CMS emulsion pictures during LS1

These images were taken at the CMS experimental cavern during Long Shutdown 1, installing pinhole cameras at different points of the cavern and exposing them for days. The development of the film was done by Donato di Ferdinando from INFN Bologna. A pinhole camera is a light-tight box where a small hole is made (diameter of the order of microns); a light-sensitive material is set in the back of the hole. As sensitive material a nuclear emulsion film from the OPERA experiment was used. It is a special photographic emulsion optimized (silver grains enriched) for the detection of charged particles. A very large amount of nuclear emulsions where used in Opera experiment, at the Gran Sasso Underground Labs; nuclear emulsions must detect the charged tau-leptons emerging from the interaction between the "oscillated" tau-neutrino coming from the pure muon-neutrino beam produced at CERN (the CNGS beam). The oscillations theory of neutrino expects that muon neutrinos oscillate to tau-neutrinos and due to this behavior neutrinos have a small mass, not as occurred in the Standard Model (in which neutrinos have zero mass). The target mass was composed of 150.000 bricks, technically called Emulsion Cloud Chamber (ECC). Each brick was composed of 57 nuclear emulsions (like the ones used for this pictures) interleaved with 56 lead plates, 1mm thick, with the same area of the emulsions. The brick was sealed to avoid light leaks. Each brick weighted 8.3 kg and the dimensions were 12.5 cm x 10.5 cm x 7.5 cm. The ECC in this way satisfies the requirements of high mass (the lead, to maximize the probability of the neutrino interaction) but overall the emulsion give us precision of micrometers in the measurements of the tracks and precision of 1-2 millirad in the measurements of angles of the tracks left on it by charged particles (decay products of the neutrinos).