Multiplicity and transverse energy flux in 16O+Pb at 200 GeV per nucleon

V01ume 184, num6er 2,3

PHY51C5 LE77ER5 8

29 January 1987

MUL71PL1C17Y A N D 7 R A N 5 V E R 5 E E N E R 6 Y F L U X 1N ~60+P6 A7 200 6 e V PER N U C L E 0 N NA35 C011a60rat10n A. 8 A M 8 E R 6 E R a, D. 8 A N 6 E R 7 6, j. 8 A R 7 K E c, H. 8 1 A L K 0 W 5 K A a, R. 8 0 C K e, R. 8 R 0 C K M A N N e, C. D E M A R 2 0 f, M. DE P A L M A f, 1. D E R A D 0 9, V. E C K A R D 7 9, C. F A V U 2 2 1 f, J. F E N 7 5, D. F E R E N C h, H. F E 5 5 L E R 9, P. F R E U N D 9, M. 6 A 2 D 2 1 C K 1 1j, H.J. 6 E 8 A U E R 9, K. 6 E 1 5 5 L E R 6, C. 6 U E R R A ~, J.W. HARR15 k,t, W. H E C K 1, 7. H U M A N 1 C ¢, K. KAD1JA h, R. KE1DEL m, M. K 0 W A L 5 K 1 ¢, 5. M A R 6 E 7 1 5 n, E. NAPP1 f 6 . 0 D Y N 1 E C k, ~ 6 . PA1C h, A.D. P A N A 6 1 0 7 0 U 6,n, A. PE7R1D15 n, J. P F E N N 1 6 1, F. P 0 5 A f K.P. P R E 7 2 L 9, H . 6 . P U 6 H k, F. P 0 H L H 0 F E R m, 6 . RA1 k, A. RAN1ER1 f, R. R E N F 0 R D 7 ~, D. R 0 H R 1 C H m, K. R U N 6 E a, A. 5 A N D 0 V A L ~, D. 5 C H A L L 1, N. 5 C H M 1 7 2 9, L.5. 5 C H R 0 E D E R k, 6 . 5 E L V A 6 6 1 f P. 5 E Y 8 0 7 H ~, J. 5EYERLE1N ~, E. 5 K R 2 Y P C 2 A K J, P. 5P1NELL1 f, R. 5 7 0 C K 6,1, H. 57Rt~8ELE 6,~, A. 7 H 0 M A 5 1, M. 7 1 N C K N E L L k,1, L. 7 E 1 7 E L 8 A U M k, 6 . V E 5 2 7 E R 6 0 M 8 1 9,2, D. VRAN1C e,h, 5. W E N 1 6 t and M. W E N 5 V E E N e a Faku1t~tf11r Phy51k, Un1ver51t~t Fre16ur9. D- 7800 Fre16ur9, Fed. Rep. 6ermany 6 CERN, CH-1211 6eneva 23, 5w1t2er1and c 1n5t1tute 0fNuc1ear Phy51c5, PL-30055 Crac0w, P01and 1n5t1tute 0f Nuc1ear 5tud1e5, PL-00681 War5aw, P01and ° 6e5e115chaf1fur 5chwer10nenf0r5chun9, D-6100 Darm5tadt 11, Fed. Rep. 6ermany f D1part1ment0 d1F151ca, Un1ver51ta d18arL and1NFN, 1-70126 8ar1, 1ta1y 9 Max-P1anck-1n5t1tuteJ~r Phy51k, D-8000 Mun1ch, Fed. Rep. 6ermany h Rudjer 805k0v1c 1n5t1tute, 41001 2a9re6, Yu9051av1a 11n5t1tut f11rH0chener91ephy511~ Un1ver51t11tHe1de16er9, D-6900 He1de16er9 1, Fed. Rep. 6ermany J 1n5t1tute 0fExper1menta1 Phy51c5, Un1ver51ty 0f War5aw, PL-00681, War5aw, P01and k Lawrence 8erke1ey La60rat0ry, Un1ver51ty0fCa11f0rn1a, 8erke1ey CA 94720, U5A t Fach6ere1ch Phy51k, Un1ver51t•1t Frankfurt, D-6000 Frankfurt, Fed. Rep. 6ermany ~nFach6ere1ch Phy51k, Un1ver51t11tMar6ur9, D-3550 Mar6ur9, Fed. Rep. 6ermany "Phy51c5 Department, Un1ver51ty0f Athen5, 157-71 Athen5, 6reece

Rece1ved 24 N0vem6er 1986

F1r5t re5u1t5 fr0m u1trare1at1v15t1c t60+P6 c0111510n5at 200 6ev/nuc1e0n are pre5ented. 7he tran5ver5e ener9y E71n avera9e centra1 c0111510n515~ 75 6ev f0r the 1nterva1 2.2 < y ~<3.8. A 16-f01dc0nv01ut10n0f the 1ne1a5t1cp + Au tran5ver5e ener9y 5pectrum, a150mea5ured at 200 6eV, repr0duce5 the mean E7 0f 160+ P6. 7he am0unt 0f nuc1ear 5t0pp1n9p0wer appear5 t0 6e h19h.

C0111510n5 0fnuc1e1 at very h19h ener9y 5h0u1d create a f1n1te v01ume 0fhadr0n1c matter at h19h ener9y den51ty. Recent re5u1t5 fr0m 5tr0n9 1nteract10n 1att1ce 9au9e the0ry [ 1 ] 5u99e5t that, a60ve a cr1t1ca1 ~ A1eXanderv0n Hum601dt F0undat10n Fe110w. 2 0n 1eave0fa65ence fr0m centra1 Re5earCh 1n5t1tutef0r Phy51c5,H-1525 8udape5t, Hun9ary.

temperature 0f appr0x1mate1y 250 MeV, the hadr0n1c 5tate 0f matter 15 tran5f0rmed t0 a new pha5e c0n515t1n9 0f dec0nf1ned 4uark5 and 91u0n5, w1th an ener9y den51ty 0f 5evera1 6 e V / f m 3, t0 6e c0mpared t0 that 0f9r0und 5tate matter, wh1ch 15 150 M e W f m 3. 5uch extreme c0nd1t10n5 c0u1d 6e reached 1n centra1 nuc1eu5-nuc1eu5 c0111510n5 6y c0nvert1n9 the 1n1t1a1

271

V01ume 184, num6er 2,3

PHY51C5 LE77ER5 8

re1at1ve CM ener9y 1nt0 1nterna1 exc1tat10n 0f a ••f1re6a11•• f0rmed at rap1d1t1e51ntermed1ate 6etween th05e 0f tar9et and pr0ject11e, pr0v1ded 5uff1c1ent 6eam ener9y and ade4uate ••5t0pp1n9 p0wer••. 7he 5t0pP1n9 p0wer 0f nuc1ear matter, wh1ch determ1ne5 the de9ree t0 wh1ch 6ary0n num6er and ener9y den51ty are 5h1fted away fr0m the fra9mentat10n d0ma1n5 t0ward5 m1d-rap1d1ty, 15 p00r1y kn0wn. E5t1mate5 der1ved fr0m hadr0n-nuc1eu5 c0111510n5 at h19h ener9y are c0ntr0ver51a1 [ 2,3 ]: the mean rap1d1ty 1055 0f the 1ead1n9 6ary0n 1n a pr0t0n-nuc1eu5 c0111510n 15uncerta1n w1th1n the ran9e fr0m Ay~ 1-2.5. At 200 6 e V per nuc1e0n 1nc1dent ener9y, atta1ned at the CERN 5P5 f0r nuc1ear 6eam5, the t0ta1 rap1d1ty 9ap 6etween tar9et and pr0ject11e 15Ay = 6.06.7he ener9y ava11a61e 1n the nuc1e0n-nuc1e0n CM frame, V/5= 19.4 6 e V per nuc1e0n pa1r, appear5 5uff1c1ent t0 create the cr1t1ca1 ener9y den51ty. H0wever, a h19h de9ree 0f nuc1ear 5t0pp1n9 15 nece55ary t0 c0ncentrate a 5uff1c1ent fract10n 0f th15 ener9y near m1drap1d1ty. 7he a1m 0f the pre5ent 5tudy, 0f the 160 + P6 react10n at 200 6eV/nuc1e0n 1nc1dent ener9y, wa5 t0 f0cu5 0n a nece55ary prere4u151te 0f 4uark matter f0rmat10n, name1y the 5t1pp1n9 p0wer. 7he data were 06ta1ned 1n an acce1erat0r te5t run 1n wh1ch th15 exper1ment, NA35, rece1ved 36 h 0f externa1 160 6eam. 7he part1c1e mu1t1p11c1ty and the tran5ver5e ener9y d15tr16ut10n at 1ntermed1ate rap1d1ty w e r e 1nve5t19ated. 7he re5u1t5 1nd1cate that a h19h de9ree 0f 5t0pp1n9 0ccur5 1n centra1 c0111510n5. 7he exper1ment wa5 carr1ed 0ut u51n9 a 200 6 e V / nuc1e0n 160 6eam extracted fr0m the CERN $P5. 7h15 ener9y 15reached v1a a cha1n 0facce1erat0r5 [ 4 ]. A h19h char9e 5tate ECR 10n 50urce p1u5 RFQ preacce1erat0r [5] 1nject5 a 6eam 0f 160(6-1- ) 1nt0 L1nac 1. After acce1erat10n t0 12 MeV/nuc1e0n and c0mp1ete 5tr1pp1n9, tran5fer t0 the P5 6005ter 0ccur5, and 5u65e4uent1y 1nt0 the P5 at 260 MeV/nuc1e0n. A 10 6eV/nuc1e0n 6eam 15 extracted fr0m the P5 1nt0 the 5P5. F1na11y, a 6eam 0f ~ 5)< 107 10n5/5 w1th 4.4 5 extract10n and a 14.4 5 0vera11 cyc1e 15 extracted fr0m the 5P5 1nt0 the externa1 6eam tran5p0rt 5y5tem. An 1nten51ty 0f 5 × 104 10n5/5 wa5 u5ed 1n th15 exper1ment. 7he NA35 5etup [ 6 ] c0n515t5 0fa 2 × 1.2 × 0.72 m3 5treamer cham6er 1n the 1.5 7 ma9net1c f1e1d 0f a 5uperc0nduct1n9 Vertex ma9net. P6 and Au tar9et5 0f 1% 1nteract10n 1en9th were p051t10ned 13 cm 272

29 January 1987

up5tream fr0m the 5treamer cham6er. 7hree camera5, each e4u1pped w1th tw0-5ta9e, ma9net1ca11y f0cu5ed 1ma9e 1nten51f1er5 0f 2000-f01d 1um1n0u5 9a1n, v1ew the 5treamer cham6er and rec0rd event5 0n 70 m m f11m. 7he 0Vera115pat1a1 re501ut10n atta1ned 1n the 5treamer cham6er wa5 a60ut 2 mm. D0wn5tream tw0 1ar9e area ca10r1meter5 c0ver the m1d rap1d1ty re910n 0f 2.5°~< 0 ~<12 °. F1r5t a h19h1y 5e9mented ph0t0n p051t10n detect0r [ 7 ] (PPD) 0f 9.6 rad1at10n 1en9th5 th1ckne55 mea5ure5 m05t 0fthe ener9y 0f ph0t0n5 and n °•5. 1t 15 read 0ut 6y a1ternat1n9 p1ane5 0f vert1ca1 and h0r120nta1 pr0p0rt10na1 tu6e5 w1th 7.7 m m w1re 5pac1n9 1nt0 3072 ADC channe15. D1rect1y 6eh1nd the PPD there 15 a r1n9 ca10r1meter [ 8 ] 0f 1.5 m 0uter and 0.28 m 1nner rad1u5 5u6d1v1ded 1nt0 240 ce115. 1t c0n515t5 0f a 16 rad1at10n 1en9th5 1ead/5c1nt111at0r fr0nt 5ect10n and a 6.9 1nteract10n 1en9th5 1r0n/5c1nt111at0r 6ack 5ect10n. 7he t0ta1 th1ckne55 0f a60ut 8 1nteract10n 1en9th5 fu11y c0nta1n5 200 6 e V hadr0n1c 5h0wer5. 7he 1nterna1 aperture 0f the r1n9 ca10r1meter 15 f111ed6y the 1ntermed1ate ca10r1meter, c0ver1n9 the an9u1ar ran9e 0f 0.3 ° ~<0 ~<2,5 °. 1t wa5 0n1y u5ed a5 a pa551ve a650r6er 1n the pre5ent exper1ment. 7he ener9y f1ux 1n the pr0ject11e fra9mentat10n d0ma1n 0 < 0 . 3 ° 15 mea5ured 6y a vet0 ca10r1meter [8] 0f 9.9 1nteract10n 1en9th5 th1ckne55. 7w0 tr199er5 were u5ed 1n the exper1ment. 7he f1r5t tr199er wa5 der1ved fr0m the ener9y 519na1Evet00fthe vet0 ca10r1meter. 1t 5e1ected var10u5 1eve15 0f pr0ject11e ener9y de9radat10n 1n the c0111510n. 7he5e ran9e fr0m ••m1n1mum 61a5••, where Evet0 wa5 ju5t 6e10w the 1nc1dent 3.2 7eV, t0 ••centra1•• where the ener9y f10w 1nt0 the pr0ject11e fra9mentat10n d0ma1n wa5 re4u1red t0 6e Evet0~<0.5 7eV. 7he 0ther tr199er wa5 06ta1ned fr0m the tran5Ver5e ener9y 519na1 E PPD der1ved fr0m the PPD. 1t 5e1eCted event5 1n Wh1Ch the t0ta1 tran5Ver5e ener9y 0f the e1ectr0ma9net1C 5h0Wer5 exceeded var10U5 1eVe15. 0 n the avera9e 3 event5 were taken 1n the Cham6er per 6eam 5p111and, 1n add1t10n, a60ut 100 event5 1n the Ca10r1meter5 w1th0Ut aCC0mpany1n9 5treamer Cham6er 1nf0rmat10n. A centra1 c0111510n event 06ta1ned w1th the vet0 ca10r1meter thre5h01d E~< 0.5 7eV 15 5h0wn 1n f19. 1. 7he char9ed part1c1e mu1t1p11c1tyfr0m the 5can 15267, and the tran5ver5e ener9y rec0rded 1n the PPD and r1n9 ca10r1meter5 15 80 6eV. 7he an9u1ar acceptance

V01ume 184, num6er 2,3

PHY51C5 LE77ER5 8

29 January 1987

~--[ -- 12.5° PpD

1 ~

.

-

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•12.5 ° F19,1.5treamer cham6er p1cture 0f a centra1 ~60+ P6 c0111510nat 200 6ewnuc1e0n, t09ether w1th the an9u1ar acceptance 0f the m1drap1d1tyca10r1meter5 (PPD and r1n9) and the 1ead1n9fra9ment ca10r1meter (vet0). 0f the P P D and r1n9, a5 we11 a5 that 0f the vet0 ca10r1meter, are 1nd1cated 1n the f19ure. 7 h e cr055 5ect10n c0rre5p0nd1n9 t0 th15 ••v101ent event•• c1a55, w1th JE7 >~80 6eV, wh1ch exh161t5 n0 5ma11 an91e jet 0f h19h ener9y 1ead1n9 fra9ment5, 15 5evera1 hundred m6. 7hu5, event5 w1th h19h tran5ver5e ener9y are n0t rare; the1r cr055 5ect10n c0rre5p0nd51n a 9e0metr1ca1 m0de1 t0 1mpaCt parameter5 6 ~<3 fm w1th c0mp1ete 0ver1ap 0f the 160 (R = 3 fm) and the P6 (R = 7 fm) nuc1e1. F19. 2 5h0w5 the acceptance5 0 f t h e 5treamer cham6er, the P P D p1u5 r1n9 ca10r1meter5, and the vet0 ca10r1meter 1n the p~ ver5u5 1a6 rap1d1ty p1ane. At tran5ver5e m 0 m e n t a 6e10w ~ 1 6 e W c , the PPD/r1n9 acceptance d1ffer5 f0r p10n5 and nuc1e0n5. 7 h e p10n acceptance 6end5 away fr0m the m1d-rap1d1ty c0vera9e, 2.2~ 5, except at very 10w tran5ver5e m 0 m e n t u m f0r 6ary0n5. 7he5e acceptance5 refer t0 run5 w1th0ut ma9net1c f1e1d, wh1ch were u5ed.t0 06ta1n tran5ver5e ener9y d15tr16ut10n5. W1th the f1e1d 0n 0n1y the neutra1 part1c1e acceptance rema1n5 unchan9ed, wherea5 a11 char9ed part1c1e5 exper1ence a def1ect10n 1n the h0r120nta1 p1ane, c0rre5p0nd1n9 t0 an add1t10na1 apparent tran5ver5e ener9y 0f a60ut 1 6eV. 7 h e pr0t0n acceptance 0f the vet0 ca10r1meter 15 5h1fted upward5 t0 y>~ 5.5, wh1t n0 chan9e 0ccurr1n9 f0r neutr0n5.

7 h e char9e-part1c1e mu1t1p11c1ty, 065erved 1n the 5treamer cham6er at 1a6 an91e5 0 ~<60 ° 15 p10tted 1n f19. 3 ver5u5 the t0ta1 ener9y 1n the vet0 ca10r1meter. 7he5e data were taken w1th ma9net1c f1e1d 0n. 7 h e mu1t1p11c1t1e5 have 6een c0rrected f0r 5cann1n9 eff1c1ency, e + - e - c0ntam1nat10n fr0m 7-c0nver510n, 5ec0ndary part1c1e 1nteract10n5 1n the tar9et, and c0ntr16ut10n5 fr0m neutra1 5tran9e part1c1e decay t0 char9ed part1c1e5 (6a5ed 0n the H1JE7 [ 9 ] pred1ct10n f0r the re1at1ve A, 1~, and 2 t0 p10n y1e1d5). 7 h e mean char9ed-part1c1e mu1t1p11c1ty 1ncrea5e5 w1th decrea51n9 ener9y f1ux 1n the pr0ject11e fra9mentat10n d0ma1n, reach1n9 a va1ue 0f a60ut 260. A150 5h0wn 15 the pred1ct10n 0f the H1JE7 event 51mu1at10n c0de wh1ch 15 6a5ed 0n a m0de1 0f 5ucce551ve nuc1e0n-nuc1e0n 1nteract10n5. F19. 4a 5h0w5 the d1fferent1a1 Ea- d15tr16ut10n, a5 5ummed fr0m the P P D and r1n9 ca10r1meter5 ~:1w1th ,1 Er 15ca1cu1ateda5 the appr0pr1ate1ywe19hted 5um 0fthe ener91e5 f0und 1n 1nd1v1dua1PPD channe15 and r1n9 ca10r1meter ce1156y the f0rmu1a Epp0 + E~n9~ n

1

4dpvD w1r~ ~ 2(21E~+Y1E~/)

+ dr1~ ce115r1~e11 " 7he fact0r ~/4 c0rrect5 f0r the effect 0fthe carte51an read0ut 0fthe PPD, dpp0and dr1~are the ca10r1meter5• d15tance5fr0m the tar9et; 21, Y1 and r~ are the d15tance5 fr0m the PPD w1re5 and the r1n9ca10r1meterce115t0 the 6eam ax15. 273

V01ume 184, num6er 2,3

PHY51C5 LE77ER5 8

2"41

29 January1987

1

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~60 - P6 200 0eV/nude0n 2.0

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1.6

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=7

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0.8

0.8

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1.6 2.4 E vet0 (7eV)

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F19.3. Mean char9ed-part1c1e mu1t1p11c1ty f0r 1a6 an91e5 0 ~<60 ° a5 a funct10n 0fthe t0ta1 ener9y 065erved 1n the vet0 ca10r1meter. 0#

0

tar9et

2

L

6

8

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E19.2. Acceptance 0f the NA35 detect0r5 f0r the ca5e 0f n0 ma9net1c f1e1d 1n the vertex ma9net, 5h0wn 1n the P7 ver5u51a6 rap1d1ty p1ane. 7he 5treamer cham6er accept5 a11 char9ed part1c1e5 w1th 0 ~<60 °. 7he PPD and r1n9 ca10r1meter5 accept a11 part1c1e5 1n m1d-rap1d1ty, the exact acceptance5 depend1n9 0n the ma55 0f the part1c1e5, Here 0n1y the acceptance5 f0r nuc1e0n5 (da5hed 11ne5) and f0r p10n5 (5haded area) are 5h0wn. F0r the vet0 ca10r1meter 0n1y the nuc1e0n acceptance 15 5h0wn. 7he dark 5haded area c0rre5p0nd5 t0 the 0n5et 0fthe acceptance.

the ma9net 0ff. 7he data p01nt5 w1th E 7 < 5 0 6 e V were 06ta1ned fr0m event5 1n the ca10r1meter5 and acc0mpany1n9 5treamer cham6er p1cture5. 7h15 en5ured the 1nc1u510n 0f 0n1y va11d tar9et 1nteract10n5. F0r E 7 > 50 6 e V the fract10n 0f n0n-tar9et 1nteract10n5 wa5 determ1ned fr0m the 5treamer cham6er t0 6e < 0.04. 5y5temat1c uncerta1nt1e5 0fthe Ea--5ca1e and n0rma112at10n are e5t1mated t0 6e 6e10w 10%. 7he data have n0t 6een c0rrected f0r the effect 0f the f1n1te E7-re501ut10n (appr0x1mate1y 5% at E7 = 75 6 e V ) . 7he H1JE7 pred1ct10n 15 a150 5h0wn 1n f19. 4a f0r c0mpar150n. 7h15 d15tr16ut10n 15 much narr0wer. 7he peak near 50 6 e V ar15e51n th15 m0de1 fr0m 1mpact parameter5 6~< 4 fm. 7he data exh161t the 5ame ••centra1 c0111510n•• peak at ar0und 75 6eV. 7hu5, H1JE7 uderpred1ct5 the m1d-rap1d1ty 6y 274

a fact0r 0f appr0x1mate1y 0.66 f0r centra1 c0111510n5. 7he t0ta1 065erved cr055 5ect10n f0r E7~> 75 6 e V 15 a5 h19h a5 250 m6, c0rre5p0nd1n9 1n a 9e0metr1c m0de1 6~< 3 fm. At h19her E7 the cr055 5ect10n fa115 near-exp0nent1a11y. H0wever, the cr055 5ect10n c0rre5p0nd1n9 t0 E7 1>110 6eV, 1.e. 1.5 ( E 7 ) 0f centra1 c0111510n5, 15 5t111 a60ve 1 m6. 7h15 re910n w111 6e 1nve5t19ated 1n upc0m1n9 h19her 5tat15t1c5 run5. A150 1nc1uded 1n f19. 4a 15 the 16-f01d c0nv01ut10n 0fthe d1fferent1a1E7 d15tr16ut10n f0r p +Au, 06ta1ned• w1th a 200 6 e V ta99ed pr0t0n 6eam and the 5ame 5etup, runn1n9 w1th n0 ma9net1c f1e1d and an 1nteract10n tr199er re4u1r1n9 Evet0 < 150 6eV. 7he E7 d15tr16ut10n 1n the PPD and r1n9 ca10r1meter5 f0r p + Au 15 5h0wn 1n f19. 46, a10n9 w1th an ana1yt1c f1t

da/dE7 =0.173 E 7 M exp( - 0 . 7 2 7 E7) [6/6eV] . 7he p-Au cr055 5ect10n c0rre5p0nd1n9 t0 th15 tr199er m0de 15 1.3 6. 7h15 am0unt5 t0 a60ut 70% 0fthe t0ta1 1ne1a5t1c cr055 5ect10n, the tr199er e11m1nat1n9 the 5urface 1nteract10n5 (6> 6 fm) 0f the pr0t0n, wh1ch 5h0u1d n0t 6e 1nc1uded 1n the c0nv01ut10n 6ecau5e we want t0 c0mpare the re5u1t1n9E7 5pectrum t0 that 0f 5ma111mpact parameter 160 .4• P6 C0111510n5.1nfact, f19. 4a 5h0W5 that th15 C0nV01Ut10n appr0X1mate1y repr0dUCe5 60th the ••Centra1 C0111510n•• peak p051t10n and the 510pe at h19h Ea•. 7he 5ma11 d1fference 6etWeen AU and P6 tar9et ma55e5 5h0U1d 6e ne9119161e. F19. 46 1nc1ude5 the re5u1t 0f a p + Au H1JE7 ca1cu1at10n f0r 6~<6 fm, wh1ch d0e5 n0t re5em61e the

V01ume 184, num6er 2,3

PHY51C5 LE77ER5 8

1

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1

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104

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120

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104

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20

(6eV)

F19.4. (a) M1d-rap1d1tytran5ver5eener9yd15tr16ut10n0f 160 ~ P6. 7he da5hed CUrve91Ve5the H1JE7pred1Ct10n. 7he fU1111ne15the 16-f01d C0nV01Ut10n0f the E7 d15tr16Ut10n f0r 1ne1a5t1Cp+AU C0111510n5at 200 6eV. 7he 1atter data (6) have 6een mea5Ured W1ththe 5ame apparatU5.A150 5h0Wn15 the H1JE7 pred1Ct10n, and a fUnct10na1f0rm f1ttedt0 the data. data. 7he 1nade4uacy 0f th15 m0de1, w1th re5pect t0 E7 5pectra, can thu5 6e traced 6ack t0 the 1eve1 0f hadr0n-nuc1eu5 c0111510n5. 7a99ed p10n5 were a150 ava11a61e 1n the 200 6 e V extema1 5P5 6eam. W1th1n err0r5, the E7 5pectrum

29January1987

f0r • + + Au wa5 f0und t0 6e 1dent1ca1 t0 p + Au 0ver the ener9y ran9e c0vered here. 7he 10w H1JE7 pred1ct10n f0r E7 1n centra1 c0111510n5 065erved 1n f19. 4a, 1n 5p1te 0fthe c0rrect va1ue f0r the t0ta1 char9ed-part1c1e mu1t1p11c1ty (f19. 3), 5u99e5t5 that H1JE7 mu5t underpred1ct the mean E7 per part1c1e 6y a fact0r 0f a60ut 0.66. 70 further 1nve5t19ate th15, the num6er 0f track5 fa111n91nt0 the PPD and r1n9 ca10r1meter acceptance wa5 determ1ned fr0m the 5treamer cham6er, thu5 e5ta6115h1n9 the c0rre1at10n 6etween char9ed-part1c1e num6er and hadr0n1c tran5ver5e ener9y. 7he hadr0n1c tran5ver5e ener9y fract10n 0f the 5ummed PPD and r1n9 ca10r1meter E7 wa5 determ1ned 6y 5h0wer 51mu1at10n. 7h15 pr0cedure wa5 carded 0ut f0r 180 event5 06ta1ned 1n a n0-ma9net1c-f1e1d PPD-tr199er m0de. After c0rrect10n5 f0r 5cann1n9 eff1c1ency, e + - e - c0ntam1nat10n, and an add1t10na1 hadr0n1c E7 fract10n due t0 part1c1pant neutr0n5, the re5u1t (E7/part1c1e)=615•+90 MeV wa5 06ta1ned. 7he err0r 1nc1ude5 5tat15t1c5 0n1y. 7he 5y5temat1c err0r 15 0fthe 0rder 0f 10%. 7he a60ve re5u1t wa5 06ta1ned f0r the fract10n 0f event5 w1th E7 1n the ran9e 60 ~
v01ume 184,num6er 2,3

PHY51c5 LE77ER5 8

u51n9 the expre5510n dE7/dy(nR2t) -1, W1th R the 0Xy9en rad1U5 and t the t1me e1ap5ed 51nCe the 6e91nn1n9 0f the c0111510n. F0r t = 1 fm, the avera9e tran5ver5e ener9y den51ty 15 a60ut 2.2 6 e W f m 3. 1t can 6e 1ncrea5ed: (1) 6y tr199er1n9 0n h19h-E7 event5. At the 1eve1 0f a 1 m6 cr055 5ect10n 0ne expect5 a 50% 1ncrea5e (c.f. f19. 4a); (11) 6y h19her pr0ject11e ma55. W1th1n the a60ve 51mp1e 11ne 0f ar9ument the t0ta1 E7 w0u1d 6e expected t0 6e pr0p0rt10na1 t0 Apr0j (fr0m A-f01d A 2/3 c0nv01ut10n), and the v01ume t0 1ncrea5e a5 .. pr0j, the net 9a1n fact0r 1ncrea51n9 a5 A 1/3 0fthe pr0ject11e. 0 u r e5t1mate 0f a60ut 180 6 e V tran5ver5e ener9y 1n the 1nterva1 0.6 ~
276

29 January 1987

act10n5. 7h15 15 n0t t00 5upr151n9 f0r 5uch a 119ht pr0ject11e 51nce 0ne expect5 the maj0r nuc1ear med1um effect t0 ar15e fr0m the heavy tar9et. F0r 119ht nuc1ear pr0ject11e5 the hadr0n-nuc1eu5 pr0ce55 5h0u1d 6e the 6a51c 1n9red1ent 0f the dynam1c5. 1t5 5t0pp1n9 p0wer and E7 d15tr16ut10n d0 n0 tr1v1a11yre5u1t fr0m kn0wn hadr0n-hadr0n phy51c5, a5 1nd1cated 6y the fa11ure 0f H1JE7 t0 repr0duce e1ther the p + Au 0r the 160+P6 E7 d15tr16ut10n. F1na11y, the 5t0pp1n9 p0wer 0fthe e1ementary p-heavy nuc1eu5 centra1 c0111510nat 200 6 e V appear5 t0 6e h19h en0u9h t0 create a tran5ver5e ener9y den51ty 1n the avera9e centra1 160+P6 c0111510n 0f a60ut 2 6 e W f m 3. H19her den51t1e5 can 6e reached 6y 1nve5t19at1n9 event5 w1th very h19h E7, and 6y emp10y1n9 heav1er pr0ject11e5; 325 w111 500n 6e ava11a61e at the 5P5. 7he c0nd1t10n5 thu5 appear t0 6e fav0ura61e f0r a c0mprehen51ve 4uark matter 5earch. 7he auth0r5 w15h t0 ackn0w1ed9e the extra0rd1nary perf0rmance 0f the acce1erat0r 9r0up5 at CERN, 651 and L8L, and the 9ener0u5 h05p1ta11ty 0f the CERN EP and EF d1v1510n5. 7he enthu51a5t1c 5upp0rt 0f V. Herman, E. Ke11er and M. Yer11 15 apprec1ated. We thank Dr. 7h. 5ch0uten f0r h15 m05t va1ua61e he1p 1n the exper1ment.

Reference5 [] J.8. K09ut, Nuc1.Phy5.A 418 (1984) 381c; H. 5at2, Nuc1.Phy5.A 418 (1984) 447c. [2] D. 8art0n et a1.,Phy5.Rev. D 27 (1983) 2580; R. 8a11eyet a1.,2. Phy5.C 29 (1985) 1; D. L155auer, Pr0c. 5th Quark Matter C0nf. (A5110mar, 1986), Nuc1.Phy5.A 461, t0 6e pu6115hed. [3] W. 8u52aand A. 601dha6er, Phy5.Lett. 8 139 (1984) 235; 5. Date, M. 6yu1a55yand H. 5um1y05h1,Phy5. Rev. D 32 (1985) 619; M. Je2a6ekand M. R02an5ka,Phy5.Lett. 8 175 (1986) 206. [4] w.C. M1dde1k00p,CERNprepr1nt 5P5/86-15. [5] 8.H. w01fet a1.,651 Rep0rt 86-2. [6] A. 5and0va1 et a1., Pr0c. 5th Quark Matter C0nf. (A5110mar, 1986) Nuc1.Phy5.A 461, t0 6e pu6115hed. [7] V. Artem1evet a1.,Nuc1.1n5trum.Meth0d5224 (1984) 408. [ 8] C. De Mar20et a1.,Nuc1.1n5trum.Meth0d5217 (1983) 405; Phy5. Rev. D 29 (1984) 363. [9] 7.W. Lud1am,8NL rep0rt 51921 (1985) 373. [ 10] 7. Ake550net a1., Pr0c. 23rd, 1ntern. C0nfer. H19hener9y phy51c5(8erke1ey,CA, 1986); A. Fran2, PhD 7he515,Un1ver51t~1t51e9en(1986).