

FROM THE LASS SPECTROMETER*

D . ASTON, 1 N . AWAJI, 2 T . BIENZ, 1 F . BIRD, ~ J . D ' A M O R E , 3 W . DUNWOODIE, 1 R . ENDORF, 3 K . FUJII, 2 H . HAYAS][III,2 S. IWATA, 2 W . JOHNSON, 1 R . KAJIKAWA, 2 P . KUNZ, 1 D . LEITH, 1 L LSVINSON, 1 T . MATSUI, 2 B . MEADOWS, 3 A . MIYAMOTO, 2 ),I. NUSSBAUM, 3 H . OZAKI, 2 C . PAK, 2 B . RATCLIFF, 1 D . SCHULTZ, 1 S SHAPIRO, 1 T . SHIMOMURA, 2 P . SINERVO, 1 A . SUGIYAMA, ~ S. SUZUKI, 2 G . TARNOPOLSKY, 1 T . TAUCHI, 2 N . TOGE, 1 K . UKAI, 4 A . WAITE, j S. WILLIAMS 1

1Stanford Linear Accelerator Center, Stanford Unwcrs~ty, 2Department of Physzcs, Nagoya Unwerszty, 3 Umvers~ty of Cincinnati, 4Institute for Nuclear Study, Univcrszty of Tokyo

A b r i e f s u m m a r y is p r e s e n t e d of results p e r t i n e n t to s ~ s p e c t r o s c o p y d e r i v e d from high s t a t i s t i c s d a t a

on K - p

interactions obtained with

the

LASS spectrometer

at S L A C .

1. I N T R O D U C T I O N T h i s p a p e r s u m m a r i z e s r e c e n t r e s u l t s on s s s p e c t r o s c o p y o b t a i n e d f r o m an e x p o s u r e of t h e L a r g e A p e r t u r e S u p e r c o n d u c t i n g Solenoid (LASS) s p e c t r o m e t e r at S L A C to a K b e a m of 11 G e V / c .

T h e s p e c t r o m e t e r a n d r e l e v a n t e x p e r i m e n t a l d e t a i l s are d e s c r i b e d

elsewhere. 1'2 T h e raw d a t a s a m p l e c o n t a i n s N 113 m i l l i o n t r i g g e r s , a n d t h e r e s u l t i n g useful b e a m flux c o r r e s p o n d s to a s e n s i t i v i t y of 4.1 e v e n t s / n b . T h e a c c e p t a n c e is a p p r o x i m a t e l y u n i f o r m over a l m o s t t h e full 4~r solid angle.

2. s s S P E C T R O S C O P Y A p r i n c i p a l o b j e c t i v e in s t u d y i n g m e s o n s p e c t r o s c o p y is t h e precise definition of t h e level s t r u c t u r e of t h e a n t i c i p a t e d q ~ m e s o n s t a t e s . T h e q u a r k m o d e l level d i a g r a m is e x p e c t e d to t a k e t h e f o r m 3 i l l u s t r a t e d q u a l i t a t i v e l y in fig.1 for t h e c h a r m o n i u m s t a t e s . 4 Here S a n d L denote total quark spin and orbital angular momentum, respectively, and C indicates t h e c h a r g e c o n j u g a t i o n p a r i t y of the r e s u l t i n g m e s o n s t a t e .

Tile p a r a - c h a r m o n i u m levels

* Work supported in palt by the Department of t~nergy under contlact No DI~;-AC03-76SF00515, the National Science Foundation under grant Nos PHY82-09t44, PHY85-13808, and I Japan U.S. Cooperatlve Research Project on High Energy Physics,

Invzted talk presented by W.Dunwoodze at th,' IX European Symposium on Antzproton- Proton Interactwns, Malnz, September 5-10, 1988

0920-5632/89/$03.50 (g) Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

W. Dunwoodie et al./ sg spectroscopy

S=O !

S,1 2

C • (-I) L+s

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(c~ LEVEL SCHEME}

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3

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(C~VI{: 2)

B

Fig.1. T h e quark model level diagram for the c h a r m o n i u m states; the mass scale is only qualitative.

Fig.2. The K K mass projections for reactions (1) and (2). 250

~0

i

I

i

I

~

I

'

I

2OO

LASS (x 0.t27)

70

i

i

I

!

(a)

ISol ~

150

MARK TT1

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%

50

5o 0

tO0

40

0

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i

,

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O I

1.0

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1.2

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w

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IA

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MK~K~

(GeV/c t)

t

I

1.8

Fig.3. T h e K soK s0 mass distribution f r o m reaction (1) and t h a t from radiative J / ¢ decay 1° from threshold to 1.9 GeV/c 2.

I 1.2

M~

I 1.4

I 1.6

t 1.8

(GeV/c5

Fig.4. T h e S wave intensity distribution (a) from reaction (1), and (b), from reaction (2) at 8.25 GeV/c. 12

34

W. l)unu'oodie et al. / ss spectroscopy

are singlets, whereas the o r t h o - c h a r m o n i u m levels, other than oS, are triplets separated m mass due to spin-orbit interaction. Within each column, the lowest-lying state is the ground state, and the higher states correspond to radial excitations of this state. The leading orbital excitations are the ground states with largest total angular m o m e n t u m , J, and, for the triplet levels, the remaining states are termed the underlying states. In e + e - collisions, the 3S tower of states is readily accessible, while information on the leading orbital excitations with J _> 3 is lacking, and that on the corresponding underlymg states is sparse. Results of a c o m p l e m e n t a r y nature are obtained from hadronic interaction experiments, where production of the leading orbital states predoinmates, and information on the underlying and radially- excited states requires careful amplitude analyses of high statistics data. The present experiment provides such data on the mainly s s meson states. The resulting light quark level structure is related to the nature of the long-range (i.e.confining) part of the q ~ interaction, and thus, in principle, provides information on non-perturbative QCD In practice, it enables us to learn about QCD potential models incorporating relativistic corrections.

5

The processes most relevant to the study of s ~ (i.e.strangeonium) spectroscopy are those in which a K K

or KK~r system is produced against a recoil hyperon.

However,

in recent years candidate glueball states which also couple to these meson systems have emerged from the study of J / ~ decay. Consequently, it has become increasingly important, to define the quark model level structure in order to distinguish those states which may be of different dynamical origin. In the present experiment, the relevant reactions which have been studied are K - p --* K soK s oh ~ ,

~

K-p -, K-K+Aseen

(1)

(2)

and K - p ~ K~0 sK

±

7: Asee,~

(3)

They are characterized by peripheral (i.e.quark exchange) production of the meson system, and it follows that the creation of glueball states should be disfavored in such processes. T h e corresponding d a t a samples are very clean, and amplitude analyses have been performed, 2'6'7's the results of which are summarized here. The raw K K mass distributions for reactions (1) and (2) (fig.2) differ, since for the former only even spin states are produced. In addition, for reaction (2), the mass region

W. Dunwoodie et hi./sg spectroscopy

35

above ~1.7 GeV/c 2 is dominated by the reflection of diffractive production of low mass AK + systems. 9 In fig.3, the K s0K s0 mass spectrum from reaction (1) is compared to the MARK III data on radiative J/~b decay 1° in the mass region below 1.9 GeV/c 2 (the LASS data have been scaled to the M A R K III data at the peak of the f'(1525)). Both spectra show a small, but intriguing, threshold rise, 2'11 followed by activity in the f2 (1270)/a2 (1320) region and then the large f~(1525) peak. At higher mass, the M A R K III spectrum is dominated by the f2(1720). There is no evidence for any such signal in the LASS distribution, and the upper limit on the production cross section is 94 nb. at the 95% confidence level; it should be noted also that there is no evidence for f2 (1720) production in reaction (3) in the •

present experiment

6

(cf.fig.9f). These results indicate that the f2(1720) is indeed a strong

candidate glueball state• The amplitude analysis of reaction (1) 2 yields the S wave intensity distribution of fig.4a. Although the uncertainties are large, the data seem to peak in the range ~ 1•5-1.6 GeV/c 2. A similar distribution (fig.4b) has been obtained in an analysis of reaction (2) at 8.25 GeV/c, 1~ and there are indications of S wave structure at this mass from the data on reaction (2) in the present experiment. These results suggest the existence of a 0 + state in this mass region which is naturally interpreted as a partner of the f~ (1525) in the 3p ground state. It is not clear whether this state might be identified with the f0(1590). 13 An immediate consequence of this observation is that the f0(975), which is usually assigned to this multiplet, may well be a weakly bound K K system, 14 or be of some other non-q~ origin. This is discussed at greater length in ref.2. For the K K system in reaction (2), the acceptance corrected spherical harmonic moments (tL M = X/~-~N(YLM~; L _< 8, M=0) in the t-channel helicity frame are shown in fig.5 for the mass region 1.68-2.44 GeV/c 2, and t ~ <_ 0.2 (GeV/c) z. It should be noted that amplitudes with spin J can contribute to moments with L_<2J. There is a peak in the mass spectrum, t °, at .~ 1.86 GeV/c 2, and similar structure is present for all moments with L < 6, but is absent for L > 7. This, together with the absence of such a signal for reaction (1), 2 indicates the presence of a j P c = 3 - - , mostly 85 state. A detailed analysis of this region 7 yields the total F wave intensity distribution of fig.6a for t' < 1.0(GeV/c)Z; the fitted curve gives BW mass and width 1855 4- 22 and 74 ± 67 MeV/c 2, respectively. A similar fit to the mass spectrum (fig.6b) gives parameter values 1851 4- 9 and 66 4- 29 MeV/c 2, in agreement with previous measurements from the mass distribution only. is,16 It should be noted that the spin of this state, which is listed as the ¢j(1850), 4 is established by the LASS data, and that the mass and width have been estimated for the first time on the basis of an amplitude analysis.

W. Dunwoodie et al /s~ spectroscopy

36

i

i l i l

400 -

i

I

J

[

~

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300 ~

++++d+++++ t++#++ ++++++ .++_+t'_ '~÷' i

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400

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400 i

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.

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.

r,

,0 .

200

1ooo 1 750 I~

.

116 2[0 2]2 214 16 lib 210 212 214 i~- ~* {GeV/c2 }

b

500 ~ [ 25O o

Fig.5. The mass dependence of the unnormalized spherical harmonic moments of the K - K + system from reaction (2) in the region 1.68-2.44 GeV/c 2 and t' < 0.2(GeV/c) 2.

J--~l 18

Mds,

19

I _! 2

(GeV/c c)

Fig.6. (a) The total F wave intensity distribution, and (b) the mass distribution from reaction (2) in the Ca region. (c) The F wave intensity distributions from reaction (2) (solid dots) and reactions (3) (open dots).

50 •

LASS {x044)

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MARK ]TI

40

200 >

i

i

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i

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~-150

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i

) 20

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24 (GeV/c2)

2.6

0

I

I

I

I

1.5

2.0

2.5

3.0

MI,(~K~Tr;

Fig.7. The K~K~ 0 0 mass distribution from reaction (1) and that from radiative J / ¢ decay z° in the mass range 1.8-2.7 GeV/c 2.

3.5

(GeV/c ~}

Fig.8. The combined raw KKTr mass distributions from reactions (3).

W. Dunwoodie et al./ s$ spectroscopy

37

A significant J P = 3 - signal (fig.9g) has been obtained in the ¢3(1850) region from the partial wave analysis of reaction (3). 6 This signal, after all corrections, is shown in fig.6c (open dots) in comparison with that from reaction (2) (solid dots); the branching ratio obtained is BR[(¢3(1850) --* ( K * K + c.c.))/(¢3(1850) ---* KK)] = 0 "~.~+0.8s in agreement ~-0.45' with theory, s The ¢3(1850) is interpreted as belonging to the 3D 3 quark model nonet which also includes the p3(1690), the w3(1670), and the K](1780). Using current mass values, 4 the mass formula 17 yields an octet-singlet mixing angle of ~ 30 °. This indicates that the multiplet is almost ideally mixed, and that the

¢3(1850) is

an almost pure s~ state, in

accord with its production characteristics. The analysis of the ¢3 region 7 has shown that the peaks observed in fig.5 are due to interference between the resonant F wave and the approximately imaginary amplitude describing the diffractive production of the low mass AK + system. In fig.5, there is also a small signal in every moment with L _> 1 at -~ 2.2 GeV/c2; no such signal is observed for L >_ 9. This indicates the existence at this mass of a small, resonant 4 + amplitude which interferes with the large, imaginary, diffractive background, just as for the ¢3. An •

•

analysis based on this interpretation

8

yields mass and width values of 2209 +17 and 60 --15

+107 --57 MeV/c 2 for this jPC = 4++ state. These values are consistent with those obtained by M A R K III for the X(2220), l° and with a signal in the r/rf mass spectrum observed by the d A M S collaboration•IS

The K K mass distribution from reaction (1) in this region has

been shown 2 to be very similar to that observed for radiative J / ¢ decay (fig.7), and, in addition, a recent amplitude analysis of the M A R K III data has yielded evidence that the X(2220) may indeed have jPC = 4++ .19

All this indicates that the X(2220), which has

been conjectured to be a glueball state, may instead be a member of the quark model 3F4 ground state nonet. The raw g K r

mass spectrum for reactions (3) (fig.8) exhibits a small signal at the

f1(1285), followed by a rapid rise at K K * threshold to a peak at -~ 1.5 GeV/c 2, and a second peak at -,, 1.9 GeV/c 2. The low mass structure is similar to that observed at 4.2 GeV/c. 2° An amplitude analysis 6 yields the partial wave intensity distributions of fig.9. The low mass peak is associated primarily with 1+ waves, while the 1.9 GeV/c 2 bump is due mainly to 2 - and the 3 - contribution discussed previously. Only K* or K* isobar production is important; amplitudes involving the a0(980) are negligibly small. The 1+ intensity at low mass shows a pronounced asymmetry in favor of the K* isobar, and also exhibits K*-K* interference, which is destructive near threshold, and constructive at -~ 1.5 GeV/c 2. This suggests the existence of two 1 + states of opposite G-parity in this region.

38

W. Dunwoodie et al./s~ spectroscopy

The corresponding jPG amplitude combinations yield 1++ and 1+ - production intensity distributions (fig.10) which ~ e well described as BW resonances of mass 1.53 -4- 0.01 and 1.38 -4- 0.02 GeV/c 2 respectively, with corresponding widths 0.10 -4- 0.04 and 0.08 -4- 0.03 GeV/c 2. The 1++ state confirms an earlier observation, 2° while the 1+ - state is new. If these are isoscalars, 2° the lower mass state, the h1(1380), completes the J P C = I + - ground state nonet, while the higher mass state, the f1(1530), is a strong candidate to replace

fx(1530) in this nonet gives a

the E/fx(1420) in the corresponding 1++ nonet. Use of the

mixing angle ~ 55°; this implies that the f1(1530) is mainly s~ and that the f1(1285) has little a ~ content, in agreement with their production characteristics. This is not the case when the E is used, since its production properties are not consistent with the predicted large s~ content. Finally, a previous analysis 21 of the 1++ nonet made use of the E mass and width to predict an al mass of ~ 1.47 GeV/c2; when the fl (1530) mass and width are used instead, the predicted mass is ~ 1.28 GeV/c 2, in much better agreement with the accepted value. 4 The 1 + states observed in the present experiment satisfactorily complete the ground state 1P1 and 3P1 quark model nonets. Furthermore, the small spin-orbit interaction ira-

1000

400

(a)

1+*o ÷ ~ i ( d1+')04

('b) 1"

800 200

!o

600

~

400

m

400

(b) 1+41*

~,~ 200

+ o

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(~)

I

I

(d) I-

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200

,

o

~200 0

I

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?.

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z ~"

PhaseSpace

400

(e) 1~'1-

,

1

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200

200

1.41.61.8 2 M~

1.4 ..4"1.6

!.8

2

16 l.B 1.4

1.6

18

M~,~ (oev/~~)

(oev/c ~)

Fig.9. The intensity distributions corresponding to the partial wave decomposition for the KK----~ system in reactions (3).

Fig.10. The G-parity eigenstate intensity distributions from reactions (3) labelled by JPGM", where M is the helicity and ~ the naturality of the t-channel exchange.

W. Dunwoodie et al./s$ spectroscopy

39

plied w h e n the new i n f o r m a t i o n on the 0 + is also t a k e n into account c o n t r a s t s m a r k e d l y with t h e c o r r e s p o n d i n g b e h a v i o r in the c h a r m o n i u m sector. son as a q~ s t a t e is dubious.

T h e s t a t u s of the E me-

However, it m a y be t h a t its p r o x i m i t y to K K * thresh-

old is significant in t h a t it could be a K K * molecule or f o u r - q u a r k s t a t e of s o m e kind.

3. C O N C L U S I O N T h e p r e s e n t e x p e r i m e n t has m a d e significant c o n t r i b u t i o n s to the u n d e r s t a n d i n g of s spectroscopy. D a t a analysis is continuing, a n d f u r t h e r results will be f o r t h c o m i n g on the prod u c t i o n of m e s o n s y s t e m s such as K* K* against a recoil A.

ACKNOWLEDGEMENT We are very grateful for the s u p p o r t of the technical staffs of the c o l l a b o r a t i n g institutions.

REFERENCES [1] D. Aston et al., The LASS Spectrometer, SLAC-I~EP-298 (1986). [2] D. Aston et al., Nucl. Phys. B301 (1988) 525. [3] W. Grotrian, Graphische Darstellung der Spektren yon Atomen und Ionen mit ein, zwei und drei Valenze]ektronen (Springer, Berlin, 1928). [4] Particle Data Group, Phys. Lett. 170B (1986). [5] S. Godfrey and N. Isgur, Phys, Rev. D32 (1985) 189. [6] D. Aston et al., Phys. Lett. 201B (1988) 573. [7[ D. Aston et al., Phys. Lett. 208B (1988) 324. [8] D. Aston et al., DPNU-88-24 / SLAC-PUB-4661 (1988), to be published in Phys. Lett. B. [9] D. Aston et al., SLAC-PUB-4202 / DPNU-87-08 (1987). [10] R.M. Ba|trusaitis et al., Phys. Rev. Lett. 56 (1986) 107. [Ii] K.L. Au et al., Phys. Rev. D35 (1987) 1633. [12] M. BaubiUier et al., Z. Phys. C17 (1983) 309. [13] D. Aide et al., Phys. Lett. 201B (1988) 160, and references therein. [14] J. Wehnstein and N. Isgur, Phys. Rev. Lett. 48 (1982) 659; Phys. Rev. D27 (1983) 588, and references therein. [15] S. A1-Harran et al., Phys. Lett. 101B (1981) 357. [16] T. Armstrong et al., Phys. Lett. ll0B (1982) 77. [17] M. Gell-Mann, Caltech report TSL-20 (1961) unpublished; S. Okubo, Prog. Theor. Phys. (Kyoto) 27 (1967) 949. [18] D. Aide et al., Phys. Lett. 177B (1986) 120. [19] T.A. Bolton, Ph. D. thesis, M.I.T. (1988) [20] Ph. Gavillet et al., Z. Phys. C16 ~1982) 119. [21] R.K. Carnegie et al., Phys. Lett. 68B (1977) 287.