ψ → γνπ+π−

Nuclear Physics B (Proc. Suppl .) 21 (1991) 132-135 North-Holland

132

STUDY OF THE RADIATIVE DECAY J/~! , -~ M. BURCHELL CERN (European Laboratory for Particle Physics) . R-presenting the MARK III Collaboration- (SLAG) . We present a Partial 1Vave Amplitude analysis of the rlr,+r, - system seen in J/t, -> yyir+r -, for zl~+r masses in has the range 1 .2 ~ 1.5 GeV/c2. XVe find evidence for two states . both decaying via aô (9S0)7r:F . One resonance 2 and width .IYC = 1++, and we associate it with the fl (1255) . The other has Jpc = 0-+, mass 1 .400 f 0.006 GeV/c 0.(1-1 :3 + (1_01:3 GeV/c2. The Branching Fractions for radiative J/-0 decays to both states are commensurate, arguing against the interpretation of the 0-+ siate as a gluebail .

1. INTRODUCTION Radiative .1/z:, decays are considered to be a good

laboratory for the study of light mesons . They are co-

piously produced, being some ï or S'X of the total rate in

JA_ ,

decays . In such decays the well defined initial

has presented" the results of a. Partial Wave Ainplit ude (PXVA) analysis of the li Ii 7r system seen in J/~, -->

(see also these proceedings) . XVe present here a similar P1VA analysis of yr+r - seen in J/V' -4 yz17r+ 7. - . iii li r;

predominantly via a single intermediate resonance. It

2. EXPERIMENTAL DETAILS AND RESULTS The ~IarkIII experiment, at the SLAG c+e- storage ring SPEAR. accumulated data. for 5.8 x 10' J /v de-

system in these decays couples to channels with JP` 0++ , O-+, -)*+ ... .. i .e. the quantum numbers accessible

for tracking charged particles, surrounded by barrel and

state ec system decays to a I and a pair of gluons . The gluons in turn couple to the observed final state mesons . has been noted since many years that the gluon-gluon

to two transverse (massless) gluons : This is the prcscripton for a glueball (a bound gluon-gluon state) .

Two strong glueballs candidates nave been observed

cays . The detector is described ill detail elsewllere s and is basically a -lr detector . with a central drift chamber endcap electromagnetic calorimeters . all inside a 1 .5T magnet .

For the decay

iiir+7r - we select events sat-

-, ill J/z, . .V . the iota' and tlly theta .` Recent atlalysis by the Mark- 111 of the theta is reported elsc "tyhere irl

isfying -lc lcinematic fits to either A yyyr+r - (cor responding to il or B îîiz+z r+r,

rnetrv brealcillg, the 517( :3) flavour and colour singget

quired imposing the il and z' mass constraints (5c for A, 6c for B) . 'I'lle iir+r - mass spectra for the selected

these proceedings . Here we consider the iota, wllicll is seen ( lecavillg l)roftisely to li I~ r . In the al)sellce of s~-rtlgluon-gluon system should couple equally to three pseii

closcalars such as li li r and il ;. r. Further it leas been claimed that the iota decays to li Ii r via o 0 (!)SO)-.+, and the a t, (!)SO) is kllowll to also decay <
-r

'1 1/7 77

Ilr .

1'lltls foe both reasons the decity

illcl'its c1os v st tlcl~' . Ilcccllt ly t Ile 1IiirlcI I I

'Pile illllllllllllll photon energy cut is 100 1le1* for A and ï0 ~Ic1 for B. Further lcinelnatic fits are re-

events are shown ill fig. 1 . 'l'lle main feature" is the Il', and we lneatillre the BI3(J/1! . -+ iii') to be : A 01 .50 f 0.1-1 f0 .:i :3) x 10 - ' 1 alld B (-1 .:30~0.:3I f0 . ï 1) x 10 -`~ . Tlie resuli s are compatible wit 11 previolts measurement- `.~~ This illdicates Illat tlle event reconstructioll and selvc-

"l'lle 11arIci1I is sllp1mrted ill Irlrt by Ille l'llited Sl ;it (,s I)c.llflrillivil) ()l' Vllerl;y (colltract --~ I)I~.- :1('(I :1-î6Sl'I)Il ;il :l . 1)l~:M'02-î61'MOl 195. DF- :1('03-8IFl{-100)l1. I)2- .\\I03-î6Sl'00010 ;111d 1)F-W()2 - S îl'Ji I031S) alld IIle Nali(i11 ;1I Sciellco l'olll ldilt ioll 0920 5632/91/$03 .50

19!)l

I:Isc!vic.r Scietice Pllblisllers II;.V . (Nordi-Ilollaucl)

M. Burchell/Study of the radiative decay J/0 --ygr+r-

A

Û 160 120 NO O O 11-1

w

200

100

N

U

75 50 CD N 25 O Ô 0

80 40 0 C

40

w 0 .92

0.96

C

1 .

100

Ô O "- 80 4-1

\ to 40

20

133

20

w 1

1 .7 2 .4 3.

Mass, GeV/c'

40 0.75

1 .25

Mass, GeV/c 2

Figure 1 : The 777rt7r- invariant mass (A,B for 77 -} -y-y, C,D for y -+ 7r+7r-7r°). A,C are the 7l' region, B,D are higher masses.

Figure 2: The yrf invariant mass where 1.2 < mass < 1 .5 GeV/c2 . A : ri -~ -y-y, B: n -+-,r+ir-7r°.

tion procedures are understood. If we select the ilr+7r- mass range 1 .2 -> 1.5 GeV/c2 , we can plot the associated n7r± masses (fig. 2) and a signal is seen for the a,± (980). Equally we can select events with mass(r17rt) compatible with an ao(980) and then plot the r7r+7r' mass (fig. 3). Looking at figs. 1 and 3 structure can be seen in the 1 .2
also tried the parametrization of Flatte' but find no change in the results), and for the fo(1400) we use a parametrization of the 7r+7r - phase shift observed by the LASS experiment at SLAC9 . The separate amplitudes are added with complex coefficients to allow for both relative magnitude and phase . A phase space term is added incoherently to allow for any background. A fit was made to the data in figs. 1 b,d in 20 MeV/c2 bins. We found that the 1++ fo(1400)77 amplitudes are not populated . The 0-+ fo(1400)r7 amplitude is populated but shows no sign of any resonant behaviour . Further if this amplitude is dropped from the analysis the fraction of events previously assigned to it is almost exactly reproduced in the previously empty background amplitude and there is no significant change in the lg(L) per bin in the fit . We thus removed all the fo (1400)ri amplitudes and repeated the analysis . The results are shown in figs. 4 (magnitudes) and 5 (relative phases) . Signals are seen for two resonances, in both variation of the magnitudes and relative phases of the amplitudes. Concentrating on the better statistics channel A (,q -+ -y-y) we see a signal around 1 .3 GeV/c2 in the JPC(X) = 1++ aô (980)rß amplitudes (the results in figs. 4 a,c are for both spin 1 helicities combined) . In

134

M. Burchell/Study of the radiative decay J/V -, yria+r

of a = 11 MeV/c2 for detector resolution) . The excess

of events above the expectation at masses around 1 .32

GeV/c2 is not explained but is a persistent feature of

U 50 N O O

the analysis . We find no variation in efficiency over the mass range 1.2 to 1.35 GeV/c 2 . Using the number of

25

events under the solid curve as an estimate of the signal strength we find BR(J/~, --, -yf,(1285)) BR(f,(1285) -., aô (980)7--+)

2

BR(aâ(980) -*

(2 .60 ± 0.28 ± 0.51) 10 - '' .

zjrrf) =

The first error is statistical, the second svstelnatic . Note

that the systematic error includes no contribution for

10

the correctness (or otherwise) of the division of observed events in the amplitude into,fl (1285) and un-

0

Figure 3: The 11 -~ ;,+r-r,° .

Mass, GeV/c' invariant mass : A q

known other events . In figs . 5 a,c we show (solid curves)

the expected phase motion for a resonance assuming its B

the mass region 1 .'26 to 1 .3 GeV/c2 we find the ratio of

lielicities (hel . 1/liel . 0) to be 0.63±0.'2'2 (in analysis B we find 1 .08 ± 0.47) . The part, of the signal compat ible" with a fl (1'285) is shown by a solid curve (representing a

shape is as given by the solid curve in fig. 4 a.

In the 0- + aO (980)7--+ amplitude a. signal is seen (fig. 4 b) and we fit, it with a BW (mass and width free) again convoluted with a gaussian for detector resolution

(this is the solid curve shown) . XVe find : Mass = 1 .400±

0.006 GeV/c 2 . widt.11 = 0.046 ± 0.013 GeV/c 2 . The efficiency is again found to be fiat in the signal region . We obtain :

N

U 1-1

>

4

0 N O O \

6

c

4

w

2

Mass, GeV/c'

Figure 4 : Magnitude of the amplitudes ill the chaiiiivI 7l -+ il : (a, ) I ++ e1ô (980)7rß ; (b) 0 - + a ct(980)7r+ ; (C) Background ; d,e ,C. f are reslxrt.iycly the saille for the r/ -+ 7<+7r- 7r 0 cliatlllel . Br vit, - Wigiier cllrvc~ with Illass ii11d width froth t 1w l'iir_ tick. Dilua ('r0111) tables,~' ( . o1lvol11t.ed with }I gllllssiiIII

6

0

4t+

1 .2

I

1 .29

1 .38

0

++ 1 1 .3

1 .4

1 .5

Vass, GeV/c' Figl1rc , 5: l'hiISV 11106011 01' a}(980)7r+ iIlul)litllclc , s 01' 0_i. -+ 11 ( . 11FI1111e1): a) I++ reljlt.i%, ( . to 0-+, b) I-elatiye to I ++ . c,d ;11 .( . l'especliyek , tlle Same fol. Ow 11 °--+ 7r + 7r a 7r 0 chiIIIII(A . (1l

135

M. Burchell/Study of the radiative decay J/0 -" ymr+z

BR(J/V, --> -yA'(1400)) BR(X(1400) -i aô(980)7r+) BR(aô (980) -; rr}) = (3.38 f 0.33 f 0 .59) 10- . In figs. 5 b,d we show the expected phase motion (solid curves) for a resonance with mass and width as found by the fit to fig. 4 h. 3. CONCLUSIONS In the PWA amplitude analysis we see signals (both in magnitude and relative phase motion) for two rl7r+7rresonances. One we associate with the fl (1285). The identity of the other (with J"= 0-+) is unknown . When considering the various possibilities for the latter (qq meson, glueball ..etc) we should consider the following: e Is it seen in any other channel ? In fig. 6 we compare our 0-+ signal with the aô(980)ßr+ 0-+ spectrum in KK7r seen by this experiment in a PWA analysis of J/0 -4 yK Kir, and also with the aô(980)7-,+ 0-+ amplitude seen by Ando et. all° in 7r - p --+ q7r+7r - n. Good agreement is seen for the mass and width of signals seen in all three analyses . e Is the signal the expected radial excitation of the rt or 7l' ? If the 77(1270) is the radially excited q, then given the 7l- q' mass difference, our signal at 1 .4 GeV/c 2 is a bit low in mass for the excited rt' . However this large mass difference may not be repeated in the excited states; this is a grey area. Note also that since BR(J/0 --+ y7l') >> BR(J/0 --> yrl) it is quite plausible to see the excited 71' without a strong 71(1270) signal . e We see no other structures in the 7t7r+7r - system, unlike in the KK7r analysis where several other structures are seen. This indicates a significant difference between J/0 -+ yrt7r+7r - and J/0 -+ yKK7r . e Finally note that we see the 1++ fl (1285), which cannot couple to two transverse (massless) gluons (it needs a. longitudinal gluon component), at a rate similar to that for the 0-+ state. This argues against any special mechanism (e.g. glueballs) being favoured by the coupling to two massless gluons. We thus conclude that whatever the nature of the 0'+ state we see at 1.4 GeV/c 2, there is no compelling need to consider it as a glueball .

Mass, GeV/c'

Figure 6: Measured aô(980)7-,4: 0-+spectra from PVVA analyses of a) 7r - p -+ rt7r+7r -n lo , b) this analysis (where the results are from the analysis which included the fo (1400)q waves), and c) J/?p --> yK0Kf7r~ ref". REFERENCES [1] D. Scharre et al., Phys . Lett . 97B, 329 (1980). C. Edwards et al., Phys. Rev. Lett . 49, 259 (1982). J. Richman, Proc. XXII Rencontres des Morionds. Les Arcs, France, 1985. [2] See the 1990 Particle Data Group Tables 3. meson full listings pVII.56 [3] Particle Data Group Tables, Phys Lett . B239. 1 (1990). .,j Z. Bai et al ., SLAC-PUB 5275, submitted to Phys. Rev. Lett . [5] D. Bernstein (1983).

et al.,

[6] J.E. Augustin

Nucl. Instr. and Meth. 226, 301

et al.,

Phys. Rev . D42, 10 (1990) .

[7] N. A. Torngvist, Ann . Phys. 123, 1 (1979) ; M. Roos and N. A. To-,ngvist, Z. Phys. C5, 205 (1980) ; N . A .Torngvist, Acta Phys. Pol. B16, 503 (1985) ; N . N. Achasov, S. A. Devyanin and G . N. Shestakov, Sov . J . Nucl . Phys. 32, 566 (l980) . [8] S. Flatte, Phys. Letts. B63, (1976) 224 . [9] Private communication . A standard relativistic B .W. with width between 0.1 and 0.4 GeV/c2 was also tried as the propagator, and yielded no discernible difference in the results .

[10] A. Ando et al., Phys. Rev . Lett . 57. (1986) 1296.