Development of a bubble chamber data analysis using several scanning-measuring-projectors on-line to a digital computer

NUCLEAR

INSTRUMENTS

AND

METHODS

:20

(196a) 384--386,

NORTH-HOLLAND

PUBLISHING

CO.

D E V E L O P M E N T OF A B U B B L E C H A M B E R D A T A A N A L Y S I S U S I N G S E V E R A L SCANNING-MEASURING-PROJECTORS R

ON-LINE

TO A DIGITAL

COMPUTER

I HULSIZER

Lawrence Radmt~on Laboratory, Berkeley, Cah/orma

I n N o v e m b e r 1960, Alvarez i n v e n t e d a new t y p e of m a c h i n e for scanning a n d m e a s u n n g b u b b l e c h a m b e r p h o t o g r a p h s l) Because of its dual function it is labelled the SMP ( s c a n m n g - m e a s u r m g projector) D u r i n g the s u m m e r of 1961, S n y d e r s t u d i e d t h e design of the m a c h i n e a n d recomm e n d e d its use m a d a t a analysis s y s t e m in which t h e s c a n n i n g a n d m e a s u r i n g m a c h i n e would be c o n n e c t e d directly on to a high speed dlgatal c o m p u t e r 2) T h e c o m p u t e r would be p r o g r a m m e d to check t h e data, to do t h e space r e c o n s t r u c t i o n of the t r a c k s from t h e stereoscopic measurements, a n d to perform the k i n e m a t i c a l analysis of the e v e n t s Errors in m e a s u r e m e n t would be reported b a c k to t h e m a c h i n e o p e r a t o r within a few seconds so t h a t corrections or r e m e a s u r e m e n t s could be m a d e while the film was still registered in t h e m a c h i n e This p a p e r will r e p o r t on t h e progress m a d e in developmg these ideas into a workable d a t a analysis s y s t e m I n t h e s u m m e r of 1961 a p r o t o t y p e SMP was c o n s t r u c t e d a n d c o n n e c t e d to the direct d a t a c h a n n e l of t h e IBM 709 c o m p u t e r a t the Lawrence R a d i a t i o n L a b o r a t o r y Tests h a v e been m a d e on t h e m a c h i n e as a m e a s u r i n g device a n d programs for c a r r y i n g o u t t h e ingestion of d a t a a n d t h e online analysis are being developed, using this p r o t o t y p e as a test model T h e first set of tests consisted in measulang s t r a i g h t wires s t r e t c h e d over the surface of the 1) L W Alvarez, " A proposed devine for the rapid measurement of bubble chamber film", Physics Note Memo No 223, Lawrence 1Radxatlon Laboratory, University of Cahforma, 1960 t) j N Snyder, "Some remarks on a data analysts system based upon the scanning-measuring projector (SMP)", Phymea l~lote Memo No 326, Lawrence Radiation Laboratory, Umveratty of Cahforma, 1961 384

image plane The wires h a d the same w i d t h as the image of a b u b b l e 0 5 m m The results are shown in fig 1 where the b a r - g r a p h shows t h e distribution of m e a s u r e d points with respect to ~sNUMBER OF POINTS

¢I~I ALONG WINE

40!

o, I$".ACH.Nt I -i.~ . t.~tAsrCOUNT L. r ± J STA.~D DEVUWWON [ -'

I03 MICHOH$ON TABLE

38

I 36

THICKNESS OF STRAIGHT WINE SHADOW 520 MICRONSON TAOL[

~. ~ 1

0 mmON TAOLE

3O 28 26

24 22

m DEVIATION FROMBEST*FIT LINE NIC~ON$ OH TABLE

Fig 1 Error analysis of SMP-1 measurement of the shadow of a straight rare

the centre of the h n e The w i d t h of this d i s t r i b u t i o n is 105# This n u m b e r is the root m e a n square fluctuation of m e a s u r e m e n t s of t h e position of m d l v l d u a l p o m t s on the wire On the average, one p o m t per m m of the wire is m e a s u r e d a n d therefore a 1 cm segment of wire can be located to a precision of 105/2/(10) t o r 33#, 1 e , 1-~th of

A BUBBLE

CHAMBER

the wlre diameter In the film plane, this is eqmvalent to 2 2 p To measure actual bubble chamber tracks, a computer program had to be written to select points belonging to a track and to reject those that came from dirt or from other tracks that appeared in the optical aperture along with the desired track A prehmlnary versmn of such a flltenng program has been written and a few tracks have been measured Fig 2 shows a plot

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pOmlfrom SMP "I" SmOOlhdol(l point • Size of bubble on lh~l Stole

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-~"

Row Ctolo

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X(cm] F i g 2 Measurement of a n a c t u a l b u b b l e c h a m b e r t r a c k v o t h SM_P-I The d o t s represent raw d a t a , t h e crosses represent s m o o t h e d p o i n t s after filtering o u t p o i n t s t h a t do n o t fit the track

of the coordinates of such a track The rms dewatlon of the 26 filtered coordinates from a best fit to a 4th degree polynomial is 108 # which corresponds to 7 # in the film plane The position of the smooth curve through the points can then be determined to an accuracy of 2/, in the film plane An ideal ffltenng program, in addition to finding the bubbles that belong to the track, would a t t e m p t to detect kinks that the operator had missed and would a t t e m p t to determine vertmes by extrapolatmg the several tracks from a vertex back to then- intersection. A n y failure of the filter program to flnd a continuous track would call forth a request for remeasurement b y the operator Some difficulty is expected on short tracks where it m a y be necessary to m a k e a measurement of the

DATA ANALYSIS

385

two end points by casting a shadow of a cross over the end points and m e a s u n n g the legs of the crosses to detexTmne the centres of the crosses and therefore the locations of the end points The organization of the SMP executive program is as follows The computer will ask for the indicative information on each event by typing clues on a typewriter to which the operator will respond with answers, mostly numerical, such as roll number, frame number, event type, etc. After the indicative informat]on has been checked and stored, the flduclal measurements and track measurements In each stereoscopic view will be called for, ingested, filtered and placed In the format desired by the space reconstruction and analysis programs In the first step of the development an output tape of these quantities will be produced Subsequently it is hoped to carry out at least part of the space reconstruction and analysis immediately so that the q u a h t y of the measurements can be checked on-hne. Time-sharing the 709 between three SMP's appears to be quite manageable and more might be accommodated w~thout saturation of the data channels Some of the relevant times are as follows Characters will be presented to the typewriters via the "sense lines" and a multiplexer on a character-by-character basis Slx sense lines will represent the character and three will designate the typewriter Two machine cycles are requn-ed for this operation, 1 e 24/~sec, and each typewriter can p n n t 10 characters per second After a typewriter has printed a character, it will interrupt the computer to request the next About one per cent of the computer time will be required for this class of operation Similarly when the operator types a character it will be ingested on the sense lmes and stored with simple tests that will again use less than one per cent of the computer time Measurement data from all of the SMP's will be fed through a multiplexer to a single directdata channel with at most two words per measured point. The 709 will ingest two successive words m 84 #sec and an SMP cannot produce successive points in less than 100 psec Words fed into the direct-data channel are stored In the main m e m o r y without disturbing the computing programs Once IX

DATA ANALYSIS

386

R

I

HULSIZER

a fiduclal or t r a c k m e a s u r e m e n t is complete, its d a t a can be filtered a n d placed in proper f o r m a t in less t h a n a second whereas it will take, on t h e average, 10-15 seconds to measure each t r a c k On the basis of these numbers, it appears t h a t the c o m p u t e r will be occupied up to 30 per cent of Its time while it is doing this class of operation s i m u l t a n e o u s l y for three SMP's M e a s u r e m e n t of a complete event in three views

will take several minutes, processing the measurem e n t s t h r o u g h kinematical analysis will take, on the average, half a m i n u t e on the 709 Since the c o m p u t a t i o n s described previously use only a neghglble fraction of the c o m p u t e r time, this last c o m p u t a t i o n would be the m a r e consumer of time I conclude t h a t the 709 could do a fairly t h o r o u g h analysis (through K I C K ) of the o u t p u t from three to eight on-line SMP's