nucleon

NuclearPhysics A525 (1991)59c-66c North-Holland, Amsterdam

PION

AND

PROTON

H. Strobele

SPECTRA

59c

32

IN

, Fachbereich NA35

S

+

S

COLLISIONS

Physik,

AT 200

University

GeV/NUCLEON

of Frankfurt

COLLABORATION

J. Baechler *) J _ Bartke 5, H . Bialkowska I'), R. Bock') 1;) ioi 6; R. Brockmann , P. Buncic , S-1. Chase 3) , I. Derado V. Eckardt"),

J. Eschke7),

C. Favuzzi2),

,

D. Ferenc13),

B_ Fleischmann6'7), M. ;;chs6'7), M. Gazdzicki"), H.J. Gebauer"), 5) E. Gladys2 , C. Guerra , J.W. Harris3), W. Heck7), M. Hoffmann*),

1) , T. Humanic 6', s . Kabana 7', K . Kadija 13), A . Karabarbounis M. Kowalski5"'), A. Kiihmiche17), R. Keidel '), J . Kosiec7”‘), M LeVine7'14) A. Ljubicic jr.13), M. Lahanas 7j Y. Lee7) '2 )' 7; 3i 6,13) , E. Nappi , G. Odyniec s. Margetis , G. Paic 9) 1,4), A . Petridis ‘), J . Pfenniq 4),A . Pioer ' A.D. Panaqiotou H.G. Pugh3), F. Piihlhofer '), 7) , D. Rijhrich 7) , H. Rothard R. Renfordt 7) A. Sandoval Schmidt N. Schmitz

F. Posa'):

G.

Rai3)]

,

Schmoetten

16,

I. Schneider'i,EP. Seyboth , J.Seyerlein 2) , R. Stock 7) , H. Strobele 7) P. Spinelli A. Thomas7), D. Vranic13

S. Tonse3), ),

S.

W. Rauch"', 8) 8)

. Skrzypcak

Al,

,

Teitelbaum 3) ,

G. Vassi1eiadis')y.G.

Vesztergombi

IO) ,

Wenig7).

di Fisica, 1) Physics Dept., Univ. of Athens 2) Dipartimento Univ. di Bari 3) Lawrence Berkeley Lab. 4) CERN 5) Inst. of Nuclear Physics, Cracow 6) GSI Darmstadt 7) Fachbereich Physik, Univ. Frankfurt 8) Fakultat fiir Physik, Univ. Freiburg 9) Fachbereich Physik, Univ. Marburg 10) Max-Planck-Institut fur Physik, Miinchen II) Inst. of Experimental Physics, Univ. of Warsaw 12) Institute of Nuclear Studies, Warsaw 13) Rudjer Boskovic Inst., Zagreb ABSTRACT Rapidity spectra of pions and participant protons in S + S collisions at 200 GeV/nucleon are compared with N + N data. The average energy loss of the participating nucleons increases by 23% and is balanced by the energy of the final state particles, through a twofold increase of strange particle production and a similar enhancement, assumed for baryon-antibaryon pairs.

Collisions

between

gy per participating is reflected

equal

in the rapidity

0375-9474/91/$03.50 0 1991-

size

nucleon.

Elsevier

nuclei

lead

Furthermore distributions

Science Publishers B.V.

to the highest

the overall

of all particle (North-Holland)

ener-

symmetry

6Oc

H. Strijbele et al. / Pion and proton spectra in j2S + S collisions

species

and brings

of-mass

system.

in mass

and isospin

and negative complete

pions

space-

tions

are well

a well

defined

practical

in only

that

one hemisphere

and isospin-symmetric

and the resulting degrees

flux

centre-

projectile

in full target

study

into produced

both

of protons

of the c.m.s.

and pions

for a quantitative

energy

common

of the symmetry

the measurement

on all nucleons

suited

average

consequence

is the fact

information

Thus,

verse

about

A more

provides phase

space.

configura-

of baryon

particles

stopping

and trans-

of freedom.

In this paper

we report

on a study

of central

and peripheral

32

s+32 S collisions at a beam energy of 200 GeV/nucleon, and preI) sent results on protons and negatively charged particles which are compared

to p + p data

previous

measurement

exclusive

analysis

ved.

The NA35

particles tiles

selected sited

central S + S interactions is achieChamber 3) was used to detect the charged 32 in interactions of 200 GeV/nucleon S projec-

a 1.13 g/cm2

trigger

condition

most

central

2%

was

analyzed

were

the

cross sample

inelastic

cross

of this event 10 < mch

are used N-N

interactions.

effects

were

measured.

cluded

from

the analysis

energy

loss of charged

in order

particles

of negative

from

Events

100

to eliminate

the

< 10

All visible

MeV/c)

biases

due

The e+e-

particles

in full phase

characteristics

charged

with mch

onset.

(p <

and positive

total

sample 2) . The

approximates

in the target.

the II- sample

and kinematical

which

tracks

section

a set of peripheral

of the trigger

Low momentum

tracks

In addi-

trigger

ensemble,with

< 100 defines

as a reference

section of 420 events

workstations.

95% of the total

to avoid

the abundance

With

bias

part

to the sample

inelastic

of 0.3".

representing

a minimum

of single

ned by infering

events

processing

were

fragmentation

angle

from

superposition

tion

the beam

An unbiased

on film. picture

were

excluded

of 10.000

collisions

1400 GeV to be depo-

opening

of the total

selected

multiplicity These

that covered

a total

(34 mb)

low multiplicity

collisions.

than

recorded

represented

particle

Central

on digital

tion 540 events which

target. of less

to an effective

this

were

Sulphur

an energy

calorimeter

corresponding

(1.7 barn)

Together with our particles 2) an almost

of average

by requiring

in a Veto

domain

energy.

strange

Streamer

produced

with

at the same

of the neutral

space

were

ex-

to the contribu-

was determi(see below)

of JI' mesons.

Their

61c

H. Striibele et al. / Pion and proton spectra in ‘% f S collisions

decay

and possible

into Photons, was

the target,

simulated

the appropriate

corrections

Identification bias due tions

the spectral

the Kz yield the c.m.s.

were

not applied

which

in central

expected

for

ture of 160 MeV trum

is wider

tions

of other

Clearly lized,

(solid

produced

holds

particles

longitudinal

preference

in Fig.

with

a source

1, in particles the one

at a tempera-

I). The experimental

in Fig.

two than

in a single

also for

the rapidity

for longitudinal

specfireball

distribu2) . elsewhere

iK", 7i) reported energy

of respec-

corrections

charged

is compared from

2 for

hemisphere

of 5% and 0.5%

presented

pions

of about

conclusion

the incoming some

line

by a factor

The same

picture.

produced

leads to a 4) simula-

in reference

of negatively

$ c S collisions

thermally

pions

The corresponding

spectra

spectra.

on Fritiof

in the backward

interval.

distribution

produced

with

to be of the order

to the pion

the rapidity

particles

is not completely motion

in

yielding

particle

and the findings

this contamination

tively, in any rapidity

procedure

of K- and 5. Based shape

is estimated

into e + e - pairs

Carlo

of the charged

of the negative

to the presence

for

conversion

by a Monte

remaining

thermain the

comparison with N f N data particles. For a quantitative 8) 7) -ni+X andp+nn-+X were averaged appropriately

produced

P+P (open circles

32S i ‘*S -3

-

24r

Fig.

in Fig.

I

NEGATIVE

1). Pions HADRONS ,~

from

. >:P

N + N data “S

have

+ =S

3

a 10% wider PROTONS

7 r---:

:

1: Rapidity distributions of negative hadrons

Fig. 2: Rapidity distributions participating protons

of

H. Strtibele et al. / Pion and proton spectra in 32S + S collisions

62c

rapidity

distribution

The reduction attributed rather

those

rapidity

multiplicity

distribution

protons

the positive rapidities The

mass.

of all particles

were

resulting

0.2
hadron

net charge spectra.

procedure

resulting

protons,

projectile

or target

excess

of K+ over This

simulation.

bias

hemisphere

(and reflected

ted for by assuming

10.0

to account

resulting tent with in which number

to account

of 54 + 6 for

a simple straight

of negative

ses by 10% from

geometrical line

particles

of a Fritiof

are trans-

(N + N - NAK+)

are

of protons

in the backward

The cut at low pT was correc-

protons

in pT. The integral per event.

the neutrons content

picture

number by

in the hyperons. nucleons

of central

are assumed.

per interacting

This

and increased

the participating

trajectories

for The

of the proton

(y) distribution

for the net baryonic

number

in the

assignment

those which

distribution

for

only

that not all primor-

are determined

22.0 _t 2.5

out,

as nucleons

mass

production

at y=3).

a thermal

0.2 < y < 6 gives

has to be doubled

points

considerations.

the result

in the spectra:

the rapidity

The data

the

the net proton

cancel

an overestimate

for by using

by associated

Fig. 2 shows

(open circles).

causes

the

yields

in the difference.

it has to be mentioned

are contained

with

The wrong

they cancel

from

particles

present

the proton

for 0.2
Subtracting

production

already

between

To this end the

on the following

be seen.

hadron

of the parti-

assuming

are identified

those

K- mesons

into hyperons

missing.

losses.

pair

is corrected

Finally,

protons

formed

over

will

distributions. recalculated

is based

because

is irrelevant,

yield.

dial

They

i.e.

the spectra

of the negative

from baryon

primordial

pions

those

of the

negative

the difference

and pT distribution

of acceptance

spectra

distributions.

This

Protons

rapidity

are free

positive

from

particle

nucleons S + S colli-

to the shape

The mean

is

S + S collisions.

S + S system

and negative

Peripheral

regard

(not shown).

can be determined

component

of the incoming

= 98 2 5 in central

In the isospin-symmetric cipating

with

S f S collisions.

momentum

of the pions.

N + N data



central

collisions

to rescattering

resemble

from

longitudinal

to the multiple

than

sion data pion

than

of the mean

S + S collisions Thus

nucleon

3.2 in N + N to 3.5 in central

The

is consis-

the mean pair

increa-

S + S collisions.

H. Strtibele et al. / Pion and proton spectra in 32S t S collisions

As to the shape central

to N-N

The N + N data

employed

Fig. 2a. peripheral

with

agreement

from data

peripheral

peaks

at beam

and target

The more

important

This

models

dip

behaviour

In order

lisions

being

energy

However, up by mean

a good

the finding

that only

loss of the incoming regard

to their

Having

of stopped

Fig.

3 a clue

dN/dy

energy

a function

particles

x- from

p + p data.

manifest

S + S data

from

stopping

from

by the inverse

col-

We obtain

a

Also

their

we are left with

of the additional in the pions,

energy

both with

.

the pions

as recipients

of the sur-

S + S collisions

of the missing

energy.

we present

in

The ratio

for h-, Kz and A particles

the pions

(open circles)

shape

difference

as

we use the

S t S and the average

mentioned

parabolic

pair goes

NN data.

Therefore

in

particles.

per nucleon

SS with

fraction

central

loss per nucleon

in the produced

is seen

The above

of the pri-

collisions

for NN data).

particles

in central

For

total the rapidity

= 5.8 2 0.3 for central

in energy

(p + p) is shown

of rapidity.

negative

mid-rapidity,

. 5.8 = 313 2 38 GeV in central

and their

to the puzzle

of the

by all models.

the average

The enhanced

central

nucleon5

number

(S + S)/dN/dy

energy

is unchanged.

a small

thus discarded

plus

around

was obtained

approximation

comparing

of central

as a consequence

is reproduced

in

of 54

momentum

is

spectra

collisions is nearly 12 ) and RQMD 9) in the Venus 2

nucleon

of negative

10% only when transverse

of

the diffractive

in peripheral

has to be visible

the number

in

in central

The difference

collisions

the sample

of the latter

to 4.7 2 0.3 GeV for peripheral

deposition

S + S collisions. central

that

energy

simulations.

protons.

is reflected

as compared

(the latter total

found

the stopped

and p T of the observed

shape

disappear

feature

is also seen

to quantify

nucleons

reveals

is observed

loss per interacting

we compare

at the same

stem from

is manifest

but not in the Fritiof

energy

mary

This

the y-distribution

distributions

inclusive proton rapidity 9) energies . The comparison

rapidity

difference

a pronounced

flat.

with

at similar

N-N-collisions.

whereas

here

S + S collisions

multiple

where

rapidity

interactions

The spectral

S + S collisions.

in qualitative derived

of the proton

S + S collisions

63c

of A+ and

in width

of the ratio.

is

The average

H. Striibele et al. / Pion and proton spectra in 32S + S collisions

64c

dn/dy(s+s)

/ dnldy(p+p)

160IZOCE 80-

I

Fig.

3:

I

I

I

I

I

1

2

3

4

5

The ratio of the rapidity densities and N+N collisions. Lines are drawn

ratio

is 30.6 up by 12% from

leons

(54/Z = 27).

The data references manifest

for the Kz mesons 2 and

which

and K" s, respectively.

For

nent

at mid-rapidity.

This

dity

distributions

significantly.

We finally

attempt

sed by the incident contained

the same

and a relative

abundance

related

energy

the total

number

from is

is most

yields

with

relea-

the energy from diffe-

1. For the charged

hype-

as for the lambdas, number

= 4 from is assumed

x0, s from

differ

the energy

The contributions

The total

of pions

rapi-

near mid-rapidity.

quantitatively

in Tab.

promi-

the proton

loss of the nucleons

distribution

of 60%.

of II-. The additional

are taken

60 and 55 for A

(54 . 5.8 = 313 GeV)

particles.

to by assuming

Likewise number

energy

particle

are listed

rons we assume

where

nuc-

production

S + S and p + p collisions

to balance

nucleons

species

to about

is the region

strange

in the produced

rent particle

particle

the K," the enhancement

the additional

in enhanced

of the participating

strange

amount

of central

Thus

32 in central s+32s to guide the eye.

and the A particles

15. An enhanced

in the ratios,

reappears

the ratio

I

6

3 body

of kaons isospin

is

symmetry.

to equal

3 times

n decays

are accoun-

the

H. Strijbele et al. / Pion and proton spectra in 32S + S collisions

ted for by assuming number ratio

known

tion rate

from

energy

agreement

with

pairs

total. energy

take

antibaryon

pairs

production

Table

1:

Energy

in the produced

II 220

*only

pair

data goes

The result

particles

the large

a decisive

produced

as an indication along

with

in central

error

on the

to be drawn

the enhanced enhanced

S + S collisions.

of an enhanced

particles YU*

47 2 5

921

production

of di-

n**

NR*

647

37 4 24

0 T[ excess

References 1.

2. 3. 4. 5. 6. 7. 8. 9. 10. Il. 12. 13. 14. 15.

baryon-

This might

(GeV)

** only from

Note

S + S collisions.

that

an equally

good

baryon-anti-

conclusion

in central

for

shows

nucleons.

in the produced

However,

produc-

the SE enhancement.

Kfi

production

state

The

the p/i

S + S collisions

yield.

lost by the 54 incoming

to be the result with

in central

particle

contained

not allow

rate

interactions. from

of the antibaryon

in the final

of NB pairs

production

along

choice

to 37 GeV.

loss does

be understood quark

energy

N-N

from

is estimated

it is enhanced

the present

strangeness

This

contained

amounts

the number

We may

212

n/r ratio pairs

as the strange

the energy

the estimated

about

that

factor

the total

baryon

p-p data.

implies

by the same

that

the known

of nucleon-antinucleon

65C

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