The HELIOS experiment

387c

Nuclear Physics A447 (1985) 387e392c North-HoIland, Amsterdam

THEHELIOSEXPERIMENT

Hans J. SPECHT Physikalisches

Institut

der Universitat,

Heidelberg,

Germany

EXTENDED ABSTRACT Since

the forthcoming

been described presented

The experiment

five

to

the HELIOS(NA34) Collaboration

calorimeter

only

component,

with separate

an extended

has

abstract

is

Fig.

detection

spectrometer

.~1-~

.~~

a forward

l),

at

of

larger

and hadronic smaller

photons.

angles

1

--?------

/

1: Top View of the HELIOSExperiment

0375-9474/86/$03.50 0 ElsevierSciencePublishersB.V. (North-HollandPhysicsPublishingDivision)

~_

1,

a 4n-

energy,

a

and an

components

A sixth

specifically

1

hadron-

system,

muon spectrometer,

is under development.

I

of

shown in Fig.

detector

Several

real

hadron-nucleon

case

lay-out,

vertex

at sideward angles.

the

nuclear case (not shown in Fig.

om

plus

to

the

electromagnetic

spectrometer,

for

an electron

for

one2 devoted collisions;

The overall

a target

sections

electron

addition,

I

two parts,

is common to both.

hadron spectrometer in

of

nucleus-nucleus

major components:

compact forward external

consists

the other3

nucleus collisions

exist,

of

in the literature’,

in the following.

collisions, contains

experiment

previously

major for

the

388~

H.J. Specht / The Helios experiment

The first

part

of the production concern

of electrons,

lepton

is

indeed

neutrinos),

e/u

pairs the

identification,

2

the experiment

the problem of

low-mass This

of

IS devoted

to a high-accuracy

study

muons and neutrinos.

The main physical

issues

universality

(200-700

first

muon

in

MeV/cZ)

experiment

in

identification,

and accurate

vertex

charm decay,

and

low-pT

the

field

which

missing

determination

and the anomalous

leptons

combines

energy

(for

((500 FleV/c). electron

measurement

the direct

(for

identification

of open charm decays). guaranteeing

The calorimeter, wall-part

R807/808 at the ISR. uranium/liquid fulfills

for

for

allows,

lepton-

for

the

and

in its

box-

and

for

precise

first

missing

further The

uranium/ calorimeter

energy determination

investigate

decay channels, the dependence of

on the hadronic environment,

The latter

hadron-nucleus

by

semi-leptonic

to

time,

in

of a new high-granularity

containment.

in the study of

energy deposition.

hadron-nucleon

point

is

collisions,

e.g.

equally

interesting

it

of

and

is

obvious

for the nuclear case.

The forward high multitrack

electron

transition

spectrometer

capability

Hadron rejection

on

radiation

a

level

detectors

Dalitz

decays

allows

a straight-line of

a beryllium

20 mm (in

the beam direction);

detectors,

at

also

determination

is

achieved

argon calorimeter.

consisting

dE/dx

>105

on the

interpolation

to

special by

wire

combining

level:

the

with a diameter detector

system,

the

respective

intersection

installed

close

to

the

of

set

integral

and the target,

50 urn and a length at

a distance

point. serve

of

and low-mass

low field

then recognizes

target,

magnet.

a

electromagnetic

between a downstream hit

a Si-pad

chambers with

(dipole)

Photon conversions

trigger

the overall

in connection

drift

weak field

(TRD) with the high-granularity

can be vetoed

matched in accuracy

utilizes

and a calorimetrized

part of the uranium/liquid

double

energy

and lepton pair production

transverse

relevance

It allows

< 2% at 450 GeV/c)

also

reuses

followed

(U/LA),

complete

a dual purpose.

inclusive large

calorimeter

modules

(resolution

hermiticity,

modules (U/SC) developed and used before

The very forward part consists

argon

scintillator

and it

full

the uranium/scintillator

close

of

for

15 cm,

pairs

Several

of by

Si-strip

accurate

vertex

with charm decays.

The muon spectrometer

uses major components of

the previous

experiment,

but rearranged

in a more compact form.

The forward calorimeter

also

the purpose of

the necessary

serves

spectrometer spectrometer

can

be

to achieve

matched

with

an excellent

the mid- and forward rapidity 250 MeV/F to beyond the J/$1.

hadron filter.

upstream

tracks

mass resolution.

h!A3 dimuon

Tracks in the muon inside

the

electron

The acceptance

part and the whole mass regime of interest

covers (from

H.J. Specht / The Helios experiment

The nuclear this

totally

possible

part

of

the experiment emphasizes the exploratory It

new field.

for

a given

hadron-nucleus

389~

aims at

event,

collisions

(i)

and (ii)

under

nature of

measuring as many observables comparing,

identical

with

high

instrumental

as

precision,

conditions,

to

drawing

from the unique advantage of a preceding hadron programme. Calorimetry flow,

rapidity

now plays

both in terms of self-interest

a key role,

structure)

and trigger

function

(central

(energy

collision-,

high-5 particle

selection). The external identification

spectrometer

with

hodoscopes

and viewing allows

calorimeter,

(in

(15-45”),

containing

Cerenkov

detectors

and

as

ref.

well

hadron spectra identical

as

2) is replaced

by an active

A) to minimize secondary

to

vertex

the

interactions The

with

spectra

approaches. crossed

of

real

The first

drift

photons

in conjunction

is

easily this

case

hadron

spectrometer

for

magnetic

covers

the angular region

of maximum particle method, still

production

of

immediately

lepton in

front

spectrometer,

analysis

of

different

either

directly,

pointing

scan a wide

immediately

three

wire planes and two

in

the

accuracy.

The

region.

The

rapidity front

converter-wireof

electron

in asymmetric nuclear

the

external

pair.

which is of particular

It

interest

collisions.

thus

because

The third

a reuse of two arrays

remarkably good:

situated

behind

the hadron filter

loads in the hundreds, will

of

It the

is

served

of 600 NaI

U/LA calorimeter

the prohibitive

resulting

in some loss

in the calorimeter). for

central

collision

minimize load

of mass resolution foreseen events

for

wire

target

the

random

upstream tracks

in the

The acceptance

the running conditions

CERN, > 3.105

to

active

Matching to

particle

and thus not

be the major tool

by a second

from TI -t uv decays.

due to

scattering at

with proportional

may exploit

pairs.

background

becomes impossible, by multiple

with

from the R808 experiment.

to charged particle

study

“O-beam

(200 wires

and eliminate

of the photons in a special

placed

under discussion,

(each)

combinatorial

is

recognize

the best possible

of 15”-45”,

The muon spectrometer,

electron

target

single

and photon conversions,

and to investigated

movable to

in

the

and

The passive

uses a small array of 36 EGOcrystals,

second method also uses conversion chamber set-up,

subject

are

chambers for obtaining

arrangement

crystals

the

production,

correlations,

multiwire

interactions

accuracy,

in

from beam fragments.

or in a converter-method whole

high

slit

(strangeness

particle

unusual charge or mass particles.

with different detect

time-of-flight

through a narrow horizontal

to study inclusive

ET to search for long-lived

wire target

at wide angles

aerogel

the target

etc.)

versus

’ pr’

silica

(unusable)

(limited

now

of the instrument

with the 200 GeV/u can

be

accumulated

39oc

H.J. Specht / The Helios experiment

in the region thereon,

of

but

anomalous lepton

still

yielding

decreasing

pairs,

about

J/v’s

lo*

steeply

(assuming

with mass from

no

new physics

to

occur). As an approach complementary to spectrometer extend

the

rapidity

is

also

mass range

coverage

to

of

dileptons

large

P, 0 separation),

connection

with lepton pairs concept

angles,

a superconducting

very

and a further

The RICH, operated

the magnetic

field

simulations

radial

is 90’

and detector

find the optimal solution

the

be used

in

(ring-like) drift

solenoid,

a Ring

chamber, all

in a threshold occurs

chosen

sufficiently

even for

electron

prototyping

are

spectro-

radial

drift Image

arranged within

mode, presents via tracking low

(npT

the

the main

in the drift s

6

MeV) to

momenta down to the RICH

?r 40) and thereby avoid any ambiguities.

-Carlo

to

a disc-like

angles

<

to

extend

symmetric magnetic of

threshold

AT

to

target

assure rotation (yeff

by desires

an improved mass resolution

the first

Momentumanalysis

for hadron rejection.

a new electron

motivated

100 MeV/c2,

obtain

consisting

short

Cerenkov counter,

chambers;

down to to

an azimuthally

e = 12-ZS”,

box calorimeter. tool

is

(more complete event information).

foresees

meter with an acceptance chamber,

It

and to allow

(complete

The present

the muon spectrometer,

under consideration.

Detailed

presently

to this extremely challenging

being

Monte pursued

to

problem.

REFERENCES 1) H.J. Specht, in Quark Matter 1984, Proc. of the fourth Int. Conf. on Helsinki 1984, Editor Collisions, Ultrarelativistic Nucleus-Nucleus K. Kajantie, Lecture Notes in Physics 221 (19841, Springer, Heidelberg. 2) H. Gordon et al., accepted as NA34.

Proposal

P189 to

the

SPSC, CERN-SPSC/83-51 (1983);

Proposal P203 to the SPSC, CERN-SPSC/84-5\;-(1984); 3) H. Gordon et al., accepted as NA34/2. The present list of collaboration members: H. Gordon, T. Ludlam, L.H. Olsen, V. Polychronakos, D.C. Rahm, I. Stumer , C. Woody (Brookhaven); T. Akesson, H. Atherton, E. Chesi, K. Dederichs, M.J. Esten, C.W. Fabjan, M. Faessler, U. Mjornmark, F. Piuz, R. Roosen, A. Rudge, J. Schukraft, M. Seman, J.P. Vanuxem, R. Wigmans, W.J. Willis (CERN); P. Glassel, U. Goerlach, V. Kroh, A. Pfeiffer, H. Riess, J. Soltani, H.J. Specht (Heidelberg Univ); N.J. Di Giacomo, P.L. McGaughey, W.E. Sondheim, J.W. Sunier, H. van Hecke (Los Alamos National Lab. ) ; S. Almehed, R. Haglund, V. Hedberg, G. Jarlskog, S. Johansson, B. Lorstad (Lund Univ.); F. Corriveau, L.A. Hamel, C. Leroy, Y. Sirois (McGill Univ.); G. Beaudoin, J.M. Beaulieu, P. Deponmrier, H. Jeremie, L. Lessard, A. Lounis trs;t;eal Univ. I; r. Gavrilgenkov, S. Mayburov, A. Shmeleva (Moscow Lebedev Dolgoshein, Yu. Golubkov, A. Kalg;;;;:;, * ; V. Cherniatin, Sumarakov (Moscow PEI); V. V. Kantserov, P. Nevsky , - A. Yu. Tikhonov (Novosibirsk); W.E. Cleland, M. Clemen, B. Collick, M. Murray: N.A. McCubbin (Rutherford Appleton Lab.); J. Thompson (Pittsburgh Univ.);

H.J. Specht / The Helios experiment

391c

A. Gaidot, F. Gibrat, G.W. London, J.P. Pansart (Saclay CEN DPhPE); B. Erlandsson, S. Hellman, S. Nielsson, B. Sellden (Stockholm Univ.); D. Bettoni (Syracuse Univ.); 0. Benary, S. Dagan, D. Lissauer, Y. Oren (Tel Aviv Univ.); J.H. Bartley, D.H. Davis, G.J. Lush, M. McCubbin, I. Roberts, P. Trent (UniversityColl./Birkbeck).