Setup of a Drift Tube Muon Tracker and Calibration of Muon ...

510Counts/(10 keV x day x 100 tons)410310210101-110-210Fit: χ 2 /NDF = 185/1747Be: 49±3 cpd/100 tons210Bi+CNO: 23±2 cpd/100 tons85Kr: 25±3 cpd/100 tons11C: 25±1 cpd/100 tons14C10C-310200 400 600 800 1000 1200 1400 1600 1800 2000Energy [keV]Figure 4.6: Fitted Borexino Data taken from [69]. The black data points alreadyinclude all relevant cuts. The Figure does not include contributions from 214 PB, pp,and pep neutrinos which are almost negligible. Again, the Compton like edge for the7 Be neutrinos can be clearly seen (red line). The fit result gives a rate of 49 ±3 countsper day. For the 11 C background, a rate of 25 ± 1 is found.100 tons.For the analysis, events were chosen by a selection of cuts. A fiducial volumeof 78.5 tons was chosen to reject external gamma background. Furthermore, eventswithin 2 ms after a crossing muon were rejected to suppress events from the decay ofshort living cosmogenic induced radionuclides. Decays due to radon daughters couldbe removed by vetoing 214 Bi– 214 Po coincidences. Events from the α decay of 210 Pocould be identified through pulse shape discrimination and were subtracted fromthe spectrum. The raw photo electron spectrum after these basic cuts is shown inFig. 4.5. The Compton-like edge from the reaction of 7 Be neutrinos is clearly visiblearound 300 photo-electrons. Below 100 photo electrons, the spectrum is dominatedby the decay of 14 C. Furthermore, the impact of the β + decay of 11 C can be seen inthe region between 400 and 800 photo electrons (cf. Section. 4.3.3).Fig. 4.6 shows the spectral fit of the data. For the 7 Be neutrinos, a rate of 49 ±3events per day and 100 tons is found. The high metallicity SSM predicts a rateof 74 ± 4 counts per day and 100 tons for no oscillations whereas the MSW-LMAscenario (assuming ∆m 2 12 = 7.6−5 eV 2 and sin 2θ 12 = 0.87) reduces this expectationto 48±4 counts per day per 100 tons. Hence, the results confirm the matter enhancedoscillation hypothesis.To test solar models, the measured neutrino flux is compared to the predictionof the SSM. The measurements also give new constrains to the ratio f Be between the7 Be neutrinos flux predicted by the high metallicity SSM and the measured value,where f is defined as the true solar neutrino flux divided by the corresponding valueof the fluxes predicted by the according solar model. For the MSW-LMA oscillationscenario, a value of f Be = 1.02±0.10 is obtained. The analysis ales gives a constraintfor the ratio f CNO for CNO neutrinos of f CNO < 3.80 and a value f pp for pp neutrinosof f pp = 1.005 +0.008−0.020 . The constraint on f CNO translates into a CNO contribution of62