RECENT RESULTS FROM DCI AND ELSEWHERE ON VECTOR MESON PRODUCTION BETWEEN 1.4 AND 2.2 GeV

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RECENT RESULTS FROM DCI AND ELSEWHERE ON VECTOR MESON PRODUCTION BETWEEN 1.4

AND 2.2 GeV

J. Buon

To cite this version:

J. Buon. RECENT RESULTS FROM DCI AND ELSEWHERE ON VECTOR MESON PRODUC- TION BETWEEN 1.4 AND 2.2 GeV. Journal de Physique Colloques, 1982, 43 (C3), pp.C3-77-C3-80.

�10.1051/jphyscol:1982315�. �jpa-00221868�

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JOURNAL DE PHYSIQUE

CoZZoque

C3,

supple'ment au n o 12, Tome

43,

de'cembre 1982 page

C3-77

RECENT RESULTS FROM D C I AND ELSEWHERE ON VECTOR MESON PRODUCTION BETWEEN 1 . 4 AND 2.2 GeV

J. Buon

Laboratoire

de Z'Acce'Ze'rateur LinBaire, UniversitB de Paris-Sud, 91405 Orsay,

France

The main problem in this energy range (1.4 - 2.2 GeV) is the possible existence of recurrences of the pwQ mesons. A recurrence of the p, the p'(1.6), is already established. Now a recurrence of the Q, named Q1(1.68), has been observed. Does it open a $ family, similar to the $ and T families of vector mesons ? the p'j1.6) and Q'(1.68) could belong to a new 1- nonet which could include also an a' and a K '(1).

Recent data in this ener y range come from the DM1 e ~ ~ e r i m e n t ( ~ - ~ ) at DCI in e+e- an- nihilation and from WA4 (8-10) and w ~ 5 7 ( ' '-I3) experiments at CEFW in photoproduction.

M ' ~ : ' n

¹

.

^-^9'⁽1.68) observation. -

r The main indication for the

existence of a Q' vector meson comes from the study of the efe- + K~K'TI reaction(2) on a sample of 250 events.

U. ^Thee n Dalitz plot shows a

I . dominant K*OKO production

(Fig. la)

,

revealing an inter-

2

-

ference between isoscalarand

isovector amplitudes. Extrac- ting these two amplitudes and

0 '

their relative phase from the

Dalitz plot population, one -1

-

, observes (Fig. lb,c,d) a bump

-2

-

around 1.65 GeV of the isos-

-3

- calar amplitude with its

a4 a6 a8 1

u

14

u

1.5 1.6 1.7 1 . 8 B phase possibly crossing 90"

at this energy. Assuming that

M~,T *, (G~v') this isoscalar resonance

(deg) and the p

'

(1.6) meson belong

I=l

to the same nonet, the cons-

200

- @

^I ⁵

-

tructive interference in

K?OKO implies that this isos-

4

-

calar resonance is of Q '

type.

f i g . I :

KRT

D&z j~.tat 0

-

I ,

¹

^-

a n d y n h :

I 0

--

a ) eve& c t h M b u h i o n ;

-100

-

-1

-

^C* ^I ^{b,c) 1=0}^$: 1=1 csrann-neotiouzn

dl I=O phane (aclnuming I = I

-2

-

_{? h u e}g i v e n by p' )

.

-200

. -

^-3, J

1.5 1.6 1.7 1.8

1.5

1.6 1.7 1.8

VS

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982315

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C3-78 JOURNAL DE PHYSIQUE

Preliminary results(11) of ~ 1 ~ 5 7 experiment on the K+K-no and K°K'aS photoproduction do not indicate such an effect. However the statistics is low

7%

^{40 and}^%^{30 exents}

respectively between 1.6 and 1.72 GeV). It must be emphasized that the $ ' + KK photoproduction should be observed according to the Vector Dominance Model. The g ' photoproduction is related to the p' photoproduction by :

leading to an about lOOnb expected cross-section. If it is confirmed that the

6'

(1.68) is not observed in KKn photoproduction at the expected level, it could be due to either a non-dominance of the 4n' channel by the p

'

(1.6)

,

as already suggested(14), or to a smaller total $'N cross-section. Otherwise one can argue a VDM failing or a misinterpretation of DM1 results.

+

-

2

.-

^Other^$I

'

(1.68) indications

.-

^{The e}^'^e^- ⁺K+K- and e e + K°KO data ( 3 ) present (Fig. 2) respectively an interference shape with pw$ tail arosn8 1.7 GeV and a bump at 1.65 GeV. These effects cannot be explained by the p'(1.6) meson alone. They need a resonant isoscalar amplitude at 1.65 GeV.

F i g . 2 :

The e'e- annikieation otrosn-nedon

.tnto :

a )

w ~ + T - ;

b)

K*K- ; C ) K ~ K ? ;

d )

K g K t r * .

vQhhU6

4 . -

- S o M

l.&es :

global 6.it luith a

p ' w l $ '

m a d e l between

1.4

a n d

1.9

GeV

^;

- Po.Cted Linen

^:

exLtapo&u5om 04 .the global

.jA.

+

-

A structure has also be seen (Fig. 3) at 1.7 keV in K K photoproduction by WA4 experiment ( * )

,

but with low statistics. The $

'

(1.68) meson, interfering with background, can explain this structure, although the spin-parity is not clearly I - .

+

-

+

-

The e e + IAT n cross-se~tion(~) shows also (Fig. 2) a bump at the same energy. Ho- wever this bump is too large (TeeB=190 ? 20eV) for a + ' meson, according to the OZI rule, and is too narrow (rtot = 140

+

50 M ~ V ) for an w ' meson, according to the available phase space for ~ t s decay channels. A possible explanation is a superpo- sition of an w' and the $ ' (1.68) interfering together. In wn+n- photoproduction

(WA4 + WA57) a very broad mass distribution is only observed(ll).

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J. Buon C3-79

+ - 0

The TI n TI photoproduction(ll) (WA57) shows (Fig. 4) also a bump over a steep background. It is also too large ( o B % 100 nb) for a $ ' meson and too narrow (Ttot %

125 MeV) for an w ' meson. Can the same explanation work here ?

+ -

^{+ - 0}

Finally present upper limits(5) of e e -t n IT n rule out the possibility of an un- mixed

@A.

^The^{$ '}(1.68) meson must be nearly pure ss.

3. $'(1.68) parameters.- A global interpretation of DM1 results (Fig. 2) between 1.4 and 1.9 GeV, assumlng a p1w'$'triplet with SU(3) symmetry leads to the following parameters :

$ ' 1.68i.01 .185+.022 .49+. 05 .036+. 004 c.05

+

-

x values obtained from e e -t 4n' in DM1 experiment(6). ( ) predicted values for the w', not seen in the DM1 experiment.

From the sum of partial widths, the electronic width of @ ' is about .7 keV, i.e. half the @(1.02) electronic width, similarly to what happens in the JI and T families.

4. p

'

(1.6) problems

.-

^{The p}' (1.6) was originally observed in the 2lr+2n- main decay channel and later in the TI+IT- channel. Now p ' (1.6) has been observed to decay into nrfn-, through npO (WA4('), DM1(5), WA57(12)), with a relative branching ratio :

(0' + QTI*T-) / (p' + 21~+21r-) Q .l. The K+K- and

KEK'T~

decays of p' (1.6) are deduced by DM1 experiment from interference with 4 ' (1.68) decays. Recently WA57 experiment (I3) has observed the p' (1.6) decay into r+nrr-roro, proceeding mainly through p'nTlrO. It rules out ponlr, and favours A ~ T I dynamics for the 471 channel.

Now p'(1.6) must be considered as a well-established resonance, seen in several channels. However this resonance is not yet well-understood and several problems are unsolved.

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C3-80 JOURNAL DE PHYSIQUE

I t s t o t a l width v a r i e s from 300 MeV t o 500 MeV i n d i f f e r e n t experiments, and i n t e r f e r - ence e f f e c t s can change n o t a b l y i t s v a l u e i n any channel.

The p ' l e p t o n i c width given by t h e sum of TeeB f o r a l l t h e observed channels ( i n c l u - d i n g pq and r+n-noro proceeding through Ala), p l u s t h e expected w r O decay, i s about 7 . keV. I t i s a f a c t o r 2.5 l a r g e r t h a n expected from t h e @11(1.68) l e p t o n i c width.

Here a g a i n a non-dominance of t h e 2~r+2n- channel by t h e p

'

( 1 - 6 ) , i . e . a lower p

'

^-t4a decay mode, could e x p l a i n t h i s d i s c r e p a n c y .

A t t r i b u t i n g t h e background i n a + r - and K+K- channels t o t h e pw@I t a i l s , t h e i n t e r f e r - ence w i t h t h e p ' ( 1 . 6 ) l e a d s t o d i f f e r e n t v a l u e s of t h e phase between p and p ' i n e'e- a n n i h i l a t i o n (180°) and photoproduction ( 0 " ) .

For s o l v i n g a l l t h e s e problems a b e t t e r understanding of background i s needed i n t h e 2r and 4 r channels both i n efe- a n n i h i l a t i o n and photoproduction.

I n conclusion new d a t a , i n t h e 1.4 - 1 . 9 energy range, have given new i n f o r m a t i o n on t h e p ' ( 1 . 6 ) decay c h a n n e l s , and have r e v e a l e d a @11(1.68) v e c t o r meson. S e v e r a l problems a r e s t i l l unsolved concerning t h e p 1 ( 1 . 6 ) , t h e photoproduction of t h e Q 1 [ 1 . 6 8 ) , and t h e p o s s i b l e e x i s t e n c e of an w ' meson. F i n a l l y around 2 GeV experimental s t u d y

( 6 r 7 , l 0 ) of 4a, 6 r and @ITIT p r o d u c t i o n seem t o i n d i c a t e a n o t h e r t y p e of mechanism.

References.

-

1 ) ETKI1.l e t a l . , Phys. Rev. (80) 42 ; ASTOh D . e t a l . , Phys. L e t t . (81) 235.

2) MANE F. e t a l . , Phys. L e t t . (82) 178.

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4) CORDIER A. e t a l . , Phys. L e t t .

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--

1 1 ) LAFFERTY G . , XVIIth Rencontre de Moriond (1982) ;

PAUL E . , 1981 I n t e r n . Symp. on Lepton & Photon I n t e r a c t i o n s a t High E n e r g i e s , Bonn (81)

.

12) ATKINSON M. e t a l . , CERN Report EP/81-111 13) ATKINSON I*. e t a l . , Phys. L e t t . (82) 55.

14) HIRSHFELD A,C and KRAI3ER G . , N u c ~ - PhyS. (74) 211 ; PENS0 G . and TRUONG T., Phys. L e t t . (80) 143.