Radiative kaon capture and hyperon weak radiative decay

NuclearPhysics A479 (1988) 7% _8%~ North-Holland,Amsterdam

RADIATIVE

75c

KAON CAPTURE AND HYPERON WEAK RADIATIVE

DECAY

B.L. ROBERTS? Department of Physics, Boston University, Boston, MA 02215 Branching ratios for radiative kaon capture at rest on both the proton and deuteron are being measured at Brookhaven National Laboratory in Experiment 811. Branching ratios for the weak radiative decays of the Cf and A are being measured as well. A new NaI(T1) detector was developed for the radiative capture experiments which has achieved resolution of 1.5% FWBM at 129 MeV. Preliminary results on the radiative capture reactions p(K;r) A or Co are presented, as well as a progress report on the other reactions.

1.

Introduction

Over the past two years Experiment 811 has been underway at the Brookhaven National Laboratory A.G.S. to study radiative decays of hyperons .l Both electromagnetic transitions from the ~(1405) to the A and COground states as well as weak radiative hyperon decays, are being studied. An example of the former is

(strangeness

changing)

A(1405)-+ A(m3)+7,

and c+ -+p+7 is an example of the latter. The electromagnetic transitions

are of interest because of the information which they

provide on the internal structure of the hyperons. Experimentally one measures a radiative width or radiative capture branching ratio which can be related to a radiative width. The study of radiative widths has already proved to be a powerful tool in understanding nuclear wavefunctions, especially where collective effects or configuration mixing is involved. The weak radiative decays (WRD) h ave remained the last low qZ frontier of weakinteraction physics for some years. Several measurements of the X+ decay listed above have been carried out. Most puzzling is the decay asymmetry parameter, a,,, which is large and has the opposite sign from that expected from broken SC+). Even though this decay has received the most attention experimentally, only 500 such events have been observed over the course of 5 experiments. At present, no satisfactory theoretical picture of these decays has emerged. A number of mechanisms have been invoked by the different authors to explain the large negative value of (L, measured in X+ decay. Although the observed branching ratio for C+ WRD is obtained by each calculation (or is used es input), predictions for branching ratios of the other decays sometimes differ markedly.

tThis work supported in part by U.S. National Science Foundation Grant PBY8612278.

0375-9474/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

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B. L. Roberts / Radiative kaon capture and hyperon weak radiative decay

2. Electromagnetic

Radiative

Transitions

and Radiative

Capture

The quark structure of the hadrons is a continuing problem in particle physics. Although the basic theory of QCD is firmly in place, there is great difficulty in making detailed predictions. Calculations of low energy properties have been limited to phenomenological models since perturbative QCD breaks down at low energies. Static properties such as baryon magnetic moments are predicted to no better than 10 to 15% by current models. These static properties are sensitive to the quark wavefunctions inside the hadrons and it is clear that additional experimental information would be very useful to theorists in developing better wavefunctions. In nuclear physics the study of electromagnetic transition rates and branching ratios has been a useful spectroscopic tool, which led to the understanding of collective effects, e.g. the giant dipole resonance, as well as providing important information on nuclear wavefunctions such as configuration mixing. In Fig. 1 we show possible radiative transitions between the neutral hyperons A and C. The ~(1405) which lies just below the K-p threshold remains an enigma after many years of study. Its mass is not predicted well by either the Isgur-Karl model’ or by bag models* which contain two possible states which might be identified with the

~(1405).

Simple quark

configurations for these states are shown in Fig. 2. We note that one photon emission implies a single particle transition. With the configurations shown in Fig. 2 the transition A(MOS) + P(1193)

is forbidden.

FIGURE 1 Radiative transitions between the hyperons

FIGURE 2 Possible quark configurations. The strange quark is represented as l .

Radiative widths have been calculated by Darewych, et al.’ using the Isgur-Karl quark modela, and by Ksxiras et al.& using both the Isgur-Karl model and the MIT bag model.* Experimentally one is faced with the problem of producing the hyperon state, and looking for its radiative decay. In principle, photoproduction of mesons should also provide structure information, but in nuclear physics this hope has not yet been realized because of uncertainties in the final-state

B, L. Roberts / Radiative kaon capture and hypetwn weak radiativedecay

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interaction of the meson with the nucleus. In particle physics, photoproduction has already served ss a useful constraint on wavefunctions. (See the review by Foster and Hughes.*). Nevertheless, experimental results are only available for non-strange baryons since one has to use nucleon or nuclear targets. The transitions which have been studied in detail are: W--‘Il”t%

TP-+ KOP

7s * Ab,

m --) z-p

Information on: is indirect and thus much more sparse. The equivalent photoproduction off strange baryons such as: -th + ToA,

7h + K-p

a,re not experimentally accessible. On the other hand, the radiative capture reactions,

K-+p+Y+?,

Y = h or Co

are possible, although difficult to observe experimentally, and should provide equivalent information. The radiative capture reaction has the disadvantage that one emnot easily vary the momentum transfer in a systematic way as can be done in photoproduction experiments. Because the h(1405) and X(lS82) are below threshold in the K-p system, we cannot produce these statea in a direct fashion. The in3uence of the h(l405) on the low energy K-p interaction has been known for years, both from scattering experiments and from kaonic atoms. In Fig. 3 the two types of diagrams which can contribute to radiative capture are schematically shown. The importance of the diagram involving the intermediate ~(1405) is the subject of some diipute,fie but both sets of authors agree that the branching ratio is sensitive to the radiative width of this state. .>(’

;>

Af+%051
z0 FIGURE 3 Schematic diagrams which contribute to radiative capture. The calculation of Rarewych, Koniuk and Jsgur* shows that, in the context of the IsgurKarl model%, the radiative capture process is dominated by the intermediate h(1405). They find that the branching ratio to C0(1192) and ~(11~) states is primarily determined by the electromagnetic decay widths to these states. This ealculation~ predicts that the rates for radiative capture to the A and X0 ground states are comparable. The calculation by Zhong et al.* using the ‘Woudy-bag” model reaches a similar conclusion. The two branching ratios Rx, Ra are defined ss Rx =

K-p * A7 K-p + everything’

%=

K-p + CD? K-p 4 everything

The calculated rates are given in Table 1 below, One notes that although the predicted branching ratios disagree in magnitude, the ratio of the branching ratios for the two channels is 1.3 for both calculations

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B.L. Roberts /Radiative

kaon capture and hyperon weak radiative decay

Table 1 Calculated Branching Ratios RI, Ra for p(K-,$

at Rest

Final State

B.R. (Ref. 8)

B.R. (Ref. 9)

A7

3.4 x 10-a 2.6 x 10-a

1.5 x 10-s

co7

1.9 x lo-*

The experimental difficulties one encounters in radiative capture experiments come from both the low branching ratio and the continuum of ~0 decay photons from the background reactions. For stopped K- in hydrogen, the dominant reactions are K-p -+ E+r-

x-r+

A no

co??

20%

46%

6.7%

27.3%

Secondary photons and x0’s are produced by the decays: co + A + 7

lOO%,

A + n+ ST0 SS.S%,

c+ +p+cP

51.64%.

Over 500 hours of radiative capture data from kaons stopped in a LH~ target have been taken at the AGS. A subset of these data have been analyzed, and preliminary results are presented below. In-flight radiative capture using a K- beam with momentum PK = 3% Mev/c to form the A(1520)would provide information on its radiative width. Specifically, a large radiative width for this state would imply that color hyperfine effects are important in this system.’ There have been two experiments which have studied K-p -+ A7 in flight. The experiment of Mast et al.‘0 used a bubble chamber and the recent experiment Bertini et al.11 used a small NaI detector to try to detect the photon directly. Conflicting results were obtained by these experiments, and an improved experiment with good resolution and statistics must be done. These are difficult experiments, but are important to resolving questions of hyperon structure. The new Boston University NaI(T1) detector, which is described below, combined with an external converter of BGO and a wire chamber array, could be the ideal detector for such an experiment. The radiative capture reaction K-+'H+A

+a+7

has also been studied at Brookhaven. With sufficient statistics and excellent energy resolution on the photon, one can use this reaction to determine the A - n scattering length just as the d(n,+n experimenP was used to determine the best value of the neutron-neutron scattering length, a,,,,. The shape of the photon spectrum in the endpoint region, where the relative momenta between the A -n pair in the final state is small, is quite sensitive to the scattering length and to the effective range. This experiment was proposed by Gibson et al.ls, but only recently has it been attempted. In the paper of Gibson, et al.rs, only the An7 final state is considered, whereas Akhiezer, et al. r4 also consider the X-W final state. Both sets of authors conclude that the shape of the photon spectrum near the endpoint is quite sensitive to the final-state A - n interaction. We note that a measurement of a*,, using this technique is not model independent, since there will be both 8 and p wave contributions. We have taken approximately 130 hours of data on radiative capture on the deuteron in E811. The photon endpoint energy for the An7 final state is 293.31 MeV. Background r” decay photons from K-+d-+A+n+u’

B. L. Roberts /Radiative

kaon capture and hyperon weak radiative decay

79c

cover the energy region up to 280 MeV so that only the endpoint region of reaction (24) will be free of substantial background in a singles experiment.

3. Hyperon

Weak

Radiative

Decay

Weak radiative decays are currently being studied in two experiments, ES11 at Brookhaven and E761 which is under construction at Fermilab. Branching ratios for C+ and A WRD will be measured at BNL and both a, and branching ratios will be measured at Fermilab for several of the charged hyperons. In Table 2 we list the experimental branching ratios (or limits) which have been measured to date for the hyperons. Table

2

ExistingData on HyperonWeak Radiative Decays Decay

Ref.

# of Events

Branching Ratio

Asymmetry Parameter

c+--rp7

15-20 21

500 23.7

-0.83 & 0.18

22,28 22

170 l?

(1.24 zt 0.08) x lo-’ (1.02 f 0.83) x 10-s (l.lLt 0.2) x 10-s < 7 x 10-a

22,24

9.4

(2.27 f 1.02) x 10-d

25

<9

c 2.2 x 10-J

A -+ n7 ?+A7 80 4 co7 8- --+ c-7 n- -+ z-7

Y

s

u.c,t

Much theoretical work has been carried out on the d weak radiative decays.ze-‘8 This work can be roughly

‘._..._’

w

(4

S/Y” w

d

(b)”

s

U

,w

(4 ”

divided into two classes: those which use quarks and consider quark transitions, and those which use baryon pole models in conjunction with symmetry principles. Gilman and WiseZ6 evaluated the one-quark transitions shown in Fig. 4a (8 -+ d7) where the other two quarks are spectators. This model predicts branching ratios to within an overall normalization. Using C+ -+ p7 to determine the normalization gives the results shown in Table 3. The predictions for the other decays are systematically higher than the current upper limits. There is the additional problem that this calculation predicts a zero asymmetry in D+ -+ p7 decay which does not agree with the experiments. (see table 2) The authors conclude that there must be additional diagrams contributing to this process. The two-quark transition 8 + D --* u + d + 7 which is shown in Fig. 4b has been considered by a number of authors.a7-J0 The results are compatible with the known limits. This two-quark diagram cannot contribute to the weak radiative decays of the D- or the 8- since there is no valence s quark in the initial state. HuahSo has also calculated the three quark transition shown in Fig. 4c, and has found it to be negligible.

FIGURE 4 Several author+-*’ have considered more complex diagrams which include gluons, such as the “penguin” diagram shown in Fig. 4d. If the photon is connected to an external quark line, then this is the same penguin diagram which is important in the AZ = i rule for

B. L. Roberts / Radiative kaon capture and hyperon weak radiative decay

8Oc

strangeness changing decays and f

in neutral kaon decays. If the photon is connected to

the interior loop, it represents completely new physics. Table 3 Theoretical predictions for weak radiative decay branching ratios in units of lOMa

n- + 8-7

Ref.

R+-+KI

A -t n7

go + ROY

8” + A-r

26

1.24.

22

9.1

4.0

11

41

27

1.24’

5.97

1.48

1.80

1.20.

0.6

27

1.24.

1.70

0.25

1.56

1.20.

0.6

28

1.17*

0.26

1.4

0

1.1

0.12

28

1.17.

0.82

S6

0.54 f 1.25

1.9 f 0.8

55

0.92?;:::

0.62

7.2

3.0

59

0.82+;:;;

1.02

5.87

2.29

1.5

10

15

40,41

0.66

B- + R-7

0

42

0.17

52

10-s - lo-’

10-z - 10-i

‘used a,ainput to determine the normalization.

The most puzzling aspect of these weak decays is the asymmetry parameter o, for the C+ weak radiative decay. Currently thii is the only asymmetry parameter which has been measured. As was discussed by Rudaz,” in the limit of CP invariance, the absence of right handed currents but with broken W(S), the asymmetry parameter for E+ weak radiative decay is given by

The experiments give a large negative value for this quantity, and there is still no clear theoretical path out of this quandary. Gaillard et al .a* claim that a large negative asymmetry can be obtained through an effective ds70 operator (the penguin term) for which the GIM cancellation is negligible. An estimate of the influence of such an operator is given using the MIT bag model. They obtained an asymmetry of -0.6 < a, < -0.S which is 1.8~ below the experimental value listed in Table 2. The branching ratio obtained assuming that this penguin contribution is the sole diagram is several orders of magnitude below the measured value. An alternate estimate, which focused on the contribution of the static color field, gave a comparable branching ratio, but an asymmetry parameter o, u -0.54 wss obtained. In conclusion, Gaillsrd et al.ss point out that their explicit calculations are “inconclusive”, and that detailed comparison with experiment may not be possible until baryon structure is better understood. The importance of a good theoretical understanding of the weak radiative decays has been emphasized by Georgi.46 He points out that an analysis of these decays involves putting together three components: 1) strong QCD (spontaneous china1 symmetry breaking), 2) the four-fermion interaction (weak) and 3) the weak gauge interaction (electromagnetism). He believes that a similar three components will be at work above the weak scale if the breaking of SU(Z) x ~(1) is dynamical. “It is crucial to understand how they fit together in a process that we can study in detail”45 Experimental investigation of these decays is quite difficult. The primary background is the usual 1p decay, rather than the weak radiative decay. While the two decays are kinematically different, it is not always easy to resolve them experimentally.

B. L. Roberts /Radiative kaon capture and hyperon weak radiativedecay

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The decay does not lend itself to high energy measurements. 11 The branching ratio will be measured at Brookhaven in E811, but the asymmetry parameter will require a separate measurement. We will use the LAMPF crystal box detector for this measurement. Stopped K- will be used to form A’S through and the monoenergetic ~0 will serve as a tag. This detector covers approximately 2~ solid angle and is 12 radiation lengths of NaI(T1) deep.‘O There are two possibilities for the decay asymmetry parameter measurement. A small A polarization is produced by stopping K- through interference of the two amplitudes46 K-+p--rC”+ro+A+9ro+7

and

K-+p-rC*+7-+A+zi”+7.

The polarization is expected to be large for the portion of the Dalitz plot on the real C’. This is a small effect and involves detecting three photons in the final state, one of them rather low in energy. Only a few such events are expected in E811, and one may need a kaon factory for this technique to work. An alternate approach is to produce polarized A’s in flight where the polarization will be transverse to the plane formed by the incident beam and the 1p trajectory. One would then need position sensitive good resolution photon detectors for the ~0 tag and the WRD photon. The A polarization has been messured4r~4ain the K- momentum range of 440 - 800 MeV/c, and this may be a promising way to measure the decay asymmetry. One would need to confirm the polarization measurements, but this could be done rather quickly using either the pi- or ,x0 decays. 4. Experimental Details The experiment is being carried out in the C8 low energy separated beam called LESBII at the Brookhaven AGS. An excellent K- beam has been developed at 680 MeVJc. The R- : K- ratio has been observed to be as good ss 3.5:1 and the flux is on the order of 64,000 K- per 10’” protons on the production target. We routinely ran with a R : K ratio of 6:l. The momentum bite is Sxed at *2%. In principle it is possible to run with 4 x 10’” protons per AGS spill on the production target. In our experiment, pile-up in the NaI(T1) detectors from the secondary beam limited the useable proton intensity on the production target to a maximum of 3 x 10’” protons per pulse. The machine runs at a repetition rate of 20 to 25 pulses per minute, with a spill width of just under a second. We estimate the K- stopping rate per beam burst to be 10 to 15 x 10’ in a 30 cm long, 20 cm diameter LHa target. The beam size entering the degrader was a 5 cm high x 11 cm wide spot. The experimental arrangement is shown in Fig. 5. An incident K- is identified by scintillation counters and a velocity selecting Cerenkov counter and then is slowed down in the Cu degrader. Two 1.27 cm thick $$ counters, a beam hodoscope and a 0.16 cm thick counter are immediately upstream of the hydrogen target. A veto counter was placed inside the vacuum vessel, but was not used ss a hardware veto since this would reject events where secondary charged particles followed a stopped K-. NaI(TI) detectors were placed on either side of the target. Charged particle veto counters were placed between the NaI(T1) detectors and the LHa target. Scintillation range telescopes were placed above and below the target. These were optimized to detect the monoenergetic X- from K-+~--PE++Tthus tagging X+ production.

82c

B.L. Roberts 1 Radiative kaon capture and hyperon weak radiative decay

A new NaI(T1) high resolution detector (hereafter referred to as BUNI) has been constructed by Bicron for these experiments. It has a central core which is 26.7 cm in diameter and is 55.9 cm deep. The core is surrounded by a four piece NaI(T1) annulus which brings the diameter up to 40.5 cm. The pieces are optically isolated but share a common hermetically sealed aluminum enclosure. The central core is viewed by 7 Hamamatsu RlQll phototubes, and each annular piece is viewed by 3 tubes. Outside of this assembly is a 12.7 cm thick plastic veto shield, The uniformity specification on the central core was ~0.2% over the front 36 cm when measured with a 6 MeV T-ray source. In this experiment a collimator of 12.7 cm diameter was used at distances of 47 and 76 cm from the target during the January-February and May running periods respectively.

FIGURE 5 A plan drawing of a top view of the experimental arrangement. 5’1 - Ss and El and & are plastic scintillation counters, F is a velocity selecting Cerenkov counter. A lucite Cerenkov counter to identify beam pions C wry physically in place, but not in the trigger. On the other side of the target wss a 49 element array of NaI(T1) which consisted of 6.35 x 6.35 x 50.8 cm8 rectangular elements, each viewed by a separate phototube.’ The excellent position resolution of this detector made it ideal for the C+ weak radiative decay measurement since it offered a relatively large solid angle with modest resolution. The detectors were calibrated using stopping pions. In Fig. 6 we show the Panofsky 7 and the +?Jbox from charge exchange for the two detectors. We obtained 1.5% FWHM at 129 MeV from the BUN1 detector and 6.5% from the 49”. The BUNI response was also studied at the MIT-Bates Linac using monoenergetic electrons and was found to have a resolution of 1.6% FWHM at 330 MeV. Only 10% of the data have been played back thus far. With this level of statistics it is still possible to draw some conclusions from the data. The neutral spectra obtained in coincidence with stopping K- is shown in Fig. 7(a). The spectrum is dominated by a “tower” produced by Doppler broadened 7’s from 9 + ~7 and by edges of # decay boxes. In Fig. 7b the region of the radiative capture 7 rays is shown and the hy and 2’7 peaks are labelled. Pulse pile-up tends to fill in the valley between the K-P -+ 18 box and the radiative capture peak, but it is still clearly visible. The ~07 peak is also visible, but one needs the full statistics

B.L. Roberts /Radiative

83c

kaon capture and hyperon weak radiative decay

before a precise determination of R2 can be obtained. 5000

l-

450 0 400 0 350 0

z x P Y

5

300.0 2500

eooo

8 1500

60

9”

150

120

ENERGY

MW (4

04 FIGURE 6 The spectra from stopping r- in LH2. Fig. 6(a) shows the response of the BUN1 and Fig. 6(b) shows the response of the 49”. In Figure 6(a) some events in the 1p box were lost because the BUN1 trigger only considered the energy deposited in the central core. There was no loss of efficiency from this effect above 100 MeV. ,500.c 1350.0 1200.0 1050.0 z a h 2 LEi L,

900.0 750.0 6000 450.0

,000.o

00

3000

1

150.0

I 0

0.0 50

100

150

MeV

(4

200

250

300

180

200

220

240

260

200

300

MeV (b)

FIGURE 7 The spectrum obtained using BUN1 from stopping K- in LHa. Fig. ‘7(a) shows the entire energy region and Fig. 7(b) shows the two radiative capture peaks corresponding to the ~97 and ~7 final states. In Fig. 8 the experimental spectrum is shown along with a calculated spectrum assuming the branching ratio for the

A7

final state is 1 x lo- a. The detector response and pile-up are

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B. L. Roberts / Radiative kaon capture and hyperon weak radiative decay

still under study to improve the agreement in shape between the observed and calculated response on the edge of the Z box. However, it is clear from a visual comparison of the calculated spectrum and this sample of the data that the experimental branching ratio RI 1 x lo-*.

A similar analysis of the Co final state shows that Ra > 1 x 1O-s.

250.0

200.0

3

P 3 5 8

150.0 100.0

00

230

240

255

260

no

280

290

300

MeV FIGURE 8 The endpoint region of the spectrum from stopping K- in L&. The triangles are the data, and the solid line represents a calculated spectrum assuming a value for RX of 1~10-~. The detector response and the pile-up shape are still under investigation. The data on d(K-, 7)hn are also being analyzed. The statistics are poor, and pulse pile-up may be a limiting factor on our ability to determine the A - n scattering length. We will be able to measure a branching ratio for this reaction, which will permit us to determine the feasibility of a longer run to measure the scattering length. The data on the 8+ weak radiative decay are still in a preliminary form. Suitable cuts on the data have been ascertained, and the analysis is proceeding. The decay 8+ + p + a0 is clearly seen, and the background has been suppressed to a level comparable to the signal. The shape of the x0 box is reproduced by our Monte Carlo calculations when pile-up is included. Because of the modest tagging efficiency-solid angle, coupled with the small branching ratio, it will be necessary to play-back all the data before a result on the C+ weak radiative decay will be available. 5.

conclllsions

From the preliiinary analysis of the radiative capture data it is clear that the calculations given in Table 1 do not describe the data. The magnitude of the branching ratio RI seems to be considerably smaller than the predicted values. The relative size of RI to Ra also appears to be opposite to that predicted by both calculations. It is unlikely that these conclusions will change very much with additional analysis and improved statistics.

B.L. Roberts /Radiative

852

kaon capture and hyperon weak radiative decay

The radiative capture data on the deuteron will provide a measurement of the branching ratio for the bn7 final state and perhaps some information on the An final state interaction. It is too early in the analysis to predict the results of our measurement of the branching ratio for the XC+weak radiative decay. The analysis seems to be proceeding well. We now seem to understand the shape of the &’ box from C+ + pro, and the background above the endpoint of the box seems to be manageable. We expect to have several hundred events in the total data sample. In the second phase of the experiment we will use the LAMPF crystal box to measure the branching ratio for the A weak radiative decay. Installation of this detector at Brookhaven is currently in progress and should be completed by the end of 1987. We expect to take preliminary data in early 1988. Acknowledgements It is a pleasure to acknowledge my collaborators in E811 for numerous discussions on the physics of radiative decays. In particular, I wish to thank J. Lowe and J. Miller for reading this manuscript and offering constructive comments. I wish to thank H. Georgi and R. Jaffe for helpful discussions on weak radiative decay and polarization respectively, and N. Isgur and R. Koniuk for useful discussions on radiative capture. References 1. Brookhaven National Laboratory Experiment 811, Radiative Kaon Capture and Hyperon Weak Radiative Decay, Birmingham, Boston, British Columbia, BNL, Case Western, KFKI and TRIUMF, B.L. Roberts Spokesman. Collaborators from LAMPF, the University of New Mexico and Princeton have joined the second phase of the experiment. 2. N. Isgur and G. Karl, Phys. Lett. 72B (1977) 109; 74B (1978) 353, and Phys. Rev. D18, 4187 (1978). 3. T. DeGrand, R.L. Jaffe, K. Johnson and J. Kiskis, Phys. Rev. D12 (1975) 2060. 4. J.W Darewych, M. Horbatsch and R. Koniuk, Phys. Rev. D28 (1983) 1125. 5. E. Kaxiras, E.J. Moniz and M. Soyeur, Phys. Rev. D32 (1985) 695. July 84. 6. F. Foster and G. Hughes, Rep. Prog. Phys. 46 (1983) 1445. 7. H. Burkhardt, J. Lowe and A.S. Rosenthal, Nucl. Phys. A440 (1985) 653. 8. Darewych, R. Koniuk and N. Isgur, Phys. Rev D32 (1985) 1765. 9. Y.S. Zhong, A.W. Thomas, B.K. Jennings and R.C. Barrett Phys. Lett. 471.

171B (1986)

10. T.L. Mast et al., Phys. Rev. Lett. 25 (1968) 1715 11. R. Bertini et al., PANIC 10, 30 July-3 August 1984, Heidelberg, abstract M18, and preprint, 1986, to be published. 12. B. Gabioud, J.C. Alder, C. Joseph, J.F. Londe, N. Morel, A. Perrenoud, J.P. Perroud, M.T. Tran, E. Winkelmann, W. Dahme, H. Panke, D. Renfear, C. Zupancic, G. Strassner and P. Tru51, Phys. Rev. Lett. 42 (1979) 1508.

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kaon capture and hyperon weak radiative decay

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p. 296.

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38. M.B. Gavela, et al., Phys. Lett. 1OlB (1981) 417. 39. K.G. Rauh, Z. Phys. Cl0 (1981) 81. 40. M. Scadron and L. Thebaud, Phys. Rev. D8 (1973) 2190. 41. M. Scadron and M. Visinescu, Phys. Rev. D28 (1983) 1117.

B. L. Roberts / Radiative kaon capture and hyperon weak radiative decay

87c

42. Y.I. Kogan and M.A. Shifman, Sov. J. Nucl. Phys. 38 (1983) 628.

43. V.I. Zakharov, A.B. Kaidolov, Sov. J. Nucl. Phys. 259 (1967). 44.

S. Rudaz, Fermilab Hyperon Conf. 7-8 Dec. 1986, unpublished.

45. H. Georgi, private communication. 46. D. Diisedau and R.L. Jaffe, Phys. Lett. 186B (1987) 425. 47. Nai-Sitt Wong, Ezperimental

Study

of K-p

Interactions

Thesis, Yale University, (1969). 48. R. Armenteros et al., Nucl. Phys. B21 (1970) 15. 49. S.L. Wilson et al. Submitted to Nucl. Inst. and Meth.

between

450

and 670 MeV/c,