Associated production of hypernuclei

Nuclear Physics A450 (1986) 129c-146c North-Holland, Amsterdam

129c

ASSOCIATED PRODUCTION OF HYPERNUCLEI

J. C. PENG Los Alamos National Laboratory,

Los Alamos, New Mexico

87545, U.S.A.

The characteristics of the (~+,k +) reaction, a new experimental tool to produce hypernuclei, are discussed. Results from a recent (~+,k +) experiment are presented. Some future prospects of the (~+,k +) reaction are discussed.

I. INTRODUCTION The (k-,~ ~) reaction has been the most important experimental produce hypernuclei.

In this strangeness-exchange

is brought in by the kaon beam and subsequently nucleus to form a hypernucleus,

as illustrated

reaction,

tool 1'2 to

the strange quark

transferred to the target in Fig. i.

One of the most im-

portant features of the (k-,~) reaction is the selective excitation of low spin "substitution

states" due to the small amount of momentum transfer.

Identification

of such states in p-shell A-hypernuclei has provided the first

evidence of a small spin-orblt potential. 3

On the other hand, the meager kaon

flux available in existing accelerators has limited the usefulness (k-,~) reaction.

In particular,

high-spin hypernuclear

expected to be weakly populated in the (k-,~)reaction,

of the

states, which are have never been

identified. It is evident that hypernuclei (k-,~).

can be produced by reactions other than the

These reactions usually fall into the category of associated

productions,

in which a pair of s and s quarks are produced.

such reactions is the n(~+,k+)A reaction, shown schematically

One example of in Fig. I.

In-

tense proton and photon beam can also be employed to produce hypernuclei through the p(p,p'k+)A and the p(~,k+)A reactions. 4'5 p(p,A)A has also been contemplated. 6'7

A more exotic reaction

In this paper we focus on the (~+,k +)

experiment 8 recently investigated at the AGS accelerator at Brookhaven. experiment demonstrates,

for the first time, that hypernuclei

This

can be produced

with the mechanism of associated production. In Section 2 we will discuss some important features of the (~+,k +) reaction.

Comparisons

of the (w+,k +) reaction with the more familiar (k-,~) reac-

tion will be frequently made. tation of the experimental

The (~+,k +) experiment at AGS and the interpre-

results are the subjects of Section 3, followed by a

discussion of the future prospects of the (~+,k +) reaction in Section 4.

0375-9474/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

J.C. Peng / Associated production of hypernuclei

130c

n/K-.'n'-)A

•

d

~-

• m

• •

d U

A

•

~

u

i,

U

s

n

d U

ni~+ K")A

I u

d U

)

IK +

(

•

FIGURE

1

Quark line diagrams for the n(k-,~-)A and the n(~+,k+)A reactions

2. THE (~+,k +) REACTION The theoretical hypernuclear Walker. 9

aspects of the (~+,k +) reaction as a spectroscopic

physics have been investigated

tool for

in detail by Dover, Ludeking and

Before discussing the (~+,k +) experimental

results,

it is useful to

review some pertinent features of the (~+,k +) reaction. 2.1. Momentum transfer Since it requires a considerable

amount of energy to produce a massive pair

of strange quarks, a common feature in all associated production of hyperons is that the reaction is endothermic.

The n(~+,k+)A reaction has a Q-value about

655 MeV more negative than in the n(k-,~-)A reaction.

This leads to a large

amount of momentum transfer (>300 MeV/c) in the (~+,k +) reaction, as shown in Fig. 2.

This situation is in contrast to the strangeness-exchange

(k-,~-) re-

action using kaons in flight, where the momentum transfer is relatively small (
It is interesting to note, however,

that the n(k-,~-)A reaction

with stopped kaons has a momentum transfer comparable to the n(~+,k+)A reaction. The large momentum transfer in the (~+,k +) reaction implies that hypernuclear states with high spins are favorably excited in this reaction. 9

This

contrasts with the (k-,~-) reaction which selectively excites low spin states at small reaction angles.

It should not be concluded, however,

that high spin

J. C. Peng / Associated production of hypernuclei

50O

i

i

i

400

i

i

!

i

'"";'k .,.o

L~

0.

I

131 c

""-- ""--..................

20O

100

i

i

200

400

~,'i

i

600

800

p~

i

I

I

I

I

1000 I~00 1400 1600 1800 2000

(MeV/C)

FIGURE 2 Momentum transfer for various reactions at 0 ° reaction angle hypernuclear

states cannot be studied with the (k-,~-) reaction.

Figure 3

shows that the momentum transfer in the 12C(k-,z-) reaction measured at 25 ° is comparable to that in the 12C(~+,k+) reaction at 0 °.

In practice, reaction has

never been measured at such large angles due to the rapid drop of the (k-,~-)

7OO

i

,

l

i

000

i

i

i

I

~C(.',K'~C

50O

>~-

4oo

n

30O

°/" 2OO

/,-/,

,,/,"" ./"

100 1 5

I

I

10

1,5

I 20

I ~

@,-,.(deg)

i

i

I

I

3O

35

40

45

50

FIGURE 3 Momentum transfer for the (~+,k +) and (k-,~-) reactions as a function of laboratory angle

J. C Peng / Associated production of hypernuclei

132c

counting rate.

In this sense, the (~+,k +) reaction complements

action for exploring a different variety of hypernuclear

the (k-,~-) re-

states.

2.2. Elementary cross section The threshold of the n(~+,k+)A reaction occurs at 888 MeV/c. target, this threshold is significantly binary reactions, the threshold.

lowered.

On a nuclear

Typical of all endothermic

the n(~+,k+)A cross section peaks at an energy slightly above

Figure 4 shows the 0 ° cross sections of the p(~-,k0)A reac-

tion I0 (equivalent

to n(~+,k+)A by isospin invariance).

The peak (~+,k +) cross

section of 0.9 mb/sr, occurring around 1050 MeV/c pion momentum,

is roughly

five times smaller than the peak cross section of the (k-,~-) reaction. Nevertheless,

the much higher pion flux more than compensates

this difference

and makes the (~+,k +) reaction even more efficient than the (k-,~-) reaction for producing high-spin hypernuclear

states.

':;

O°'°b

=.e

f., ~

\

/I .5

%00'

,oo"

, oo

Plab MeV FIGURE 4 0 ° cross section for the ~-p ÷ k°A reaction as a function of beam momentum 2.3. Penetrability The mean-free-path

of hadrons in nuclei is usually taken as i/po.

Since the

total cross section o of k + meson is much smaller than the k- meson, the (~+,~)

reaction is expected to probe the nuclear interior somewhat better than

the (k-,~) reaction.

This implies that deeply bound hypernuelear

cially for medium and heavy hypernuclei,

states, espe-

are more accessible by the ( ~ + , ~ )

re-

Z C Peng / Associated production of hypernuclei action.

133c

An even better reaction to probe the nuclear interior is the (~,k+)

reaction. 2.4. (~+,k +) versus (k-,~-) reactions Comparisons between the (~+,k+) reaction and the (k-,~-) reaction as a tool for A-hypernuclei spectroscopy are shown in Table I.

In addition to the char-

acteristics discussed earlier, we note that the experimental environment for these two reactions is significantly different.

The available pion flux in a

typical beam line is at least two orders of magnltude greater than the kaon flux.

The purity of plon beam is also superior to the kaon beam, making the

beam particle identification in the (w+,k+) reaction somewhat less critical. The k- ÷ p-v, k- + 2~ and k- + 3~ decays, sources of background for the (k-,~) reaction, do not contribute to the background in the (~+,k+) reaction.

More

discussions of the experimental aspects of the (w+,k+) reaction will be given in the next section.

TABLE I Comparison between the n(k-,~-)A and the n(~+,k+)A reactions n(k-,~-)A

n(~+,k+)A

momentum transfer


~300 MeV/c

selectivity

low spin states

high spin states

mean free path

~- = 1.9 fm k- = 2.0 fm

~+ = 1.6 fm k + = 4.6 fm

cross section

Omax(O °) = 5 mb/sr

o Omax(0 ) = 0.9 mb/sr

beam intensity (purity)


~101/beam spill (~/all = 80%)

3. THE 12C(~+,k+)l~CO REACTION 3.1. Experimental setup The feasibility of the (~+,k+) reaction for populating A-hypernuclei was investigated II at AGS using the Low Energy Separated Beam (LESB-I) and the hypernuclear spectrometer "Moby-Dick." line and the two spectrometers.

Figure 5 shows the layout of the beam

The beam momentum was chosen at 1054 MeV/c,

which is near the peak of the n(~+,k+)A elementary cross section.

The mass

separator in the beam llne, together with the tlme-of-flight measurement, provides good ~+ separation from k+ and p. However, the e+ contamination, not separable by the TOF technique, is estimated to be about 15%.

J.C. Peng / Associated production of hypernuclei

134c

C2 BEAM LINE AND SPECTROMETERS

//- . . . . . . . / OC 6,7 \

PR. . . . TInNTA . . . . . . . . . . . . . .

hh£

~.1"-h-"~

4

l~',~

s,

Experimental

~II ~ L ~

\

~Q5 uo

.,

J/

¢i OH

N2~

0 E OMETER ROTATION

S2

oc,

FIGURE 5 setup for the 12C(~+,k+)I~C

experiment

at AGS

The pion beam momentum was measured by drift chambers placed near the mass sllt and the reaction target.

High rate drift chambers 12 were constructed

handle the high beam flux near the mass slit region. was about 3 x 10G/splll.

This flux was limited not by the drift chambers,

rather by the scintillation segmented

to

The pion flux on target

counters

SI and $2.

For future

(~,k) experiments,

SI,$2 counters would allow a higher plon flux to be used.

The energy deposited in the target was measured by using an active scintillation target.

Reaction products were detected by the kaon spectrometer

sitting on a rotatabl~ platform.

Identification

of kaons was achieved by the

liquid nitrogen Cherenkov counters vetoing the fast plons and by the TOF infor mation.

Note that only 25% of the kaons emerging from the target survive the

flight path of 7.9 meters. desirable

A shorter kaon spectrometer would be quite

for future (~+,k +) experiments.

B.2. Experimental The 12C(~+,k+)

results

spectra at @lab = 5 ° , i0 ° and 15 ° are shown in Fig. 6.

The

number of pions on target are 2.4 × I0 I0, i.I x I0 II, and 1.8 x I0 I0, respectively,

for @lab = 5 ° , I0 °, 15 ° .

hours.

The spectra are plotted as a function of missing mass, with

state corresponding

This corresponds

to zero missing mass.

to a total beam time of 70 I~C ground

Two peaks clearly stand out on the

J. C. Peng / Associated production of hypernuclei

135c

5O

0,® = 5 a ~ - ~

4O

,PJ~n

,o0

i1/!-'

6O

2O

i

0

I

I

20

u 5

0 -~

nnnnlA -~

-~

0

~

~

U~'JNC~SS~e~0

~

40

FIGURE 6 Spectra of the 12C(~+,k+) reaction at three detection angles 12C(~+,k+ ) spectra,

The peak with smaller missing mass is assigned as the I~C

ground state, even though the location of this peak is 4 MeV more negative than expected.

This slight discrepancy is attributed to the difficulty of calibrat-

ing the central momenta of the pion and kaon spectrometers, a task complicated by the large mismatch of the two spectrometers (pion spectrometer at 1054 MeV/c, kaon spectrometer at 716 MeV/c) and by the lack of any reference reaction, Figure 6 shows that the (~+,k+) spectra are not completely free from experimental background.

This background most likely originates from a pion beam

entering the kaon spectrometer and producing slow moving particles (~+,k+,p)

J.C. Peng / Associated production of hypernuclei

136c

which simulate the flight time of a good (~+,k +) event. 13

Despite this back-

ground, the l~c ground state peak and the peak at E x = ii MeV are clearly visible.

The spectra have not been corrected for the spectrometer

acceptance,

which accounts for the spectra shape at higher excitation energy. It is instructive 12C(k-,~-)l~c

to compare the 12C(~+,k+)l~c

spectra.

spectra with the

Figure 7 shows 12C(k-,~-)

flight 2'14 and with stopped kaons. 15

spectra measured with kaon it

The gross features of the 12C(k-,~-)

spectra are similar to those of the 12C(~+,k+) spectra.

However,

the relative

intensity of the g.s. versus the ii MeV state depends on the reaction and the angle of detection.

As will be shown in a later section,

observed in the (k-,~-) reaction at 0 ° is different

the ii MeV state

from the state observed in

the (~+,k +) reaction.

I

I

I

I

i

50~ I

I000

,,>, 500

"JI

;

~"

"

,"- "," .'..." ..... 6

--

o

-ee. oo ° • e

•

k 225 MOMENTUM

250 275 300 O F ~- - M E S O N S (MeV/c)

FIGURE 7a Excitation spectra for the 12(K-,~-) reaction with stopped kaons. 15 The inset shows the bound state region after subtraction of the underlying continuum.

J. C. Peng /Associatedproductionof hypernuclei

I

I

I

i

137c

I

-I ( I P3/2, I P3/Z)A n ~C ( 7 2 0 MeV/¢)

400 Z

ILl > Ld

-I

200

1( I S l / a , l P 3 / Z ) A n $

.._._/b 20

•

•

l

-20

O

I,

I

-40

-60

I

-80

I

-I00

BA(MeV) FIGURE 7b The 12C(K-,~-)12C excitation spectrum 1 4 at 0 = 0 ° and PK- = 720 MeV/c.

I

60

>

I ! I-L] '2 C ( K;?r')l~C I I 800 MeV/c K-

40

01 I-Z ,,i

I U"

>

bJ

20

_J

I 0

/~///

I I0 MASS (MeV)

I 20

FIGURE 7c The 12C(K-,~-)12C excitation s p e c t r u ~ at 8 = 15 ° and PK = 800 MeV/c.

J. C. Peng / Associated production of hypernuclei

138c

The angular distributions of the two peaks populated in the 12C(~+,k+)I~c reaction and in the 12C(k-,~-)I~C reaction are shown in Fig. 8.

The two states

in the 12C(~+,k+)I~c reaction both have angular distributions peaking at forward angle and falling gradually at larger angles.

Similar angular distri-

bution shape is also observed for the II MeV peak in the (k ,~ ) reaction.

In

contrast, the ground state populated in the (k-,~-) reaction has a bell shaped angular distribution peaking at ~ = i0 °.

!

11 M e V

lO

t

I.( ~ E A t < 0.7 '~

0.1

=

..... I •"o

i K)

,

~ o.s

,

~ 0.3

=C(Tr'X')^'=C , o MeV

~ o.,

,,

i I

O.3

J

I

J

t

i

I

• GROUN0 STATE PE&K

o 214 218 1 0

i

,

,

5

10

15

20

FIGURE 8 Angular distributions for the 12C(~+,k+)I~c and the 12C(k-,~-)I~C reactions 3.3. DWBA analysis DWBA (Distorted Wave Born Approximation) calculation has been employed in tbe past to describe successfully the (k-,w-) reaction populating p-shell A-hypernuclei. 16

A simple one-step reaction mechanism, in which a neutron in the

target nucleus is turned into a A-particle, is assumed in this calculation. The spectroscopic amplitude for each neutron-hole lambda-particle configuration is obtained by shell model calculations,

In the analysis of the (~+,k +) data,

we follow closely the steps used in the previous (k-,~-) analysis. 16

Two

ingredients entering the (~+,k+) calculation are different from those in the (k-,~-) calculations.

First, the optical model potentials for describing the

distortion of the ~+, k + waves are obtained by fitting the elastic scattering

J. C Peng / Associated production of hypernuclei data of w+, k + on 12C at 800 MeV/c. 17

The fits to the scattering data and the

sets of optical model parameters are shown in Fig. 9. potential for k + + 12C is repulsive. tary reaction n(w+,V+)A, Ferml-averaglng

IOO0

Note that the real

Second, the cross section of the elemen-

required in the DWBA calculation,

procedure.

is obtained with a

As shown in Fig. 4, the n(~+,k+)A cross section is !

I

I

K++'2C 800 MeV/c

10

1

I

I

l

0

10

20

3O

I

I

I

0

10

20

30

0,1

nn

40

IOO0

10

1

0.1

139c

40

FIGURE 9 Elastic scattering data 17 of ~+ and k ÷ on 12C at 800 MeV/c. The solid curves are optical model fits. The optical model parameters are (V, W, Y0' a) = (24.83 MeV, -38.84 HeV, 0.857 fm$ 0.473 fm) for k + and (-47.3 MeV, -44.6 HeY, 0.944 fm, 0.529 fm) for ~ .

3. C Peng / Associated production of hypernuclei

140c

strongly energy dependent, making it important to consider the Fermi motion of the target nucleons. Fermi-averaged. 16

Ideally, the amplitude of the n(~+,k+)A reaction is

However, such amplitudes are not available and instead the

cross sections are Fermi-averaged. been assumed:

Three different momentum distributions have

(I) uniform sphere with k F = 220 MeV/c;

(2) diffuse Ferml-gas

model, p(k) = P0(1 + exp(k - k0)/Ak)-I , with k 0 = I00 MeV/c, Ak = 50 MeV/c; and (3) harmonic oscillator model, p(k) = P0(kb)2exp(-k2b2), with b = 1.64 fm.

The

Fermi-averaged cross section o(~+n + k+A) is 0.49 mb/sr, 0.50 mb/sr, 0.47 mb/sr, respectively,

for the three different momentum distributions.

The

effect of Fermi-averaglng is a reduction of 50% from the peak cross section. The results of the DWBA calculations using the code CHUCK 18 are shown in Fig. i0.

The spectroscopic amplitudes for various transitions are taken from !

I

{

10

•

=C('rr÷,K+)A=C 0 MeV II

i

~

I

i

i

11 MeV

D

0.1 0

l

t

I

5

10

15

8=(d g)

20

FIGURE I0 Solid curves are DWBA predictions for the I~C ground state and the I~C ii MeV state

J. C Peng / Associated production of hypernuclei Ref. 16.

141 c

The calculation for the I~C ground state, with a weak-coupllng

figuration of (P3/2,1/2)nI(SI/2)A,

underestimates

con-

the data by about 30%.

This

is acceptable considering the 30% systematic error in the data and the uncertainty in the optlcal model parameters.

The I! MeV state has a particle-hole

configuration of (P3/2,1/2)nI(P3/2,1/2)A

coupling to either 2+ or 0 +.

The cal-

culations, which describe the data well, show that the 0 + state is about a factor of 50 more weakly excited than the 2+ state.

Furthermore,

has an angular distribution shape different from the data.

the 0+ state

Therefore,

it can

be concluded that the i! MeV state observed in the 12C(~+,k+)I~c reaction is dominantly a 2 + state.

This is different from the situation in the

12C(k-,~-)I~c reaction, where both the 0 + and 2+ states contribute to the observed cross sectlons. 19 There is an indication that a third peak, about i0 MeV higher than the E x = II MeV state, might be excited in the 5 ° spectrum. state is close to the edge of spectrometer acceptance.

Unfortunately, Nevertheless,

this

the

location of this state coincides with the expected position of the [(P3/2)~I(d5/2)A]3 - - _

state and the [(SI/2)~I(sI/2)A]0 + _

In fact, a

state.

previous (k-,w-) experiment 20 reported the observation of the [(SI/2)nI(SI/2)A]0 + state.

For the (w+,k +) reaction,

the [(e3/2)nl(d5/2)A]3 -

state is expected to be more strongly excited, as shown in Fig. II.

In any

event, both states are expected to be rather broad, and further experiments

are

needed for clarification.

4. FUTURE PROSPECTS The success of the 12C(~+,k+)l~C experiments has clearly demonstrated feasibility of the (~+,k +) reaction as a tool for hypernuclear

the

spectroscopy.

From the good DWBA description of the data, the reaction mechanism appears to be well understood.

This allows us to concentrate on the structure information

of the hypernuclel.

Two future (~+,k +) experiments have been proposed at KEK

and at AGS. 21'22 motivations

In this section, the proposed measurements

and the physics

of the AGS experiment are discussed.

4.1. (~+,k +) reaction on heavy nuclei There are two major reasons for measuring the (~+,k +) reaction on heavy nuclei.

First, the knowledge of A-hypernuclei,

ments and the (k-,~-) experiments, pernuclel.

Properties

of heavy hypernuclel are very poorly known.

ple, the ground state mass of A-hypernuclei I~N.

obtained from emulsion experi-

is largely on light s-shell and p-shell hyAs an exam-

is only known 23 accurately up to

Second, the (~+,k +) reaction is most suitable for populating hlgh-spin

states, expected to occur more frequently in heavier hypernuclel.

J. C Peng / Associated production o f hypernuclei

142c

=C(~+,K+)~aC 1050 MeV/C lel

•

'

I

'

I

'

I

"

I

'

~I~^

C

b 11~~ "rl

lo-'

5

10

15

20

@c.m.(deg) FIGURE ii DWBA predictions for the cross sections of the [(Pq/9)~l(dq/p)A]3[(SI/2)nI(SI/2)A]0 + states in the 12C(~+,k*)I~c r e ~ t i ~ n ~'~ Measurements proposed. 22

of the (~+,k +) reaction on 28Si and 40Ca nuclei have been

A 4 + state with the configuration

expected to be strongly excited in both cases. configuration broad.

and

(d3/2,5/2)nl(d3/2,5/2) A is A 5- state in 4~Ca with the

(d3/2)nl(fT/2) A should also be observable

Although such high-spin hypernuclear

they have never been identified experimentally, the high-spin hypernuclear expected to be very simple.

the main physics interest of

states is that the configuration

of these states is

Unlike the situation for low-spin substitution

states, not many particle-hole Clear identifications

if its width is not too

states are predicted to exist,

configurations

can couple to high spin states.

of such high-spin states provide direct measurement

the location of different A-orbitals.

In particular,

check the strength of spin-orbit interaction

of

this would allow us to

for d-shell A-hypernuclei.

Z C Peng / Associated production ofhypernuclei

143c

The ground states of medium or heavy hypernuclei usually fall into the category of high spin states.

For example, the 28Si ground state is expected to be

a 2+ state with the configuration of (d5/2)nl(Sl/2)A.

Figure 12 shows the DWBA

predictions of the (~+,k+) cross sections for 28Si ground state and the 4+ state.

Although the ground state is not as strongly excited as the 4+ state,

the fact that the ground state is well separated from the quasi-free peak should make it easily identifiable,

We recall that the I~C ground state was

strongly excited and well identified in the (~+,k +) reaction.

A similar situa-

tion is expected for the 2~Si and 4~Ca ground states.

lo5o MeV/C 10t

I-

'

'

'

5

10

15

m 10 °

b 10 -~

20

Oc.m.(deg) FIGURE 12 DWBA predictions for the [(d~/~)~l(d~/9)^]4 + and [(d5/2)nl(Sl/2)A]2 + states in the 28Si(~ ,k )2~Si reaction An accurate measurement of the mass of 2~S~ and 4~Ca could shed some light on the problem 24 of overbinding for ~He.

A recent work by Biedenharn and

Hungerford 25 considered the possibility of deconfinement for the s-shell A particle, causing the up and down quarks to be Pauli blocked and hence a smaller binding energy fo~ ~He.

One expects that the effects of deconfinement and

144c

J. C Peng / Associated production of hypernuclei

quark blocking should be more striking for A particles deeply bound in heavy nuclei.

One possible manifestation of such effects could be an anomalous

binding energy for heavy hypernuclei. 4.2. A-hypernucleus in the continuum and E-hypernucleus We propose to extend the 12C(~+,k+) measurement to cover more highly excited I~C states all the way up to the region of I~C states.

In addition to obtain-

ing better information on the possible existence of the third peak at E x = 20 MeV, this measurement would allow us to investigate the region of quasi-free A-production and the production of ~-hypernuclei. The quasi-free A-production in the (k-,~-) reaction has been clearly observed and the data have been interpreted by Dalitz and Gal. 26

Due to the

larger momentum transfer, the quasi-free peak is expected to be much broader in the (~+,k +) reaction. 9

The fact that the quasi-free peak in the (k-,~-) reac-

tion has a narrow width and large strength makes it difficult to study the A-hypernuclear states in the continuum.

In contrast, the situation is much

more favorable for the (~+,k +) reaction. The predicted cross section 22 for the 12C(w+,k+)l~c cross section is rather small, on the order of a few tenths of ~b/sr.

Whether these E-hypernuclear

states could be observed depends on the strength of the A quasl-free background. 4.3. The d(~+,k+)H reaction The theoretical and experimental situation on the S = -I dibaryons has been discussed at this conference by Dover 27 and by Piekarz. 28

Among all the S = -i

dibaryons predicted by Mulders et al., 29 the 2.6 GeV, L P = I-, spin triplet state is of particular interest.

This state has the same spin as deuteron and

could be produced in the d(k-,~-) or the d(~+,k +) reaction with AL = i. Intriguing results on the d(k-,~-) reaction have been obtained in a recent AGS experiment 28 and a CERN experiment. 30 In order to shed more light on the important issue of the existence of strange dibaryons, we plan to measure 22 the d(w+,k +) reaction using the same multiplicity hodoscope previously used 28 in the d(k-,~-) reaction.

Since it

requires AL = i to produce the strange dibaryon, the large momentum transfer in the (~+,k +) reaction is rather favorable.

The cusp at the EN threshold is

formed via a AL = 0 process and should not be strongly populated.

We expect

the separation between the dlbaryon peak and the cusp background to be adequate in the d(~+,k +) reaction.

A prediction on the zero degree d(~+,k+)H cross sec-

tion at 1.05 GeV/c was given by Aerts and Dover 31 as 0.7 ~b/sr, roughly a factor of three lower than the peak cross section of the d(k-,~-)H reaction.

J. C Peng / Associated production of hypernuclei

145c

This is rather encouraging considering the available plon flux is about two orders of magnitude higher than kaon flux.

ACKNOWLEDGEMENTS The author sincerely thanks Drs. J. F. Amann, R. E. Chrlen, C. B. Dover, J. Millener, E. C. Milner, P. H. Pile, and H. A. Thiessen for discussions on this work.

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146c

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