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S. G. W. D. J. D.

A SEARCH FOR MAGNETI C MONOPOLE CATALYSI S OF NUCLEON D ECA Errede2 J . L . Stone2 , J . C . van der V�l de2 , R . M . B i onta2 , Bl ewi tt4 i C . B . B ratton5 , B . G . Co rtez 10 mb and monopol e vel oci ti es 10- 4 .; S m .; 10For l ow c ross secti ons , we obtai n vel oc i ty i ndependent l imi ts on the monopol e fl ux. Limits on the monopol e i nteraction rate are presented. •

*Presented by S . Errede

Theoreti cal and experimental i nterest i n magnetic monopol es has not c eased s i nce Di rac ' s p i oneeri ng workl i n 1 931. Recently , a resurgence of i nterest has resul ted from the work of 't Hooft and Polyakov2 i n 1974 which s howed that superheavy magnetic monopol es are a natural consequence of g rand uni fied theori es ( G UTs) whi ch s pontaneously b reak and even­ tual ly y i e l d a U( l ) g auge g roup. The monopol e mass i n GUTs i s expected to be of the order of the u n i fi cation scal e , M m - 1 0 16 GeV _ 3 ,4 Such superheavy monopol es cou l d have b een p roduced i n l arge numbers i n the early moments of the u n i verse. 3 , 5 In the p resent epoch the fl ux of a s uperheavy magneti cal ly c harged parti cl es i s constrai ned by the mass dens i ty of the u n i verse. 6 ,9 The most s tri ngent astrophysi cal l imi t on the monopol e fl ux can b e esti mated from the maximum fl ux wi thi n our gal­ axy that can b e tol erated wi thout destroy i ng the ob served gal acti c magnetic fiel d (- 3 µ G ) . Th i s upper l imi t, k nown a s the Pa rker Bound? , i s Fm < 6 x 1 0- 16 cm- 2 s r- 1 s - 1 . Furthermore , various consi derati ons s uggest thei r present vel oci ti es are of order 1 0- 4 < $ m < 1 0- 2 i n our g al axy and solar system. 8 ,9 Monopol es wi thi n thi s vel oci ty range a nd mass are unl i kely to be s topped i n thei r passage th rough the ea rth . In 1980, Dokos and Tomaras suggested that the presence of a g rand u ni fied monopol e i n proximi ty to hadroni c matter may act as a catalyst, s trongly enhanci ng b a ryon number v i ol ati ng processes lO . Sub sequently , Rubakovl l and Cal l an1 2 i n s tudy i ng the i nteraction mechan i sm o f fermions w i th monopol es s howed that p rocesses such as M + p,n

+

M + e+ + mesons

(1)

a re essenti al ly i ndependent o f the u n i f i cati on mass . Catalysi s cross s ecti ons typi cal of s trong i nteractions a c - 10- 26 c m2 are predi cted , b ut w i th a l arge uncertai nty . Kol b , Col gate , and Ha rvey1 3 have ob tai ned an i ndi rect, model dependent l imi t on the fl ux of monopol es i nci dent on neutron s tars from consi deration of the i ncrease i n l umi nos i ty due to catalys i s of nucl ear matter wi thi n the s tar. From the u se of experimental l imits on the i nter­ s tel l ar x- ray l umi nosi ty , they ob ta i n a l i mi t on the monopol e fl ux times catalys i s c ross secti on , Fm x a c < 5 x 10- 49 sr- 1 s - 1 . Other authors 14 have suggested neutron star model s wh i c h y i e l d far l ess stri ngent l i mi ts , compatib l e even wi th the Parker b ound for l arge catalysis cross secti ons.

435 Di rect experimental evi dence for monopol e cataly zed nucl eon decay woul d b e of profound i mportance for g rand u n i fi ed theori es s i nce a s i ng l e u namb iguous ob servati on coul d s i mul taneously p rove the exi stence of magneti c monopol e �
--------------

For catalysi s cross secti ons , cr c " 1 mb the i nteraction l ength , " c • b ecomes l arger than the mean path l ength , consi derably reduci ng the p robab i l i ty for mul ti pl e i nteractions i n the detector . Under these c i rcumstances we can, neverthel ess, set l imi ts on the monopol e fl ux and i nteraction rate from s i ng l e i nteracti ons i n the detector. In deri vi ng these l imi ts one must consi der the b ackground due to atmospheri_£ neutri no i nteractions and possibly " spontaneous" n ucl eon decays and/or nn o sci l l ati ons . Spontaneous 2-b ody n ucl eon decays wi l l have a c haracteri sti c b ack- to-b ack s i g nature wi th the openi ng ang l e o f the decay products typi cal ly > 1 50°. The s i g nature for a monopol e catalysi s nucl eon decay

438

can b e qu i te di fferent d u e t o t h e k i nemati cs of t h e reacti on . I n i ts own rest frame , the h eavy monopol e ab sorb s a negl i g i b l e fracti on of d i si nteg rati ng nucl eon rest energy . It can , however , acqui re u p to 1 GeV/ c momentum whi c h , by momentum conserv�t i on , i s transferred to the decay p roducts. Thus , catalyzed decays or nn transi ti ons can have the same g eneral appearance as atmospheri c neutri no i nteracti ons of Ev < 2 GeV i n the detector. Duri ng our i ndependent search for spontaneous nucl eon decay in the detector, a total of 69 s i ng l e i nteraction events i n 80 days of detector t ime were found. 1 7 The event rate and c haracteri sti cs of these events are c onsi stent wi th neutri no i nteracti ons i n the detector. Of the 6 9 events , 6 6 have energ i es b e l ow twi ce the nucl eon rest mas s , M N · We use these events to ob tai n conservati ve l imi ts on the monopol e fl ux and i nteracti on rate wi th fu rther event sel ection i n order to i ncorporate the b roadest range of possib i l i ties for monopol e catal ysi s of nucl eon decay . T h e absol ute rate of neutri no i nteractions whi ch pass o u r fi l teri ng i s cal cul ated to be Rv = 0 . 9 ± 0 . 4 events per day1 7 , based on estimated fl uxes and c ross sections appropri ate to the energy range we ob serve. The e stimated overal l effi ci ency for the detection of atmospheri c neutri nos Nv = 48 ± 7 ( s tat.) ± 25 ( syst.) events i n 80 days of detector l i ve time, to be compared wi th the 6 6 events b el ow 2 M N · Thu s , as many as 5 2 events ( 90% C . L . ) coul d be due to monopol e i nteracti ons . We use equation ( 2 ) i n determi n i ng fl ux l imi ts for s i ng l e i nteractions. The detecti on effi ci ency for s i ng l e catalysis i nteractions i n the fi duci al vol ume i s cal cul ated to be E d = 0 . 9 ± 0 . 1 for neutri nol ess decay modes. 1 6 The geometri cal acceptance E g for si ngl e i nteracti ons i n the fi duci al vol ume i s s hown i n Fig ure 1 . The effi ci ency dcr c l i s merely the Po i sson probab i l i ty for s i ngl e i nteracti ons wi thi n the detector. The upper l i mits on the monopol e fl ux, Fm , and i nteraction rate , F m x a c , for s i ngl e i nteracti ons are vel oci ty i nde��n_9_en�, and are shown i n Fi gure 4 . Th e 9 0 % C . L . upper l i mit o n the monopol e fl ux h a s a mi nimum of Fm ( mi n ) = 1 . 1 x 1 0- 1 2 cm- 2 s r- 1 s - 1 at a catalysis c ross section cr c = 1 mb . For cross sections cr c .; 0 . 1 mb , the upper l i mit on the monopol e s i ngl e i nteraction i s Fm x cr c < 3 . 6 x 1 0- 40 sr- 1 s - 1 ( 90% C . L . ) .

439

Th i s experiment has searched for magneti c monopol es v i a the new and u ni que mechani sm of magneti c monopol e catalysi s of nucl eon decay . The c ross secti on dependent l i mits o n the monopol e fl ux encompass a s ig nfi cantly wi der vel oci ty range and a re consi derably l ower than , o r c omparabl e t o those of previous experiments 18 , which a re sensitive to the e l ectromagnetic i nteraction of magnetic monopoles with matter. F i g ure 5 s hows l imits on the monopol e fl ux a s set these experi ments . ACKNOWLEDGEMENTS We wi sh to thank the many peopl e who made th i s detector a real i ty and e speci al ly the empl oyees of Mo rton- Th i okol who operate the Fai rport m i ne . T h i s work i s supported i n part b y the U . S . Department o f Energy .

REFERENCES AND FOOTNOTES ( a) Al so at Ha rvard Un i versi ty . ( b ) Permanent address: Warsaw Un i versi ty , Pol and. 1.

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1 1 . V . A . Rub akov , Nucl . Phy s . B2�, 3 1 1 ( 1 982 ) ; J ETP E· 644 ( 1981 ) . 1 2 . C . Cal l an , J r . , Phy s . Rev. D26, 2058 ( 1 982 ) ; Phy s . Rev. 025, 2 141 ( 1 982 ) ; ( L PTENS prepri nt 8 2-n-o ( 1 982 ) . See al so C . Cal lan;- tal k p resented at conference .

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14. V. A. K u zm i n and V. A . Rubakov , I CTP prepri nt I C/83/1 7 , to be p ub l i shed. S. Di mopou l o s , J . Preski l l and F . Wi l c zek , submi tted to Phys. Lett . ( U CSB prepri nt NSF- I TP - 82 - 9 1 ) ; F . A . B a i s , J . El l i s , D . N . Nanopoul os and K . A . 01 i ve , CERN prepri nt 3383 -C ERN ( August 1 982 ) . 15. J . C . van der Vel de , in the " Proceedi ngs of Neutri nos ' 81 , " M aui , Hawai i ( J u l y , 1981 ) , ed. by R . J . Cence , E . M a , A . Rob erts , Vol . 1 , p . 205. 16. The detection effi ci ency for s i ng l e and mul ti pl e i nteractions w i th decay modes i nvol vi ng neutri nos i s E d = 0 .6 ± 0 . 2 . The fl ux l imits for for mul ti pl e and s i ngl e i nteractions for these modes s houl d therefore b e i ncreased accordi ngl y . 1 7 . R . M . B i onta , et al . , Phy s . Rev. Lett . 50 ( 1 983 ) . See a l so J .C.v an der Ve l de , tal k presented a t thi s conference. 18. J. D. Ul l man, Phys. Rev. Lett. 47 , 289 ( 1 981 ) ; R . Bonarel l i , e t al . , Phy s . Lett. 1 12B , 100 ( 1982 ) ; D . E . Groom, e t al . , Phy s . Rev. Lett . 50, 573 ( 1983 ) ; B . Cabrera , Phys. Rev. Lett. 4 8 , 1378 Tf982 ) ; J . Ba rtel t , e t al . , Phys. Rev-:-Lett. 50, 655 ( 1983 ) ; D . Ayre s , e t al . , i n the Snownass DPFlfroceedi ngs , p . 603 ( J une/J u l y 1 982 ) , ed. by R . Do nal dson , H . R . Gu stafson and F . Pa ige. See al so B. Bari sh, tal k presented at thi s conference.

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