PHYSICS POTENTIAL OF SUPERNOVA NEUTRINOS

1
PHYSICS POTENTIAL OFSUPERNOVA NEUTRINOS

• Alessandro MIRIZZI
• Dip.to di Fisica di Bari Sez. INFN di Bari

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.
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
• Galactic SN 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 TO SUPERNOVA NEUTRINO PHYSICS
4
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 driven
  explosion.

?
SN

• TIME SCALES Neutrino emission lasts
  10 s
• EXPECTED 1-3 SN/century in our galaxy (d ?
  O (10) kpc).

5
RESULTS OF CORE-COLLAPSE SIMULATIONS
L(t)
In the following, we refer to the thermal burst,
unless otherwise noticed.
6
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 a2 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
powerlaw parametrization
As we will see in the following, this static
potential may be profoundly modified by
shock-wave propagation effects.
9
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 lt 0.067 (3 s)

• OPEN QUESTIONS
• Mass ordering? normal vs inverted
• How large is q13?
• Absolute masses? Hierarchical vs degenerate

10
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
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
SURVIVAL PROBABILITY
The analytical form of Pee is exceedingly simple
PH modulates Pee
Pee
If PH ? 1 (sin2q13 ? 10-5), it helps to
discriminate mass hierarchy

• Earth matter crossing induces additional n flavor
  transitions. Under hierarchical hypothesis
  the crossing probability in the Earth is PE
  PE(dm2,q12)

13
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
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,t e- ne,m,t e- (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
Very high 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 ltExgt)
There are, however, effects largely independent
from astrophysical uncertainties
21
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
Is it possible to extract more from the Earth
effect?
Is it feasible?
Yes, if one can see
the reaction
Normally it is a background for the isotropic
nep n e but

• 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.

ne 16O (backward peaked) events might be
detectable
23
PH ? 1 no mass hierarchy discrimination
24
Oscillations as n thermometer
ne 16O 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
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
HOW TO 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
for sin2q13 ? 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
for sin2q13 ? 10-5 the effect is small.

• for sin2q13 ? 10-3 the signature of the shock is
  more pronounced.

29
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,
  ne ne will 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 (d1 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
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
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 na can be
identified in natural unit (c1) with the relic n
flux per unit of time, area and energy.
35
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
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?

• In principle, we can extract information on
• Star formation rate
• Neutrino masses and mixing parameters
• SN neutrino energies

not all at the same time, however! (degeneracy
of effects)
but also on new neutrino properties, such as
neutrino decay
see our hep-ph/0401227
39
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
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
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.