c per nucleon

Nuclear-Physics B (Proc. Suppl.) 16 (1990) 409-412 North-Holland

409

STRANGENESS PRODUCTION IN SULPHUR-TUNGSTEN INTERACTIONS AT 200 GeV/c PER NUCLEON Presented by J .B . Kinson, University of Birmingham WA85 Collaboration S . Abatzisl, H . Bensyouns, W . Beusch °, I .J . Bloodworths, A . Brauara, H . Caponeror, J .N . Carneys, J .P . Dufey °, D . Evanss, R . Falconer, R . Finir, B .R . Frencha, B . Ghidinir, A . Jacholkowskia, J . Kshanes, J .B . Kinsons, A . Kirks, K . Knudsona, J .C . Lassallea, V . Lentir, Ph . Lerustes, R .A . Loconsoler, A . Malamants, F . Navachr, J .L . Narjouxs, A . Palanor, A . Penzoa, E . Quercigh ®, L . Rossaa, H . Senés, R . Senés, 1l. Stassitaakil, H .T . Trainor4 , G . Vassiliadisl, 0 . Villalobos Baillies, A . Voltes, B .F . Votrubas and R . zitoun° a r s ® s a

Athens University, Athens, Greece University di Bari and Sezione INFN, Bari, Italy Birmingham University, Birmingham, U .K . CERN, European Organization for Nuclear Research, Geneva, Switzerland Collège de France, Paris, France INFN, Trieste, Italy Preliminary results from the WA85 Experiment at the CERN Omega Spectrometer are presented . A 200 A GeV/c beam of 22S ions was used with a tungsten target . The apparatus is used to detect V° s and charged tracks in the range PT > 0 .9 GeV/c and 2 .3 < Vlab < 3 .0 . Production of A, 1 and cascade particles is discussed . A study of the multiplicity dependence of A, A and negative hadron production is presented . In this paper we present a study of the

1 . INTRODUCTION The WA85 Experiment (1) was performed using the CERN Omega spectrometer with a 200 A GeV/c beam of sr S ions on a tungsten target .

The ex-

multiplicity dependence of both A and A at PT > 0 .9 GeV/c and central rapidity thus allowing a direct comparison of baryons and antiWe also present the multiplicity de-

periment studies strangeness production at

baryons .

PT >, 1 GeV/c and central rapidity in order to probe the dynamics of hadronic matter under

the same kinematic region .

extreme conditions where it has been suggested that a Quark-Gluon Plasma (QGP) may be formed . Strange particle [3--4) and in particular strange antibaryon (3D production is expected to be a useful probe for the dynamics of hadronic matter in heavy ion collisions .

In

addition, it has been proposed (5I that in the event of plasma formation strange particles with medium pT (>,'0 1 GeV/c) would originate from the early stages of the QGP, allowing a more direct observation of the QGP than via the large number of particles produced at low pT during hadronisation .

0920-5632/90/$3.50 © Elsevier Science Publishers B.V . North-Holland

pendence for negative hadrons (mainly pious) in It has been suggested that multi-strange baryon and antibaryon production are of particular interest in the search for the QGP (3) . As yet no results have been presented on production of these particles .

We show that ß

and W-- decays can be reconstructed in the high multiplicity heavy ion environment and present a preliminary lF to 0- production ratio .

2 . THE EKPERINENTAL SET-UP The WA85 set-up is designed to enable the

central rapidity, medium pT region to be studi-

J.B. Kinson et al., WA85 Collaboration/Sulphur-tungsten interactions at 200 GeV/c per nucleon

410

ad at high rates .

handful of tracks are re-

corded out of several hundred produced in a

a

central collision making reconstruction of both

c

lti-strange baryons possible in

strange and this kin

tic region .

10 7 triggers were re-

corded in ten days of data taking . The apparatus and trigger have been described previously [6] .

A system of multiwire

proportional chambers with a "'butterfly"

8000

2000

r..N 7000 C 6000

1600

5000

1200

W

4000

geometry (7' was used to measure tracks with

3000

PT ) 0 .6 GeV/c and 2 .2 < Ylab < 3 .2 . o arrays of 50 pitch silicon micro-

2000

800 400

1000

strips, each with 512 channels, were placed above and below the be

A l

9000

0 1

15 cm downstream fran

the target in order to sample the overall multiplicity for central rapidities, i .e . in the pseudorapidity range 2 .1 < e < 3 .4 .

icrostrip

1 .4 M(pn- ) GeV

1

1 .2

1 .4 M(pn . ) GeV

FIGURE 1 Mass distributions for A and  candidates

multiplicity, henceforth called multiplicity, is defined as the total number of strips Mt

1 .2

Fig . 2 shows the A, Â and negative hadron

in the upper and lower microstrip arrays .

yields as a function of multiplicity .

3.

uding correction for decays outside the fidu-

LTIPLICI

DEP

DENCES

'e have made a preliminary study of A, Ft and

production as a function of the aharged

ultiplicity measured by the silicon microstrips .

For this paper

e consider the multi-

plicity region from 24 to 70 where statistics are good .

e note that the multiplicity range

from 24 to 35 is contaminated by interactions

taking place in the silicon microstrips rather than the tungsten target . The method used to select A and  candidates has been described previously (8] . For this study we condider the region 2 .3 < Y lab < 3 and pT > 0 .9 GeV/c where the acceptance is good . The effective mass distributions for the candidates interpreted as and j;w* are shown in fig . 1 .

e select events in a 50 MeV mass interval centred on the A mass, giving 8671 A and 2103 X candidates . e have also studied

the production of negative hadrons in the same Y - pT region .

The data

are corrected for geometrical acceptance, incl cial region and unseen decay modes (triangles) and in addition for reconstruction efficiency (circles) .

The reconstruction efficiencies are

good over the multiplicity range considered, decreasing from N 9

to ro 60

tracks and from - 85

to N 40% for As and Re as

for single

the multiplicity increases from 24 to 70 . The yield for negative hadrons rises linearly over the multiplicity range considered .

The

A and R yields are also compatible with a linear rise in the multiplicity region 35 to 70 .

A study of the effect of the contamination

in the low multiplicity region is in progress . A preliminary simulation study using the FRITIOF 3 .1 Monte Carlo program (9l adapted for our set-up shows that the rapidity density for tracks in the region 2 .3 < Ylab < 3 is proportional to the multiplicity . the lower scale of fig . 2 .

This is shown in

J.B . Kinson et al ., WA85 Collaboration /Sulphur-tungsten interactions at 200 GeV/c per nucleon

411

WA85 PRELIMINARY 2

0.5

ee

0.4

ee

+

f

0

1 .2

0.3

(n- )

(nA )

0.8

0.08 0.06

N)

0.2

.0 .04

0.4

0 .02

0L 0

20 40 60 80 100 Microstrip Multiplicity 40

0L 0

L

80 120 160 200 Rapidity Density

20 40 60 80 100 Microstrip Multiplicity 'j40

80

0L 0

120 160 200

20 40 60 80 100 Microstrip Multiplicity 40

Rapidity Density

80

120 160 200

Rapidity Density

FIGURE 2 , and as a function of multiplicity The simulation predicts, under our experimental conditions, a linear rise with multiplicity for

100

A, fl and negative hadron production in the

1

WA 85

s - w at 200-A GeV/c

range considered, as expected for models baséd on a superpositon of independent NN collisions .

50

A comparison of the A and fl yields with proton-tungsten reference data is underway . 4 . H - and 1- PRODUCTION High P multi-strange baryon and antibaryon T production are considered to be of particular interest in the search for the QGP (31 .

The

Eu

0

-50

method used to select H- and 1i- cascade decay candidates has been described previously (10) . Fig . 3 shows a fully reconstructed 1F candidate . The effective mass distributions for the candidates, interpreted as Av - and

w+

-100

1

so

x (cm)

1

200

are

shown in fig 4 ; clear peaks are seen et the R and lt' positions .

-100

FIGURE 3 A reconstructed W = candidate .

J.B. Kinson et al., WA85 Collaboration /Sulphur-tungsten interactions at 200 GeV/c per nucleon

412

Et is shown that the 8- and W decays can be reconstructed with little background .

> 100 80

c W

ô

The

N= to 2- ratio is 0 .44 ± 0 .10 .

80

60

60

REFER

40

40

(1)

20

20

WAGS Proposal, . Apostolakis et al ., CE /SPSC 84-76, SPSC/P206 (1984) and CERN/SPEC 87-18, SPSC/P206 Add . 1 (1987) .

121

J . Rafelski and B . Millier, Phys . Rev . Lett . .48 (1982) 106b ; 56 (1986) 2334 (E) .

(3)

P . Roch, B . Müller and J . Rafelski, Phys . Rep . 142 (1986) 167 .

141

T . Matsui, B . Svettisky and L .D . He Lerran, Phys . Rev . D34 (1986) 2047 .

(5)

J . Rafelski and . Danos, Phys . Lett . B192 (1987) 432 ;

0

1 .5

2.5

2

0

3

M(An") GeV

1 .5

.M . J_ 2 2.5

3

M(nn+) GeV

FIGURE 4 ass distributions for cascade candidates . The acceptances and reconstruction efficiencies for the cascade candidates are being calculated but are similar for 2- and 11'. uncorrected

Nmr

The

J . Rafelski, "Hadronic Matter in Collision 1988°" , Tucson, AZ, USA (1988) .

to H- ratio is 0 .44 t 0 .10 .

5 . CONCLUSIONS

161

WAGS Coil ., presented by F . Navach, I Autumn School, "The Physics of the Quark-Gluon Plasma", Lisbon (1987) 103 .

171

. Bausch et al ., Nucl . Instr . and Meth . A249 (1986) 391 .

'e present a preliminary study of pT a 0 .9 GeV/c central A, 1, B- and 1' production in 200

GeV/c sulphur-tungsten interact-

ions .

181

WAGS Coll ., presented by E . Quercigh, '°Hadronic Matter in Collision 1988°°, Tucson, AZ, USA (1988) .

191

B . Andersson et al ., Lund preprint, LUTP 87-6 (1987) ;

The multiplicity dependence for A, 1 and negative hadrons has been studied in the s region . The average number of negative Y-PT hadrons shows a linear rise over the whole multiplicity region . behaviour .

We note that the Fritiof model,

which is based on a superposition of independent collisions, predicts a linear rise in all three cases .

B . Nilsson-Almgvist and B . Stenlund, Camp . Phys . Comm . 43 (1987) 38? .

In this preliminary study

the A and X ratios are compatible with this

CES

1101

WARS Coll ., presented by M .T . Trainor, 24th Rencontres de Moriond, Les Arcs, France, 5-12 March 1989 .