PRODUCTION OF LARGE TRANSVERSE MOMENTUM GAMMA RAYS IN pp COLLISIONS FROM 50 TO 400 GeV (P. 248)

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Submitted on 1 Jan 1973

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PRODUCTION OF LARGE TRANSVERSE

MOMENTUM GAMMA RAYS IN pp COLLISIONS FROM 50 TO 400 GeV (P. 248)

D. Theriot

To cite this version:

D. Theriot. PRODUCTION OF LARGE TRANSVERSE MOMENTUM GAMMA RAYS IN pp COLLISIONS FROM 50 TO 400 GeV (P. 248). Journal de Physique Colloques, 1973, 34 (C1), pp.C1- 414-C1-417. �10.1051/jphyscol:1973158�. �jpa-00215238�

D. THERIOT N.A.L.

1.- APPARATUS AND DATA ACQUISITION.- T h i s e x p e r i - ment was performed u s i n g an i n t e r n a l t a r g e t i n t h e CO s t r a i g h t s e c t i o n of t h e N a t i o n a l A c c e l e r a t o r . Data were taken o v e r t h e complete range of p r o t o n energy a v a i l a b l e d u r i n g t h e a c c e l e r a t i o n c y c l e .

The t a r g e t was e i t h e r a hydrogen gas j e t [ l - 2 1 o r a r o t a t i n g carbon f i b e r t a r g e t . The d a t a p r e s e n t e d h e r e were obtained f o r both t a r g e t s a t a f i x e d l a b o r a t o r y a n g l e of 100 mrad f o r t h e d e t e c t e d gamma r a y . A l e a d c o l l i m a t o r r e s t r i c t e d t h e a p p a r a t u s t o d e t e c t i n g only one o f t h e two photons from a no decay.

The schematic of t h e a p p a r a t u s i s shown i n F i g . 1.

The d i s t a n c e t o t h e t a r g e t was 1 6 . 4 6 m and t h e s o l i d a n g l e a c c e p t a n c e was 9.5 p s t e r . The l e a d c o n v e r t e r was 1.1 r a d i a t i o n l e n g t h s t h i c k and t h e l e a d - g l a s s t o t a l - a b s o r p t i o n c o u n t e r had a n e f f e c t i v e l e n g t h of 14 r a d i a t i o n l e n g t h s .

The photon d a t a was t a k e n u s i n g a i . 2 . 3 . 4 t r i g g e r . When a t r i g g e r o c c u r r e d , t h e p u l s e h e i g h t s i n a l l c o u n t e r s , t h e main r i n g magnetic f i e l d (which gave t h e p r o t o n i n c i d e n t momentum) and o t h e r s c a l e r i n f o r - mation were w r i t t e n o n t o magnetic t a p e f o r l a t e r ana- l y s i s . Data were taken both w i t h t h e c o n v e r t e r i n and t h e c o n v e r t e r o u t . The c o n v e r t e r - o u t d a t a r a t e was l e s s than 1 . 5 % of t h e c o n v e r t e r - i n r a t e . F u r t h e r - more, t h e c o n v e r t e r - o u t s p e c t r a were p a r a l l e l t o t h e c o n v e r t e r - i n s p e c t r a t o t h e h i g h e s t t r a n s v e r s e mo- menta. T h i s behavior was c o n s i s t e n t w i t h photon con- v e r s i o n i n t h e c o u n t e r s themselves and no c o r r e c t i o n was made f o r c o n v e r t e r - o u t background.

2

.-

.-

f u r t h e r a n a l y s i s . A c u t on t h e p u l s e h e i g h t i n t r i g - g e r c o u n t e r 2 r e q u i r e d t h a t e v e n t s have a doubly i o - n i z i n g o r g r e a t e r p u l s e h e i g h t i n t h a t c o u n t e r .

Examples of t h e energy s p e c t r a of t h e l e a d - g l a s s c o u n t e r a r e shown i n F i g . 2 and 3 f o r 50 GeV and 375 GeV i n c i d e n t p r o t o n energy. The observed photon s p e c t r a were f i t t e d w i t h a f u n c t i o n of t h e form

F i g . 1. - Schematic of t h e a p p a r a t u s .

An energy c a l i b r a t i o n of t h e l e a d - g l a s s Cerenkov c o u n t e r 4 was made u s i n g 1 . 8 t o 5 GeV/c e l e c t r o n s and muons a t Argonne N a t i o n a l Laboratory. The photo- m u l t i p l i e r and base were t e s t e d and found t o be li- n e a r up t o a r e s p o n s e e q u i v a l e n t t o 280 GeV photon energy. The r e s p o n s e o f t h e c o u n t e r t o muons ( d e f i - ned by a 1 . 2 . 3 . 5 . 6 t r i g g e r ) was monitored d u r i n g d a t a t a k i n g . The p u l s e h e i g h t d i s t r i b u t i o n from c o u n t e r 4 f o r t h i s t r i g g e r showed a c l e a n peak w i t h a 30 % FWHM. The muon peak provided a c a l i b r a t i o n check d u r i n g t h e r u n s .

where A and B a r e f r e e parameters. With t h e e x c e p t i o n of t h e 50 GeV d a t a , t h e s e f i t s d i d n o t g i v e a c c e p t a - b l e X2

.

where A, B and C a r e f r e e parameters. Acceptable f i t s t o t h e d a t a were o b t a i n e d i n a l l c a s e s .

The same f u n c t i o n was then used t o f i t t h e carbon d a t a . There i s good agreement between t h e parameters o b t a i n e d f o r t h e hydrogen and carbon d a t a .

The i n v a r i a n t no c r o s s - s e c t i o n c a n be d e r i v e d

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973158

LARGE TRANSVERSE MOMENTUM GAMMA RAYS

F i g . 2 . - S i n g l e photon i n c l u s i v e c r o s s - s e c t i o n d u l d k d ~ f o r t h e r e a c t i o n p+p-+y

+

fo? i n c i d e n t p r o t o n energy of 50 GeV.

F i g . 3 . - S i n g l e photon i n c l u s i v e c r o s s - s e c t i o n d o /dkdQ f o r t h e r e a c t i o n p+p-n(

+

L-)

where A i s a normalLzaclon r a c c o r . Using t h e para- from t h e i n c l u s i v e photon spectrum by means of t h e

u s u a l Sternheimer a n a l y s i s [ 4 ] . m e t e r s B and C from t h e f i t s t o t h e photon spectrum we can t h u s d e r i v e a n i n v a r i a n t

2

cedure a r e shown i n F i g . 4 and 5. The 50 GeV d a t a i n F i g . 2 were a d e q u a t e l y f i t t e d by a s i n g l e e x p o n e n t i a l

dun

-

E 3 = A ( B + ~ c P ~ ) (dkdQ)

d P d a t a (i .e

.

.

2

I7ig. 4.- Derived i n v a r i a n t KO c r o s s - s e c t i o n d u f o r t h e r e a c t i o n p+p+y + a n y t h i n g f o r E

d3p

i n c i d e n t proton energy of 50 GeV.

F i g . 5

.-

+

&

i n c i d e n t p r o t o n energy of 375 GeV.

375 GeV d a t a shown i n F i g . 3 had a non-zero C . There- f o r e , t h i s procedure changes t h e shape s l i g h t l y , sup- p r e s s i n g t h e high pl v a l u e s s i n c e our f i t t e d C i s n e g a t i v e

.

The d e r i v e d no i n v a r i a n t c r o s s - s e c t i o n s were t h e n f i t t e d t o t h e f u n c t i o n Ae-BpL-CpL 2

,

3 . - DISCUSSION OF RESULTS.- I n F i g s . 6 and 7 we

p r e s e n t p l o t s of t h e v a l u e s of t h e parameters B and C v e r s u s i n c i d e n t p r o t b n energy f o r t h e gamma s p e c t r a from t h e hydrogen and carbon t a r g e t s . We f i n d a g r e e -

example a t 100 mrad l a b o r a t o r y a n g l e and 50 GeV, a pL o f 2.3 GeV/c corresponds t o a n x o f 0.4 w h i l e a t 200 GeV/c a l l v a l u e s o f p, correspond c l o s e l y t o x=O

.

R e s u l t s a r e given i n F i g s . 8 and 9 f o r t h e f i t s t o t h e i n v a r i a n t $ s p e c t r a . These p l o t s show t h e same

F i g . 6.- Values of t h e parameters B and C f o r t h e F i g . 8.- Values of t h e parameters B and C f o r t h e de- photon i n c l u s i v e c r o s s - s e c t i o n s from t h e hy- r i v e d i n v a r i a n t 4 c r o s s - s e c t i o n s from t h e drogen j e t t a r g e t f o r p r o t o n e n e r g i e s b e t - hydrogen j e t t a r g e t f o r p r o t o n e n e r g i e s bet-

ween 50 and 375 GeV. ween 50 and 375 GeV.

F i g . 7.- Values o f t h e parameters B and C f o r t h e pho- F i g . 9 . - Values of t h e parameters B and C f o r t h e de- ton i n c l u s i v e c r o s s - s e c t i o n s from t h e carbon r i v e d i n v a r i a n t no c r o s s - s e c t i o n from t h e f i b e r t a r g e t f o r p r o t o n e n e r g i e s between 50 carbon f i b e r t a r g e t f o r p r o t o n e n e r g i e s b e t -

and 400 GeV. ween 50 and 400 GeV.

ment between t h e two t a r g e t s f o r t h e p a r a m e t e r s . The d a t a g i v e n h e r e r e p r e s e n t a l l of t h e hydrogen d a t a t a k e n a t t h i s a n g l e , b u t only about 25 % of t h e c a r - bon d a t a . The d a t a seem t o r e q u i r e a B parameter t h a t does n o t vary s i g n i f i c a n t l y w i t h energy. On t h e o t h e r hand, t h e C parameter s t a r t s o u t a t z e r o , i n c r e a s e s

s h a r p l y between 50 and 125 GeV, t h e n i s approximately independent of i n c i d e n t p r o t o n energy. T h i s C parame- t e r e f f e c t i v e l y measures t h e d e v i a t i o n from simple e x p o n e n t i a l b e h a v i o r .

~t should be emphasized t h a t our experiment i s per- formed a t f i x e d l a b o r a t o r y a n g l e and t h a t t h e r e i s

g e n e r a l f e a t u r e s d i s c u s s e d i n c o n n e c t i o n w i t h F i g s . 6 and 7. The v a l u e s of C f o r t h e no s p e c t r a a r e i n good agreement w i t h t h o s e found a t t h e ISR [ 5 ] f o r charged p i o n s i n t h e energy r e g i o n where o v e r l a p o c c u r s .

I n c o n c l u s i o n , we c o n f i r m t h e r e s u l t s from t h e ISR [5-6-71, t h a t t h e s i n g l e p a r t i c l e i n c l u s i v e d i s t r i b u - t i o n d e v i a t e s markedly from a simple e x p o n e n t i a l be- h s v i o r . I n a d d i t i o n , we have o b t a i n e d p r e l i m i n a r y r e - s u l t s t h a t show t h e energy dependence of t h i s devia- t i o n between 50 GeV and 400 GeV.

LARGE TRANSVERSE MOMENTUM GAMMA RAYS

REFERENCES

[I] Development and Operation of Hydrogen Jet Target [4] STERNHEIMER (R.M.), Phys. Rev. 2 (1955) 277.

Supported by the State Committee for Utiliza- [S] BANNER (M.) et al., Phys. Lett. (1972) 547 ; tion of Atomic Energy of the USSR, Moscow. Phys. Lett. 44B (1973) 537.

[6] ALPER (B.) et al., Phys. Lett. &B (1973) 521.

[21 BARTENEV (V.) et al., Phys. Rev. Lett. 2 (1972)

1755. [7] CERN-Columbia-Rockefeller, Batavia Conference

[31 At the present time we auote a

+

-.

calibration of the lead glass counter.