- Email: [email protected]
nucleon
NEUTRAL
STRANGE
PARTICLE
375c
PRODUCTION
IN S-S COLLISIONS
AT
200 GEV/NUCLEON
Marek Gazdzicki Institut fiir Kernphysik, Universitgt D-6000 Frankfurt/Main, W. Germany NA35
Frankfurt
COLLABORATION:
A. Bamberger R. Brockmann68': C. Favuzzi P. Freund"':
",' Gazdzicki
,J.;.
C. Guerra6),
Harris3),
J. Kosiec::), M. Kowalski'), K. Kadlja13), R. Keidel') 3) 7i M. Lahanas7, S. Margetis , E. Nappi , G. Odyniec , 1) 13) 1,4) , A. Petridis , J. Pfennig 7) , G. Paic , A.D. Panagiotou F. Posa*),
K.P. Pretzl"),
H.G. Pugh3),
F. Piihlhofer'),
G. Rai3)
A. Ranieri2),6y. Renfordt7), D. Rb;hrich7), ic, 10) K. Runqe , A. Sandoval , N. Schmitz , L.S. Schroeder 3) , io, ii) 2) Selvaggi , P. Seyboth G. , J.Seyerlein 10) , E. Skrzypcak P. Spinelli *). R. Stock4'7), H. Str6bele7), M. Tincknell 3j , L. Teitelbaum D. Vranic13),
S. Wenig7)
,
A. Thomas7'. .lO) ’
’
and :~'W~~S::~~'C'""""
1) Physics Dept., Univ. of Athens 2) Dipartimento di Fisica, Univ. di Bari 3) Lawrence Berkeley Lab. 4) CERN 5) Inst. of Nuclear Physics, Cracow 6) GSI Darmstadt 7) Fachbereich Physik, Univ. Frankfurt 8) Fakultgt fiir Physik, Univ. Freiburg, 9) Fachbereich Physik, Univ. Marburg, IO) Max-Planck-Institut fiir Physik, Miinchen 11) Inst. of Experimental Physics, Univ. of Warsaw 12) Institute of Nuclear Studies, Warsaw 13) Rudjer Boskovic Inst., Zagreb. High lity
energy
to study
teracting
properties
particles
ted during hundreds
nucleus-nucleus
stage
transverse
expect
that an increased
to a higher
change
dimension
level
of the final
From
Such
life
this point
0375-9474/89/$3.50 @ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
strongly
increa-
covering
to the characte-
It is reasonable
time and energy and
possibi-
a system,
expands,
proportional
of the system.
of equilibration
a unique
containing
densities.
of the collision
volume,
state.
offer
systems
energy
of fm3 and has a life-time
ristic
lead
of large
at high
the first
collisions
therefore of view
density result
to will in a
the production
37Gc
The NA35
of strange
particles
of the strange gas)
causes
interesting.
equilibration
times
one expects
of light
a change
hadrons
with
life-time.
suggested'
as a signature
gluon plasma
quarks
longer
of strange
of the reaction
gluon
mass
(or pions).
yield
of strangeness
volume
production
plasma
was
formation.
yields
of strange particles, in a quark gas are not very different 2,3 the
be distinguished
shorter
to be much
and gluons
the increase
of quark
or a hadron
can perhaps
of its much
times
The large
in a hadronic
in the relative
Enhancement
the equilibrium
plasma
production
particles
and hence,
Although
partide
(or the strange
strangeness
and non strange
strange
is particularly
quark
than equilibration Therefore
Collaboration/Neutral
(- 10 times)
from
the hadron
strangeness
gas because
equilibration
time1J3. In this paper collisions study
the volume
report
The data
a beam
were
placed
tions
in a magnetic
were
was dp/p
to K"
A,
S’
ii
gain
were
at the CERN
was placed
cameras
in
measured
measurement
to SPS.
8 cm upstream
equipped
registered
scanned
and for V" decays
fitted
to fulfill
(3C fit)
(1C fit).
decays
with
image
the interac-
for S interactions interactions.
these
and reconstructed uncertainty
in
for V" decay
In both
positive
decay
decay
cases
equations
and
hypotheses.
symmetry
for Kz and y's.
of
production
the fit corresponded
on the fit results,
in the V" cm system products
kinematical
and the V" fit without
and r conversion
was based
V0 decay
the exponential
cen-
of a forthcoming
= 3.6%.
fit
constraint
Three
luminous
momentum
were
vertex
identification
We
of 1.5 T and exposed
thickness
window.
subsequently
The average
The events
production.
to
.2 x 0.72 m 3 Streamer
1
to 200 GeV/n
The films
target
the V" pointing
field
of 1.18 g/cmL
on 70 mm film.
products
in S-S in order
of collision
be the subject
a 2 x
accelerated
entrance
in the sulphur
space.
will
from
of 2000 fold
The V" tracks
of the strangeness
section
obtained
target
of the chamber intensifiers
production
and analyzed
study.
of S nuclei
A sulphur
particle
are presented
of A and Kz as a function
The ii cross
statistics
Chamber4
on strange
dependence
on the yield
trality. high
data
at 200 GeV/n
The final
on isotropy
between
negative
Two methods,
law and on an uniform
V" of the
based
V" distribution
and on around
The NA35 Collaboration/Neutral strange particle
the beam volume' ). random
were
axis,
mer Chamber,
which
Results
used were
to select
of systematic
of a second
scan were
regions losses
used
377C
in the Strea('good fiducial
to correct
data
for
losses. for each V" registered
Finally rection
factor
was calculated
the detection
in the selected
according
region
a cor-
to the expression:
l/P,
w = with
in order free
production
probability,
P given
by
. B Cm) . / p(x) d3x.
P=e
act Here
E is the detection
B (m) the branching probability
density
gral
is taken
data
have
thus been
The data Monte
Carlo
estimation
decay
chain
momentum.
to be smaller by solid
been
Only
2. The inte-
and random
was
cuts)
losses
checked biases would
against due
lead
and overestimation
statistical
errors
The systematic
than statistical
lines,
For charged
losses, is the
The presented
systematic
(too soft
observables.
indicated
have
above
The possible
estimated
points.
described
of the losses
particle
point
volume'.
for systematic
of the mean multiplicity
for strange
and p(x)
modes.
V" decays.
transverse
for random
decay
at the space
'good fiducial
corrected
analysis
underestimation
mean
the
accounting
for V" charged
for V" decay
over
and for neutral
efficiency
ratio
and equal
ones
multiplicities
below
obtained
of the
are presented are
errors
for all data
to statistical
particle
to to under
ones
systematic
for
points dashed
errors
included.
The data
reported
were
under
two trigger
con-
essentially
all
ditions. a. A minimum inelastic b. A forward
bias
interactions energy
interactions, calorimeter
trigger
veto
with
('MBT') 4
.
trigger
the total
(covering
('FET') energy
being
smaller
than
being
TeV).
It essentially
1 TeV
selecting
deposited
the projectile
63 < 0.3") 6.4
selecting
"central" in the Veto
fragmentation
region
(the total beam
energy
vetoes
events
having
more
The NA3.5Collaboration/Neutra/ strange particle production
378~
than
about
Its cross reaction
5 projectile section
cross
The MBT sample rent
total
together refered
with
Fig.
particle
other
having
to in the following
The acceptances 1. These
(out of 32).
2% of the total
two subsamples with diffe5 , N+, one with multiplicities
the FET sample
tral collisions.
nucleons
to about
section.
was divided
charged
0 < N+ < 100,the
spectator
amounted
Their
These
N+ > 100. give
as peripheral,
in the y-pt
plane
of data
intermediate
are summarized
for all data
I
I
r-----
h
sets
and cenin Table
for h's and Kz are shown
are used
I
two subsamples
three different
characteristics
acceptances
I
into
.i!
I \ \ \ \ \ \ \
-----
I
samples.
-1
I I \ /) \
\
! \
:
L__-_J
-----------1
K!
1..- j I
\\
/I
//
\ \
\L_----J/
1
2
3
4
/I
5
6
Y
FIGURE 1 Acceptance in the rapidity-transverse momentum p&ane indicated by solid lines for A's (Fig. la) and KS (Fig. lb). Dashed regions follow from reflection symmetry about mid-rapidity (equal mass collision).
in
1.
The NA35 Collaboration/Neutral
The p-p data about
and 20% of Kz emitted
Y < 3, are covered obtained These
using
numbers
8, Kz yields the Fritiof
may differ
total model
is shown
charged
was calculated
where
= act
using
is
.
the mean
estimates
of the total
the S + S y and pT
to this
is plotted
topic below. as a function
multiplicity,
NN
by the dashed
to the S-S case, In the
model
and
called
in Fig-
2a-
line. NN
model,
the /! multiplicity
the formula:
act is the probability
is an effective
return
is indicated
line.
numbers
respectively7.
the p + p extrapolations
particle
of p-p data
by the dotted
We shall
prediction
The extrapolation
because
that
hemisphere,
The corresponding
are 34% and 24%,
from both
A multiplicity,
to estimate
in the backward
semi-quantitative
predictions.
of the mean
model
in S + S collisions
The average The Fritof
by the acceptance_
the Fritiof constitute
distributions
allow
on A and Kz production6
50% of A's
37%
strange particle production
, to have
A multiplicity
number
of
N-N
(1) a A in the acceptance
for p-p collisions
collisions
calculated
(0.50),
and NNN as N,,,,=
32S+S--h+X
ZOOGeV/n PRELiMlNARY
FIGURE 2 Average A (Fig. 2a) and KE (Fig. 2b) multiplicities in the acceptance versus mean total charged particle multiplicity in the three selected data samples. The black point shows the NN data. Dashed and dotted lines show Fritiof and NN model predictions, respectively. Double solid and sclid lines indicate the results of secondary interaction calculations performed for the cases of a parton gas and a hadron gas, for central S-S collisions.
32S+S-K; +X 200GeVln PRELlnlNARy
*
‘t
Y.7
5
The NA35 Collaboration/Neutral strange particle production
380~
A strong central
enhancement
of the A multiplicity
S-S collisions
in comparison
predictions8.
In Fig.
2b the average
as a function
of
Also
predictions
underestimate
collisions.
However,
yield
increases
of independent ticle
multiplicity
charged
KE yield
model
is plotted
the Fritiof
is smaller
as well
particles
and thus grows
NN
and
model
for central
S+S
than in the A
briefly
rapidity
than
discuss
The ratio
linear
below
= A
-
<“*>=A’. The first
V
.
the high
energy
density
interactions
(provided
S
- V
_ V4/3.
system
where
= -
of finding rather
thus
and we will
this behaviour. linearly
with
h production
term as shown
in primary below,
is characS
interactions,
In fact
the number
of secondary
of A's produced
fireball
in these
the strangeness approach
equili-
by
v/s
I
d
, _
1s the system
a given
cause
,
(2)
is far from
C"/(-$1"3 "l/3
V. The A yield
10
or
the number
in the static
- ‘I . P
proportional
volume
2
stages.
and therefore
2
by secondary
interactions
by these
approximately
the second
of A production
could
the standard
whereas
is given
+B'-V.
teristic
bration)
physics
of 9 models .
one can write:
B
term describes
collisions,
volume,
par-
momentum
in the interaction
the reaction
increases
+
the charged
characteristics
transverse
described
reaction with
which
hand event
that N+ is roughly
participating
3) and therefore
and mean
N+ in contradic-
on the superposition
global
are satisfactorly one concludes
of nucleons
with
based
On the other
as other
to the primordial
faster
than linearly
of all models
energy,
this facts
to the number
N-N
faster
N-N collisions.
transverse
From
the observed
the difference
to the prediction
like
Kz multiplicity
in this case
for
and Fritiof
case.
The
is observed NN
to the
small
life
volume
than in the surface
layer
3
(3)
time and P v,s is the probability
of matter
inside
(thickness
the system,
d). The dotted
line
The NA35 Collaboration/Neutral
in
Fig.
3
shows
the
the normalization hand
side
the second
of
dependence
factor
strange
given
fixed
(2) migh t
38lc
point.
The right
V2 behaviour.
overall
result
production
(31 for d = 1 fm and
by the central
(3) has an approximate
term in
by
partjcle
from secondary
0
-!----
Thus
interactions.
+--A
32S+S+Kt
+X
200 GeVln
-p +__.+ .___--_____-___---.... ......... ... .._....__._._....^.. “..^...
0.5; t
I
I
loo
200
: 0
fNz> FIGURE 3 Ratio of
FIGURE
4
Mean rapidity,
, for h's and K" rn the accep T ante as a functiog of C&It>. Dashed and dot,ted lines show Fritiof and NN model predictions.
382~
The NA35 Collaboration/Neutral strange particle
One can consider tal results:
an alternative
the observed
A and Kz multiplicities due
to a change
A population acceptance
in y-pT domain
of the A yield A yield.
central
have
could
acceptance.
This
acceptance and
in Fig.
are independent
that
the quadratic
be primarily
caused
Two simple quark-gluon
feeling processes.
which
were
.
calculated
produced hadrons NN
quark
and i?N - hn were the classical The ratio parton
gas
for a hadron
been
done
to
and/or
cases
gas and for a
in order
quarks
of different
proton
numbers
of the hadron mechanism
into
to be equal
quarks
state
approach
was
rapidity
of the fireball and number
of
or non strange equilibrium. were
considered
account.In
time evolution
(Kz) to strange
final
the parton
from
the only
was
the reac-
reactions
picture
Ini-
obtained
gas scenario
important
a better
and pion
momentum
and gluons
particle
The potentially
to get
a two-fireball
and the temperature
Light
not taken
is assumed
p-p collisions.
NN
of the pT distribution
to be in thermodynamical
strangeness
of A's
The
unlikely
or strange
(+ x).
centrality.
our
The
is highly
on transverse
A and Kz production
tion nN - AK
within
of cN+>.
of the A yield
by the observed
In the case
model.
secondary
.
assumed
As an example
momenta
We conclude
In both
The energy 11
be
the data.
of the importance
from data
particles were
tial strange the
11
would
with
have
is suggested
distributions
4, as a function
calculations,
interaction
and transverse
distribution.
gas scenario
quantitative
used
and transverse
by a broadening
model
in
our experimental
centrality
of the collision
increase
by this effect
in rapidity
agree
increase
of the total
in the experiment.
approximately
the rapidity
in
inside
change
the
all A's produced
the collision
is not observed
predictions
than linear
exclusively
A and Kz rapidities
model
a shift
with
of the
centrality,
the data
a strong
are shown
a more
of the can be
a shift
increase
are produced
Therefore
the average
increasing
that essentially
acceptance
an unusual
to explain
distributions
required.
with
then receive
to assume
y-pT
of the experimenwith
If one assumes
to occur
S-S collisions
momentum
increase
in the limited
even without
In order
one would
explanation
non-linear
of kinematics.
production
IIX - Ki?
gas scenario
is employed'.
in the freeze-out
to the corresponding
of the
ratios
in
The NA35 Collaboration/Neutral strange particle production
The resulting life-time radius.
numbers
of the system They
are indicated
gases,
respectively.
little
additional
gas
illustrates
the source
of h's and Kz were assumed
in Fig.
We see
A yield. the known
of the yield
that
1.5 times
2 for the parton
the hadron
Our naive fact'
calculated
to be equal
that such
for a the system
and hadron
fireball
calculation
383c
gives
very
for the parton
a mechanism
might
be
enhancement.
References: 1
)
2)
P.
Koch,
B. Miiller and J. Rafelski,
K. Redlich,
Z. Phys.
C27
3) T. Matsui, B. Svetitsky (1986) 2047. 4) A. Sandoval Nucl. Phys.
6) K. Jaeger
Rep.
and L.D. McLerran,
et al., Phys.
et al., Phys.
142
(1986)
167.
(1985) 633.
et al., Proc. 5th Quark A461 (1987) 465~.
5) A. Bamberger
Phys.
Lett.
Rev.
Matter
B205
Dll
Phys.
Rev.
Conf.
(Asilomar
(1988)
(1975)
D34
86)
583.
2405.
G. Gustafsson and B. Nillson-Alqvist, 7) B. Andersson, Nucl. Phys. B281 (1987) 289. 8) The version of the Fritof Monte Carlo code (Fritiof 1.6, Jetset 6.2) used here overpredicts
S.P
.
of the 7th Quark Sorensen
et al.,
Conf.
(Nordkirchen
Matter
Conf.
Z. Phys.
C38
87 ),
(Lenox (1988)
88) to be published. 3.
to be published II) J.W. Harris and the NA35 Collaboration, Proc. 7th Quark Matter Conference, 1988.
Table trigger
Nt
in
1
c[rnbl
No.of events 802
peripheral
MBT
O-100
42
1200
intermediate
MBT
> 100
160
600
344
central
FET
all
250
34
2776