Multi-PeV Signals from a New Astrophysical Neutrino Flux Beyond the Glashow Resonance

Transcription

1 Multi-PeV Signals from a New Astrophysical Neutrino Flux Beyond the Glashow Resonance Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) Stanford University and SLAC National Accelerator Laboratory Kistler and Laha arxiv: (submitted)

2 Discovery of astrophysical neutrinos IceCube Preliminary High Energy Starting Event analysis year data set Fit performed including all events between 60 TeV < E dep < 3 PeV No Glashow resonance event E 2 assumption: 1:1:1 flavor ratio, 1:1 neutrino:anti-neutrino 0.92 (E) =2.46 ± E GeV cm 2 s 1 sr TeV Steep spectral index from the HESE excess No statistically significant clustering in space See talks by Halzen, Kowalski, Wandkowsky, Niederhausen, Richman, Lu, Yuan, Mancina, Wood, Weiler, Ando, Murase, Petropoulou, Sudoh, Denton, Bustamante, Auguelles, Kheirandish, Stecker, Lai, Klop, Yuan, Cerruti, Rodrigues, Fang 1

3 Discovery of astrophysical neutrinos E 2 + / GeV 1 cm 2 s 1 sr IceCube Conv. atmospheric µ + µ (best-fit) Prompt atmospheric µ + µ (flux limit) Astrophysical µ + µ (best-fit) HESE unfolding: PoS(ICRC2015)1081 Northen Hemisphere through going muons year data set Fit of through going events between 194 TeV < E ν < 7.8 PeV E /GeV + = E 100 TeV No statistically significant clustering in space 2.13±0.13 GeV 1 cm 2 s 1 sr 1 See talks by Weiler, Ando, Murase, Petropoulou, Sudoh, Denton, Bustamante, Auguelles, Kheirandish, Stecker, Lai, Klop, Yuan, Cerruti, Rodrigues, Fang

4 2.6 PeV track event IceCube Deposited energy 2.6 ± 0.3 PeV Reconstructed equatorial coordinates: decl RA Does not point towards any known astrophysical source Immediate questions: Highest energy track event detected till date --- very important to analyze it thoroughly 1. What flavor of neutrino produces such a track? 2. What are implications for astrophysical neutrinos in light of prior discoveries?

5 What neutrino flavor produces a track? Muons are assumed to give rise to all through-going track like events To deposit 2.6 PeV of energy, the muon typically requires & 5 PeV energy at detector entry point --- it is probable that this is a super-glashow (energy 6.3 PeV) neutrino An overlooked possibility in the literature: very high energy through going taus can also give rise to track-like events To deposit 2.6 PeV of energy, the tau requires at detector entry point & 50 PeV energy Can IceCube individually distinguish a through going tau from a through gong muon? We discuss astrophysical scenarios for each of these possibilities

6 track Double bang Muon tracks cascade IceCube µ µ Wandkowsky TeVPA 207 νμ+n μ+x Muon track νe+n e+x νx+n νx+x Many muon observed in IceCube ±15% energy resolution factor ~2 tracks energy resolution <1 angular resolution ~10 angular resolution Many theoretical studies on muon tracks!d Muon tracks in IceCube have been well studied Nancy Wandkowsky, Measurement of neutrino events above 1 TeV

7 Double bang v/s tau tracks Tau tracks are produced by with energy & 50 PeV IceCube IceCube rino 2 bang CC Double tau neutrino Tau track double bang Wandkowsky TeVPA 2017? How do tau tracks look in IceCube? ν!+n!+x

8 A generic equation for event numbers d de` apple Lepton energy loss: for through going leptons b`(e`) dn` de` b` de`/dx + m` c ` E` dn` de` = Q(E`) Kistler and Laha arxiv: Lepton energy E` Lepton lifetime ` Volumetric source term Q(E`) N A includes Earth absorption ` E` h1 yi CC E` h1 yi /h1 yi Regeneration is important for taus Earth absorption is important for all neutrino flavors

9 Where does it come from? Galactic coordinates E dep 2.6 PeV IceCube track event contours of E ν > 1 TeV Fermi emission smoothed by 5 0 j 8 muons HE m >5 PeVL 0 1 Upgoing Downgoing Kistler and Laha arxiv: Fermi TeV Shaded: Sky density of E µ > 5 PeV muons from model φ 8 Solid: The horizon demarcates upgoing and downgoing directions Dashed: The rough 10 0 downgoing boundary for atmospheric muons No gamma-ray source was reported by HAWC The 2.6 PeV track event probably comes from a diffuse astrophysical neutrino flux

10 Astrophysical neutrino fluxes Kistler and Laha arxiv: phenomenological fluxes with varying normalization: φ 7, φ 8, and φ 9 φ 7, φ 8, and φ 9 extend to higher energies => essential for through-going τ interpretation φ 7 and φ 8 resemble BL Lac AGN models Rescaled combinations of φ 7 and φ 9 approximate GZK neutrinos from EBL and CMB E interactions " E ' i (E )=f i E i + E i # 1/ i =7, 8, and 9 E i = 10 i GeV

11 Energy distribution Kistler and Laha arxiv: Muon energy as it enters detector Muons of energy 100 GeV can traverse the full IceCube detector Taus of energy 50 PeV can traverse the full IceCube detector General conclusion: in order to deposit 2.6 PeV energy inside IceCube, the energy of tau as it enters the detector must be approximately an order of magnitude larger than that of muon: enormous physical significance Must optimize tools for this new signal in IceCube Tau energy as it enters detector

12 Kistler and Laha arxiv: Event numbers TABLE I: Events in 5 km 2 yr (µ, tracks) or 5 km 3 yr (showers). E 2.6 ' 7 ' 8 ' 9 upgoing µ: E µ >5 PeV down µ: E µ >5 PeV; cos nadir > upgoing : E,up >50 PeV down : E >50 PeV; cos nadir > Total tracks e e shower: E em >5 PeV e + e CC: E em >5 PeV NC: E em >5 PeV The normalizations of φ 7, φ 8, and φ 9 can be made variable The harder spectra adopted by us is more favorable to give rise to the 2.6 PeV track event The E produces too many Glashow resonance events (~ 3), and might be disfavored Is the 2.6 PeV track event hinting at a super-glashow astrophysical neutrino flux? E 3 ev 2 m -2 s -1 sr -1 D

13 Conclusions Common knowledge: Muons give rise to all through going tau track events in IceCube ---- incomplete! We show for the first time that a through going tau can also give rise to tracks The through going tau track is a new signal in IceCube ---- needs more research ---- can we distinguish a through going muon track and a through going tau track? Questions: rlaha@stanford.edu

14 0.5 D o w n g o i n g Atmospheric m U p g o i n g 0.5 Angular distribution Kistler and Laha arxiv: D o w n g o i n g U p g o i n g dnêdhcos -2 yr -1 D I c e C u b e 2.6 PeV t r a c k Muons: E m >5 PeV j 7 j 8 j 9 E -2.6 dnêdhcos -2 yr -1 D Atmospheric m I c e C u b e 2.6 PeV t r a c k Taus: E t >50 PeV j 7 j 8 j cos q nadir Angular spectra of E µ > 5 PeV muons and E τ > 50 PeV taus cos q nadir For the same spectra, the angular distribution is different --- through going muon tracks and through going tau tracks probe different energy ranges of the underlying astrophysical neutrino spectrum For φ 7 φ 8 φ 9, the tau/ muon track ratio approaches unity