IL NUOVO CIMENTO
VOL. XXXIX, N. 1
lo Settembre 1965
Experimental Observation of Antideuteron Production. T. )/~ASSAlV[, TIL. 1V[ULLE~ (*), B. I{IGIIINI, 1V[. SOHNEEGAI~S (*) a n d A. ZlCHICHX C E B N - Geneva
(rieevuto il 13 Marzo 1965)
Summary. - - The results of an experiment which show the existence of antideutorons in the production process proton-beryllium are reported.
We report here the results of an experiment on the p r o d u c t i o n of antideuterons in p r o t o n - b e r y l l i u m collisions. The b e a m used for the investigation was the high-intensity, partially-separated negative beam of the C E R N P r o t o n Synchrotron. The b e a m l a y o u t is shown ill Fig. 1 and its earaeteristies are s u m m a r i z e d in Table I. T h e details of the b e a m are described elsewhere (1), so we will m e n t i o n only the points relevant to the detection of antideuterons TABLE I. -- Basic parameters el the beam. Production angle Target Horizontal angular acceptance Vertical angular acceptance Maximum momentum band Total length Beam size in the experimental area
111 mrad Be; ~ l • :t: 32 mrad • 6.2 mrad
at 100mrad
~-2% 61 m horizontal 3 cm; vertical 2.2 cm
(*) Institut des Recherches Nueleaires, 8trasbourg. (1) G. BRAUTTI,G. FIDECARO,T. MASSAM,M. MORPURGO,TIt. MULLER, G. PETRUCCI, E. Bocce, P. SCHIAVON,M. SCHN~EGANS and A. ZICHICHI: ~rUOV0 Cimento, 38, 1861 (1965). See also report presented by A. ZICHICHIat the I~te~natConal Con]erencc on HighEnergy Physics (Dubna, August 1964): (~A high-intensity, partially-separated, beam el antiprot~ne and K-mesons ~.
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T. MASSAM~ TH. MULLER, B. RIGHINI, Mo SCHNEEGANS
and A. ZICHICHI
in it: the beam came from an internal beryllium target of the CERST ProtonSyncrotron and was momentum and velocity analysed by bending magnets and an electrostatic separator, thus allowing the mass spectrum of the particles produced in the internal PS target to be determined. In order to be able to detect masses produced at very low rates with respect to t h e pions~ it was necessary to improve the mass resolution by adding gas ~erenkov counters (2) and time-of-flight counters. The position of these counters in the beam is indicated in Fig. 1. The function of the gas (~erenkov counters ~1 and ~2 was to provide a good antieoincidence for pions. These two counters were filled with 5 kg/cm 2 of ethylene and each had 99.99% efficiency for the rejection of pions. Counters 1, 2, and 3 were used for time-of-flight measurements. Fig. 2. - Electronics block diagram. All counters were timed to 0.3 ns using the relative FD are fast discriminators; D arc antiprotons of 2.5 Geu delays; M is a passive mixer; GU is timing of the counters was then corrected a coincidence circuit; anti is the for the difference in time of flight which input anticoincidcnce; SC is a scaler. exists between antiprotons and antideuterons of 2.5 Geu This correction is obtained b y adding delays of 8.2 and 3.7 ns to counters 1 and 2 respectively, while keeping counter 3 fixed in time. The full width at half height of our coincidence unit was 3.4 ns. The electronics block diagram is shown in Fig. 2. The Proton-Syncrotron was operated at 19.2 Geu with an average circulating beam of 8.1011 protons/burst; the burst length was 300 ms and the repetition rate (2.3 s)-1. About 80 % of the total circulatingbeam was steered onto our target (target 1) and each point of the results which are shown in Fig. 3a corresponds to 200 bursts. This graph shows the counting rate as a functiop of the excitation of the compensating magnet of the electrostatic separator. The lower curve is drawn by eye to estimate the background. The results after the subtraction of this background are shown in Fig. 3b. The expected shape of this curve is known from measurements which were made at the antiproton peak. The position and normalization of the curve were varied so as to find the X2 minimum fit. This corresponds to the curve shown in Fig. 3b; this curve, when added to the background, is shown in Fig. 3a. T h e position of the observed peak agrees to within one mY with the position predicted for the antideuteron peak from the experimental knowledge of the
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(2) M. VIVARGENT: ~ c l . Instr. and Meths., 22, 165 (1963).
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pion and a n t i p r o t o n peaks. The value of Z +- relative to the best fit is 16.4 for 14 degrees of freedom. This corresponds to a 30 ~o p r o b a b i l i t y of obtaining a worse fit. The dashed curve shows an a t t e m p t to fit the d a t a b y eye w i t h o u t the antideuteron peak. T h i s gives a Z ~9 of 26 and a value of Pz' less 30[ x\ o t h a n 3 %. The v a r i a t i o n of X~ I[* with the value used for the mean 2O of the distribution is shown in g o 101 ~ j Fig. 3c, where the value of %" i obtained w i t h o u t the antideuteo[ ]90 200 210 220 *ron peak is shown for refermagnet excitation mV
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Fig. 3. - a) Shows the esperimental points and the iitted curves. The lower curve is an estimate of the background. The upper curve is obtained by adding the fitted curve of Fig. 3b to the background curve. The broken curve is drawn under the assumption that the peak does not exist, b) Shows the result of fitting the expected shape of antideuteron peak with the background subtracted, c) Shows the variation of Z~ with the mean position of the peak.
The results reported (a) imply the conclusion t h a t a negative particle exists with mass equal to (1867 5 = 8 0 ) ~ e Y / c ~ (*). The most simple interpretation of these data is to identify this particle with the antideuteron. According to our monitor, the ratio of a n t i d e u t e r o n flux detected to pion flux in the beam is ( 8 T t)-10 -9. When this n u m b e r is corrected for attenuation of the a a t i d e u t e r o n s in our counter system and for decays of the pions
(3) Similar investigations have been performed at Brookhaven by L. LEDERMAN, ]:[. TING et al.: communication given by Prof. B. GREGORY at a CERN Seminar. (*) An important source of error is the uncertainty in the separator calibration. The error indicated by the Z~ curve of Fig. 3e would only be -_t=40 MeV/c 2.
14
T. MASSAM~ T H . M U L L E R , B. R I G H I N I ~ M. SCHN]~]~GANS
and
A. Z I C H I C H I
in flight, the ratio of antideuteron to pion at the production point is (1.2 • 0.2). 10 -8.
Concerning the comparison of antideuteron production with Hagedorn's statistical theory (,.5) we would like to point out that: i) our data refer to the production of antideuterons from primary protons of 19.2 Geu while Hagedorn's calculations (4) refer to 25 Geu primary momentum; ii) moreover Hagedorn's calculations are valid for nucleon-nucleon collisions while our data refer to the production of antideuterons in proton-beryllium collisions. After a detailed discussion with Prof. I-IAGEDOR~ the conclusion reached is t h a t only an experiment on hydrogen can be decisive towards agreement or disagreement with the statistical theory.
We would like to thank Prof. W. PAUL and Prof. P. PREISWE~K for the support and interest given to the present investigation; Prof. R. ttAGEDORN and Dr. H. PILKHU~ for discussion on the theory of antideuteron production; our technicians, messrs, d. BERBIERS~K. ~LEY and B. 2qlC0LAI for their appreciated help.
(4) ~n. HAG:EDORN:2~UOVOCimento, 25, 1017 (1962). (5) H. PIL•HUN: CER~ report 64-40.
RIASSUNT0 Si riportano i risultati di un esporimento ehe dimostrano l'esistonza dogli antideutoni nel proeesso di produziono protone-beriUio.