Holthuizen, D J

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CJi;UH - ])]) /DA/ 6 7 /1 D. Holthuizen February 1967 A Measurement of the Position of the Fiducials on Bubble Chamber Film Introduction Using the measurements of HPD 1 on pictures of stopping anti-protons in the 81 cm Saclay bubble chamber (taken about February 1965), a study was made of the relative coordinates of the fiducials in the frames of a roll. The deviation of each fiducial from a mean position was plotted, both for the X and for the Y direction. The result is thought to be a test for the quality of the roll. The method Initially, follovring a suggestion of Peter Villomoes, a comparison was made between the measured fiducials and a fixed system of fiducial coordinates, allovring a translation for the whole, in the X and the Y directions. These translations are found by calculating the translation of each fiducial of a certain frame and taking the mean value. The individual translations are compared with this mean value and then deviations from the mean of more than 3 least counts, (one least count is equal to 2.54 microns), are excluded from the sample which determines the next approximation of tLe mean translation. In fact this is done step by step by excluding the worst value in each step. After the determination of the mean translation in X and Y directions, the difference between this mean value and the translation for each fiducial is calculated. These values are plotted for each roll using the SUJ.Vf.X program (applied to the SMOG output tape). The result of the.first run is in general not particularly good, because the fixed system of fiducial coordinates is itself different for each roll. If a wrong set of given positions is chosen, the translation of the different fiducials are different and the method of finding the mean tran?lation does nQt rrork v:ery well. But from the first run a better approximation is obtained for the coor-dinates of the fixed frame. These values are in general accurate enough so that the second run gives the final result. 67/173/3/ck Output of the prograig_ For each roll a set of histog;rams waf:i produced giving the position for each fiducial rri th respect to t1w mean position. This was done for each view, for X and Y directions. Moreover a set of cards vms punched vri th the X and Y coordinates of each fiducial and the root mean square value of the distri-bution. For stable ficlucials this value is 1 or 2 least counts (Fig. 1), for moving fiducials much higher values can be obtained, of mo.re than 10 least counts, as shown in Fig. 2. A complication arises by the fact that in some cases (in about 0.2 % of all measurements) the HAZE program finds completely wrong fiducials. This is perhaps caused by crossing tracks or scratches or dust on the film or something like that. To exclude these values from the sample, all deviations from the mean translation, bigger than 30 least counts, are excluded from the histograms and from all calculations. The punched cards are used as input for tho program LIST which makes a list of the coordinates of the fiducials for each roll vri th respect to one of them, nhich is taken as origin of the system. Also the root mean square valuos of tho distributions are printed in the list. A comparison is made with the THRESH titles. Because the result is also wri ttcm on tape, the SID/IX program can again be applied to give an overall picture. In this way the histogram of Fig. 3 has been obtained in vrhich all root mean square values from 30 rolls a.re plotted. Conclusions for the quality of the rolls To say something about tho result for 30 rolls, we will use the units used in tho THRESH titles, obtained from tho program PYTHON. Tho translation from least counts (on tho film) into those units (on a virtual front glass) is done by a multiplication factor. The THRESH program accepts deviations of the position of the fiducials from a given value up to 0.4 mm. We call a fiducial "bad" when the root mean square value of the histogram for X or Y coordinates exceeds 0.2 mm, and this has given the following bad fiducials (Table l)g Fiducial 4 4 6 7 67/173/3/ck View 1 3 2 1 Table 1 Number of rolls (out of 30) 1 2 1 1 ) ) ) - 3 -The numbers of tho fiducials on front and backward glass are given in Fig. 4. Al.so tho positions on view 2 of thG film are given there. 'I1he most important region of the film is between fiducials 7, 8 and 9. Since tho interactions which occured in this region are those -.vhich aro being measurod. Tho result for fiducial 7 is tho worst bocauso this is a central fiducial. Fiducial 6 nill not influence tho rosults by a significant amount as ·was provod by an investigation of Philippe Gavillot (appendix 1). Fiducial 4 is presumably moro important, so we can conclude that out of a sample of 30 rolls, 4 have low quality and should be considered seporately in tho study of the final results. Cause for tho movement of tho fiducials Ten frames of roll 5261, vrhich has the worst fiducial movement of this experiment (fiducial 6 in view 2), wero also measured on the IEP, to look if the effect of moving was caused by the HPD i tsolf, The distance in X and Y coordinates botvrnen fiducials · 6 ,and 7 and botvrnen 5 and 7, "\rnro compo,red in those 10 frames for HPD and IEP measurements. To make tho comparison (in Table 2) easier, the deviations are given relative to the distance observed in one of tho frames. ---------------------------------------------------------------------Table 2 Frame Fid 6 -Fid 7 Fid 5 - Fid 7 HPD IEP HP:D IEP (2.54µm) (2.54µm) (2.54µm) (2.54µm) 96 65 67 0 0 97 4 5 3 1 102 6 6 1 3 103 8 9 2 2 106 13 14 1 -1 107 4 8 3 1 108 24 17 2 6 109 27 20 1 4 111 0 0 3 3 112 25 19 l 9 ---------------------------------------------------------------------67/173/3/ck - 1)- ·-We drov the conclusion that tho offoct of tho moving of fiducial 6 was found in tho sc~ma uay on HP:D and IEP. It is thought that it might be caurrnd. by n, bc1d functionning of tho camera film gn to. Systematics in the moving of the fiducials For roll 5201 a plot was mado of the daviation of tho position of tho moving fiducial 4 from tho moan position, as a function of tha frame number. No correlation bohrocm tho motion and framo number rms found, tho fiducial movomonts being complotoly irregular. (Fig. 5) Further tho direction of the motion in tho XY plane uas stucliod. As shmm in Fig. 6 thoro is n special direction for the moving of tho fiducials in ono roll, but for different rolls the directions are often difforcmt. Sometimes thoro is a clear kink in tho distribution (Roll 5225, viou 3). One gets tho impression that tho moving of fiduci:::1,ls 4 oxtd 0 :::ore caused by a rrrong functionning of tho film gate of tho camera. If tho pressure on tho end pnrt of tho film comoD to early 9 tho film vrill be shifted a bit, rrhich nill have a bigger effect for fiducial 4 than for fiducio,l 0 (see Fig. 4) but goos along tho samo line. 67/173/3/ck APPENDIX 1 Some details concerning the investigation of fiducial 62 roll 5261, by Philippe Gavillet. A comparison was mo,de of tho values of the momentum ( p) and of the tvrn angles in space ( /\ and ~1 ) obtained both with fiducial 6 cmd without fiducial 6 in view 2( Also a comparison was made betvrnen the ori"ginal values and tho values obtained after suppressing viei;r 2. Because deviations are only important if they are of the same order of magnitude as (or bigger than) the (external) errors of measurements, a plot vas made of tho differences observed, divided by the error of measurements. The root mean square values ( (}-) wore calcule,tod. Also the occurrence of a systematic shift of the mean value ( ~ ) of any one of the quantities was studiGd. The percentage of the frames (%) where the difference caused by suppressing a fiducial (or a view) is more than one root moan square value, is also given. In Table 3 all those values are given as a function of the value of the fiducial residue (Ros) found by THRESH. ---------------------------------------------------------------------Table 3 Ros Number \ ._,_T .. /\ (mm) of frames " % .':...~ . % ,} ~~\ % . ~\ 0 - .8 3175 ~45 -.09 .89 -.01 p:: 0 .J .65 0 - .2 1013 .10 -.01 .2 .15 -.01 . 3 .12 - .02 . 3 .2 - .4 1532 .44 -.12 4.s .80 -.03 19.0 .so .22 4.2 .4 - .6 561 • 68 -.13 12.5 L53 .04 28.7 .69 .25 11.4 .6 -.8 69 1.04 -.21 24.6 1.85 -.04 49.3 .83 .37 18.4 suppressing view 2 0 -.2 824 1.24 .02 15.7 1.38 .03 15.3 1. 76 -.14 20.4 ---------------------------------------------------------------------No difference uas found between the deviations of positive and of negative tracks with RES .4 mm. 67/173/3/ck - 2 -In Table 4 the differences ( _i 1 - (1 2 ) of the mean values for positive ( 1 ) and negative tro.cks ( 2 ), are compared with the calculated errors (:r··). Res. (min.) \1. ·-;·-.. 1 0.006 0,02 ; . .) ! 0.0058 0.025 Table 4 /\ I /' -· /\ f ! ,,Li -~ 1. 0.01 0.02 v 0.012 0.055 //1 ,., ' . . -· iJ . \ j "~' 0.04 0.02 0.080 0.040 This roll ·~vill not be used for tho meo.suremont of tho invariance of strong interaction for charge conjugation, but it will be used for investigations of invariant mass plots and so on. 67/173/3/ck ~ i JOO 200 100 ( Fiducia I 0 / X coo rd 1 view 1 / Roi I 5405 ) I NUMBER -10 FIG. 1 0 Deviation from the mean position for a ''good'' fiducial 10 DEVIATION FROM MEAN (stage least count!) (2.S4 j-) (Fiducia I 4 , X coo rd / view 3 , Roll 5405 ) 20 r NUMBER 10 - 20 -10 0 FIG. 2 Deviation from the mean position for a '1 bad" fiducial 10 20 ...... 7 DEVIATION FROM MEAN (stage least colllts) (2.st. r> 600 500 400 300 200 100 5 10 ROOT MEAN 50.UARE VALUES FOR ALL FIDUCIALS IN ALL VIEWS 15 20 25 FIG. 3 stage I east counts (2. 54 ,,µ-) 30 x 6 x 5 x 7 x 9 x 8 x 0 x 1 x 3 x 2 Backward glass plate Forward glass plate x x 3 x 6 9 x x xx 1 7 04 x x 5 x 8 2 Fiducia ls 1n view 2 FIG 4 Position of the fidl.l:ials x 4 30 20 10 0 -10 -20 -30 0 Coord. r2.s4r1 FIG. 5 50 100 Moving of Fid .4 . View 1 . Roll 5 201 X Coord. as a function of the frame number -150 200 FRAME NUMBER ---~ 250 Roll 5201 view 1 Fid . 0 Roll 5237 view1 Fid . 0 Roll 5261 view2 Roi I 5405 view3 Roll 5225 view3 Fid. 0 y I FIG . 6 2 5.4 /"'" L x 2S.4r" Fid. 7 Fid. 6 1 DIRECTION OF MOVING IN THE XY PLANE Fid . 4 Fid. 4 fid . ' 

A measurement of the position of the fiducials on bubble chamber film

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