MASK

id:) At present visitor at CERN. OCR Output

CERN Fellow.

Istituto di Fisica dell'Universit5 e Sezione INFN, Roma.

University of California, Riverside.

Istituto di Fisica de1l'Universita e Sezione INFN, Pisa, Italy.

Istituto di Fisica Sperimentale dell'Universit5 e Sezione INFN, Napoli, Italy.

Istituto di Fisica del1'Universita e Sezione INFN, Genova, Italy.

CERN, Geneva, Switzerland.

The Netherlands.

Nationaal Instituut voor Kernfysica en Hoge-Energiefysica, NIKHEF—H, Amsterdam,

1978

G E N E V A

C. Vannini , F. Visco , R. Wojslaw

M. Napolitano , G. Sanguinetti, C. Sciacca , G. Sette ,5*)

G. Chiefariu, A.N. Diddensi, E. Dragoi, G. Matthiaeé, L. Merolai,

R. Carrera , R. Castaldi , F. CeradiniM’, F. Cervelli ,

M. Battiston , M. Bozzo, P.L. Braccini, F. Carbonara~,5**)3*)

Amsterdam -CERN-Genova —NapolvL—PvLsaCollaboration1 23" S

AT THE CERN ED COLLIDER

AND OF THE TOTAL CROSS-SECTION

THE MEASUREM NT OF ELASTIC SCATTERING

2% { @5 0 sA1. pn po

.. Lt R P3 · r“%f`,;?SC00000497

gc IMIMIHIIHIMlllNlM|HMllb||Il|I

6 October 1978

spsc/P uaCERN LIBRARIES, GENEVAcmm/spsc/78-105

W cfEuaopmu 0RcAN1zAT10N mn Nucmm mzsmncu

REFERENCES AND FOOTNOTES OCR Output 24

the small-angle telescopes 22

APPENDIX D Precision of vertex reconstruction in

21elastic scattering

APPENDIX C Calculation of the angular resolution for

APPENDIX B The calibration of the elastic scattering chambers 2O

APPENDIX A Machine parameters for norma1—B crossing 18

CONCLUSIONS 16

THE SITING OF THE EXPERIMENT 16

4.5 Acceptance of the apparatus 15

4.4 Vertex reconstruction and background 14

l34.3 The drift—chamber modules of the 4W detector

4.2 The 4H detector l2

llh.l The experimental method

THE MEASUREMNT OF INELASTIC INTERACTIONS ll

l03.5 Elastic event rate and background

3.4 Event selection and t—res01uti0n

3.3 The accessible angular range

3.2 The drift chambers for elastic scattering

3.1 The elastic scattering apparatus

THE MEASUREMENT OF ELASTIC SCATTERING

THE EXPERIMENTAL PROGRAMME

INTRODUCTION

Page

CONTENTS

- 111 —

particle and particle—antiparticle cross-section at very high energy. OCR Output

permit tests of present theoretical ideas on the com on behaviour of particle

with the pp cross-section which will be measured at the ISABELLE storage rings, will

The comparison of the ip total cross-section, as measured at the CERN Collider,

particles.

rise to the leading hadrons while the gluons produce the central region inelastic

interact strongly and are left behind. The quarks then redress themselves giving

gluon interactions. In these collisions quarks go straight through while gluons

cesses which dominate hadronic interactions may be interpreted in terms of gluon

actions at a more fundamental level. It has been argued6=7) that the low pg pro

However, the ultimate aim will be to make a connection with a theory of strong inter

conveniently described, for instance, by means of a simple inelastic overlap function

will remain valid in the new energy range opened by the Collider. These ideas are

the diffractive picture of elastic scattering and the notion of geometrical scaling

model incorporating geometrical scaling“’. It is of great interest to test whether

sections are successfully correlated within the framework of a simple diffractive

In the energy range which has been explored at present, total and elastic cross

ing to Fig. lb.

forward region is expected to be in the range 14-16 GeV-2 at JE = 540 GeV, accord

be measured. The value of the logarithmic slope b of the elastic peak in the very

For these measurements outlined above, the elastic scattering process has to

tition of the extrapolation procedure of Fig. la.

ing amplitude, by the method of Coulomb interference, would moreover allow a repe

of strong interactions. An additional measurement of the real part of the scatter

convincing evidence that cross-sections rising with energy are a true characteristic

A measurement of the pp total cross-section at the Collider could thus give more

noticed from Fig. la that the extrapolation breaks down completely at high s.

energy range to a value of the order of 60 mb at fs = 540 GeV. However, it may be

go through a minimum in the ISR energy range and rise dramatically over the Collider

the pp scattering amplitude at ISR energies. The pp cross-section is predicted to

sections to Collider energies°), using results of measurements of the real part of

Figure la shows a dispersion relation extrapolation of pp and pp total cross

the ISR energy range.

cross-section over the energy range IOO S JE 5 540 GeV, an order of magnitude beyond

Collider project’will provide an opportunity to measure the antiproton-proton12)

be a general property of strong-interaction total cross—sections. The CERN ip

Intersecting Storage Rings (ISR). Later, at Fermilab, this rise has been found to

rally acknowledged to be one of the interesting experimental results from the CERN

The measurement of the rise in the proton-proton total cross-section is gene

ro: 1 * O Nu "` NinaiO= `—`—`i (3) OCR Output

16wr ne1(t=O)

ing L from Eqs. (l) and (2) leads to the expression

tude. Present extrapolationsg) indicate that pz is of the order of 10-2. Eliminat

where p is the ratio of the real to imaginary part of the forward scattering ampli

, not ·\/l + D2 LG = (2)

l6n ne1(;=0)

theorem

the total cross-section is derived by extrapolating to t = O and applying the optical

_ HE- · H6]-(C)/L »do

cross-section for elastic scattering and the differential elastic rate

where L is the machine luminosity. From the relation between the differential

Gtot = (Nel + Ninel)/L ’ (1)

respectively, the total cross—section is given by

terms of the total rate for elastic and inelastic interactions, Nel and Ninel

of lZ, without the need for a direct measurement of the machine luminosity. In

rate will permit the total cross-section to be measured to an accuracy at the level

urement of both the elastic scattering rate at small t and the inelastic interaction

Following the procedure already employed at the ISR”’, the simultaneous meas

escape detection by the large coverage system.

At the Collider, elastic scattering is confined to such small angles that it will

about 8 mrad.

charged secondaries produced in inelastic interactions at angles greater than

ii) a large coverage system of hodoscope counters and chambers will observe

the range from about 0.4 up to 4.5 mrad;

i) telescopes of small high-precision chambers will detect elastic scattering in

Js = lO0 GeV up to the maximum Collider energy by means of two sets of detectors:

We propose to measure elastic scattering and study inelastic interactions from

2. THE EXPERIMENTAL PROGRAM E

- 2

in the ISR elastic scattering experiment of Ref. ll, and it was shown to provide a OCR Output

must be smaller than 7 X lO`GeV. A resolution of this order was in fact reached3 2

is equal to the resolution is required to be less than 10%, then the t—resolution

l5 GeV". Thus if the relative variation of the cross-section in a t—interval which

as eand therefore AO/G = bAt. The numerical value of b is of the order ofbt

of t. In the region of the diffractive peak the differential cross-section goes

values of —t of about 0.5 GeV‘. Momentum analysis is needed only at larger values

easily be identified by measuring the direction of both scattered particles up to

From past experience at the ISRwe know that elastic scattering events can11)

3. THE MEASUREMENT OF ELASTIC SCATTERING

the central F quadrupole and the next D quadrupole in LSS4.

in LSS4. Hence, the Set·up has been designed around a crossing point midway between

argued that for a number of reasons it is highly desirable to locate the experiment

The siting of this experiment will be discussed in Section 5. It will be

secondaries could be studied with nearly complete coverage of the solid angle.

As a by—product, multiplicities and angular distributions of the charged

measurements at four or five different energies starting from fs z lOO GeV.

continuity with pp experiments at the ISR, we therefore propose to perform these

only if their energy dependence is carefully investigated. In order to ensure

The study of elastic scattering and total cross-section is really meaningful

Of equal importance, a measurement of 0 will also be obtained.

scattering rate and hence another independent check of the total cross-section.

at low energy (/s 5 150 GeV), will provide the absolute normalization of the elastic

The measurement of elastic scattering in the Coulomb region, feasible at least

able.

independent ways. A consistency check of the experimental data will then be avail

apparatus will be capable of measuring the total cross-section in two essentially

measuring the luminosity by means of the generalized Van der Meer method, thislo)

If electrostatic deflectors are installed in the machine for the purpose of

by a comfortable extrapolation.

inelcomplete coverage of the full solid angle, thus permitting Nto be obtained

The large detector system will observe inelastic interactions with nearly

and nel(t=O).el

t—range and down to very low values of t to allow both the determination of N

€lThe elastic scattering detectors will measure n(t) over a conveniently wide

- 3

d = 0.3 G 2 a/p, where G is the field gradient of the quadrupoles (G = l9.2 T/m OCR Output

The parameter d, which is independent of the beam momentum, is defined by

GR = @(1 - d) dR = 8LEff

SL = 0(l + o) dL = 0L€ff

a point-like interaction region, these measured quantities are given by (see Fig. 2)

drift chamber telescopes are strictly proportional to the scattering angle 0. For

L R L Rparticles. The angles Gand B, and the displacement dand d, measured with the

The left and right telescopes will determine the trajectories of both scattered

sketched in Fig. 4.

there will be four of these systems, two above and two below the beam line as

detector moves in (out) as shown in Fig. 3b. On either side of the intersection

is rigidly connected to the one containing the detector and moves out (in) when the

refined design which balances the atmospheric pressure on the pots; a dum y pot13)

beam. Our previous experience with a similar system at the ISR suggests a more

0.2 mm of steel) and to minimize the thickness of the part of the wall near the

tained. Great care will be taken to provide the pots with thin windows (0.l5 to

vertically towards the beam when, after injection, stable beam conditions are ob

or "Roman pot" a, which is sketched in Fig. 3a. Each pot will be displacedalz)

Each detector is installed within a movable section of the vacuum chamber,

quadrupoles, as shown in Fig. 2, in order to obtain a sufficiently long lever arm.

four drift chamber telescopes. These telescopes are placed behind the machine

Elastic scattering events are detected in the vertical plane with a system of

3.l The elastic scattering apparatus

sections are large.

tic scattering or for the total interaction rate measurement where the cross

Appendix A). The corresponding loss of luminosity is not serious for small-t elas

modified long straight section of the SPS suffice for a small angular spread (see

tion. Fortunately it turns out that the B values at the crossing point of an un

of the beams, which is in fact proportional to 1//E, where B is the betatron func

for elastic scattering measurement because of the excessively large angular spread

region. A low-B crossing region, which provides high luminosity, is not suitable

This requirement imposes conditions on the characteristics of the crossing

tude better at the Collider than at the ISR.

tion. Therefore the angular resolution will have to be about one order of magni

tion will then be obtained at the Collider in experiments with a similar t resolu

good rejection against the background of inelastic processes. A comparable rejec

- A

are staggered•in the four different planes. This staggering permits the OCR Outputl516)

An important feature of these drift chambers is the manner in which the cells

should be sufficient to avoid breakdown due to beam splashes.

The separation between an isolation grid and a neighbouring cell is l2 mm, which

electrons produced between drift cells will not be fed into the cells themselves.

wire used in the field-shaping net. These grids are at ground potential so that

grids have 2 mm separation between individual wires and are made of the same l00 um

drift cell, isolation grids are inserted between each drift chamber plane. The

In order to avoid the unwanted influence of a neighbouring plane on a given

shaping wires have diameters of 20 um and l00 pm, respectively.

is 2 m to provide good field uniformity. The single sense wire and the field

with a drift space of 2l mm. The separation between individual field-shaping wires

An enlarged view of a single cell is shown in Fig. Sb. The cell is 6 mm deep

drift cells.

strips which will carry the voltages that are required to properly terminate the

as close as possible to the beam. The thin wall is provided with four conducting

will be a thin wall approximately l mm thick, allowing the sensitive region to be

grids. A module is shown in Fig. 5a. The side of the module nearest the beam

in turn is composed of three drift cells. The planes are separated by isolation

A single module contains four independent drift chamber planes, each of which

nique.

by a set of eight drift chamber moduleslu) using the traditional drift-time techThe main, vertical component of the elastic scattering angle is measured

3.2 The drift chambers for elastic scattering

used as a help in tagging unwanted inelastic events.

4 The counter telescopes of the large—angle detector (Section L.2) could be

located at the end of each telescope and strobed by the RF signal of the machine.

The drift chambers will be triggered by a left-right coincidence of counters,

of the beam has its minimum.

quadrupole of the machine; that is, in the position where the vertical dimension

In this geometry, both the left- and right-arm detectors are placed near an F

. . . . : :L ·; _ tive distances are approximately the same with Leif Leif eff 24 mL R

(left) telescopes at 26 m (4.5 m) from the centre of the D (F) quadrupole the effec

terms of d. Numerically Q = 0.7l, while for the geometry of Fig. 2, with the right

momentum. The effective distances Lgff and Lgff can in turn be calculated inis the distance of the quadrupoles from the crossing point, and p is the beam

at h00 GeV/c), 2 = 3.085 m is the effective length of the quadrupoles, a = l6 m

-5

points are discussed in detail in Section 3.4. OCR Output

beyond that given by the drift-time measurement in the vertical plane. These two

The hodoscope alone would not, however, provide additional background rejection

provide a sufficient measure of the horizontal component of the scattering angle.

time resolution, should somehow prove unfeasible, then the hodoscope alone would

iment, namely adequate current division resolution without impairment of the drift

as a fall-back system. lf the one bit of undemonstrated technology in this exper

The vertical finger hodoscope can be thought of as having a subsidiary role

indistinguishable.

less than about 8 m , the resulting unclipped current division signals will be

elastically scattered p or p accompanied by a 6-ray, have a vertical separation of

lution, will help in two-particle separation, If two particles, for example an

cal finger counters (see Fig. 6c) which, although having a poorer horizontal reso

The current division read-out will be assisted by a small hodoscope of verti

required 100 um resolution of the drift time.

can be obtained from current division over a 50 mm wire without impairing the

yet demonstrated, it seems reasonable that r.m.s. resolutions of the order of l mm

ing a r.m.s. resolution of 2 mm over a full wire length of 600 mm. Although not

the drift chamber module. This technique has been shownto be capable of attain2°)

ing angle through the use of current division techniqueson the sense wires oflg)

We expect to measure the less important horizontal component of the scatter

supports, which will have to carry a load of about 80 kg.

The two wire—positioning plates are held apart by two prestressed stainless-steel

same location without the need to open the chamber or to disturb any other wire.

technique allows any wire to be removed and a new wire inserted at exactly the

crimp connectors fixed to the end of each wire17»1H) as shown in Fig. 6b. This

by a pair of precision-drilled epoxy/fibre-glass plates, through the use of special

where only the sense wires are indicated. The individual wires are held in place

A mechanical support which permits a thin wall construction is shown in Fig. 6a

sufficient.

redundancy of the planes will make this solution to the ambiguity problem quite

experiment. The low multiplicity expected in these small chambers and the high

cause small inefficient regions in the chamber, which should be avoided in this

at a pattern recognition level via the staggered wires. All other known methods

The fundamental left-right ambiguity problem of drift chambers is solved here

than 100 um in the drift-time read-out, which is adequate for our needs.

calibration. We expect to attain a r.m.s. single—wire resolution of no worsels)

resolutions of 60-65 um for nearly perpendicular tracks when care is taken with the

This type of chamber has been shown to be capable of reaching single-wire r.m.s.

chambers to be self-calibrated on the data itself, as discussed in Appendix B.

- 6

nulllllllllf OCR Output

pond to a minimum angle of 0.43 mrad.

minAt JE = l00 and 540 GeV we have the values listed in Table l, where the tcorres

The t-range covered by the S€t·up at various energies is shown in Fig. 8.

is about l20 mm for both arms.

is ll and 40 mm, for the left and the right arm, respectively, while vertically it

acceptance determines the sensitive region of the detectors, which horizontally

and $0.31 mrad in the vertical and horizontal plane, respectively. This angular

in the horizontal direction. The corresponding angular acceptance is 14.5 mrad

traverse the quadrupoles within t70 mm in the vertical direction and within i5 mm

Elastic scattering events will be accepted by the apparatus when particles

»- direction to a half height of 90 mm as sketched in Fig. 7.

these quadrupoles will have to be replaced with new ones, enlarged in the vertical

a thousand up to about 70 mm from the beam axis. The standard vacuum pipe inside

inscribed circle is 54 mm and the field gradient is constant within a few parts in

for the elastic scattering measurement. For these quadrupoles the radius of the

larger than the normal quadrupoles of the machine and are therefore well suited

which are at present installed in LSS4 (QFA4l8 and QDA4l9), have an aperture 20%

two quadrupoles on the left and right sides of the crossing point. The quadrupoles,

The maximum value of the scattering angle is determined by the aperture of the

determined directly over a more extended energy range.

energies, allowing the absolute normalization of the elastic scattering rate to be

Coulomb scattering will be feasible not only at /s 5 150 GeV but also at higher

extrapolation needed to reach the optical point. Furthermore, the measurement of

able scattering angle could be reduced to 0.2-0.3 mrad. This would reduce the

to 7 m from the centre of the beam. lf such were the case, the minimum detectzz)

to shield the chambers may permit the active area of the detectors to begin at 5

Appendix A), the use of existing scrapers and dump blocks to remove beam tails and

However, given that the SPS beam at high energy is about tl m in size (see

the beam, the minimum detectable angle is 0.43 mrad.

work. With the active region of the chambers beginning l0 mm from the centre of

and this value can be retained as the limit at which the detectors are expected to

location the aperture required by the beam during the injection is only tl0 mm 21)

of the beam pipe at the location of the elastic scattering detectors. In this

of this technique the experiment is not limited by the i2l mm vertical dimension

angles, which would otherwise remain hidden inside the beam pipe. With the use

The pot technique permits the detection of particles scattered at very small

3.3 The accessible angular range

-7..

the horizontal displacements are measured in a pair of separated chambers, not only OCR Output

from the current division in the pair of drift—chamber modules in each arm. Since

general background is provided by the measured horizontal displacements of the tracks

A subsidiary criterion to assist in selecting elastic events from among the

270 | 0.03 0.01 0.07 0.08

50 I 0.06 0.05 0.07 0.1

(GeV/c)I(mrad) (mrad) (mrad) (mrad)p I Beams §;;;é Measurement Over-all

Table 2

measurement error.

for positioning errors of the chambers. The over-all error is dominated by the

of i0.l mm is added to the intrinsic drift chamber accuracy of 10.1 mm to account

Table 2 below (details are given in Appendix C), where an additional uncertaintyurement errors. The various contributions to the error in (0L+0R)/2 are listed in

of the beams, ii) multiple scattering in the front detector and pot, and iii) meas

on this quantity is affected by i) the size of the crossing region and the spread

the effectiveness of the GL, BR constraint in selecting elastic events. The error

the vertical scattering angle 0, can be considered in order to get a feeling forLR

and Gp (see Fig. 2). The error on the quantity (9+0)/2, which is an estimate of

of inelastic processes uses the correlation between the measured vertical angles G

The main criteria for selecting elastic events from among the general background

scattered particle by two drift chambers which are separated by a distance of 3 m.

As discussed in the previous sections, the track position is measured for each ,`

3.4 Event selection and t-resolution

error on the extrapolation factor will be only 0.42.

assuming b = 16 GeV A. It the slope is measured with an accuracy of 22, then the

At /s = 540 GeV the extrapolation factor to the optical point exp (bItI) is 1.23,

540 I0.0l3 I 1.5

100 I 0.00046 I 0.05

(GeV) I (Gevf) I (GeV‘)/s I —t. I c min max

Table 1

-8

values of the t-resolution, as given by At = 2p v—t A8, are listed in Table 4. OCR Output

size of the crossing region and the angular spread of the beams. Corresponding

As a consequence, the angular resolution is mainly determined by the finite

scattering angle uncertainty is never more than lOZ.

fractional error contribution of either horizontal measurement to the over-all

Limiting the ¢ acceptance to 10% of the full azimuthal range implies that the

vertical finger counters are equally suitable in terms of necessary precision.

jection, measurements of the horizontal displacement by either current division or

ing angle. In contradistinction to the question of assistance in background re

horizontal component does not contribute appreciably to the error on the scatter

By limiting the azimuthal acceptance, the error in the determination of the

270 1 0.02 - 0.006 0.02

50 I 0.04 - 0.006 0.04

(GeV/c)[(mrad) (mrad) (mrad) (mrad)

. Beams Measurement Over-all scatt.Mlu t

Table 3

by the beam spread.

the error in 0 are listed in Table 3. The uncertainty in 0 is completely dominated

track position in the vertical direction is 10.2 mm, the various contributions to

plane for both arms. Still assuming that the error on the absolute value of the

where Leif = 24 m is the common value of the effective distance in the vertical

= d d G ( L + R)/(2L€ff) ,

expression

Ldand dR at the front detectors of the left and right telescopes, according to the

component of the scattering angle will be derived from the measured track positions

After extraction of the elastic events from the data, the main, vertical

encountered.

selecting elastic events depends in detail on the background conditions actually

the one-space-point measurement. The necessity for this additional criterion in

ing the horizontal displacements; this is because of their poorer resolution and

if only the vertical finger hodoscopes at the end of each arm are used in determin

be computed. This subsidiary criterion in background rejection is effectively lost

can the displacements be correlated, but the horizontal position of the vertex can

- g

crossing of two bunches. OCR Output

tectors will be of about 30 events/sec, which corresponds to W l0_° events at each

parameter with a statistical accuracy of 1-2%. The elastic rate seen by the de

One day of running time would be sufficient to determine the forward slope

0.5 I 0.03 I 2 >< 10

0.3 I 0.01 I 7 >< 10

0.1 I 0.005 I 5 >< 10

0.05 I 0.003 I 6 X 10

0.01 I 0.002 I 8 X 10

—t AI;E d (GeV;) I (Gevg) I vents/ ayAm

Table 5

at /§ = 540 sev.

(13 GeV_‘) for -t < 0.1 GeV; (-t > 0.1 GeV‘). These assumptions are thought t0 apply

3 X 10cmsec, a total cross-section of 65 mb, and a slope parameter of 16 GeV28 —2 `1

range A¢/2H = 0.1. The table assumes a luminosity in the normal B crossing of

is listed in Table 5. The elastic scattering detectors cover an average azimuthal

The expected number of elastic events collected in one day for different t bins

3.5 Elastic event rate and background

a factor of 2-3, due to scattering in the residual gas or to other instabilities.

the diffractive peak region. This implies that we can tolerate a beam.blow-up, by

the Coulombadequate in region and very good inThe expected 1:—res01ut:i0n is

10 106.6

10'310"

5 I1.270 I O. 10`2 10"3

10 10

10 10..9

5 I6.50 I 0. 10`° 10'“

(cev‘) (0ev‘)(GeV/c) I (mtad)Au

Table iv

.. lg ..

to make a reasonable vertex cut. OCR Output

to an accuracy at least comparable to the length of the interaction region in order

SPS with its bunched beam structure. Chambers are needed to reconstruct the vertex

at the ISR, for discrimination against beam-gas events, is not applicable to the23)

with counters. The use of time—of—flight techniques, which were highly effective

rate, this coverage should be realized with triggered chambers rather than merely

that whatever the angular coverage needed for the measurement of the total inelastic

The first of the requirements listed above, beam-beam discrimination, implies

total cross-section must be avoided or at least minimized.

a special topology but still representing a non—negligible fraction of the

/__ ii) maximum inclusiveness —— any rejection at the trigger level of events having

any appreciable loss of beam-beam events;

as beam-gas or beam—pipe interactions have to be efficiently rejected without

i) discrimination of beam-beam events —- all sources of background events such

has been designed to satisfy two basic requirements:

angles, with respect to the beam axis, that are larger than M O.5°. This set—up

and trigger counters which is capable of detecting charged secondaries produced at

Inelastic interactions will be observed by a large coverage system of chambers

4.1 The experimental method

inelastic interactions.

described in Section 3. This Section describes the measurement of the rate of

elastic and the inelastic rates. The measurement of the elastic rate has been

total interaction rate is made up of two independent contributions, which are the

of the elastic scattering rate at small t and of the total interaction rate. The

The total cross-section is basically obtained by combining the measurements

4. THE MEASUREMENT OF INELASTIC INTERACTIONS

ponding increase in the residual pressure by about one order of magnitude.

beam tails with the vacuum pipe could be tolerated if it is equivalent to a corres

background is due to beam—gas. Additional background due to interactions of the

lO`°. We therefore do not expect any problem at the trigger level if most of the

than lO'°. The corresponding left—right coincidence probability is then less than

detector (N 50 cm‘) each time a bunch passes through the intersection region is less

region. The probability of having a background particle over the full area of a

with the assumption of a residual pressure of lO`Torr of N2 in the intersection1°

Expected background from beam-gas interactions can be calculated (see Appendix A)

-

all tracks will be largely determined by the drift—time measurement, as opposed to OCR Output

tersect either 5 or l0 planes. This design is chosen so that the polar angle of

noted from Fig. ll that each particle traversing a small-angle telescope will in

The angular range covered by each of the detectors is given in Fig. 9. It can be

will be built with the same design used in the chambers of the large-angle detector.

scopes as indicated in Fig. 9. The l2O drift chambers comprising the six telescopes

the large-angle detector, each arm in turn being composed of three chamber tele

The small-angle detector is made of two symmetric arms, one on each side of

over a distance of about 20 cm.

volume. A particle emerging from the crossing region will traverse five chambers

detector will be composed of 180 drift-chamber modules in a compact l.8><0.8X 0.8 m

will be somewhat altered to accommodate differences between the ISR and SPS. The

Half of the detector is pictured. The exact configuration for the pp experiment

is shown in Fig. ll in its present configuration for the TSR experiment R—209.

The large-angle detector, covering angles from W 6° up to 90° in each hemisphere,

detector is given in Fig. l0.

detailed sketch of the large-angle detector and one element of the small-angle

angle detectors covering angles above and below 6°, respectively. A somewhat more

chamber modules described in the next section, is subdivided into large- and small

Fig. 9. The hw detector, composed of a set of small, almost identical drift

extends from M 0.5° up to 90° in each hemisphere. A schematic layout is given in

of almost hw sr. The azimuthal coverage is complete, while the polar angle coverage

The total interaction rate is measured by a detector covering a solid angle

4.2 The AW detector

from a normal beam-gas interaction is through vertex reconstruction.

to 20% of the total cross—section. The only way to distinguish this type of event

the other fragments into a rather small number of secondaries, could represent 152

icles scatters at very small angles and still travels inside the beam pipe while

ISR studieshave shown that diffractive events, where one of the incoming part25)

also implies the need for chambers in detecting certain classes of events. Previous

The criterion of maximum inclusiveness, in addition to requiring hw coverage,

masses in the region of several hundred GeV may be commonplace.

eventsfrom cosmic-ray physics suggest that isotropic decays of fireballs with2°)

range should be treated with extreme caution. For example, the well-known Centauro

that any prediction of the angular distribution of particles in this new energy

educated guesses about the over-all detection efficiency, it should be remembered

models, such as the one outlined in Section 4.5, can be used in order to make some

first of all an angular coverage as close as possible to QW sr. Although simple

The second of the requirements listed above, maximum inclusiveness, demands

figures include contributions to the over-all error from both calibration and OCR Output

2 mm are obtained in the drift and delay-line measurements, respectively. These

Under real experimental conditions, single-wire resolutions of 0.5 mm and

being negligible.

be built up by a series of similar adjacent modules, the dead space between modules

only appreciable contribution to dead space in the chambers. Planes of wires can

and provide rigidity for the module. The 8 mm thickness of the end caps is the

end caps. The end caps seal the chamber, support the wires and the delay lines,

The mechanical support for each module is completed by a pair of fibre—glass

drift cells.

providing a measure of the other coordinate for tracks through the two adjacent

seen in Fig. 13, a 3 mm diameter delay line services each pair of sense wires,

Each drift cell has a depth of ll mm and a drift space of 41 mm. As can be

between a pair of sense wires is 1.8 mm so as to avoid 1eft—right ambiguity.

of 20 um gold·plated tungsten wires in between the circuit boards. The spacing

on the circuit boards. There are four drift cells in each module with two pairs

construction the usual field-shaping wires are replaced by cathode strips printed

is shown in Fig. 12, while a cross-sectional view is given in Fig. 13. ln this

are bounded by a pair of epoxy fibre-glass printed circuit boards. A typical module

The construction of the drift chamber modules is such that the drift regions

the ISR experiment R—209.

Approximately half of these modules already exist and are at the moment in use in

different lengths along the sense wires but the same cross-sectional structure.

The entire An detector is made up of small drift—chamber moduleshavingzs)

4.3 The drift-chamber modules of the Aw detector

with a thin window, 0.5 mm thick, in front of the small-angle telescope D3.

central section is followed, on each side, by a wider normal cylinder which ends

10 m long, l2 cm in diameter, having a thin corrugated wall 0.2 mm thick. This

pose a chamber of the type sketched in Fig. 9. The central part is a cylinder,

multiple scattering which affect the accuracy of vertex reconstruction. We pro

The hn detector needs a special vacuum chamber to minimize interactions and

of the necessary 2h00 channels already exist, has performed reliably at the ISR.

and each group of 8 wires can accept up to 1Q hits. This system, for which 2000

will be re-used for this experiment. Times are digitized in bins of 1.5 nsec,

The read-out electronics being used at present in these chambers in R-209

longitudinal coordinate of the interaction point will thus be obtained.

the delay-line measurement of the chambers. A more precise determination of the

I S

section will still be possible at the 1Z level. OCR Output

is several times higher than calculated here, the measurement of the total cross

The system has a sufficient safety margin so that even if the background tate

¤_ (cm) I S l 2 |2 3 5I 7 10 25 |20 25 40

6 (deg.) I 90 10 I7 5 3I 3 2 1 I l 0.8 0.5

D0 I D1

Table 6

of 50.

D0 or D1, the reduction factor in the beam-gas background pk_ will be of the order

comparable to the size of the interaction region. For events without tracks in

Table 6, vertices reconstructed from tracks in D2 and D3 will have resolutions

a poorer vertex resolution. As calculated in Appendix D and summarized in

Events which have no tracks in D0 or D1 but only in D2 and/or D3 will have

W 0.3 X l0_‘ after the vertex cut.

for example, single-arm events are expected to have a background of the order of

a cut will reduce the beam-gas background Pk_ by a factor of around 100 so that,

cut on the vertex is determined by the size of the interaction region alone. Such

reconstruction is far smaller than the crossing region. In this case the fiducial

For events with one or more tracks in Du or D1, the uncertainty in the vertex

occur anywhere in the 100 m of the long straight section.

with the rather pessimistic assumption that detected beam-gas interactions canbgbbP/PW l/3 for single-arm events. These quantities are estimated in Appendix A

the order of Paz/Pbb M l0'$ for the left-+right—arm events, and of the order of

At the trigger level, the expected contamination due to beam-gas events is of

fractive events with secondaries in only one arm.

events with secondaries in both the left and right arms of the detector, and dif

depend strongly on the topology of the event. Two extreme cases are inelastic

ness, as discussed in Section 4.1. The amount of background contamination will

source of background, while still satisfying the requirement of maximum inclusive

The 4W detector must be capable of disentangling beam-beam events from any

4.4 Vertex reconstruction and background

the interaction region.

which is at least comparable to and generally better than that of the length of

sufficient precision to reconstruct the vertex of inelastic events to an accuracy

positional uncertainty. As will be shown in the next section, this will provide

-

detection efficiencies. OCR Output

through the chambers implies that the apparatus will not be overly sensitive to

indication that a large fraction of events will send at least two charged tracks

tant for a precise determination of the total cross-section. Furthermore, the

region, makes the acceptance essentially complete at all energies, which is impor

clusion of D2 and D3, where the resolution is comparable in size to the interaction

ance for observing at least one track even at the lowest energy. In fact, the in

resolution is far smaller than the interaction region, provides a very good accept

This simple model indicates that using Dq and D1 alone, where the vertex

99.9 I 99.6 I 100 I 99.8540 I 99.4 I 97.9 I 99.8 I 99.1(GeV)

99.9 I 99.3 I 100 I 99.6300 I 99.2 { 96.7 I 99.7 I 98.4/g

99.6 I 98.0 I 99.8 I 98.8100 | 98.3 | 94..:. | 99.2 I 96.8

2 1 I 2 2 I 2 1 I 2 2No. of tracks | 3 l | 3 2 [ 3 l | 3 2

DO + D1 D0 +D1+D2 I Dg+D1+D2+D3Detector

Table 7

secondary tracks through various combinations of detectors is given in percent.

the fraction of generated events which send at least one (at least two) charged

The results of the acceptance calculations are sumarized in Table 7, where

The ratio of normal inelastic events to diffractive events was taken equal to 3.

system of mass M, with a l/ML probability distribution.

ii) diffractive events where one of the incoming particles is excited into a

bution corresponding to a rapidity plateau;

i) normal inelastic events where secondaries are produced with an angular distri

of events:

model based on the extrapolation of ISR data was used with two different classes

acceptance of the proposed set-up for detecting inelastic events. A simplified

A Monte Carlo simulationhas been used as a crude guide to evaluate the27)

4.5 Acceptance of the apparatus

in computer time.

beam in nature, the reconstruction can stop, thus producing a considerable saving

been found so as to reconstruct the vertex and determine that the event was beam

detector D0 and proceed to the lowest D3. Once a sufficient number of tracks have

The actual reconstruction of events will start with the highest resolution

-15

tunnel at the end of 1980. Setting-up and data-taking could start in early 1981, OCR Output

We plan to have the experimental apparatus ready for installation in the SPS

nor are any modifications required in the SPS tunnel.

wide t-range. No additional magnetic elements are needed for this experiment,

section at the 1% level is feasible. Elastic scattering will be measured over a

We have shown that, at the ip Collider, a measurement of the total cross

6. CONCLUSIONS

run in parallel with UA1.

For these reasons we propose to install the experiment in LSS4, where it could

sible angle would be 4.5 mrad in LSS4.

7E = 100 GeV, and -t = 0.14 GeV2 at JE = 540 GeV. In contrast, the maximum acces

ing angle would be only 1.4 mrad. This corresponds to -t = 0.0049 GeV‘ at

Fig. 7 is assumed, with vertical aperture of t70 mm, the maximum accessible scatter

If for the vacuum chambers inside the quadrupoles a shape of the type sketched in

the left-arm detector, placed at 20 m on the left side of the F quadrupole, is 50 m.

stantial reduction of the accessible angular range. The effective distance for

scopes in LSS5 behind the additional quadrupolesfor the low—B implies a subzg)

scattering measurement. In fact the installation of the elastic scattering tele

tible with experiment UA1 and it is also rather inconvenient for the elastic28)

Taking data in LSS5 with the low-B quadrupoles switched off would be incompa

inelastic rate in this precision experiment.

which could greatly affect the final accuracy of the determination of the total

single crossing demands a relatively complicated pattern recognition procedure

same crossing of two bunches (10-152). Recognizing multiple interactions in a

with the low-B crossing produces a large multiple interaction probability in the

the forward peak rather difficult. In addition, the high luminosity associated

of Coulomb scattering impossible and the accurate determination of the shape of

seven times worse than that calculated in Section 3.4, thus making the observation

crossing is about l m. The t-resolution for elastic scattering would then become

In LSS5 the expected value of the betatron function in the vertical plane for low-8

measure the total cross-section to the 1% level, should run with normal-B crossing.

We first emphasize that it is essential that this experiment, which intends to

5. THE SITING OF THE EXPERIMENT

extrapolation.

of the data; 4w coverage should be sought irrespective of the results of any such

of magnitude beyond the energy range where it has given a reasonable representation

It must, however, be stressed that the model has been extrapolated by an order

home countries. OCR Output*) The participation of the various laboratories is subject to approval in the

background conditions in the proximity of the proton beam.

be installed as soon as possible in LSS5 near an F quadrupole in order to study

We also ask that a test be made using an existing spare pot system, which can

participating institutions

Responsibility for the construction of the detectors will be shared among the

special vacuum chambers needed for this experiment, including the pot system.

We expect that CERN will take care of the construction and installation of the

total cross—section.

lower machine energies in order to study the s-dependence of elastic scattering and

(fs = 540 GeV), a reasonable amount of time will be needed for this experiment at

While the Collider will probably run most of the time at the maximum energy

major new development of software will be required.

A large part of the AW detector exists and is operational at the ISR. No

of simple beam—gas calculations.

handle background conditions that are rather worse than those foreseen on the basis

The set—up has been designed with a sufficient safety margin to be able to

obtained with a luminosity one order of magnitude less than the nominal one.

of information on low t—elastic scattering and on the total cross-section could be

at the time when the first proton·antiproton collisions are foreseen. A great deal

..]-7

are listed in Table A1. OCR Output

Values of the size and angular spread of the beams at momenta of 50 and 270 GeV/c

H vfor i = H and V where, for normal—B crossing, B= gz 50 m_

G l I Ts. ¤· = i /E.i. i 2 wr ’ i 2 7rBi

of the betatron function B; according to the expressions

the crossing point are determined by the beam emittance E; and by the local value

The r.m.s. values of the size 0: and of the divergence GQ of the beams at

values.

where Y is the Lorentz factor. These figures correspond to two—standard-deviation

Eu/W = 20 X l0—°/Y m·rad ,

Ev/H = l0 X l0`°/Y u1·rad

horizontal (Eu) plane, are 3°»31)The numerical values of the invariant beam emittance in the vertical (EV) and

2) Size and angular spread of the beams

0.30 and 0.04, respectively.

is 4 X 10'°. We notice that in the low-B section the corresponding figures are

for 0* = 65 mb. The probability of having more than one interaction in a crossingbb

that the interaction probability at each crossing of two bunches is P= 0.9 Xl0",

Assuming there will be five circulating bunches in each beam, it is foundza)

L = 3 X 1028 cm'2 s'1

conservative value

H Vnormal—B crossing (B= B= 50 m) is about 4 X 10cms. We use the slightly

28 '2 '1

the low—B crossing, where Bu = 5 m and BU ¤ l m. The corresponding value in azg)

_The nominal value of the luminosity of the Co11ider2·3°) is 1030 cm2 $1 in

l) Luminosity

MACHINE PARAMETERS FOR NORMAL—B CROSSING

APPENDIX A

-18..

unnmnmd OCR Output

about l0 ° Torr.

the previous formula scaled up to present SPS conditions where the pressure is

dence and is only a factor of two to three higher than expected on the basis of

from the beam have shown that the particle flux approximately follows a l/r depen

Background testsmade in LSS5 with counters at distances of 3 cm to 70 cmaz)

optimistic assumption that there is no secondary interaction in the vacuum chamber.

which assumes that all secondaries are produced with pT = (pT) under the rather

TN . A F(r) = -———-————— - —-———-——— particles/cm , 20 (p > r r (cm)

Nbg pbeam 4 X 10

from the beam axis, can be estimated by means of the following formula

The flux of secondaries produced by beam-gas interactions at a distance r

P, 2: 3 X 10

straight section (M 100 m) is

The corresponding probability of interaction over the full length of the

section equal to 10’Torr of N2.1°

tributed in five bunches, and for a pressure of the residual gas in the straight

for a total number of circulating particles in each beam of 6 X 10, equally dis11

N, ¤ 3 X 10

The number of beam-gas interactions per centimetre at each crossing is

3) Beam-gas background

the length of the bunches, we assume a r.m.s. value of 25 cm.

For the longitudinal extension of the crossing region, which is determined by

tical and horizontal beam widths.

straight sections so that betatron oscillations dominate in determining both ver

This is due to the fact that the momentum compaction factor is very small in the

The horizontal width of the beam is not much larger than the vertical width.

oé (mad) I 0.0413 I 0.019G6 (mrad) I 0.031 I 0.013GH (mm) I 2.2 I 0.93¤V (mm) I 1.5 I0.66

p (sev/¤> I 50 I 270

Table Al

- lg

for the experiment, will be carried out in a similar fashion. OCR Output

The calibration of the current division read-out, although much less critical

the central region of other cells.

by the use of tracks passing near the ends of a cell under consideration, but in

implies a non—linear relationship between position and time, can be investigated

The lack of velocity saturation very near the ends of the drift cells, which

way by the more traditional track-fitting approach.

the list of unknown parameters, the xo, and vi parameters can be found in a simple0themselves without any a priori information. Once the ti's have been removed from

parameters of any wire i can be determined to high precision from the data tracks

cities of the four wires. With only a small number of such track pairs, the t

more, tg; depends weakly on the assumed velocities, namely only on ratios of velo

not depend on any Xoi (i = l,4) nor on any tn, (i = 2,4) of the four wires. Further

particular configuration of these chambers, the unknown constant parameter tg; does

by the pair of tracks crossing the four planes. With these two tracks and the

In this expression A, B, C, D are composed purely of measured drift times generated

to; = A " B(V2/V1) ‘ C(Vs/V1) ’ D(VM/V1)

cross a single drift space of each of the three wires 2, 3, and 4, it follows that

sloped tracks fall on opposite sides of sense wire l, while on the other hand both

wire configuration shown in Fig. 5a. For a pair of events where two arbitrarily

othe effects of uncertainties in xi, tui, and vi, is solved here via the particular

The traditional difficulty in drift chamber calibration, namely disentangling

from its otherwise constant value.

A second-order effect arises near the ends of the drift cells where v. can deviate

iwhere xni, tai, vare constant parameters which must be determined for each wire.

x = xoi + vi(T — toi) ,

is

The equation relating the measured drift-time T to the spatial coordinate x

calibration15—16).data itself. The chamber configuration is such as to facilitate this self

drift direction, all the parameters of the chamber will be calibrated using the

In order to obtain a r.m.s. single·wire resolution of at least l0O um in the

THE CALIBRATION OF THE ELASTIC SCATTERING CHAMBERS

APPENDIX B

- 20

O.5 mm of steel. OCR Output

Multiple scattering in the front detector was calculated for a total thickness of

a typical angle 9 = l mrad using the beam parameters as listed in Appendix A.

The numerical values quoted in the tables of Section 3.4 were calculated for

on the measured angles.

less affected by the finite size of the crossing region than is the derivation based

This last expression shows that the derivation of 8 from the displacements is

of the front detectors of the left and right arms.

where b is the average value of the distances from the centre of the quadrupoles

eff eff\.L ——~— = B + ——2—~— (y - Sz ) + (6 — 6 )/2 , La LI I R L

b

d = (dL + dR)/2. The following relation holds:

effective distance from the crossing point of the left and right arm, and

placements dL and dR is given by d/Leff, where Leff is the com on value of the

The best estimate of the true scattering angle in terms of the measured dis

sing region and of the angular spread of the beams.

in Section 3.1. This expression shows the effect of the finite size of the cros

right- and left—going beam, respectively. The quantities d and a were defined

R Laction point, while Gand Gare the angles with respect to the beam axis of the

l Iwhere yand zare the vertical and longitudinal coordinates of the actual inter

(€>L+6R>/2=9+;(yI··9zI)+T(1·¤¤)·jZ—(1+¤O ,

event the following relation holds:

L Rmeasured by the drift chamber telescopes is (G+ G)/2. For each individual

The best estimate of the true scattering angle G in terms of the angles as

CALCULATION OF THE ANGULAR RESOLUTION FOR ELASTIC SCATTERING

APPENDIX C

...21

G= il z P J 0 @2mult O°015 2Ccorr

lengths, so that

cctr OCR Outputthrough a corrugated pipe with wall thickness 0.2 mm or t= 0.012 radiation

On the other hand, for detectors D1 and D2, particles exit upstream of the chambers

Umult = 0.015 tWind};[}][) Z P 0

winness of t . = 0.034 radiation lengths, so that d

front of the detector through windows of 0.5 mm steel with a corresponding thick

angle telescope is considered. For D3, particles exit from the vacuum chamber in

The uncertainty GTin z due to multiple scattering depends on which smallult

is a typical value which in fact depends somewhat on chamber efficiencies.

where G = 0.5 m is the single-wire resolution of the chambers. The factor /2/d

[z d 0Gmeas =/2 o

error in the chambers can be expressed as

The uncertainty OTin the z-component of the vertex due to measurementaaS

responds to an average over the full azimuthal acceptance.

telescope. Since the detectors are rectangular in shape, the 6 range quoted cor

region, and d is the distance between the outermost pair of detector planes in a

The quantity L is the distance of the centre of the telescope from the interaction

D3 | l2.5 I 3 | 0.47-1.10

D2 | 4.5 | 1 \ 0.97-2.84

D; { 1.7 I 0.6 I 2.77-7.07

Detector | L d 0 rangeI l (rn) (rn) (deg-)

Table Dl

telescopes shown in Fig. 9.

Table D1 collects geometrical characteristics for the three small-angle

IN THE SMALL-ANGLE TELESCOPES

PRECISION OF VERTEX RECONSTRUCTION

APPENDIX D

..

oz (cm) | 2 3 5 I 7 ll 26 I 2l 25 110 OCR Output

c(cm) { 1 2 3 I 3 6 18 [ ll 13 2lmu

“€"‘S¤}(¤m>!2 2 416 9 19|18 21 34

0 (deg) { 7 5 3 | 3 2 1 | 1 0.8 0.5

Detector

Table D2

. G_ in quadrature.mult

all r.m.s. uncertainty 0_ in the z of the vertex is obtained by adding GTand€aS

able approximation for the momentum, Table DZ can be compiled, where the Over

Using p = 0.35/0 (GeV/c) for D; and D2, and p = 20 (GeV/c) for D3 as a reason

geometry, while b = 60 mm is the radius of the pipe.cofr

where the effective wall thickness Zt/0 is calculated for a typical corrugation

.. ...

19) W.R. Kuhlmann et al., Nuclear Instrum. Methods 40, 118 (1966). OCR Output

18) We are grateful to J. Perez and P. Queru for useful suggestions on this technique.

Rings, paper presented at the Wire Chamber Conference, Vienna (1978).F. Ceradini et al., Multiwire drift chambers for the CERN Intersecting Storage

17) G. Lecoeur, Chambres 5 fils, CERN/D.Ph.II/BT 75-08-260 (1975).

16) N.A. Filatova et al., Nuclear Instrum. Methods 143, 17 (1977).

15) E.N. Tsyganov, private communication.

G. Charpak and F. Sauli, CERN ip Note 4 (1977).14) G. Charpak et al., Nuclear Instrum. Methods 62, 262 (1968).

solution.

13) We are grateful to J.C. Godot of the ISR Division who has studied the technical

12) U. Amaldi et al., Phys. Letters 43B, 231 (1973).

11) G. Barbiellini et al., Phys. Letters 39B, 663 (1972).

10) C. Rubbia, CERN pp Note 38 (1977).

CERN-Pisa-Rome-Stony Brook Collaboration, Phys. Letters 62B, 460 (1976).

Collider", CERN/SPSC/78-ll, sPsc/1 100 (1978)."The measurement of elastic scattering and total cross-section at the pp

S. Nussinov, Phys. Rev. D 14, 246 (1976).F.E. Low, Phys. Rev. D 12, 163 (1976).

Van Hove and S. Pokorski, Nuclear Phys. B86, 243 (1975).

Henzi and P. Valin, Phys. Letters &8B, 119 (1974).Van Hove, Rev. Mod. Phys. 36, 657 (1964).

Institute, Budapest, 1977), p. 55.European Conf. on Particle Physics, Budapest, 1977 (Central ResearchWinter, Diffraction scattering at ISR energies, Invited talk given at the26, 385 (1976).

See, for example: U. Amaldi, M. Jacob and G. Matthiae, Annu. Rev. Nuclear Sci.,

U. Amaldi et al., Phys. Letters 66B, 390 (1977).

(1978).Design study of a proton—antiprot0n colliding beam facility, CERN/PS/AA 78-3

Vieweg, 1977), p. 683.Aachen, 1976 (eds. H. Faissner, H. Reithler and P. Zerwas), (Braunschweig,vector bcscns with existing accelerators, Proc. Internat. Neutrino Conf.,

C. Rubbia, P. McIntyre and D. Cline, Producing massive neutral intermediate

REFERENCES AND FOOTNOTES

-24

SPS Commissioning Report No. 59 (1977). OCR OutputBatzner, D. Coward and H. Hoffmann, Background measurement in LSS5,

32) Hoffmann, private communication.

SPS beam by scraping, SPS Improvement Report No. 114 (1978).31) Olsen, P. Sievers and A. Warman, Emittance measurement of the circulating

30) Rubbia, CERN ip Note 35 (1977).

proton—antiproton colliding beam project, CERN—SPS/AC/78-10 (1978).29) SPS-AC Groups, Beam transfers and modifications to the SPS accelerator for the

a centre—of-mass energy of 540 GeV", CERN/SPSC/78-06, SPSC/P 92 (1978)."A Aw solid angle detector for the SPS used as a proton—antiproton Collider atr- 28)

We are grateful to H.T. Sjostrand for assistance with the Monte Carlo programme.27) D. Linglin and A. Norton, CERN pp Note 17 (1977).

be published in Nuclear Instrum. Methods).paper presented at the Wire Chamber Conference, Vienna, 1978 (Proc. to

26) A. Bechini et a1., A modular drift chamber vertex detector at the CERN ISR,

25) M.G. Albrow et al., Nuclear Phys. B108, 1 (1976).

Phenomena, Tokyo, 1974 (Cosmic—Ray Laboratory, Univ. Tokyo, 1974), p. 1.24) C.M.G. Lattes et a1., Proc. Internat. Cosmic—Ray Symposium on High-Energy

23) S.R. Amendolia et al., Nuovo Cimento 17A, 735 (1973).

22) B. de Raad, private communication.

21) "The 300 GeV programme", CERN/1050 (1972), p. 19.

20) A. Fainberg et al., Nuclear Instrum. Methods 12g, 277 (1977).

-25

for small-angle elastic scattering. OCR OutputFig. Z Schematic drawing of the experimental S€t·up

GR=G(1-cz) {dR :Leff·9

dL:LeH.GG,:G(1•(1) {LL:2m L,,=42mO

Gl N

detectors

V PLANE

pointcrossmg

H PLANE

OCR OutputOCR OutputSMALL ANGLE ELASTIC SCATTERING

c) The hodoscope of vertical finger counters. OCR Output

b) The wire support pin.

is shown schematically.Fig. 6 a) The mechanical construction of a drift chamber to be inserted in a pot

Wirei 5 40 45

° 1.510.01

finger counters

Vertical

¢ 0.1·°•0.¤s

° 0.7:0.01

(dimensions in mm)

WIRE SUPPORT PIN

tight guides

Bent lucite

120mm

Thin woll• 50l’TITT\ : :1 ' ’ If--,-+-0

-.}-1-4-—r—

·- —·I 1:·I·

--»—‘— Is_]__ "`I

wiresl•- I -4-4Sense_[_ I- T

4; - 1 1 •—|———‘-"‘ 1 I" I/ { I/ ; I ’Ci"

(6 mm thick)

fiberglass

Epoxy

Steel plctes (8 mm thick)

CHAMBER MODULE

OCR OutputOCR OutputOCR OutputSKETCH OF ONE DR»FT

uu OCR Output2-U'• gS9.U Cc

Qi

$»• +¤\[QuoE EE E

----·-`, `EEE> I DQu"ET*\bIGU7

? mm

OGL "G ps

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