(* last = last confidently-identified fully-reconstructed Ds Ds* event)

CLEO-c stopped taking data earlier this week.  We looked in the last data run (7:38 am to 8 am) of just over 61 thousand events for collisions that produced Ds mesons, and we actually found one.  Even better, we found an event where you could see both the Ds+ and Ds, and where the photon from the Ds*+ → γ Ds+ transition was visible.  Above, you can see the event display, with all the tracks labeled; the event is consistent with the following sequence of events:

  • e+ e → γ → Ds*+ Ds
    • Ds*+ → γ Ds+
      • Ds+K K+ π+ π+ π
    • DsKS K
      • KSπ+ π

It was actually unlikely that we’d find such a nice event.  For the amount of data in the last run, we would expect roughly 75 Ds* Ds events.  Our full reconstruction efficiency (getting both Ds candidates) is somewhat less than 1%, so we had a good chance of winding up with zero events like this.  It’s nice to be lucky though.

The original incarnation of the CLEO detector first started looking at the products of e+ e collisions in 1979; the latest (and last) version, CLEO-c, recorded its last event at 8 am Eastern today – an electron and a positron bouncing off each other. Along the way, 450 papers have been published on CLEO data. We had a little celebration in the counting room as the last run, 234607, ended:

Last CLEO run

There’s still a lot of work to do – we need to decommission CLEO and reconstruct and analyze the last data!