IEEE Transactions on Nuclear Science, Vol. NS-26, No. 4, August 1979 The Crystal Ball Data Acquisition System R. Chestnut, C. Kiesling, E. Bloom, F. Bulos, J. Gaiser, G. Godfrey, M. Oreglia SLAC Stanford University R. Partridge, C. Peck, F. Porter California Institute of Technology D. Aschman, M. Cavali-Sforza, D. Coyne, H. Sadrozinski, Princeton University W. Kollmann, M. Richardson, K. Strauch, Harvard University R. Hofstadter, I. Kirkbride, H. Kolanoski, A. Liberman, J. O'Reilly, J. Tompkins, Stanford University, HEPL T. Burnett University of Washington, Seattle ABSTRACT The data acquisition system for the Crystal Ball project at SLAC is described. A PDP-11/t55 using RSX-11M connected to the SLAC Triplex is the basis of the system. A "physics pipeline" allows physicists to write their own equipment-monitoring or physics tasks which require event sampling. As well, an interac- tive analysis package (MULTI) is in the pipe- line. Histogram collection and display on the PDP are implemented using the Triplex histo- gramming package. Various interactive event displays are also implemented. INTRODUCTION The Crystal Ball is a non-magnetic detector system with a large solid angle acceptance. It emphasizes the complete detection and pre- cise measurement of energy depositions of all particles produced in positron-electron anni- hilation events. The detector has five major components: 1. A compact 672-segment NaI detector of 16 radiation lengths which is almost spherical and covers 94% of the total solid angle. 2. A set of cylindrical magneto-strictive spark chambers and multi-wire proportional chambers around the beam pipe to define charged particle trajectories. 3. End caps of magneto-strictive spark cham- bers, and mildly segmented (60 segments) NaI crystals closing the solid angle to 98% of the full sphere. 4. A multicounter luminosity monitor to mea- sure the beam luminosity to about 2%. 5. A muon-hadron selector consisting of pro- portional tube arrays sandwiched between several layers of steel plates covering about 15% of the solid angle. The detector system was designed and built by the Caltech, Harvard, Princeton, Stanford, SLAC collaboration and is now running this ex- periment at SPEAR (Stanford Positron Electron Asymmetric Rings). An online-computer system was planned as an integral part of the experiment. The design goals of the data acquisition system were: Flexible computer access to the hardware using CAMAC, Read-out and logging of data onto tape, Provide a diagnostic tool so that any physicist in the group could easily moni- tor some portion of the equipment, Deliver an accurate overview of the sta- tus of the detector and electronics at any time, Do as much physics analysis online as possible to efficiently monitor the ex- periment's progress. HARDWARE A PDP-11/t55 computer with the full compliment of core, including 64kBytes of fast core and a fast floating point arithmetic unit was chosen to meet these goals. This configuration is ten percent faster than the similarly equipped PDP-11/70, according to Digital Equipment Cor- poration benchmarks. Peripheral devices in- clude two 1600 b.p.i magnetic tape drives, an RK07 (28 Megabyte), an RK06 (14 Megabyte) and two RK05 disk drives, a Versatec prin- ter/plotter, three Tektronix 4013 displays and an IBM System/7 which serves as a link to the U.S. Government work not protected by U.S. copyright. 4395