nucleon 32S + 32S and 16O + AU collisions

385~

Nuclear Physics A498 (1989) 385c-390~ North-Holland. Amsterdam

SEARCH

FOR

RADIAL

+ 32S AND

32S

FLOW

IN

CENI-RAL

200 GEViNUCLEON

I60 i- AU COLLISIONS*

R. RENFORDT Physik,

Fachbercich

Uni\Pcrsit5t

Frankfurt,

D -- 6000

Frankfurt,

Fetlcral

Rcpuhlik

of Germany

NM.5

COLLABORAI‘ION

ABSTRACT Strcamcr

Chamber

collisions

arc an:~lyzcti

impowtl

r:ldial

and

protons

fairly

gord

at low

agrccmcnt

of

100 McV.

antI

central

200 GcV/Nuclcon

of a model

of the

overall

in p

from

The transvcrsc

flow.

(lambdas)

:I ttmpcraturc found

data

in term<

two

incorporating

momentum systems

using

good

i p collisions

at the same cncr-gy.

high

llic prcdictionc

pt from

spectra

+ 32S and

agrccmcnt

if the proton

midrapidity

flow

using

velocity

of

pions A

of 0.7X+c and

the pion

(lambda)

+ Au

prctiictions.

the same

howcvcr

I60

and a supcr-

to the motlcl

;I radial

1n &tail

fireball

around

arc compared

can bc obscrvctl A similarly

32S a thermal

parsmctcrs spectra

distributions

is

deviate

arc fitted

simultaneously.

I. INTRODUCT’ION The sho\vn

analyci? that

:I large

trensformctl rcachcd crgy

into

in those collisions

bc ;I rathcr

mal a

pure

pansion pend fcrcnt light

dew

would

The

spectrum.

rcsuit

spccics.

Slow

of the incoming

leading

hc :I rapid woultl

motion

mo\ing

heavy

assuming par-ticlc

B.V.

This

Iargc

ways.

transverse

particlc~. the same

on the velocity This

of cn-

way

would

momcn turn with

in turn

tcmpcrature

hc mot-c affected

is

dcasity

amount One

has

cncrgy

some

of the pt spectrum

tlcpcnds

would

beam the cncrgy

(explosion)

bc a distortion

particles.

0375-9474/89/$3.50 @ Elsevier Science Publishers (North-Holland Physics Publishing Division)

[I].

in various

to thcrm:ll

of the cmittcd

obscr\al

cstimntcs

cxpanSion

of distortion

Ion cxpcrimcnts

longiturlinul

\;I~~OLIS

to

2 and 3 GcV/fm-~

The tlcgrcc

to the thermal

the SPS Heavy

can bc dcgratlctl

of particlcc

possibility

from

According

1 olumc

on the mass of the particles particle

spectra

lies hctwecn

evaporation

supcrimposcd. thcrmz1

rclntivc

cncrgy.

in 3 small

Another

motion

cncrgy

(SO 16 tcj 70%)

fraction tl-ansvcrsc

conccntratcil

tribution<.

to

of transvorsc

tlisther-

rclativc of the cxwould

for than

dc-

the diffaster

386~

The NA35 Collaboration/Search

The

pt spectra

bution

[Z].

constant

velocity)

fcaturc ting

c>f negative

In rcf [3]

to distort

(not

shown

model

isentropic gardcd

radial

and

fitr

This

expansion

as an cxtcnsinn

The

using

protons

In the following

is described.

found

with

of this radial

in a way

rccluircd

the resulting

of the mttdcl

agreement

of our from

3 since

expansion

has the

and

flow

and

velocity. radial

a

fit-

v&city

to

is found

of a more

fireball

for constant

When

the data

in tcrtns

expansion

distri(with

with

a thermal

increasing

in ref.

data

a thermal expansion

by the data.

tcmpcrature

poor

analysis

also starts

a radially

from

a radial

inclusion

a very

the

model

to deviate

superimposing

of the pions

of the n-

here).

[4]

firchall.

the pt spectrum

the pt ~~istribut~(~n

are indeed

was dcvetoped

on a thermal

the pt spectrum

calculate

pions

a model

for radial flow

recent

assumes It can

velocity

an

hc rc-

it yields

the same result.

2. EXPERIMENTAL Streamer 32S

+

Bttth

32S and

datascts

most central Au.

The

using

After

particles by their

midrapidity density.

for

Thcrc

pt(ftftns.

Since the S + S system

tiw

ncgativc

of tho ncgativc the

from

proton

prnccdurc 3 good

pions

image

trigger

collab~~ration cut

processing

(FET)

stations.

representing

the

I .6?41(Xi mb) for 0 -t

with

rcyuiring

A more &tailed

three

momentum

were

the same cxpcrimcna charged

dcscripti~~n

the dccny in the 0

of #

to be 71~.

was corrcctcd

-t Au system

charged

the visual

particle

multiplicity of the cxpcri-

identification mcthotl

has been chcckcd

particles

and assuming

a small

using

the Lund

between

the true

proton

FLOW

ANALYSIS

event

the yields

used

b~causc

and spectra

the prcjton by

of pclsi-

one

cxipcct?

is expected.

FRI’l‘lOF

of

the pt spectra

mass Km“

(version

~~~stril?Llt~t~n and the result

the

is insufficient

the pt spectra

by subtracting

generator

contami-

In the S + S system

to analyze

contamination

all charged

for.

of VCC decays

is an isctspin zero syctcm

Only

of Electron

the A0 wcrc

decay.

arc cx~~cotccl to be the same. Thus

the positive

components

assumed

we used an indirect

pt distribution.

agrcclnctlt

the particles

of the y’s from

idcntificd

track

veto

offline

to thcsc data.

Ncgativc

due to high

An

resolution

of 200 GcV/nucleon

for S -1 S and

by the NAS

rcconstructiOn

around

cross section

trigger.

stereoscopic

of heavy

find

energy

were obtained.

the analysis

and

on high

intcrsctions

in ref. 2.

can be uniquely

cfficicncy

of central

analyzed

bias

can be found

taken

a forward

we1.c obtained

a minimum

due to conversion

For they

and with

7 has been applied

setup

particlcs nation

-t Au taken

wcrc

2% (34 mb) of the total

than

mental

pictures

‘%

wcrc

p tm p data

tal setup larger

PROCEDURE

Chamber

to

This

1.6) anti

of the s~l~stl-~lcti(~n

has been found.

3. RESULTS The radius 0

OF

following

analysis

uses the p:~rasnctrization

has been set to 7.4 fm, a radius

-I- Au

datact.

For

the radial

suggcstcd

dcpcndcncc

described by pion

of the flow

in ref.

illtcrfcr~~rn~trj~ velocity

4.

The

frcczct>ut

analysis

Lhc quadratic

of the dcpcn-

The NA35 Collaboration

/Search

for radial

flow

387c

------

$ = 078,T= WI WV

-----p*Trromii ....

It strongly

dcviatcc

hcst fit nssuming

from a purely

3 thcrm:ll thcrm;~l

the best fit crht;5id

using

tcmpcraturc

parameters.

(0.8%). gcstccl

as free

Als;o shown

the model

for both

from

the

in both

rd.

4, lcaving

lint

pT tail.

Both

in both

the radial

is the rather

is the distribution high

LXSCS as can

The solid

~~~n~rk~b~e systems

in ref. 4. It urrtlcrestimatcs

low pt region.

clistributic)n distribution.

high

using

fltlw i’iow

bc SCCII from figurcc vclncity vclncity

and Lhe of O.Wc

the parametrization

fits tend

the

rcprcscnts

to undcrcstimate

sugthe

388~

The NA35

Collaboration

/Search

for radial i-low

ZOOGeV/n "Ot AU 3 A".FETTrigger

200 GeV/n Ot AU -+ R‘,FElTrigger

(i

0.25 0.5 0.75

1

1.25 1.5 1.75

2

0

0.25 0.5 0.75

1

1.25 1.5 1.75

P,(GeV/c)

P,(GeV/c)

Fiplrc 3

z0

at midr:lpitlily Au

-I-

for for

the

T2

casts

: the data rcquirc of with that

170 McV.

togcthcr

to the sccontl = 43 McV,T2

from

=

fits arc shown thcrtnal

distribution

the fixed

p:iramclcr

B stccpcr

slope

sccmy

arc less pronounced. set fits

statcmcnts and

can

(0 hc some

bc

of the pt

of the 7~ _ distribution

thcrc

at Iow and

high

may hc :I similar

as

for S +

quite

well

changes with

quite

when [2]

fitted

to a

and

Surprisingly well

with

the ngrcfs

Au

+

can

by a sin@

pt though.

On the other

colli+ms.

[S].

The hand

incrcnsing

multiplicity

3s in nuclear

and

S and 0 dc~cribctl

at low

surprising.

pt incrcasc situ:ltion

the data

deviation

the shape

pp collicions

+ Au

a

casts.

for the p + p system.

in pp is somewhat

‘central

in 0

with

in both

in S + S.

Thcrc

yicltls

dictribution points

of the n-

153 McV

cs-

In fig. 4 the same is

thermal

tcmpcraturc

assumption

the rclativc

of

200 GcV/n

the crrrrcsponding

close to ~hc data

the flow

tiplicity:

with

the n-.

is a purely

1.0 hc very

Tl

a pure with

is shown

both

tlktribution

from

-t- Au collisions.

sets ohtainctl

claw

183 McV

from

for

It seems

S and 6 the wmc

xsumption

tempcraturc

ic known

=

‘protons’

rrcc fit.For the 'protons' the same

he made

agrccmcnt

shown

is rather

The deviation flow

Also

distribution:

T1 = 7.5 McV, figures

the

momentum

at mitlr:lpitlily

,\(I

paramctcr

170 McV.

tcmpcrnturc

radia1

fiv

4

Transwrsc

0

A().

of

two tcmpcraturc

iii

01

200 GcV/n

the cliffcrcnt

the

tcmpcraturc This

from

spectrum

In fig. 2 the

shown

dktribulion

collisions.

pcctakns

with

Fiyrc

momentum

Transvcrsc

2

it

mul-

Thus

in

The NA35 Collaboration

ZOOGeV/u

P + P +

/Search

for

n-, N, > 7

389c

radial Aow

ZOOGeV/u

PtP

+

(+) - (-1. N, > 7

r $10 > El0 \ Tt t'

..,..,.........p - 0.00. T - 131uev

10

10 0

0.25

05

0.75

1.25

1.5

1.75

2

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

p, (GeV/c)

Fig ii I-C.5

We applictl

the wmc for

event gcnctxtor

procedure

reaction

200 G&/n

S +

St S 3

BS &scribed

S. ‘The

I‘CCLI~~C arc

3bovc

to cvcnts

from

the FRITIOF

shown

in t?gurcs

7 and

8.

200 GeV/n S t S -3 (+) - (-).

ri, b=O, FRITIOF

b=O, FRITIOF

7 -----p,Tfmmri

0

0.75

0.5

0.25

1

1.25

1.5

1.75

2

0

0.25

0.5

0.75

1

1.5

1.25

1.75

PT@V/c)

PT@V/c) Figure ‘l‘ransvcrsc n-

8t

simul;~tion sions.

Figure

7 rnomcntum

midrapidity of

200

tlistril~lriion from

GcVjn

S

of

X

‘l‘r;in\vcrsc

FRl7’10F

proton5

-t

simulation

S colli-

2

siwis

nicmicnlurn at

midrapidity of

ohtainctl

200

tlktribulion from

(.k\‘/n

lay subtraction

S

of

F:RI +

FIEF

S colli-

rnctl~o~l.

39oc

The

It is interesting

NA35 Collaboration/Search

for

radial Aow

to observe that in gcncral the same bchaviour

as in the S + S data is

obscrvcd. In detail the tlcviation from a thermal spectrum is less pronounced. The paramctcr set from ref. 4 gives a rcasonablc fit. For the protons again a tlisagrecment with the flow assumption is obscrvcd, whcrens a thermal spectrum with a rather low tempcrature of 115 McV gives a gootl agrecmcnt.

4. CONCLUSIONS An attempt has been ma& to analyze the pt spectra of x-- and protons (lambdas) gcncratcd in central collisions of 200 GcVjnuclcon S t S and 0 t- Au within a single motlcl assuming a thermal fireball with a superimposed radial flow. Using the original paramctcr set suggcstcd in ref. 4 a rather good agrccmcnt with the data is found. In &tail howcvcr systematic deviations arc observed: the low and high pt regions of the ontl the slope for the protons (lambdas) is too shallow. When TK- arc untlcrcstimatcd fitting the tempcraturc ancl the flow velocity to the n - spectrum the discrepancy to the proton (lambtla) spectrum hccomcs cvcn larger. The same bchav-iour as in the nuclear systems is fount1 in pp collisions at the same cncrgy. This may cast some doubt on the intcrprctation in terms of a radial flop. On the other hand it is possible to imagine cvcn in single pp collision radial flow provided there is enough cncrgy tlcnsity. The fact that the Gmilarity bctwccn pp collisions and nuclear collisions increases with multiplicity supports this point. It seems ncccssary to first undcrstand the simple pp system bcttcr before going to final conclusions about the nuclear system. With the prcscnt statistics it is not possible to tlcciclc whether the pt distribution of heavy part&s (protons and lambdas) arc simply thermal or more complex like the 71spectra. In or&r to make the analysis less dcpcndant on assumptions about the particle composition

it is tlcsirablc to have direct particlc idcnlificat ion for the protons.

REFERENCES

Cl1

I21 131 C4l CSl

NA3S Collaboration, A. Bambcrgcr ct al.: Phys.Lctt. IX4Bjl987) 271 WAX0 Collaboration, R. Albrcoht et al., Phys. Lctt. 8199(19X7)297 NA34 Collaboration, F. Corrivcau et al., Z. Phys. C 3X(19X8)15 NA3S Collaboration, W. Heck ct al., Z. Phys. C 38(198X)19 NA3S Collaboration, H. Stroebelc ct al.: Z. Phys. C 3X(198X)X9 P..I. Sicmens and J.0. Rasmussen, Phys. Rev. Lctt. 42(1979)X80 K.S. Lee and U. Ileinz, Preprint TPR-XX - 16, Inst. f. Thcoretischc Univcrsitit Rcgcnsburg, 198X, to be published H.G. Fischer, Z. Phys. C 38(lYXX)lOS

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