Neutrino astronomy Lutz Kpke Johannes GutenbergUniversitt Mainz Schule

Neutrino astronomy Lutz Köpke Johannes Gutenberg-Universität Mainz Schule für Astroteilchenphysik Obertrubach-Bärnfels 12. 10. 2010 – 14. 10. 2010 9: 00 -9: 45 10: 00 -10: 45

Subjects covered • • • Why neutrino astrophysics? Some history …. Sources of neutrinos and their propagation Neutrino oscillations Neutrino cross sections Detection of neutrinos Angular resolutions Background processes Detection principles The problem with natural media … Ice. Cube Antares and Km 3 Net

Why neutrino astronomy? • Understanding of fusion processes in the sun • Understanding of supernova explosions • Understanding of neutrino properties (oscillations, mass hierarchy, …) • Identification and understanding of cosmic ray sources – Universe is transparent to neutrinos! • Search for the „not yet found“ and unexpected

History of neutrino astronomy Can one see the sun in O(1 -10) Me. V neutrinos? Discussions started after 1958 (cross 3 He + 4 He 7 Be+ 1000 x expectation) Homestead proposal 1964

Clorine Experiment/Super-K Clorine Experiment (no direction resolution) Observation solar neutrinos … but deficit w. r. t. theory!!! Super-Kamiokande evidence that neutrinos arise from sun

Supernova 1987 A by chance discovery of 20 -23 O(10) Me. V neutrinos in 2 -3 detectors … Kamiokande result dust ring illuminated by SN-shock

High energy neutrino astronomy Moisei Markov (mid 1950‘s): proposal for deep underground and underwater neutrino observatories Motivation: are weak interactions of Fermi-Type or is there an intermediate boson? Does the cross section rise with E 2 forever? Could there be 2 different neutrinos? MACRO, FREJUS, DUMAND „We propose to install detectors deep in a lake or in the sea and to determine the direction of charged particles with the help of Cherenkov radiation“ Proc. 1960, ICHEP, Rochester, p. 578 Lake Baikal, AMANDA, …

Moisei Alexandrovich Markov warned the soviet leaders in 1947 about „dangerous political-ideological moves that threaten to separate soviet science from thre rest“ This was a brave (almost suicidal) move, as he and other scientists were charged of not sufficiently quoting Russian scientists and „uncritically receiving western physical theories and propagandizing them in our country“ Stalin, however, „chose the atomic bomb over ideology“ which saved their lives … Later, Markov became active in promoting disarmament

Dumand 4800 m depth at Hawaii shore

Dumand junction box at 4800 m depth sea floor Prototype string 1987 1993/94 deployment failed due to leak in penetrator original project (256 PMTs) was abandoned

Lake Baikal / AMANDA 1993 -1998 1. 1 km deep 192 modules 1993 -2000 1. 5 km deep 576 modules

Neutrino sources te la – Sun – Supernovae – Geo neutrinos etc r…. • Direct production of neutrinos • Acceleration of nucleons • Neutrinos from „beam dumps“ of accelerated nucleons – nucleon proton and nucleon gamma interactions – Waxman Bahcall bound

Astrophysical neutrino flux 1. 9 K cosmic background neutrinos 6 x 60/cm 3 σ@ 1. 7 x 10 -4 e. V ~10 -55 cm 2 Solar O(1 Me. V) neutrinos Supernova O(10 Me. V) neutrinos Atmospheric O(1 -1000 Ge. V) μ-neutrinos AGN O(10 Te. V) neutrinos 20 decades in energies 30 decades in fluxes 20 decades in cross sections

How does the acceleration work? example: acceleration in supernova remnant shock fronts A. Reimer • Supernova explosion emits fast matter streams O(106… 7 m/s) • Shock fronts from when matter stream hits interstellar matter • some “lucky” particles pass shock fronts frequently and obtain accelerating “kicks”

Dynamics of a shock front the shock front as such the shock front rest system the downstream rest system the upstream rest system Each time a particle crosses front, it enters “an approaching medium” Charles Jui

Acceleration in a shock front • Assume relativistic particle, p~E, at one side of shock • If particle crosses shock, its energy in the rest frame on the other side for vertical crossing is given by: • Multiple crossings yield increasing energy; require “turn-around” of particle in magnetic fields • Escape probability per cycle ~u/c

The Hillas plot • Which object accelerates to what energies? protons • Difficult to explain energies >~1021 e. V for protons • Easier for heavy nuclei c: velocity of scattering centers, transforms R< 2 Rgyro/

High energy neutrinos • Neutrinos from „beam dumps“ – Proton proton and proton gamma interactions – Waxman Bahcall bound , N μ , K p, N μ 0 isospin! expect: μ : e : = 2 : 1 e μ e however, energy distributions different! Nucleons interact with ambient photons around source and baryonic matter …

Proton proton cross sections

Proton gamma cross section Cross section ~ 400 times smaller than for pp

Transparency of the Universe excluded due to messenger interaction with photon background photons of all energies abound in universe (3 K visible) interactions with p and γ: Energy p + γ(3 K) (1232) p + π γ + γ(IR + 3 K) e+ elimits „seeing“ range … „seeing“ range

99% of universe 99. 999999% …transparency of the Universe • Only ’s can “see” beyond local Universe above 100 Te. V • Only ’s can escape from dense environments • Only ’s can unambiguously prove hadronic acceleration useful range for point searches: 3 x 105 3 x 107 3 x 109 Ly

Our vicinity Local group Not to scale ! us 25 x 1 0 60 Mi. ILLION LIGHTYEARS 5 Ly 5 10 Ly 1. 5 x 1 5 0 Ly

Our vicinity us 25 60 Mi. ILLION LIGHT YEARS x 1 05 Ly 5 10 Ly 1. 5 x 1 5 0 Ly 1020 e. V p, 100 Te. V : seeing range 60 million light years

Galaxies and stars within 60 million Ly

… our vicinity us 25 400 Mi. ILLION LIGHT YEARS x 1 05 Ly 5 10 1. 5 x 1 5 0 Ly 100 Ge. V : 500 million light years Ly

Absorption length for neutrinos • average path length LA for a particle A travelling through medium of particles B with number density r. B LA = 1 / (r. Bs. A B) Order of magnitude for 1 Te. V neutrinos in open space: s(1 Te. V) = 10 -39 m 2, r = 0. 4/cm 3 L = 2. 5 x 1022 Ly larger than size of universe … • Blessing and curse of neutrino astronomy: – neutrinos pass through almost everything … also through the detector

Waxman-Bahcall limit Idea: constrain possible neutrino flux from extragalactic cosmic ray intensity power required over 1010 years to produce cosmic ray flux: Assume that nucleons interacting in surrounding material by p (and pp, pn) interaction pions and kaons neutrinos Assume „optically thin sources“: I=I 0 exp(- p ) with p <1 Extrapolate to lower energy assuming E-2 flux conservatively assume that energy generation rate increases with redshift at maximal rate astronomically observed …

…. Waxman Bahcall bound for p Δ+ +n for pp NN+pions limit mostly quoted as 5 x 10 -8 Note that oscillations give factor 0. 5 Note that this is a (conservative) upper limit for „thin“ sources! Waxman-Bahcall: expected flux factor 5/ p smaller ! Optical thick sources (like AGN cores) absorb cosmic rays ( p~100) limit not applicable

… Waxman-Bahcall bound Include oscillations: Waxman-Bahcall limit x 3/2 for sum of all neutrino flavors

Neutrino Oscillations • Oscillation phenomenons • MSW effects in Sun, Earth and Supernovae • Collective Oscillations Bruno Pontecorvo 1913 -1993

Bruno Pontecorvo (born 22. 8. 1913, Pisa, died 24. 9. 1993, Dubna) an Italian-born physicist who was a pioneer in the study of the elusive subatomic particles called neutrinos and who defected to the Soviet Union in 1950, died in Dubna, outside Moscow. He was 80. Mr. Pontecorvo was one of a group of talented young physicists who worked with Enrico Fermi in Rome in the early 1930's on experiments that proved radioactive isotopes of a number of elements can be produced by exposing the elements to neutrons that have been slowed down. After Mussolini passed laws that discriminated against Jews, Mr. Pontecorvo moved to Paris and left for the United States in 1940 after the Nazi invasion. He worked briefly for an American oil company and then moved to Canada, where he applied to become a British citizen. In 1948, after he completed his naturalization, he moved to England to join the Atomic Energy Research Laboratory at Harwell, near Oxford. But in the late summer of 1950, Mr. Pontecorvo and his family disappeared during a vacation in Rome. They were last seen in Helsinki on Sept. 2, 1950, and were believed to have taken a ship to the Soviet Union with the help of Soviet diplomats in the Finnish capital. It was not until 1955, when Mr. Pontecorvo published articles in Pravda and Izvestia, that officials were certain he was working in the Soviet Union. His defection, which came the same year that one of his colleagues, Klaus Fuchs, was convicted of espionage in Britain, raised fears that the Italian scientist had fled with secrets that could be used to help build a hydrogen bomb. Another colleague, Alan Nunn May, was convicted of espionage charges in Canada in 1946. But in frequent statements to the press in the Soviet Union, and during his first trip back to Italy in 1978, he maintained that his research in Canada and England had no military applications. He said he had defected to pursue nuclear research for peaceful purposes because investigations into scientific espionage had made it too difficult for him to work. "In 1950, the atmosphere was such that I could no longer breathe, " he wrote in the 1955 article in Pravda. In the article, he also said that he had signed a petition along with several other nuclear scientists calling for a worldwide ban on nuclear weapons. His British citizenship was revoked because it was believed he defected with military secrets, but he was never charged with espionage. He is known in his field for being one of the first physicists to suggest using a solution containing chlorine to detect neutrinos.

Introduction Basic idea (Pontecorvo, 1957): If neutrinos have small and different masses: flavour eigenstate = e, μ , of weak interactions propagation mass eigenstate i = 1, 2 , 3 Eigenstates connected by unitäry 3 x 3 matrix U i … nothing special, typical quantum mechanical effect relating orthonormal vectors

Neutrino Oscillation (3 flavors) …this formula assumes that all components of U are real, there is no CP-violation, and neutrinos are of Dirac type

Simple case: 2 neutrino flavors Assume you produce a at t = 0: Losc

3 -Flavor neutrino oscillations sin 22θ 13 = 0. 08 Red: blue: black: e

Status of neutrino oscillation parameters Mixing angles: Mass differences: CP-violation parameter , Majorana parameters 1, 2 and sign of m 232 unknown if m 1=0: m 2 0. 009 e. V 5 x 10 -7 me; m 3 0. 05 e. V

Cosmological relevance Contribution to energy budget of the Universe: stretching cosmology < 0. 2 e. V?

Neutrinos from far away sources 1. Which information does a neutrino carry when it is created? 2. What happens on the way to detector? 3. What can be measured in the detector? ad 1: Neutrinos are created as flavor eigenstates ( e, μ , ) identified by energy, momentum, spin direction and neutrino flavor ad 2: • • Neutrino oscillation length much shorter than travel distance Source extension larger than oscillation length Broad energy spectrum leads to varying oscillation lengths Wave packets separate so that oscillations are no longer possible What remains is an averaged effect:

…neutrinos from far away sources assume that Ue 3 = 13 = 0, 23=450 … first assume only e production at source: e : μ : = 1 : 0 fluxes at Earth: e : μ : = 1 -2 b : b

…neutrinos from far away sources flux at source: e : μ : = 1 : 0 flux at Earth: e : μ : = 1 -2 b : b flux at source: e : μ : = 0 : 1 : 0 flux at Earth: e : μ : = b : c (*) flux at source: e : μ : = 0 : 1 flux at Earth: e : μ : = b : c from pion decay with subsequent muon decay at source expect: e : μ : = 1 : 2 : 0 flux at Earth: e : μ : = 1 -2 b+2 b : b+1 -b =1: 1: 1 for pion decay expect equal fluxes of neutrino species at Earth, independent on value for 12 !! however, energy distribution of e and μ and thus detection thresholds are different … (*) 2 sin 2 cos 2=1 -sin 4 -cos 4 2 c=1/2(a+1)=1 -b

…neutrinos from far away sources ad 3: What is measured at the detector? Before reaching the detector several additional effects happen: • the neutrino undergoes oscillations in Earth (not relevant for high energies) • the neutrino may get absorbed mean free path length in the Earth: