On Friday 7th October the LHC delivered, for the first time in the history of High Energy Physics, proton-proton collisions at the design frequency of 40 MHz, with bunches of protons colliding every 25 nanoseconds (ns), doubling the frequency achieved so far. By doubling the collision frequency, the LHC can fit twice as many bunches in the machine and potentially double the luminosity. Friday's test was a reduced scale test, since the number of bunches in the machine (60 out of which 57 were colliding in CMS) was not as high as in the project design (2808). The LHC ran very smoothly in these conditions for about 3 hours confirming once again what a superb accelerator it is.
Although the new collision frequency represents a big challenge, CMS met the special rendez-vous well-prepared after many years devoted to the development of the read-out electronics, suitably designed to handle collisions so closely spaced in time. CMS successfully recorded 0.5 pb−1 of data, which are extremely useful for better understanding of the detector response in preparation for future running at 40 MHz.