Understanding High Energy Neutrinos

Transcription

1 Understanding High Energy Neutrinos Paolo Lipari: INFN Roma Sapienza NOW-2014 Conca Specchiulla 12th september 2014

2 An old dream is becoming a reality : Observing the Universe with Neutrinos ( A new way to look at the Sky ) The Sun SuperNova 1987A The Earth (geo-neutrinos) Neutrinos from the High Energy Universe (recent result from IceCube) [!?]

3 A glimpse of the promised land Christian Spiering:

4 A glimpse of the promised land 1. Could the glimpse be a Mirage? (playing the devil's advocate ) 2. What can we say about the high energy neutrino land from the shape of the very first outline? 3. When can we expect the first landing? [the first detection of an astrophysical source]

5 Neutrinos from the High Energy Universe Neutrino associated to the production and propagation of very high energy relativistic particles (hadrons). 1. Astrophysical object (or event) that accelerates protons and nuclei to relativistic energies. 2. Target material (gas, or radiation field) 3. Interactions of the relativistic particles with the production of unstable [weakly decaying] particles. 4. The decays produce neutrinos.

6 Jakob van Santen

7 Foreground to the astrophysical neutrino signal Atmospheric Neutrinos

8 Neutrino Flux: decomposition of the flux into an astrophysical signal of extraterrestrial neutrinos and a foreground of atmospheric neutrinos

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10 Each component of the neutrino flux has characteristics: Flavor composition Angular distribution Energy distribution

11 The atmospheric neutrino flux depends only on the zenith angle. The astrophysical neutrino fluxes depend on celestial coordinates. The establishment of a celestial coordinate dependence of the neutrino fluxes would be unambiguous evidence for an astrophysical signal. But: largest predicted astrophysical neutrino flux is expected as a featureless isotropic extragalactic flux.

12 125 m string separation 17 m between PMT's IceCube

13 Analysis of contained events in ICECUBE SCIENCE (16 december 2013) Evidence for High Energy Extraterrestrial Neutrinos in the IceCube Detector New publication Phys.Rev.Lett astro-ph/ years 3 years of data

14 Contained events

15 TRACK

16 Shower

17 IceCube contained events 3-years Total Number of Events : Background from Down-going Muons Atmospheric Neutrinos Excess = 5.7 sigmas 36(+1)

18 IceCube contained events 3-years Total Number of Events : 37 Background from Down-going Muons Atmospheric Neutrinos conventional Excess = 5.7 sigmas charm

19 Estimate of the neutrino flux by IceCube in the energy range: 40 TeV - 2 PeV (isotropic, equal flux for all flavors)

20 Playing the Devil's Advocate Could the extraterrestrial neutrino excess be attributed to atmospheric neutrinos? Atmospheric Neutrinos conventional charm Are these theoretical predictions (and their estimated uncertainties) correct?

21 Significance of the excess of events: naive (incorrect!) way. Poisson statistics [37 events, background of 15= ] Significance =

22 Each component of the neutrino flux has characteristics: Flavor composition Angular distribution Energy distribution Analysis of Energy Spectrum. angular distribution flavor composition of the data

23 A caveat from the old experts

24 Predictions of Magister Eligius : Neutrino induced muons

25 Confirming Evidence from neutrino-induced muons!

26 IceCube 3 years data [Contained events (from PRL)]

27 Excess at HIGH ENERGY

28 Excess at down-going vertical direction

29 Estimating the Fluxes of Atmospheric Neutrinos 1. Cosmic Ray fluxes 2. Modeling of Hadronic Interactions. 3. Geometry of the Earth atmosphere (density profile)

30 Primary Cosmic Ray Flux [only some data points are shows] p He Direct Measurements Air Shower Measurements all particles

31 Primary Cosmic Ray Flux [Spectral features] p He Knee Ankle

32 Primary Cosmic Ray Flux p He Knee Is this the flux (and energy density) of extragalactic Cosmic Rays? Ankle

33

34 1. Readjust the results of different experiments

35 2. Composition model [3 source components] [3 Peters cycles

36 Nuclei very ineffective for neutrino production All nucleons (bound + free) p

37 Gaisser, Stanev, Tilav (fit + composition p He model) Proton Flux All nucleon Flux

38 Angle integrated Neutrino fluxes

39 Angle integrated Neutrino fluxes Charm decay component

40 IceCube fit of the extraterrestrial component (per each flavor) GZK neutrinos

41 Flavor Content [flux ratios]

42 Flavor Content 1. More than Decay forbidden (tau mass) 2. Absence of 3. More 2-body decay of pion/kaon than Kinematics of pion decay

43 Charged Pions decay into muon-neutrinos Electron neutrinos generated by 3-body decays of kaons. [2-body decay V-A structure of the interaction]

44 Flavor Content 1. Equal and Universality 2. Small (10%) 3. slightly less 2 body decay of Ds than Kinematics of charm decay

45 Flavor Content 1. Equal and,

46 Oscillation Probability Average to zero (for size of source region)

47 Relative fluxes at the observers starting from 2 nu_mu and 1 nu_e (standard mixture for a pion chain-decay origin) = best fit

48 More in general: For an arbitrary flavor composition emission Significant presence of tau-neutrinos

49 Flavor Content In principle key role for

50 Tau neutrinos can be directly detected [ Double Bang events ] But also the ratio Shower / Tracks is sensitive to the presence of tau neutrinos.

51 Is there an excess of showers versus tracks in the IceCube data? Result is compatible with Equal fluxes for all neutrino flavors. A more quantitative statement would be desirable

52 Angular Distribution : Atmospheric standard: Atmospheric charm: characteristic enhancement for horizontal directions quasi-isotropic Decay probability: [Competition between decay and interaction]

53 Geometry of Particle Decay Zenith angle dependence

54 Characteristic zenith angle distribution of Standard atmospheric neutrinos

55 Absorption of neutrinos in the Earth

56 Up/Down Ratio

57 Tom Gaisser

58 From Jacob Van Santen

59 Effect of VETO on rejecting atmnospheric neutrinos

60 Effect allows to separate Atmosphericcharm from isotropic astrophysical

61 [2 years data] Down-going Up-going Very large asymmetry [why?] 24 4

62 [2 years data] Down-going Up-going Time dependence?! (at 3 sigma level). very unlikely. [3 rd year]

63 Energy distribution of Atmospheric Neutrinos. (and absolute normalization of the fluxes) Reflects: 1. The shape (and normalization) of the primary all nucleon flux [Problem of CR at Knee ] 2. The properties of particle production in Hadronic interactions. [Large uncertainties for charmed particle production]

64 Devil's advocate ad hoc additional proton component All particle spectrum All nucleon spectrum proton spectrum

65 Dynamics of charm production in hadronic interactions Perturbative QCD calculation (gluon flusion dominant)

66 Recent measurements of charm cross section at LHC (small phase space coverage).

67

68

69 Possibility of Intrinsic charm Qualitative idea: Large component of charm in the Proton Parton Distribution Function.

70 (Very) speculative possibility to increase significantly the charm neutrino production, without direct conflict with the data. [example P.L. astro-ph/ ].

71 The study of neutrinos around 1 PeV sees the intersection of 3 problems: 1. Astrophysical Neutrino Sources 2. The determination of the ALL NUCLEON flux [proton component and mass composition above the knee] 3. The dynamics of non-perturbative charm production in hadronic interactions The available information is sufficiently redundant to solve the three problems simultaneously.

72 Super-Kamiokande Analogy with the discovery of Neutrino oscillations from the study of atmospheric neutrinos, Determination of Oscillation Parameters: and the determination of the oscillation parameters. Set of parameters that describe the MC prediction

73

74 Simultaneous Fit of Astrophysical Component (with a number of parameters) Atmospheric Component (set of parameters) [5.7 sigma evidence of Astrophysical neutrinos. (what are the chi2 of the fits?) Estimating the All-nucleon flux (from the VHE atmospheric flux) is very interesting for an understanding of VHE cosmic rays

75 Interpreting an Astrophysical Neutrino Signal Compare the (high energy) Neutrino Sky with the Gamma Ray sky

76 Prediction on the Neutrino Sky based on observations of Gamma Rays [in the GeV energy range] FERMI telescope

77 Superposition of a diffuse flux (disk of the Galaxy) and an ensemble of point-like or quasi point-like sources

78 1. Ensemble of (quasi)-point sources 2. Diffuse Galactic Flux (generated by cosmic rays magnetically confined in the Milky Way) 3. Isotropic flux. (attributed to an ensemble of unresolved extragalactic sources)

79 2FGL 2nd FERMI Catalog 24 months of observations 1873 sources E > 100 MeV

80 Diffuse Emission Galactic coordinates

81 Inverse Compton Description reasonably successful. [but several ambiguities and open problems remain.] Bremsstrahlung

82

83 Angle integrated (4pi) Gamma Ray fluxes

84 Remarkable matching between the isotropic gamma-ry flux and the neutrino-flux. Same origin?

85 Extragalactic Flux of Neutrinos Isotropic flux of particles (reflecting the isotropy of the Universe) Neutrino injection [Particles injected per unit volume, unit time and unit energy. ] Time (redshift) dependence Cosmological evolution.

86 Relation between the injection and the neutrino flux

87 Injection is a power law Flux is a power law:

88 Power Density of the neutrino sources

89 Cosmological evolution Constant injection

90 Gamma Rays sources in the FERMI-LAT 2nd catalog. (galactic declination distribution)

91 FLUX of all sources

92 Flux (E = [1-100 GeV]) distribution of the 1015 sources in the Galactic Pole region

93 Flux (E = [1-100 GeV]) distribution of the 1015 sources in the Galactic Poles region 2 brightest sources PSR J (galactic) Blazar 3C 454.3

94 Brightest extragalactic source In the FERMI-LAT catalog blazar 3C454.3 z=0.859

95 Cumulative Flux (1015 sources)

96

97 Gamma Rays in [1-100 GeV] energy interval. Resolved flux Unresolved flux

98 Gamma Rays in [1-100 GeV] energy interval. Resolved flux Unresolved flux Brightest extragalactic source 2% of total flux? Indication for IceCube

99 EXTRA-GALACTIC or include GALACTIC contribution?

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101 Galactic versus extra-galactic

102 Distribution in Galactic Latitude (concentration on the galactic plane?) Distribution in Longitude (concentration near galactic center??)

103 Fluxes from resolved sources in the FERMI-LAT 2nd catalog

104 Extrapolation of flux pf the FERMI-LAT Galactic sources of IceCube energies

105 Diffuse isotropic flux Extragalactic Resolved sources Milky Way resolved sources IceCube Astrophysical Neutrinos

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107 The evidence for an astrophysical component in the IceCube data is becoming compelling. The disentangling of the different components is delicate Astrophysical/galactic, Astrophysical/extragalactic Atmospheric/conventional Atmospheric/charm need to take into account carefully all systematic uncertainties. The astrophysical neutrino land is in sight. more data is needed. Perhaps source identification soon. [Obviously]