Counting analysis of Borexino Phase-III data for the detection of CNO solar neutrinos Riccardo Biondi on behalf of Borexino Collaboration 1Laboratori Nazionali del Gran Sasso Abstract An accurate measurement of the Solar Neutrino Flux from CNO cycle can shed light on the so called “solar abundance problem“: new determinations of the photospheric abundances of heavy elements indicates that the Sun metallicity is lower than previously assumed, however Solar Models incorporating lower abundances are no more able to reproduce the helioseismic results. We propose a method for detecting the CNO interaction in the Borexino detector from a counting analysis in a Region of Interest determined maximizing a Figure of Merit and using both analytical and Monte Carlo modeling of the detector response. In such a way we can keep under control all systematics and avoid unwanted sources of uncertainties. The procedure itself is inspired by a CNO sensitivity[1] study pointing out that the sensitivity to CNO is basically given by the knowledge of the background from Bi210 and pep neutrinos, being the other backgrounds negligible or constrainable. Mini-abstract: CNO interaction rate in the Borexino detector from counting analysis Poster Id: 93 Contact: riccardo.biondi@lngs.infn.it Motivation and Strategy We want to use counting analysis to determine CNO neutrinos interac- tion rate in Borex- ino detector[2]. Muon PMTs Stainless Steel Sphere Internal PMTs Water Tank Nylon Vessels Scintillator Non-scintillating Buffer Motivation: Complementary to a full spectral study[3] without the uncertainty of background and de- tector response modeling. Systematics can be reliably evaluated. This method could give high sensitivity[1]. Strategy: Choose an energy Region of Interest (ROI) where the expected discovery signiﬁcance of CNO neutrinos is maximized(Figure of Merit). Count the events in ROI Subtract all identiﬁed background events Proﬁle parameters to estimate uncertainties Results obtained with analytical response of the de- tector and Number of Photo-Electrons (Npe) as en- ergy estimator will be shown in this poster. Figure of Merit Figure of Merit is deﬁned as: F = NCNO σCNO (Sys.⊕Stat.) Major contributions of systematics comes from 210Bi and detector response parameters such as 11C quenching and Light Yeld 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Tot σ / iσ Relative contribution of Systematics Bi 210 C Qch 11 LY C 11 (pep) ν Be) 7( ν Others Relative contribution of Systematics 200 250 300 350 400 450 500 550 600 min Npe 200 250 300 350 400 450 500 550 600 max Npe 0 1 2 3 4 5 Figure of Merit 200 300 400 500 600 700 800 900 1000 Npe 1 − 10 1 10 2 10 3 10 4 10 events / Npe Data (CNO) ν Bi 210 (pep) ν C 11 Be) 7 ( ν Others Selected Energy Range Optimum Range: [375 - 429] Npe Region of Interest Species (Si) Events Fraction N 823 ± 28.7 210Bi 261.5 ± 29.6 0.31 ν(pep) 171.7 ± 2.4 0.21 ν(7Be) 86.8 ± 2.6 0.10 11C 57.9 ± 5.8 0.07 Others 15.6 ± 1.6 0.02 P i Si 593.5 ± 30.4 0.71 In the selected ROI we have a total of 823 ± 28.7 events. The expected values and errors on number of events for each species is calculated according to bounds coming from independent studies[4][5][6] and using a reference response model of the Detector. If we subract the sum of the species Si from the to- tal N we are left with the sought after signal: NCNO = N −P i Si = 229.5 ± 41.8 events Systematics Systematics are obtained as the width of the distri- bution of CNO rate after varying parameters on 104 Toy-MC realizations where we determine the num- ber of CNO events subtracting all the other species from the total events in the ROI. Parameters are varied according to: 210Bi: independent determination[4]. ν(pep) Luminosity constraint [5]. ν(7Be) rate according to Solar Models[6]. Light Yeld: generated according to its correla- tion with ν(7Be) rate, adding a 0.7 % smearing. All the other species and detector response parame- ters are varied in a conservative way with respect to the reference