Nuclear Physics B (Proc. Suppl.) 24B (1991) 207-210North-Holland

TECHNOLOGICAL IMPLICATIONS OF STABLE STRANGE QUARK MATTER

Mukesh S . DESAI and Gordon L . SHAW

Department of Physics, University of California, Irvine CA 92717

1 . INTRODUCTIONThe possibility suggested by Witten 1 in his semi-

nal article that strange quark matter, S-matter, mightbe the lowest energy state of large baryon number, A,matter would have enormous consequences . In ad-dition to the fundamental physics, astrophysics, andcosmology relevance 1-23, there would be technologi-cal applications due to the fact that small A drops ofS-matter, S-drops, become more stable as A increasesin contrast to nuclei, which after iron, decrease in sta-bility as A increases due to the Coulomb energy. Thestability of S-matter will not be decided by funda-mental QCD calulations in the near future, so it isstrictly an experimental question . There are two ap-proved experiments, E864 24 and E878 25 , at BNL, andpotential ones at CERN 26,27 which will be searchingfor metastable S-drops produced in the fixed targetheavy-ion facilities (which are being upgraded to a Aubeam at BNL and a Pb beam at CERN). Recent 2s

rough calculations have shown that these experimentscan be made sensitive enough to detect expected ratesof production if indeed S-matter is stable .

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Experiments to look for metastable, small drops of strange quark matter, S-drops, at present relativisticfixed-target heavy-icon facilities are in progress at BNL and are proposed at CERN. Recent calculationshave shown that these experiments can be made sensitive enough to detect expected rates of production,if indeed strange quark matter is stable . It has been proposed that, if found, these small metastable S -drops could be rapidly grown to larger stable S-drops thmiigh neutron capture in a. confining apparatus .This would form the scientific basis for subsequent studies of using S-drops as an energy source . Here wepresent some further exciting technological aspects: breeding of S-drops, disposal of radioactive waste,and use as a compact, safe, and efficient energy source for space travel . We note that the S-drops cannotbe used to give a chain reaction; also, the possibility of stable S-drops with negative electric charge, Z,(which would interact with normal matter and grow without bounds) can be ruled out .

T

Thus wy will assume that S-matter is stable, i .e.,that e,,, the energy per baryon for large A is less than930 Me-V i and S-drops will he produced and detectedat BNL and/or CERN. It has already been proposed 12

that such small metastable S-drops could be isolatedand rapidly grown to large stable S-drops through neu-tron capture in whicl the S-drops pass through tanksof deuterium in a confining apparatus (or a linear ar-ray) . The highly schematic diagram in Fig . 4 of Ref.12 shows this and the mbsequent use of S-drops as anenergy source : a neutron will be readily absorbed andtlic ûiaüiag enei;y given off mainly in gamma rays .The purpose of this note is to present below some fur-ther technological possibilities obtained in this samespirit from very rough estimates : breeding of S-drops,disposal of radioactive waste, and use as a compact,safe and efficient energy source for space travel . Weshow that S-drops cannot Lp used to gave a, chain re-action, which ensures the safety of their use . We notethat the possibility of stal)ie S-drubs with negativeelectric charge Z (which would interact with normalmatter and grow without bounds) can be ruled out .

208 M.S. Desai, G.L. Shaw/Technological implications ofstable strange quark matter

2. CALCULATIONS2.1 . Growing S-drops as a compact energy sourceEssentially all of our rough calculations are inde-

pendent of the precise details provided that eo is sub-stantially less than 930 MeV. To be specific, we willuse the Berger-Jaffe mass formula 1° with e, = 880MeV and m, = 150 MeV 29 . With these parameters,fairly small A S-drops will be stable. Some of theirproperties are shown in Table 1 where Zmi,, and Smi,,are the electric charge and the strangeness respectivelyof the most stable S-drop, SAZ, for a given A. We seethat in the range shown, the charge Zmia, of the moststable drop SAZ for a given A is roughly 5A1/3. Nowsince these S-drops have radii R roughly A1/3 fm, theywill have a Coulomb barrier V. with a light ordinarynucleus of charge Zi of only

Vr = 7 - Zi(MeV ) .

We also see that in this range, a baryon will havea binding energy of roughly 50 MeV . Thus, considergrowing S-drops from an A of 500 to an A of 1000 .This could be nicely doneby using a beam of deuteronsaccelerated to an energy of 7 MeV. Each absorbed(cross-section of several barns) deuteron would give

Table 1 : Scnzp iroperties of S-matter for eo = 880.0and m, = 150 (MeV).

off an energy of roughly 105 MeV, mainly in gammarays : As proposed in Ref. 12 and 28, the absorbednucleons would immediately go into excited u and dquarks, and then rapidly share their energy with theother quarks to form a super compound state, SCS,in which it would be very hard for three quarks tocombine with the correct energy, spin, flavor and colorto be reemitted as a baryon. Thus the SCS wouldrapidly decay to the SAZ ground state by a series ofgamma emissions . Subsequent decays to Zmi,, and toSmin would occur via weak decays having small energyrelease . We suggest that this could provide the basisfor a compact, safe, and efficient energy source forspace travel.

2 .2 Breeding S-dropsThe production S-drops might be very infrequent,

perhaps one produced every 101° relativistic heavy-ion collisions . Thus each S-drop becomes extremelyexpensive to produce and one might question thereasonableness of these technological proposals. Thecrucial idea is that once an S-drop has been grown toan "optimum" Ao through its use as an energy sourceas described in Section 2.1 by feeding in light ions orneutrons, it can be fissioned into two (or more) smallerS-drops . This breeding process could be done by feed-ing in a somewhat heavier ion to supply the energy tosplit the the S-drop .Perhaps an Ao of 1000 would be optimum . We see

then from Table 1 that we need roughly 2.2 GeV tosplit this S-drop. The use of air icn of ordinary nucleuswith (roughly) an Ai of 30 and Zi of 15 with roughly 1GeV of kinetic energy could be used to split it . Eachabsorbed nucleon would supply an excess binding en-ergy of roughly 40 MeV so that together with the in-cident kinetic energy, there would be sufficient energyto split the S-drop into two smaller ones ; further, wesee from Table 1 that the Zi of 15 would supply thecorrect charge to bring the daughter S-drops near totheir energy minima values Zmi,, . From Eq. (1), wesee that the ion would need only 105 MeV kinetic en-ergy to go over the Coulomb barrier.Thus an initial supply cf S-drops will not only give

A Smin Zmin E/A Energy ofthe lastbaryon

100 -79 9 898 89206 -157 16 894 890-300 -236 22 893 888400 -315 27 891 888500 -393 32 891 887600 -472 37 890 887700 -551 41 890 886800 -630 45 889 886900 -708 48 889 -88ê-1000 -787 52 888 8862000 -1574 80 887 8843000 -2361 100 886 8844000 -3147 117 885 8845000 -3934 131 885 88310000 -7868 181 884 883100000 -78683 451 882 880

M.S. Desi, G.L. ShawlTechnological implications ofstable str

an energy source that will not be used up, but also itcan be bred with a quite short doubling time!

2.3 . Disposal of radioactive wasteThe possibility of using radioactive ions to feed into

S-drops for energy release offers the bonus of disposingof radioactive waste material . For example, we mightimagine using tritium as the fuel for S-drops.2.4 . No chain reactionOne far reaching technological possibility readily

comes to mind concerning a chain reaction formed byimmersing thin rods of S-drops in liquid D2 togetherperhaps with a small neutron source. The idea wouldbe that when a neutron is absorbed by an S-drop, itwould give off roughly 50 MeV in a rapid burst ofgammas . The possibility arises then that these gam-mas would photodisintegrate deuterons with the emit-ted neutrons then being absorbed by the S-drops in achain reaction . The cross-section y -i- d -+ n + p peaksnear the threshold of E., = 2.2 MeV with a value of2 mb. However, the Compton scattering cross-sectionis more then 200 mb over the entire range of relevantgamma energies . We conclude that no chain reactionis possible . This may be viewed from a positive pointof view since then no run-away accident could occurand no bomb could be built .2 .5. No stable negative Z S-dropsIt was prainted out by Farhi and Jaffe 8, that a lim-

ited range ofparameters in the MIT bag model allowedfor the possibility that stable S-drops would have elec-tric charge Z < 0 rather than the expected Z > 0 .This would hav ,~ disasterous consequences since theseS-drops would interact with normal matter to growwithout bounds . We can turn this statement aroundto rule out, with extremely high probability, the exis-tence of stable negative Z S-drops [S(Z-)-drop] sinceour earth is still here : Consider the presence of onesuch S(Z-)-drop reaching the earth or being producedin the atmosphereby ahigh-energy heavy-element cos-mic ray. This S(Z-)-drop, due to the absence of aCoulomb barrier, would interact with ordinary nucleiand rapidly grow, especially after reaching the sur-face of the earth, with a rate proportional to its cross-

sectional area :

_dA=

2/3

1dt

500~ A

s-

so that an initially small S(Z- )-drop would grove as

with o ;z~~ 7r - A2/3 fm2 , N° , the number of baryonsper unit volume and wi th is the thermal velocity of theatoms in the earth. This gives a rate

A(t) = 108 . t3(sec)

(4)

Thus, in only 105 years, one S(Z-)-drop would con-sume a sizable portion of the earth . (Better lim-its can be obtained from the known heat productionin the earth.) Now primary cosmic rays with iron(or heavier) and having an energy of greater than100 GeV/nucleon hit our earth at a rate of roughly10-7/cm2/ster/s, so that over the history ofour earththere would have been 1032 primaries capable of inter-acting with the heavier elements in our atmosphereto produce a S(Z-)-drop . Thus not only can we ruleout the production of such a S(G = )-drop by cosruicrays (since we are still here), but be totally relievedabout the possibility of producing such an object inthe heavy-ion experiments at BNL and CERN wherewe. might expect perhaps 1016 beam particles in a year .

3 . CONCLUSIONv'8 ûave presented here just a few of the potential

technological implications of stable S-drops . Perhapsthe key feature is the breeding scheme described inSection 2.2 which will enable production of ever in-creasing numbers of S-drops as a byproduct of grow-ing them for energy production. This will eventuallyprovide enough S-drops for potential uses in manyother areas of technology where new materials alwaysfind new and fascinating uses. Further, the conclu-sions, in Section 2.4 that no chain reaction can beobtained with S-drops and in Section 2.5 that stableS-drops with negative Z do not exist, reassure us aboutthe safety of S-drops . In fact, as we note in Section

nge quark matter 209

_dA _- ' 'dt

N° vth (2)

M.S. Desai, G.L . Shawl Technological implications ofstable strange quark matter

2.3, S-drops could be used to dispose of normal ra-dioactive waste matter. We conclude with the hopethat the ideas presented here will give further impe-ti.s to the dedicated high-sensitivity searches for small,metastable S-drops produced at BNL and CERN.

ACKNOWLEDGEMENTSWe thank C . Alcock, N. Rostoker, J . Sandweiss, and

M. Shin for helpful discussions.

REFERENCES1 . E . Witten, Phys . Rev . D30 (1984) 272 .

2 . A. Bodner, Phys . Rev. D4 (1971) 1601 .

3. B. Friedman and L . McLerran, Phys . Rev . D17(1978) 1109 .

4. S . Chin and A. Kerman, Phys. Rev . Lett . 43(1978) 1291 .

5. J . Bjorken and L . McLerran, Phys . Rev . D20(1979) 2353.

6. A . Mann and H . Primakoff, Phys . Rev . D22(1980) 1115.

7 . H . Liu and G. Shaw, Phys. Rev . D30 (1984) 1137 .

8 . E . Farhi and R . Jaffe, Phys . Rev. D30 (1984)2379 .

9 . C . Greiner, P. Koch and H. Stocker, Phys . Rev .Lett . 58 (1987) 1825; Phys . Rev . D38, (1988)2797 .

10 . M . Berger and R . Jaffe, Phys . Rev. C35 (1987)213. Erratum for the surface energy term (Phys .Rer, C . in press and R . Jaffe, this Volume) .

11 . C . Greiner, D . Rischke, H . Stocker and P . Koch,Z. Plays . C38 (1988) 283.

i2 . G . Shaw, M. Shin, R. Dalitz and M. Desai, Nature337 (1989) 436.

13 . A. De Rujula and S . Glashow, Nature 312 (1984)734.

14 . C . Alcock and E. Faxhi, Phys . Rev. D32 (1985)1273 ; J . Madsen, H. He"selberg and K. Riisager,Phys. Rev . D34 (1986) 2947.

15 . G . Baym et al . , Phys . Lett . 160B (1985) 181 .16 . M. Baxnhill et al . , Nature 317 (1085) 409 .17 . G. Shaw, G. Benford and D . Silverman, Phys.

Lett . 169B (1986) 275 .18 . C . Alcock, E . Farhi and A. Olinto, Phys . Rev.

Lett . 57 (1986) 2088.19 . K . Takahashi and R. Boyd, Astrophys . J . 327

(1988) 1009 .20 . C . Alcock and A. Olinto, Ann . Rev . Nucl . Part .

Sci . 38 (1988) 161 ; A . Olinto, Z . Phys . C38 (1988)303 .

21 . N . Glendenning, LBL Report (1990) 29101 .22. R . J . Dewey et al. , in Greenbank Workshop on

Millisecond Pulsars, ed . S . P. Reynolds, D. R .Steinberg, (Greenbank, W. Va . , Natl . Radio. As-tron . Obs) (1984) p . 234 .

23. T . Saito, Y . Hatano, Y. Fukuda, and H. Oda,Phys . Rev . Lett . 65 (1990) 2094.

24. J . Barrette et al . Phys. Lett . B252 (1990 550 ;Also see : J . Sandweiss, this Volume and

. Ro-tondo, this Volume.

.25. Also see : H . J . Crawford, this Volume.26. "Proposal to search for neutral strange matter

in heavy ion collisions at CERN", K. Pretzl,spokesman, SPSLC P259 March, 1991 .

27. "Strangeletter", P. Sonderegger, ed . , CERN,April, 1991,

28 . H . ,1 . Crawford, lvi . S . Desai, and G . ï . SnawProduction caf Drops of Strange Matter in Fixed-Target Heavy.-Ion Collisiuns, this Volume .

29 . H . Hamber, Phys . Rev . D 39 (1989) 896, reportseven lower values of m, from lattice QCD calcu-lations .