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PHYSICS POTENTIAL OF SUPERNOVA NEUTRINOS

PHYSICS POTENTIAL OF SUPERNOVA NEUTRINOS. Mainly based on: [1] G.L.Fogli, E.Lisi, D.Montanino, and A.Palazzo, “ Supernova neutrino oscillations: A simple analytic approach ”, Phys.Rev. D 65 , 073008 (2002) [hep-ph/0111199].

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PHYSICS POTENTIAL OF SUPERNOVA NEUTRINOS

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  1. PHYSICS POTENTIAL OFSUPERNOVA NEUTRINOS Mainly based on: [1] G.L.Fogli, E.Lisi, D.Montanino, and A.Palazzo, “Supernova neutrino oscillations: A simple analytic approach”, Phys.Rev. D 65, 073008 (2002) [hep-ph/0111199]. [2] G.L.Fogli, E.Lisi, A.M., and D.Montanino, “Analysis of energy- and time-dependence of supernova shock effects on neutrino probabilities”, Phys.Rev. D 68, 033005 (2003) [hep-ph/0304056v2]. [3] G.L.Fogli, E.Lisi, A.M., and D.Montanino, “Three-generations flavor transitions and decays of supernova relic neutrinos”, submitted to PRD [hep-ph/0401227]. Alessandro MIRIZZI Dip.to di Fisica di Bari & Sez. INFN di Bari + new simulations for a 0.4 Mton detector

  2. OUTLINE • Introduction to Supernova (SN) neutrino physics • Expected n signal from a SN explosion • SN n oscillations effects on the signal • GalacticSN neutrinos detection: status and perspectives • SN 1987-A n detection • Current SN n detectors • Potentiality of a future “Megaton” detector • What can we learn (astrophysical and n physics information) • Relic SN neutrinos detection • Summary and Conclusions

  3. INTRODUCTION TOSUPERNOVA NEUTRINO PHYSICS

  4. ENERGY SCALES:99% of the released energy (~ 1053 erg) is emitted by n and n of all flavors (only 0.01% of the emitted energy is carried by photons). Ln 3 x 1019 Ln Flavor conversion n emission Shock wave Core Collapse INTRODUCTION Core collapse SN is one of the most energetic events in nature. It corresponds to the terminal phase of a massive star [M 8 M] which becomes instable at the end of its life. It collapses and ejects its outer mantle in a shock wave drivenexplosion.  SN • TIME SCALES:Neutrino emission lasts ~10 s • EXPECTED:1-3 SN/century in our galaxy (d O(10) kpc).

  5. NEUTRONIZATION BURST:ne • Physical process: Fe dissociation by shock wave propagation. • Reaction: e- p n ne • Duration: 10 –20 ms after the explosion • Energy emitted: E~ 1051 erg • (1/100 of total energy) 0.1 1.0 10 t (s) T.Totani et al., Astrophys. J. 496, 216 (1998). • THERMAL BURST: ne , ne , nx , nx • Physical process: Cooling of the neutron star. • Reactions: e- p n ne, e+n p ne, e+ e- nn, NN NN nn • Duration: ~10 s • Energy emitted: E~ 1053 erg RESULTS OF CORE-COLLAPSE SIMULATIONS L(t) In the following, we refer to the thermal burst, unless otherwise noticed.

  6. ne + p FLAVOR DISTRIBUTION OF FLUX • Neutrinos of different flavor have different interactions in the medium “Hierarchy”of the spectra ne + n NC only ~ 9 – 12 MeV ~ 14 – 17 MeV ~ 18 – 22 MeV • “Equipartition” of Luminosity between flavor within a factor of 2 (Le ~ Le ~ Lx ~(1-5) x 1052 erg/s) [M.T. Keil, G.G. Raffelt, H.T. Janka, Astrophys. J. 590, 971 (2003)]. • Exponential decrease of luminosity: L(t) ~e-t/t (t = 3 s).

  7. SUPERNOVA NEUTRINO ENERGY SPECTRA A very useful parametrization for the energy spectra at the neutrino-sphere is a power-law “a-fit” where a plays the role of a “pinching” parameter [M.T. Keil, G.G. Raffelt, and H.T. Janka, Astrophys. J. 590, 971 (2003)] : Note that a=2 corresponds to the thermal Maxwell-Boltzmann spectrum. In the following we will refer to the values in the figure as our default choice, unless otherwise noticed. These original spectra may be strongly modified by the peculiar matter effects associated to n oscillations in the stellar matter.

  8. STATIC NEUTRINO POTENTIAL [T.Shiegeyama and K. Nomoto, Astrophys. J. 360, 242 (1990)] Matter effects on n oscillations crucially depend on neutrino potential in SN: power–law parametrization As we will see in the following, this static potential may be profoundly modified by shock-wave propagation effects.

  9. n3 • Dm2 inverted hierarchy “solar” M2 = - , + , ± Dm2 “atmospheric” n1 • dm2/2 n1 • dm2/2 n2 n2 -dm2/2 -dm2/2 dm2 dm2 2 2 n3 -Dm2 normal hierarchy 3 n framework Mixing parameters:U = U (q12, q13, q23) as for CKM matrix Mass-gap parameters: dm2 7.3  10-5 eV2 sin2q12  0.290 Dm2  2  10-3 eV2 sin2q23  0.5 sin2q13 < 0.067 (3 s) • OPEN QUESTIONS • Mass ordering? normal vs inverted • How large is q13? • Absolute masses? Hierarchical vs degenerate

  10. Neutrino flavor evolution equations must be solved to obtain the relevant Pee = P( ne ne ) < 1 ( ) ( ) SUPERNOVA NEUTRINO OSCILLATIONS Rotation to eigenstates in matter (at the neutrinosphere) V(x) Final rotation to the flavor eigenstates in vacuum Higher level crossing transition. 0  PH1 depending on q13 Lower level crossing transition. PL 0 (adiabatic) since q12 large and dm2 small

  11. Extremely non adiabatic (PH1) Adiabatic (PH0) ANALYTICAL RECIPE The smallness of q13 suggests Landau-Zener (LZ) form: where is a scale factor sensitive to the matter density profile. It will allow to extract important information on shock wave effects on matter density. • In the next we will focus on the two extreme cases • PH0 (i.e. sin2q13 10-3) • PH1 (i.e. sin2q13  10-5)

  12. sin2q12PH (n, normal) cos2q12 (n, normal) sin2q12 (n, inverted) cos2q12PH (n, inverted) • sin2q12PE • cos2q121-PE Substitutions in Pee SURVIVAL PROBABILITY The analytical form of Pee is exceedingly simple PH modulates Pee • Earth matter crossing induces additional n flavor transitions. Under hierarchical hypothesis the crossing probability in the Earth is PE = PE(dm2,q12) Pee≈ If PH1 (sin2q13 10-5), it helps to discriminate mass hierarchy

  13. NH is indistinguishable from IH (PH = 1) • PH = 0 corresponds to a complete conversion into nx Example of mass hierarchy effect Example of Earth effect (mantle crossing) • Earth crossing induces an oscillatory modulation on the spectra • The amplitude of this effect increases with the difference among the original fluxes. EFFECTS OF OSCILLATIONS ON NEUTRINO FLUXES(before detection)

  14. DETECTION OF SUPERNOVA NEUTRINOS … with emphasis on 0.4 Mton water detector (*) (*) As suggested, e.g., in J. Burguet-Castell et al., hep-ph/0312068

  15. SN 1987-A SN 1987-A seen by naked-eye (23 February 1987, Large Magellanic Cloud, d 50 kpc) • The best studied SN of all times: • Study of SN dynamics • Study of n physics The birth of SN neutrino astronomy

  16. SIMULATION SN 1987-A NEUTRINO DETECTION • Small statistics of events • Lot of uncertainties Basic features understood … … but still many questions

  17. WHAT COULD WE SEE TODAY (“SN 2004-A”)? (e.g. for normal hierarchy, PH = 0 ; d = 10 kpc) • WATER : SUPER-KAMIOKANDE [Japan, 22.5 kton] nep n e+~ 6000 events ne,m,te- ne,m,te- (E.S.) ~ 100 + 30 + 30 ne O F e- ~ 100 • HEAVY WATER: SNO [SUBDURY, Ontario, 1 kton] ne d p p e- ~ 180 ne d n n e+ ~ 120 ne,m,t d p n ne,m,t ~ 490 • SCINTILLATOR: KamLAND [Japan, 1 kton] nep n e+ ~ 280 n p n p ~ 300

  18. WHAT COULD WE SEE “TOMORROW” ? Simulations in NH A 0.4 Megaton detector might open a new era in SN neutrino detection Veryhigh statistics of events (104 events/s) will be reached

  19. What can we learn from the next galactic SN with a Megaton detector? • Probe oscillations parameters: • Mass spectrum • q13 mixing angle • Neutrino magnetic/transition moment • Neutrino flavor changing neutral currents (FCNC) • ….. • Astrophysical properties: • Physics of neutrino spectra formation and transport • (spectra and luminosities of observed signal) • Physics of collapse/shock wave propagation • (time distribution of the signal)

  20. Oscillation parameters: mass hierarchy, q13 From the observation of one of these spectra one could, in principle, extract information on the hierarchy and on q13 . Problem: The spectra are largely affected by astrophysical uncertainties (e.g., on <Ex>) There are, however, effects largely independent from astrophysical uncertainties

  21. If the Earth effect is not seen The hierarchy is inverted and sin2q13 10-4. • If the Earth effect is seen degeneracy either normal hierarchy, or inverted hierarchy with sin2q13  10-5. EARTH MATTER EFFECTS The main signature of Earth matter effects – oscillatory modulations of the observed energy spectra – is unambiguous since it can not be mimicked by known astrophysical phenomena SK perhaps too small to detect Earth matter effects

  22. Yes, Comparing ne and ne Earth effects in the same detector ne16O F e- ~ 2 x 103 events (0.4 Mton) Is it possible to extract more from the Earth effect? Is it feasible? It has been recently proposed to add 0.2% of gadolinium trichloride in a large water Cerenkov detector to tag the reaction nep n e+by radiative neutron capture [J.F.Beacom, and M.R.Vagins, “GADZOOKS! Antineutrino Spectroscopy with Large Water Cerenkov Detectors”, hep-ph/0309300]. Yes, if one can see the reaction Normally it is a background for the isotropic nep n e+but … ne16O (backward peaked)events might be detectable

  23. sin2q13 N.H. I.H. ne ne 10-4 nene nene 10-5 It will be possible to study both n and n channels in the same detector, partially breaking the degeneracy between the mass hierarchy and q13. 0.4 Mton water + gadolinium More about ne16O PH 1 : no mass hierarchy discrimination

  24. Oscillations as n “thermometer” ne16O events have tremendous sensitivity to Ex, while are quite insensitive to Ee. It will allow to determine very accurately Ex which is loosely constrained by SN computer simulations.

  25. from R.C.Schirato, and G.M.Fuller, astro-ph/0205390 rarefaction zone Shock front Progenitor static profile NEUTRINO OSCILLATIONS AS A “CAMERA” FOR SHOCK WAVE PROPAGATION Recent core-collapse SN simulations have obtained the propagation of the shock wave in a range of time of ~20 s after the core bounce. The main feature of shock wave physics is that the matter density profile is • nonmonotonic and time- dependent • step-like at the shock front

  26. HOWTO FOLLOW IN REAL TIME THE SHOCK WAVE PROPAGATION? • Conventional observations (optical, radio, X-rays) of SN events and remnants give little direct information on the shock propagation. • However, we have realized [2] that SN shock propagation can produce interesting effects in the energy and time structure of n signal, through peculiar modifications of the crossing probability PH. (see our hep-ph/0304056v2) A 0.4 Megaton detector could reveal these effects opening a unique opportunity to follow the shock dynamics in “real time”.

  27. SHOCK-WAVE EFFECTS ON TIME SPECTRA The shock wave induces deviations from the exponential decrease of luminosity: forsin2q1310-5 the effect is small. • for sin2q1310-3 the signature of the shock is easily distinguishable. The shock-wave propagation can be followed in real time

  28. SHOCK-WAVE EFFECTS ON ENERGY SPECTRA The shock wave propagation induces time-dependent deformations forsin2q1310-5 the effect is small. • for sin2q1310-3 the signature of the shock is more pronounced.

  29. From the reactionnee- nee-there will be ~ 150 events in a 0.4 Megaton detector.These events should occur in a very short time (10-20 ms). It will produce up to 6250 (15600) events in N.H. (I.H.) from nep n e+ in the short interval of 10- 20 ms. DETECTION OF THE NEUTRONIZATION BURST [See also, E.K.Akhmedov, and T.Fukuyama, JCAP 312, 007 (2003)] • Possibility to probe spin-flavor transitions: In presence of a strong magnetic field B~ 1010 G, nenewill be possible The neutronization burst will contain a fraction of ne . figure taken from T.A.Thompson, A. Burrows, and P.A.Pinto, Astrophys. J. 592, 434 (2003)

  30. DETECTION OF n FROM EXTRAGALACTIC SUPERNOVAE A Megaton detector can detect SN neutrino events also from Andromeda (d~1 Mpc). The total number of events/explosion will be modest (comparable to SN 1987-A) but this additional possibility will allow to observe about 3 times more SN explosions than in observations limited to our galaxy. This will allow to start to accumulate a statistics on a “population” of SN explosions.

  31. SN n data A REMARK A Supernova explosion will produce an enormous number of events in a Megaton Cerenkov detector. Actually the analysis of these data could be affected by the (many!) uncertainties both in n physics, both in astrophysics. However, the collected data will constitute an unique reservoir of information. Theoretical models and computer simulations of SN explosions are likely to improve with time, so the collected SN data will be repeteadly reexamined to extract increasingly refined information.

  32. SUPERNOVA RELIC NEUTRINOS

  33. n n n n n n n A galactic SN explosion is a spectacular event which will produce an enormous number of detectable n, but it is a rare event (~ 3/century) Conversly, there is a guaranteed n background produced by all the past Supernovae in the Universe, but leading to much less detectable events. A Megaton detector will be able to measure this background of neutrinos: Supernova Relic Neutrinos (SRN)

  34. The number density of SRN of a given specie a is given by where is the Hubble constant as function of the redshift z, RSN(z) is the Supernova formation rate per comoving volume [P.Madau et al, Mon. Not. Roy. Astron. Soc. 283,1388 (1996)]. Note that for ultrarelativistic n nacanbe identified in natural unit (c=1) with the relic n flux per unit of time, area and energy.

  35. In the energy window En  [20-30] MeV, the background of low-energy atmospheric neis relatively small. But, in this window, there is a large background due to “invisible” m (i.e. below Cerenkov emission threshold) decay products, induced by low energy atmospheric nm and nm. SUPERNOVA RELIC NEUTRINO AND BACKGROUND In order to detect SRN, we should find an “energy window”, free of other backgrounds. figure taken from S.Ando, K.Sato, and T.Totani, Astropart.Phys. 18, 307 (2003).

  36. No distortion flux limit SRN signal should manifest as distortion of Michel spectrum of invisible m. SIMULATION Super- Kamiokande collaboration has recently investigated the SRN flux using 1496 days of data [M.Malek et al., Phys.Rev.Lett. 90, 061101 (2003)]. It fixed an upper bound on SRN signal: ~ 3 times larger than “typical” theoretical predictions

  37. SRN SIGNAL AND ITS BACKGROUND IN A MEGATON DETECTOR SIMULATION A 0.4 Mton detector will see in an year as much SRN as SK in ~ 20 years of detection. • In general, • Better separation signal/background • If doped with Gd, signals emerges from background for Epos [10,20] MeV GOOD CHANCE TO OBSERVE SRN WITH A MTON DETECTOR

  38. WHAT CAN WE LEARN FROM SRN? … not all at the same time, however! (degeneracy of effects) In principle, we can extract information on: • Star formation rate • Neutrino masses and mixing parameters • SN neutrino energies but also on new neutrino properties, such as neutrino decay [see our hep-ph/0401227]

  39. MAJORON DECAY: Among all the possible neutrino decay scenarios, we consider a decay in an invisible massless (pseudo)scalar particle, a “Majoron”: ninj X , mi > mj The most stringent limit on n decay comes from the SN 1987-A: where t is the rest frame neutrino lifetime. The SRN offer the possibility to probe a decay time (in lab frame) t E/m ~1/H0~ 1017 s, • Results: A complete decay can produce either an enhancement of the signal up to a factor of 2 (in the case of quasi degenerate n masses in NH) either a complete disappearance of the signal (IH). • The case of incomplete decay should interpolate between the complete decay and no decay case.

  40. Enhancement of a factor ~2 of the signal Complete disappearance of the signal NH IH The modification of the signal induced by the decay is below SK upper limit. Future SRN measurements in a Megaton detector could constrain at least some extreme decay scenarios.

  41. In particular: • The missing pieces of neutrino mass spectrum and mixing matrix can be probed. • Models of core-collapse, shock-wave propagation, and SN n production can be “calibrated”. • Non-standard n properties can also be tested. In conclusion: • Galactic SN explosion: spectacular but rare • Relic background, guaranteed (modulo n decay suppression) SUMMARY AND CONCLUSIONS In future the detection of neutrinos from supernovae will be one the “next frontiers” of neutrino astrophysics. The physics potential of a “Megaton” water detector in this context is enormous, both for particle physics and astrophysics (expecially with Gd). SN n physics program with 0.4 Mton detector is a no-loose project, and probably a high-winner one.

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