7 years of IceCube data Christian Haack , RWTH Aachen University For - PowerPoint PPT Presentation

Constraints on diffuse neutrino emission from the Galactic Plane with 7 years of IceCube data Christian Haack , RWTH Aachen University ꟷ For the IceCube Collaboration ꟷ ICRC 2017, 07/15/2017

Galactic Cosmic Rays ▪ During propagation protons interact with material near the source or interstellar gas ▪ Interactions produce pions which decay into γ and ν → Diffuse γ / ν emission 𝜈 𝜉 𝜈 𝜌 +/− 𝛿 p 𝛿 𝜌 0 07/15/2017 Christian Haack 2

Galactic Cosmic Rays ▪ During propagation protons interact with material near the source or interstellar gas ▪ Interactions produce pions which decay into γ and ν → Diffuse γ / ν emission 𝜈 𝜉 𝜈 γ / ν are tracers of acceleration, 𝜌 +/− 𝛿 p propagation and interaction 𝛿 𝜌 0 mechanisms 07/15/2017 Christian Haack 3

Modelling Galactic Neutrinos ▪ Diffuse Galactic γ and ν are created by π -decays ▪ Fermi provides model of diffuse Galactic γ emission Simple model: Spatial: 𝜌 0 -component of Fermi diffuse γ background model Energy: 𝐹 −𝛿 powerlaw → No prediction for flux normalization Two free parameters: Normalization & Spectral Index 07/15/2017 Christian Haack 4

Sophisticated Models Daniele Gaggero et al 2015 ApJL 815 L25 ▪ Model by Gaggero et. al. provides consistent picture of ν and γ diffuse emission ▪ Based on KRA γ CR-diffusion model Assumes diffusion coefficient depending on galiocentric radius ▪ Developed to solve problems of conventional propagation models (e.g. “ Milagro excess “) ▪ 5 PeV or 50 PeV CR cutoff 07/15/2017 Christian Haack 5

Sophisticated Models Daniele Gaggero et al 2015 ApJL 815 L25 ▪ Model by Gaggero et. al. provides consistent picture of ν and γ diffuse emission ▪ Based on KRA γ CR-diffusion model Assumes diffusion coefficient depending on galiocentric radius ▪ Developed to solve problems of conventional propagation models (e.g. “ Milagro excess “) → ν measurement can help constrain ▪ 5 PeV or 50 PeV CR cutoff diffusion models 07/15/2017 Christian Haack 6

The IceCube Neutrino Observatory ▪ Cherenkov detector at the geographic South Pole ▪ 5160 D igital O ptical M odules (PMT 𝜈 with onboard digitization) ▪ 86 Strings in a depth of 1450m to 2450m ▪ 125m string spacing 𝜈 ▪ Detection Principle: Cherenkov emission of secondary particles produced by ν -interaction in or near the detector ▪ Energy threshold ~10GeV (with DeepCore) 𝜉 𝜈 𝜉 𝜈 07/15/2017 Christian Haack 7

The 𝜉 𝜈 -Channel (Tracks) Update to 8 years ▪ Allows precise characterization of the of data see: NU022 (Board No. 116) isotropic astrophysical neutrino flux Astrophys.J. 833 (2016) no. 1, 3 New eight year result! ▪ No associated neutrino point sources found ▪ Measured flux parameters differ from other channels ▪ Might be an indication for second component (Galactic?) in neutrino spectrum ▪ How robust is this result against a subdominant Galactic component? 07/15/2017 Christian Haack 8

Analysis Methods Q: Does the data include a contribution of Galactic neutrinos? Binned Method Unbinned Method ▪ Binned poissonian template fit in ▪ Unbinned spatial LH fit with energy weighting reconstructed neutrino energy and direction ▪ Data-driven background model („ scrambled data “) ▪ Signal & background PDF calculated from MC ▪ Fits anisotropic Galactic plane contribution in ▪ Systematic uncertainties included as isotropic background continuous nuisance parameters ▪ Fits neutrino flux parameters of conventional + prompt atmospheric, isotropic + Galactic astrophysical Consistent picture of ~10% better sensitivity all neutrino fluxes 07/15/2017 Christian Haack 9

Galactic Plane Templates Baseline Model KRA γ (50 PeV cutoff) Fermi 𝜌 0 spatial template Spatial template from tuned diffusion model 𝐹 −𝛿 energy spectrum (baseline: 𝛿 = 2.5 ) 𝐹 −𝛿 energy spectrum ( 𝛿~2.4 5) Prediction: ~ 30 𝜉 𝜈 /yr 07/15/2017 Christian Haack 10

Galactic Plane Templates Baseline Model KRA γ Fermi 𝜌 0 spatial template Fermi 𝜌 0 spatial template 𝐹 −𝛿 energy spectrum (baseline: 𝛿 = 2.5 ) 𝐹 −𝛿 energy spectrum (baseline: 𝛿 = 2.5 ) Normalization: 10 −5 𝐻𝑓𝑊 −1 𝑑𝑛 −2 𝑡 −1 @1GeV Upgoing 75 ν /a Downgoing KRA γ is stronger ↔ Fermi is stronger 07/15/2017 Christian Haack 11

Results #1: Unbinned Method ▪ Using the unbinned method, we set an upper limit of: 1.2 x 𝐋𝐒𝐁 𝛅 (50PeV cutoff) ▪ For the Fermi 𝜌 0 model: −2.5 𝐹 Φ 90 = 2.97 ⋅ 10 −18 GeV −1 cm −2 s −1 100 𝑈𝑓𝑊 ▪ Not more than 14% of the diffuse flux @ 𝛿 = 2.5 from the Galactic plane ▪ New ANTARES (arXiv: 1705.00497 ) limit: http://arxiv.org/abs/1707.03416 1.3 x 𝐋𝐒𝐁 𝛅 (50PeV cutoff) 07/15/2017 Christian Haack 12

Results #2: Binned Method Using the binned method and the Fermi 𝜌 0 http://arxiv.org/abs/1707.03416 model, we obtain an insignificant non-zero best fit: 2.11 , 𝛿 = 2.07 ± 0.25 0.22 Φ 0 = 3.13 ± 1.85 ▪ P-Value of no Galactic flux: 7% ▪ Consistent with unbinned method −𝛿 𝐹 Φ = Φ 0 ⋅ 10 −18 GeV −1 cm −2 s −1 100𝑈𝑓𝑊 07/15/2017 Christian Haack 13

Results #2: Binned Method ▪ The binned method delivers consistent http://arxiv.org/abs/1707.03416 picture of isotropic & galactic astrophysical fluxes ▪ Check the influence of inclusion of galactic component on isotropic flux measurement ▪ Scan isotropic flux parameters with galactic plane parameters (norm. + spectral index) free to float ▪ Significance of isotropic astrophysical component still > 3 σ -> Inclusion of galactic component in fit does not strongly affect ability to constrain isotropic astrophysical flux. 07/15/2017 Christian Haack 14

Summary & Conclusions ▪ A measurement of a diffuse galactic neutrino emission can provide valuable insight into CR propagation mechanisms ▪ IceCube is already able to probe models for diffuse 𝜉 𝜈 emission: 90% UL: 1.2 x KRA γ (50PeV) −2.5 𝐹 For Fermi 𝜌 0 model: Φ 90 = 2.97 ⋅ 10 −18 GeV −1 cm −2 s −1 100 𝑈𝑓𝑊 ▪ Binned analysis results in an overfluctuation (~7% p-value) ▪ The best-fit galactic spectral index for Fermi 𝜌 0 is suprisingly hard ( 2.07 ± 0.25 0.22 ) → But no conclusions can be drawn yet ▪ Measurement of the isotropic astrophysical flux is robust against a subdominent galactic component Outlook : Global analysis combining multiple detection channels & combined analysis with Antares Paper submitted to ApJ http://arxiv.org/abs/1707.03416 07/15/2017 Christian Haack 15

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Sensitivity Calculation ▪ Sensitivity is defined as median upper limit, when no signal is present ▪ Neyman construction: ▪ Generate BG & Signal pseudoexperiments ▪ 90% UL is found when 𝑅 50 𝑈𝑇 𝐶𝐻 = 𝑅 10 𝑈𝑇 𝑇𝑗𝑕𝑜𝑏𝑚 ෝ Signal distribution Signal distribution 𝑜 𝑗𝑜𝑘 = 𝑜 𝑉𝑀 𝑜 𝑗𝑜𝑘 = 𝑜 𝐸𝑗𝑡𝑑𝑄𝑝𝑢 07/15/2017 Christian Haack 18

Event Selection Requirements ▪ Pure sample of 𝜉 𝜈 (tracks) (>99%) ▪ High neutrino statistics ▪ Well reconstructed events (good pointing) Diffuse Sample ▪ Six (Seven) years of data combining multiple detector configurations ▪ Purity: >99.7% ▪ High neutrino statistics: 350.000 events (2009 – 2015) ▪ High signal statistics: ~500 astrophysical 𝜉 𝜈 (2009-2015) 07/15/2017 Christian Haack 19

Event Selection Atmosph. 𝝃 𝒇 Atmosph. µ Atmosph. 𝝃 𝝂 Requirements ▪ Pure sample of 𝜉 𝜈 (tracks) (>99%) ▪ High neutrino statistics ▪ Well reconstructed events (good pointing) Astroph. 𝝃 𝝂 Neutral Currents Exp. data Aachen Diffuse Sample (developed by Sebastian S. & Leif R.) ▪ Six (Seven) years of data combining multiple detector configurations ▪ Purity: >99.7% ▪ High neutrino statistics: 350.000 events (2009 – 2015) ▪ High signal statistics: ~500 astrophysical 𝜉 𝜈 (2009-2015) 07/15/2017 Christian Haack 20

Flux Templates Atmospheric Neutrinos Astrophysical Neutrinos ▪ Prompt (heavy meson decay) ▪ Diffuse Galactic (powerlaw) ▪ Conventional (pion / kaon decay) ▪ Diffuse isotropic (powerlaw) 07/15/2017 Christian Haack 21

Flux Templates Atmospheric Neutrinos Astrophysical Neutrinos ▪ Prompt (heavy meson decay) ▪ Diffuse Galactic (powerlaw) ▪ Conventional (pion / kaon decay) ▪ Diffuse isotropic (powerlaw) 07/15/2017 Christian Haack 22

Systematic Uncertainties Detector Effects: position change Ice properties, optical sensor efficiency Flux Uncertainties: shape change Rate, shape and composition of the CR flux, rate of pion-to-kaon decay in air showers, neutrino cross sections S. Schoenen Influence of every sys. effect on analysis variables is parametrized continously and Detector is symmetric in azimuth (and located at South Pole) implemented as nuisance parameters → RA not influenced by sys. Effects 07/15/2017 Christian Haack 23

Flux Templates Atmospheric Neutrinos Astrophysical Neutrinos ▪ Conventional (pion / kaon decay) ▪ Diffuse Galactic (powerlaw) ▪ Prompt (heavy meson decay) ▪ Diffuse isotropic (powerlaw) 07/15/2017 Christian Haack 24