study of (π n) and (ππ n) mass enhancements in nucleon diffraction dissociation) mass...

$: Study of (π N) and (ππ N) mass enhancements in nucleon diffraction dissociation) mass enhancements in nucleon diffraction dissociation$
IL NUOVO CIMENTO VOL. 58 A, N. 3 1 Agosto 1980

Study of (rcoV) and (7~7~oV) Mass Enhancements

in Nucleon Diffraction Dissociation.

C. FUKUNAGA, l~. HAMATSU, T. HIlCOSE~ S. KITAMURA and T. YAtVIAGATA

Department o] Physics, Tokyo Metropolitan University - Setagaya, Tokyo

(ricevuto il 26 Maggio 1980)

Summary. - - A study of (n,N') mass enhancements in the diffraction dissociations, r:+p---~n+(,':°p)dd and n+(n+n)d d at 16 GeV/c, has been made in terms of the mass M and width P of diffractively produced (nJT) and (==J~) mass enhancements. The values of M and F observed are M = (1344 ± 5), (1451 ± 7), (1639 ~ 7) MeV and F = (66 ~ 14), (132 ~= 22), (96±20) MeV, respectively. From the detailed comparison of world data, we found the systematic difference of 3I and F between (=~V) or ( r :~ ' ) enhancements and resonances produced in formation experiments. It is shown that Deck-resonance interference cannot give an adequate explanation for these observations. We discuss possible inter- pretations for reaction mechanisms of producing nucleon mass enhancements in connection with the nature of the pomeron exchanged.

1 . - I n t r o d u c t i o n .

In order to make a detailed s tudy of production mechanisms of resonances,

(noV) systems have the unique aspect tha t they can be investigated both in

the formation and the production reactions. Actually, over the past then years,

nucleon resonances decaying into (~OV) or (::~oV) systems have extensively

been investigated by phase-shift analyses (1), utilizing data obtained in the

r:oV formation experiments. These nucleon resonances can be well explained

by models based on three consti tuent quarks, as far as the mass of resonances

with the isospin I = 1 is lower than 1.8 GeV.

(1) R. J. CASItMOR]~: Proceedb~gs o] the I X International Con/erence on High-Energy .Physics (Tokyo, 1978), p. 811.

199

2{}0 C. FUKUNAGA, R. tIAMATSU, T. IIIROS:E, 8. KITAMURA ~lld T. YAMAGATA

There are also many production experiments (2,~) in which ~3~' and ~ 3 q '

nucleon resonances with I = ½ are diffractively produced. We demonstrate in

fig. I the compilation of masses M and widths F of the enhancements observed

in diffraction dissociations (dd), Ap -~ A(7:A ~) or Ap --~ A ( ~ J T ) , where A stands

for r,, K, p or ~ beams. One can see a wide spread of values of M and 1" with

different experimental errors, in particular for the (~A ~) mass enh,~ncements

between 1A and 1.5 GeV. Recent ly we have found a narrow (7:2T) mass enhancements at M(~JV) =

1.36 GcV with F = 67 MeV (~), which could not be accommodated in the con-

(2) ~3W systems: a) R. B. BELL, D. J. CRENNELL, 1 ~. V. C. 110UGlt, 11. KARSHON, K. W. LAI, J. M. SCARR, T. G. •CtlUMANN, I. O. SKILLICORN and R. C. STRANI~: Phys. ~ev..Lett., 20, 164 (1968); b) A. SHAPIlZA, O. B:ENAYY, Y. EIS:ENB:ERG, E. ]~. RONAT, D. YAFFE and G. YEKUTI:ELI: Phys. Rev. ~ett., 21, 1835 (1968); c) T. H. TAN, M. L. P:ERL, F. MARTIN, W. CHINOWSKY, R. KI:NS:EY, S. KL:EIN, P. SCnMIDT, M. ~IANDELKERN and J. SCHULTZ: Phys..Lett. B, 28, 195 (1968); d) Z. M. MA and E. COLTON: Phys. ~e~,. .Lett., 26, 334 (1971); e) W. GAGE, E. COLTON and W. CrlI~OWSKY: .Nucl. Phys. B, 46, 21 (1972); ]) D. LISSAUER, A. FIRESTON:E, J. GIN:ESTET, G. GOLDIIABER and G. H. TRILLING: Phys. l~ev. D, 6, 1852 (1972); g) B. MUSGRAV:E, 1'. P:E:ET:ERS, P. SCttREINER, J. WnITMOR:E and H. YUTA: Nucl. Phys. B, 87, 365 (1975); h) R. R. APeLE, ~V. ~V. ASH, D. C. CtIENG, D. G. COYNE, D. GROSSMAN, G. K. O'N:EILL, M. CAVALLI-SFORZA, G. FERMI, G. GOGGI, F. IMP:ELLIZZ:ERI and M. LIVAN: Lett. Nuovo Cimento, 18, 167 (1977). (3) = ~ " systems: a) J. J. RHODE, R. A. LEACOCK, V~ ~. J. KERNAN, R. A. JESP:ERSI,:N and T. L. SrlALK: Phys. l~ev., 187, 1844 (1969); b) J. BALLAM, G. B. CHADWICK, Z. G. T. GUIRAGOSSIAN, W. B. JOIII~SON, D. W. G. S. L:EIGH and K. MORIYASU: Phys. Rev. D, 4, 1946 (1971); c) K. BOESBECK, H. GRA:ESSLER, G. KRAUS, R. ScnuT:E, H. BO}:rTCn:ER, U. GEUSII, J. KALTWASSER, D. POS:E, K. BOECKI~IANN, J. G. BOSS]~N, 11. DREVERMANN, W. JOnNSS~N, E. PROrACI[, M. REST, K. ST:ERNB:ERG:ER, A. A~G:ELOrOULOS, T. B:ESLIU, V. T. COCCONI, P. F. DALPIAZ, P. ])UII~KEV, J. D. t[AUSEN, W. KITTEL, i). R. O. MOR- RISEN, J. B. WIIITTAK:ER, S. BRANDT, T. P. SHAII, H. ST:EIL, ~I. J. COUNIIIAM, S. J. GOLDSACK, G. A. GRAMMATIKAKIS, ~I. J. LOSTY, B. BL'SCHBECK-CZAPI', G. OTTER, P. PORTII and 1 ). SCHM1DT: Nucl. Phys. B, 33, 445 (1971); d) J. G. RUStlBROOK, J. R. WILLIAMS, N. C. BARFORD, J. J. ZESTY and K. PONGPOORSKSRI: Phys. J~ec. D, 4, 3273 (1971); e) U. KARSHON, G. YEEUTIELI, D. YAFFE, A. S]IAPIRA, E. E. RONAT and Y. EISENBERG: N~tcl. Phys. B, 37, 371 (1972); ]) E. E. RONAT, Y. EIS:EI~BERG, L. LYONS, A. S~tAeIRA, S. TOAF}" and G. ¥:EKUTI:ELI: 2Yucl. Phys. B, 38, 20 (1972); g) S. LICHTMAN, N. N. BISWAS, ~N. M. CASON, V. P. KE~-NY, J. T. McGAIIAM, W. D. SH:EPHARD and P. H. SMITH: Nucl. Phys. 13, 81, 31 (1974); h) M. CAVALLI-SFORZA, C. CONTA, M. FRAT:ERNALI, G. GOGGI, F. IMPELLIZZERI, G. (~. ~[ANTOVANI, F. PASTORE, S. RATTI, B. ROSSINI, D. SCANICCIIIO and I[. SANDROZINSKI: Lett. Nuovo Cimento, 14, 345, 353, 359 (1975); i) It. W. ATERTON, B. R. FRENCh, J. SKURA, J. BoIl.~t, J. CVACn, M. JIRES, J. SEDLAK, V. SIMAK and J. ZAC:EK: Nucl. Phys. B, 103, 381 (1976); j) P. M. HEIN:EN, J. J. EN,}LER, E. W. K1TT:EI., W. J. METZG:ER, ~[. ~]. SIIOUTEN, J. S. M. V:ERGE:EST, R. T. VAN D:E WALL:E, B. JONGEJANS, H. VOORTHUIS, ~|. CERRADA, R. J. HEMINGWAY, S. 0. HOLMGREN and M. J. LOST¥: Nucl. Phys. B, 122, 443 (1977); k) G. W. VAN AP:ELDOORN, D. HARTING, I). J. HOLTnNIZ:EN, B. J. I)IJLGROMS, M. M. H. M. RIJSSENB:E:EK and J. M. WARM~RI)AM-D:E L:EENW: _Nucl. Phys. B, 159, l l l (1979). (*) T. HIROSE, K. KANAI, S. KITA~IURA P~Ild W. KOBAYASHI: ~to?'o Cime*~to A, 50,

120 (1979).

STUD~" oF (~A') AXD (==A') _~IAss ~:Nm~.~CE~F~NTS m'C. 201

300

2OO

% ~oo

20O

X

~ ~oo t.

/

cz) I c . . . . . I

÷ c+t, I I

t)) i - . . . . . I

t i i ( i i

,,,, L]

0 I 1 1.3 I.Z. 1.5

H(GeV)

I I

jr

F p ~ 5 :---]!! "T ,if'U, E v

t I 1.6 1.7 1.8

Fig. 1. - Masses (M) and widths (F) of a) (~V) mFd b) (-=.A ~) enhancements. open circles in a) arc results obtained in the reaction :~+P--~=+(~,-~))d,~ at 16 GcV/('.

The

v e n t i o n a l f r~mework of S U6~ Oa b~sed on the three c o n s t i t u e n t qm~rks. This

sigmfl has ~lso been confirmed in other diffractive l)roe(;sses with incident k~on (~i), pion (~) aml nucleon (s,~) at different energies. MAC G]~n~on inter-

pre tcd this enhancement as a band head of (=A ~) non:~diabatic ro ta t ional b~'md (s).

I t has genera l ly been aecei)ted ~hat two e n h a n c e m e n t s a t aa'ound 7.45

(5) G. ])). CHADWICK, J. T. CARRO].I., V. CHALOUFKA, J . BALI,AM, J . BoucnEz, P. HERQUET, D. KINGLIN, K. C. ~IOI.'I.'EIT. R. STEV)]NS, V. ])AVI1)SON, A. FIRESTONE, F. NAGY, C. PECK, L. ROSENFELD, R. ELY. D. (~RETH]~;K and ]'. ODDONE: Phys. Rec. D, 17, 1713 (1978). (6) J. BIEL, E. BLE8ZV, T. FEtCB:~;L, D. FRI~YTAG, B. GOBBI, L. KENAtt, J. Ro~E_',-, R. RUCI{TI, P. ~LATTERY and D. UNDERWOOD: Phys. Z'er..Lett., 36, 504, 507 (1976). (~) H. DE KERlCET, E. NAGY, )1. REGLE]¢, W. SCttMIDT-I'ARZEFALL, K. R. SCIIUBERT, K. ~\rINTEI~, A. BRANDT, H. DIBON, G. FLU(;G~?, F. NIEBERGALL, P. E. SCIFUMACIlER, J . J . AUBERT, C. BROLL, G. COIGRET, J . PAVI]~R, L. ~IASSONNET, .~,|. VIVASt(¢EN'r, ~:V. BARTL, t[. I"ACHIN(;~ER, ('Ft. GOTTFRIED and G. NEUIIOF]~R : ])hy,~'. Lett. B, 63, 477 (1976). (s) M. tI. MAC GREGOI~: Phys. ~ec. D, 20, 1616 (1979).

202 C. FUKUNAGA, R. HAMATSU, T. HIROSE, S. KITAMURA and T. YAMAGATA

and 1.7 GeV bo th in the (~A °) and (nn2~ o) systems might correspond to

1~11(1.47) and F15(1.69), respectively, L2m being the usual spectroscopic no- ta t ions with an orbital angular m o m e n t u m L, an isospin I and a to ta l spin J for the (TrA o) or (nnW) diffractive systems. In some experiments (2,), the authors

claimed tha t D13(1.52) could also be seen. In what follows, we will distinguish resonances having so far been clarified in the format ion experiments (called F-resonances) f rom resonances observed in the diffractive processes (called D-resonances) if necessary.

I t was proposed tha t the diffractive process could selectively produce par- t icular resonances which satisfy the spin-pari ty relation, i.e. the Gribov-Mor- rison rule (9) AP ---- ( - -1 ) a j, where AP represents par i ty change and A J spin change between a target nucleon and a diffractive system. According to this

selection rule, three F-resonances Ply, D~3, F~5 should also emerge in the diffractive ( : :~) and (~ndX o) systems. Figure 1, however, indicates tha t m a n y data points of M and F significantly deviate f rom the repor ted values of 1)~1, D13 and F15 shown with the dashed line. A °* resonances produced by dd are always associated with broad low-mass enhancements near the ( n S ) and (r~nJV) thresholds due to one-pion exchange Deck mechanism (lo). I t should be noted tha t the values of M a n d / ' are ra ther sensitive to the Deck background which causes wide scatterings of data points especially a t around

1.45 GeV. In this paper, we precisely investigate the (::2V) mass distributions in the

reactions

(1) 7:+p -+ ~+,:+n,

(2) rc+p ~ r:+nOp

measured in a bubble chamber exper iment using the CEI~T 2 m hydrogen bubble chamber at the incident pion momen tum 16 GeV/c. Comparing systematical ly world data of three-body and four-body diffraction dissociations, we will make a detailed analysis of d~* resonances observed in product ion ex-

periments in terms of mass and width. In sect. 2, we briefly describe a method to separate diffractive processes

(3) 7:+p -~ 7:+(7:+n)~d,

(4) ~:+p -~ u+(::°p)~d •

Assuming a smooth background, we tr ied to fit the (rc0V) mass distributions and est imated the product ion cross-sections of the (nW) mass enhancements .

(9) V. N. GIClBOV: Yad. Eiz., 5, 197 (1967); D. R. 0. Mom~ISO~': Phys. Bey., 165, 1699 (1968). (lo) S. D. DR~LL ~nd K. HIIDA: Phys. Rev. Lett., 7, 199 (1961).

STUDY OF (7~ ~) AbID ( ~ ; ~ ) MASS ENHANCEMENTS ETC. 203

I n sect. 3, we inves t iga ted the nature of the broad background using an one-

pion exchange Deck model. Presenting, in sect. 4, the values of M and F ob-

ta ined in other exper iments , we compgre the method of analyses, in whici~

broad backgrounds were t rea ted in a different manner , and derive world averages of M and F for the ( r :~) and (~:~A o) enhancements . In sect. $, we discuss

interference effects between resonances and Deck backgrounds. Section 6

is devoted to a discussion on the possible in te rpre ta t ion of the new mass

enhancements , in relat ion with reaction mechanisms in which the pomeron plays an impor t an t role. S u m m a r y and discussion are given in sect. 7.

2. - Separation and purification of diffraction dissociation.

For tile separat ion of various re~ction channels emerging in the reactions (1)

and (2), we have per formed a mult idimensional analysis, i.e. a pr i sm plot anal-

ysis (PPA). A detailed description of the technical aspect has been given in

ref. (H). Here we briefly i l lustrate the method concerning the separat ion of the dd channel.

The P P A is an i tcrat ive comparison between exper imenta l da ta and a set of Monte Carlo (MC) sample grouped into different classes of reaction mechanisms. Comparison is carried out by count ing how m a n y MC events belong

to a four-dimensional box around each exper imenta l event (tagging). A possible choice of full k inemat ica l variables to define an event is to combine two

Van Hove ' s longitudinal variables and two kinetic energies.

F r o m n u m b e r of MC events falling into each box, one can c~lculate ~ weight

represent ing the probabi l i ty for this event to belong to one of the react ion channels in t roduced as follows:

~+p -+ ::+A + ,

-~ ~+(x+n)d a ,

--> phase space ;

~z+p -+ tz+p, -+ g+p,

.-~ 7xoA++,

7~+(7~Op)dd ,

- + p h a s c space .

(al) M. DEUTSCIIMANN, l ). SCHMITZ, R. SCnULT~, M. KL~Iz~, R. NAHNIIAUER, K. BOCK- MANN, ]I. I'LOTNOW, G. ZONBEI~NIG, T. COGHI~N, M. J. COUNIHAN, S. HUMBLE, W. KITTldL, D. R. O. •[ORICISON, H. RUDNICKA, L. SUSZYCKI, T. HIROSE, E. LEITNER and T. STIEWE: Nucl. Phys. B, 86, 227 (1975).

20z~ C. FUKUNAGA, R. t[AMATSU, T. ltIROSJg, S. KITAMU:RA ~lld T. YAMAGATA

At the initial generation of MC events, we adopted a Brei t-Wigner funct ion for resonances and a squared-mass shape for dd and all angular distributions

were chosen to be flat. After the initial tagging procedure, one gets the input to construct the MC samples for the subsequent step by plot t ing invariant

masses, product ion and decay angular distributions. After 10 (13) interactions for the reaction I (2), no significant variat ion is observed in the shape and magni tude of the differential cross-sections in the two subsequent steps. We can thus consider t ha t the i terat ion procedure has finished.

I t should be noted tha t the P P A can simultaneously separate the con- tam]nat ions due to elastic scattering and mult ineutral product ions which are misfit ted as the reactions (1) and (2). Data samples obtained in 1C fits consist

of 7020 events and 10997 events for the reactions (1) and (2), respectively,

with a X -~ probabil i ty higher than 5 %. Using separated events by :PPA, we tr ied to purify the dd sample from k ~.

We define the ampli tudc M z describing product ion of ~ (=3~ ~) state with ~m isospin I through an I E exchange. The isospin analysis of 7:±p -~ 7~(,~3~ °) at

16 GcV/e ( ,2)has shown tha t the contribution of ['IM~IdR and the interference w3

effects among M~, M~, M~ were negligible. I t is, therefore., justified to impose the constraint of the isospin relation among the cross-sections a(A ~+ ~-::~p)" :a(A+ - ~ o p ) : a ( A + ~ rc~n) . , . 2 1 .~ .a . If we assume tha t A+ and A++ produc-

tions proceed via same reaction mechanisms, we can m~ke use of A ++ saml)les to achieve cleaner dd separation from A + events. After this purification, wc obtained 6460 ~n(1 3945 events corresponding to the cross-sections aa,~(.-:~n)

(259~10)[zb and a,,(~(~°p)---- (17] ±7)[~b for the reactions (3) and (4), respectively. Hereaf ter the ana.lysis is mainly based on purified (1(1 samples. Fig- ures 2a) and b) show the (~3~ ~) mass distributions of purified dd events for the reactions (3) and (4). Selecting the t' region with It ' l~0.1 (GeV/c)", t' being the four -momentum transfer squared between the t}~rget l)roton and the outgoing diffn~ctive system, w,: considerably enhanced the signal at 1.34 GeV over the bro,~d low-mass background, whereas the signals ~t 1.45 and 1.64 GeV are pronounced in the mass distribution with lt']~ 0.2 (GeV/c)'-'. This is a t t r ibu ted

to the well-known fact tha t the slope of the forward peak of da/dt de(.reases quickly as the (wOg) mass increases. In order to increase the statistica.l ac- curacy, we combined the data saint)los of (~+n) and (,=Op) systems as sho~vn in

fig. 3 with It'l<0.1 (GeV/c)'-' and in fig. 4 with It'l>~0.2 (GeV/c) 2. Adopting the Brei t-Wigner functions and second-order polyncmi;~ls, we

separately fitted the m:~ss distribution of fig. 3 and 4. The best-fit values thus

(~2) j . V. B ~ : A u P ~ , II . (~tCASSL]SR, P. LAUSCH:I'~R, G. OTTI~]~, •- ~|ATTI[AJGUS, ik. ~|]~Y~R, K. BOCKMANX, G. FRANZEN, U. IDSCtIOK, ]). KOB~, E. P1~,OPACII, V. T. COCCONI. G. T. JON};S, G. KELLNER, W. KITTEL, D. R. (). ~[ORRISON, O. SOTII~,IOU, N. ~ . BISWAS, ~N. 5I. CASON, V. P. KENNEY, W. D. SIII';I'HARD, •. J . BAR181I, \V. SELO¥:E and tI . YUTA:

.Nucl. Phys. B, 66, 93 (1973).

STUDY OF ( r ~ ) AI~D (~r:.~ ~) 3IASS ENIIANC]~MENT$ ETC. 205

o 160

80

d

0

120

6O

c,q

~o

o

d

4.0

0 1.0 3.0 1.5 2.0 2.5 3.0

M (n r~+)(GeV)

e3

b)

63

1,0 1.5 2.0 2.5

H ( p "~°)(GeV)

Fig. 2 . - I n v a r i a n t (vzjT) mass d i s t r ibu t ions of pur i f ied events for the react ions r:+p--~:+(7:+n)d d (a), c), e)) and T:+p--~r:+(=°p)dd (b), d), ])). The d is t r ibu t ions c) and d) are for ]t'[ < 0.1 (GeV/c) 2 and e) and ]) for It'[ >/0 2 (GeV/e) 2.

300

200

%-

ql

~ loo

f

0 1.0 2.5 1.5 2.0

~"/( J~ n)(GeV)

Fig. 3 . - I n v a r i a n t ( r : ~ ) mass d i s t r ibu t ion wi th I t ' [<0 .1 (GeV/c) 2. The solid and dashed curves show the f i t ted rcsuI~s for the mass enhancements and the background , respect ive ly . The con t r ibu t ion of the Deck background is given b y the do t t ed curve,

206 c . FUKUNAGA~ R. IIAMATSU~ T. HIROSE~ S. KITAMURA a n d T. YAMAGATA

] i I ]

"~ 80

1.0 1.5 2.0 2.5 3.0 3.5 M(,/Cn)(GeV)

Fig. 4 . - Invariant (T:JV') mass distribution with [t']~>0.2 (GeV/e) 2. Three curves indicate the same functions as in fig. 3.

ob ta ined are summar i zed in t ab le I t oge the r wi th the ;/2 probabi l i t ies a n d the

confidence levels. The mass a nd wid th M = (1344=}=5), F ---- (66 4-14) MeV are cons is ten t wi th the values ob ta ined before (4) wi th in the s ta t i s t ica l error .

To check sens i t iv i ty of M a nd Y to a va r i a t ion of t he backg round , we also t r i ed

TABLE I. -- Masses and widths of the (=J~?) mass enhancements obtained by the Z ~- ]ittings and the cross-sections ]or the (7:+n)+(~°p) systems.

Mass Width •2/d.o.f. Confidence level a (~b)

1344 -4- 5 66 4- 14 21.5/15 ~ 15% 26 =[= 6

1451 ± 7 132 4- 22 48 =t= 11 19.2/22 ~ 85%

1639 4- 7 96 -4- 20 29 J= 8

to fit t he mass d is t r ibut ions of fig. 3 a nd 4 b y chang ing the m a g n i t u d e of t he

b a c k g r o u n d b y :10 %. This modi f ica t ion of the b a c k g r o u n d led to no signif icant

change of the mass values for th ree e n h a n c e m e n t s b u t to a b o u t =t=20 MeV

devia t ion of t he w id th f r o m the bes t f i t ted values.

P a r a m e t r i z i n g the fo rward p e a k of t' dis t r ibut ions as

d ( l (5) d-t = A exp Ibm'],

STUDY OF (~N') A~D (~:r:~') MASS ENHANC]~MENTS ETC.

we obtained the values of the slope pa rame te r b by fit t ing

207

b---- 9.0 ± 0.2,

b---- 3.8 ~ 0.2,

b = 3.4-~ 0.1,

1.28 < M < 1.41 ~ I e V ,

1.32 < M < 1.58 MeV,

] . 5 4 < M < 1.74 MeV.

Using these values, we es t imated the product ion cross-sections for the three

enhancements as given in table I . Note tha t the to ta l cross-section of diffrac-

t ion dissociation is add = ~d~(~+n) ~- ad~(~:°p) = (430:~13) ~b.

3. - Inves t igat ion o f broad background based on the D e c k model .

I t is widely accepted t h a t the broad background under the relat ively narrow-

mass enhancements is main ly a t t r ibu ted to the one-pion exchange Deck mech-

anism. I n order to check to what ex ten t the Deck componen t contr ibuted

to the background, we constructed the Deck ampl i tude given as

(6) Y = M==(s~, t~, t~) A,Jt.,, M') V=ovov(t ~)

with kinemat ica l variables i l lustrated in fig. 5. The pion p ropaga tor A n is

pa ramet r ized as

A~(t, M '~) = Oi2)~'( '~ ' t~__#2

S~ M ~

M n [

P

s

Fig. 5. - Deck model diagram for the reaction up - , 7:~:2~'. For details see the text.

2 0 8 C. FUKUNAGA~ R. HAMATSU~ T. IIIROSE~ S. KITAMURA ~tnd T. YA)IAGATA

where ~(t2) = t+-- #2 with the pion mass/~. The pion-nueleon ver tex is de- fined as

(7) V~.v.v(t2) : GF'(t2)~(q~)75 ~ u(p.~)q~ ,

where G2/4~ = 14 and .~r~'(t2) is a ver tex form factor which satisfies F'(/~:)----1.

Assuming pomeron exchange for the process (3) and pomeron + f-reg- geon exchanges for the process (4), we formulated the scattering ampli tude

as follows:

(8) M(sl, tl, t2) ---- F'(t~)(mp -~ m,) ,

\So / 2 '

(10) m ~ - / ' (1 ~- a,(t~)) a,(tl) ~ ( t ~ \so/

with the trajectories a=(t~) ---- i + 0.3tl and a,(tl) ---- 0.5 -~- t~.

The overall form factor F(t2)= F'(t~).F"(t2) was assumed to be

(11) ~(t .) = exp [ / ( t ~ - ~'-)].

The adjustable parameter / was determined to be ] = 1.8 by the detailed comparison with the experimental data, as described in ref. (13). This first-order ampli tude can well reproduce the gross features of various distributions, e.g. mass, t' and decay angular distributions. The Deck backgrounds thus calculated for the (7:+n) and (7~°p) systems are exhibited in fig. 3 and 4. Figure 3 shows tha t the (7:A ~) threshold region lower than 1.3 GeV is near ly filled with the Deck background, whereas the background in the higher-mass region cannot be well described only by the Deck mechanism; this becomes more apparen t in the higher-t ' region (fig. 4). I t seems tha t , even if a more complex Deck ampl i tude is employed, the sil~uation will not drastically be changed. Such an insufficient magni tude of the Deck contr ibut ion suggests us tha t there exists

addit ional contr ibutions other t han three (7:W) mass enhancements and the Deck background. There may be contr ibut ion f rom various F-resonances, e.g. Pn, D13 etc., which one cannot recognize as clear peaks due to either broad

widths or small cross-sections.

4. - Comparison with other data.

a) 7:A e mass enhancements. Masses and widths of (7:A e) enhancements

so far obtained are given in table I I and those of (Tw:A ~) in table I I I . They

(13) T. HI ,ps i , K. KAXAI and T. KOBAYAStII: Prog. Theor. Phys., 57, 1334 (1977).

STUDY OF (7~v~) AND ( 7 7 ~ ) I~IASS ENI-IA:NC:EM]~NTS ETC. 209

are also exhib i ted in fig. 1. where the dashed squares indica te M and F of the

F- resonances e.g. P ~ , D~3, ~'~5 (~) a nd the open circles show our results. I u

add i t ion to the expe r imen ta l results used here, there are some o ther exper iments

to inves t iga te dd, in which mass and wid th have no t been ob ta ined in fi t t ing.

The a lphabe t ica l marks in fig. i refer to da t a in tables I I and I I I . Fo r a lmos t

TABLet II . - World data o] masses and widths o] the (=~\)) system obse~'ved in three-body di]]ractio~ dissociations.

3L~ss Width Reaction Momentum Ref. (GeV/c)

a)

A 1405 4- 30 100 ~+p --~ rz+(nr: +) 6.0 (2a)

B 13904-20 1504- 60 pn --~p(p=-) 7.0 (2c)

C 14624- 6 54~: 12 pp - ~ p ( ~ ) 6.0 (2~)

D 14104-33 212~: 62 pn -~p(p~,-) 6.6 (2e)

E 1390 4- 10 145 4- 35 K+p-+ K+(~l'~:) 2.53-- 3.2 ("g)

2' 15104- 7 1014- 26 K + p - + K + ( ~ ) 2.53--3.2 (2g)

G 1458 ~: 20 120 ~ 20 pp -+ p(pr: °) 28.5 (2n)

H 1473 ~: 5 30 ± 30 pp -~p(n~ +) 28.5 (.)h)

b)

A ' 1641 4- 30 100 ~+p -+ =+(n~ +) 6.0 (2,)

B' 1650 ~ l0 94 i 20 pp -~p(~N~) 6.6 (-.a)

C' 1686 4- 12 135 :[: 20 K+p-+ K+(~N~T:) 2 .53+ 3.2 ('-'g)

D' 1680 4- 25 150 ~ 10t) pp --~p(w: °) 28.5 (2h)

E ~ 1660 4- 20 150 :J: 70 pp -+ p(n~, +) 28.5 (2a)

all da ta , on ly s ta t is t ica l errors were t a k e n into account , b u t the values of M

and I" are h igh ly dependen t of backg round . I n order to calcula te the wor ld aver-

age values of M a n d / ' for tile e n h a n c e m e n t a r o u n d 1.45 GeV, we should careful ly

check the m e t h o d of analysis . I n some analyses, e.g. (~b), the Deck b a c k g r o u n d

itself was t r ea t ed as resonance enhancemen t , so t h a t the au tho r s ob ta ined an

ex t r eme ly b road wid th 1 ~ 200 MeV and a cent ra l mass value a round 1400 MeV.

F u r t h e r m o r e , the b r o a d S and P wave e n h a n c e m e n t (2t) a t 1.2 and 1.4 GeV,

respec t ive ly , should also be referred to the Deck c o m p o n e n t : these d a t a were,

therefore , excluded. Two mass e nha nc e men t s (E and F in tab le I I a ) ) in

¢he mass reffion of 1.45 GeV were s imul taneous ly observed in the reac t ion

(14) PARTICLE DATA GROUP: I'hy,~. Lett. B , 75, 1 (1978),

15 - II Nuovo Uimertto A.

210 c. FUKUNAGA, R. IIAMATSU, T. HIROSE, S. KITA)IURA and w. YAMAGATA

TABLE I I I . - World data o] masses and widths o] the (~3~) system obsem~ed in ]ou~- body diMraction dissociations.

M~ss W i d t h React ion M o m e n t u m Rcf. (GeV/c)

a)

A 1443 :j: 15 100 ~ 15 pp -+p(pr:+r~-) 22.0 (as)

B 1430 4- 20 150 ± 40 ~:~p -+ r:±(r:+~-p) 16.0 (ab)

C 1460 ± 10 80 ± 9 ap -+a(r:+~-p) 8 .0-- 16.0 (3c) a=,~ ±, K

D 1425 :J: 25 125 ~: 25 pp --~ p(pr:+~-) 16.0 (~)

E 1464 4- 7 124 i 20 p n -+ p(n~+~ -) 7.0 (z~)

17 1440 :j: 15 100 ± 30 u+p - , rc+(prc+r¢-) 3.5 (aQ

G 1430 ± 8 62 ± 18 r:-p -~n - (p~+n- ) 18.5 (3g)

H 1479 :J: 8 50 ~ 25 r:+p -+~+(pn+n-) 18.5 (3g)

I 1450 -F 10 145 ± 18 ~p --).~)(pn+r:-) 5.7 (3i)

J 1460 ± 10 120 j : 20 K - p - + K-(p=+n -) 4.2 (3~)

K 1470 4- 10 90 ± 30 K - p - + K°(n,~+~-) 4.2 (at)

.5 1 4 2 0 ~ 7 1 2 0 ~ 1 0 ~p - ~ ( p r : + r : - ) 7.23 (3~.)

b)

A ' 1693 ~ 15 235 ± 50 pp -+p(p=+r:-) 22.0 (3~)

B' 1730 :J: 20 120 ± 50 "~±p -~-n±(=+n-p) 16.0 (3b)

C' 1712 -4- 12 60 ~= 6 ap --~ a(p~+~:-) 8.0-- 16.0 (3~) & = ~:t=, K

D' 1720 ± 20 120 =t= 40 pp --~p(pr:+=-) 16.0 (3~)

E ' 1 7 5 0 ± 1 0 8 0 ± 4 0 pp --~p(A++= -) 16.0 (3d)

i~' 1668 ~: 19 188 ~ 64 pn --~p(n~+~ -) 7.0 (~)

G' 1720 :J: 15 60 ± 40 g+p --~ ~+(pr~+=-) 3.5 (a])

H ' 1694 ± 10 48 ± 20 ~:-p -,-r:-(pr~+r:-) 18.5 (a~)

1' 1 7 3 2 ~ 7 3 4 ± 14 7:+p --~7:+(p~+~:-) 18.5 (~)

J ' 1691 =t= 4 1 9 4 ± 10 ~p --~l~(p~+~: -) 5.7 (ai)

K ' 1690 ± 10 120 ~= 20 K - p - + K-(~+~-p) 4.2 (3~)

.L' 1670 ± 10 90 ± 30 K - p - + K(r:+r:-n) 4.2 (aQ

.M' 1690 ~ 6 120-V 10 ~p --,-~)(pr:+=-) 7.23 (a~)

STUDY OF ( ~ ) AND ( ~ , ~ ) MASS I~NHANCEMENTS ETC. 211

K+p-+K+(7:~ ") a t (2.5 --3.2) GeV/e. Since the enhancement E wa stoo faint to be recognized as ~L peak, we adopted the data point F to calculate the world av-

erage value. Selecting data B, C, F, G, H of table I I a ) and our da ta of the 3.45 enhancement in which fit t ing was made by the Brei t -Wigner funct ion and a

smooth background, we obta ined the world average M = (1471~-3), F---- (86 ~: :t:8) MeV. Taking into account large statist ical errors and the inconsistency of

M and F among each d~ta, wc cannot take seriously these values themselves,

a t least for the 1.45 enhancement . We should, however, p a y par t icular at-

tent ion to the fact t h a t mos t of the dat~ show deviations of M and F f rom

t h o s e of P l l a n d D~3. Regarding the 1.66 enhane(.ment, d-~ta points appear to concentra te be t te r

in the small M-F region because of less dis turbance due to the Deck background than for the :1.45 enhancement . The averaging procedure, therefore, makes more sense for this peak. Using the data A' , B' , C', D', E' and ours,

we got the worhl a~-erage M = (1655±5) , 1 ' ~ (110 :~ l l )MeV.

We find no significant dependence of M and 1' on beam particles 7~, K, p

and on incident energies. This fact can be natura l ly unders tood as a nature

of f~etoriz,~tion (~f dd. The da ta of K+p ~ K+(~W) al~alysed b y Mus(~AW.:

etal., however, show systemat ica l ly higher values of M (F, C' in fig. ]a) and

table ] I ) . This m a y be par t ly due to the lower in('ident energy, PL ~- 2 .5- -3 .2 ,

for which ~he nondiffract ive component is mixed, giving rise to the 1-~rge overlap between different in termediate states.

b) (r:wA ~) mass enhancements. As compared with the (7:~ ~) systems, more reliable da ta of (==A °) enhancements have so far been obta ined in bubble

chamber experiments . Values of M and F for ( ~ = ~ ) enhancements are given in t~ble ] I I and displayed in fig. lb), where we can clearly see :r popula t ion of da ta points in two M-I' regions. In the first group emerging ~t a round 1..45 GeV,

the major i ty of the da ta shows narrower widths t han t ha t of P~i- The second group is in the hi~'her-mass side of F~5 and more t h ' m half da ta have narrower

widths than t ha t of F~ . The world averages for the da ta of table I I I a ) and b) are obtained to be

M = (1450 ± 3) )~IeV, F ~-- (98 ± 7) MeV,

M = (3 705 ± 2) MeV, F = (84 ± 4) MeV.

I t is interest ing to point out tha t , as seen in fig. lb), the M-F region ~round

D13 is a lmost empty . This tendency is still observed in the (7~JT) ease. Since

D13 has a narrower width than Pn , the mass enhancement of DI~ should clearly

be seen. This will be discussed in sect. 5 in connection with the Deck-resonance inte~ference effect.

Final ly we will make a brief comment on the results obtained in the missing-

212 c. FUKU~AGA, 1~. IIAMATSU, T. IIIROSE, $. KITAMURA and T. YAMAGATA

mass exper iment (~5). ANDERSOI~ et al. clarified var ious enhancements in the

missing-mass spectra of the reactions 7 : - p - ~ = - + X and pp ~ p + X . Ap-

p ly ing the t ' -cut ( 0 . 0 2 6 < t ' < 0 . 0 5 (GeY/c)°-), t hey obta ined M and F of the en-

hancements which migh t be I - ~ ½ resonances (M ~ 1412~=4, F = 210±15) ,

(M = 1503±6 , F = 320-t-10) and (M = 1691~4 , F = 130+10) . The authors

claimed t h a t these enhancements might correspond to the F-resonances,

-Pn(1.47), D~(1.52) and F~5(1.69), implying similari ty of resonance product ions

bo th in the fo rmat ion and the product ion experiments . Comparing, however, the missing-mass spectra with the exclusive data , we can clarify the impor t an t

fact t h a t the b road enhancements a t 1.41 GeV assigned as Pn mus t have been a t t r ibu ted to t im (7:iV) and ( ~ J ~ ) Deck components , and the peaks observed

a t ] .69 GcV are a mix tu re of the enhancements a t 1.66 and 1.71 GeV in the

~JV and ~=J~ diffractive systems, respectively.

5. - D e c k - r e s o n a n c e i n t e r f e r e n c e e f fec t .

I n order to check how the interference effect modifies the mass and width

of an original resonance, wec arr ied out the par t ia l -wave decomposi t ion of the Deck ampl i tude of eq. (6), because the interference effect for a mass distr ibution takes place only for ampl i tudes having the same spin and pa r i ty (,j3). Thus

.Q

11

0 1.0

o.)

\ \

.... " ' . ~ ,."" I I I

1.2 1.4. 1.6 1,8 2.0

i . i d i

/'/}i)i °' / /i!;i

1,0 1.2 1,4 1.6 1,S 2,0 ,w (r~ ¢~)(Gev)

Fig. 6. - Deck-resonance interference with various relative phases for a) the p-wave and b) the d-wave components : -- Deck, • - • Pn or D~3, - - . . . . 90 °, 180% . . . . . . . . . 270 ° .

(15) ]~]. \V. ANDERSON, ]",. J . BLI~SER, H. R. BLIED]~', G. B. COLLINS, D. GAR:ELICK, J . MEN~£S, F. TURKAT, D. BIRNBAUM, 1~. M. ED)3LST]~IN, N. C. I I I~x , T. J . MACMAnO~-, J . F. MuCCI and J . S. R u s s : Phys. Rev. ~ett., 25, 699 (1970).

STUDY OF (=~o) AND (7~=~ 3) MASS :ENHANCI~M:ENTS ]~TC. 213

the mass distribution is given as

dd 7J~P , J , p - - T I ~ w ( ]2) dg]/ 2 [~Deck("Z]f) -~ (M) e x p [ i w ] l ~ ,

J , P

where Z +'~ #TJ'P~ represents the Deck (the Breit-Wigner) amplitude for the Deck ~ B~'! spin J, the parity P and the relative phase angle %

The most probable case to create the enhancement around 1.34 GeV should be the interference effect between Pn(1.47) and the ~P-wave component of the

i i,

,I 160 ~ i o..)

li" , , b)

> I I

--- 4 o 1 - 1 , ~ u ; I

1~ I I I

~, ,

,~ o ' , I , i ~ ° ° " . ,

I i i n!ll ',~ J C )

4C

i i

r i

a)

i [

ii, % 21o 3.0

M(,N'rt)(G eV) 4.0

Fig. 7 . - Invariant (r~°p)+(,~+n) mass distributions as functions of t': a) [t'l<0.03, b) 0.03<It'l l<0.1, c) 0 .1<[ t ' l<0 .2 , d) 0 .2<It 'I<0.4 .

214 C. FUKUNAGA, JR. HAMATSU, T. I I IROSE, S. KITAMURA and T. YAMAGATA

Deck ampli tude; M and / ' of Pl l are M = 1.47 GeV and / ' ~- 200 ~eV, respectively. In a similar manner, D13 with M ~-- 1.52 GeV and ]1---- 0.125 GeV is util ized for the calculation of the D-wave interference effect.

Assuming a reasonable magni tude of the resonances Pll and D13, we

calculated the (7:~) mass distributions with various phase angles ~. Fig- ure 6a) e]arifies t ha t any choice of ~ cannot yield a narrow peak at a round 1.34 GeV, al though the original shape of Pll is dramatically modified. As seen in fig. 6b), it is also unlikely to reproduce the mass enhancement with M ~-- ,-- 1.45 GeV a n d / ' ~ 0.1 GeV. I t is generally t rue that , if the mass of resonances shifts f rom its original position due to the Deck-resonance interference, the width of resonances gets broader and the shape of Breit-Wigner funct ion is skew. This general behaviour will remain unchanged even if the Deck am-

pl i tude is modified by incorporat ing different types of react ion mechanisms, e.g. nucleon exchange, Born term, absorpt ion effects, etc.

MI~AKA et al. (~6) invest igated details of interference effects incorporat ing

various types of reaction mechanisms, e.g. baryon exchange, direct nucleon pole and absorpt ion effects. The authors achieved the creation of the broad enhancement at 1.34 GeV in the reaction np -~ (pT:-) p at PL ---- (50 -- 300) GeV/c (6) by manipulat ing many amplitudes, bu t the shape and width appeared somewhat different f rom what we really observed. Since they a t t empted to create the 1.34 enhancement by the negative interference effect between PI~ and the / ' -wave Deck amplitudes, they could not, on the other hand, reproduce the enhancement at 1.45 GeV, which actual ly emerged in the data.

I t should be remarked tha t , as seen in fig. 7, the three ( ~ ) mass enhancements do not change their position with t', whereas the Deck background moves towards higher mass as It'l increases. This par t icular behaviour contradicts the s tandpoint of interpret ing the enhancements only by interference effects.

6. - Interpretation o f (7~2V) and (7:r:JV) enhancements .

We show in fig. 8 the mass values of diffractively produced enhancements together with those of normal resonances with the isospin I = ½ having so far been revealed in phase-shift analyses. Here we assume t h a t two

enhancements at M(~2V) ~ 1.47 and M ( ~ 2 ~ ) ~- 1.45 originate f rom the same resonance. We thus denote the four enhancements as 2~*(1.34), ~*(1.45), ~*(1.66) and 2V*(1.71). The characteristics of these four enhancements are

summarized as follows:

i) The width of 2V*(1.34), i.e. ~ ~- (66~:14)~IeV, is significantly narrow and no resonance with I ~ ½ in the format ion experiments has so far been observed in the (~:o~') mass lower than Pl1(1.47).

(16) A. ~[INAKA and H. SuMIYOSm: Prog. Theor. Phys., 60, 456 (1978).

STUDY OF (r¢,~) AND (7~J~ ~)) MASS ENEIAIqCEMENTS ETC. 215

22[ 2.0

GeV

1.8

1,6

1.4

1.2

p rodL uc t/on formoL&/on

S H

DI3 F15 F17

PI 3

Sll D13 F15 DIs

P13 S D~ 3 11

P11

Fig. 8. - Mass values of the (=~N') and (r:=~) mass enhancements and the formation resonances for which spectroscopic assignments are given, Except oV*(1.34), the world average values are shown.

ii) The world average values F(7:J~) = ( 8 6 ~ 9 ) and (~7:d~') ---- ( 9 8 ± 7 ) lV[eV for J~('*(1.45) are considerably smaller than /1 of Pn~ i.e. (180 --240)lV[eV.

Furthermore, the mass M ( T : J ~ ) ~ l . 4 5 GeV is different from M of Dis, i .e. (1510 -- 1530) )/[eV. However, as shown in fig. la)~ each datum adopted to

M and F of 2('*(1.45) shows a rather wide spread: M ---- (1400 -- 1500) )/[eV

and /1 ----- (30 -- 200) MeV. An experimental reconfirmation should be neces-

sary.

iii) Since the mass difference of J~'*(1.66) and &°*(1.71) looks statistically

significan% we m a y regard J~*(1.66) and ~f'*(1.71) as different objects. It is

unlikely to consider that these enhancements are due to the single resonance

F~ whose mass and width were determined to be M = (1670 -- 1690) MeV and F ~ (120 - - 145) M e V .

216 C. FUKUNAGA, R. HAMATSU, T. HIROS]~, S. KITAMURA 3aid T. YAMAGATA

iv) Among the F-resonances reported, D13 of M ~-- (1660 -- 1710) MeV and F - - - - ( 8 0 - 120) MeV decays into 7:7:J~ with a rat io of 9 0 % . Thus

J~*(1.71) m ay be assigned to D13.

v) On the other hand, 2/'*(1.66) observed only in the (7:J~) mass dis- t r ibut ion does not have any par tner in F-resonances because three normal

resonances s t around 1.7 GeV, i.e. D15, F~5 and Sxx, have a large fract ion ((30 -- --" 55)%) decaying into 7:7:J~.

vi) (~:J~) mass enhancements do not change this masses with t', as seen

in fig. 7.

We thus conclude tha t the three enhancements J~*(1.34) -*7:oV, J~'*(1.45) -~ -*7:JV, ~7:J~', and J~* (1 .66 ) - -~J~ might be different types of resonances

which emerge only in the diffraction dissociation being materialized by the pomeron.

MoRmso~ (~7) has proposed the existence of such resonances called (~ D-resonances ~) including a broad threshold enhancement which was not regarded as a real resonance bu t as a Deck- type reaction mechanism. In many respects, the pomcron has a character so different from real particles 7:, K, JV tha t dd m a y create a new type of resonances which cannot simply be expected from format ion experiments.

Concerning resonance production, we encounter a question of whether or not dd yields F-resonances, e.g. P~, D~3, F~5 in addit ion to J~*'s observed here. As discussed in sect. 3, we still have a large gap between the Deck background and the JV* peak (fig. 3 and 4). This par t ma y be ascribed to the contribu- t ion f rom various F-resonances which we cannot see as a clear peak due to either a broad width or a small cross-section.

7. - S u m m a r y and discuss ion.

The (7:J~) mass enhancements in the diffraction dissociation were precisely

investigated, based on the separate dd sample of the reactions 7:+p-~7:+(7:+n)d~

and 7:+(7:0p)dd at 16 GeV/c. Using world data of mass and width for the ( , ~ ) and (~:7:J~) systems diffractively produced, we re~-ealed various interesting features of mass enhancements in the diffraction dissociation. Obviously the data, except for J~*(1.34), are not accurate enough to make a reliable deter-

minat ion of M and F for the (7:J~) and (7~J~) mass enhancements. Never- theless, plots of M and F in fig. la) and b) show as a clear tendency tha t the da ta deviate systematical ly f rom the results of the formation experiments and tha t ~*(:l.66) and J~*(1.71) might have different mass. Thus, as discussed in

(17) D. R. O. MO]CRISON: Proceedings o] the International Con]erence on .High-Energy Physics (Kiev, 1970).

STUDY OF ('n',j~ r)) AND (~7~,;"~ '~') ~,IASS :ENI-IANC:EMENTS ETC. 217

sect. 6, we conclude tha t the diffraction dissociation or equivalently the pomeron can create a new type of resonances, i.e. ~.V*(1.34), ~*(1.45), 3~'*(1.66).

All of the F-resonances shown in fig. 8 are well predicted by the S U6~ 03 scheme based on three const i tuent quarks. We, therefore, have no place to ac- commodate addit ional resonances as far as we are concerned with a three-quark

system. I t ~-as suggested (~s) tha t the ~N'*(1.34) might be a possible candidate

of a five-quark exotic state. Taking into account recent experimental situations in which many exotic states such as baryoniums ~nd dinucleons have been observed, we will natural ly exp4,ct five-quark states in the r:A ~ and ~:~A ~ systems.

ISHIDA et al. have extensively studied exotic states with various quark con- figurations, i.e. (qq~O), (4q~l) , (6q) based on the joint spring model (19), in which authors est imated the mass of the five-quark states. I f we fix the mass of quark m~---- mz~/la = 336 MeV, where m~. represents a nucleon mass (940 Me¥) and # the anomalous magnetic moment (2.79), the ground-state mass of the five-quark system (4q+~) is est imated to be 1.69 Ge¥. Eightfold degeneracy

will be solved by spin-spin interaction between two quarks. Based on a eoloured- quark model (Fermi statistics) and a Bose quark model, the level scheme is calculated. The interest ing results of this model is that , if Bose statistics is considered, the lowest level is predicted at around 1.4 GeV with JP---- ½-, which may correspond to 2V*(1.34). According to the partial-wave analysis of the reaction T:+p=~+(rc+n) a t 16 GeV/c (-~o), the J~ --~ 1~ component shows a peak at around 1.35 Ge¥, being also consistent with this model prediction. Since exotic baryons consist of five quarks, we will have much a more complex level

s t ructure than the ordinary three-quark levels in the mass region we arc now concerned with. Details of this model calculation will be published else- where (:1).

In the diffraction dissociation, the pomeron would play an impor tant role to pick up a quark-ant iquark pair from the sea, creating highly peripheral resonances. In this viewpoint, one can expect ~ ra ther large yield of five-quark exotic states in dd, in which the s trange-quark pair s~ or the charm-quark pair c~ is materialized.

We wish to thank the courtesy of the Aachen-Berl in-Bonn-CERN-Heidelberg Collaboration for lett ing us use the experimental data.

(18) K. KANAI, A. :NAKAMURA and I. 0HBA: Prog. Theor. Phys., 58, 1047 (1977). (19) S. ISnID), and M. ODA: Prog. Theor. Phys., 61, 1401 (1979). (so) D. SOTI•IOU: Nucl. Phys. B, 107, 457 (1976). (31) T. HIROSE and S. ISHIDA: tO be published.

218 C. FUKUb[AGA, R. HAMATSU, T. I I IROSE, S. KITAMURA and T. YAMAGATA

• R I A S S U N T O (*)

]~ stato fatto uno studio dell ' incremento di massa (=W) nelle dissoeiazioni diffrattivo ~+p--~T:+(T:0P)dd e r~+(7:+n)dd a 16 GeV/c in termini della massa M e dell 'ampiezza 2" di inerementi di massa (T:jV) e (r~=jT) prodotti diffrattivamente. I valori di M o F osservati sono M=(1344~5) , (1451~=7), (1639~-7) MeV e / '= ( 664 - 14 ) , (132±22), (96~=20) MeV, rispettivamente. Dal confronto dettagliato dei dati globali si trova una sistematiea differcnza di M e / ' fra incrementi (~W) o (==3~) e risonanze prodotte in esperimenti di formazione. Si mostra che l ' interferenza fra risonanza e i l Deck non pub dare una spiegazione adeguata a queste osservazioni. Si diseutono interpretazioni possibili per i meecanismi di reazione di produzione di incrementi della massa del nucleone in con- nessione con la na tura del pomerone seambiato.

(*) Traduz ione a cura della Redaz ione .

PealoMe rte no.rty~leHo.

study of (π n) and (ππ n) mass enhancements in nucleon diffraction dissociation) mass...

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