| Centrality:
Participants vs. Spectators |
|
|
|
| The collision geometry (i.e. the impact parameter) determines |
||
| the
number of nucleons that participate in the collision |
||
| “Spectators” |
| Only
ZDCs measure Npart |
|
|
|
| Zero-degree |
||
| Calorimeter |
||
| “Spectators” |
| “Participants” |
| Detectors
at 90o |