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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

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

outline
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
introduction

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).
results of core collapse simulations

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.

flavor distribution of flux

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).
supernova neutrino energy spectra
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.

slide8

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.

3 n framework

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
slide10

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

analytical recipe

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)
survival probability

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

effects of oscillations on neutrino fluxes before detection

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)
detection of supernova neutrinos
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

sn 1987 a
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

sn 1987 a neutrino detection

SIMULATION

SN 1987-A NEUTRINO DETECTION
  • Small statistics of events
  • Lot of uncertainties

Basic features understood …

… but still many questions

what could we see today sn 2004 a
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

what could we see tomorrow
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

what can we learn from the next galactic sn with a megaton detector
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)
oscillation parameters mass hierarchy q 13
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

earth matter effects

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

is it possible to extract more from the earth effect

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

slide23

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

slide24

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.

neutrino oscillations as a camera for shock wave propagation

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
how to follow in real time the shock wave propagation
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”.

shock wave effects on time spectra
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

shock wave effects on energy spectra
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.
detection of the neutronization burst

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)

detection of n from extragalactic supernovae
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.

slide31

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.

slide33

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)

slide34
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.

supernova relic neutrino and background

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).

slide36

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

srn signal and its background in a megaton detector
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

what can we learn from srn
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]

slide39

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.
slide40

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.

summary and conclusions

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.