Detector issues for relativistic heavy ion experimentation

Nuclear Physics A461 (1987) 37s~. 390~ North.Holland, Amsterdam

37%

DETECTOR ISSUES FOR RELATIVISTIC

HEAVY ION EXPERIMENTATION

Howard GORDON Physics Department, Brookhaven New York 11973*

National Laboratory, Upton,

Several aspects of experiments usiny relativistic heavy ion beams are The problems that the current generation of light ion experidiscussed. ments would face in using gold beams are noted. A brief review of collidiny beam experiments for heavy ion beams is contrasted with requirements for SSC detectors.

1.

INTRODUCTION The interest in relativistic

heavy ion experiments has been growing as

the series of fixed target experiments the floor.

at the CERN SPS and the BNL AGS takes

The hope of studying a totally new state of matter may be reached

by the current round of experiments. mental siynatures is given.

A brief review of the typical experi-

It may be that this round of light ion experi-

ments does not find any anomalous

behavior.

Then the next step would be to

accelerate a truly heavy beam, for example, gold ions.

In the next section

of this paper, some problems are discussed that the current experiments have in this case.

Another step would be to dramatically

density by building a relativistic

heavy ion collider.

would

raise the energy

In this type of col-

lider a central rapidity plateau will be achieved which may be optimal for observing the phase transition.

A short review is given of the type of

experiments that can be designed

for such a collider.

this paper compares requirements

for detectors for this type of collider with

those needed at the Superconducting

2.

Super Collider

The last section of

(SSC).

BELLWETHER SIGNATURES OF A QUARK GLUON PLASMA A bellwether is the sheep who leads the flock on

hung.

whose neck the bell is

In the field of quark matter there are a number of signatures that

*Research supported by the U.S. Department DE-AC02076CH00016. 0375-9474/87/$03.50 @ Elsevier Science Publishes (North-Holland Physics Publishing Division)

of energy under contract NO.

B.V.

H. Gordon /Detector

376~

have been

mentjoned

state.

Eventually

totally

different

issues for relativistic heavy ion experimentation

over the years

that may signal the occurrence

when real data is available signal may leap out.

them into 3 categories.

to guide our thinking,

some

Fig. 1 lists these probes and divides

First, there are the global event parameters.

Here

C~~~E~TS

SIGNAL &CX$;;$E

of this new

INDICATORS

PARTICLE

OF TEMPERATURE,

SIZE

AND DENSITY

GLOBAL EVENT PARAMETERS

PARTICLE INTERFEROMETRY

MULTI-PARTICLE CORRELATIONS RAPiDlTYiENERGY

IN FLOW

COLOR SCREENING EFFECTS IN PLASMA DIFFERENT FROM NORMAL PAIR PRODUCTION BY VACUUM POLARIZATION

LOCAL CHARGE CORRELATIONS

PARTICLE

LONG RANGE CORREiATlONS AND MACROSCOPIC FLUCTUATIONS CHARACTERISTIC OF FIRST-ORDER PHASE TRANSITION

FLAVOR

RATIOS

CHEMICAL EQUILIBRIUM IN HOT PLASMA LARGE NUMBER OF STRANGE PARTICLES ENHANCED A/b RATIO

~~~~~~MULT’“UARK

6-QUARK AND HIGtiER CONFIGURATIONS ASSEMBLED IN THE PLASMA

DIRECT PHOTON PRODUCTION (mT=pT)

mT5

50 MeV:

5OCm,

5 500

500Sm,s mT2

COHERENT EMISSION CHARGE FLUCTUATIONS

DIRECT

EMISSION

A

READILY

FROM

Mev: HADRONIC DECAYS; COHERENT EFFECTS

3 GeV:

3 GeV:

GIVES AND

INDICATORS OF A PHASE TRANSITION

LOCAL

PENETRATING PROBES DIRECT INFORMATION FROM THE PLASMA

SOME

FROM

PLASMA

APPROACH TO EQUILIBRIUM;STRUCTURE FUNCTIONS OF QUARKS AND GLUONS CHANGE AND ARE COMPUTABLE IN PERTURBATIVE QCD

LEPTON PAIR PRODUCT ION (VIRTUAL w+oTo~-. m:=4~If++PBl

HIGH-

pT

FIGURE 1.

Experimental

by measuring energy

MEASURES PROPAGATION OF QUARKS AND GLUONS THROUGH NUCLEAR MATTER; HADRONIZATION PROPERTIES REFLECT THE “REAL SEA” OF QUARK-GLUON PLASMA

JETS

probes

in a single event the inclusive

flow in a calorimeter,

and density transition

than the ordinary into quark matter

number of strange

particles,

the plasma by measuring surrounding

for new states of matter.

event. perhaps

spectra

or

of higher temperature

Next, one looks for the phase by, for example,

Finally,

particles

the quark matter

single particle

one may see indications

measuring

one may try to measure

that can penetrate

such as direct

CERN SPS' shown in Fig. 2 has components

a large

the extent

the hadronic

or virtual

photons.

that attempt to measure

of

matter NA34 at the these three

H. Gordon /Detector

issues_for relativistic heavy ion experimentation

Active

FIGURE 2. Experimental layout of NA34 - all but external reflected about the beam line.

apsects

The uranium

of the collisions.

calorimeters

cover nearly the entire

The external

spectrometer

scintillator

spectrometer

and uranium

phase space to measure

with its time-of-flight

with the energy

and muon spectrometer

3.

CAN PRESENT

can measure

FIXED TARGET

The main difference beam is the increase increase = 26.

like Aa.

Finally,

flow.

the electron

the virtual

EXPERIMENTS

that occurs

in the average

the energy

the average multiplicity

in going from an oxygen beam to a gold One may expect this to

= 12 while for a=1.3

identification

spectrometer

while the aerogel

was designed

increase

could not.

has only 4 elements.

with the multiplicity

in the calorimeter

of sulphur

for an oxygen beam where

Perhaps the drift chambers

in it is one.

system

(197/16)I=3

amount.

still work with an order of maynitude particle

in

pair spectrometer

USE GOLD BEAMS?

Of course this also means that the average energy

For NA34 the external

flow.

counters

photons which probe the plasma.

multiplicity.

For a=l, (197/16)I

goes up by this corresponding

liquid argon

(TOF) and Cerenkov

can sample a small part of the phase space for strange particles correlation

is

beams.

of particles.

could

However

the

The TOF has only = 30 elements

The silicon detectors The calorimeters

do not work

can work provided

H. Gordon /Detector

378~

On the scintillator

the gain is lowered. the high voltage

issues for relativistic heavy ion experimentation

devices

However,

needs to be lowered.

the gains of the preamps must be lowered. encased

in hermetic

replacement. multiplicity.

containers

The electron

normally

tion just in front of the liquid

mentation

would help some aspects

this challenging

possibility

The design philosophy

are

in the liquid, this means

would not work in this increased

may work if the target

argon calorimeter,

there would be too much background

since only

Since some of the preamps

residing

spectrometer

The muon spectrometer

this is easier

on the liquid argon device,

from 7~ decays.

is in the posi-

In its normal position

In conclusion, more seg-

of NA34 cope with gold beams but probably

requires more thought.

for AGS experilnent 802, Fig. 3, was to insure that

with sulphur beams 95% of the elements

would have no more than 1 double

?

1

?

hit.2

y

SCALE WETER)

EXPERIMENT

FIGURE 3.

Experimental

Basically,

the segmentation

multiplicity, pads. is met.

layout of AGS 802.

must be larger than the square of the average

ii. For example,

One particle

the target multiplicity

fires on the average

2 pads.

By going to gold the multiplicity

So the number of pads in target multiplicity by w (6-11)2 = 100.

The wire chambers

are unambiguously

counter

has 5000

At ti=50 the 95% requirement

increases

by (197/32)a

* 6-11.

counter would have to increase

in the spectrometer,

made up of 5x2 planes x,y,u,v,w,x',y',u',v' tracks

#802

and w'.

found in 99% of the cases.

Tl-4, are each

For ?1=20 hits, the However

the performance

H. Gordon /Detector

decreases track

exponentially.

finding

issues for relativistic heavy ion experimentation

Only doubling

impossible.

the average multiplicity

There are 15 particles

beam in the TOF implying

a theoretical

are 166 actual strips of scintillator. get enough photons

out to measure

ers have a limited number of elements, The lead glass calorimeter

multiplicity

one would

multiplicities

accurately.

the neutral

energy

100 in the aerogel

individual

x0's,

there size to

it would

the Cerenkov

count-

and 32 in the gas Although

even

at low

at the highest

flow could be well measured.

Fig. 4, uses a CC0 array surrounding

and in phase 1 a time projection

s

Actually

Therefore

Similarly

the

from a sulphur

of 226.

has 256 + 64 pieces.

hope to measure

The AGS 810 experiment,

makes

These strips are of a minimum

the timing

take a new concept to make such a measurement.

section.

expected

segmentation

379c

chamber

(TPC) downstream.

the target

The track to

CCDARRAY AROUNDTARGET

FIGURE 4.

Experimental

pixel density

layout

for a sulphur

of AGS 810.

beam is 1:lOO

There have been Monte Carlo studies3 be possible density

which

if this ratio deteriorates

becomes

prohibitive,

where the pixel size is 3x4 mn2. show that pattern

to 1:lO

or even 1:4.

recognition

may

Even if this

the TPC can be moved downstream

to decrease

the

number of hits per pixel. In conclusion, demands

the use of gold beams leads to higher multiplicity

more segmentation

cases this can be achieved lower multiplicity,

in detectors

other than calorimeters.

in the context

but in most cases,

of an experiment

this requires

which

In some

designed

a new design.

for a

H. Gordon / Detector issues for relativistic heavy ion experimentation

380~

4.

DETECTOR

DESIGNS

Recently

there was a workshop

such experiments

FOR RELATIVISTIC

and estimate

be only an extremely

HEAVY ION COLLISIONS

at Brookhaven

to explore the designs

the cost of these detectors.

tiny part of all the interesting

workshop

covered,

readable

proceedings

so the interested

target.

This same arrangement

directly.

contributions

reader is encouraged

to that

to consult

Fig. 5 shows a generic detector can be used in a collider

for

Here there will

the quite

for fixed

as shown in Fig. 6.

Y=-2

/ / CALORIMETER

lOOGeV/amu

FIGURE 5. A generic calorimetry.

Basically

the central

fixed target

rapidity

fixed target environment becomes

experiment

region

showing tracking

and

(y=O) which is quite forward

is transformed

to 90° when the laboratory

in the frame

the center of mass frame.

One group in the workshop A detector

in Fig. 6.5 drift chamber

or streamer

covers the pseudo granularity of nuclear

designed

to measure

rapidity

a calorimeter

the multiplicity

tube technique. (3) interval

based experiment

There is a calorimeter InI < 2,

shown

could be made using a which

It has a rather coarse

(As, AQ,* 0.2). Also it does not need to be very deep in terms absorption

lengths.

The authors

point out that since there are so

H. Gordon /Detector

issues for relativistic heavy ion experimentation

EM-HAD.

CALORIMETER

-25q’2

-4.4~~~2 ENDCAP

2 < q < 4.4

CENTRAL

ENDCAP

URANIUM

MULi'lPLlCiTY DETECTOR

Pbl Fe

3.5XI

6hr

10x 10cm' CELLS

1

I

0

lOxlOcm* EM 20x20cm2 HADRONIC

I

1

381c

2m

-800 EM

CELLS

-200 HABCELLS Sketch of calorimeter

FIGURE 6. beams.

many particles energy

mainly

of low momentum,

is measuring

leading

particle

to the requirements the fragmentation

it would be serious

open question

was whether

multiplicity

physics

calorimeter

In that case the of the energy

if its energy were not fully measured.

the albedo

from the calorimeter

would destroy

An the

measurement.

flow characteristics

gluon plasma the concept nal spectrometer

with respect to their multiplicity

and then to probe for a signature

of a small port was introduced

in NA34. analysis

of such a spectrometer

of charged

particles

Magnetic

is provided

magnet.

Inside the field region may be a TPC which measures

tory of the track as well as dE/dx to help identify there can be a TOF counter Finally

and perhaps

a small calorimeter

and

of the quark

much like the exter-

An example

Fig. 7.

(RICH).

leaks out.

can have a large fraction

Now the events can be categorized energy

for a particle

heavy ion

on the transverse

of a few particles

of a quark or gluon.

of the fragmentation

and therefore

for colliding

the fluctuations

is small even if some of the energy

This is in contrast which

based experiment

is shown in by the small both the trajec-

the particle.

a ring imaging Cerenkov

may pick up the energy

Later

particle

lost in the port

382~

H. Gordon /Detector

issues for relativistic heavy ion experimentation

SLIT SPECTROMETER

(ml

4.0 -

I

TOF \

z F 8

I

CAL

I

35 -

DC B

3.0 -

DC+

RICH

1

B

H

2.5 20 -

BEAM

v

v

BEAM

v

-25cm

FIGURE 7. Typical ine and+aty=O.

measured

"port" spectrometer

before they decay.

for experiment

in Fig. 6, covering

Such a port may have many locations

10'

in phase

space as listed below: Average Charged Multiplicity for Au + Au Collisions

LX_

e

Special Characteristics

1.

0.2

0.2

2"-8"

2.

0.5

0.5

8O-20'

3.

0.8

20"

3&0.5O

4.

8.4

90" z"

90°+1" 9oo+45o

"Mills cross" for interferometry.

5.

1.5

10"

90?5O

6.

2.2

lo

90%70”

Single particle plus multiparticle correlations. Search for rapidity fluctuations.

H. Gordon /Detector

Another dimuons.6 pions.

group designed

a detector

First at low momenta

realized

large amounts

At 90", see Fig. 8, there

of absorber

and optimized although

to measure

muon to be identified absorber.

the energy

direction scattering

air core toroid collisions

a large amount

the angle measurement

of

so that the multiple that follows

= 70 p+p- events/hour

the energy

the area of good acceptance

Thus a

In the forward

resolution

in an

for gold and gold The mass

of the muon pair is displayed

Near Ye,, = 0 where

can

also is a

heavy ion beams.

at L = 3 x 1O26 cm-* set-' at 100 GeV/nucleon.

a ElE~e12~.

which

rlml

for colliding

The group estimated

domains.

iron toroids.

the x decay background.

..T=--

tion as a funct ion of the rapidity

dominates,

of the absorber

flow, are magnetized

degrade

This group

which tries to over-

there is a long low Z(A1) absorber/calorimeter does not overly

At higher momen-

in two kinematic

at large angles must penetrate

Dimuon experiment

of from

1 cm beam pipe so the absorber

Outside

This reduces to a minimum

---cl”‘&,;

FIGURE 8.

of muons

to mimic muons.

a detector

differently,

is a special

start very close to the collisions. calorimeter

for the detection

with the separation

X'S decay and give real muons.

these characteristics

come both of these problems,

Q,

specifically

There are two main problems

ta, pions punchthrough

383~

issues for relativistic heavy ion experimentation

resolu-

in Fig. 9.

of the muons

is for %cL 2 3.5 GeV.

For

L 2, there is a region of good resolution near the J/G (m = 3.1 GeV)

ly4 but the $ probably

would

be hard to see.

the length of the track measured lengths that the muon must travel

In this region e a /L/x0 where L is

and x0 is the total number of radiation through.

384~

H. Gordon /Detector

IRON

7,

issues for relativistic heavy ion experimentation

AIR CORE TOROI DS

TOROIDS I

a

<4c 1

6-

M,+ RESOLUTIOF %


<3 ‘0

5-Y 4-

%+ ( GeVk21 _ 3-

<20 /

-z IO

----.y

q+=o

<3*

2-

::

-\

EXCLUDED

Q

I-

IO IO -

‘.

IO <

**

3

FIGURE 9. Mass resolution at PT = 0 for dimuon spectrometer of Fiy. 8. Contours of equal percentage mP,),resolution are plotted versus dimuon rapidity and mass.

The initial complement built with essentially

of detectors

current

for RHIC looked like it could be

state of the art technology

at a cost of -

$55,000,000.

5.

COMPARISONS

WITH SSC DETECTOR

REQUIREMENTS

There may be some area of overlap ion collider detectors

in detector

and SSC detectors.

technology

between

heavy

The physics of.the SSC is quite

different: Physics Topic

Signature

High mass Z', W'

High PT leptons

Supersymmetric

Jets & missing

PT with no leptons

Jets & missing

PT with leptons

New generations

particles of heavy quarks

Leptoquarks

Jets & leptons with no missiny

Compositeness

High PT jets

PT

H. Gordon /Detector

A typical

detector

It features

comparison

Fig. 10, at the Snowmass

was sketched,

a central tracking

and muon tracking

chambers

of requirements

385~

issues for relativistic heavy ion experimentation

and electron

in magnetized

identifier,

iron sheets.

for detectors-the

in 1984.7

a deep calorimeter, Here is a table

of

SSC versus heavy ion collisions.

Heavy

-ssc

workshop

Ion Collider

(central collisions) 103/sec S+S lO*/sec Au+Au

lo* interactions/set 1.6 interactions/crossing radiation damage is a concern

Rate

103/sr all over. The average multiplicity with a 5% occupancy requires more than lo5 elements.

103/sr in jets

Particle Density

Calorimetry

Missing PT requires a deep calorimeter with no cracks, high accuracy and large dynamic range ATJ, A+ = 0.03 + number of elements = 200,000

Energy flow requires only a shallow coarse calorimeter number of elements s 10 .

Leptons

Multi TeV I(+,R-

Low mass 9.+X-

Y

All

Low PT y

p,e in TeV range Particle Identification

Low PT e,l-r,k',p,!

Trigger and Data - lo* trigger rejection Acquisition needed on line - Large amount of data/event Big offline load

Large amount of data/event Big offline load

Dead Material

Tenths of radiation length allowed

Try to minimize material to minimize conversions, scatters, etc.

Physics

Striking signatures hoped for

Interpretation

cost

= $250 million

n $55 million

Since the maximum ask whether

approaches

have application gested bicycle

for 1

particle

density

is similar

that have been suggested

in the heavy ion collider.

a way to improve the number wheel drift chamber,

for 4

in the two cases,

one may

for the SSC environment

For example,

of independent

see Fig. 11.

difficult

readouts

Normally

V. Radeka'

may

has sug-

in a tradition

each axial wire

is read

386~

H. Gordon /Detector

I

0

issues for relativistic heavy ion experimentation

I

I

I

I

4

6

I2

16

t

I

I

I

I

20

24

28

32

36

Iml

FIGURE

10.

Typical

out separately the wire. measure

detector

for the SSC.

perhaps with charge division

With proper electric

multiple

the multiple

cathode

many separate resistively

would

normally

tracks

strips sketched

Although

scale, the idea deserves H. Walenta

et al.'

rate environment

accuracy signals

With

up into

The pads are

amplifiers

this has not been implemented

have proposed

the induction

can be on a large

drift chamber

like the SSC as well as for good spatial

in Fig. 12 together

comes from measuring

chamber

tracks.

attention.

from the two nearest

prototype

segmentation.

can

However,

in Fig. 11, the wire is broken

would help resolve the high track density is outlined

the multiple

coupled so that the number of separate

along

the electronics

arrive at the wire.

not separate

pieces to improve the effective

tuned to the optimum.

the coordinate

field and pulse shaping,

hits in time as several

the second coordinate

to measure

of heavy ion collisions.

with the readout technique.

which This idea

The spatial

both the anode signal and the difference potential

have given a position

that it can even be improved

for a high

resolution

wires.

The first measurements

resolution

of the from a

o = 25 um with some hope

by a factor of up to 2.5 by using different

gases. Finally an alternative recently constructed size.

It has 128 separate

hexagonal

to the successful

by R. Bouclier anodes

array of 6 cathode

et al."

soda straw tube chambersI'

each 80 cm long and each surrounded

wires.

was

using the idea of a small cell

The position

resolution

achieved

by a was

H. Gordon /Detector

issues for relativistic heavy ion experimentation

387~

(b)

c ‘k

‘k+l

FIGURE 11. Method of improving adding cathode pads.

CI < 100 urn with a two track track event is pictured

6.

the number of pixels in a drift chamber

resolution

by

of - 500 urn. The data from a two

in Fig. 13.

CONCLUSIONS The study of heavy ion collisions

from higher energy densities, meet the challenges

is anxiously

Although

that lie ahead,

for the SSC where

We gratefully V. Radeka.

acknowledge

experiments

the individual

seem to be within the state of the art. situation

existing

a significant stimulating

awaiting

detector

experimental

are not able to elements

This is to be contrasted amount of detector conversations

data

required

with the

R&D is required.

with C. Fabjan

and

388~

H. Gordon /Detector

issues for relativistic heavy ion experimentation

The curve shows the FIGURE 12. Schematic design of the induction chamber. ratio of the difference of the potential wire signal to the anode signal versus position.

0.6 . z 0

0.4. .

0” o5 LJ 0 -0.4 -

-0.6

-1.2

.

. . . . .

. . . . . . .

-

.

. ._... . . . . . . . . . . . . . .

.

.

. .

.

. . . .

. .

.

. .

. .

. . . .

. . . . .

.

.

.

.

.

.

.

.

.

.

.

. . . . . . . .

. . . . . .

. . . . .

. .

._

. .

.

.

-

- 1.6 -1.6

I

I - 0.8

I

I 0

DISTANCE

I

I 0.8

I I.6

(cm I

FIGURE 13. A picture of a two track event as seen in the multicell drift The dots indicate the position of the sense wires, the circles the chamber. measured drift times.

H. Gordon /Detector

389c

issues for relativistic heavy ion experimentation

REFERENCES

1.

H. Gordon et al. Study of High Energy Densities over Extended Nuclear Volumes viaN=leus-Nucleus Collisions at the SPS, CERN-SPSC/84-43.

2.

0. Hansen,

3.

S. Lindenbaum, private communication and T.W. Morris, Recognition Program, BNL Informal Report (1986).

4.

RHIC Workshop on Experiments for a Relativistic Heavy Ion Collider, April 15-19, 1985 (Brookhaven National Laboratory, 1985) eds. P.E. Haustein and C.L. Woody.

5.

T. Akesson

et al. ibid., --

6.

S. Aronson

al ibid., -et -*

7.

G.J. Feldman, M.G.D. Gilchriese and J. Kirkby, Proc. of the 1984 Summer Study on the Design and Utilization of the Superconducting Super Collider, eds. R. Donaldson and J.G. Morfin (American Physical Society, 1984) p. 624.

8.

V. Radeka,

9.

E. Roderburg -et al. Paper submitted Conference.

private

private

communication. TPC TRack

pp. 49-76. pp. 171-208.

communication.

10.

D. Rust -et al. SLAC-PUB-3311 3390 (1984).

11.

R. Bouclier et al. Francisco, CKEt.

Presented 1985.

to the 1986 Vienna Wire Chamber

(1984) and E. Fernandez Gal.,

at the IEEE Nuclear

Science

SLAC-PUB

Symposium,

San