TECNOLOGÍAS DE LA INFORMACIÓN Y DE LA COMUNICACIÓN

I performed a similar study also for the Target Trackers (TT) which interleave the brick walls in the Neutrino Detector. In this case I estimated the rates collected in 2×1019p.o.t.s, corresponding approximately to six months of data taking, assuming that we replace the emulsions ten times during the whole data taking.

Figure 5.14: Implementation of a lead shield on both sides of the MMS to study the effect on the e±rates in the RPCs.

(a) (b)

Figure 5.15: Ratio between the e±_{rates without and with the shield for 7 mm (left) and 15 mm}

(right) shield.

than 1 GeV/c as shown in fig. 5.17(a). These less energetic muons traverse only a few planes and suffer from a large bending in magnetic field, as well as a large scattering when they traverse the lead plates in the ECC bricks. Therefore they are not easy to reject. Instead, high momentum muons suffer less from both bending and scattering. They can be reconstructed as penetrating tracks, used for emulsion alignment and then virtually erased and thus excluded from the event analysis. Optimisation of the muon shield is ongoing to reduce the rates of muons entering the Neutrino Detector.

(a) (b)

Figure 5.16: e± _{rates without and with a shield with a thickness of 7 mm (left) and 15 mm (right).}

bremsstrahlung in the muon shield. The rates of the few MeV electrons and positrons (fig. 5.17(b)) hitting the TT planes are more than double with respect to the muon ones, hence a solution with a lead shielding surrounding the Neutrino Detector, as already for the MMS, has to be considered.

The spatial distribution of all hits integrated on all the TT planes is shown in fig. 5.18(a), while that of the muons alone is shown in fig. 5.18(b). Once again, in fig. 5.18(b) the structures with consecutive hits are more evident and represent the trajectories of muons crossing several active planes. Differently from the spatial distribution observed for the electromagnetic component on the RPC layers, hits are placed also on the upper region of the TT planes being the magnet hosting the Neutrino Detector open on the top to allow the neutrino target extraction.

(a) (b)

Figure 5.17: Momentum of muons (left) and e± (right) hitting the electronic detectors in the Neutrino Detector.

(a) (b)

Figure 5.18: Position distribution on the TT surface of hits released by all particles (left) and only by muons (right).

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6.1

Design and implementation of the test for the emulsion

detector

In view of the Technical Design Report to be submitted in 2018, it is important to test the innovative technological solutions foreseen for the neutrino detector. We have tested the Compact Emulsion Spectrometer (CES) and the matching between emulsion films and gaseous detectors, GEM.

With the ECC technique in magnetic field it is possible to determine the electric charge and the momentum of the charged particles by measuring the track curvature. It is thus important to separate the consecutive films in order to create a sufficient lever arm and to minimize the effects of multiple Coulomb scattering on the measurement of the magnetic deflection.

The Emulsion Cloud Chamber technique in a magnetic field was tested in 2008 with a pion test beam performed at the KEK facility in Japan [94]. The spectrometer prototype was composed of three OPERA-like emulsion sheets interleaved with two vinyl chloride plates with a 4×4 cm2 hole in the center, thus limiting the sensitive detector area. The two spacers were used to produce a 1.5 cm air gap each. Two 200µm thick Plexiglas plates were also placed on both sides of the spacers to prevent the emulsion films from bending. The momentum was determined for charged pions of 0.5, 1.0 and 2.0 GeV/c with a resolution of 13%. Results showed that, in this momentum range, the electric charge could be determined with a significance level better than the three standard deviations. With that setup, a Geant4 simulation, performed assuming 1µm accuracy on the alignment of the emulsion films, showed a good agreement with the data. Using the simulation results, it was seen (see paragraph in sec. 3.1.1) that it was possible to distinguish the charge and to measure the momenta up to 10 GeV/c.

In SHiP, the challenge is designing a detector with a larger sensitive area with respect to the Japanese prototype, while still maintaining the emulsion films perfectly equidistant and with an overall thickness of a few centimetres. The idea is to fill the gaps between the emulsion sheets with materials of very low density instead of using air gaps. Rohacell spacers, with a density of 57 mg/cm3, satisfy this requirement: they allow the necessary spacing between two consecutive emulsion films while minimising the effects of multiple coulomb scattering on the measurement of the magnetic deflection.

I have actively taken part to a test beam performed in September 2015 to evaluate the performances of the so-designed CES at different impinging angles and momenta of the tracks and thus either validate or discard the possibility of using Rohacell as spacer.

Testing the matching between emulsion films and gaseous detectors is necessary to choose which technology to use for the electronic tracking chambers that are foreseen to interleave the walls of ECC bricks. As already mentioned in the paragraph on Target Trackers in sec. 3.1.1, at the moment the options under study consider, among the gaseous detectors, either the GEM or the MicroMegas. In October 2015, I took part to the first exposure of detector obtained by coupling GEM and emulsion films.

All the tests have been performed at CERN, using the test beam facilities at both the PS and the SPS. I performed the analysis of emulsion films in the emulsion laboratory at the University of Naples. Results are presented in sec. 6.4.