Proton production from Si+Au collisions at 14.5 A-GeV

Nuclear Physics A498 (1989) 409c-414~ North-Holland, Amsterdam

PROTON PRODUCTION

FROM Si+Au COLLISIONS AT 14.5 A.GeV

Presented by M. SARABURA T 4..

ARRnIvk XLYYVl

I

) VI.

AKTRAe ‘XIXIU‘I

, Tl U.

(MIT) for the E802 collaboration.

AT.RTTRCPRb ‘:LYY”ICUUlb

Tl , U.

RPAVTSb IU YYLL.

R R ) *S.&r.

RT?.TTSa YYL 2.v

,

L. BIRSTEINb, M.A. BLOOMER’,

P.D. BONDb, C. CHASMANb, Y.Y. CHUb, B.A. COLE’, J.B. COSTALES’, H.J. CRAWFORDi, J.B. CUMMINGb, R. DEBBEb, E. DUEKb, H. ENGE’, J. ENGELAGEh, S.Y. FUNGk, D. GREINERg, L. GRODZINS”, S. GUSHUEb, H. HAMAGAKP, 0. HANSENb, P. HAUSTEINb, S. HAYASHI”?‘, S. HOMMAe, H.Z. HUANG’, Y. IKEDAf, S. KATCOFFb, S. KAUFMAN”, K. KITAMURAd, K. KURITAC, R. LANZA’, R.J. LEDOUX’, M. J. LEVINEb, P. LINDSTROMS, M. MARISCOTTI b,2, Y. MIAKEb~3, R.J. MORSE’, S. NAGAMIYA’, J. OLNESSb, C.G. PARSONSi, L.P. REMSBERGb, M. SARABURA’, A. SHORb, P. STANKUSC, S.G. STEADMAN’, G.S.F. STEPHANS”, T. SUGITATEd, M. TANAKAb, M. J. TANNENBAUMb, M. TORIKOSHI”, J.H. VAN DIJKb, F. VIDEBAEK”, P. VINCENTb, E. VULGARISi, V. VUTSADAKIS”, B. WADSWORTHi, W.A. WATSON IIIb, H.E. WEGNERb, D.S. WOODRUFF”, Y. WU”, AND W. ZAJC” a ’ ’ d e f 9 ’

Argonne National Laboratory, Argonne, IL 60439 Brookhaven National Laboratory, Upton, NY 11973 Columbia University, New York, NY 10027 and Nevis Laboratories, Irvington, NY 10533 Hiroshima University, Hiroshima 730, JAPAN Institute for Nuclear Study, University of Tokyo, Tokyo 188, JAPAN Kyushu University, Fukuoka 812, JAPAN Lawrence Berkeley Laboratory, Berkeley, CA 94720 Lawrence Livermore National Laboratory, Livermore, CA 94550 ’ Massachusetts Institute of Technology, Cambridge, MA 02139 j University of California, Space Sciences Laboratory, Berkeley, CA 94720 k University of California, Riverside, CA 92507 ’ JSPS Fellowship for Japanese Junior Scientist ’ Permanent address: Comision National de Energia Atomica, Buenos Aires, Argentina 3 On leave of absence from University of Tokyo Recent results are presented from the study of central Si+Au+p+X, Si+Au+ r*+X, and Si+Cu+p+X at 14.5 A.GeV. The distribution of protons in rapidity indicates that many target protons are found above 0.5 units. The variation of the slope parameter in rapidity is consistent with a thermal source of protons at the geometric center-of-mass rapidity. The E802 spectrometer cleanly separates protons from other particle species, and for

the first time we will present cross sections for production of protons as a function of the rapidity.

The data presented was squired

at the Brookhaven National Lab Alternating

Gradient Synchrotron for silicon projectiles incident on gold and copper targets at the energy of 14.5 AaGeV. For protons, the rapidity coverage of the ES02 spectrometer is 0.5 to 1.9 units; the projectile rapidity is 3.4 units. In this paper we will show that the proton spectra for gold and copper targets are consistent with a thermal source of protons at the geometric center-of-mass rapidity. 0375-9474/89/$3.50 @ Elsevicr Science Publishers B.V. (North-Holland Physics Publishing Division)

The E802 Collaboration/Si+Au collisions

41oc The acceptance

of the ES02 spectrometer

is large (25 msr) to allow for analysis of ‘The spectrometer

semi-inclusive spectra and iike-particie correlations.

rotates about the

target position so that we can detect particles in the angle range 5” < 0 < 58”.

There

are four sets of tracking chambers, two between the target and the magnet, and two after the magnet. Each set is composed of 10 planes of multi-wire drift chambers, configured in various orientations to allow for multi-track reconstruction. central rapidity setting (spectrometer detected in the spectrometer

For the Au target, and at the

covering 14” to 28”) the average multiplicity of events

is 2.1. High multiplicity events are rare: less than 1% of the

events have multiplicity of 6 or more. Tracks are reconstructed in the chambers, starting at the back chambers T3 and T4, projected onto the TOF wall and verified, and then projected through the magnet toward the target to get intercept positions on the front chambers Tl and T2. The track momenta are determined using the information on Tl and T2. For data presented in this paper we have gated on central collisions by measuring the multiplicity of the event using the total multiplicity array (TMA)‘.

The granularity and acceptance of the

TMA allow us to detect a large percentage of the total charged multiplicity created in each event. Only events for which the multiplicity of charged tracks was in the upper 7% of the distribution were used for this analysis. The time-of-flight wall (TOF) resolution of 100 ps allows us to cleanly separate protons from deuterons for momenta up to 5 GeV/c and protons from kaons for up to 3.8 GeV/c. A conservative estimate of the kaon contribution GeV/c; hence, no corrections

to the proton spectrum is 2% at p = 5

were made to the proton spectra.

To obtain cross sections

m

m a

% g d‘-I E 4

2

I

:) 0

m,

-

0.95

<

section vs pi. arbitrary units.

y

proton <

1

PI

m0

Fig. 1: Fit of the interval

0

1

0.5

1.05.

spectrum for Si+Au+p+X a)

I

1 2

i

j:, Ob 0

1

0.5

m,

-

central collisions in the rapidity

Invariant cross section vs ml - mo. b) Invariant

c) A - rnle- ml/T’ vs ml

mo

cross

for 1.0 < Y < 1.2. AJJ cross sections in

1.5

The E802 Collaboration/Si+Au

the yields

are corrected

reconstruction

for geometric

efficiency

been reconstructed

corrections

by hand and compared

also data have been simulated that

the reconstruction

upon momentum

to obtain

seen

corrections.

Currently,

to the cross sections. reconstructed

to the reconstructed

is = 85% and that

have

by our program,

and

tracks.

the efficiency

track

Raw data

Both

checks

is not strongly

imply

dependent

multiplicity.

in Fig.

on ml

and decay

to the tracks

and compared

efficiency

or event

As is clearly exponentially 2 129~73~ *dmldY

acceptance

are not applied

4llc

collisions

=

1 e) and b), the invariant

dm,

= A.K~~/~’

where

we obtain

pi

cross

psinB.

=

section

From

a slope 2” and an intercept

the

is found

to depend

fit to the

spectrum

A. It is a simple integration

m: dY dN -= dY

------==

=

Z”Ap(l

+

$J)e-m/T’.

otrig

Since ml

the limits

of integration

is required.

in Fig.

1 c) in which

spectrum plots

However,

may be accepted Fig. 2 shows

g

< co, some

extrapolation

cover a large percentage

the integrand

does not change

gold and copper

are mo < ml

the data

is plotted.

radically

Therefore,

from the straight

at low and high

of the integral

as can be seen

as long as the behaviour

line extrapolations

of the

at low ml

the g

as reliable. versus

targets.

rapidity

Indicated

for protons

produced

in central

collisions

on this plot is the nucleon-nucleon

of silicon

center-of-mass

with

rapidity

and the silicon-gold geometric center-of-mass (also called the 28 + 80 rapidity because in a L--J -- __11:_:-_ _.._ ______I -_-.._, on _-lJ _..-I-___ L- ~_i-_--r . ..1LL LL ~11:--_ ~~ _1~_ \ neau-on comsilon we enpecb arounu 0” goru uucreons LO mr,erac~ wren dne smcon uucreons,. Our spectrometer can see that

acceptance

a considerable

Y = 1.7, though We believe

@L for copper dY

is roughly

and 200 A.GeV

“dragged” the WA80 suggests

about

sulphur

protons

protons,

results,

because

over our acceptance Since

there

Also,

and correct

observed

collisions

measured nucleons

cannot

be compared

However, should

for reconstruction in the projectile in our acceptance

limiting

with of 60

the rapidity

the target

region

collisions,

is consistent

in central

that

are different.

are only 14 protons

of YNN, most of the protons

for gold, which

our data

in the target

we

Y = 0.5 and

At Y = 0.5, for central

nuclei.

and it was noted

the results

between

the WA80 collaboration

2. Unfortunately,

the acceptances

at 14.5 A.GeV

at Y = 0, however,

and how many are “spectators”.

reasons.

target

region

are observed

of 2.5 to 3 lower than

on gold at CERN,

considerably

g

for three

in the respective

of the target

28 protons.

up forward

of target

protons

a factor

forward

that

we integrate

are target

of nucleons

dependence

number

to the target

it is not clear how many are “participants”

that they

the numbers

does not extend

seemed

to be

directly

to

fragmentation

be similar.

Finally,

efficiencies

we obtain

and some of them are target

protons.

if

end

The E802 Collaboration /Si+Au collisions

412~

=Si+Au+p+X

-

lSi+Cu+p+X

04

0

Fig. 2:

1.5

1

R&tidity $$

f

Rapidity

f

Y 28+80

YNN

Fig. 9:

vs rapidity for central

collisions of Si+Au-+p+X Si+Cu-+p+X

-

g

vs rapidity for central

collisions of Si+Au-+p+X

@) and

(0).

and a-

Fig. 3 shows $$ for A* in the central region, where the uncertainty in s At lower rapidities the extrapolation in the intercept position so 5

@), n+ (0)

(*).

is not too large.

of the spectrum to rno introduces a large uncertainty

is poorly determined. Note $$ for ?y* is roughly the same as

for the protons, as predicted by LUND FRITIOF3

and the thermal model of Ko and Xia4.

The upper curve in Fig. 4 is the sIope parameter T’ versus Y, for the proton spectra resulting from the Si+Au collisions.

The error bars indicated are due only to statistics.

Note that the distribution is centered about the 28+80 participant center-of-mass,

suggest-

ing a hot source of protons where the silicon nucleus is fully stopped in the gold nucleus. For a thermal point source emitting particles isotropically one expects to see an “effective temperature”

which varies as the inverse cash of the rapidity: T’ = T/ cosh(Y - Yo)

The data are fit surprisingly well by this dependence. not proof of an isotropic emitting source. fit of the LUND FRITIOF &

However, the &

dependence is

The lower curve in Fig. 4 is T’ versus Y for a

proton spectra to e?“liT’.

The LUND spectrum also fits to

reasonably well. Note, however, the width of the peak is wider than the data and it

is centered on 1.75, i.e., the nucleon-nucleon rapidity YNN, and not the participant centerof-mass rapidity. Also note the experimental values of T’ are considerably higher than the LUND values. Perhaps it is not surprising that the LUND model fits so poorly to the data; after all, it relies on single-particle kinematics with no inter-nuclear cascading and our data borders on the cascade region.

Because we anticipated that LUND would do poorly, the

The E802 Collaboration /SifAu

Rapidity Fig. 4: Slope parameter and for central data is T’ = T’ zz

data

ykN

T’ vs rapidity

Si+Au+pfX

413c

collisions

for central collisions

of Si+Au+p+X

events (0). The curve which overlays

LUND

cosb~~~-1,2j and the curve superimposed

on the LUND

output

(01

the is

156 cosh(Y-1.7)’

were also compared

to the relativistic

quantum

molecular

dynamics

(RQMD) model

which includes nuclear medium effects. Refer to the contribution by H. Sorge in this volume for more details. In conclusion, the behaviour of the slope parameter as a function of rapidity is consistent with, but not proof of, an isotropically emitting thermal source centered at the geometric center-of-mass. The measured slope parameters are consistently higher than predictions by the LUND model FRITIOF.

In addition, the $$ distributions for the Au and Cu targets

indicate that many target protons are found in the rapidity region above 0.5 units, though the shape of the spectra do not strongly support the existence of a thermal source. Thanks to H. Z. Huang, who generated the LUND distribution in Fig. 4, and to H. Sorge for useful discussions. This work was supported in part by the U.S. D.O.E. under contract with ANL, BNL, Columbia University, LBL, MIT and U.C. Riverside, by NASA under contract with University of California and by the U.S.-Japan High Energy Physics collaboration treaty. REFERENCES 1) E802

collaboration,

2) H. R. Schmidt, 3) B. Andersson,

to be submitted

WA80

collaboration,

G. Gustafson,

to Nut. Z. Phys.

G. Ingelman

4) C. M. Ko, private communication.

Inst. Meth. C38

(1988)

109.

and T. Sjostrand, Phys. Rep. 97 (1983) 31.