Hello everyone, As I've mentioned in a thread in the cosmology forum, I'm currently reseraching dark matter. I am often confronted with 'exclusion plots' for the results of WIMP direct detection (via nuclear recoil) experiments, where one axis depicts WIMP mass, and the other depicts cross section. Am I correct in saying that these plots illustrate the experimental sensitivities for which the presence of a particle has been investigated and - in the event of a null result - ruled out? In which case, I understand how an experiment could be sensitive to a range of particle masses/energies, but I am a bit confused about the cross-section part. Am I right in thinking that cross-section is the likelihood of a collision event? here is an example!: http://img55.imageshack.us/my.php?image=exclusionplot6sc.jpg if anyone could go any way towards answering these questions I would really appreciate it!