End of Y2K data taking
On November 2nd 2000, at 8:00 LEP dumped the last physics fill of the year in an heroic effort to ramp up the
energy to what would have been a new world record of 210 GeV. The beams were lost during this ultimate effort and we don't know
whether they reached the top. Here a the very last events collected in DELPHI (in inverse chronological order) :
- Last multitrack event : it was collected at 07:59:55 when the miniramp had started 35 seconds earlier. It is
however a gamma-gamma collision with only 20 GeV of energy, but it becomes historical due to its time of birth.
- Last Z return event : it was collected at 7:57 and you can
see here two jets coming from the
decay of a Z particle. A photon recoils opposite to the Z and is not observed since it is in the beam pipe.
- Last multijet event : taken at 7:50, it is
too early at 12:20 to precise its very nature, but it looks
like a 3 or 4 jet events with almost the full beam energy observed in the detector. One can see
on this view that a high energy
photon is measured in the forward electromagnetic calorimeter (the orange bar on the left. The other orange bar on the right
originates from a noisy lead glas crystal).
- Last Z return with photon : This event taken at 7:48:21 also shows the jets
from a Z, but here the associated photon can clearly be seen on the barrel electromagnetic calorimeter (on the right of the