ψ decay into five pions

Nuclear Physics B320 (1989) 1 19 North-Holland, Amsterdam

STUDY OF THE J/+

DM2

D E C A Y I N T O FIVE P I O N S

Collaboration

J.E. AUGUSTIN, G. COSME, F. COUCHOT, F. FULDA, G. GROSDIDIER, B. JEAN-MARIE, V. LEPELTIER, F. MANE, and G. SZKLARZ Laboratoire de 1',4ce~ldrateur Lin{aire, Universitd de" Paris-Sud, F-91405 Orsav, France

D. BISELLO, G. BUSETTO, A. CASTRO, L. PESCARA, P. SARTORI and L. STANCO Dipartimento de Fisica dell'Universitgl di Padova, e INFN, Sezione di Padova, 1 35131 Padua, ltah'

Z. AJALTOUNI, A. FALVARD, J. JOUSSET, B. MICHEL and J.C. MONTRET Laboratoire de Physique Corpm'culaire, Universitd de" Clermont I1, BP 45, F-63170 A ubibre, France

R. BALDINI and A. CALCATERRA Laboratori Nazionali di Frascati dell'lNFN, CP 13, I 00044 Frascati, Italy

Received 15 Februaw 1989

A high statistics study of the J / ~ ---, w +v - v ~~r ~v° decay is performed from the 8.6 million J / + ' s produced by the DM2 experiment at DCI. 0- and ~o-associated production is evidenced and branching ratios for 0a2(1320), inclusive ~o~r+v , ~of2(1270) and bl+(1235)~v~ dynamics are given. In the w~r+~r final state a bump is observed at a low (~r+~r) mass and a possible 0)f0(975) contribution is discussed. Moreover first measurement of J/'+ --, ~0v% ° is reported and branching ratios for this decay and for 0~f2(1270) and bl(1235)~r {}dynamics are given. Evidence is found of the low ( v v ) mass bump observed in the charged mode.

1. Introduction The

8.6 m i l l i o n J / ~ ' s

produced

by the DM2

experiment

at D C I ,

the Orsay

c o l l i d i n g r i n g , a r e u s e d to s t u d y t h e d y n a m i c s p r e s e n t i n t h e J / ~ ~ 5~r d e c a y . T h e J/+

---, ~-+v

MARK

w+Tr-Tr ° d e c a y c h a n n e l h a s a l r e a d y b e e n s t u d i e d b y t h e M A R K

II [2] a n d t h e P L U T O

[3] e x p e r i m e n t s .

0550-3213/89/$03.50;~Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

I [1],

2

J.-E. Augustm et al. / J / ~ ~ 5pions

The high statistics accumulated by the DM2 experiment makes it possible to refine hadronic spectroscopy and to search for rare processes contributing to this decay. Dynamical analysis of final states involving o~-production is presented in detail. Related channels, namely ()Tr~r, @KK and ~0KK were analyzed in a previous paper [4] in which the whole study of J / + decays into Vector + Tensor in the SU(3) symmetry framework has been presented. The 0a2(1320 ) dynamics is also evidenced. Finally first measurement of J/q~ ~ ~oTr%r° decay is presented along with the dynamical analysis of such a final state.

2. Experimental set-up The DM2 magnetic detector (fig. 1) is described in detail elsewhere [5]. Its main features relevant to the present analysis are summarized in the following.

l~.~,',/ ' , - ' / ~ I ~I'I II Ir I I

'7-~-~

r,

MUONDETECTOR FLUXRETURNYOKE

[---r-~,,~5,~---~r--~4..t~/...(-~[--~.~!~L

/ PHOTONDETECTOR

'''~

°M, ~~~~~'~"~G

i ~.~i DMRwlFCHAM pTc BER

HI ITM/tlf(L(Lf//fffd?,f~t~\~i~ IVi-T11HVAI

VACUUMPIPE

1~J,'~'~t~'

TOF

7)

"I//j'

CERENKOVCOUNTER

COUNTER

3R

YOKE

CTOR !R

'OR

Fig. 1. DM2 experimental set up: (a) transversal view; (b) longitudinal view.

J. E. Augustin et al. / J/@---' 5 pions

3

Two proportional and 13 drift chambers in a 0.5 T magnetic field measure charged track momenta over 87% x 4~r sr. with a resolution of 3.5% at 1 GeV/c. Outside the coil, the photon detector barrel is divided into 8 octants, each of which consists of 14 planes of delay line-streamer tubes separated in 4 groups by 5 layers of scintillator counters. Showers are measured in a total of five X 0 lead, eight 0.25 X o layers followed by six 0.5 X 0 ones. The barrel covers 70% × 4Tr sr. with a detection efficiency greater than 96% for Er> 110 MeV. The photon direction resolution from the apex measurement is 10 mrd in azimuth and 7 mrd in polar angle. Matching is performed between the charged tracks and the tracks reconstructed in the photon detector in order to distinguish true photons from fake ones induced by ~r and K interactions in the coil or in the photon detector. The photon energy is measured by combining the information on the number of tube hits and the A D C signals. The resolution scales as 0.19/~/E(GeV) below 300 MeV and stays at the level of 35% above 300 MeV. The two end-cap photon detectors placed inside the magnetic field and covering 12% of the solid angle have been used in this analysis only as a veto due to the small angular resolution and the lack of energy measurement. 3. Event selection 3.1. ~ + v

7r~

~0 C H A N N E L

Four track total charge zero events with one or two detected photons have been selected if the charged particles momentum is greater than 62 M e V / c (2% of the

'-%-0 5 ,=, 4 c~

2

0 -10

0

10

20

30

40 x 103

Fig. 2. Y7 squared mass for 4C2 y events.

4

J. K Augustin etal. / J / ~

5pions

J / + mass), and if the reconstructed energy, assuming pions for the charged particles and the missing momentum, is equal to the J / + mass within 125 MeV. Events with two detected photons are kinematically 2C-fit. One gets two categories of events: if the X 2 is lower than 14 and the two photon mass lies within the 0 - 1 9 0 M e V / c 2 range (fig. 2), the two photons from the 7r° decay have been detected and the event is sorted in the 4C2~, sample providing each calculated photon energy to be greater than 20 MeV and the cosine of the angle 0* between the photon and the Tr° direction in the ~r° rest frame to be lower than 0.98. If one of the cuts is not satisfied, either the event is not a v+~r-~r+~r-v ° event or at least one of the two detected photons is a fake one. Such events are added to the one-detected photon events to form the 4 C I y sample. This last sample is contamined by ~r+~r-~r+~r "f events whose total energy distribution is nearly identical to that of the five pions. However the decay branching ratio [6] is 6 times lower than the ~r+~r-~r+~r-~r ° one. Consequently, the 4C1~, sample will be used only for dynamics studies which bring additional constraints. 3.2. ~r+v ~r%% ° CHANNEL

Two charged track and six photon events have been selected. The two oppositely charged prongs must come from a common vertex within the interaction region. The six photons have to be detected in the barrel and to be separated by more than 10 degrees in space. Events are processed through two kinematical fits: a 4C fit to isolate real ~r+v-67 events (X 2 < 25), and then a 7C fit to get ~r+Tr 3Tr° candidates (X 2 < 12). The X 2 cuts have been set from a Monte Carlo study. In the 7C fit, 15 combinations being possible to construct three 7r° from six photons, the one with the lowest X 2 is retained. Furthermore all the photon energies must be greater than 20 MeV. In order to eliminate fake Tr°'s from very unbalanced photons the cosine of the previously defined angle 0* must be lower than 0.98 for all three v0,s. This cut rejects an additional 1% of the Monte Carlo events and 3% of the experimental sample. C o m p a r e d with the Monte Carlo, the X2c distribution of the accepted events indicates the presence of residual background and these events will be used only for dynamics studies.

4. Analysis 4.1. J / ~ - - - * ~ , n

~'+,rr ~.0

Only the 4C2~, sample is used to measure the J / ~ ~ ~r+~r Tr+Tr-~r° branching ratio. The detection and selection efficiency has been determined from phase space generated events. The K ° contamination from K ° K ±~r %r ° events has been measured from a fit of the ~r÷Tr- mass spectrum to a gaussian curve plus a quadratic background to be 1507 + 130 events. After subtraction, one gets 46055 + 254

Jm-E. Augusta7 el al. / J / t ~ --+ 5 piotls

M (x--+r T )

5

~V/c 2

24

@

lo ~

20

16 IE

12 8

20 x I0a

(~)

17.5 15

12.5

l

10 7.5

2.5 x10 3

6

z

4

E

0.5

1 1.5 M (~'+--;,r°) GeV/c2

2

Fig. 3. rrcr m a s s s p e c t r u m for J / ~ " + v ÷ 0 r 'a'~'a " 'al l events: (a) ~r t~r~- c o m b i n a t i o n s : (b) ~r !~r° c o m b i n a t i o n s : (c) rr "¢r ° m a s s s p e c t r u m for at least o n e ~r ~ rr p a i r with (0.680 ~ Y~I~.=- ~< 0.860) G e V / c ~.

6

J.-E. Augustin et al. / d / } --* 5pions

~r+Tr-~r+Tr Tr° events and the branching ratio:

B R ( J / + --* ~r+vr ~r+v rr °) = (3.25 + 0.49) × 10 2. T h e statistical error can be neglected The systematic error comes from the normalisation [7]. T o c o m p a r e to previous measurements, it should be noticed that the first m e a s u r e m e n t s by M A R K I [1] and P L U T O [3] used only charged tracks whereas the value published by M A R K II [2] was obtained with only 152 fully reconstructed events.

4.2. J/~b --* O°O+~r+ T h e Tr+Tr mass spectrum (4 entries/event), fig. 3a, shows strong pO, f2(1270) and K ° signals. These K ° are due to a contamination by J / + ~ "r~sr,, 0,, + ~r -v-~ro events and a m o u n t s to 2% of all events. Similarly, the ~r +~r ° mass spectrum (4 entries/event), fig. 3b, exhibits a strong p± signal. Moreover, if one selects p°~r%" 7r ° events by requiring one v % r mass in the 680-860 M e V / c 2 range, the p+ signal from the two remaining vr-%r ° mass combinations is unchanged (fig. 3c). The best p°p+Tr ~ c o m b i n a t i o n is obtained by minimizing the quantity

[(M~

-Mo)2+(M~.o-MO)

,211/2

]

and a cut at 100 MeV is applied to select p°p+-~rT- candidates. Events dynamically c o m p a t i b l e with the wTr+~r dynamics, see sect. 4.3, are already discarded. A pa2(1320 ) p r o d u c t i o n can be seen on the Dalitz plot (fig. 4) as well as on the 0% + and p--~r ~- mass spectra (fig. 5a, b). In the following analysis events compatible with b o t h p°a°(1320) and p+-a2~(1320) dynamics have been eliminated to get rid of any interference effect. A fit to a free width Breit-Wigner distribution over a quadratic background in the 1.0-1.8 G e V / c 2 range yields the following results*: for a2± (1320)

M = 1323.8 + 2.3 M e V / c 2,

x2/dof = 55.2/34,

F = 107.0 _+ 9.7 M e V / c 2

B R ( J / ~ ~ p±a2T(1320)) = (0.84 _+ 0.05 ± 0.21) X 10 -2 , * Here and in the following, due to the lack of experimental results, the efficiencies have been calculated by generating the JP states with equal helicity amplitudes.

J.-E. Augustin et al. / J/if; --* 5 pions

>=

7

4

+-7-

~3

1 1

2

3

4

5

M'(p+-Tr~) [(3eV/c2]~ Fig. 4. Dalitz plot for J / ~ ~ [I)p ~ .';7T.

for a°(1320)

M = 1320.6 + 3.1 M e V / c 2 ,

x 2 / d o f = 39.2/34,

F = 118.5 + 12.5 M e V / c 2

B R ( J / + ~ 0°a°(1320)) = (0.33 + 0.02 + 0.05) × 10 -2.

The a°2(1320) parameters do not vary by changing the fit range. That being not true for the af(1320), the fit giving the most consistent a2-(1320) mass and width has been used and a 10% systematic error in the branching ratio accounts for this effect. The quadratic form introduced in the fits could be inadequate to reproduce the different background behaviours in Figs. 5a and 5b. The ratio BR(J/+--* p ° a t ~ ) / B R ( J / + -~ p +-a2T) = (0.39 + 0.06) is found to be consistent within 20 with the expected 0.5 value. By adding the previous results the following branching ratio is set

B R ( J / ~ ~ paz(1320)) = (1.17 _+ 0.07 -t- 0.25) × 10 -2

These results have been obtained from 3562+201 a°(1320) and 4022 + 201 a f(1320). The only published measurement has been performed by M A R K I [1] from 36 _+ 12 events.

8

J.-E. Augustin et al. / J / ~ ~ 5pions

M(p ° n"-+)6eV/c 2 2.00 f

xlO 3

, ,L

i

2.4

®

2 ~ 1.25"

%

1.6

too

~

1.2

~

1?.8

~0.75 0.50

0.4

0.25

1.75~ xlOa

14

,F

1.50

10oo

(~ 8o0

"-- 1.25 1.00

i

®

600

z0.75 4oo

0.50 2O0

0.25 0

t 0.8

.

x _ ~ 1.2 1.6 2 M (p+ ~-) 6eV/c2

Fig. 5. p~r mass spectrum for J/~ ~ p°0±~r;: (a) p%r ± mass combinations; (b) 0%r- mass combinations.

0 500

600

700 800 900 M(r-+x-r "°) GeV/~

i000

Fig. 6. ~r+~r ~r° mass distribution for J/+-~ rr +~r ~r~~r ~r°: (a) for 4C17 events; (b) for 4C2¥ events.

4.3. J / ~ ~ ~ 4.3.1. J / ~ ~ 0~','r+'/7" . The ~r+Tr ~r° mass s p e c t r u m (4 e n t r i e s / e v e n t ) shows a very clean w signal owing to the g o o d mass resolution ( F W H M = 20 M e V / c 2 for 4C2-/ a n d 30 M e V / c 2 for 4C1y) and the p r o x i m i t y of the phase space limit (fig. 6a, b). T h e ~ r + T r - events are selected requiring that ] m ~ ~ , , - m~l ~< 40 M e V / c 2. A f t e r b a c k g r o u n d subtraction, as evaluated from side bins, the n u m b e r of ~ r + ~ r events is f o u n d to be 18058. T h e ~Tr+~r D a l i t z p l o t (fig. 7a) shows ~f2(1270), b((1235)~r-v- p r o d u c t i o n s and a striking ~r+~r low mass accumulation. T h e d e t e c t i o n efficiency varies from 39% for M~+~ = 500 M e V / c 2 to 29% for M~+~ = 1500 M e V / c 2. Thus the o~v+~r b r a n c h i n g ratio is c o m p u t e d b y weighting

J.-E. A u g u s t m et aL / J / ~

--* 5 p i o n s

9

M 2 ( ~ +) [GeV/c2]~ 140

.; 5.

Q

120 % 100

Y

6 >= .~.

5

80

'1~ 4 :;

) 6o

3

40

20 i

•

,

i

140

,~

,-:.. ::2,.. .:~;. -,', ,~

•

6 5

@

' .'9.;., , ,,,..

..,'~, ." %4 • :.. .

"'.', :=.:

%

...7.'.. :'-...., "::;:

:';:.

.: ...,

,,.-..~.

•

...

•

• ''

..

... ; ". .

•

"',,;

.

-..'

,"

.

• ...

.

..

.

.~

;

""

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• "..~..

..

.

,, •

60

,...~,

.

.~...~'~. '':'..

"'tic

...: ".." "'.. ::.. ,, ,.

;.

.

.

..:.'".,

.....

:....:,

" ".'" ) ' ; ' : ; ~ :"~:.;d.:. ': n

n

n

i

L

n

i

2

3

4

5

6

7

8

fflo,

100

=~ 80

"..:: . . ' . . . . : ' , , .... ':,'%. ":,,;..-,." ..

3

120

-,

°) [aeV/e]

Fig. 7. D a l i t z p l o t : (a) for J / ~ , -~ ~o~r ~ 7r : (b) for

J/~k -* ~o~%°

40

2O 0 0.6

0.8

1. 1.2 1.4 1.6 1.8 M (Tr+7r-;,ro) (GeV/cz)

2.

Fig. 8. ~ + v v ° m a s s s p e c t r u m for J/kb --', ~r~cr ~r°v%r ° e v e n t s : (a) all the c o m b i n a t i o n s (3 e n t r i e s / e v e n t ) ; (b) for the c o m b i n a t i o n n e a r e s t to the ~o-mass.

the efficiency and amounts to

BR(J/¢ --, ~r+~r - ) =

(0.70 + 0.16) × 10 2

Statistical errors can be neglected. The reported error is related to normalisation and efficiency uncertainties. 4.3.2. J / ~ - - * ~ov% °. The raw ~r+v vo effective mass for the 2C67 events is shown in fig. 8a (3 entries/event): a large and clean ~0-signal is present with the expected mass resolution ( F W H M = 35 M e V / c 2 ) . The fig. 8b shows the vr+~r ~r° mass nearest to the ~o-mass. A fit to a gaussian function added to a polynomial b a c k g r o u n d gives a total n u m b e r of 509 events compatible with the ~vr°vr ° signal.

J.-E. Augustin et al. / J / ~ ---* 5 pions

10

The ~oTr%r° Dalitz plot of fig. 7b shows c0f2(1270), b°(1235)~r ° production and the same low ~r~ mass accumulation already observed in the charged mode. The distribution of the ~r%r° mass recoiling in front of the best ~0-mass (0.733 M~+. =,, ~< 0.833 G e V / c 2) and in the ~o-side-bands are shown in the figs. 9a and 9b, respectively. The detection efficiency varies from 3.3% to 1.6% at the M ~ values reported above. Thus the c0vr°~r° branching ratio amounts to

BR(J/g`

~ ~o~r°vr°) = (0.34 + 0.03 + 0.07) × 10 2.

This value if compared to the ~o~r+~r result agrees with the expected isoscalar dominance in the ~o-associated production. The systematic error takes into account the normalisation and the efficiency uncertainties from dynamics and low-energy photon simulation. 4.4. J/~b ---, bl + (1235)~r ~

The ,0~r mass distribution for events with M(Tr+cr - ) > 1550 M e V / c 2 (fig. 10a) shows a strong signal around the b1(1235 ) mass. But a fit over a 1040-1780 M e V / c 2 mass window to a Breit-Wigner with 150 M e V / c 2 fixed width added to a quadratic background leads to a mass value of 1193 _+ 4 M e V / c 2, X 2 = 85/34 dof, instead of the standard 1235 M e V / c 2 one. Leaving the width free, one gets the following results, M = 1186.4 _+ 4.8 M e V / c 2, F = 227 ± 20 M e V / c 2, which by taking into account a possible threshold effect become M = 1190 _+ 10 M e V / c 2 ,

F = 210 _+ 19 M e V / c 2 ,

x2/dof = 42/33.

These values are scarcely consistent with the b1(1235 ) standard parameters, although m a n y discrepant measurements exist [8]. Our discrepancy may be due to a wrong estimation of the background under the b1(1235) signal. On the other hand the Breit-Wigner description of such a wide resonance could not be sufficient to take into account other effects as a ba(1235 ) width variation with the phase space and possible interference with the ~of2(1270 ) channel (see fig. 7). In order to evaluate the last effect we have analyzed Monte Carlo interfering J/g, decays into ¢of2(1270 ) and bl(1235)vr, assuming real amplitudes, the bdr to ~of2 ratio having been adjusted to reproduce the measured mass distributions. One gets the following parameters (fig. 10b): M = 1213.0 _+ 4.0 M e V / c 2 and F = 198.0 +_ 11.0 M e V / c 2 for x 2 / d o f = 43/33. This Monte Carlo study gives b~(1235) mass and width shifted toward the experimental values, although not enough to fully account for the observed difference. Using the efficiency deduced from this last simulation and the 4600 events obtained from the fit to the data the following branching ratio can be calculated:

BR(J/g` ~

bt+(1235)vr ; ) = (0.31 _+ 0.06) × 10 2,

J.-E. Augustin et al. / J / + ~ 5 pions

11

400 28

350 24

300

2O

% 250 200

12

150

8

100 50

12

120

G

100 ~-

8

%

80

:~ 60 4

z

..>.

0

O.5

1.0 1.5 M (Tr ° 7r°) GeV/c 2

2.0

Fig. 9. Distribution of the vr°vr° mass recoiling in front of the best ~0-mass: (a) for 0.733 ~ M3~ ~< 0.833 G~e V / c - ; (b) for the w-side-bands.

40

0 0.8

,1

,

1.2

1.6

M (6o7r-+)

~ v -

i

2 GeV/c~

2.4

Fig. 10. Fit of the w~r : mass spectrum for J / + ---, ~ r % r events: (a) for experimental events; (b) for Monte Carlo events.

where the quoted error includes the systematic errors on the background estimation and efficiency. The PLUTO previous value [3] was calculated from 87 _+ 18 events for a 125 M e V / c 2 wide b1(1235 ) peaked at 1182 _+ 32 M e V / c 2.

4.5. J/~b---*v0(~+rr ) D Y N A M I C S

The spectrum of the ~r%r- mass pair recoiling against the ~ (fig. l l a ) is dominated by the f2(1270) production and a low ( ~ r % r ) mass accumulation. In addition, since the 0f0(975) --+ 0 . associated production has been measured [4], the same state is looked for in the ~o~r%r- final state. The small bump below the f2(1270) has been attributed to this decay. The background coming from channels

12

J.-E. Augustin et al. / J / ~ -~ 5 pions

@

600 500 400 300 2OO

100

@

320 280

240rl

;°°It "'

0.5

l.O 1.5 M (~r+~) 6eV/c~

2.0

Fig. 11. ~r+~r mass spectrum for J/q~ ~ w~r"7r : (a) all the events: (b) after the b1(1235) cut.

without ~0-production is evaluated from ~0-sidebins and subtracted in the ~r+Tr distribution. Then the residual background mainly comes from the bx(1235)Tr dynamics. T h e shape of its contribution is deduced by fitting the M o n t e Carlo 7r+Tr mass distribution of this decay (fig. 12) and introduced with a free normalisation p a r a m e t e r in the mass spectrum fit. This method has been preferred to a simple cut on the Dalitz plot of the events compatible with the bl(1235)Tr dynamics because it is insensitive to the production helicity amplitudes which are unknown. T h e result of such a cut (M,o,, < 1370 M e V / c 2) is already shown in fig. l l b . T h e fig. 13a shows a fit of the overall ~r+cr distribution taking into account the three observed structures and the bt(1235)~r background.

13

J.-E. Augustin et al. / J / t k ---'5 pions

40

>= 30

t--Z

20

10 0 LZY'~ I

L

0.25

I

0.75

1

I

I

1.25 1.-/5 M (Tr+~) GeV/c 2

Fig. 12. Fit of the ~r%r distribution for J/~b

~

I

Ihl

2.25

b 1(1235) ~~r= Monte Carlo events.

4,5.1. J/~b--* ~(rr +or )low The observed large b u m p at vr+~r low mass does not c o r r e s p o n d to any known resonance. A fit to a single B r e i t - W i g n e r curve folded to a ~r~r phase space gives the following parameters . . . .

"

M = (414 + 20) M e V / c 2,

r = (494 + 58) M e V / c 2 .

T h e o b t a i n e d branching ratio is B R ( J / ~ b ~ w(vr+'rr-)l

. . . . . .

) = (0.16 + 0.03) × 10 -2 .

T h e error takes into account the systematics from dynamics uncertainties and from normalisation. The efficiency has been calculated for an S-wave state production. However, the angular analysis shows the limits of this hypothesis: the acceptance corrected distribution of the angle 0 between the ~r+ and the (~r%r-) system direction in its rest frame (fig. 14) varies with the (~r +Tr - ) system mass and disagrees for M , < , < > 600 M e V / c 2 with the flat distribution expected for an S-wave. N o i m p r o v e m e n t is found if J P = 2 + or 4 + hypotheses are assumed, so suggesting a c o m p o s i t e nature of this low mass enhancement. A full wave analysis is in progress. 4.5.2. J / ~ p ~ ~f2(1270). T h e f2(1270) signal has been fit to a B r e i t - W i g n e r curve. The following parameters are obtained: M = (1269.7 _+ 5.2) M e V / c 2 ,

r = (169.0 + 7.5) M e V / c 2

in a g r e e m e n t with the world average values. The branching ratio is calculated to be B R ( J / g , --+ tof2(1270), f2 -~ ¢r+~r ) = (0.26 + 0.05) × 10 - 2 .

14

J.-E. Augustin et al. / J / + ~ 5 pions M

hr+~) GeV/c2

@

600 500

400

300 I--

>

200 100 0

30 %

25 2o

--.

tt

15

I

o 0.4

0.8

1.2

[

1.6

I

2.0

M hr°Tr°) GeV/c~ Fig. 13. F i t o f the ~rv d i s t r i b u t i o n : (a) for J / ~ ~ w'/r + ~

events; (b) for J / + ~ co~v°~r° events.

The statistical error is neglected (5730 events). The efficiency takes into account the interference with the b1(1235 ) as indicated above and the corresponding uncertainty is introduced in the quoted error. The branching ratio value is somewhat higher than the measurement by MARK I [1] (81 _+ 20 events) and agrees with the PLUTO [3] value (70 _+ 24 events). The ratio of the ~0f2(1270 ) and pa2(1320 ) productions is well explained by SU(3) symmetry [4]. 4.5.3 J / ~ ~ ~ofo(975). The signal around 960 M e V / c 2 is attributed to the fo(975). However, the fit of the whole ~r+~r- mass spectrum is insensitive to its presence. This comes from the weakness of the signal and the lack of knowledge of the nature and tail behaviour of the low (~r~r) mass signal. Thus the fo(975) mass

J.-E. Augustin et al. 100

/

J/~b ~ 5 pions

250- 350 MeV/c2

15

550 - 650 MeV/c2

50

1

,,=, ,.>,

I

1

L

350-450

MeV/J

L

1

t

l

J 1 _ 650 - 750 MeV/c2

50

1

1

[ (x5)

L__l__i__±__ ALL

50

0

-1.0

-0.6

-0.2

+0.2

+0.6

+1.0 cos

-0.6

-0.2

+0.2

+0.6

+1.0

0~r

Fig. 14. cos 0* distributions in several ~r~r low-mass ranges for J / t ~ --~ ~",'r+q7 Monte Carlo acceptance for 0 + events.

.

The cu~'es represent the

and contribution have been calculated from a fit of the Tr+Tr mass spectrum in the 900-1400 M e V / c 2 range to two Breit-Wigner functions (fig. 15) added to a polynomial background, the f0(975) width having been fixed to F = 35 M e V / c 2 and the f2(1270) parameters to the above values. One gets M(fo(975)) = 959.4 _+ 6.5 M e V / c 2, and the following branching ratio

BR(J/~ ~ ¢ofo(975)) × BR(fo(975 ) ~ ~r~r) = (1.10 _+ 0.21 + 0.16) × 10 4. The systematic error to be added from the f0(975) width uncertainty and the fit range choice is of the order of 30%. The mass value obtained by this procedure agrees with our result in 0~r~r and ~,KK [4] and with a previous larger statistics M A R K II [9] measurement, 956_+ 6 M e V / c < Comparison between the ~0- and

16

J.-E. Augustin et aL / J / + ~ 5 pions

°00

500

:

,00 ,>.,

~

j \+

200,00-,, 0 I

I

0.9

[

[

I

[

L1 1.3 M(Tr+~) 6eV/cz

[

I

1.5

Fig. 15. Fit of the fo(975) signal.

~-production of the fo(975) and a tentative interpretation of the nature of this state has been given in ref. [4]. 4.5.4. J / q , ~ bF(1235)rr z-. The adopted method gives also a measurement of the J/q, ~ b~(1235)~r-V branching ratio by the normalisation of its contribution. The following result is obtained:

B R ( J / + ~ ba-+(1235)~r ~) = (0.32 _+ 0.06) × 10 -2 in agreement with the value of subsect. 4.4. 4.6. J/~b -+ ¢o(~r°rr0) DYNAMICS

In this final state the low mass accumulation (350-850 M e V / c 2) is still contaminated by J/q,--+ oaT, ( ~ - ~ 7r%r%r°) events where a rr ° is missing. Its contribution, calculated with the branching ratio of ref. [10] and an efficiency of 1.4%, shows the 7r°rr ° mass distribution reported in fig. 16 and has been subtracted. In order to evaluate the contribution of J/q, --+ ~of2(1270 ), f2 -+ q'r°'a0 and J/q, --+ °a(~r%r°)l . . . . . . we have fit the ~r%r° mass distribution in front of the ~0 to two Breit-Wigner phase space folded curves added to a function representing the b°(1235)vr ° contribution (fig. 13b). The latter has been obtained by fitting the M o n t e Carlo ~r°vr° mass distribution of this decay. The mass and width of the two Breit Wigner functions have been fixed to the values found in the charged mode. 4.6.1. J / q , ~ w(rr°rr°)l The detection efficiency for this channel is calculated from Monte Carlo simulations assuming an S-wave distribution of the ~r°vr° system. It is m a x i m u m for m=%o = 500 MeV and slowly decreases for higher masses. . . . . . . .

"

J.-E. Augt~tin et al. / J / + ~ 5 pions

17

! (a)

25

.>.

20 15

Z

,>,,

10 5 0

I{b -~ l

0.5

i

I

L

1.0 1.5 M(?T°/1-°) 8eV/e2

J

~

i

2.0

Fig. 16. w%r ° mass distribution for J / f ~ ~ow%°: (a) all the events: (b) evaluated contamination from J/~b ---) toT, (r/---, ¢r%r°Tr°); (c) after subtraction.

Using an efficiency mean value of (2.4 _+ 0.2)% the branching ratio for the low mass accumulation is consistent with the result obtained in the charged mode

BR(J/~

--~ co (~r°~'°)]ow . . . . ) = ( 0 . 0 8 -t- 0.01 + 0 . 0 2 ) × 10 -2.

4.6.2. J / t p - - ~ wfe(1270). The wf2(1270 ) production is found to contribute to 130 events. This result leads with the efficiency of subsect. 4.3 to the following branching ratio:

B R ( J / ~ ~ ~af2(1270), f2 ~ 7r%r°) = (0.11 _%0.02 _+ 0.02) × 1 0 - 2 in good agreement with the value found in the charged mode. This value does not change by varying the fit bounds. 4.6.3. J / + ---) b°(1235)~ °. The normalisation of the J / + --, b°(1235)w ° contribution gives an estimate of the branching ratio of this decay. The 229 events found to contribute to this channel lead with the efficiency of subsect. 4.3 to the following branching ratio:

B R ( J / ~ ~ b°(1235)w °) = (0.23 _+ 0.03_+ 0.05) × 10 2 which agrees, although only within 2.5 o, with the value obtained in the charged mode.

18

J.-E. Augustin et al. / J / }

---, 5 pions

5. Conclusion The J / ~ r + T r Tr+Tr ~r° decay has been studied from a high statistics of constrained and fully reconstructed events. The 0a2(1320), inclusive ~ov+~r-, ~f2(1270) and b{(1235)Tr ~ branching ratios have been measured from 7584, 18058, 5730 and 4600 events, respectively. The inclusive ~0~r+Tr production is saturated by the measured dynamics. However, the measurement accuracies are not substantially improved because of the systematics. First observation of the J / + ~ ,07r°~r° decay is reported and a study of this decay and of b°1(1235)Tr °, ~f2(1270) dynamics is performed. All results are in agreement with those found in the ~oTr+~r- analysis. A large b u m p at low ~Tr mass is observed in ~o-associated production in both ~r+~r and 7r%r° modes. However, the J P assignment seems to vary with the ~r~r mass value, thus making it difficult to recognize the observed signal as a well-defined state. At low ~r~r mass a bump has been already observed in ~,,{ ~ ~r+~r [11], not confirmed by a ~,y ~ Tr%r° study [12]. A similar enhancement is also observed by the C L E O experiment [13] in T(3s) --* T ( l s ) ~ + v and by the AFS collaboration in pp ~ ppTr+~r [14]. The CLEO group [15] claims to need a o-resonance whose parameters are fit by Belanger and Moxhay [16] to M = 450 and F = 150 M e V / c 2. All of these observations remain difficult to reconcile with what is presently known from low-energy TrTr interaction in this mass region [17]. By analyzing the ~,~, results Barnes et al. [18] showed that the low-mass bump can be interpreted by TrTr final state interaction closely related to the K K potential in the same manner as the fo(975) thus accounting for the low value measured for this state associated with the to in the J / + --* ~oTr~r channel. Another theoretical approach has been proposed by Dosch and Gromes [19] by a spontaneous creation of a quark antiquark pair in a color-electric field. Such an interpretation takes into account the non-observation of this ~rTrenhancement in yTr~r and ~TrTr modes. Finally the high statistics accumulated in the ~oTr+~r mode has possibly allowed the first observation of the J / + -~ ~of0(975 ) decay and a direct measurement of the f0(975) mass. We have greatly appreciated the efforts of the technical staff of the LAL for the construction of the apparatus and constant support and of the DCI storage ring group led by P. Marin.

References [1] [2] [3] [4] [5]

F. Vannucci et al., Phys. Rev. D15 (1977) 1814 M.E.B. Franklin et al., Phys. Rev. Len. 51 (1983) 963 J. Burmester et al., Phys. Lett. B72 (1977) 135 A. Falvard et al., Phys. Rev. D38 (1988) 2706 J.E. Augustin et al., Phys. Scr. 23 (1981) 311

J.-E. Augustin et al. / J / ~ -* 5 pions

[6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [161 [17] [18] [19]

19

D. Bisello et al., Phys. Rev. D in press and Orsay preprint LAL 88-12 (1988) J. Jousset et al., Orsay preprint LAL 88-26, 1988, to be published in Phys. Rev. D Particle Data Group, Review of Particle Properties, Phys. Lett. B204 (1988) G. Gidal et al., Phys. Lett. B107 (1981) 153 Z. Ajaltouni et al., VIII International workshop on photon-photon collisions, Jerusalem, Israel, April 24-28, 1988, and Orsay preprint LAL 88-06 Z. Ajaltouni et al., Phys. Lett. B194 (1987) 573 H. Marsiske et al., VIII International workshop on p h o t o n - p h o t o n collisions, Shoresh, Israel, April 24-28, 1988 T. Bowcock et al., Phys. Rev. Lett. 58 (1987) 307 T. Akesson et al., Nucl. Phys. B264 (1986) 154 S. Stone et al., APS-DPF Meeting, Salt Lake City, USA, Jan. 1987, and Cornell preprint CENS 87/56 G. Belanger and P. Moxhay, Univ. of Colorado preprint COLO-HEP-173 (1988) D. Morgan and M.R. Pennington, Phys. Lett. B214 (1988) 273: G. Mennessier and T.N. Truong, Phys. Lett. B177 (1986) 195 T. Barnes, K. Dooley and N. Isgur, Phys. Lett. B183 (1987) 210: J. Weinstein and N. Isgur, Phys. Rev. D27 (1983) 588 H.G. Dosch and D. Gromes, Zeit. Phys. C34 (1987) 555