Help on Interactive Event Display

A number of events of different types are provided (move between them by selecting Next Event and Previous Event), all the results of the annihilation of an electron and positron in the LEP Collider (as seen by the DELPHI Detector).

Although it's almost certainly easiest to see the topology of the event by rotating at random, you can think of it as dragging the surface of an (invisible) globe centred at the e⁺e^- collision point.

More details (perhaps only for experts) on running the Interactive Event Display follow.

Display Elements

• Tracks are displayed from the primary or secondary vertex to their last-measured point in the tracking detectors (excluding the muon chambers). To simplify the display, all tracks without a reconstructed secondary vertex are forced through the primary vertex. The primary vertex is defined as the origin (to simplify zooming).
• Calorimeter energy deposits are shown as "boxes". There are two layers of calorimeter: electromagnetic (on the inside) and hadronic (outside).
• Note that, contrary to some of the event descriptions, muon chamber hits are not visible with this version of the event display. This makes it difficult to distinguish muons from hadrons.
• The jet assignments are shown by the colours on all the above elements.
• The scale and orientation of the detector is implied by the wire-frame view of the barrel electromagnetic calorimeter (HPC), shown in white.
• The initial window size represents about 10.4 x 6.5 m. Each zoom in/out magnifies/reduces by a factor of two, giving
   

  Zoom In	Factor	Width (mm)	Height (mm)
  -1	0.5	20800	13000
  0	1	10400	6500
  1	2	5200	3250
  2	4	2600	1625
  3	8	1300	813
  4	16	650	406
  5	32	325	203
  6	64	163	102
  7	128	81	51
  8	256	41	25
  9	512	20	13
  10	1024	10	6

Known Bugs

• Charged tracks are displayed incorrectly with the most recent versions of the Java runtime environent (JDK 1.1) - specifically with Netscape 4.5, Netscape 4.03-4.05 with the JDK 1.1 support patch, Internet Explorer 4, and HotJava. The track curvature in the magnetic field is displayed correctly, but a second straight line is drawn between the two ends of each track. This is due to a change in the Java specification: from polyline in JDK 1.0 to polygon in JDK 1.1. The solution is to use the new version of the Event Display.
• Muon chamber hits are not displayed.
• Each time the event display is restarted (eg. by displaying another event or visiting another page and then returning) a new instance is created. Unfortunately the browser does not free all the resources from the previous instance. This means that if the event display is restarted many times problems can ensue: the browser will consume more and more virtual memory getting slower and slower. Java or the browser may eventually crash. The only solution is to restart the browser.