We calculate limits on the properties of neutrinos using data from gamma-ray
detectors on the Pioneer Venus Orbiter and Solar Max Mission satellites. A
massive neutrino decaying in flight from the supernova would produce gamma rays
detectable by these instruments. The lack of such a signal allows us to
constrain the mass, radiative lifetime, and branching ratio to photons of a
massive neutrino species produced in the supernova. Presented at Beyond The
Standard Model III, June, 1992.Comment: 5 Pages, 2 Figures (avalable on request). LaTeX, WorldSci.st

Fenimore, Ed

Jaffe, Andrew H.

Turner, Michael S.

English

arXiv

We calculate limits on the properties of neutrinos using data from gamma ray detectors on the Pioneer Venus Orbiter and Solar Max Mission satellites. A massive neutrino decaying in flight from the supernova would produce gamma rays detectable by these instruments. The lack of such a signal allows us to constrain the mass, radiative lifetime, and branching ratio to photons of a massive neutrino species produced in the supernova

Fenimore, ED

NASA Technical Reports Server

NASA-CR-193262
/
Final Report for Grant NAG 2-765
LIMITS ON NEUTRINO RADIATIVE DECAY FROM SN1987A ° • /
I _ L _;
ANDREW H. JAFFE
Enrico Fermi Institute and Department of Astronomy _ Astrophysics,
University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637-I433, USA
ED FENIMORE
MS D436, Los Alamos National Laboratory, Los Alamos, NM 87544, USA
and
MICHAEL S. TURNER t
Enrico Fermi Institute and Departments of Physics and Astronomy _ Astrophysics,
University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637-1433, USA
and
NASA/Fermilab Astrophysics Center,
Fermi National Accelerator Laboratory, Batavia, IL 60510-0500, USA
ABSTRACT
We calculate limits on the properties of neutrinos using data from gamma-
ray detectors on the Pioneer Venus Orbiter and Solar Max Mission satellites. A
massive neutrino decaying in flight from the supernova would produce gamma
rays detectable by these instruments. The lack of such a signal allows us to
constrain the mass, radiative lifetime, and branching ratio to photons of a
massive neutrino species produced in the supernova.
1. Introduction
The occurence of Supernova 1987a in the Large Megellanic Cloud has proven to
be among the most fruitful experiments in the heavenly laboratory for the confirmation
of "known" physics and the constraining of new physics. Aside from its obvious impact
upon the study of the late stages of stellar evolution in generai and upon supernova
physics in particular, models for SN87a have become an industry for the study of the
couplings of light particles (neutrinos, axions) to ordinary matter. In this work, we
discuss limits upon the properties of neutrinos independent of specific model for the
supernova.
When a supernova occurs, the bulk of the binding energy of the progenitor star
(--, 3 × 10 sa erg) is released in neutrinos, a fact predicted by theory and confirmed by the
"The NASA Technical Officer for this grant is L. Lasher, NASA Ames
lPrincipal Investigator
( _,AS A-C,_I-193262 ) LI_;ITS gN
,hEUT_I>_,L] ,_AOIATIVE OECAY FROM
S_Jlg_JT,t, (Chic,]go univ.) o p
N93-29164
Unclas
G3/93 0174963
https://ntrs.nasa.gov/search.jsp?R=19930019975 2020-03-17T04:50:25+00:00Z
observation of a neutrino burst from the supernova, with a characteristic temperature
of about Tv _ 4.5 MeV. If at least one species of neutrinos is unstable and if it couples
to the photon, then some of these neutrinos will decay to photons en route, which
are potentially detectable as MeV gamma rays. At the time of the supernova burst's
arrival at earth and environs, there were several satellites operating in the solar system
capable of detecting the decay photons in the course of their watch for gamma ray
bursts. Analyses of the data from one of these detectors, on board the Solar Max
Mission (SMM) satellite, has already been presented. TM Here, we examine the data
from Gamma Burst Detector on the Pioneer Venus Orbiter (PVO).
2. Expected Gamma-Ray Signal
We assume that 1/3 of the total supernova energy is released in a species of
massive neutrinos. These neutrinos then decay in flight into a photon and a light
neutrino (e.g., an electron neutrino). Typically, the decay products will each have
energies of 1/2 × 3 x Tv _ 7 MeV.
We will consider decays of the form v --* v'+3'. We expect that the parent neutrino
will be a massive exotic neutrino, while the daughter neutrino will be a member of a
light family such as v_. In particular, this decay allows two possibilities: the helicity of
the daughter neutrino may either be flipped or the same with respect to the parent as
the photon takes away a unit of spin (assuming both neutrinos are relativistic). From
quantum mechanics, then, we know that the distribution of the photon in the rest
frame of the parent will be proportional to either cos2(¢/2) or sin2(¢/2), where ¢ is
the rest-frame angle between the directions of the parent neutrino and the photon.
At a given time at the detector, photons are received that resulted from neutrinos
decaying on the surface of an ellipsoid defined such that the sum of the time between
the supernova and the neutrino decay and the time between the decay and the detection
of the photon is equal to the time of detection. Actually, this is only approximately
true--there is an additional delay incurred due to the finite mass of the parent neutrino.
Furthermore, due to the relativistic beaming of the decay products into the forward
direction, many more photons are received from long, skinny ellipsoids (corres0nding
to short delay times) than from others (corresponding to longer delays). Thus, the
relativistic delay will play a correspondingly larger role in these events.
From relativistic kinematics, the angular distribution of daughter photons in turn
determines the distribution of photon energies as a function of neutrino energy, for each
of the two possible decays (flip or no flip). The time delay is determined by the energy
of the neutrino and the decay ellipsoid above. Thus, the photon spectrum as a function
of time is determined. It is given by
dN = B.y L# (E) e -t_/_
4rD 2 "yr f_(E, I_) dt dtd dE dg
(1)
where B-v is the branching ratio of the parent neutrino to photons, N is the neutrino
number flux at the detector, L# is the differential number luminosity as a function of
2
E, the parent neutrino energy, D = 1.7 x 10_cm is the distance to the supernova, td
is the time of the neutrino's decay, v is the neutrino's velocity and _ = E/m,, is the
relativistic factor, r is the neutrino lifetime, t is the time of the photon's arrival at the
detector, # is the cosine of the "lab-frame" decay angle between the parent neutrino's
direction and the photon, and .fi(E, _) is the distribution of angles as a function of
neutrino energy for each of the two helicity possibilities. The Dirac // function enforces
the arrival ellipsoid. In this paper, we will concentrate on the limit of short decay times,
t_ ,-, "rr << D, so the delta function becomes _ (t - t_(1 - v_)).
Changing variables from g to the photon energy k, and integrating over the decay
time td gives
dg = .a., L--_t_e -_''/'''" 2k ./,(E, kl dk dE dt, (2)
4_ D rn_r
where fi(E, k) now gives the distribution of photon energies as a function of parent
neutrino energy:
f(E,k) = { 2k/E2 no flip(E - k)/E 2 flip. (3)
Similar results have been derived for related cases before. 5-r Note that this distribution
is a function only of the combination of neutrino parameters m_r and B,; to break this
degeneracy between m_ and r, we must relax our assumption of short decay times.
We will also assume that the initial neutrino luminosity is given by a zero-
chemical-potential Fermi-Dirac distribution. Normalized to the known temperature and
total energy of the suprenova, this gives
120 ET E 2
L#(E) = 77r4 T) 1 + eg/n" (4)
Finally integrating over this distribution, this gives the photon spectrum as a
function of time,
dN 240 B._ ET 2k e_2kt/_,.hi(k/T_,). (5)
dk dt 7_r4 4rD 2 T2. m,,r
where hi is a separate function for each of the helicity possibilities that is of order unity
for the energies and temperatures of interest.
3. PVO Instrumentation
The Pioneer Venus Orbiter Gamma Burst Detector (OGBD) s was designed to
detect gamma ray bursts--transient, high energy events that last from milliseconds to
tens of seconds. It has four separate bands, 0.1-0.2 MeV, 0.2-0.5 MeV, 0.5-1 MeV, and
1-2 MeV. In the background mode that we will be using, it has a timing resolution of
12 or 16 seconds with full spectral information (i.e., counts in each of the four bands).
Because gamma-ray bursts are singular events, the OGBD was designed to have
full-sky coverage, although it is incapable of independently providing directional infor-
mation about the photons it receives. However, the OBGD detectors do, in fact, face
the South Ecliptic Pole, and thus are ideally suited for measurements of gamma-rays
from the LMC. Thus, even though it was not "pointing" at the'LMC at the time, it
can still be used to analyze data associated with the supernova. Although the response
of the instrument changes for is a function of the gamma-ray direction, the bulk of the
decay photons come from the direction of the supernova itself on the sky (the excep-
tions are the rare photons which reach us after decaying at a very large angle from the
outgoing neutrino).
4. Analysis
After a brief look at the data from the four OGBD channels in Fig. 1, it is clear
that there is no obvious signal of gamma rays over the background (the variation in
the signal is in fact consisitent with pure _ noise). Thus, we will be putting limits
on our free parameters: rnvT and B_.
(2
br}
O
C)
150[-i i i , i i i i i , , --
0.I - 0.2 MeV -
100
5O
0
B
0.2 - 0.5 MeV
i
m
0.5 - 1.0 MeV
- -
0 2000 4000 6000 8000
UT- 27325 [sec]
Fig. 1. Raw counts/sec in each of the four OGBD channels for the time surrounding the
arrival at Venus of the supernova's opticM burst, at time UT - 27325 = 0 sec.
To do this, we utilize the SPANAL code which was developed for analyzing the
instantaneous spectra of gamma-ray bursts. Given the spectrum averaged over 12- or
16-second bins, SPANAL calculates the best fit set of parameters, m,r and B.y, for
the data (thus far, we simulataneously fit the data for up to six time bins, or about
90 seconds after the supernova). In Fig. 2, we show the results for a small area of
parameter space, only analyzing the first time bin after the expected arrival of the
4
supernovagamma-rays.The points are X 2 minima, with X 2 m 22 (with 2 degrees of
freedom) for all of the points. For the point rn_r = 10a keV sec, we show in addition
the 1-a upper limit on B_; it is not very far from the X 2 minimum, so we expect that
the actual upper limits are not far from these points throughout. The area below the
line is roughly excluded; the area above is allowed by the OBGD data. To compare
with previous analyses, Kolb and Turner 2 found a limit in a similar area of parameter
space of B-_ < 2.8 x 10-l° without taking into account the angular distribution of decay
photons (by simply assuming k = E/2).
In order to more fully map the limits of parameter space, we must keep the full
information of the arrival ellipsoid in the delta function of Eq. 1, and compare to longer
signals from the spacecraft. For such long arrival times that this effect matters, however,
the expected number of gamma rays is much lower (since fewer neutrinos would have
decayed before reaching earth), so the limits will be somewhat weaker. Nonetheless,
because of the quality and amount of the PVO data, we expect to strengthen the
current limits on the radiative-decay properties of neutrinos. We are currently pursuing
the analysis in this realm2
10 -1
10 -2
10 -3
I 0 -4
_. 10 -s
10 -6
10 -7
10 4
10 -°
10 z 10 a 104 10 s
m'r [keV sec]
Fig. 2. X 2 minima for the fit of the theoretical spectrum of photons (Eq. 5) to the OGBD
data after the supernova. For m_r = 103 keV sec, we also show the 1-a upper limit.
References
1. E.L. Chupp, W.T. Vestrand and C. Reppin, Phys. Rev. Left. 62 (1989) 505.
2. E.W. Kolb and M.S. Turner, Phys. Rev. Lett. 62 (1989) 509.
3. F. yon Feilitzsch and L. Oberauer, Phys. Left. B200 (1988) 580.
4. J.M. Soares and L. Wolfenstein, Phys. Rev. Lett. 64 (1990) 1310(C).
5. S. Dodleson, J.A. Frieman and M.S. Turner, Phys. Rev. Lett. 68 (1992) 2572.
6. J.M. Soares and L. Wolfenstein, Phys. Rev. D40 (1989) 3666.
7. A. Burrows, D. Klein and R. Gandhi, Phys. Rev. D45 (1992) 3361.
8. R.W. Klebsadel, W.D. Evans, J.P. Glore, R.E. Spalding and F.J. Wymer, IEEE
Trans. Geosci. Rein. Sens. GE-18 (1980) 76.
9. Earlier versions of this document have previously appeared as Jaffe, A., Fenimore,
E. and Turner, M., in Beyond the Standard Model III, Ottawa, Ontario, Canada,
June, 1992; Jaffe, A., in The Fermilab Meeting, C. Albright et al., eds. (1993) 1456.


Limits on Neutrino Radiative Decay from Sn1987a

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server