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Measuring the atmospheric oscillation parameters and constraining the 3+1 model with the ANTARES neutrino telescope Ilenia SALVADORI Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, On behalf of the ANTARES Collaboration

A new analysis, aimed to provide a new measurement of the atmospheric parameters with ANTARES is presented. Ten years of data collected by the ANTARES neutrino telescope are used, and two different track reconstruction procedures are combined in order to increase the statistics. A complete 3-flavour description of the oscillation probability including matter effects in the is used, and different sources of systematic are considered. By performing a two-dimensional fit of the event rate as a function of reconstructed energy and zenith angle, the oscillation parameters are derived. Using the same data set, constraints on the 3+1 model, which foresees the existence of an additional , can be computed as well.

The ANTARES neutrino telescope [1] was deployed in the , 40 km off the coast of Toulon (France), at a depth of 2475 m. It was completed in 2008. It is composed of 12 detection lines, each equipped with 25 floors of 3 optical modules (OMs). ANTARES is optimized for detecting with energies up to TeV. On the other hand, constraints on the atmospheric neutrino oscillation parameters can be inferred by studying the distortion on the energy and angular distributions of up-going neutrinos of a few tens of GeV, crossing the Earth and interacting close to the detector. Highly relativistic produced by such interactions emit , which is recorded by the ANTARES OMs. The main source of background is due to misreconstructed atmospheric muons, whose contamination has been estimated by means of a data-driven technique. In order to obtain a sample as pure as possible event selection criteria have been applied as well. After reconstructing the track direction, the Cherenkov photons are projected back to the track in order to estimate the first and last track point and Figure 2: Schematic representation of the muon track length reconstruction [3]. compute the muon track length (see Figure 2). The muon energy, which is in turn related to the neutrino one, is computed taking into account the ionisation Figure 1: Schematic representation of ANTARES neutrino telescope and its de- energy loss of 0.2 GeV/m for minimum ionising muons in sea water. tection principle.

Measuring atmospheric neutrino oscillations parameters Constraining the 3+1 neutrino model µ Neutrino oscillation is a quantum mechanic phenomenon, which occurs since The existence of additional neutrinos, which do ν 1.0 ->

µ No Sterile ν

2 2 P sin θ =0.10; sin θ =0.00 the neutrino mass eigenstates (ν , ν , ν ), which are used to describe neutrino not take part in the interactions but whose pres- 24 34 1 2 3 2θ 2θ sin =0.00; sin =0.10 0.8 24 34 sin2θ =0.05; sin2θ =0.05 propagation through space, are not the same as the neutrino flavour eigenstates ence could introduce distortions in the oscillation 24 34 (νe, νµ, ντ ), which are the ones taking part in interactions (see Figure 3). At- probability patterns, has been posited as a possible 0.6 mospheric neutrino analyses are most sensitive to the mixing angle θ23 and the explanations for some neutrino experiments anoma- 0.4 2 mass splitting ∆m32. lies [12]. In this work, data collected by ANTARES from 2007 to 2016 are considered. At energies around 20-30 GeV, atmospheric neutri- 0.2

0.0 nos crossing the Earth would be affected by the 2 Selected events have been binned in a 2-dimensional histogram in terms 10 10 Eν [GeV] of reconstructed energy and zenith angle (see Figure 4). Event selection Figure 3: Schematic representation of presence of an additional sterile neutrino (see Fig- criteria have been applied in order to optimize the signal/background ra- the neutrino mixing [4]. ure 7). Depending on the value of the two mixing tio. angles, θ and θ , the survival probability of atmo- Figure 7: Example of the distortion caused by the presence 24 34 of a sterile neutrino on the oscillation probability pattern, spheric muon neutrinos is modified with respect to for a vertical up going νµ as a function of the neutrino en- 1.0 the standard pattern described by the 3-flavour sce- ergy.

reco ANTARES PRELIMINARY θ 300 nario [13].

cos 0.9

0.8 250 • 2830 days of lifetime; 24

θ This work • Same data set used for the standard oscillation anal- 2 0.35 ANTARES PRELIMINARY 0.7 cos DeepCore (2017) 200 • Track channel only; 34 ysis; θ 2 0.3 SK (2015) sin 0.6 • 7710 events selected; • Same fitting procedure; 150 0.25 0.5 • • 3-flavor oscillation probability through matter taken 0.2 Muon contamination fixed at the best fit found in the 0.4 100 into account [5]; oscillation analysis; 0.15 2 2 0.3 • ∆m fixed at 0.5 eV ; 50 • Atmospheric µ background extrapolated from data; 0.1 41

0.2 • Standard atmospheric oscillation parameters treated • Binned likelihood fit in 2D (log10 Ereco and cos θreco) 0.05 0 0.8 1.0 1.2 1.4 1.6 1.8 2.0 with priors; Log (E ) [GeV] 0 10 reco − − − 10 3 10 2 10 1 sin2θ 24 • δCP and δ24 left unconstrained in the fit.

Figure 4: Data event distribution after selection. Figure 8: Exclusion limits at 99% CL for this work (black), compared to the ones published by IceCube (red) [14] and SK 2 2 2 ANTARES PRELIMINARY (green) [15], in the parameter space of sin θ24 and sin θ34 cos θ24. 1000 MC no osc # Evt MC best fit The exclusion regions are on the right-hand side of the curves.

MC world best fit 800 Data • Free normalization for neutrinos; Results 600 2 • Correction to spectral index; • New measurements of ∆m32 and θ23 by ANTARES have been performed; • Uncertainty on Φ(ν)/Φ(ν) (provided by the IceCube • Results show good improvements with respect to the previous analysis and consistency with other published Collaboration and derived by [6]); 400 measurements; • Non-oscillation hypothesis discarded with 4.6σ; • Cross-section related systematic; 200 • Muon contamination estimated from data and fitted • First ANTARES constraints on sterile neutrino parameters show agreement and some improvements with with a prior. 0 respect to other published results. 50 100 150 200 θ Ereco/cos reco [GeV] References Figure 5: Ereco/ cos θreco distribution for data (black), MC without oscillations (red), MC at world best fit (blue) and MC at best fit point [1] ANTARES Collaboration, ANTARES: the first undersea neutrino telescope, ISSN: 0168-9002 Nuclear Instruments and Methods in Physics Research A of this analysis (green). 656 11-38 (2011). 2 −3 2 The best fit value is found for ∆m32 at 1.9×10 eV and for θ23 compatible with maximal mixing. Figure 6 (left [2] ANTARES Collaboration, Measurement of atmospheric neutrino oscillations with the ANTARES neutrino telescope, Physical Letters B 714 224-230 panel) shows the results obtained in this work at 90% CL, in comparison to the ones from the previous ANTARES (2012). oscillation analysis [2]. On the right panel, results of this work are shown in comparison with the ones published [3] KM3NeT Collaboration, Letter of Intent for KM3NeT 2.0, Journal of Physics G: Nuclear and , 43 (8) 084001 (2016). by other collaborations [7, 8, 9, 10, 11]. [4] S. F. King et al., Neutrino mass and mixing with discrete symmetry, Reports on Progress in Physics, 76 5 (2013). [5] J. Coelho, OscProb, https://github.com/joaoabcoelho/OscProb/.

] 5 ] 4.5 2 2

ANTARES PRELIMINARY [6] G. D. Barr et al., Uncertainties in atmospheric neutrino fluxes, Physical Review D, 74 9 (2006). eV eV ANTARES PRELIMINARY

-3 4.5 -3 4

[10 [10 [7] IceCube Collaboration, Measurement of Atmospheric Neutrino Oscillations at 6-56 GeV with IceCube DeepCore, hep-ex/1707.07081 (2017). 2 32 4 2 32

m m 3.5 th ∆ ∆ [8] Super-Kamiokande Collaboration, Recent Atmospheric Neutrino Results from Super-Kamiokande in proceeding of 7 International Conference on 3.5 Interconnection between Particle Physics and Cosmology 1604 hep-ex/1310.6677 3 , 345-352 (2014) [ ]. 3 [9] Alex Himmel, New Oscillation Measurements from NOvA, https://indico.cern.ch/event/696410/ (2018). 2.5 2.5 [10] T2K Collaboration, Measurements of neutrino oscillation in appearance and disappearance channels by the with 6.6 × 1020 protons on 2 2 target, Physical Review D 91 072010 (2015). 1.5 1.5 This work [11] MINOS Collaboration, Combined Analysis of νµ Disappearance and νµ → νe Appearance in MINOS Using Accelerator and Atmospheric Neutrinos, 1 DeepCore (2017) ANTARES (Phys. Lett. B174 (2012) 224.) SK (2015) Physical Review Letters 112, 191801 (2014). 1 0.5 NOνA (2018) T2K (2015) This work [12] MiniBooNE Collaboration, A Combined ν|µ → νe and νµ → νe Oscillation Analysis of the MiniBooNE Excesses, hep-ex/1207.4809v2. MINOS (2014) 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 θ 2θ [13] S. Razzaque and A. Yu. Smirnov, Searches for sterile neutrinos with IceCube DeepCore, Physical Review D 85 (2012) [hep-ex/1203.5406]. sin (2 23) sin 23 [14] IceCube Collaboration, Search for sterile neutrino mixing using three years of IceCube DeepCore data, hep-ex/1702.05160v1. Figure 6: Left: 90% CL obtained in this work (black line) and compared to the results of the previous ANTARES oscillation analysis (red [15] Super-Kamiokande Collaboration, Limits on sterile neutrino mixing using atmospheric neutrinos in Super-Kamiokande, Physical Review D 91 052019 dots) [2]. Right: 90% CL obtained in this work (black line) and compared to the results by other collaborations [7, 8, 9, 10, 11]. (2015) [hep-ex/1410.2008].