Low energy protons from the LHC were dumped in a collimator just upstream of the CMS cavern. The calorimeters and the muon chambers of the experiment saw the tracks left by particles coming from the dumping point (a so-called 'splash event', see images). During the rest of the weekend, bunches of protons were also sent in the clockwise direction passing through the ALICE detector and were dumped at point 3.
All detectors saw 'splash' events on their monitoring pages. Castor and the Preshower detectors saw particles for the first time! Some beautiful pictures from the events seen: