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NEW EXPERIMENTAL TECHNICS
T. Ypsilantis
To cite this version:
T. Ypsilantis. NEW EXPERIMENTAL TECHNICS. Journal de Physique Colloques, 1982, 43 (C3),
pp.C3-223-C3-228. �10.1051/jphyscol:1982344�. �jpa-00221897�
JOURNAL DE PHYSIQUE
CoZZoque C3, suppZ6ment
aun o 12, Tome
4 3 ,dgcembre 1982
NEW EXPERIMENTAL TECHNICS
T . Y p s i l a n t i s
LPNHE,
EcoZe PoZytechnique, Route de Saclay, 91128 Pazaiseau, France
Al) S . White o f R o c k e f e l l e r U n i v e r s i t y d e s c r i b e d t h e development and performance of h i g h p r e s s u r e (15 b a r ) hydrogen g a s time p r o j e c t i o n chamber (TPC) w i t h o u t magnetic f i b l d . A t t h i s p r e s s u r e and w i t h a d r i f t f i e l d of 2 K V / ~ a n e l e c t r o n d r i f t v e l o c i t y of about . 5 cm/psec was measured. Over a wide range of p r e s s u r e s and e l e c t r i c f i e l d s a p a r a m e t e r i z a t i o n of t h e d r i f t v e l o c i t y v = 1.52 cm/ps (E/P) - 6 , with E i n K V / C ~ and p i n b a r s , was obtained. A s a consequence of t h i s n o n - s a t u r a t i o n o f t h e d r i f t v e l o c i - d
t y i n t h e o p e r a t i n g regime, p r e s s u r e , t e m p e r a t u r e and e l e c t r i c f i e l d s t a b i l i t y was c o n t r o l l e d t o a l e v e l of 0.1%. The l o n g i t u d i n a l d i f f u s i o n c o e f f i c i e n t f o r a s i n l e e l e c t r o n d r i f t i n R2 a t 15 b a r s and 2 W/sm was measured t o b e c r t = .068 m m / ~ m ' 7 ~ which corresponds t o a d i f f u s i o n c o e f f i c i e n t of .263 mm/cm1/2at atmospheric p r e s s u r e . MWPC d e t e c t o r s , a t t h e end of t h e 76 om long d r i f t r e g i o n , o p e r a t i n g i n H2 g a s gave an a m p l i f i c a t i o n lo4 a t p r e s s u r e between 1 and 15 b a r . Loss of d r i f t i n g e l e c t r o n s by e l e c t r o n e g a t i y e 02 i m p u r i t i e s was n e g l i g i b l e because of t h e Bigh p u r i t y (.Olppm) of t h e H2 g a s .
T h i s d e v i c e h a s been used i n a FNAL experiment t o d e t e c t t h e p r o t o n r e c o i l energy and d i r e c t i o n when high energy tagged photons (20-170 GeV/c) i n t e r a c t e d w i t h p r o t o n s of t h e H2 g a s f i l l i n g t h e TPC. P d e n t i f i a t i o n of t h e p r o t o n r e c o i l mass was achieved
&
by measurement of s p e c i f i c i o n i z a t i o n (--). D e t a i l s o f t h i s d e v i c e a r e now p u b l i s h e d
( 1 ) . dx
A2) C. Hargroye of t h e N a t i o n a l Research Council of Canada r e p o r t e d on t h e s p a t i a l r e s o l u t i o n of t h e TRIUMF TPC ( 2 ) . I t i s comprised of a c y l i n d e r l i k e volume a b o u t 69 cm i n l e n g t h w i t h two hexagonal end c a p s (1M between o p p o s i t e f a c e s ) w i t h a c e n t r a l high v o l t a g e p l a n e and a 30 cm diameter c e n t r a l tube which d e f i n e s t h e i n n e r l i m i t of t h e d r i f t volume. The s i x MWPC d e t e c t o r s a t each hexagonal end cap have t h e form of t r u n c a t e d t r i a n g l e s with 12 p r ~ p o r t i o n a l w i r e s p e r module s t r o n g p a r a l l e l t o t h e t r u n c a t e d edge with 25 mm wire spacing. Cathode pads o f dimensions 20 mm perpendicu- l a r and a b o u t 6
mm
p a r a l l e l t o t h e w i r e s a r e r e a d o u t with ADC'S and a c e n t e r o f gra- v i t y c a l c u l a t i o n p r o v i d e s t h e p o s i t i o n measurement o f a t r a c k segment. The MWPC wire i s i n s i d e a box 20mm
wide, 18 mm deep b u t with an e l e c t r o n e n t r y s l o t ( p a r a l l e l t o t h e w i r e ) of only 6.35rmn. The g a s mixture used was 80% Argon and 20% methane and t h e d e v i c e o p e r a t e s i n a s o l e n o i d a l magnetic f i e l d of up t o I0 KG.S e v e r a l s o u r c e s of p o s i t i o n a l e r r o r were i d e n t i f i e d and measured i)
+
diffusion 3 o f d r i f t i n ? e l e c t r o n s i n t h e d r i f t volume ii) e f f e c t s p r o p o r t i o n a l t o E x B p r i m a r i l y i n s i d e t h e MWPC box and iii) e f f e c t s due t a c l u s t e r i n g of t h e t r a c k i o n i z a t i o n . The f i r s t e r r o r was found t o be small ( e s p e c i a l l y s o i n a n 8.5 KG magnetic f i e l d ) where- a s t h e second and t h i r d e r r o r s were dominant even f o r a maximum 34 cm d r i f t l e n g t h . A3) J. A l l i s o n of t h e U n i v e r s i t y of Manchester p r e s e n t e d a paper on e l e c t r o d e l e s s d r i f t chambers ( 3 ) . I n t h i s concept, t h e f i e l d shaping e l e c t r o d e s of a normal d f i f t r e g i o n a r e suppressed and f i e l d s h a p i n g i s provided by t h e charging of g l a s s f i b e r( G 10) ~ n s u l a t i n g s u r f a c e s which d e f i n e t h e edges of t h e d r i f t gap. The e x t e r n a l s u r f a c e s of t h e G 10 a s w e l l a s t h e end p l a t e s of t h e d r i f t gap a r e a t e i r t h poten- t i a l w i t h a c e n t r a l amplifying wire a t p o s i t i v e p o t e n t i a l . I t was shown t h a t from an i n i t i a l uncharged c o n f i g u r a t i o n (of t h e G 10 s u r f a c e s ) p o s i t i v e i o n s produced by avalanches around t h e a m p l i f y i n g w i r e (caused by cosmic r a y s o r a r a d i o a c t i v e sour- c e ) w i l l c h a r g e t h e i n s u l a t i n g s u r f a c e s t o produce an i d e a l d r i f t f i e l d configura-
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982344
C3-224 JOURNAL DE PHYSIQUE
t i o n i . e . one i n which a l l l i n e s of f o r c e connect t h e amplifying w i r e t o t h e c o l l e c - t i n g end p l a t e . When t h i s c o n d i t i o n i s reached, a d d i t i o n a l charging of t h e i n s u l a - t i n g s u r f a c e s c e a s e s and t h e d r i f t f i e l d should remain i d e a l . I n t h i s c o n f i g u r a t i o n t h e d r i f t f i e l d Ed and t h e f i e l d a t t h e wire s u r f a c e Ew, a r e r e l a t e d a s Ew = E d x k
nR
where 2a i s t h e d r i f t g a p width and R t h e wire r a d i u s .T e s t s were made with cosmic r a y s on a d r i f t gap 2 an wide w i t h a maximm d r i f t d i s - tance of 45 cm w i t h a 90% Argon, 10% methane d r i f t and counting g a s . I n s h o r t d r i f t l e n g t h s an e f f i c i e n c y of 97% was o b t a i n e d whereas f o r t h e maximm d r i f t l e n g t h 85%
e f f i c i e n c y was observed. This l o s s f o r l a r g e d r i f t d i s t a n c e s was thought t o be due t o e l e c t r o n e g a t i v e i m p u r i t i e s i n t h e g a s and n o t due t o i n h a n o g e n e i t i e s kn t h e d r i f t f i e l d . S p a t i a l r e s o l u t i o n of about 1.5 mm (r.m.s) was o b t a i n e d l i m i t e d by d i f f u s i o n and time binning. This technique has n o t y e t been t e s t e d i n high f l u x p a r t i c l e beams where charging of t h e d i e l e c t r i c s may be more severe and would c o n s t i t u t e a r e a l i s - t i c t e s t of t h i s method.
A4)Neat M. Medinnis of UCLA d e s c r i b e d t h e performance of a 16000 w i r e m i n i - d r i f t system i n u s e a t an ISR experiment. To improve t h e s p a t i a l r e s o l u t i o n of 3 mm p i t c h MWPC p l a n e s , while m a i n t a i n i n g t h e high r a t e c a p a b i l i t y of MIPC's, e a c h of 16000 PC w i r e s was equipped w i t h a 4 b i t TDC. The time b i n width was 5 n s which w i t h a d r i f t v e l o c i t y of 50 p / n s corresponds t o a l i m i t i n g (r.m.s.) r e s o l u t i o n of 72 PIU. The space-time r e l a t i o n s h i p i n a W,PC c e l l was found t o be l i n e a r f o r d r i f t d i s t a n c e s l e s s than 125 mm. I n l a r g e r d r i f t d i s t a n c r s ( i . e l . 2 5 t o 1.5,mm) non l i n e a r correc- t i o n s were n e c e s s a r y correspondinq t o d r i f t i n t h e low f i e l d r e g i o n of t h e MWPC cells..
Each d r i f t time measurement g i v e r i s e t o a l e f t - r i g h t ambiguity hence 4 MGPC planes produce a p o s s i b l y 16 f o l d ambiguity. CJhen each p a r t i c l e t r a j e c t o r y was f i t t e d without using t h e d r i f t time information and t h e n t h e d r i f t time information was im- posed using t h e l o c a l d i r e c t i o n c o s i n e s a s c o n s t r a i n t s t h e n a unique s o l u t i o n was found f o r 80%of t h e tracks.The measuredspace p o i n t r e s o l u t i o n was 180 pm which repre- s e n t s a g a i n of a f a c t o r 4 , 8 over t h e intrinsic r e s o l u t i o n of t h e MWPC c e l l s .
A5) S.J. Lindenbaum of BNL and C i t y College of New York d e s c r i b e d t h e c h a r a c t e r i s t i c s of t h e new MPS 11: spectrometer system a t t h e AGS a c c e l e r a t o r a t Brookhaven. I t con- t a i n s seven p a r t i c l e d e t e c t i o n p l a n e s ( o r modules) downstream f r g n a l i q u i d hydrogen t a r g e t a l l contained i n s i d e a 10 KG d i p o l e magnetic f i e l d volune. Each module con- s i s t s of seven MWPC p l a n e s , 3 i n t h e X (momentum d e f i n i n g ) d i r e c t i o n , 2 i n t h e Y d i r e c t i o n , 1 i n t h e U d i r e c t i o n (+ 30°
/
X) and 1 i n t h e V d i r e c t i o n (-30"). One of t h e X p l a n e s and one o f t h e Y p l a n e s a r e d i s p l a c e d by h a l f a w i r e spacing t o h e l p r e s o l v e l e f t - r i g h t a m b i g u i t i e s and t h e W p l a n e s p r o v i d e s t e r e o 3 D information.Each MWPC c e l l h a s an anode-cathode d i s t a n c e of 6.35 mm and a p i t c h of 6.35 mm with f i e l d w i r e s i n t h e anode p l a n e t o symmetrize t h e e l e c t r i c f i e l d . The seven modules c o n t a i n a t o t a l of a b o u t 12 000 w i r e s and each is equipped a n a m p l i f i e r , d i s c r i m i n a - t o r and 2 5 6 b i t , 2 5 0 MHz s h i f t r e g i s t e r . The s h i f t r e g i s t e r a l l o w s d i g i t i z a t i o n o f t h e d i s c r i m i n a t o r o u t p u t i n 4 n s time b l n s f o r measurement o f d r l f t time. The measu- rements show 200 pm space p o i n t r e s o l u t i o n and a l i n e a r space-time r e l a t i o n s h i p o v e r t h e f u l l d r i f t c e l l . T h i s corresponds t o a f a c t o r 9 g a i n i n space r e s o l u t i o n r e l a t i - ve t o t h e i n t r i n s i c MWPC v a l u e . T h i s performance was o b t a i n e d u s i n g 80% Argon, 1 5 % Isobutane and 5% Methyl g a s f i l l i n g which h a s a f u l l y s a t u r a t e d d r i f t v e l o c i t y a t t h e e l e c t r i c f i e l d v a l u e s of t h e u n i t c e l l .
The system was o p e r a t e d a t h i g h beam i n t e n s i t i e s (% 3 x 10 / b u r s t ) t o measure t h e 6 r e a c t i o n s-p -t $$n a t 2 2 ~ e V / c in c i d e n t p i o n momentum.
Bl) G. Charpak of C E m opened t h i s s e s s i o n on new t e c h n i q u e s by p r e s e n t i n g a minx- review of d e t e c t o r developments i n h i s group a t CERN. The f i r s t t o p i c was t h e use of e l e c t r o s t a t i c imaging of c h a r g e s p a r t i c l e t r a c k s i n high p r e s s u r e (C02) g a s de- t e c t o r s equipped w i t h a g a t e . The g a t e d charges d e p o s i t e d on mylar f o i l s may be scan- ned t o l o c a t e with high accuracy (% lpm) t h e p o s i t i o n of t h e d e p o s i t e d charge. A t a p r e s s u r e of 400 b a r t h e d i f f u s i o n c o e f f i c i e n t i n C02 should be 4 pm/cm1l2 hence t h e l i m i t i n g s i z e of t h e d e p o s i t e d charge of 4 pm, f o r 1 cm of d r i f t . Development of n r o t a t i n g probe e l e c t r o d e (of dimensions 5
mm
x 0 . 1 mm) of s u f f i c i e n t s e n s i t i v i t y t o d e t e c t t h e b a r y c e n t r e o f t h e d e p o s i t e d charge t o a p r e c i s i o n of abour 1 pm i s underway.T. Y p s i l a n t i s
The second t o p i c d e s c r i b e d was t h e use of photons a s a method of d a t a r e t r i e v a l from gaseous d e t e c t o r s of primary i o n i z a t i o n . A s an example of t h i s method one may c i t e t h e p h o t o i o n i z a t i o n p r o p o r t i o n a l s c i n t i l l a t i o n d e t e c t o r where primary i o n i z a t i o n e l e c t r o n s produced i n a gas a r e d r i f t e d i n t o a zone of high e l e c t r i c f i e l d ( i . e . a multi-seep gap) t o produce s c i n t i l l a t i o n l i g h t which i s t r a n s f e r r e d t o a phototube v i a a wave l e n g t h s h i f t e r b a r . The g a s f i l l i n g was A
+
N2+
CO2- The good t i m i n g c h a r a c t e r i s t i c s of t h e phototube a l l o w t h e o b s e r v a t i o n of avalanches due t o s i n g l e e l e c t r o n s hence c l u s t e r s of primary i o n i z a t i o n may be i d e n t i f i e d .F i n a l l y , a development of l i q u i d W photocathodes h a s shown promise. Here a l i q u i d l a y e r of TMAE (tetrakis-methyl-amino e t h y l e n e ) h a s produced p h o t o e l e c t r o n s when il- luminated w i t h photons above 4 eV from X r a y e x c i t e d s c i n t i l l a t i o n i n Ba F2 c r y s t a l . . The t h r e s h o l d f o r p h o t o i o n i z a t i o n of t h i s molecule i n t h e gaseous phase i s 5.4 eV hence s o l i d ( o r l i q u i d ) s k a t e e f f e c t s a r e o p e r a t i v e t o reduce t h e photo-threshold.
Quantum e f f i c i e n c i e s of % 1% a t 5.5 eV have been observed. E x t r a c t i o n of t h e photo- e l e c t r o n s from t h e l i q u i d s u r f a c e r e q u i r e s high e l e c t r i c f i e l d s which were n o t pos- s i b l e i n t h e f i r s t measurements. A p p l i c a t i o n s f o r s e e n f o r t h i s technique a r e i n e l e c t r o m a g n e t i c c a l o r i m e t r y .
B2) F. S a u l i of CERN p r e s e n t e d a r e p o r t on t h e c o n s t r u c t i o n and o p e r a t i o n of a l a r g e r i n g imaging Cherenkov d e t e c t o r f o r t h e E605 experiment a t Fermilab. Downstream from t h e a n a l y z i n g magnet o f t h e E605 spectrometer h a s been p l a c e d a 15 m long atmosphe- r i c p r e s s u r e Helium g a s Cherenkov r a d i a t o r v e s s e l (dimensions t r a n s v e r s e t o s p e c t r o - meter a x i s a r e 3m x 3m). Cherenkov r a d i a t i o n e m i t t e d by p a r t i c l e s t r a v e r s i n g t h i s r a d i a t o r h a s been focused by s p h e r i c a l m i r r o r s ( 8 m f o c a l l e n g t h ) o n t o two
80 x 40 cm2 image s u r f a c e s a t which have been p l a c e d photon d e t e c t o x s equipped with a mosaic of Ca F2 m o n o c r y s t a l l i n e windows. The d e t e c t o r , p l a c e d immediately a f t e r t h e window, i s comprised of 3 p a r a l l e l gaps and a MWPC. The f i r s t gap ( 5 mm t h i c k ) i s a conversion gap where t h e W Cherenkov photons of t h e r i n g image a r e c o n v e r t e d , t o e l e c t r o n s by p h o t o i o n i z a t i o n of t r i - e t h y l - a m i n e (TEA). The d e t e c t o r i s f i l l e d t o atmospheric p r e s s u r e w i t h a Helium, Methane, TEA m i x t u r e (83, 14, 3 % ) . The TEA t h r e s h o l d f o r p h o t o i o n i z a t i o n i s 7.5 eV photon energy while t h e l i m i t o f methane t r a n s m i s s i o n i s 8.5 eV. The second gap i s t h e p r e a m p l i f i c a t i o n o r m u l t i s t e p avalan- che gap ( E % 8 k ~ / e m ) where a s i n g l e e l e c t r o n from t h e conversion gap i s a m p l i f i e d by about 104. The t h i r d gap i s t h e t r a n s f e r gap (E
a
1 W / m ) where a b o u t 10% of t h e e l e c t r o n s from t h e m u l t i s t e p gap g e t t r a n s f e r e d i n t o t h e MWF'C. The MWPC d e t e c t i o n gap i s equipped with cathode w i r e s a t 2 45' r e l a t i v e t o t h e anode wire p l a n e a l l with a p i t c h of 2 mm. A l l cathode and anode w i r e s a r e r e a d o u t w i t h ADC and a cen- t r o i d c a l c u l a t i o n g i v e s t h e p o s i t i o n of t h e converted photon t o a n accuracy ox % Oy % 400 pm. T h i s system i s now running a t FNAL and h a s t a k e nl o 5
e v e n t s with a p i o n t e s t beam and 3 x 104 e v e n t s w i t h t h e f u l l experiment i n o p e r a t i o n .I n an e a r l i e r 8 m long Helium r a d i a t o r t e s t a s i x s t a n d a r d d e v i a t i o n s e p e r a t i o n of 200 GeV/c p i o n s from kaons was o b t a i n e d i n accordance with Cerenkov r a d i a t i o n theory.
A v a l u e of t h e q u a l i t y f a c t o r No = 50 cm-I h a s been o b t a i n e d i n t h e t e s t measure- ments.
B3) J . V . Morris of Rutherford-Appleton Laboratory p r e s e n t e d experimental work on a r i n g imaging Cherenkov d e t e c t o r f o r t h e CERN-SPS m e g a spectrometer. T h i s d w i c e i s scheduled t o b e i n s t a l l e d a t t h e S2 s p e c t r o m e t e r d u r i n g 1983 t o c o i n c i d e w i t h t h e upgrade of t h e beam energy i n t h e West Area of t h e CERN-SPS. I t i s comprised of an atmospheric p r e s s u r e Argon g a s r a d i a t o r 5 meters i n l e n g t h with 81 hexagonal, 5 m f o c a l l e n g t h s p h e r i c a l m i r r o r s which produce r i n g images on a (3.2 m h o r i z o n t a l , 1.6 meter v e r t i c a l ) f o c a l s u r f a c e . The f o c a l s u r f a c e i s instrumented by a mosaic of 16 TPC d r i f t modules (80 x 40 cm2) each w i t h a f u s e d q u a r t z window which s e p e r a t e s t h e Argon r e d i a t o r gas from t h e p h o t o i o n i z i n g and d r i f t gas(TamE, CH4) o f t h e d r i f t d e t e c t o r . The d r i f t r e g i o n c a u s e s t h e s i n g l e p h o t o e l e c t r o n s o f t h e r i n g image t o d r i f t a maximum d i s t a n c e of 20 cm t o a p i c k e t fence o f square p r o p o r t i o n a l c o u n t e r s
( p i t c h 4 mm, anode-cathode d i s t a n c e 4 mm). Both h a l v e s ( + 20 cm) of a s i n g l e (80 x 40 cm2) TPC d r i f t module d r i f t e l e c t r o n s i n t o t h e same p r o p o r t i o n a l c o u n t e r p i c k e t f e n c e s o t h e d e v i c e h a s a l e f t - r i g h t ambiguity which i s r e s o l v e d by t h e
JOURNAL DE PHYSIQUE
t r a c k i n g c a p a b i l i t y o f t h e R spectrometer system. The f u l l d e t e c t i o n s u r f a c e i s 5.1 m2 w i t h 3200 p r o p o r t i o n a l w i r e s each equipped with 60 n s b i n s of time s l i c e encoders corresponding t o a g r a n u l a r i t y of 3.2 x l o 5 p i x e l s . T h i s high g r a n u l a r i t y i n s u r e s t h a t high m u l t i p l i c i t y e v e n t s can be recognized and t h e Argon g a s r a d i a t o r a l l o w s T/K p a r t i c l e i d e n t i f i c a t i o n up t o 80 G ~ V / C w i t h r i n g images having 30 p o i n t s on a c i r c l e .
I n i t i a l measurements w i t h a s m a l l e r d e t e c t o r module h a s produced r i n g images of t h e expected r a d i u s . The f u l l (80 x 40 cm2) TPC d r i f t module i s now b e i n g t e s t e d . B4) Next S. T a v e r n i e r o f B r u s s e l s reviewed t h e performance of t h e holographic bubble chamber HOBC i n t h e experiment NA25 a t t h e CERN-SPS. I t s aim was t o s t u d y t h e charm p r o d u c t i o n c r o s s s e c t i o n v e r s u s beam momentum and f o r v a r i o u s beam p a r t i c l e t r i g g e r s . The i d e n t i f i c a t i o n of charmed e v e n t s i s by v i s u a l i d e n t i f i c a t i o n of a secondary decay v e r t e x (rC: s e c decay l i f e t i m e = 30 pm)in a heavy l i q u i d (Freon 115 = C2F5 C 1 ) bubble chamber with holographic photography and secondary muon d e t e c t i o n and high m u l t i p l i c i t y iis p a r t - o f t h e t r i g g e r . The muon t r i g g e r enhances t h e charm con- t e n t of t h e p i c t u r e s by a f a c t o r 20 while t h e holographic r e c o r d i n g of t h e e v e n t allowed f u l l depth of view o v e r t h e 10 cm deep chamber with a n u l t i m a t e t h e o r e t i c a l l i m i t on space r e s o l u t i o n of 1 vm. I n t h e experiment t h e r e s o l u t i o n was l i m i t e d by r e l a y o p t i c s t o 6 um and
l o 4
holograms were recorded,l o 3
analyzed and charm decays found. I t was found t h a t h i g h r e s o l u t i o n holography i s very s e n s i t i v e t o v a r i a t i o n s of r e f r a c t i v e index caused by thermal t u r b u l e n c e . when bubbles a r e recompressed h e a t i s g e n e r a t e d and d i f f u s e s slowly throughout t h e bulk l i q u i d . To a v o i d t h i s d e t e r i o r a t i o n of t r a c k q u a l i t y t h e time between expansions had t o be l i m i t e d t o 1 Hz. Under t h e s e c o n d i t i o n s bubble d i a m e t e r s of about 12 pm were found with bubble d e n s i t i e s o f 200/cm. Operation of t h e bubble chamber a t h i g h e r temperature (lO°C) w i l l probably a l l o w 10 expansions p e r second w i t h o u t thermal t u r b u l e n c e .B5) G. Sandweiss of Yale U n i v e r s i t y d e s c r i b e d c u r r e n t work t o develop a second gene- r a t i o n high r e s o l u t i o n streamer chamber f o r heavy quark p h y s i c s . At p r e s e n t , s t r e a - mer chambers of s i z e 4 x 4 x
-
1 cm3 o p e r a t i n g a t 40 b a r of Ne/He (90/10) produce streamer t r a c k s o f 100 t o 150 2 urn width. The t r a c k i s photographed u s i n g t h e s e l f luminous l i g h t of t h e streamer and high g a i n image t u b e s . Two major improvements a r e f o r e s e e n f i r s t t h e t r a c k w i d t h s reduce t o 25 um o r l e s s and secondly chamber d i - mensions i n c r e a s e d t o allow 20 cm o f f i d u c i a l l e n g t h along t h e beam d i r e c t i o n . To reduce t h e t r a c k width, o p e r a t i o n of t h e chamber a t 100 b a r should s u f f i c e however e l e c t r o n d i f f u s i o n t h e n becomes t h e dominant s o u r c e of t r a c k width. I t i s proposed t o s u p p r e s s t h e d i f f u s i o n by s t o r i n g t h e t r a c k i n f o r m a t i o n i n t h e form of n e u t r a l m e t a s t a b l e neon dimers. A t t h e p r o p e r moment ( j u s t b e f o r e t h e a p p l i c a t i o n of t h e high v o l t a g e p u l s e t o form s t r e a m e r s ) e l e c t r o n s a r e l i b e r a t e d from t h e neon dimers by p h o t o i o n i z a t i o n u s i n g a 4.2 eV photon beam. The s t r e a m e r s a r e then photographed by r e s o n a n t l i g h t s c a t t e r i n g from t h e streamer and holographic r e c o r d i n g o f t h e image. T h i s w i l l allow a l a r g e depth of f l e l d and r e s o l u t i o n much s m a l l e r t h a n t h e t r a c k width.B6) F. S a u l i of C E m p r e s e n t e d a paper on r e d i s c o v e r i n g t h e g a s f i l l e d photodiode.
Such a d e v i c e may b e considered a s a replacement f o r a p h o t o m u l t i p l i e r t u b e i n EM shower c o u n t e r s with t h e c o n s i d e r a b l e advantage of almost complete i n s e n s i t i v i t y t o magnetic f i e l d . I n a d d i t i o n such d e v i c e s a t atmospheric p r e s s u r e can b e made t o co- v e r l a r g e s u r f a c e a r e a s i n f l a t t h i n geometries. I n t h e c a s e of vacuum phokodiodes only small s u r f a c e a r e a s can b e made f l a t and t h i n and some s e n s i t i v i t y t o magnetic f i e l d s remains. T e s t s w i t h a b i a l k a l i photocathode f i l l e d t o 2 t o r r Argon p r e s s u r e showed t h a t a g a s g a i n of about 50 i s p o s s i b l e . With metal photocathodes (low quan- tum e f f i c i e n c y ) a t Argon g a s p r e s s u r e s up t o 800 t o r r t h e r e l a t i v e quantum e f f i c i e n - cy g e t s reduced by a s much a s a f a c t o r o f 10 w i t h l i t t l e g a s g a i n p o s s i b l e .
Eikh
methane g a s f i l l i n g s ( a g a i n up t o 800 t o r r ) i t was found t h a t f u l l quantum e f f i c i e n - cy could b e achieved a t a l l p r e s s u r e s . Gas g a i n of 10-20 seems p o s s i b l e however it remains t o be seen i f a r e a l b i a l k a l i photocathode w i l l b e a d v e r s e l y a f f e c t e d O r d e s t r o y e d by p o s i t i v e i o n s .
T . Y p s i l a n t i s
C1) To open t h e c a l o r i m e t r y s e s s i o n M.N. Kienzle-Focacci of t h e U n i v e r s i t y of Geneva p r e s e n t e d r e s u l t s on a sampling e l e c t r o m a g n e t i c c a l o r i m e t e r c o n s i s t i n g of l e a d p l a t e s and l i q u i d s c i n t i l l a t o r c o n t a i n e d i n t e f l o n tubes. The b a s i c s t r u c t u r e o f t h e d e v i c e i s a s u c c e s s i o n of 5mm t h i c k , l e a d p l a t e s w i t h 5mm o u t e r diameter t e f l o n t u b e s a l t e r - n a t i n g t o g i v e X and Y p r o j e c t i v e r e a d o u t of t h e shower. The d i s t a n c e f o r one reduc- t i o n l e n g t h i s 11.5m. S c i n t i l l a t i o n l i g h t produced by e l e c t r o n s o f a shower which c r o s s t h e t e f l o n t u b e s i s c o l l e c t e d ( t o t a l i n t e r n a l r e f l e c t i o n ) by a p h o t o m u l t i p l i e r t u b e a t one end. The a t t e n u a t i o n l e n g t h f o r s c i n t i l l a t i o n l i g h t i n t h e t e f l o n t u b e s h a s been measured t o be a b o u t 1.9 m e t e r s and s t a b l e (2-3%) o v e r a p e r i o d of 1 y e a r . The measured f r a c t i o n a l energy r e s o l u t i o n aE/E i s 16%/& i n q u a d r a t w e with a cons- t a n t term of 3.6%. The s p a t i a l r e s o l u t i o n with which t h e shower a x i s has been mea- s u r e d i s 2.5mm, 1.5mm and 0.8mm a t e l e c t r o n e n e r g i e s of 5, 16 and 35 GeV/c r e s p e c t i - vely. The two shower s e p a r a t i o n d i s t a n c e h a s been found t o be about 1.5 nm i n a- greement w i t h Monte-Carlo s i m u l a t i o n s . T h i s d e v i c e h a s a f a s t response and may b e used a s p a r t of a t r i g g e r and can o p e r a t e i n a high f l u x environment (> l o 7 p a r t i - c l e s / b u r s t ) . S i x t e e n s q u a r e meters of t h i s c a l o r i m e t e r (27 Xothick) w i l l b e b u i l t and i n s t a l l e d a t t h e S1 s p e c t r o m e t e r a t t h e CERN-SPS.
C2) Next D. Wegener of t h e U n i v e r s i t y of Dortmund described t h e Argus shower c a l o r i - meter which i s i n s i d e t h e c o i l of t h e Arqus d e t e c t o r a t DESY. The c a l o r i m e t e r con- s i s t s of a b a r r e l c o u n t e r and two end cap p a r t s and i s segmented i n 1760 modules each r e a d o u t v i a i t s own wave s h i f t e r p l a t e . The u n i t module c o v e r s 22.5 x 11 cm2 and i t s d e p t h i s 40 cm o r 12.4 Xo comprised of a l t e r n a t e l a y e r s of 1 mm t h i c k l e a d s h e e t s and 5 mm t h i c k p l a s t i c s c i n t i l l a t o r . The re-emitted l i g h t from t h e wave s h i f - t e r p l a t e i s c o l l e c t e d by an a d i a b a t i c l i g h t g u i d e and f e d i n t o a 2.5 cm @ photo- m u l t i p l i e r . T h i s d e v i c e h a s been c a r e f u l l y t e s t e d f o r l i n e a r i t y down t o photon ener- g i e s a s low a s 10 MeV. I t was found t o b e l i n e a r w i t h a f r a c t i o n a l energy resolution aE/E = 7%/& i n t h e r e g i o n between 7 MeV and 7 GeV and a shower a x i s s p a t i a l r e s o l u - t i o n of a b o u t 20 m.
C3) V. B r i s s o n o f Ecole Polytechnique n e x t p r e s e n t e d a work on a s o l i d Argon and s o l i d Neon e l e c t r o m a g n e t i c c a l o r i m e t e r . Such a d e v i c e works l i k e a l i q u i d Argon ca- l o r i m e t e r with l e a d s h e e t s added t o d e c r e a s e t h e r a d i a t i o n l e n g t h . I n f a c t it i s found t h a t l i q u i d neon g i v e s no s i g n a l b u t l i q u i d Argon, s o l i d Argon and s o l i d Neon work well. For e l e c t r o m a g n e t i c c a l o r i m e t r y i n s i d e bubble chambers s o l i d Argon o r Neon a r e p o s s i b l e . The d e v i c e t e s t e d had a volume of 40 l i t e r s ( i . e . 6 0 x 3 0 ~ 2 0 cm3) and was 20 cm i n t h e beam d i r e c t i o n ( 8
x,).
I t c o n t a i n e d t h i r t y 3 mm t h i c k gaps i n which were d i s p e r s e d f i f t e e n l e a d p l a t e s (10 of 2 mm t h i c k and 5 of 4 mm t h i c k ) and f i f t e e n p r i n t e d c i r c u i t boards with 3 cm wide charge c o l l e c t i o n s t r i p s . The f i r s t 2 Xo were r e a d o u t i nx
p r o j e c t i o n , t h e second 2 Xo i n U and V p r o j e c t i o n (+ 45') and t h e l a s t 4 X, a g a i n i n X p r o j e c t i o n . The f r a c t i o n a l energy r e s o l u t i o n o b t a i n e d i s compatible with oE/E = 1 3 % / h w i t h good u n i f o r m i t y a c r o s s t h e e n t r a n c e s u r f a c e . I t was shown t h a t l a r g e volumes of s o l i d Argon o r Neon can be k e p t f o r long p e r i o d s without l o s s of s e n s i t i v i t y and furthermore t h a t p o l l u t e d Argon works a s a s o l i d . Also it was shown t h a t s o l i d Neon and Hydrogen m i x t u r e s a l s o work a s c a l o r i m e t e r s . C4) D.E. Groom of t h e U n i v e r s i t y o f Utah p r e s e n t e d new work on s i l i c o n photodiode d e t e c t i o n of BGG s c i n t i l k a t i o n l i g h t . The advent of BGO c r y s t a l s having 1 Xo = 1.13cm and non hygroscopic shows g r e a t promise f o r e l e c t r o m a g n e t i c c a l o r i m e t r y . It h a s a l i g h t o u t p u t of about 10% t h a t of NaI peaked around 525 nm. An EGS program simula- t i o n of an EM shower i n d i c a t e s t h a t 20 cm t h i c k BGO could a c h i e v e a f r a c t i o n a l energy r e s o l u t i o n =~%FE
and i s l i m i t e d by leakage. The advantages of r e a d o u t ofaG0 with s i l i c o n photodiodes a r e h i g h s t a b i l i t y ( u n i t l a r g e dynamic range l i n e a r i t y and o p e r a t i o n i n magnetic f i e l d . With c e r t a i n m o d i f i c a t i o n s of t h e Mamomatsu S1336-1010BR s i l i c o n photodiode ( t o reduce s e r i e s r e s i s t a n c e ) a n o i s e e q u i v a l e n t si- g n a l v a l u e of 320 KeV was o b t a i n e d . T h i s l e v e l would allow f r a c t i o n a l enerqy r e s o l u - t i o n of 1% o r b e t t e r even down t o 100 MeV photon o r e l e c t r o n energy.
JOURNAL DE PHYSIQUE
C5) Next P. S l a t t e r y o f t h e U n i v e r s i t y o f Rochester p r e s e n t e d t h e o p e r a t i o n a l p e r - formance o f a l a r g e l i q u i d Argon photon c a l o r i m e t e r . T h i s d e v i c e c o n t a i n e d 3000 li- t e r s o f l i q u i d Argon and 61 l e a d s h e e t s 2 mm t h i c k with 62 copper c l a d G-10 p l a n e s with a l t e r n a t e X and Y p r o j e c t i v e read-out. The l i q u i d Argon l a y e r s were 2 mm t h i c k and t h e t o t a l t h i c k n e s s of t h e d e v i c e corresponds t o 25 r a d i a t i o n l e n g t h and 1.2
@on i n t e r a c t i o n l e n g t h s . The f r a c t i o n a l energy r e s o l u t i o n aE/E = 1 0 % / 6 w a s o b t a i - ned f o r s i n g l e 50 Gev/c e l e c t r o n s and space r e s o l u t i o n of 0.67 mm. I n d a t a t a k i n g r u n s a t high beam i n t e n s i t i e s t h e f r a c t i o n a l energy r e s o l u t i o n c o n s t a n t degrades from 10% t o 14% due t o i n t e n s i t y e f f e c t s , o v e r l a p p i n g showers long term d r i f t s and leakage. The mass r e s o l u t i o n u 111 i n s i n g l e n o ' s was approximately a c o n s t a n t 6 MeV over t h e no energy range o r 20 t o 200 GeV. I n gamma m u l t i p l i c i t i e s of 2 , 3 and 4 peaks were found a t t h e no mass and t h e 11' mass w i t h e s s e n t i a l l y c o n s t a n t width am.
For m u l t i p l i c i t y g r e a t e r t h a n 4 o n l y t h e no peak i s seen.
References
1 ) T. CHAPTN e t a l . , N . I . M .
