The result of a new calculation of the atmospheric muon and neutrino fluxes and the energy spectrum of muon-neutrinos produced in individual extensive air showers (EAS) initiated by proton and gamma-ray primaries is reported. Also explained is the possibility of detecting atmospheric nu sub mu's due to gamma-rays from these sources

Edwards, P. G.

Protheroe, R. J.

English

NASA Technical Reports Server

318
HE 6.2-18
MUONAND NEUTRINO FLUXES
P.G. Edwards and R.J. Protheroe
DePartment of Physics, University of Adelaide
Adelaide, South Australia 5001
_bst_act. We report the result of a new calculation of the
atmospheric muon and neutrino fluxes and the energy spectrum of
muon-neutrlnos produced in individual extensive air showers (EAS)
initiated by proton and _-ray primaries. We also examine the
possibility of detecting atmospheric v_'s due to y-rays from
sour c es.
1. IHTRObUCTIOH. Interactions of ~1 eeV neutri_Io_ can mimic nucleon decay
events and it is therefore important to know the atmospheric neutrino flux
in order to calculate the expected rate of background events in nucleon
decay experiments. With the development of large nucleon decay detectors
this topic has received much interest over the past few years (Baisser et
al., 1983a,b; Dar 1983). These large detectors can also be used for other
purposes, however. Their large masses make them good neutrino detectors
allowing searches for neutrinos from bright extra-terrestrial sources.
Here again an accurate knowledge of the atmospheric neutrino background due
to cosmic rays is important.
The detection of UHE _-rays from Cygnus X-_ {Samorski and Stamm,
1983; Lloyd-Evans et al., 1983), Vela X-I (Protheroe ef al., 1984) and
LMC X-4 (Protheroe and Clay, 1985) has added further impetus to the
neutrino observations as it is usually considered that a neutrino signal
would almost certainly suggest a nO-decay origin for the _-rays. Gaisser
and Stanev (1985a,b) have recently calculated the expected v_ flux and
light curve for Cygnus X-3 on this basis together with the response of deep
detectors to extraterrestrial neutrinos.
l_re, we report the results of a new calculation of the sea level
atmospheric muon and neutrino fluxes. We have also calculated the energy
spectrum of v_'s in individual EAS initiated by primary protons and _-rays
to te_t whether atmospheric neutrinos from Y-ray initiated EAS could be
detected with existing detectors.
2. THE C_LCUL_TIOH. The simulation procedure was identical to that used
in our earlier work (Edwards et al., 1985) and consisted of numerical
solution of the following coupled equations (see e.g. Gaisser et aI.,
1978):
aN_ (E,x) 1 (dh/dx) a
= - N_ (E,x)[..... . ........ ] + --[N_(E,x) (dE/dx)_]
ax x_(E) (cE/m_)_ aE ,
FjI(E,E') Nj(E',x)
+ _ J [......... ]dE', (I)
d t E xj(E')
where N_ is the energy distribution of particles of type i at depth x; x_
is the mean interaction length, m_ is the res_ mass, _ is the mean decay
time, and (dE/d_)_ is the mean ionization energy loss rate of particles of
https://ntrs.nasa.gov/search.jsp?R=19850027841 2020-03-20T17:09:57+00:00Z
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HE 6.2-18
103 , _ ,_.,,,,| _ , , =_.
type i; and _ 103 f,,,(, ,_((HJi ii
• (_SBL V EP
Fij(E,E' )dE/E • _ _ _ _F "
probability of a'_ _ --- o
r.
partlcle of type_E 102 ._ 102
j and energy E' > " i_ 7_ \_,_producing a °o _G
particle of type - --40" - --;_10_
i and energy E -_ _0"
to E+dE per __ 1°I
interaction. _ iThe particles _ O:-----x_ x
considered in ' _:_ _. 10d
the simulation "_were; nucl eonst 100 . F-
charged piofls, =
charged and 1°° 1°1_., l°Z ,_ lO1 _"
neutral kaons, ENERGY: E_(GeV) o
moons and both ri.. :. s.. =...I .t_.ph._'_cn*.t_i.ofl._ =t :, ,,,t , ,, .....t_
nuon and _, 40 ° and 60° to the zenith. I I f
el ectron 10° 101
neutrinos (by ENERGYE_)(GeV)
"neutrinos" we Fig. 2. Vertical neutrino flux from present work
(EP) compared with the predictions of Volkova
include ,lSe0) (v) and eaisser ¢¢ aI. (1983a,b) (GSBL).
ant i-newt rinos).
The model of inclusive particle production in proton-air nucleus
interactions used in the simulations is that described by Gaisser,
Protheroe and Stanev (1983). The nucleon-air nucleus interaction length
used was that given by Ellsworth et al. (1982). The Non and kaon-air
nucleus interaction lengths were suitably scaled from this (Hillas, 1979).
The primary cosmic ray nucleon flux used _
was based on the results of satellite and
balloon-borne detectors (Simpson et a]. 1983; _-10 _ "
Ryan et al. 1972; Gregory et _I. 1981; Simon et '>=
al. 1980; Juliusson et aZ. 1983; Sood 1983) and T_.10
the superposition model, r_
3. RESULTS. First we present our results on ,_=L101
the flux of atmospheric muons and neutrinos. _=L
The calculated sea level neutrino flux is shown
- in Fig. 1 for a number of zenith angles and is x 10_-
seen to increase with increasing zenith angle "_ "
(i.e. atmospheric thickness). We have compared z I_3
our calculated neutrino fluxes with previous _=
results. Fig. 2 shows the good agreement found _ I_
with the vertical flux calculated by eaisser et ,-_
al. (1983a,b) and V lkova (19B0). The results
of Tam and Young (1969) (not plotted) are _> I05 oMITSU,_.L(_983)
similarly in agreement. --P_S_,T_OR_
The vertical _uon flux we calculate is I_ • _
plotted in Fig. 3 where it is compared with the I0° _01 I0z i0_
experimetal results obtained by Mitsui et aI. MOONENERGYE_(GeV]
(1983) and Allkofer et aI. (1971) and found to n,.3. Calculatedv rticalmoon fl..... pared
with recent observations.
320
HE 6, 2-18
-I I' = ' i i I i' I"
be in good agreement. IWe turn now to neutrinos -2 ))H*_I _
produced in individual cosmic ray
and Y-ray initiated EAS. In Fig. 4 __ -3 PROTONS
we show the differential energy
spectra of v.s produced In
individual EAS divided by the _
primary energy. Over the I0TM - _ .x
10TM eV primary energy range, the _o -6 4_
v_ spectrum in Y-ray initiated F-AS _'_ 3
is ~lO to 100 times lower than in _-7
proton initiated F_AS. Also, the _-RAYS
_8 5 \
number of neutrinos divided by
primary energy decreases with -_ 6
increasing primary energy in cosmic 7
ray EAS but is approximately -10 ' ' ' , , i
independent of primary energy for 0 I z 3 _ 5 _ "/
_-ray initiated EAS. This l°g10(E/SeV)'
behaviour is similar to that of Fig.4. Differentialenergyspectrumof muon
muons in cosmic ray and y-ray neutrinosin protonand Y-rayinitiatedEAS
dividedby primaryenergy,F.=. (Numbers&reached
initiated EAS (Edwards etal., to the curvesare _Og_o[E=IEeV]).
1985). -3 , _ _ _ I
4. OISCUSSIOH. Recently 6atsser __, ._ CYGNUS.X-3
and Stanev (1985a) have calculated
the expected v_ flux and llght -5
curve of Cygnus X-3 assuming it is -
due to protons produced near the _ -6 \ _
neutron star interacting in the _
atmosphere of its companion to
produce a mini-EAS in in the star's _ -8
atmosphere. Cocconi (1985) has ""
also suggested that LMC X-4, being _-_-9
a bright Southern UHE _'-raysource, ._ .
would be a good neutrino source _-I°F \ li
candidate for study by Northern _-11 \observers. - , ,_
It is possible (although we \
consider it unlikely) that the -IZ \
Y-rays from Cygnus X-3 are due to -_ , , , ,\ ,
interactions of electrons 0 1 2 3 _ 5 6
accelerated to extremely high [0g_0(E_/SeVl .
energies. If this were the case, Fig. 5. Expected flux of atmospheric v_s due to
we would expect no neutrinos from _°rays from Cygnus X-3 (dot-dash 11ne) compared
with the flux expected directly from the source
the source. Observation of (solid and dashed lines) under two different
neutrinos from Cygnus X-3 assumgtio,s(aaisserandStanev, 1985a).
would then indicate that the y-rays were almost certainly due to
interactions of high energy protons. Atmospheric neut¢inos due to f-rays
from Cygnus X-3 might also be detectable, however. If this was so, then
such a conclusion would be invalid although it may be possible to
distinguish the two origins through the light curve= which would be
different in each case. Here, we calculate the differential v_ flux due
to Y-rays from Cygnu= X-3 by convolving the vs. spectra in Y-ray initiated
321
HE 6.2-18
EAS of Fig. 4 with the N-ray spectrum of the source:
N(E) = 4.5xlO-4(E/GeV) -= (photons m-= s-_ GeV-:). (2)
This is based on the integral flux reported by Lloyd-Evans et al. (1983).
The result is shown in Fig. 5 where it is compared with the expected v_
flux due directly to the source as calculated by Gaisser and Stanev under
two different assumptions. At 1TeV the atmospheric v_ flux is ~10=
lower than that due directly to the source and would be considerably below
current detector sensitivities (Stenger 1985).
5. CONCLUSIONS. Our calculated atmospheric muon flux is in good agreement
with observations. The calculated neutrino flux is in agreement with other
recent predictions. We support the view that a neutrino observation of a
UHE _-ray source would be strong evidence that the UHE N-rays and neutrinos
result from high energy interactions of protons or nuclei.
_ck,owIedgme, ts. P.G.E. is in receipt of a Commonwealth Postgraduate
Research Award. This research has been supported by the provision of a
Queen Elizabeth II Fellowship a grant from the A.R.G.S. to R.J.P.
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Muon and neutrino fluxes

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