Neutrino Astronomy LY NN HEYDASCH STEFAN BERNEGGER UZH FS 2017 / AST 202 – 11. APRIL 2017 Neutrino astronomy Goal: Understand the basics of neutrino astronomy. Definition: “Branch of astronomy dealing with the detection and measurement of neutrinos emitted by the sun and other celestial objects.” Table of contents: 1. What are neutrinos? 2. What are the sources of neutrinos? 3. How to detect neutrinos? 4. What are neutrinos telling us? Q&A Rest mass of elementary particles Tauon Charm quark Charm Top quark Electron Bottom quarkBottom Down quarkDown Strange quark Strange Upquark Neutrinos ? Muon 1 meV 1 eV 1 keV 1 MeV 1 GeV 1 TeV 1. WHat are neutrinos? LOW MASS, NEUTRAL ELEMENTARY PARTICLES, PROPAGATING VERY CLOSE TO THE SPEED OF LIGHT, QUITE DISTINCT FROM THEIR COUNTERPARTS. Neutrinos • Elementary particle(s) • Electrically neutral • Three generations (flavors) of neutrinos: Standard model of particle physics • ��, ��, �� (and ��, ��, ��) • Partners of e, μ and τ • Interacting via the weak force (Z, W) only (and gravity) • Very low (≤0.12eV/c2) but non zero rest mass Solar neutrino problem • 1960’s Homestake experiment: Number of measured solar ��-neutrinos only 30%-50% of expected • No errors found in solar models and experimental setup • Hypothesis: Neutrinos have small mass and can oscillate • 2001 Sudbury Neutrino Observatory experiment: 35% ��, 65% �� and �� Neutrino astronomy vs photon astronomy NEUTRINO ASTRONOMY PHOTON ASTRONOMY • Interaction partner • e-, p+, n • e-, p+ • Flux from the sun • 6.5 ∙1010/sec/cm2 • 3.5 ∙1017 /sec/cm2 • Processes between source • Neutrino oscillations, red shift • Interaction with matter, red and detector shift • About 1 in 1036 • Detection rate • Close to 100% 5 20 • Energy range • ?... 10 eV up to 10 eV … ? • 10-4 eV to 1014 eV • Energy resolution • 0.2 (log energy) • 1/100’000 • Viewing angle [sr] • 4π • 10-8 to 10-4 • Spatial resolution • 1° to 10° (IceCube) • 0.01 arc sec (e.g. E-ELT) 2. Sources of neutrinos? BIG BANG, EXTRA-GALACTIC, GALACTIC, SOLAR AND TERRESTRIAL � –PROCESSES. Sources of neutrinos • Extraterrestrial sources: • LS/S: Low-energy-/Solar neutrinos → �� • LSN/SN: Low-energy-/Supernova Neutrinos, e.g. SN 1987A → 24 neutrinos within 13s • GRB: Gamma Ray Burst neutrinos • CR: Cosmic Ray neutrinos • PUL: PULsar neutrino • AGN: Active Galactic Nuclei neutrinos • CNB (CνB): Cosmic Neutrino Background (Big Bang) • ATM: ATMospheric neutrinos: cosmic rays • Terrestrial sources • Man made sources 3. How to detect neutrinos? ANY � –PROCESS CAN - IN PRINCIPLE - BE USED, BUT A LARGE AMOUNT OF MASS IS NEEDED. ASTRONOMY: WATER/ICE IS THE ONLY CHOICE! Detection via neutrino capturing and scattering • Neutrino astronomy: • Low neutrino flux: • Need for very massive detectors • Solution: Large water or ice body (order of km3) • Čerenkov detector: • 3D array of Digital Optical Modules (DOM’s) • Largest neutrino telescopes: • IceCube: South Pole, 1 km3 ice, 5’160 DOM’s • ANTARES/KM3NeT: Mediterranean, 5 km3 water, 10’800 DOM’s • Multiple neutrino reaction channels • Particle showers created by high energy neutrinos Neutrino interactions (Source: Thesis Erwin Visser) Example: IceCube 4. What are neutrinos telling us? NEUTRINO ASTRONOMY IS COMPLEMENTARY TO PHOTON ASTRONOMY. IT CAN PROVIDE A DEEP INSIGHT INTO OTHERWISE OBSCURED PROCESSES. Topics to be (potentially) addressed by neutrino astronomy • Properties of high energy particles absorbed by the atmosphere • Validation of solar nuclear reaction model • Validation of supernova models • Understanding of galactic high energy processes and view into the galactic center • Big Bang footprint • Test of cosmological models (dark matter, dark energy) Solar fusion process • Several β-processes as per Standard Solar Model: • Most relevant: pp reaction • Real-time monitoring of the nuclear fusion processes • Measuring the neutrino flux is the foundation for model validation Solar neutrinos (proton-proton chain) in the Standard Solar Model. Remark: Lepton conservation requires an even number of leptons to be involved in each reaction. Supernova + − 0 • Proton-electron recombination: � + � ⟶ � + �� • A huge number of high energy neutrinos is emitted within 10 sec • Neutrino signal is emitted some hours ahead of the electromagnetic signal • Network of neutrino detectors can be used as a SN alert system 11 • Dissipation of thermal energy (10 K): γ ⟶ �� + �� • Neutrinos carry away most of the gravitational energy (2∙1046 J) Big Bang • Nucleosynthesis and cosmological models: • Decoupling of neutrinos from matter 1s after BB (380’000yrs for photons) • Cosmic neutrino background: CNB or CνB (CMB for photons) • Estimated as-if temperature: Tν = 1.95K vs Tγ = 2.75K (CMB) • Direct detection most difficult but not impossible • Compelling indirect evidence: • Number of neutrino species is encoded in CMB • Standard Model perfectly consistent with empirical data Q&A References • https://en.wikipedia.org/wiki/Neutrino • https://icecube.wisc.edu/ • https://icecube.wisc.edu/icecube/static/reports/IceCubeReview2010.pdf • http://www.astro.caltech.edu/~golwala/ph135c/16WilburNeutrinoAstronomy.pdf • https://www.nikhef.nl/pub/services/biblio/theses_pdf/thesis_EL_Visser.pdf • https://www.nasa.gov/topics/universe/features/wmap_five.html • https://www.nasa.gov/centers/marshall/news/news/releases/2014/14-169.html • https://www.bnl.gov/science/neutrinos.php Appendix Neutrinos • Postulated in 1930 by Wolfgang Pauli (conservation laws in β-decay) • Detected in 1956 by Clyde Cowan and Frederick Reines The first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. Image: Argonne National Laboratory. Neutrino oscillations • Neutrino oscillations: • Each flavor eigenstate is a superposition of 3 mass eigenstates • Dispersion of mass eigenstates when propagating inside dense bodies (e.g. Sun or Earth): • The phase velocity is mass-dependent and varies for the three mass eigenstates, leading to respective phase shifts • The neutrino is no longer a flavor eigenstate by the time it leaves the sun • Solar neutrinos reaching Earth can be represented as a superposition of flavor eigenstates • Quantum Mechanics: The detection likelihood for each flavor depends on the respective amplitude Sources of neutrinos • Extraterrestrial sources • Terrestrial sources: • T: Terrestrial/geologic neutrinos (β-decay) → �� • ATM: ATMospheric neutrinos (cosmic rays) → ��, �� • Man made sources: • R: Reactor neutrinos (fission and fusion) • AN: Accelerator neutrinos (e.g. CERN) • Nuclear bombs (fission and fusion ) Detection via neutrino capturing • Many isotopes are decaying via a β– process: • A neutrino is emitted together with the electron or positron • Any β–process can in principle also be used for the detection of neutrinos • Very low reaction rate: Only a few approaches are technically feasible Weak reactions • Nuclear reactions can be transformed (Feynman): • Example: emission vs capturing process: • Neutrino emission: �0 ⟶ �+ + �− + � + � − 0 � + � ⟶ � + �� • Neutrino capturing: � + �+ ⟶ �0 + �+ � 0 + − �� + � ⟶ � + � • Preservation of lepton-number • Any β-decay process can in principle be used for detection • The cross section (reaction rate) for neutrino capturing is very low • The energy range covered by a detector depends on the isotope used • Multiple reaction channels: • ES: Elastic Scattering • NC: Neutral Current (Z-boson) • CC: Charged Current (W-boson) • BB: Double β-decay ? Big Bang • Very low energy and direct detection most difficult, but not impossible: • The tiny �− energy difference allows in principle to discriminate between (PTOLEMY experiment): 3 3 − • capturing of CνB neutrinos: � + 1� ⟶ 2�� + � 3 3 − • natural beta decay of tritium: 1� ⟶ 2�� + � + � • Compelling indirect evidence: • Interaction of ν with matter and photons permits to derive Nν (= 3 neutrino species + correction term): • Standard Model: Nν = 3.046 • Planck (CMB): Nν = 3.15 ± 0.23.