V01ume 184, num6er 2,3 PHY51C5 LE77ER5 8 29 January 1987

085ERVA710N 0F CHARMED M E 5 0 N 5 1 N P H 0 7 0 N - P H 0 7 0 N C0LL1510N5

JADE C011a60rat10n

W. 8AR7EL, L. 8ECKER, R. FEL57, D. HA1D7, 6 . KN1E5, H. KREH81EL, P. LAUR1KA1NEN 1 N. MA6NU55EN 2, R. ME1NKE, 8. NAR05KA, J. 0L550N, D. 5CHM1D7 2, p. 57EFFEN Deut5che5 E1ektr0nen-5ynchr0tr0n DE5Y, D-2000 Ham6ur9 52, Fed. Rep. 6ermany

7. 6REEN5HAW, J. HA6EMANN, 6 . HE1N2ELMANN, H. KAD0, C. KLE1NW0R7, M. KUHLEN, A. PE7ER5EN 3, R. RAMCKE, U. 5CHNEEKL07H, 6 . WE8ER 11. 1n5t1tut far Exper1menta1phy51k der Un1ver51tdt Ham6ur9, D-2000 Ham6ur9 52, Fed. Rep. 6ermany

K. AM8RU5, 5 .8E7HKE, A. D1ECKMANN, E. EL5EN, J. HE1N72E, K.-H. HELLEN8RAND, 5. K0MAM1YA 3, j. V 0 N K R 0 6 H , H. R1E5E8ER6, H. V 0 N DER 5CHM177, L. 5M0L1K, J. 5P172ER, A. WA6NER, M. 21MMER Phy51ka115che51n5t1tut der Un1ver51t11t He1de16er9, D-6900, He1de16er9 1, Fed. Rep. 6ermany

C.K. 80WDERY, A.J. F1NCH, F. F057ER, 6 . HU6HE5, J.M. NYE, 1.W. WALKER Un1ver51ty 0f Lanca5ter, Lanca5ter LA1 4Y8, UK

J. ALL150N, R.J. 8ARL0W, J. CHR1N, 1.P. D U E R D 0 7 H , F.K. L0E81N6ER, A.A. MAC8E7H, H.E. M1LL5, P.6. MURPHY, K. 57EPHEN5, P. WARM1N6 Un1Ver51ty 0f Manche5ter, Manche5ter M89 PL, UK

R.6. 6LA55ER, P. H1LL, J.A.J. 5KARD, 5.R. WA6NER 4 6 .7 . 2 0 R N Un1ver51ty 0f Mary1and, C011e9e Park, MD 20742, U5A

5.L. CAR7WR16H7, D. CLARKE, R. MAR5HALL, R.P. M1DDLE70N Rutherf0rd App1et0n La60rat0ry, Ch11t0n, D1dc0t 0X11 0QX, UK

K. KAWA60E, 7. MA5H1M0, 7. 7AKE5H17A and 5. YAMADA 1nternat10na1Center f0r E1ementary Part1c1e Phy51c5, Un1ver51ty 0f 70ky0, 70ky0, 113, Japan

Rece1ved 10 0ct06er 1986

7he 1nc1u51ve pr0duct10n 0f D *-+ me50n51n 51n91e ta99ed ph0t0n-ph0t0n c0111510n5151nve5t19ated u51n9 the JADE detect0r at PE7RA. D *-+ me50n5 are rec0n5tructed thr0u9h the1r decay 1nt0 D0+7r -+ where the D ° decay5 v1a D°~K~r~ °. 7he event rate and t0p0109y are c0mpared t0 the expectat10n5 0fc 4uark pr0duct10n 1n the 4uark-part0n m0de1:77 ~ce.

Un1ver51ty 0f He151nk1, 5F-00170 He151nk117, F1n1and. Un1ver51t~1t-6e5amth0ch5chu1e Wupperta1 D-5600, Wupper- ta11, Fed. Rep. 6ermany.

288

3 Pre5ent addre55: 5LAC, 5tanf0rd, CA 94305, U5A1 4 Pre5ent addre55: Un1ver51ty 0fC010rad0, 80u1der, C0 80309,

U5A.

0370-2693/87/$ 03.50 • E15ev1er 5c1ence Pu6115her5 8.V. (N0rth-H011and Phy51c5 Pu6115h1n9 D1v1510n)

V01ume 184, num6er 2,3 PHY51C5 LE77ER5 8 29 January 1987

ReCent exper1ment5 at e1eCtr0n-p051tr0n C0111d1n9 6eam faC111t1e5 have C0nf1rmed the ex15tenCe 0fjet5 ,1 at h19h m0mentum, tran5Ver5e t0 the e+e - 6eam aX15, 1n 9amma-9amma C0111510n5 [ 2-4 ]. When the detected hadr0n1C 1nvar1ant ma55, W~5, 15 9reater than 3 6eV, the t0ta1 Cr055 5eCt10n 15 d0m1nated 6y jet-11ke event5 pr0dUCed at 10W p~* a5 de5Cr16ed 6y 9enera112ed veCt0r-me50n d0m1nance ( 6 V D M ) [ 5 ] and f0r p~t> 3 6eV, 6y the 4uark-part0n m0de1 (QPM). 8ecau5e the c0up11n9 0f tw0 ph0t0n5 t0 tw0 part0n5, v1a the 60x d1a9ram, 15 pr0p0rt10na1 t0 the f0urth p0wer 0f the part0n char9e, a 1ar9e c0ntr16u- t10n t0 the h19h-p~ t cr055 5ect10n 15 expected t0 c0me fr0m charmed 4uark5. 0 n the 0ther hand, 1e55 than 1% 0fthe 6 V D M cr055 5ect10n 15 expected t0 c0nta1n charm, 6a5ed 0n 065ervat10n5 made w1th rea1 and v1rtua1 ph0t0n c0111510n5 0n pr0t0n tar9et5 [ 6 ]. 51nce ann1h11at10n exper1ment5 5u99e5t that charmed 4uark5 fra9ment preferent1a11y t0 the vect0r D* (2010) me50n5 [ 7 ], the 1501at10n 0f a D* 519na1, part1cu1ar1y 1n h19h p~t event5, pr0v1de5 a meth0d 0f 5tudy1n9 the QPM 1nteract10n and 1t5 QCD m0d1f1cat10n5.

1n th15 exper1ment, mu1t1hadr0n1c tw0-ph0t0n c01- 11510n5 were 1501ated 6y re4u1r1n9 a 51n91e ••ta99ed•• e1ectr0n 1n 0ne 0f the tw0 5ma11-an91e e1ec- tr0n-ph0t0n detect0r5 (37.5~<0ta9~75 mrad). A c0mp1ete de5cr1pt10n 0f the JADE detect0r and 1t5 part1c1e mea5urement and 1dent1f1cat10n pr0pert1e5 15 91ven e15ewhere [ 8 ]. 7he e55ent1a1 c0mp0nent5 f0r the pre5ent ana1y515 are the centra1 jet cham6er, pr0- v1d1n9 n0t 0n1y track1n9 1nf0rmat10n 6ut a150 up t0 48 5amp1e5 0f the 10n12at10n ener9y 1055, dE/dr, per track, and the 1ead-91a55 e1ectr0ma9net1c ca10r1meter 5urr0und1n9 the jet cham6er. Rather 5evere cut5 were p1aced 0n the 5e1ect10n 0fhadr0n1c event51n 0rder t0 pr0duce a 5amp1e free fr0m ann1h11at10n 6ack9r0und and 5u1ta61e f0r part1c1e 1dent1f1cat10n 1n the D* ana1y515. Here we can 5ummar12e the 1mp0rtant cut5 1n the data 5e1ect10n:

Char9ed- and neutra1-part1c1e m0mentum:

1P~1 1> 100 MeWc.

Num6er 0f char9ed hadr0n5:

*~ 1n the JADE ana1y515, jet5 are def1ned u51n9 a c1u5ter a190r1thm [ 1 ] and/~ t 15 the c0mp0nent 0fthe t0ta1 jet m0mentum tran5- ver5e t0 the e-e- 6eam ax15.

nch 1> 4.

V15161e t0ta1 hadr0n1c ma55:

4 6eV ~< Wv15 ~ E 6 . . . .

70ta1 10n91tud1na1 m0mentum 1nc1ud1n9 the ta99ed e1ectr0n:

~P2, 12 6eV. 1>

Ener9y 0fthe ta99ed e1ectr0n:

Et,9 ~ 0.6 E60am •

7he maj0r1ty 0fann1h11at10n event5 were rem0ved 6y the Wv15 and 51n91e-ta9 c0n5tra1nt5. 7h05e ann1h1- 1at10n event5 where 0ne 0f the 1nc0m1n9 1ept0n5 rad1ate5 a hard ph0t0n 1nt0 the ta991n9 5y5tem were further 5upre55ed 6y the 10n91tud1na1 m0mentum cut. M0nte Caf10 5tud1e5 u51n9 the 8erend5 and K1e155 51mu1at10n [9 ] 1nd1cate that the rema1n1n9 ann1h1- 1at10n 6ack9r0und wa5 0n1y 1% 0f the t0ta1 event 5amp1e. 7he t0ta1 1nte9rated 1um1n051ty wa5 90 p 6 - w1th an avera9e 6eam ener9y 0f 19 6eV.

0 u r ana1y515 f0110w5 the u5ua1 ma55 d1fference techn14ue wh1ch exp101t5 the 10w-Q va1ue 0fthe decay D*~D°~ [ 10]. 7he D ° decay channe1 w1th the 1ar9- e5t 6ranch1n9 rat10 15 D ° ~ K - n +n ° ( D ° ~ K + x - n °) and 51nce JADE ha5 900d ~01dent1f1cat10n, th15 m0de wa5 ch05en a5 the m05t 11ke1y 1n wh1ch t0 5ee a char9ed D* 519na1. F1r5t, p055161e x ° cand1date5 were 5earched f0r 6y pa1r1n9 a11 ph0t0n5 detected 1n the 6arre1 and end-cap 1ead-91a55 array5 w1th ener91e5 9reater than 100 MeV and 5e1ect1n9 th05e pa1r5 wh05e 1nvar1ant ma55 1ay 1n the re910n 50~<M~v~<200 MeV. 7he pr06a6111ty that a part1cu1ar pa1r wa5 fr0m a n ° decay, P~0, wa5 determ1ned fr0m a 1C k1nemat1ca1 f1t, 1n wh1ch the 1nvar1ant ma55 0f the ph0t0n5 wa5 c0n- 5tra1ned t0 the x ° ma55. A 900d n ° wa5 def1ned t0 6e a ph0t0n pa1r w1th P~0 > 0.01. A11 pa1r5 0f 0pp051te1y char9ed track5 were then c0m61ned w1th the n°~5 t0 make D ° cand1date5. Each track wa5 c0n51dered 1n turn t0 6e e1ther a ka0n 0r a p10n, w1th an add1t10na1 c0n5tra1nt that the pr06a6111ty 0fthe ka0n cand1date 6e1n9 a rea1 ka0n, a5 ca1cu1ated fr0m the dE/dx mea- 5urement, wa5 9reater than 0.01. Fr0m th15 5amp1e the c0m61nat10n wa5 accepted a5 a p055161e D ° 1f the Knn ° 1nvar1ant ma55 1ay 1n the ran9e 1.45 <M1~,~,~0 <2.20 6eV.

289

V01Ume 184, num6er 2,3 PHY51C5 LE77ER5 8

Next, the D ° cand1date5 were c0m61ned w1th a fur- ther char9ed track, a55umed t0 6e a p10n, t0 f0rm p055161e D*•5. 1n 0rder t0 reduce the c0n51dera61e am0unt 0f 6ack9r0und fr0m rand0m c0m61nat10n5, a cut wa5 made 0n the fract10na1 ener9y 0f the D*; 51nce the D* wa5 expected t0 take m05t 0f the 0r191- na1 4uark•5 m0mentum, D* cand1date5 were rejected 1f xD. =DD*/E6eam W a 5 1e55 than 0.5. Further c0n- 5tra1nt5 were then app11ed t0 the D ° and 10ne rc can- d1date5. F1r5t, the 10ne p10n had t0 have a m0mentum 0fa t 1ea5t 50 MeV/c 1n the yy centre 0f ma55 5y5tem, 51nce very 10w m0mentum track5 tend t0 pr0duce 10w-ma55 D* cand1date5 51mp1y due t0 k1nemat1c5. 5ec0nd1y, 1n 0rder t0 c0m61ne 0n1y track51n appr0x- 1mate1y the 5ame hem15phere, the D°-rc 0pen1n9 an91e, 1n the Y7 centre 0f ma55 5y5tem, wa511m1ted t0 90 °. F1na11y, the rat10 0f the 10ne p10n t0 the D ° m0mentum wa5 c0n5tra1ned t0 6e 1e55 than 0.3.7h15 c0me5 pure1y fr0m the decay pr0pert1e5 0f the D* where, due t0 the 10w-Q va1ue, the 10ne p10n 06ta1n5 m05t 0f 1t5 m0mentum fr0m the L0rent2 6005t 1nt0 the 7Y re5t frame, rather than fr0m the D* decay 1t5e1f. C0n5e4uent1y, 1t 5h0u1d 6e 0f 0n1y 10w m0mentum c0mpared t0 the D ° , the 1atter tak1n9 away m05t 0f the 0r191na1 D*•5 m0mentum. A11 4uant1t1e5 were eva1uated 1n the Y7 centre 0f ma55 5y5tem, a5 def1ned 6y the f1na15tate re5t frame.

7he re5u1t1n9 D*-D ° ma55 d1fference, AM, 15 5h0wn 1n f19. 1. A c1ear peak 15 v15161e ar0und 145 MeV. 70 dem0n5trate that the pre5umed D* 519na1 15 n0t cau5ed 6y 5pur10u5 k1nemat1c effect5 and t0 he1p e5t1- mate the 6ack9r0und c0ntr16ut10n under the peak, the ana1y515 wa5 repeated f0r tw0 1ndependent c0n- tr01 5amp1e5. 7he5e were:

(1) D ° c0m61nat10n5 w1th 2.30 <~MD0 <~ 3.00 6eV, and

(11) D* c0m61nat10n5 w1th the c0rrect D ° ma55, 6ut w1th a11 track5 hav1n9 the 5ame char9e, 5uch a5 K+rc +~r0~ +.

7he re5u1t5 are 5h0wn 1n f195. 2 and 3 and n0 peak 15 v15161e.

1t wa5 p055161e t0 e5t1mate the c0ntr16ut10n fr0m 6ack9r0und ann1h11at10n event5, wh1ch can tr199er the ta991n9 5y5tem 6y hard ph0t0n rad1at10n, a5 a 50urce 0f the D* event5 1n tw0 way5. F1r5t, the ana1y515 wa5 repeated 0n a 1ar9e 5amp1e 0f ann1h11at10n M0nte Car10 event5 9enerated u51n9 the Lund Pr09ram [ 11 ] w1th 1n1t1a1 5tate rad1at10n acc0rd1n9 t0 8erend5 and K1e155 [ 9 ]. Fr0m th151t wa5 p055161e t0 c0nc1ude that

290

29 January1987

t53

r~7

15.0

10.0

5.0

0 . 0

0.14

519na1

0.18 0.22 0.26

D*-D ° Ma55 D1fference, hM (6eV)

F19. 1. D * - D ° ma55 d1fference, AM, f0r entr1e5 w1th 1.45~< MK~0 < 2.20 6eV.

there wa5 ne9119161e ann1h11at10n 6ack9r0und t0 the 065erved D* 519na1. 5ec0nd1y, the rea1 data were re- ana1y2ed w1th the 10n91tud1na1 m0mentum cut rever5ed 1n 0rder t0 5uppre55 the tw0-ph0t0n 519na1,

t 0

r ~

15.0

10.0

5.0

W r 0 n 9 Ma55

0 . 0 1

0.26 0.14 0.18 0.22

D*-D ° Ma55 D1fference, AM (6eV)

F19. 2. AM, f0r entr1e5 w1th 2.30 ~<MK~0 ~< 3.00 6eV.

V01ume 184, num6er 2,3 PHY51C5 LE77ER5 8 29 January 1987

>

15.0

10.0

5.0

0.0

Wr0n9 519n

0.14 0.18 0.22

,n, 0.26

1)*-D ° Ma55 D1fference, AM (6eV)

F19. 3. AM, f0r entr1e5 w1th 1.45<MK~0~<2.20 6eV, 6ut a11 char9ed track5 w1th 5ame 519n.

1eaV1n9 ma1n1y the ann1h11at10n 6ack9r0und. 0nce a9a1n, there wa5 ne9119161e ann1h11at10n 6ack9r0und 1n the re910n AM< 160 MeV.

A 5earch f0r D* me50n5 v1a the decay D ° ~ K - n •, wh1ch ha5 a 5ma11er 6ranch1n9 rat10, wa5 a150 made 6ut n0 5tat15t1ca11y 519n1f1cant 519na1 c0u1d 6e 5een. 7h15 d0e5 n0t, h0wever, c0nf11ct w1th the num6er 0f D*•5 065erved 1n the Knn ° channe1.

7he num6er 0f event5 065erved 1n the re910n AM< 160 MeV 15 32 and, u51n9 the ••wr0n9 ma55•• p10t 0f f19. 2, we e5t1mate the 6ack9r0und t0 6e 13 event5. 7h15 wa5 ca1cu1ated 6y n0rma1121n9 the ••wr0n9 ma55•• t0 the ••519na1•• p10t 0ut51de the 519na1 re910n. 7he num6er 0fD* event515 theref0re 19 w1th a 5tat15t1ca1 uncerta1nty 0f + 7. A1ternat1ve meth0d5

0f e5t1mat1n9 the 6ack9r0und, 5uch a5 u51n9 the ••wr0n9 519n•• p10t, 5u99e5t an add1t10na1 5y5temat1c err0r 0f + 3.

1n 0rder t0 1nve5t19ate the 11ke1y 50urce 0f the charmed me50n5, the t0p0109y 0f the 32 event5 065erved wa5 c0mpared w1th c~ event5 9enerated 6y QPM M0nte Car10 r0ut1ne5 and a150 w1th 6 V D M MC event5, n0t c0nta1n1n9 charm [ 12 ] ,2 7he event var1a61e5 c0n51dered were the mean Q2, the mean jet p2 determ1ned fr0m the 5pher1c1ty and thru5t axe5 and 6y the D0rfan c1u5ter a190r1thm [ 1 ], and the mean va1ue5 0f 5pher1c1ty ( 5 ) and thru5t ( 7 ) . 7he re5u1t5 are 91ven 1n ta61e 1.1t can 6e 5een that the event5 are typ1ca11y jet-11ke, a5 0ne w0u1d expect fr0m 60th QPM and 6 V D M 6ut the mean Q2 0fthe event5 and the mean jet tran5ver5e m0mentum 15 much c105er t0 the QPM expectat10n.

61ven a5 kn0w1ed9e 0f the D*--,D°n and D ° ~ K - n +n ° 6ranch1n9 rat105 and the eff1c1ency f0r detect1n9 D*•5, and 1f add1t10na1 a55umpt10n5 are made 0n the fra9mentat10n 0fc 4uark5, 1t 15 p055161e t0 c0mpare 0ur 065erved 519na1 w1th the QPM expectat10n.

7he event detect10n eff1c1ency wa5 determ1ned fr0m a QPM M0nte Car10 u51n9 the Verma5eren 9en- erat0r f0r 9amma-9amma t0 1ept0n pa1r5 [ 13 ] and the Lund fra9mentat10n 5cheme. Charmed 4uark5 w1th a ma55 0f 1.5 6eV were pr0duced and f0rced t0 fra9ment t0 D* me50n5, w1th the D* f0110w1n9 the re4u1red decay m0de5. 7he M0nte Car10 event5 were then pa55ed thr0u9h a detect0r 51mu1at10n pr09ram and ana1y2ed 1n the 5ame way a5 the rea1 data. 7he 0vera11 detect10n eff1c1ency f0r D* event5, 1nc1ud1n9 the ta991n9 eff1c1ency, wa5 (0.4 + 0.1 ) % where m05t 0fthe err0r 15 due t0 5y5temat1c uncerta1nt1e5, and 1n

,2 7he f1na1 5tate hadr0n5 have a 11m1ted P7 acc0rd1n9 t0 d a / d p 2 ~ exp ( - 2.5P 2 ).

7a61e 1 C0mpar150n 6etween 065erved D*, QPM ce MC and 6 V D M MC event t0p01091e5. <jet p2 ) 15 91ven f0r three ca5e5. Ca5e (a): u51n9 the c1u5ter a190r1thm 0freE [ 1 ]. Ca5e (6): a5 def1ned 6y the 5pher1c1ty ax15. Ca5e (c): a5 def1ned 6y the thru5t ax15.

70p01091e5 (Qa) (jetP~r) ( 6 e V 2) ( 5 ) ( 7 ) ( 6 e V 2 )

ca5e (a) ca5e (6) ca5e (c)

D* event5 0.91+0.10 2.3_+0.3 1.9_+0.3 2.3+0.4 0.45_+0.03 0.74+0.01 QPMc~ 0.86+0.02 3.1_+0.1 2.3+0.1 2.6+0.1 0.43_+0.01 0.75+0.01 6VDM 0.72_+0.02 1 . 4 + 0 . 1 1 . 2 + 0 . 1 1 . 4 + 0 . 1 0 .44+0 .01 0.74+0.01

291

V01ume 184, num6er 2,3 PHY51C5 LE77ER5 8 29 January 1987

part1cu1ar err0r5 a550c1ated w1th the dE/dx 51mu1at10n.

7he D* and D ° 6ranch1n9 rat105 were taken t0 6e ( 6 4 + 11 )% f0r D * ~ D ° n [ 14] and (20.1 + 3.5)% f0r D°--.K-n+n ° [15]. F0110w1n9 5tud1e5 0f ann1h11a- t10n pr0duct10n 0f D* me50n5 [7] 1t wa5 a55umed that charmed 4uark5 mater1a112e a5 e1ther D 0r D* me50n51n the rat10 1:3, and that char9ed and neutra1 D*•5 0ccur w1th e4ua1 pr06a6111ty, wh1ch 1ead5 t0 0~7y-~D*-+ X = 0.61 aVV.ce. C0m61n1n9 the5e 6ranCh1n9 rat105 W1th the detect10n eff1c1enCy 91Ve5 a pred1Ct10n 0f 3.4 +--1.4 event5 fr0m the QPM, t0 6e C0mpared W1th 0Ur 065ervat10n 0f 19•+ 7•+ 3 event5. EVen a55Um1n9 that Charmed 4Uark5 1nVar1a61y man1fe5t them5e1Ve5 a5 D* me50n5, the QPM pred1ct10n 15 0n1y 4.2 •+ 1.6 event5. A5 We have 5een, the event t0p0109y d0e5 n0t faV0Ur 6 V D M pr0Ce55e5 and 1ndeed a 5tUdy 0f the detect10n eff1c1enCy f0r 5UCh pr0Ce55e5 91Ve5 a Very 10W Va1Ue 0f (0.06--+ 0.03)%. 1f the fract10n 0f D* event51n a11 yy C0111510n5 V1a 6 V D M pr0Ce55e515 0f the 5ame 0rder a5 the fract10n 065erVed 1n yp C01- 11510n5 (1.e.~ 1 % ) t h e n We eXpeCt e55ent1a11y 2er0 C0ntr16Ut10n 1n th15 exper1ment.

Fr0m preV10U5 5tUd1e5 0f jet pr0dUCt10n 1n tW0- ph0t0n C0111510n5 there 15 5tr0n9 ev1denCe that 1n an 1ntermed1ate 1ff t re910n, 2~<p~ t ~< 3 6eV, the event rate 15 1n eXCe55 0f that pred1Cted 6y the 5Um 0f 6 V D M and QPM. 7h15 15 a5Cr16ed t0 the pre5ence 0f 5Ca1e 1nVar1ant QCD m0d1f1Cat10n5 t0 the 6a51C QPM "60X~ d1a9ram (7y--•4C1) Wh1Ch pr0dUCe hard 5Catter1n9 three- (Y7 ~4(19) and f0Ur-part0n (77--,4f14~1) pr0ce55e5. At P E 7 R A ener91e5, the5e add1t10na1 pr0ce55e5 cann0t 6e d1rect1y 065erved a5 three- 0r f0ur-jet event5 6ecau5e the Y7 centre 0fma55 ener9y 15 effect1ve1y 11m1ted t0 15 6eV. 1n the P L U 7 0 ana1y515 [ 3 ] they appear a5 an exce55 0f 10w thru5t event5, and 1n the JADE c1u5ter ana1y515 [ 2] a5 event5 c1a551f1ed a5 ••2er0 jet•• 0r ••0ne jet••. 7he prev10u51y mea5ured exce55 0f event5 0ver the QPM expecta- t10n, f0r X7=pJ~t/E6eam 6etween 0.1 and 0.3, 15 r0u9h1y 1n a9reement w1th the ca1cu1at10n5 0f 5t1r11n9 [ 16 ] and 6ray50n [ 17 ], wh1ch 5u99e5t a rat10 0f (tw0- + three-+f0ur - je t ) event5 t0 tw0-jet event5 0f 6etween 2.5 and 1.5.7he mean p~t 0f the 32 065erved D* event5, fr0m ta61e 1, c0rre5p0nd5 t0 an x7 va1ue 0f0.1.

70 5ummar12e, we have 065erved char9ed D* event5 1n ph0t0n-ph0t0n c0111510n5, w1th a mean Q2 0f 0.91 6 e V 2 and a v15161e 1nvar1ant ma55 Wv15>~4

6eV, at a rate h19her than that expected fr0m QPM a10ne. 7h1515 c0n515tent w1th the 9enera1 065ervat10n 0n jet pr0duct10n, at the 5ame mean x7 va1ue, wh1ch exceed5 the QPM expectat10n and ha5 6een a5cr16ed t0 the pre5ence 0f QCD c0rrect10n5 t0 the 6a51c d1a9ram.

We are 9ratefU1 t0 the P E 7 R A mach1ne 9r0Up and the DE5Y C0mputer Centre f0r the1r exce11ent 5erv1Ce dur1n9 th15 exper1ment. We a150 ackn0w1ed9e the eff0rt 0f a11 the en91neer5 and techn1C1an5 wh0 have part1C1pated 1n the C0n5truCt10n and ma1ntenance 0f the apparatU5, and 1n part1Cu1ar, we w0u1d 11ke t0 thank th05e wh0 1n5ta11ed the ta991n9 5y5tem5. 7h15 exper1ment wa5 5upp0rted 6y the 8unde5m1n15ter- 1um ft1r F0r5chun9 und 7echn01091e, 6y the Japane5e M1n15try 0f Educat10n, 5c1ence and Cu1ture, 6y the U K 5c1ence and En91neer1n9 Re5earch C0unc11 thr0u9h the Rutherf0rd App1et0n La60rat0ry and 6y the U5 Depar tment 0f Ener9y. 7he v151t1n9 9r0up5 w15h t0 thank the DE5Y d1rect0rate f0r the h05p1ta1- 1ty extended t0 them.

[ 1 ] J. D0rfan, 2. Phy5. C 7 (1981) 349. [2] W. 8arte1 et a1., Phy5. Lett. 8 107 (1981) 163;

A.J. F1nch, C0ntr16. V111ntern. W0rk5h0p 0n Y7 c0111510n5 (Pad5, 1986).

[3 ] Ch. 8er9er et a1., 2. Phy5. C26 (1984) 191. [4] M. A1th0ffet a1., Phy5. Lett. 8 138 (1984) 219. [5] 1.F. 61n26ur9 and V.6. 5er60, Phy5. Lett. 8 109 (1982) 231. [6] D. A5t0n et a1., Phy5. Lett. 8 94 (1980) 113.

J.J. Au6ert et a1., Nuc1. Phy5. 8 213 (1983) 31. [7] W. 8arte1 et a1., Phy5. Lett. 8 146 (1984) 121. [8] W. 8arte1 et a1., Phy5. Lett. 8 88 (1979) 171; 8 92 (1980)

206. [9] F.A. 8erend5 and R. K1e155, Nuc1. Phy5.8 178 (1981 ) 191.

[ 10] 6.J. Fe1dman et a1., Phy5. Rev. Lett. 38 (1977) 1313. [ 11 ] 8. Ander550n, 6.6u5taf50n and 7. 5j65trand, 2. Phy5. C 6

(1980) 235; Nuc1. Phy5.8 197 (1982) 45. [ 12] J.M. Nye, PhD the515, Un1ver51ty 0f Lanca5ter (1986);

A.J. F1nch; C0ntr16. V111ntern. W0rk5h0p 0n y7 c0111510n5 (Par15, 1986).

[ 13] J. 5m1th, J.A.M. Verma5eren and 6. 6rammer, Phy5. Rev. D 15 (1977) 3280.

[ 14 ] Part1c1e Data 6r0up, Rev1ew 0f Part1c1e Pr0pert1e5, Rev. M0d. Phy5. 56 (1984) 1.

[ 15] R.H. 5ch1nd1er, 5LAC prepr1nt, 5LAC-PU8-3799 (1985). [ 16 ] 5.J, 8r0d5ky, 7. De6rand, J. 6un10n and J. We15, Phy5. Rev.

D 19 (1979) 1418; W.J. 5t1f11n9, Pr0c. V 1ntern. W0rk5h0p 0n 117 c0111510n5 (Aachen, 1983), ed. Ch. 8er9er, Lecture N0te5 1n Phy51c5, V01. 191 (5pr1n9er, 8er11n) p. 142.

[ 17 ] 5. 6ray50n, C0ntr16. V111ntern. W0rk5h0p 0n yy c0111510n5 (Par15, 1986).

292