PHYSICS POTENTIAL OF SUPERNOVA NEUTRINOS. Mainly based on:  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].
Mainly based on:
 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].
 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].
 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].
Dip.to di Fisica di Bari & Sez. INFN di Bari
+ new simulations for a 0.4 Mton detector
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
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.
T.Totani et al., Astrophys. J. 496, 216 (1998).
In the following, we refer to the thermal burst, unless otherwise noticed.
“Hierarchy”of the spectra
ne + n
~ 9 – 12 MeV
~ 14 – 17 MeV
~ 18 – 22 MeV
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.
[T.Shiegeyama and K. Nomoto, Astrophys. J. 360, 242 (1990)]
Matter effects on n oscillations crucially depend on neutrino potential in SN:
As we will see in the following, this static potential may be profoundly modified by shock-wave propagation effects.
M2 = - , + , ± Dm2
normal hierarchy3 n framework
Mixing parameters:U = U (q12, q13, q23) as for CKM matrix
dm2 7.3 10-5 eV2
Dm2 2 10-3 eV2
sin2q13 < 0.067 (3 s)
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)
Final rotation to the flavor eigenstates in vacuum
Higher level crossing transition.
0 PH1 depending on q13
Lower level crossing transition.
PL 0 (adiabatic) since q12 large and dm2 small
Adiabatic (PH0)ANALYTICAL RECIPE
The smallness of q13 suggests Landau-Zener (LZ) form:
is a scale factor sensitive to the matter density profile. It will allow to extract important information on shock wave effects on matter density.
cos2q12 (n, normal)
sin2q12 (n, inverted)
cos2q12PH (n, inverted)
Substitutions in PeeSURVIVAL PROBABILITY
The analytical form of Pee is exceedingly simple
PH modulates Pee
If PH1 (sin2q13 10-5), it helps to discriminate mass hierarchy
Example of mass hierarchy effect
Example of Earth effect (mantle crossing)
… with emphasis on 0.4 Mton water detector (*)
(*) As suggested, e.g., in J. Burguet-Castell et al., hep-ph/0312068
SN 1987-A seen by naked-eye (23 February 1987, Large Magellanic Cloud, d 50 kpc)
The birth of SN neutrino astronomy
(e.g. for normal hierarchy, PH = 0 ; d = 10 kpc)
nep n e+~ 6000 events
ne,m,te- ne,m,te- (E.S.) ~ 100 + 30 + 30
ne O F e- ~ 100
ne d p p e- ~ 180
ne d n n e+ ~ 120
ne,m,t d p n ne,m,t ~ 490
nep n e+ ~ 280
n p n p ~ 300
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
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
The hierarchy is inverted and sin2q13 10-4.
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
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
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
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.
Progenitor static profileNEUTRINO 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
(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”.
The shock wave induces deviations from the exponential decrease of luminosity:
forsin2q1310-5 the effect is small.
The shock-wave propagation can be followed in real time
The shock wave propagation induces time-dependent deformations
forsin2q1310-5 the effect is small.
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)]
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)
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.
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.
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)
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.
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).
SRN signal should manifest as distortion of Michel spectrum of invisible m.
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
A 0.4 Mton detector will see in an year as much SRN as SK in ~ 20 years of detection.
GOOD CHANCE TO OBSERVE SRN WITH A MTON DETECTOR
… not all at the same time, however!
(degeneracy of effects)
In principle, we can extract information on:
but also on new neutrino properties, such as
[see our hep-ph/0401227]
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,
Complete disappearance of the signal
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.
(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.