ANALYSIS OF THE REACTION π-p →π+π-n AT HIGH | t |

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ANALYSIS OF THE REACTION π-p →π+π-n AT HIGH | t |

I. Sakrejda

To cite this version:

I. Sakrejda. ANALYSIS OF THE REACTION π-p →π+π-n AT HIGH | t |. Journal de Physique Colloques, 1985, 46 (C2), pp.C2-289-C2-293. �10.1051/jphyscol:1985234�. �jpa-00224548�

JOURNAL DE PHYSIQUE

Colloque C2, supplement au n°2, Tome 46, f evrier 1985 page C2-289

ANALYSIS OF THE REACTION IT p •* TT+T: n AT HIGH | t |

I . Sakrejda

Institute of Nuclear Physios, Cvaaow, Poland

Résumé - La réaction ir p ->- ir TT n a été étudiée à 17,2 GeV et à 63 GeV. Une analyse des ondes partielles dans la région des

grands transferts d'impulsion (|t|>0,2 GeV2) révèle un objet assez large (^ 250 MeV) avec une masse de 840 MeV. Cet objet, qui est déjà visible dans l'analyse de la distribution angulaire par la méthode des moments, apparaît dans l'onde D (JPC- = 2+ +) avec hélicité m=2. Nous n'avons pas pu éliminer cet effet en invoquant des raisons expérimentales triviales comme l'acceptance du

détecteur ou les réflections des N*. L'absorption de cet objet dans le noyau atomique fournirait peut être des indications sur sa nature.

Abstract - The reaction TT p + i i n has been studied at 17.2 GeV and 63 GeV. A partial wave analysis at high four-momentum tran- sfer (ItI>0.2 &eVz) shows an evidence for a fairly broad (~250 KeV.) object at about 840 MeV. This object, already visible in moments of the angular distribution, appears in the D wave

(J*- =2f f) with helicity m=2. We have not been able to 'explain awayx this effect by trivial experimental reasons like acceptance and/or N* reflections. A hint on the nature of this object may be given by its absorption inside the nucleus.

I - INTRODUCTION

n^rr" system produced in the reaction rr'p-snVnrx with a high four- -momentum transfer (ltl>0.2 GeV3) has been studied using data obtained in the three experiments:

I CDRN-Munich experiment at 17.2 GeV on a hydrogen target L11, II C3RN-Cracow-Munich experiment at 17.2 GeV on a polarized butanol

target L 2 ] ,

III WA-3 experiment /ACCMOH collaboration/ at 63 GeV on a hydrogen target C33•

Partial wave analysis of this system yielded a new phenomenon in the D wave above the <j(.770) resonance.

II - D3FINITI0NS, MOMENTS AND AM1IITUD3S

At fixed beam momentum the reaction n"jp •*> n*n~f\ as described in refs. L2,4l is completely determined by 5 variables /see fig. 1/:

mnir - effective mass of the (Vir pair,

t - square of the four-momentum transfer to the nucleon,

^ - angle between the normal to the reaction plane and the

transverse polarization, 9,f - decay angles of the f t ' i n P i g . 1 Definition of the kinematic

q u a n t i t i e s .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985234

C2-290 JOURNAL DE PHYSIQUE

t h e i r + n - r e s t frame.

Because of t h e p a r i t y c o n s e r v a t i o n and t h e s p i n 1/2 of t h e nucleon t h s a n g u l a r d i s t r i b u t i o n a t f i x e d center-of-mass energy /s/ c a n be f o r t h e t r a n s v e r s e p r o t o n p o l a r i z a t i o n I? w r i t t e n i n t h e f o l l o w i n g form:

Z [ m d ~ , t , + , Q , f ) = l O ( m \ ~ n , t ~ @ t ~ ) t ? ~ m Q I , ( ~ m s n , t , Q t f ) + P& yl I ~ ( ~ f i ~ , t , @ ~ p ) where

I o ( m t r , t 1 Q, 9 ) ^{= &tLn}( ~ i i r f'k3; (cos'4fl 1, (nncii,tl@, y) = (mllilt) %Y;(m@t?J

1, (rm,ji.t,Bl y) ⁼

6

and " 2 ~ L - N ) t ~ f/% L

~h ( m ~ , g ) ⁼ i - ~ ) ~ j-iii;

G.4

L , I a r e expressed i n terms ff s p i n j and h e l i c i t y m of produced s t a t e s . A s i t can be s e e n t h e ti, p,, and rh moments c a n t a i n i n g t h e mar; and t dependence r e p r e s e n t t h e f u l l e x p e r i m e n t a l i n f o r m a t i o n , h i g h h' b e i n g e n t i r e l y due t o h i g h h e l i c i t y s t a t e s .

T:oments of t h e a n g u l a r d i s t r i b u t i o n a r e b i l i n e a r combinations of a m p l i t u d e s which i n t u r n g i v e a complete d e s c r i p t i o n of t h e r e a c t i o n . The formalism of n u c l e o n t r a n s v e r s i t y a m p l i t u d e s has been used C2,43.

There a r e two s e t s of nucleon t r a n s v e r s i t y a m p l i t u d e s

Ugi -

0 ,

E ' h k - r e c o i l t r a n s v e r s i t y up where

U ( N )

-

Reasons f o r u s i n g t h e s e a m p l i t u d e s , t h e i r a d v a n t a g e s and disadvan- t a g e s a r e d e s c r i b e d i n r e f . 161.

111

-

T h i s p a p e r i s based on t h e r e s u l t s of t h e t h r e e experiments mentio- ned i n Se,ct_ion I.

The n fr mass s p e c t r a f o r t h e s e experiments f o r \t\<0.2 ~ e v ' a n d 0.2[\tl<l .O ~ e V ' a r s shown i n f i g . 2.

F i 2 ntf m a s s s p e c t r a from exp. Ftg. 3 High it1 normalized 9 ,

I./&, exp

.

.

f o r low/a/ and high/b/ f o u r - I/@/ and exp. III/O/.

-momentum t r a n s f e r r e g i o n .

The main d i f f e r e n c e s between t h e h i g h ana t h e low It[ r e g i o n s a r e connected w i t h t h e growing r o l e of t h e n a t u r a l exchange. But t h e r e i s a h i g h I t \ e f f e c t which cannot be i n t e r p r e t e d i n s u c h a way. We mean h e r e a p e c u l i a r b e h a v i o u r of t h e t;, ti, t: and t o some e x t e n t t h e ti mo-

- merits / s e e f i g . 3/ between 700 MeV and 1200 YeV. These moments while weaker t h a n t h e dominant ones showing t h e ~ ( 7 7 0 ) and f (I 270) resonan- c e s a r e n e v e r t h e l e s s s i g n i f i c a n t l y d e v i a t i n g from t h e z e r o v a l u e i n t h i s mass r e g i o n t h u s s t r o n g l y s u g g e s t i n g a new broad o b j e c t . I t should be s t r e s s e d t h a t t h i s e f f e c t i s observed a t both 17.2 GeV and 63 GeV and t h e moments u n d e r c o n s i d e r a t i o n do n o t change w i t h t h e beam energy.

A more d e t a i l e d i n v e s t i g a t i o n shows t h a t t h i s e f f e c t i n c r e a s y w i t h i n c r e a s i n g i t \ / s e e f i g . 4/ b e i n g n e g l i g i b l e a t i t lc0.2 GeV ,

weak below 0.35 G ~ and s t r o n g above t h i s v a l u e , i n p a r t i c u l a r above V ~ 1 . 0 GeV2.

F i 4 +dependence of t h e t:, t3, t: 3 and t: moments f o r experiment 1/87 and experiment I I I / O / . The shaded a r e a d e n o t e s t h e r e g i o n of v a l u e s f o r ltlL0.2 GeVL, 0 - 0.2(1t140.35 GeVz/a/, @

-

-

The most i n t e r e s t i n g f e a t u r e i s i t s t a r g e t dependence. The t;

moments i n q u e s t i o n a r e c l e a r l y

a0 2 weaker on a b u t a n o l t a r g e t t h a n

.O on a hydrogen one / f i g . 5/. T t

OW s h o u l d be s t r e s s e d t h a t f o r s(770)

and f (1 270) t h e r e is no d i f f e r e n c e between t h e hydrogen and b u t a n o l t a r g e t s . I t s u g g e s t s t h a t t h i s o b j e c t i s s t r o n g l y absorbed i n s i d e

-0.0 2 t h e nucleus. I n s p e c t i n g t h e a m p l i t u d e s con-

.a 1.0 1.2 1.4 , 8 t r i b u t i n g t o t h e moments d e s c r i b e d

3 4 above C41 one c a n guess t h a t t h i s

Fig. 5 t:, t3, t3 and t t ^moments o b j e c t i s produced i n t h e wave D from experiment T on hydrogen/@/ w i t h h e l i c i t y m=2 through t h e un- and from experiment T I on b u t a n o l n a t u r a l exchange. Such a n unusual /0/ t a r g s t , b o t h a t 17.2 GeV. mason h a s n e v e r been observad may be because t h e h i g h \ t i r e g i o n was n e v e r thoroughly i n v e s t i g a t e d .

S i n c e v,e seem t o observe a n u n u s u a l o b j e c t some e f f o r t s were d e d i - c a t e d t o s e a r c h f o r p o s s i b l e non-resonance e x p l a n a t i o n s . Both e r r o r s i n a c c e p t a n c e c o r r e c t i o n s and c o n t r i b u t i o n s from d i f f r a c t i v c l j r produced N " r e s o n a n c e s were excluded.

c2-292 JOURNAL DE PHYSIQUE

IV

-

In this section we describe a model independent partial wave analy- sis at 17.2 GeV where experiments I and 11 srovide us with a full set

of momants. This is an energy independent analysis i.e. each

m = 4 0 MeV mass bin has been treated separately. This analy- sis is very similar to that performed at low t for the same experiments and we refer re

:F]

Rybicki ll42 for more details.

In our case S, P and D waves are taken into account with all possible values of helicity m up

a2

~I+I,+

ti

and unnatural spin-parity

o exchange.

Tn general unique solutions are found or solutions with overlapping errors as it can be seen in fig. 6. The wall known resonances ~ ( 1 3 0 0 ) , ^{gU70) and}

f U 2 7 0 ) are clearly visible. In the D t u wave there is weaker but very significant broad object previously seen in the high M moments around 900 MeV. The re- sults of Breit

-

the observed resonances are shown in table 1.

A consistency of our fits to the well known resonances rith the acceptable values of 3

mmrlcevl yields more confidence to all

our results including the unusu- Fig. 6 I:lass dependence of the par- al new object in the D, rave.

tial waves intensities in the high Although in this analysis t region. Solid lines show the phases provide less information Breit

-

ces. in qualitative agreement with

the Breit-Wigner behaviour of

the D,,J wave thus representing additional though weaker argument in fa-

v o y o f the D,,C840) resonance.

Table 1.

Breit - Zigner fits to the resonances.

resonance mass region wave mass width J ~ N D F Laevl CMeVJ

f[l 300) 1020-1 500 MeV S 1287512 137224 1.3

~(7.770) 580-1 020 MeV P o 7 6 5 ~ 5 141+10 7.1

f (1 270) 1020-1 500 YeV Do 1 2 7 5 ~ 8 39121 5 1.2 '2~ (840) 680-1 200 MeV _{D 2 ~ 84221} 9 248245 1 . I

Thsn energy depzndsnt partial wave analysis was done for 17.2 GeV and 63 GeV in order to compare rssults with the energy independent

a n a l y s i s and t o determine the c r o s s s e c t i o n energy dependence f o r t h e production of our new s t a t e . The r e s u l t s of t h e s e two analyses were i n good agreement one with another. Assuming a d d i t i o n a l l y c ; , , ~ E , ~ i ~ d e p e n - dence we have obtained n=2.1+0.3. I t agrees w i t h t h e r e s u l t s f o r t h e u n n a t u r a l exchange.

V

-

Let us r e c a p i t u l a t e t h e f e a t u r e s of our new meson s t a t e : mass = ( 8 4 0 + 2 0 ) - ~ e ~ ,

width ~250-YeV.

J PC = 2 t t h 2 l i c i t j r -2,

production v i a t h e unnatural exchange,

cross-section b j a n o r d e r of magnitude lower than t h a t of - ( l . h f 0 , S ) 770 ,

energy depandence p , , ~

s t r o n g coupling t o n'n- channel. + t

#e do not s e z any simple grplanationof t h i s o b j e c t . The ^{J PC =} 2 n o a e t 1 3 completely f i l l e d t h u s one can suspect e i t h e r gluonium o r f o u r :uark o b j e c t . The z i t gluonium s t a t e s a r e p r e d i c t e d a t higher mass e.g. by De T a r and Donoghue L5J.

A r e l a t i v e l y l a r g e width of our o b j e c t could i n t u r n i n d i c a t e a f o u r quark nature. Another h i n t i n t h i s d i r e c t i o n may be represented by t h e observation t h a t t h i s o b j e c t i s f a i r l y s t r o n g l y absorbed even i n such r e l a t i v e l y l i g h t n u c l e i a s carbon ones. I t can be deduced from t h e d i f f e r e n c e s between the moments from hydrogen and butanol. Ac_co_r- d i n g t o Lipkin C61 such behaviour i s expected f o r l o o s e l y bound qqqq s t a t e s . I f what we observe i s indeed a four-quark o b j e c t then t h e e s t i m a t i o n of 1500 MeV f o r t h e mass of such s t a t e C5J w i l l have t o be reconsidered.

However even f o r a ^q<qq s t a t e we do not s e e any simple production mechanism l e a d i n g t o a m = 2 s t a t e through an u n n a t u r a l exchange.

Thus, t h e Dzu(840) which we claim t o have discovered c e r t a i n l y needs f u r t h e r e f f o r t b o t h experimental and t h e o r e t i c a l .

Cll B.Hyams e t al.,Nucl,Phys.B7311973) ,189.

123 H,Becker e t al, ,Nucl.Ehys ,B150 (7 979) ,301.

C3j B,Alper e t al., E l a s t i c and T o t a l f f 3 \ - Cross S e c t i o n from a High S t a t i s t i c s Eileasurement of t h e Reaction ii-p 9 nin-m a t 63 GeV, XX 1nt.Conf. on High Energy E w s i c s , Geneva 1979

.

C4J G, Lutz and ^'E o l a r i z a t i o n i n t h e Reaction n-p+ ntmITm

hTI r e p o r t C5J C.E.De T a r

UUIDT 83/3 UMHEP-17,

L6J ~ . ~ i p k ~ n ; ~ h e ~ ~ ~ u c c e s s e s and F a i l u r e s of t h e C o n s t i t u e n t Quark lFodol , Fermilab Pub-82-82 (November 1 982) ,