1 THE KM3NET/ARCA DETECTION CAPABILITY TO A DIFFUSE FLUX OF COSMIC NEUTRINOS R. Coniglione for the KM3NeT collaboration INFN - LNS Catania (Italy)
KM3NeT 2 KM3NeT is a distributed research infrastructure in the Mediterranean Sea hosting neutrino detectors � KM3NeT/ARCA (Astroparticle Research with Cosmics in the Abyss) ¤ discovery and observation of high energy (GeV ÷ PeV) neutrino sources ☛ a telescope offshore Capo Passero (Sicily-Italy) is in construction at a depth of 3500m � KM3NeT/ORCA (Oscillation Research with Cosmics in the Abyss) ¤ determination of the neutrino mass hierarchy 👊 a detector offshore Toulon (France) able to detect neutrinos of tens of GeV is in construction at a depth of 2500m ORCA and ARCA same detector technology Highlight talk by Aart Heijboer 👊 July 19th(Wed.) ORCA Talk by Antoine Kouchner 👊 July 15th(Sat.)
The KM3NeT/ARCA design 3 a 3D array of optical sensors 36m The optical sensor: Digital Optical Module (DOM). Each DOM comprises 31 3’’ PMTs 90m The Detection Unit (DU) 3 /block) � 2 building blocks of 115 Detection Units (DU) each (0.5 km � Each DU with 18 Digital Optical Modules (DOM). � Power and data distributed by a single backbone cable with breakouts at DOMs � Sea network of submarine cables and Junction Boxes connected to shore via a main electro-optical cable � First two DUs already installed and first data analyzed Talk on first ARCA results by Martijn Jongen 👊 July 13th(Thur.)
Event classes in a neutrino telescope 4 “Track-like” events mainly from v μ CC “Cascade-like” events mainly from v e CC and interactions NC interactions 👈 👈 Cascade reconstruction algorithm Track reconstruction algorithm 👈 👈 Cascade analysis - full sky - contained Track analysis - up-going events events
A telescope in the Northern hemisphere for the observation of diffuse cosmic neutrinos 5 � Existence of astrophysical neutrinos proven by IceCube � 6 year analysis with up-going tracks (Astrophys. J. 833 no.1 - 2016) 👊 spectrum ∝ E -2.13 � Combined analysis (Astrophys. J. 809 no.98 - 2015) 👊 spectrum ∝ E -2.5 Evidence for a multicomponent spectrum (Galactic + extragalactic ?) expected ARCA performances for a Estimate of the ARCA performances for diffuse diffuse flux (from LoI) and neutrinos sources in the published Letter of KM3NeT Intent 6 ] σ Significance [ • update on diffuse flux in this talk 5 • update on point-like sources in poster session 4 tracks cascades 3 combined conventional uncertainty ν atm prompt uncertainty ν atm 2 1 -8 -2 -1 -1 -1 -2 flux per flavour 1.2 10 (E/1 GeV) exp(-E/3 PeV) GeV sr s cm 0 0 0.5 1 1.5 2 2.5 3 3.5 Observation time [years]
What’s new since the LoI 6 � Update of results for diffuse from all-sky and Galactic Plane region � new track reconstruction algorithm � better angular resolution � higher efficiency � Multi-variate analysis (Scikit-learn) Talk on ARCA reconstruction algorithms by Karel Melis 👊 July 13th(Thur.)
All-sky analysis with tracks 7 � Two assumed benchmark fluxes (same fluxes as the LoI) Benchmark fluxes compatible with the measured IceCube fluxes � Analysis steps � Pre-selection cut on events reconstructed as up-going or few degrees above the horizon ( θ zen >85° optimized) � Multivariate analysis 👊 Scikit-learn � distinguish between three event samples ( μ atm , ν atm , ν sign ) � 11 “features” to train the algorithm 👊 from the reconstruction code or from the topology of the events � Max likelihood 1 flavour fluxes P sig and P bkg are the probability n sig number of expected density function (PDF) for signal and events in the detector background events estimated from the multivariate analysis as probability to belong to the “signal” class
All-sky analysis: results 8 Discovery fluxes as a function of the observation years KM3NeT ARCA Preliminary KM3NeT ARCA Preliminary 5 − 10 ) ) -1 -1 sr sr 3 50% σ 3 50% σ -1 -1 s s 5 50% σ -2 5 50% σ -2 (GeV cm (GeV cm 8 − 10 6 − 10 0 0 Φ Φ flux ɸ 0 E -2 exp(-E/3PeV) -2 flux Φ E exp(-E/3PeV) flux ɸ 0 E -2.46 0 -2.5 flux E Φ 9 − 10 0 7 − 10 0 1 2 3 4 5 6 0 1 2 3 4 5 6 observation years observation years About one year to reach a 5 σ discovery for E -2 spectrum with cutoff* and less if the spectrum is softer (E -2.46 no cutoff) *in the LoI 1.5 years
� Galactic plane region |l|<30° |b|<4° 9 Neutrino flux (one flavour) estimated from a non uniform cosmic-ray transport model with a radially dependent diffusion coefficient (same flux as the LoI) � Analysis steps � Track analysis � Pre-selection cut on events reconstructed as up-going or few degrees above the horizon θ zen >80° � Max likelihood � Cascade analysis � Selected events with the reconstructed vertex inside the detector geometry � according to the reconstructed zenith angle from the tracking algorithm, events are classified as upward- going (sample “A”, cos θ track > -0.4) or downward-going 3 flavour flux (sample “B”, cos θ track < -0.4). � Cut on the total Time-over-Threshold (related to the total charge of the hits) of the event to reject low energy events on both samples � Random Decision Forest � Max likelihood D. Gaggero et al.,2015. arXiv:1508.03681. ICRC2015
Galactic plane region |l|<30° |b|<4° 10 Discovery fluxes and sensitivity as a function of the observation years KM3NeT ARCA preliminary ) -1 sr Track - 5 σ 50% -1 Track -3 50% σ s Track -sensitivity 90% C.L. -2 Cascade - 5 50% σ (GeV cm Cascade - 3 σ 50% 5 − 10 Cascade - sensitivity 90% C.L. 0 Φ -2.3 flux Φ (E/1GeV) exp(- E/1 PeV ) 6 0 − 10 0 1 2 3 4 5 Observation years About 4 years to reach a 5 σ discovery both for track and cascade analysis* *in the LoI 4.8 years for track analysis cascade analysis not presented in the LoI
Comparison 11 |b| < 3° and |l|<30° ANTARES Upper Limit 7y (ArXiv:1705.00497v1*) KM3NeT track analysis (same values for cascade analysis) discovery 3 σ 4y sensitivity 4y Improvement expected combining cascade + track events *region |b|<3° |l|<40°
Summary 12 Update of the results presented in the LoI for diffuse emission from all sky and Galactic Plane region � all-sky search 👊 improvement of about 0.5 year for the 5 σ discovery all-sky with tracks � GP region |l|<30° |b|<4° � track analysis 👊 improvement of about 1 year for the 5 σ discovery � cascade analysis 👊 new estimates for the cascade analysis give similar results to the track analysis Analysis not yet completed 👊 better results expected combining cascade with track events
Conclusions 13 � KM3NeT/ARCA can observe the diffuse high energy neutrino flux in few years from a different field of view and with different systematic uncertainties � With its good angular resolution (<0.1° @ E ν >100 TeV) it can better discriminate the emitting region in the sky thus helping in the understanding of the origin of the observed astrophysical neutrinos
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