373

MARK n ENDCAP ELECTROMAGNETIC CALORIMETERS·

G. Abrams, A. Baden, R. Birge, J. Boyer, F. Butler, G. Gidal, G. Goldhaber, J. Haggerty, D. Herrup, R. Jared, I. Juricic,

J. Kadyk, F. Kirsten, K. Lee, K. Mirk, M. Moebus, S. Olson, W. Pope, W. Schmidke, C. Sojourner, G. Trilling and D. Wood

Presented by J. Kadyk

ABSTRACT

A set of two electromagnetic calorimeters have been built and installed on the end-

caps of the Mark II detector at SLAC. One of these calorimeters was tested in a posi­

tron beam and in a pion beam to determine the optimal operating conditions and the

performance characteristics. Each endcap consists of 36 layers of aluminum proportional

tubes, interleaved with 0.5 Xo lead sheets, arranged to lie along four coordinate direc­

tions. The mechanical and electrical designs are described, and results given for the per­

formance in the positron beam. The energy resolution obtained was

o(E)/E !:::' 18%/~.

I. Introduction

The Mark II detector has undergone a major upgrade in the past 1-1/2 years to

prepare for the demanding operation at the SLC collider at SLAC, due to begin opera.­

tion near the beginning of 1987.1 AB part of this upgrade program, electromagnetic

calorimeters were designed and built at LBL for the endcap region of the Mark II, where

only two-layer shower detectors had previously existed. These endcap calorimeters

(ECC's) cover the angular region between about 15 0 and 45 0 from the beam axis, and

together with the existing liquid argon calorimeters (LAC's),2 provide electromagnetic

'Thill work was .uppor~.d in p...~ by ~h. U.S. D.p...tm.n~ or Enorgy und.. eon~raota DE-AC03-78SFlJOOG8 and DE-AC03-78SFOOSIS.

374

calorimetry over 9S% of the total solid angle.3 Although only an additional Illf 25% of

solid angle coverage is added, this ill expected to be of great importtace in the s~udy of

'lfJ decays. This is partly becaulle or the fact tht.t hermeticity haa been shown to be an

important factor in the interpretation of events, and partly because some of the more

interesting physics arises from events which concentrate in the email-angle re~on.

The principal design philO8Ophy for the EOO's were: (1) to extend EM calorimetry

beyond that of the LJ\.O's down to the smallest angle having tracking coverase with the

central drift chamber; (2) to match cloeely the energy and spatial resolutioJl of the LAC's

(IS%/~, and A9 - 4-8 mr); (3) to minimize the coet and the risks of delay,

leading naturally to a design that emphasizes known techniques.

II. Mechanical Design

A. Overall Geometry

Figure 1 is an isometric view of the Mark II detector, with some components with­

drawn or cut away for clarity. Figure 2 shows a sectional view alon~ the beam axis.

The ECC's are annular in shape, having ..pproximately .. 3 m outside diameter, 11.0.7 m

inside diameter, and an active depth of about O.S m. The design waa based upon gas

sampling calorimetry because this measurement technique ia capable of providin~ fine

resolution, projective geometry, and also the compactness needed to minimize the

amount of dead space between the LAO and ECC systems. Figure 3 exhibits the vari..

tion in radiation lengths vs. COfltt. showing that a minimum or 10 Xo is reached at an

angle of about 44· to the bean:' axis. The readout geometry was chosen to be from p~

jectively ganged sense wires of the aluminum tubes, i.e... "strip" geometry rather than

towers. This choice was made partly from the expectation of somewhat hisher costs and

375

more development for a tower geometry, and partly because a Monte Carlo study indi­

cated that the strip geometry, with four coordinate directions, performed quite ade­

quately.

B. Tube Size

The tubes are all rectangular in cr088 section with a lateral width of 15 mm chosen

to avoid significant b,ll") pileup. This is illustrated in Table I. The tube depth of 9 mm

(along shower direction) W8l!l kept 8l!I small 8l!I pOllllible (for compactness) consistent with

what was judged to be a reasonable aspect ratio for the tube crOllll section. There is

lIOme evidence that deviation from a square cross section leads to a loss in energy resolu­

tion, and a small tube depth requires more stringent mechanical tolerances to achieve

the intrinsic energy resolution. The t = 0.5 Xo sampling thickness of Pb radiator was a

compromise between cost (scaling 8l!I lit) and energy resolution (scaling &8 vi) which

W8l!l to match that of the LAC, or - l5%/~. The tube wall thickness is

0.635 mm. The tubee were made of aluminum, prepared to the various lengths needed,

and with holes prepunched in the tube wall for the g8l!l circuit.·

The space resolution for the ECC's is about 4 mm, corresponding to about 3 mr

angular resolution, better than that of the LACs which have 38 mm and 54 mm strip

widths.2

C. Projective Strip Ganging

The tubes are ganged in depth along planes parallel to the coordinate directions X,

Y, V, and V, respectively, 1IO that these planes intersect at the center of the Mark II

detector, the beam collision point (IP). Thus, a close approximation of projective

376

geometry is achieved without tower geometry.

D. Ga.nging

The ca.lorimeter readout is bllSed upon three distinct ganging segments in depth.

Proceeding from the IP outwards, the first two segments, which combine to form one

physical module of 20 layers, have X, Y, and V, V (at 4S' with respect to X, Y) coordi­

nates with tube directions oriented in this order in successive layers to measure these

directions. Thus, tubes of the same coordinate direction are ganged together, and are

interleaved in depth with the others, there being 2 Xo between layers in the same ganged

channel. The third segment is another physical module of 16 layers, and has only coor­

dinates X and Y. This scheme is summarized in Table II, which also indicates the extent

of longitudinal and lateral ganging.

E. Layer Fabrication and Module Assembly

Each of the 36 tube layers is formed from two "D"-shaped sections (69 tubes each)

and two "C"-shaped sections (53 tubes each), as shown in Fig. 4. These sections are

made from individual tubes glued together by strips of thermal curing epoxy& cured at

about 250' F for one hour in a vacuum press built for this purpose. The tubes were

then wired with 50 #lm-diameter Stablohm 800 wire, and the wire crimped under 150g

tension in a 0.8 mm stainless steel capillary tubes (200 JIm-diameter hole) molded into

fiberglllSS-loaded epoxy feedthrough insulators.6 The individual "C" and "0" sections

were checked for gain uniformity using Cd HID sources, and then these sections were fitted

together to form complete layers of tubes. Alternating layers of tubes and lead sheet

were bonded together using epoxy curing at room temperature. This is illustrated in

Fig. 5. This WllS accomplished by saturating 0.008" thick fiberglass cloth with the

377

epoxy, and using this to form the finite glue-line thickness between each lead and tube

layer. Without this, the bond would have very little strength. It was necessary to pre­

pump the epoxy to remove dissolved gases. Using this technique, about 1-1/2 layers of

the (lead plus tube) sandwich were bonded per day and allowed to cure overnight under

partial vacuum (about 10 psia). The wire centering tolerance requirement for gain uni­

formity required that all tube layers be flat to about 0.025" and this was accomplished

by measuring the layers after each gluing operation, then shimming with additional

pieces or fiberglass cloth where needed to keep the next layer within the flatness toler­

ance. The outer two covering layers of each module consisted of 1/4" aluminum plates

bonded in the same manner as described above, and these support the entire weight of

each module on the bore tube. The weight causes a shear force loading on each epoxy

interrace of about one psi, which gives a very high safety factor (l":::l 100) for rupture, and

the creep in the lead (antimony-loaded) is predicted to be negligible. Finally, the com­

pleted modules weighing almost six tons each were lifted with specially-built vacuum

pickup and transport fixtures.

F. Gas Circuit

The gas Bow path is through slots cut into the 9-mm walls at alternate ends or the

tubes (see Figs. 4 and 5). The gas inlet is on the inner radius and the outlet at the outer

radius, the gas circulating through one "C" and one "D" section in each circuit giving

two circuits per layer. The gas is fed through the back plate into the bore tube, which

acts as a manifold communicating with 72 inlets. It exits at the outer radius of each

layer and is contained by the 1/16" stainless steel gas-tight shell enclosing the entire

calorimeter, and finally exhausts through the back plate. All potential external leak

problems are a.voided with this design, and an equalized gas flow through the gas paths

378

was insured by Bow and pre88ure drop measurements as each tube layer was glued into

place. Measures were taken to prevent parallel leak paths between the bore tube and

outer shell, which would short-circuit the intended gll8 path, and tests on the completed

modules showed these leaks to be negligible.

G. Mechanical Tolerances

In order to achieve the expected ~ 18%/v'E(GeV) energy resolution at the highest

energies p088ible at SLC, it is nece88ary to limit random gain variations to about ±5%,

which will contribute an rms error of about 1% to 17(E)/E. This WIl8 done by control

and monitoring of three mechanical parameters to insure the following tolerances:

(I) Tube inner narrow dimension: ±O.OO4"

(2) Sense wire diameter: ±I%(0.002")

(3) Wire centering in tube: ±0.025".

These mechanica.l tolerances were both mell8ured and calcula.ted, with consistent results.

The fabrica.tion was held to these tolera.nces by: (1) measuring the tube size with a.

strain-gauge feeler device pulled through the tube (sampling every 10th tube); (2)

measuring the wire resistance over a - 3 foot span; (3) measuring the Jlataeu of each

glued layer, and shimming when necessary (as discu88ed ea.rlier).

The "C" and "D" sections were individually checked for gain uniformity using

Cd 1lKl sources. Figure 611. shows a typical puise height distribution for Od10ll, and Fig. 6b

shows the response of a tube in which an Fe&& gain monitoring source has been

implanted. Gain determinations with Od10ll were precise to better than 1%. Figure 7

shows the distribution of gains for 30 "0" sections, found by fitting the Od10ll peaks.

379

III. Monitoring and Control of Gain

In addition to the mechanical control of gain variations just discuB5ed, temperature

and barometric pre55ure must be controlled and monitored. Gain varies with p, the gas

density, due to temperature and pre55ure changes:

AG = _ Ct Ap ~ _ 5 Ap . G P P P

The ECC's are both surrounded by heat shields kept at constant temperature. Thermis­

tors are encapsulated within the modules as a means of monitoring changes of temper..

ture (to - 0.1 0 C) and temperature gradient within each ECC. There are also sensitive

pressure transducers across each ECC and a precision barometer as part of the inform..

tion readout. Finally, there are 14 Fe66 button sources (0.3 pC) glued into various tube

walls of each ECC, and these specific channels will be monitored to use the Fe" peak for

a direct observation of gas gain (for example, see Fig. 6b).

IV. Electronics7

Figure 8 illustrates the components of each signal channel. The signal cables are

typically 3 m long and are brought out through a gas seal in the back plate (see Figs. 4

and 5). These 0.1" diameter coaxial cables carry both HV and signal to the electronics

crates mounted on the endcap doors. There are a total of 1276 electronic chIJ-nnels for

each endcap. Each channel consists of several tubes ganged together, laterally and in

depth (see Table II). The number of tubes varies from 2 to 24 per gang. Different chan­

nels will sample different fractions of the total shower energy, depending both on the

number of ganged tubes and the location of those tubes. This requires amplifiers of two

different gains and llubsequent equalization of the channel gains when the total energy is

380

summed. The ganged channels feed into charge-sensitive preamplifiers driving shaper­

amplifiers. The output travels via about 25 m of twisted pair to SHAMS (sample-and­

hold modules) read out by BADC's (l2-bit ADC's which can digitize and process up to

608 analog channels) via CAMAC.8 The preamplifiers and shaping amplifiers are cali­

brated by injecting charge into the front end under CAMAC control. A fast sum signal

is taken from the shaping amplifiers to form an independent trigger based on an analog

sum of the total ECC energy in the first two sections. The gain of the preamplifiers and

shaping amplifiers is determined by the gas avalanche gain and the need to measure the

energy of 50-GeV electrons without saturation. The maximum charge which can be

mell8ured by the two gain types are 200 and 400 pC. However, saturation within the

calorimeter already requires the gas gain be low enough 80 that these limits are not

exceeded. The 12 bit capacity of the BADC's is just enough to accommodate the

dynamic range between a muon signal and a 5O-GeV shower in the amplifier with the

largest dynamic range. For example, this places the muon signal in channel 4, well above

noise, and the maximum shower pulse at about channel 2000, with another factor of two

for possible shifts in operating point.

V. Performance

A. Beam Tests

One ECC was tested in beams at SLAC: first in an e+ beam of 3, 5, 10, and IS

GeV, and later in a 1r- beam at energies of 2, 4, and 8 GeV. Results are presently avail­

able only for the e+ data. The ECC was oriented to simulate particles produced at the

IP traveling in a straight line at an angle e with respect to the beam line and. striking

the ECC. The results presented here are based upon an analysis of the e+ test-beam

381

data.o

The positron beam at SLAC ("beam 19") is essentially pure e+, and has a very

small emittance (- 1 mm spot size) and momentum spread (~ - ±t%l The beam

intensity could be increased to obtain several e+ per beam-pulee, with a very short pume

« 30 liS rms). Hence beam pulees with several e+ could be used to simulate energy

deposits in exceee of the beam energy. Figure 9 shows an example of the ECC total

energy spectrum obtained. By fitting these peaks to find the mean value and width, and

subtracting the pedestal value, tbe energy resolution and linearity of reeponse to energy

deposit wae determined. This wae done for five gae mixtures, and the beet voltage and

resolution found for each. The degree of saturation was found to depend only on the

gain and not upon the gas. The resolution, corrected for saturation, generally described

a shallow minimum with respect to HV, and was nearly the same at the minimum for all

gases, C7(E)/~ t:::::1 18%, except one (93% A:r + 4% CRt + 3% CO2), which gave

C7(E)/~ t:::::1 20%. Saturation was about a factor of two worse than expected: at a

gas gain of about 25,000, the deviation from linearity is about 10% at 50 GeV. An illus­

tration of how the linearity changes witb voltage for Ar(5O%) + C2Hs(5O%) is seen in

Fig. 10, and a plot of saturation for all g88es is shown in Fig. 11. The variation of reso­

lution with voltage for the five gases can be seen in Figs. 12a through 12e, and a similar

plot vs. gain can be seen in Fig. 13. Within errors, the response and energy resolution

both appear to be constant with respect to the angle of incidence for e+ from the IP hav­

ing e = 20 0 40 ° where the shower is fully contained. _

As a result of these beam tests, the gas Ar(89%) + COi10%) + CH4(1 %) W88

cbosen, since it appears to give as good resolution as any other gas, is non-flammable,

and bas a higher gain than most gases, allowing a lower operating voltage. A1eo, it can

382

be obtained at much higher prell5ure than, for example, Ar(50%) + C2H6(50%), allowing

a running period about three times longer than for the latter gas.

The results from the lI'- beam test are not yet analyzed.

B. Performance in the Mark II Detector

There have been BOme data collected from colliding beams at PEP, as well as

cosmic ray eventa. A tracking algorithm is used which searches for local maxima in

pulse height in each coordinate of the /rOfll section, and then (X,Y) and (U,V) intersec­

tions are found corresponding to these maxima. If these intel'8ection points lie within ±1

tube width, then this determines .. point on a "class AU track. Lower class tracks

fulfilling leBB stringent requirements are also determined. Other intersections are located

in the middle and back sections along the line connecting the IP and front section inter­

sections. These points taken together form tracks. Tracks are also formed by following

drift chamber tracks correlating with intersections found independently in the ECC's.

Both minimum ionizing cosmic ray tracks and energetic showers from Bhabha events are

found with these techniques. A reconstructed Bhabha event is illustrated in Fig. 14.

VI. Summary

A set of two endcap electromagnetic calorimeters has been designed, built, tested

and installed at the Mark II detector at SLAC in preparation for the first SLC experi­

ment. Each calorimeter consists of 36 layers each of 0.5 Xo lead sheet and aluminum

proportional tubes 15 mmX9 mm in crOBB section. There is a total of 8784 tubes per

calorimeter. Four coordinates are used, with tubes ganged projectively toward the

interaction point, for a total of 1276 channels per calorimeter. The energy resolution

383

achieved is O'(E)~!::! 18%.

Acknowledgements

We wish to give our thanks to Otto Draeger and his IItaR' in the LBL Allllembly

Shop for their very IIkillf'ul and professional elort in fabricating the endcap calorimeters.

We aIIIo wish to thank Roger Gearhart for his help with the poIlitron beam test, and Ber­

nie Denton and Sean Dyer for their _istance in setting up, moving, and mounting the

calorimeters in the Mark II detector.

References

1. Mark D/SLC Propollal, April 1983, CALT 68-1015.

2. G.S. Abrams, et.aI., IEEE Tranll. Nucl. Sci. MS::2i. No.1, 309(1978).

3. The solid angle coverage for EM IIhowers will extend down to 50 mr from beam axis

upon the addition or a amall-ehower counter at SLC.

4. The manufacturer of the tubes is A.T. Wall, Warwick, R.I.

&. American Cyanimide product FMI23-5.

6. The technique or crimping Stablohm 800 wire (California Fine Wire Co.) in IItain­

less llteel capillary tubes W8ll learned from the U.C. Santa Cruz group who ueed it

very successfully in building the Mark In calorimeters: D. Bernstein, et.aI., NIM vol.

au. 198.,301-318.

7. R.C. Jared, et. ai, "Mark II End Cap Calorimeter Electronics," 1985, IEEE Sympo­

Ilium on Nuclear Science.

384

8.

9.

E.L. Cienel'Oll, et.al., IEEE Trans. Nuel. Sci., ~ No.1, 413(1977)..

Darien Wood, et.al., Mark ll/SLe Note *99, "Resulta or End Cap Positron Beam

Test."

385

Table I

Ml8lcleDtl8catloD Due to Particle Overlap

Pileup or r* and q ill same tube channel which can result ill r* miaidentiBcation u e:l:, from 1fJ deeay .imula&ed eventl. Tube width - 15 mm. P - ,..:t momentum, PT = traD8Yene momentum or ,..:t relative to thrlllt axil.

Misidentification P(OeV/c) PrtGeV/ c) Probability (%)

1-3 <D.6 3.2

3-11 <0.5 1.3

1-11 0.5-1.0 0.2

>11 all

Qt 0.2

aU >1

TableD

TubeQ-a....

Section

LakraJ CanlPnl (tubes)

Lonlitudillal Gulinl (tubea)

Depth illXo Layers Channell/EC

Front (X,Y,U,V) 1 2 4 8 784

Middle (X,Y,U,V) 2 3 8 12 384

Back (X,Y) 3 8 8 18 128

Totu. 18 38 1278

386

Fic·I.

Fic·2.

Fic·3.

Fic·4.

Fic. 5.

Fia. 6.

Fia·7.

Fia·8.

Fic. i.

Fla. 10.

Fis·n.

FIGURES

Isometric view or Mark U.

Sectional view or Mark II.

Radiation lenltbs, IIlUDpling layers vs. cos9.

"D" and "C" sections in a layer.

Exploded views or calorimeter module rabrication and or calorimeter 888embly. Detail of tube signal/HV cabling.

(a) A pulse heisht distribution from one tube or a layer section tested with Cd l •• (b) A similar spectrum for a tube having a 0.3 pC Fe" gain monitoring source installed.

The distribution or relative gains for 30 "c" sections found by fitting the Cd l • peaks (as in Fia. 6a.).

Block diaaram of the electronics for an individual signal channel.

Pulse heicht distribution from the ECC in the e+ test beam tuned to 10 GeV.

Calorimeter respoDM vs. enerl1 uain, Ar(5O%) + Ethue (50%), (a) for HV - l1JOO.2100 yol&8; (b) for HV - 2150-2300 volta.

Saturation vs. gain for IaseB tested.

Fise. 12a-12e. Enel'81 Reeolution ft. HV for five pees: L Ar(&O%) + CtH.(&O%); b. Ar(49.3%) + CtHe(49.3%) + C~60H(1.4%); c. Ar(8O%) + CH..(2O%); d. Ar(8e%) + COs(IO%) + 00.(1%) ("HRS OAS"); e. Ar(i3%) + CH..(4%) + COs(3%) ("Drift Chamber Gas").

Fig. 13. Energy reeolution for be gllBe8 vs. gain (all beam energies plotted).

Fig. 14. Computer reconstructed event display 01 a Shower from a Bhabha event.

MUON DETECTOR

FLUX RETURN

SCINTILLATION CTRS.

DRIFT CHAMBER

FINAL FOCUS SYSTEM

END CAP CAL. LIQUIDARGON- CAL.

FLUXAETURN

w co

Fig. 1. Isometric view of Hark II. -.I

388

HOR IZONTAL CROSS SECTION

t-l METER

MUON DETECTOR -

FLUX RETURN

COIL

LIQUID ARGON CAL.

END CAP DRIFT CAL. CHAMBER

1~~~~~3~~~~~~~~~f--VERTEX DET.;' & LUM. MON.

FINAL FOCUS SYTEM STAY CLEAR

-

Fig. 2. Sectional view of Mark II.

en == 240' c Q)-5 20

"0

Total calorimeter thickness and samples vs. cos 8, LA and EC calorimeters

\~\C~t\1

:2 1"0 101 T~(!L'l!Irn.R.~ .... ________,

o 16 LA -------- ­ I~ ------ ­ I

~ Vr-------­,

I I

• I • , I .. I , ~ 12 I : .- 1 U I ,~

~ 8 ~- .'.Q)

E

2 ~

4 o

U

00

-en ~ Q) >­.2-en Q,)

40 0. E 0 en Q)30 ~

-~

en0 ~

20 0 ~

Q) .Q

E10 :::3 C

-0-~0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Cos 8 w Q)

\D

XBL lI33-122 Fig. 3. Radiation lengths, sampling layers Ys. cos 9.

390

Tube Section Fabrication Technique

,," . "

J!'­ {FM 123-5\= B-Stage Epoxy Strips """~~4--I- ~

Gas Supply Port (2 PLCS/layer)

"C" Section

Fig. 4. "D" and "C" sections in a layer.

"0" Sectio"

Gas Out (2 PLCS/layer

I Outer Gas II (1/1611' 5.5.)

391

\~'rrT 'V' \/

ALUM LEAD GLUE TUBES GLLIE LEAD GLUE n..eeS TYPICAL MODULE CONSTRUCTION

Adaptor Flange

OUTER CABLING PICTORIAL

Fig. 5. Exploded yl~s of calorimeter module fabrication and of calorimeter assembly. Detail of tube slgnal/HV cabling.

392

(a)

80.

(b)'01

604

SOl

401

:sOU­

204~

104

\.. -_ ...... 1 0.20.40.6 0.8 1 1.2 J.4 1.6 1.1.' 2.10 3

Fig. 6. (I) A pulse hei8ht distribution from one tube of I llyer section tested with Cdl 9. (b) A s1m1llr spectrum for I tube hiving I O.3~C Fe55 gl1n monitoring source instilled.

393

.-' .

J.l1.9 CEES, MEA", RI8HT SID!

Fig. 7. The distribution of relative gains for 30 "c" sections found byfitting the Cd l09 peaks (as in Fig. 6a.).

-TEST Pl.LSES

IN ON DlIICH' ...~~-------- -----------. CQ.NTING

HOUS£

IIVWV\l 1/32 SH'tIIr-----....IooI MIle

15

i .....

CFtf'lC== !!l

J~

TEST Pl.L.5E

COfTRClL

)(II.. 1511-461'

w Fig. 8. Block diagram of the electronics for an individual signal channel. ..'"

'150

U 100Pt N· '-.. U) E-t Z ::J o o

50

to GeV Positrons Argon ,Ethane

1900 Volls

141 I ", 'L' , "" t .1.,· I ct. I AtI I ....... urn ?­ IS I I

100 200 300

TOTAL CHARGE (pC)

0' I, , I

o 400 IN ID

Fig. 9. Pulse height distribution from the ECC in the e+ test beam tuned to 10 GeV.

VI

I

396

2500

2000

--tt 1500 ~ en r:a::l Cl r&I 0. 1000I r&I

~ u

500

0

(a) ARCONEnIANE ,-

,-,-

r,-,-

0 10 20 30 40 50 60 6000

~ooo

-u 0.- 4000

~ en r:a::l 3000 ~ 0. I

i 2000

u

1000

0

ARGON ETHANE

/'m_.... T.-.a-..

---­--

0 10 20 I 30 40 50 60 EME~GY (GeV)

Fig. 10. Calorimeter response vs. energy using Ar(501) + Ethane (501), (a) for HV = 1900-2100 volts; (b) for HV = 2150-2300 volts.

60

-.. 40 ~-> ~ t.'

20o ltJ

E-t < Z o o-Eo­

~ ~ E-t < -20

+ ARGON ETHAN"E )( ARGON METHANE o BRS GAS

o D.C. GAS

+ AR-E'I1:I + ALCOHOL

I

4 I.,Ii<r

!

i ±I

101 102

GAIN (pC/GeV)

IN \D

Fig. 11. Saturation ys. gain for gases tested. -.J

CI.l

27.5

25.0

.- ­~ 22.5-~ ~

20.0

Argon Ethane

!I17.5

+ 3 GeV )( 5 GeV

o 10 GeV

! f

I I! f !

1.9

Fiqure 12(a)

2 2.1

HIGH VOLTAGE (KV) 2.2 2.3

IN ID

Fig. 12a-12e - Energy Resolution vs. HV for five gases: CD

a. Ar(50S) + CZH6(5OS); b. Ar(49.3S) + C2Ha(49.3S) + C2HSOH(1.4S); c. Ar(8OS) + CH4(2OS); d. Ar(89S) + C02(lOS) + CH4(lS) (aHAS 6ASa~ e. Ar(93S) + CH4(4S) + C02f3S) (nDrift Chamber Gasn).

399

)(

x

-0.c: O (J

< + Q)

r:= CO

..c= +' ~

r:= 0

~ ~

)(

c»...

)(

1)(

cD....

)(

*

~...

.­N~N­~ ~

~ ~ 0 > ::c ~-:= ....

N

~

..c ~

N

CIJ I­~ c:n .~

I.L.

28 L.

281­ I Argon Methane )(

c 5 GeV

15 GeV

- 24~ ~ ~ "-J

~ ~

22~

20 t­

181­

t t

f I

I I

1.7 I I I I I I I I I I

1.8 1.9

HIGH VOLTAGE (KV)

I I I I l 2

...Figure 12(c) 0 0

401

)( ~-It)

8 )( r-:... --~ !! tzJ

0"'~ I I IJ' r-: -0 ...... N)( a ~~

...::I

> <II0 ~

.-::I C)

u­::c: 0rn

«I I 8 I It:l ~ -::c:t!J * -en

c:: ::t:

)(8 ~-N ... ce~

C\I '" C\I C\I 2 ... ...

26

Drift Chamber Gas o 15 GeV

24

-~-­~ 't;­

22

f ! I! 20 ! I

1.4 1.5 ! 1.6 1.7 1.8

HIGH VOLTAGE (KV)

F1~ure 12(e) .... o IV

27.5

I25.0

-~22.5 - !~

~ 20.0

~ I 17.5

i" .aGOM E'l1IAJtE )( dCOM~

o HIlS GAS o D.C. GAS

f1~1 Irijij 101 102

GAIN (pC/GeV)

oFig. 13 Energy resolution for five gases vs. gain (all beam energies plotted). ~

w

404