First SVX Colliding Beam Data

CLEO took its first e+e- colliding beam data with the silicon vertex detector (SV) turned on at 8 PM on November 21, 1995. The movable radiation shields were closed, but as they only block very low momentum particles, it was possible to see a variety of events. We took about 4000 SV events at a luminosity of about 50 x 10^30.

Bhabha event

This is an event display of a Bhabha event, e+e- -> e+e-. We see the electron and positron tracks in the drift chambers, and their corresponding showers in the calorimeter. Looking more closely at the SV

Bhabha close up

we see that the two tracks pass through it, and the electrons have left energy clusters that are well-matched to the tracks. The tracks shown have not been fit using information from the SV. The SV does not appear to be perfectly aligned with the rest of CLEO yet. The events that are really interesting to CLEO collaborators are e+e- -> hadrons. Here is a closeup of one of these events:

Hadronic event

The SV hits match up with the tracks that have been found, and unused hits can be associated with the curling track that the (simple) tracker did not find. The power of the SV is more obvious in a busier event:

More complicated hadronic event

Here there are many curling tracks, including some that spiral many times, but it is much easier to find their track parameters by matching them with track segments made in the SV. You can do this association by eye with several tracks in the event.

This is just the beginning of the SV era in CLEO -- to get this data, all we did was turn the detector on. In the near future, we hope to improve the signal to noise in the SV, the alignment of the SV with the rest CLEO, and the pattern recognition in general, in our effort to bring the physics done at CLEO and CESR to an even higher level.

Read onwards to learn about our latest progress in charged particle tracking.

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