HyperCP Spectrometer

The HyperCP spectrometer is the highest-rate particle physics detector in the world, with an ability to record 80,000 events per spill second to tape, or about 15 MB/s. Its salient features, beside high rate, are good charged particle momentum resolution, and good acceptance for Xi -> Lambda + piminus decays. For a complete description of the HyperCP spectrometer, see hep-ex/0405034.

Elevation View

Click on image to see photos of detector elements

A target assembly consiting of four different targets immediately followed by a collimator with a 4.88 microsr solid angle acceptance embedded in a 6 m long dipole magnet defines a charged secondary beam of 167 GeV/c average momentum, bent up at a 19.5 mrad angle to horizontal. Following a vacuum decay region is a magnetic spectrometer employing nine high-rate, narrow-pitch wire chambers. The switch from Xi to anti-Xi running is done by periodically flipping the polarity of both the hyperon and spectrometer magnets.

The spectrometer analyzing magnet has sufficient strength to ensure that the proton and pions from the Xi -> Lambda + piminus, Lambda -> proton + piminus, and K -> 3pi decays are always well separated from each other as well as from the charged beam exiting the collimator. This allows a simple, yet selective trigger to be formed by requiring the coincidence in hodoscopes at the rear of the spectrometer of charged particles on either side of the spectrometer. A hadronic calorimeter on the proton side is used to make the trigger blind to muons and to reduce the trigger rate from interactions of the channeled beam in the spectrometer. A simple muon system at the rear of the spectrometer allows access to rare and forbidden hyperon decays.

The data are recorded with two data acquisition (DAQ) systems: a fast DAQ to read out events to tape and a slow DAQ used to read out the scalers and other beam-line information to disk. The fast DAQ reads data from two front-end latch systems: one for the spectrometer chambers and the other for the muon chambers. The data are transferred into a large (1 Gbyte) fast buffer via five parallel optical paths. The events are then built in parallel in five VME crates by 15 MVME167 single board computers and written to 45 Exabyte 8505 tapes. The data acquisition system has a maximum rate to tape of 17~Mbytes/s or approximately 100,000 events per spill second. It is the fastest DAQ in the world.

Descriptions of HyperCP Detector Elements