Neutrino astronomy

Lutz Köpke Johannes Gutenberg-Universität Mainz Neutrino astronomy 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 … • IceCube • Antares and Km3Net

Why neutrino astronomy? • Understanding offusionprocesses in thesun • Understanding ofsupernovaexplosions • Understanding ofneutrinoproperties (oscillations, masshierarchy, …) • Identificationandunderstandingofcosmicraysources • Universeis transparent toneutrinos! • Search forthe „not yetfound“ andunexpected

History of neutrino astronomy Can oneseethesun in O(1-10) MeVneutrinos? Discussionsstarted after 1958 (cross 3He + 4He 7Be+ 1000x expectation) Homestead proposal 1964

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

Supernova 1987A by chance discovery of 20-23 O(10) MeV 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 E2 forever? Could there be 2 different neutrinos? MACRO, FREJUS, DUMAND  Lake Baikal, AMANDA, … „Weproposetoinstalldetectorsdeep in a lakeor in theseaandtodeterminethedirectionofcharged particleswiththehelpof Cherenkov radiation“ Proc. 1960, ICHEP, Rochester, p. 578

Moisei Alexandrovich Markov Markovwarnedthesovietleaders in 1947 about „dangerouspolitical-ideologicalmovesthatthreaten to separate sovietsciencefromthrerest“ This was a brave (almostsuicidal) move, as he andotherscientistswerechargedof not sufficientlyquotingRussianscientistsand „uncriticallyreceiving western physicaltheoriesand propagandizingthem in ourcountry“ Stalin, however, „chosetheatomic bomb overideology“  whichsavedtheirlives … Later, Markovbecameactive in promotingdisarmament

Dumand 4800 m depth at Hawaii shore

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

Lake Baikal / AMANDA 1993-2000 1.5 km deep 576 modules 1993-1998 1.1 km deep 192 modules

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

Astrophysical neutrino flux 1.9 K cosmic background neutrinos 6 x 60/cm3 σ@ 1.7x10-4 eV ~10-55 cm2 Solar O(1 MeV) neutrinos Supernova O(10 MeV) neutrinos Atmospheric O(1-1000 GeV) μ-neutrinos AGN O(10 TeV) neutrinos 20 decades in energies 30 decades in fluxes 20 decades in cross sections

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

Each time a particle crosses front, it enters “an approaching medium” the shock front as such the downstream rest system the shock front rest system the upstream rest system Dynamics of a shock front 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? • Difficult to explain energies >~1021eV for protons • Easier for heavy nuclei protons c: velocity of scattering centers, transforms R< 2RgyroR< 2Rgyro/

High energy neutrinos , N expect: μ : e :  = 2 : 1 : 1 however, energy distributions different! μ p, N , K e μ e 0 μ  isospin!  Nucleonsinteractwithambientphotonsaroundsourceandbaryonic matter … • Neutrinos from „beam dumps“ • Proton proton and proton gamma interactions • Waxman Bahcall bound

Proton proton cross sections

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

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

…transparency of the Universe • Only ’s can “see” beyond local Universe above 100 TeV • Only ’s can escape from dense environments • Only ’s can unambiguously prove hadronic acceleration 99% of universe 99.999999% useful range for point searches: 3x105 3x107 3x109 Ly

Our vicinity Local group Not to scale ! us 25 x 105 Ly 60 MiILLION LIGHTYEARS 105 Ly 1.5 x 105 Ly

Our vicinity us 25 x 105 Ly 60 MiILLION LIGHT YEARS 105 Ly 1.5 x 105 Ly 1020 eV p, 100 TeV  : seeing range 60 million light years

Galaxies and stars within 60 million Ly

… our vicinity us 400 MiILLION LIGHT YEARS 25 x 105 Ly 105 Ly 1.5 x 105 Ly 100 GeV  : 500 million light years

average path length LA for a particle A travelling through medium of particles B with number density rB LA = 1 / (rBsAB) Order of magnitude for 1 TeV neutrinos in open space:s(1 TeV) = 10-39 m2, r = 0.4/cm3 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 Absorption length for neutrinos

Waxman-Bahcall limit Idea: constrain possible neutrino flux from extragalactic cosmic ray intensity power required over 1010 years to produce cosmic ray flux: Assumethatnucleonsinteracting in surrounding material by p (and pp, pn) interaction  pionsandkaons  neutrinos Assume „opticallythinsources“: I=I0exp(-p) with p<1 Extrapolatetolowerenergyassuming E-2flux conservativelyassumethatenergygeneration rate increaseswithredshiftat maximal rate astronomicallyobserved …

…. Waxman Bahcall bound for pΔ++n for ppNN+pions limit mostly quoted as 5x10-8 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 thicksources (like AGN cores) absorbcosmicrays (p~100)  limit not applicable

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

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

Bruno Pontecorvo Bruno Pontecorvo (born 22.8.1913, Pisa, died 24. 9. 1993, Dubna) an Italian-born physicistwho was a pioneer in thestudyoftheelusivesubatomicparticlescalledneutrinosandwhodefectedtotheSoviet Union in 1950, died in Dubna, outside Moscow. He was 80. Mr. Pontecorvo was oneof a groupoftalentedyoungphysicistswhoworkedwith Enrico Fermi in Rome in theearly 1930's on experimentsthatprovedradioactive isotopes of a numberofelementscanbeproducedbyexposingtheelementsto neutronsthathavebeenslowed down. After Mussolini passedlawsthatdiscriminatedagainst Jews, Mr. Pontecorvomovedto Paris andleftforthe United States in 1940 after the Nazi invasion. He workedbrieflyfor an American oilcompanyandthenmovedto Canada, where he appliedtobecome a British citizen. In 1948, after he completed hisnaturalization, he movedto England tojointheAtomicEnergy Research Laboratory atHarwell, near Oxford. But in thelatesummerof 1950, Mr. Pontecorvoandhisfamilydisappearedduring a vacation in Rome. Theywere last seen in Helsinki on Sept. 2, 1950, andwerebelievedtohavetaken a shiptotheSoviet Union withthehelpofSovietdiplomats in theFinnishcapital. It was not until 1955, when Mr. Pontecorvopublishedarticles in PravdaandIzvestia, thatofficialswerecertain he was working in theSoviet Union. His defection, whichcamethe same yearthatoneofhiscolleagues, Klaus Fuchs, was convictedofespionage in Britain, raisedfearsthattheItalianscientist hadfledwithsecretsthatcouldbeusedtohelpbuild a hydrogen bomb. Anothercolleague, Alan Nunn May, was convictedofespionagecharges in Canada in 1946. But in frequentstatementstothe press in theSoviet Union, andduringhisfirsttrip back toItaly in 1978, he maintainedthathisresearch in Canada and England hadnomilitaryapplications. He said he haddefectedtopursuenuclearresearchforpeacefulpurposesbecause investigationsintoscientificespionagehadmadeittoodifficultforhimtowork. "In 1950, theatmosphere was such that I couldnolongerbreathe," he wrote in the 1955 article in Pravda. In thearticle, he also saidthat he hadsigned a petitionalongwithseveralothernuclearscientistscallingfor a worldwideban on nuclearweapons. His British citizenship was revokedbecauseit was believed he defectedwithmilitarysecrets, but he was neverchargedwithespionage. He isknown in hisfieldforbeingoneofthefirstphysiciststosuggestusing a solutioncontainingchlorinetodetectneutrinos.

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 … nothingspecial, typicalquantummechanicaleffectrelatingorthonormalvectors

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 nm at t = 0: Losc

3-Flavor neutrino oscillations sin22θ13 = 0.08 Red:  blue:  black: e

Status of neutrino oscillation parameters Mixing angles: Mass differences: CP-violation parameter,Majoranaparameters1, 2andsignof m232 unknown if m1=0: m20.009 eV  5x 10-7me; m30.05 eV

Cosmological relevance Contribution to energy budget of the Universe: stretching cosmology < 0.2 eV?

Neutrinos from far away sources • Which information does a neutrino carry when it is created? • What happens on the way to detector? • What can be measured in the detector? • ad 1: Neutrinos arecreatedasflavoreigenstates (e, μ , ) • identifiedbyenergy, momentum, spindirectionandneutrinoflavor • ad 2: • Neutrino oscillationlengthmuchshorterthantraveldistance • Source extension larger thanoscillationlength • Broadenergyspectrumleadstovaryingoscillationlengths • Wave packets separate so thatoscillationsarenolongerpossible • Whatremainsis an averagedeffect:

…neutrinos from far away sources assume that Ue3 = 13 = 0, 23=450 … firstassumeonly e productionatsource: e : μ :  = 1 : 0 : 0 fluxesat Earth: e : μ :  = 1-2b : b : b

…neutrinos from far away sources flux at source: e : μ:  = 1 : 0 : 0 flux at Earth: e : μ :  = 1-2b : b : b flux at source: e : μ:  = 0 : 1 : 0 flux at Earth: e : μ :  = b : c : c (*) flux at source: e : μ:  = 0 : 0 : 1 flux at Earth: e : μ :  = b : c : c frompiondecaywith subsequent muondecayatsourceexpect: e : μ :  = 1 : 2 : 0 fluxat Earth: e : μ :  = 1-2b+2b : b+1-b : b+1-b = 1 : 1 : 1 forpiondecayexpectequalfluxesofneutrinospeciesat Earth, independent on valuefor12 !! however, energydistributionof eand μandthusdetectionthresholdsare different … (*) 2 sin2cos2=1-sin4-cos4 2c=1/2(a+1)=1-b

…neutrinos from far away sources • ad 3: Whatismeasuredatthedetector? • Beforereachingthedetectorseveral additional effects happen: • theneutrinoundergoesoscillations in Earth (not relevant for high energies) • theneutrinomaygetabsorbed meanfreepathlength in the Earth:

Neutrino astronomy