Using MBNIM electronics for the trigger in a high-energy physics experiment

Nuclear Instruments and Methods 175 (1980) 543-547 © North-Holland Publishing Company

USING MBNIM ELECTRONICS FOR THE TRIGGER IN A HIGH-ENERGY PHYSICS EXPERIMENT T. ARMSTRONG, W. BEUSCH, A. BURNS, I.J. BLOODWORTH, E. CALLIGARICH, G. CECCHET, R. DOLFINI, G. LIGUORI, L. MANDELLI, M. MAZZANTI, F. NAVACH, A. PALANO, V. PICCIARELLI, L. PERINI, Y. PONS, M.F. WORSELL and R. ZITOUN Istituto di Fisica dell'Universith and Sezione INFN, Bari, Italy University of Birmingham, Department of Physics, Birmingham, England CERN, Geneva, Switzerland LPNHE, Universitd de Paris VI, Paris, France Sezione INFN, Milan, Italy lstituto di Fisica dell'Universitd and Sezione 1NFN, Pavia, Italy

Received 17 December 1979

The Multi-Bit-Nuclear-lnstrument-Module electronics has been used to provide the trigger for an experiment performed with the I2' Spectrometer at CERN. This trigger required the detection of an outgoing K÷ or proton in a wide range of angles and momenta. Its performance and advantages are reported.

1. Introduction

and C2 for particle identification, and three arrays of scintillation counters H I , H2 and H3 for triggering purposes. The thresholds of the Cherenkov counters for pions and kaons were at 2.8 and 9.8 GeV/c for C 1 and 5.7 and 20 GeV/c for C2, respectively. The hodoscopes H1, H2, H3 arranged in vertical slabs, made it possible to select particles in a given momentum band using the correlation as produced by the magnetic field. Fig. 2a shows this correlation simulated by Monte Carlo method for several reactions of type (1) and

An experiment has been performed at the ~2' Spectrometer [1] using a new type of electronics as a basic tool to build the trigger. This electronics is based on a set of Multi-Bit-Nuclear-Instrument-Modules (MBNIM) designed by the ~2' electronics group [2]. This paper reports briefly on the performance of the trigger: (1) first we give a sketch of the apparatus and we explain which process we want to trigger on; (2) then we describe the electronic logic and the results obtained with it; (3) finally, we comment on the MBNIM as compared to traditional NIM electronics.

OMEGA PRIME SPECTROMETER

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2. Principle of the trigger

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The aim of the experiment [3] is to study processes of the kind: K- + p ~ K÷/p + anything,

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where a forward K ÷ or proton has to be selected out of the copious production of 7r÷. Fig. 1 shows the experimental layout which consists of a set of MWPC and two drift chambers in a large gap magnet, two large Cherenkov counters C1

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Fig. 1. Experimental layout of the Omega Prime Spectrometer. Horoscopes H1, H2, H3 (scintillation counters) and C1, C2 (Cherenkov counters) are used to define the triggering forward particle. Two tracks are shown corresponding to two types of trigger. 543

544

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fig. 2b shows that the corresponding data, taken with a rather loose trigger, are in agreement with the expectations. With this setup we can have two types of trigger (see also fig. 1): a) SLOW TRIGGERS for particles between 2.8 and 9.8 GeV/e, which are accepted when giving correlated signals in H1 and H2 and none in C1 and H3; b) FAST TRIGGERS for particles between 5.7 and 20 GeV/c, which are accepted when giving correlated signals in H I , H2 and H3 and none in C2. The new MBNIM system [2] has been used to impose the correlation between the hodoscopes and Cherenkov by means of the so called Bit Assigner (BA). This module has an ECL Random Access Memory (RAM) which can be loaded via the CAMAC function F16. The 16-bit output of the BA can be regarded as the acceptable configuration of a given

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Fig. 4. Actual content of the Bit Assigners (BA) used for experiment WA60: (a) Three BA are used to impose the H2 vs H1 correlation taken from fig. 2 and two for the correlation between H2 and C1 which requires the anticoincidence of pions in trigger (a). (b) Similarly, two BA are used to impose the correlations corresponding to trigger (b).

545

T. Armstrong et al. / MBNIM electronics

array of counters which corresponds to the one presented on the 16-bit input. Each bit in input can predict up to 16 different bits in output and if several bits are present at the same time the OR is taken.

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.,[c,] Fig. 5. Electronic logic diagram for trigger conditions (a) and (b). The lines indicate 16-bit flat cables carrying ECL signals (see text).

546

T. Armstrong et al. / MBNIM electronics

needed for the MBNIM. The principle of operation is shown in fig. 3, which is taken from ref. 2: the MULTILOGIC AND module verifies bit to bit the coincidence between the prediction made for H2 by the BA, let us call it H2 (HI), and the actual value of the hodoscope H2.

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In order to be compatible with the MBNIM 16-bit word modules, both hodoscopes H1 and H2 were arranged in two parts: H1F, H2F for the first 16 channels and H1L, H2L for the last 15, starting furthest from the beam. Hodoscope H3, which was actually made of 15 channels was treated in one word. Similarly, each Cherenkov counter, which consisted of 8 cells above the beam line and 8 below, was treated in one 16-bit word. Using these definitions, it is easy to verify that the following predictions correspond to triggers (a) and (b), respectively:

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H2 F(H 1F), H2F(H 1L), H2 F(C 1), H2L(H 1F), H2L(H1L), H2L(C1), H2F(H3), H2L(H3),

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H3(C2). But, as can be deduced from fig. 4, the actual number of BA needed is only five for trigger (a) and two for trigger (b), because H2L(H1F) and H2L(H3) happen to be always empty. Fig. 5 shows the logic diagram of the trigger. Notice the wired OR between the two predictions made for H2F, and how the high irnpedence inputs make the use of costly FAN-OUT's unnecessary * The anticoincidences for the Cherenkov signals are obtained by inverting the prediction H2(C1) and H3(C2), replacing AND functions by NOR in the same multilogic modules. The possible correlation between H3 and H2L is vetoed for trigger (a) because "SLOW TRIGGER" particles can never satisfy it. The final logical functions satisfying triggers (a) and (b) are therefore: H2F • H2F(H1) • H2F(C1) + H2L" H2L(H1) • H2L(C1) H 2 L - H 2 L ( H 1 ) ' H2L(H3C2). Notice that the anticoincidence cannot be obtained by loading the matrices complementary to the * The termination at the end of the BUS is obtained by simply plugging an array of resistors into a socket placed inside the module.

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Fig. 6. The data, when selecting events with single hits, shows: (a) H2 vs HI correlation, to be compared with fig. 2. (b) H2 vs C1 correlation, showing the absence of pions. The full lines represent the content of the BA as from fig. 4a. ones given in fig. 4 for the Cherenkov counters, because the BA gives a trivial prediction in such a case. In fact, the BA making an OR of the output predictions of each input bin, any empty input would fulfil the condition.

T. Armstrong et al. / MBNIM electronics

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4. Results and conclusions

Fig. 6 shows the correlations obtained on-line for ( H I , H2) and (C1, H2) during the data taking of this experiment, selecting events with a single hit. This proves that the electronics logic is always satisfied. Furthermore, 75% of the triggers analysed by the offline geometrical reconstruction program [4] have a track compatible with the trigger conditions. An indication of the correct identification of K + is given by the two-prong events which should correspond mainly to the reaction: K-+p~K÷+K-+Y

° .

During the data taking, it was checked that the

547

invariant mass distribution for these events clearly shows the expected ~ peak (fig. 7), if one assigns the K mass to the two tracks. In the light of our experience, some advantages of this new MBNIM electronics are: 1) Flexibility and computer control. 2) Versatility of the multilogic modules (AND, OR, NOR, EX-OR). 3) Simple cabling for multi-slab counters. 4) It avoids FAN-OUT and gives the possibility of WIRED-OR. 5) No timing is required, since static levels are used. 6) Cheapness. We would like to thank the ~ ' electronic group, and F. Bourgeois in particular, for the friendly collaboration before and during the data taking.

References

[ 1 ] W. Beusch, Omega Prime, CERN/SPSC/77-70/T-17. [2] A. Beer, F. Bourgeois, A. Corre, G. Critin, M.L. Huber, R. Pegaitaz, H. Pflumm and G. Schuler, Nucl. Instr. and Meth. 160 (1979) 217. [3] M. Baubillier et al., Proposal to study Strangeonium and Baryonium produced in K-p interactions using the Omega Prime spectrometer, CERN/SPSC/79-29/P125. [4] J-C. Lassalle, F. Carena and S. Pensotti, TRIDENT, report CERN/DD-EE/79-7.