DELPHI Events at 205 GeV and above

• Events at 205 GeV
  • First hadronic event at 205 GeV : Run 108614, event 3871, taken at 12:28:47 on saturday 8/4/2000
    This 2 jets event can be seen in the R-Phi view and in the Y-Z view.
  • Yet another event collected on Sunday April 9th, two jets in R-Phi view and Y-Z view.
  • This fully hadronic event has been selected by our online Higgs search algorithm. Further checks are being done on its compatibility with being a real Higgs candidate. It was collected on April 19th at 03:20 and here is and OED view of it (Run 109003, Event 3230).
  • This event contains only one collimated jet with 2 pi+ and 2 pi-. Together with an additional pi0, the mass of this monojet is very close to 3.1 GeV. Hence it is a very good candidate for being J/Psi return to the Z (decaying into a pair of invisible neutrinos). (Postscript)
  • This event is a beautiful ZZ candidate with one Z into e+e- and one into tau+tau- (each tau decaying into one charge track and neutrinos, more precisely one muon and one electron). Here is the view from the top.
• Events at 207 GeV
  • First multihadron at 207 GeV : At 13:00 on April 20th, LEP has reached another record energy of 207 GeV. This very nice 2 jet events was recorded during this first 24 mn fill, here in the XY view and in the YZ view of that event recorded at 13:27:45 on April 20th (Run 109058, Event 24598)
  • This event is the first 4-jet event collected at 207 GeV (note that only half of the detector is shown). (Postscript)
• Events at 208.8 GeV
  • On April 29th at 11:21 a coast reached the record energy of 104.4 GeV per beam, hence 208.8 GeV for the collision energy. Data were collected for more than 40 mn at this energy.
  • WW pair at 208.8 GeV : This event is a very clean candidate for a pair of charged gauge bosons W+W- decaying each into a pair of quarks giving a four jet topology (particles are colored according to their belonging to a specific jet). This ideogram shows the di-jet mass for each of the 3 combinations of the jets. The combination very close to 80-80 GeV corresponds to grouping the green and blue jets into a W (and the two others as well). (Postscript of the event and of the ideogram)
• Other nice events
  • This dimuon event was taken at 204 GeV. It is perfectly well measured and is seen by all detectors including the electromagnetic calorimeter. The muons are signed in the so-called surrounding muon chambers. Each muon is measured within the measurement error at 102 GeV/c. (Postscript)
  • This event was taken at 204 GeV and is very likely a triple-radiative Bhabha event. An electron and a positron are visible on the right of the image while two photons are detected in the detector. The red arrow shows the direction of the missing momentum, suggesting that a forth photon escaped detection in the beam pipe. (Postscript)
  • This event recorded at a center of mass energy of 204 GeV contains 2 jets and 2 muons. The muons are very well identified in the forward muon chambers (on the right of the picture) and the dimuon system has a mass of 9.3 GeV. The di-jet system is very well compatible with the hadronic decay of a Z, indicating an event Z(qq)+Upsilon(mu-mu). An other view can be seen here. (Postscript Z view) and (Postscript RPhi view)
  • Peace and Love event! (Run 111308, evt 25625), taken June 14th 2000.

• 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 picture)