1. Shih-Hao Wang 王士豪 Graduate Institute of Astrophysics & Leung Center for Cosmology and Particle Astrophysics (LeCosPA), National Taiwan University 1 This talk is based on : S.H. Wang, P. Chen, J. Nam, and M. Huang, JCAP 11 (2013) 062; arXiv:1302.1586

2. Cosmic rays with E > 10 18 eV (UHECR) are observed.  Source (AGN, GRB)?  Acceleration mechanism? Neutrinos can be generated when UHECR interact with photon or matter  CMB photon  GZK cutoff in CR spectrum  Cosmogenic neutrinos! 2 Astrophysical: Cosmogenic: from http://www.physics.utah.edu/~whanlon/spectrum.html UHECR F. Halzen and S. Klein, Physics Today 2008 ~E -2.8 Charged pion decay GZK cutoff at ~5×10 19 eV

3. Being electrically neutral and weakly interacting, UHECNs carry information from their sources  Energy spectrum ▪ CR composition, source distribution, max acceleration energy  Flavor ratio: relative flux between ν e : ν μ : ν τ ▪ Source size & B-field strength  ratio transition with E ν (1:2:0  0:1:0) 3 Kotera et al., JCAP (2010); S. Hümmer et al., Astropar. Phys (2010). decay v.s. synchrotron cooling

4. UHECN is an unique probe with  Extremely high energy (>10 17 eV) pc  Extremely long baseline (>10 Mpc) Flavor ratio at Earth is determined by :  Flavor ratio at source  Flavor transition in propagation  Neutrino oscillation  Non-standard physics? 4 J. Beacom et al., PRL (2003, 2004), PRD (2003); G. Barenboim et al., PRD (2003); D. Hooper et al., PRD (2005).; P. Keraenen et al., PLB (2003)

5. 5 Bustamante et al., PRL (2015); J. Beacom et al., PRL (2003, 2004), PRD (2003); G. Barenboim et al., PRD (2003); D. Hooper et al., PRD (2005).; P. Keraenen et al., PLB (2003) (ν e :ν μ :ν τ ) Flavor ratio at Earth is determined by :  Flavor ratio at source ▪ Source environment  Flavor transition during propagation ▪ Neutrino oscillation ▪ Non-standard physics?  Neutrino decay & mass hierarchy  Sterile neutrinos with small Δm 2  CPT violation, Lorentz violation, etc. f e +f μ +f τ =1 this neutrino decay model is used in our work ν e fraction ν μ fractionν τ fraction

6. ~4000 km Antarctic ice as target Vast :thousand km across, 2-3km deep Quiet: less human activity Clean: radio attenuation length ~1km Askaryan effect ~20% excess in negative charge of shower Coherent radio Cherenkov pulse 37 stations, 3 deployed ~200km 2 coverage NTU in collaboration ~50 UHECN events is expected in 3 year 6 ARA collaboration, Astropar. Phys (2012), ARA collaboration, arXiv:1507.08991; http://ara.wipac.wisc.edu/home ARA 2&3 10 months

7. Antenna Low Noise Amplifier RF over Fiber DAQ 7 Adapted from J. Nam

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9. MMC: http://dima.lbl.gov/work/MUONPR/ SADE: D. Seckel et al. 9 1.Neutrino generation with given spectrum 2.Neutrino and secondary lepton propagation (with MMC package)  Stochastic E-loss > 1PeV is converted to shower 3.Event detection (with SADE package) Credit: MMC ARA Earth ARA37 Spectrum of radio Cherenkov emission Ray propagation in ice ν μ  μ  showers

10. Assuming initial ratio of 1:1:1 Interaction length at 1 EeV is ~500km Neutrino CC interaction produces charged lepton, making the angular distribution different ν e releases all its energy with short distance τ decay & ν τ regeneration (ν τ  τ  ν τ ) Stochastic energy loss of μ & τ 10 red:ν e green:ν μ blue:ν τ Earth shadowing νeνe νμνμ ντντ μ τ zenith angle (cosθ) Up-going e θ red:ν e green:ν μ blue:ν τ

11. 11 red:ν e green:ν μ blue:ν τ Very rare interaction at shallow depth νeνe νμνμ ντντ zenith angle (cosθ) Down-going Assuming initial ratio of 1:1:1 Interaction length at 1 EeV is ~500km Neutrino CC interaction produces charged lepton, making the angular distribution different ν e releases all its energy with short distance τ decay & ν τ regeneration (ν τ  τ  ν τ ) Stochastic energy loss of μ & τ cutoff due to the orientation of Cherekov cone

12. Assuming initial ratio of 1:1:1 12 red:ν e green:ν μ blue:ν τ Interaction length ~ traveling distance νeνe νμνμ ντντ zenith angle (cosθ) Quasi-horizontal νμνμ ντντ μ τ Assuming initial ratio of 1:1:1 Interaction length at 1 EeV is ~500km Neutrino CC interaction produces charged lepton, making the angular distribution different ν e releases all its energy with short distance τ decay & ν τ regeneration (ν τ  τ  ν τ ) Stochastic energy loss of μ & τ

13. υ e has higher detection efficiency due to electron energy loss ν τ distribution is the most different τ decay & ν τ regeneration (ν τ  τ  ν τ ). υ e and υ μ have similar shapes, extra constraint is required  υ μ -ν τ symmetry is assumed (i.e. they are of equal ratio). Initial ratio 1:1:1  detected ratio 0.59:0.15:0.26 13 By fitting event angular distribution, UHECN flavor ratio can be extracted red:ν e green:ν μ blue:ν τ Assuming initial ratio of 1:1:1 Comparison of curve shape

14. Due to random sampling, sometimes fitting gives unphysical f e  fail Generate ensemble of data sets to get the success probability depend on number of events N obs and angular resolution Δθ With Δθ =6 ° and N obs = 200, the success probability is about 85%, 60%, and 50%, respectively 14 ~50% ~60% Δθ =0° (red), 2° (green), 4° (blue), 6° (black) Pseudo- experiment data ~85% Standard 1:1:1 (f e =1/3) Decay with NH 6:1:1 (f e =0.75) ~50% Decay with IH 0:1:1 (f e =0) ~60%

15. Spread of extracted f e from expected one depend on number of events N obs and angular resolution Δθ With Δθ =6 ° and N obs = 200, the resolution (~68%CL) is about 0.3, 0.4, and 0.15, respectively 15 ~0.15 ~0.3 Δθ =0° (red), 2° (green), 4° (blue), 6° (black) ~0.4 Standard 1:1:1 (f e =1/3) Decay with NH 6:1:1 (f e =0.75) Decay with IH 0:1:1 (f e =0) Preliminary constraint on neutrino decay can be set.

16. Measuring UHECN flavor ratio is important in both astrophysics and particle physics By fitting the direction distribution of neutrino events, a preliminary constraint on its flavor ratio can be set for the planned ARA37 configuration. Additional information (e.g. event topology, Cherenkov pulse characteristics) can be exploited to improve the resolution.  Identification of ν e CC events.  Discrimination between electromagnetic and hadronic showers 16 J. Alvarez-Muniz et al. Phys. Rev. D (1999) J. Alvarez-Muniz et al. Phys. Rev. D (2000)

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