Pion production in high energy nucleus-nucleus collisions

Pion Production in High Energy Nucleus-Nucleus Collisions C. BESLIU*, V. BOLDEA%, V. TOPOR POP**, R. T O P O R POP*, V. POPA**, A. OLARIU* AND A. JIPA* *University of Bucharest, Department of Nuclear Physics, Bucharest, P.O. Box MG-6, Romania **Centre of Astronomy and Space Sciences, Bucharest, P.O. Box MG-6, Romania i'lnstitute for Physics and Nuclear Engineering, Bucharest, P.O. Box MG-6, Romania

ABSTRACT New data are reported on the pion production in relativistic centra~ collisions especially for 3.6 GeV/N oxygen beams on Pb and Ne targets using the SKM-200 Dubna streamer chamber facility. Multiplicities and kinematical characteristics of negative secondaries are analyzed. The ratio of the average negative meson number to the average number of interacting protons is discussed. A comparison is made with other pion data. The technique of pion interferometry is used %o study the pion source for central collisions of oxygen beam on lead. The temperature and density phase of nuclear matter in O+Pb collisions is estimated from pion data and the results are compared with Those of other experiments. KEYWORDS Nucleus-nucleus collisions; streamer chamber; pion production; pion interferomerry; temperature and density of nuclear matter. INTRODUCTION The analysis of nucleus-nucleus collisions offers an efficient way to observe and study the unusual states of nuclear matter. Many experiments were carried out (Agakishiev and co-workers, 1984; Anikina and co-workers, 1985; Fredrickson and co-workers, 1984; Nagamiya and Gyulassy, 1984a) in order To test theoretical predictions within the nuclear matter at high energy. A Transition to The quarkgluon plasma may be expected even at the Dubna energy, especially if the full stopping of The colliding nuclear matter Takes place (Anikina and co-workers, 1985). Pion and proton emission was used to investigate the thermal equilibrium in central collisions of Ar+KCI at 1.8 GeV/N (Brockmann and co-workers, 1984; Sandoval and co-womkers, 1984). ThermalizaTion and stopping in nuclear collisions was also investigated by Strobele and co-workers (1985) and by Stock (1985a, 1985b). Composite pamticle and entropy production was analyzed by Stocker (1984) and by Doss and co-womkers (1985). In the work of The GSI-LBL PlasTic Ball group and streamer chamber collaborations a tendency is noted to replace the inTranuclear cascade model by the collective flow and other more efficient hypotheses, like the analysis based on nuclear fluid dynamics (Buchwald and co-workers, 1984; Molitoris and co-workers, 1984a; MoliToris and Stocker, 1984b) or on the microscopic Vlasov-Uehling-Uhle~beck approach, including the nuclear mean field, two body collisions and Pauli blocking (Kruse, Jacak and ST~cker, 1985a; Kruse and co-workers, 1985b; MoliToris and Stocker, 1985). A detailed analysis of the particle production in various classes of nuclear collisions and intercorrelations between various characteristics was performed (Anikina and co-workers, 1985) using the data from the 2m streamer chamber spectrometer SKM-200. The basic data on pion production in inelastic and ten-

353

354

C. Besliu et al.

ira1 nuclear collisions have recently been published (Anikina and co-workers, 1984). Two excelent reviews on the current experimental and theoretical status of pion and strange particle production at the Bevalac and Synchrophasotron accelerators have been made by Stock (1985a, 1985b). Experimental efforts in investigating the high temperature and high density phase of nuclear matter in nucleus-nucleus collisions were reviewed by Nagamiya (1984). Relativistic nuclear collisions produce hot matter that radiates protons, pions, and composite particles. The effective source size of this par. ticipant region has been investigated by a number of groups by means of either pion-pair correlations (Akhabadian and co-workers, 1982~ Beavis and co-workers, 1983a; 1983b; Zajc and co-workers, 1984; Crowe and co-workers, 1984) or proton-pair-correlations (Agakishiev and co-workers, 198q; Akhabadlan and coworkers, 1982; Gustafson and co-workers, 1984). In addition if we measure the nucleon multiplicity () we can directly obtain the density of nuclear matter (Nagamiya~ 1984). In this paper, the new experimental results of pion production in inelastic and in central nucleus-nucleus collisions are presented, especially for two systems O+Pb and 0+Ne at the laboratory kinetic energy 3.6 GeN/N. Multiplicity distributions of negative pions and semi-inclusive distributions of various kinematical characteristics like rapidity and transverse momentum, are studied. The mean number of negative pions per charged participant particles in the symmetric and non symmetric case is determined. Pion correlations are analyzed in detail for O+Pb and space t i m e dimensions of the nuclear interaction region are reported. The temperature and density which are obtained in the O+Pb system from pion production are discussed and the data are compared with those of other experiments. EXPERIMENT The data were obtained from pictures of a 2 m streamer chamber SKM-200, placed in a magnetic field of ~ 0.8 T and exposed to beams of nuclei accelerated in the syncrhophasotron up to a 4.5 GeV/c momentum per incident nucleon. The chamber, filled with pure neon under atmospheric pressure I contained a solid target mounted within the fiducial volume of the chamber. The targets had the form of thin discs ~0.2+0.5 g/cm 2, only in the case of Li targets the thickness was 1.6 g/ cm )~ the neon gas was also used as a nuclear target. The pictures were taken using an optical system with 3 objectives (see Fig. 1).

8KM-200

comefo sysfem

~cuum \ s tut?e ~

d~

/magnet

/1

tu~e

maonaf/c turgef Streomer Ple/d cnom#e,~

sn

~. n

~5 s6

~ S. o o

"INELASTIC" TR/OSER.a! AS2 ,~S3 ^ S44 $~ A "~6 "CENTRAL" TRIgGER= SI A 52 A Sj A S4 A Sn a ~ch

Pig, I. Experimental set-up. The trigger and the trigger distances are not up to scale.

Pion Production

355

The quality of the calibration (determinaTion of optical consTanTs, measurements of The magnetic field and its space disTribuTion and error determination) was Tested by K~ and A ° mass measurements. The selection of inelastic and central events was carried out using two triggering systems: - The minimum bias Triggering system consisting of two sets of counters mounted upstream and downstream The chamber, has selected inelastic interactions of nuclei within The chamber. - The central Triggering system consisting of the same upstream part as in The minimum bias system and of scintillation veto counters, regisTerin E a projecTile and/its charged fragments, in The downstream part. In some runs a sandwich of five layers of 10 cm iron and 4 cm scintillators in each layer was additionally included in The veto system for recording stripping neutrons. Thus The trigger selected central collisions defined as Those without charged relativistic (p/Z > 3 GeV/c) secondaries emitted at angles 8 < 8ch = 2.4 °, 2.9° (The trigger efficiency was - 99% for one charged particle) and, in some runs, without relativistic (p > 3 GeV/c) neutrons emitted at angles e < 8 n = 1.8 °, 2.8 ° (The Trigger efficiency was -- 80% for one neutron. Since several combinations of 8ch and 8 n values was used, The Trigger mode for each exposure was defined as T (ech, en). The streamer chamber pictures were scanned Twice, and a subsequent Third scan resolved ambiguities om discrepancies beTween The first Two scans. For each sample of central events selected by The central triggerin E system two subsamples were further selected during the scanninE, namely Those consisting of events in which no relativistic positive secondary was recorded (p/Z > 3 GeV/c) which was emitted at a projected angle less Then a) 4 u, b) 14 ° and a dip angle less Than 14 °. Further analysis dealt Therefore with The following samples of events: T(0,0) - inelastic collisions T(2,0)~ T(5,0); T(14,0)~ T(2,2); T(5,2); T(14,2)~ central T(3,3); T(5,3); T(14,3)J collisions The discussion of possible sources of experimental biases and appropriate correction procedures is made by Anikina and co-workers (1984). PION CHARACTERISTICS We present The data on negative pion multiplicities ( n ) , Transverse momenta (pm) and rapidities in The laboratory system (y). Full information on The form of-the spectra considered (n_, p~, y distributions) is replaced by values of three pa~ameTems, average distribution values () its dispersion (Dx = <(x-)~> % ) and its asymmetry coefficient (~x = ~3/D~; ps = <(x- ~>). Parameters of multiplicity distribution for 0-Ne and O-Pb reactions at 3.6 GeV/N are given in Table 1. TABLE

1

Ap-A T

Characteristics

T(ech,8 n)

Nev 290

of Negative

n_

160-Ne

T(2~o)

l"O-Ne '°O-Ne leO-Pb ¥'O-Pb 160-Pb

T(5,0) _ 99 6.12~.25 T(14~0) 20 5.48~.48 T(2,0) 2191 11.07±t31 T(5,0.) 891 ..12.41~.35 T(1410) 491 12.76¢.37

5.95~T17

Pions

Dn_

¥~.

2t19~.12 .... .44~.25

2.24±.18 2.15Z.3~

3.49~.05 3.16¢.08 3.12~.11

.65~.24 .63Z.55 -.03¢~05 -.06±.10 .01¢.15

In Table 2 we give The values for the mean rapidity () and The mean Transverse momenta , for fixed n_ values in the interactions O-Ne and O-Pb (trigger T(2,0)). Anikina and co-workers (1985), studied rapidity and Transverse momenta versus The variable n /Ap. Also different possible intercorrelations are discussed. In Fi E . 2 we show The relation between The width of The pion multiplicity dis-

356

C. Besl'iu

Characteristics of the Rapid!t~ and Transverse Momenta Distribution

TABLE 2

Ap-A T

n.

Dy



Nev

l~U, 5 6

O-Ne

et aL

% (HeY/c) (HeY(c)

263 218 259

1.1~2.05 .76~.03 252~11 _172~10 1.26z.06 .82==0q 2 0 ~ 1 1 15~15 1.12±.06 77±.9,_239* 9 lq9¢'-8 1.13~.06 . 8 2 ± , 0 3 218± 9 : 1 ~ 1 ~ 1 0 ~59. ~.09Z.06 .7~¢.05 225~1~ 170±18 9*11 200 1.I5±.05 .77=T03 2 3 7 ± 1 1 156¢ 9 all 1378 1.I5±o02 .782.01 2292 ~ 159~ 5 1~7 2~ .91¢v06 .79~.03 218¢ 9 161¢ 9 8~9 ' ~91 . . 8 0 ¢ . 0 3 ' .75±.2~'190¢ 6 1~8¢ 8 10 219 .82¢.05 .7~.03 195¢ 9"' 1~5~I8 ~! ..... 3 2 7 ' .74=.06 .71¢.02 201* 9 " 168e1~ 12 .70e.Q2 205± 8 " ~ 6 3 d ~ 1~ ...... ~36 .~1¢;0~ .?3±.02 178t 6 _127± 6 1~ ~03 .66*~0q . 7 0 i o 0 2 180± 7 126¢ 6 15,16 319 .62X.03 .68¢?02 1 7 5 T ? ~32~-7 17*18 "2~6 .B0Z.05 ~ 7 ~ . O 3 169~_8 T29~I0 all _2693 .72~.01 ±73,.O1 1 9 0 ¢ _ 3 Iq5± 3

'eO-Pb

_ ,

|

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~

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•

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FiE. 2. Compilation of Dubna S%reamer Chamber results for the mean via the dispersion of negative pion multiplicity distributions measured at 3.6 GeV/N. tribution, as given by the dispersion D and the mean multiplicity measured for a reaction of incident ~He, laC and leO with targets rangin E from carbon to lead, in both the minimum bias and central trigger mode. Whereas the central trigger data with I=C and 160 projectiles follow closely the curve D a = , characteristic of a Poisson distribution, the minimum bias data alone with the 4He - projectile reactions, follow more closely the Wroblewski relation D -- which is specific for hadron-hadron reactions. One defines the mean number of the charged participants (Sandoval and coworkers, 1980) _ (s) > _ _ (s)> _ 2 (1) = - ¢nproj ~nta r

|

Pion Production

357

where N~ i s t h e t o t a l m u l t i p l i c i t y , n~q - p r o j e c t i l e s p e c t a t o r s , n%~1 - t a r g e t spectators. In Fig. 3 we show the'r&tio of the mean number of negative pi-

• Ar'KC/ 5o,~dowl (]980)T o At'+ KCl }Nagamiya (/98I) D Ne+NaFJ /r ¢ Ne÷ Ne Anikma

$ •

A

No} O+ Pb

O+

0.3-

our resu/fs

7-s'22T~=2 z/5

,q

" 02-

(Ig83~-

/FB

~\

/

/.,.,<.. 01 /,,~.// ~- LLI //'° !

Fig.

2

3

EL.4,( aeV/N)

3. Predictions for the energy dependence of the I- multiplicity per participant protons obtained from the fireball (FB) and hydrodynamical model without friction (, = 1.0) and with the inclusion of friction (, > 1.0) (St~oker, 1984) ape compared to the data ((.) Sandoval and co-workers (1980)~ (o) (~) Nagamiya and co-workers (1981), ¢ Anikina and co-workers (1983) • O+Pb - our results,)

ons per charged participant particle R = / ' in the central collisions (T(2,0)) for the O-Ne, Ne-Ne and O-Pb. We compare our results with those measured in high multiplicity selected central collisions Ar+KCI (Sandoval and coworkers, 1980) and with the data fop large angle inclusive I-/Z ratio (Nagamiya and co-workers, 1981) where Z is the total number of positive charges in reactions of AP+KCI and Ne+NaF. The calculations in the nuclear fireball model (short broken curve) made by Bohrmann and Knoll (19819~yield absolute values of the ratio R which are too large. The absolute values of the ratio R, as well as the linear energy dependence obtained, are well described in a relativistic fluid dynamical model, when the effects of the viscosi~., that is, deviations from the perfect local equilibrium are incorporated (Stocker, 198~). Our resuits show a continuation of This linear dependence for O-Ne and Ne-Ne. Ratio R was systematically analyzed in the symmetric case by Anikina and co-workers (1983). In the non-symmetric case the ratio R systematically decreases as the target mass increases, due to a kinematical effect. PION INTERFEROMETRY Pion inTerferomeTry has been proposed as a tool for measuring the radius and lifetime of The pion source. This work describes preliminary results for the

358

C. Besliu et al.

I =-

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600

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4. The source temperature, Tn, plotted against the beam ~inetlc energy, EBEAM •

lines

in Fig.

4.

To evaluate the density of the excited nuclear matter 2 the method of Nagamiya (198~b) has been used. The method is based on measuring the size of the interaction volume via identical particle interferometry and on the estimation of the number of interacting nucleons from the colliding nuclei. One can estimate the density of nuclear matter from the relation of: (E) P = /(WxR~/3)_ where is The average number of participant nucleons. If colliding nuclei hav~ the same numbers of protons and neutrons, the mean number of interacting nucleons equals twice the mean number of interacting protons. In this sense the lead nuclei are not symmetrical. In the estimation of the mean number of nucleons we take I) = (2~2.5) .3The normal nuclear density fop the lead nucleus was assumed-to be Po : 0.17 fm- . The density Patio P/Po was equal to PlPo : 2.7±0.6 for : 2 and P/Po : 3.W~0.7

for



= 2.5

In Fig. 5 we show the theoretical boundaries fop possible phase tmansitions of the nuclear matter on a temperature-density diagram and the experimental d a t a on central collisions 0+Pb along with the results of the othem experiments (Agakishiev and co-workers, 198~; Nagamiya, 198~b).

1)The author wish to acknowledge a valuable conversation concerning this estimation,

y a and H. Stocker

he had with S. Nagami-

I

Pion ProducUon

359

radius, lifetime and second order coherence of pion pairs from the reaction 3.6 GeV/N --0+Pb - 2t-+X. The standard deviation of the momenta lies between 25-40 MeV/c. A number of 12028 pairs have been analyzed. The measured pion momenta are transformed to the center of the mass system, where the relative momentum and energy of each pair are calculated and then used to determine the correlation function (Zajc, 1982) C=(q,q6).= N(q,qo)/B(q,qo) (2) where

q : I~:-~,1 , qo : IE=-E,I are t h e magnitude o f t h e r e l a t i v e momentum, and r e l a t i v e

ener gy .

N(q,qo) is the number of pions observed with q and qo" B(q,qn) is the background in the absence of Bose-Einstein correlations, which is generated by mixing pion momenta from different events. The correlation function is fitted assuming that: (3) C=(q,q o) = 1 + ~ exp(-(qaRA/2+q~Ta/2)]_ where R A and T are the radius and lifetime of the corresponding Gaussian distribution function (r,~) ~ exp{-(r=/RA+ta/~=)]

(q)

In our first fit, X is fixed to the value of one (maximal chaotic pion sources) and no Coulomb correction has been applied to the data. Then, A is left as a free parameter. The results of such fit may be found in Table 3. TABLE 3

The Results

for Source Parameters

k

RA(fm)

3.68~.29 3.68±.29

1" .77±.26

4.29~.23"*

.30~.28"*

cT(fm)

6.94Zl.29 6.63±0.53 6.8*

xalNDF

1.12 1.14

.92**

*fixed parameter **the data are summed over qo It would be premature to conclude that these values of k indicate appreciable source coherence. Aside from the question of statistical significance, k is also affected by other factors. We note that the radius R A determined from t~ interferometry (3.2*3.9 fm) is larger than that determineH from pp interferometry (2.4 fm), since pions would probe the coldest, and thus, the most expanded state of the collision at which the radius must be largest (Nagamiya, 198Wb). TEMPERATURE AND DENSITY OF NUCLEAR MATTER In this report we have made an attempt to estimate the temperature and density of nuclear matter created in 0+Pb central collisions at 3.6 GeV/N. The average temperature, To, of the thermal sources of particles can be obtained from transverse momentum data (Anikina and coworkers, 1988) assuming that the particles are emitted directly from the sources and using the following formula:

(zmTol2)%Kb/2(m/To)/K2(mlT o)

= (5) where Ka(x) are the Mc Donald functions. The obtained T O value for pions produced in "A out events" (events without production of A hyperons) is T O = (11N~11) MeV and the temperature for A'S produced in central C+C, C-Ne and ONe collisions is T = (150~19) MeV. These results are represented in Fig. 4 where our temperature data and those from other experiments (Nagamiya, 198~b) are plotted against the beam kinetic energy EBFAM. The experimental T O values are consistent with the results of c a l c u l a t i o n s p e r f o r m e d assuming full thermalization of nuclear matter (Hagedorn and Rafelski, 1980) shown as solid

360

C. Besliu et al.

Reark-gluon plasma C÷C 20~ Tron~~ (3G SeV/n) r e , on ~.T/ Hodromc p ; L ~ f . ~ 106

0.1

Fig.

. ~ < ~

1

Ne +Pb 0 +Pb

Io P/Po

S. TheoPetical boundaPies for possible phase tPansitions of nucleaP matter on the tempematuPe-density diagram. The result obtained fop O+Pb collisions is shown along with the results of Agakishier and co-womkers (1984), and Nagamiya (1984b). For dotted ciPcles only the values of tempePatuPe weme estimated t whePeas the values of p ape unknown.

0uP expemimental point fop O+Pb is neap the boundaPy of the transitional region between hadPonic matteP and quaPk-gluon plasma. OuP PeSults seem to confiPm theoPetical estimations made by STock (1985b) and Stocker (1985). CONCLUSIONS The new experimental data fop centPal nucleus-nucleus collisions ape obtained using the SKM-200-Dubna stPeameP chamber. The Patio of the avePage negative meson number to the avePage numbeP of interacting pPotons seem to have a lineap enePgy dependence fop symmetPic systems (Ap-AT). The size of the paPticle emission Pegion was determined by two pion correlations fop 0+Pb collisions. At energies of about 3.6 GeV/N it is possible to reach the transitional Pegion between hadPonic matteP and the quaPk-gluon plasma. ACKNOWLEDGEMENTS We would like to thank our colleagues and co-workers M. Anikina, A. Golokhvastoy, K. Iovchev, S. KhoPozov, E. Kuznetzova, J. Lukstins, E. 0konov, T. Ostanevich, G. Vamdenga, M. Gazdzickl, E. Skrzypczak, R. Szwed fop having provided some experimental data prior to publication and for stimulating discussions. We are also indebted to all other membePs of the SKM-200 collaboration who have helped in obtaining the data pPesented in this paper. One of us (V. Topor Pop) wishes to acknowledge a scholarship at EPice, from the EuPopean Physical Society, and financial suppoPt fmom The Romanian National Council fop Science and Technology duping the International School of Nuclear Physics - in EPice - Italy (ApPil 1985).

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REFERENCES Akhababian, N., J. Bartke, V. G. Grishin and M. Kowalski (1983). Two proton correlations in nucleus-nucleus collisions. Preprin% JINR, EI-83-670, Joint Institute of Nuclear Research, Dubna (1983). Alma-Ata-Baku-Belgrade-Bucharest-Dubna-Kishinev-Leipzig-Moscow-Prague-Samarkand-Sofia-Tashkent-Tbilisi-Ulan-Bator-Varna-Warshaw-Yerevan. Collabomation (Agakishiev, H. N. and co-workers, 1984). Investigation of correlation phenomena in nucleus-nucleus intemactions at 4.2 GeV/c per nucleon. Preprint JINR, Dubna 1984, EI-84-448 - Joint Institute of Nuclear Reseamch - Dubna. Anikina, M., K. Beshliu, G. Vardenga, M. Gazdzitskii, A. Golokhvastov, T. D. Dzhobava, S. N. Komarova, E. S. Kuznetsova, J. LuksZins, E. Okonov, T. G. Ostanevich, V. Topor and S. Khorozov (1983). Ratio of Average x-meson number To average number of interacting protons in central nucleus-nucleus collisions. Soy. J. Nucl. Phys., 38, 901-903. Anikina, ~., A. Abdurak~'~mov, V. Aksinenko, E. Dementiev, N. Glagoleva, A, Golokhvastov, K. Iovchev, N. Kamlnsky, S. Khorozov, E. Kuznetzova, J. Lukstins, A. Matyushin, V. Matyushin, E. Okonov, T. Ostanevich, E. Shevchenko, G. Vardenga, O. Balea, N. Nicorovich, T. Ponta~ C. Begliu, V. Topor, L. Chkaidze, M. Despotashvili, T. Dzobava, I. Tuliani, M. Gazdzicki, E. Skrzypczak, R. Szwed, T. Tymieniecka, E. Khusainov,_N. Nurgozin, B. Suleimanov, Yu. Pol, G. Ta~an (1984). Experimental data on • mesons produced in inelastic and central nucleus-nucleus interactions at a 4,5 GeV/c momentum per nucleon. Preprint JINR-Dubna-EI-84-785. Joint Institute of Nuclear Research - Dubna (198~) Anikina, M., A. Golokhvastov, K. Jovcev, S. Khorozov, E. Kuznetzova~ J. Lukstins, E. Okonov, T. Ostanevich, V. Toneev, G. Vardenga, L. Chkhaldze, T. Dzobava, M. Gazdzigki , E. Skrzypczak, R. Szwed, K. Gudima (1985). Pion production in inelastic and central nuclear collisions at high energy, Preprint IFD/2/85 - Warsaw University. Beavis, D., S. Y. Fung, N. Gorn, A. Huie, D. Keane, J. J. Lu, K. T. Poe, B. C. Shen and G. van Dalen (1983). Pion source parameters in Ar on KCI collisions. Phys. Rev., C27, 910-913. Beavis, D~, S.-~. Chu, S. Y. Fung, W. Gorn, D. Keane, R. T. Poe, G. van Dalen, M. Viant (1984). Pion interferometry analysis for 1.2 GeV/nucleon Ar on KCI. Phys. Rev., C28, 2561-2564 Bohrmann, S. an--~J. Knoll (1981). Finite particle number effects in high energy nucleus-nucleus collisions: implication on pion spectra. Nucl. Phys., A356, 498-516. Broc--~ann, R., J. W. Harris, A. Sandoval, R. Stock, H. Strobele, G. Odyniec, H. G. PuEh, L. S. Schroeder, R. E. Renfordt, D. Schall, D. Bangert, W. Rauch and K. L. Wolf (1984). Phys. Rev. Left., 53, 2012-2015. Buchwald, G., G. Graebner, J. Theis, J.'Maru--~n, W. Greiner and H. Stocker (1984). Kinetic energy flow in Nb (400 A MeV) + Nb: Evidence for hydrodynamic compression of nuclear matter. Phys. Rev, Lett., 52, 1594-1596. Crowe, K. M., J. A. Bistirlich, R. R. Bossingham, H. R.-~owman, C. W. Clawson, K. A. Frankel, O. Hashimoto, T. J. Humanic, J. G. Ingersoll, M. Koike, J. M. Kurck, C. J. Martoff, W. J. McDonald, J. P. Miller, D. L. Murphy, J. O. Rasmussen, J. P. Sullivan, P. Truol, E. Yoo and W. A. Zajc (1984). Pion source parameters in heavy ion collisions. To be published in Proc. 7th High Energy Heavy Ion Study, G. S. I. Darmstadt, Octomber 8-13 (1984). Doss, K. G. R., H. A. Gustafsson, H. H. Gutbrod, B. Kob, H. Lohner, B. Ludewigt, A. M. Poskanzer, T. Rennet, H. Riedesel, H. G. Ritter, A. Warwick, H. Wieman (1985). Composite particles and entropy production in relativistic nuclear collisions. Preprint GSI-85-4, GSI-Darmstadt (1985). Fredrikson, S., G. Eilam, G. Berlad, L. Bergstrom (1984). High Energy Collisions with Atomic Nuclei. Royal Institute of Technology Report TRITA-TFY-8~06, STockholm (1984) (to be published in Physics Report). Fung, S. Y., W. Corn, G. P. Kiernan, J. J. Lu, Y. T. Oh, R. T. Poe (1978). Observation of pion interferometry in relativistic nuclear collisions. Phys. Rev. Left., 41, 1592-1594. Gustafsson, H.-~., H. H. Gutbrod, B. Kolb, H. Lohner, B. Ludewig%, A. M. Poskanzer, T. Rennet, H. Riedesel, H. G. Ritter, A. Warwick, F. Weik and H. Wieman (1984). Freezeout density in relativistic nuclear collisions measured by proton-proton correlations. Phys. Rev. Lett., 53, 544-547. Hagedorn, R. and J. Rafelski (1980). Hot hadr~nic m ~ t e r and nuclear colli-

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