(* 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.

Want to read about several years of progress in open charm physics – lattice QCD tests, standard candle measurements, D0 mixing – in a compact 30-page article? Try “Charm Meson Decays” (Artuso, Meadows, Petrov).

The latest Heavy Flavor Averaging Group results on D0 mixing are to be found in Alan Schwartz’s writeup for the recent BES-Belle-CLEO workshop.  The continual drip of new results has pushed the mixing significance to 6.7σ.

Accumulating evidence for nonstandard leptonic decays of Ds mesons“… I’m happy that some people think of us when they think of new physics tests, though I’m skeptical.  Anyway this gives BES-III something extra to do.

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!