JEM-EUSO space observatory is planned with a very large exposure factor which will exceed the critical exposure factor required for observing the most of the sources within the propagational horizon of about one hundred Mpc. The main science objective of JEM-EUSO is the source-identifying astronomy in particle channel with extremey-high-energy particles. Quasi-linear tracking of the source objects through galactic magnetic field should become feasible at energy > 10(exp 20) eV for all-sky. The individual GZK profile in high statistics experiments should differ from source to source due to different distance unless Lorentz invariance is somehow limited. hi addition, JEM-EUSO has three exploratory test observations: (i), extremely high energy neutrinos beginning at E > 10(exp 19) eV: neutrinos as being expected to have a slowly increasing cross section in the Standard Model, and in particular, hundreds of times more in the extra-dimension models. (ii). fundamental physics at extreme Super LHC (Large Hadronic Collider) energies with the hierarchical unified energy much below the GUT scale, and (iii). global atmospheric observation, including large-scale and local plasma discharges, night-glow, meteorites, and others.

Takahashi, Yoshiyuki

NASA Technical Reports Server

mazC - a
30TH INTERNATIONAL COSMIC RAY CONFERENCE
ICRCt°
mi rida, Mexico
Science Objectives of the JEM EUSO mission on International Space Station
JEM-EUSO COLLABORATION
yo,shiCcosmic.uah.edu (Yoshiyuki Takahashi, The Univ. of Alabama in Huntsville, USA, and RIKEN, Japan)
Abstract: JEM-EUSO space observatory is planned with a very large exposure factor which will exceed
the critical exposure factor required for observing the most of the sources within the propagational hori-
zon of about one hundred Mpc. The main science objective of JEM-EUSO is the source-identifying ats-
ronomy in particle channel with extremey-high-energy particles. Quasi-linear tracking of the source ob-
jects through galactic magnetic field should become feasible at energy > 1020 eV for all-sky. The indi-
vidual GZK profile in high statistics experiments should differ from source to source due to different
distance unless Lorentz invariance is somehow limited. hi addition, JEM-EUSO has three exploratory test
observations:
(i), extremely high energy neutrinos beginning at E > 10 19 eV: neutrinos as being expected to have a
slowly increasing cross section in the Standard Model, and in particular, hundreds of times more in the
extra-dimension models.
(ii). fundamental physics at extreme Super LHC (Large Hadronic Collider) energies with the hierarchical
unified energy much below the GUT scale, and
(iii). global atmospheric observation, including large-scale and local plasma discharges, night-glow, meteoi-
tes, and others..
1. Introduction
JEM-EUSO (Extreme Universe Space Observato-
ry on Japanese Experiment Module) uses the
whole earth as a detector and can observe ex-
tremely high-energy cosmic ray (EHECR) parti-
cles with energy above 1020eV and other lumi-
nous phenomena in atmosphere. This remote-
sensing instrument orbits the earth every — 90
minutes on board International Space Station
(ISS) at the altitude of — 430km (Figure 1) having
a wide Field-of-View (±30°) camera with two
double sided curved Fresnel lenses, It will record
the track of an EAS with a time resolution of
2.5µs and a spatial resolution of about 0.75 km
(corresponding to 0.1 degrees)..
JEM-EUSO has two possible modes of operations
on board ISS, namely, the nadir and the tilted
modes. The latter mode gives up to 5 times larger
aperture of the former mode and is specifically
considered to observe higher energy regime close
to 1021 eV.
2. Main Science Objective: Extremely
high energy Astronomy in particle
channel
Particles with energy above about 7 x 10 19 eV are
suitable for astronomy in particle channel. They
are not deflected more than several degrees by
galactic magnetic fields and their propagational
horizons do not extend to the whole universe
where there are too many background single-
event sources that would interfere the extraction
of some strong sources. When the statistics above
7x 1019 eV exceeds thousands, the propagational
horizon exceeds the critical value to 'observe all
the sources at least once within a few hundred
Mpc when the Greisen-Zatsepin-Kuzmin (GZK)
cutoff is at work. Hence, JEM-EUSO may initiate
a new astronomy' with these particles (7 x 1019eV
<E< 1021eV). This experiment can
https://ntrs.nasa.gov/search.jsp?R=20090028656 2019-08-30T07:32:14+00:00Z
SHORT TITLE
• possibly identify the particle and energy
sources using the arrival direction, and study
acceleration mechanisms with the observed
events at each multi-event sources
• clarify the trans-GZK intensity profile [1] of
distant sources and make a systematic sur -
vey of nearby sources with distinct pile-up
below 1020 eV for each sources; and
• separate gamma-rays and neutrinos from
nucleons and nuclei, which allows testing of
the top-down models (Super-Heavy-Particle
(SHP) models) that assume long-lived parti-
cles produced in the early era of universe.
The EHECR particles can be traced back to the
astrophysical origin in the measured arrival di -
rection with accuracy better than a few degrees.
AGASA experiments [2] reported small-scale
anisotropy (cluster) and some correlation existed
in the arrival direction of EHECR with
AGNsBlazars. Hi-Res [3] also indicated such a
point-source correlation with AGNs. If they come
from isotropically-distributed point sources in
three-dimensional space, several dozen clusters
would be found with the statistics expected for
JEM-EUSO (Fig.l) [4]. In a global anisotropy
analysis, arrival directions are integrated for
spherical harmonics. Such an analysis should
reveal the source distributions of EHECRs. For
the best analysis, the exposure must be uniform
over all sky. ISS has an inclination of 51.6 degree,
and JEM-EUSO on it can observe both north and
south sky equally and would offer a nearly uni-
form exposure for all sky.
wY`ra	 ,  yd	 ^,^	 -`' x s ® 10" eV<E<101'eV
,a^	 1, ^, ^,	 ^'. 	 •:^	 X701&1'eV<E<101^eV
°-fit	 k 	 ,.^¢.z.„•° $^,.^ 	 ;'	 1 , ^ 16,Aa eV<E<t01s^eV
:. ^^^;. A 
	
^ ^x ^, .. „ ^	
^r	
^ k -.A i0Y&d eV<Eat013^eV
'1,	 ti' ycs t,'^.a ,'	 1101^eV<E
With the EGMF and the GMF
Figure 1. Annisotropy of the bright galaxies [4].
If the EHECRs come from cosmological dis-
tances as those of gamma-ray bursts and active
galactic nuclei or clusters of galaxies [5], these
point sources might indicate global isotropy.
The spectrum region with energy above 1020eV is
also a regime where SHP (m _ 1022 -25 eV/c2) is
speculated to produce EHECRs without accelera-
tion. SHPs are certainly CDM (Cold Dark Matter)
and can be broadly distributed with an enhance-
ment toward the galactic center. It could show
small clumps, too, in the outer halo region where
these clumps would not be destroyed by the
gravitational frictions and tidal effects in the
Galaxy. If EHECR source is such a SHP dark
matter, it could be concentrated in our Milky Way
Galaxy and might show an enhancement in the
direction of Sagittarius, too. If they belong to
galaxy clusters, they may show an enhancement
at nearby clusters such as Virgo, Pisces, Peruses,
and Heracles [6]. On the other hand, topological
defects are expected to extend to the whole uni-
verse and do not bear such local characteristics.
Galactic magnetic field is poorly known due to
the limited data only from Faraday rotation of
polarized radio sources. When the point sources
are seen for events above 10"eV, other member
events of these sources at different energies could
also be identified. If there are changes in apparent
Point-spread-function depending' on energy, the
galactic magnetic field can be measured [7].
Southern sky experiment has some difficulty to
make a comprehensive analysis of the arrival
direction due to the very high galactic magnetic
fields dominated by the galactic center and galac-
tic plane. If one uses lower energy events, for
example, at 4 x 101 9' eV, the deflection by mag-
netic field (— x 5 higher)' is as large as 10 degrees:
and is more than enough to erase possible signa-
tures of any small angle anisotropy.
At very high energies, observations from the
ground have other problems in the energy region
above 5 x 1020eV, even if a large area for obser-
vation becomes possible. An air, shower at such
high energies in dense atmosphere develops quite
differently from the scaled Nishimura-Kamata-
Greisen (NKG) lateral'-spread function [8] due to
the Landau-Pomeranchuk-Migdal (LPM) effect
[9]. The lateral distribution method being used for
energy determination by ground array experi-
ments might cease to be usable for individual
LPM showers due to large fluctuations. JEM-
EUSO is relatively free from these problems of
30TH INTERNATIONAL COSMIC RAY CONFERENCE 2007
the ground-based experiments: in particular, far
more immune from uncertainties of the LPM
effects for longitudinal calorimetry method of the
multi-peaked LPM showers, because it can use a
successive shower analysis. Moreover, many
showers observable from space develop at high
altitudes (above 20km) and at low densities,
whose longitudinal shower developments suffer
much less LPM uncertainties.
3. Exploratory Objectives
JEM-EUSO has several exploratory objectives in
addition to the major science objectives of ex-
tremely high-energy astronomy in particle chan-
nel.
3.1 Constraint of the extra-dimension the-
ory by extreme energy neutrino
Neutrino events can clearly be distinguished by
JEM-EUSO from those of gamma-ray, protons
and nuclei in terms of the shower maximum X,,X:
Neutrino events will be recognized as EAS that
interacted deep in the atmosphere with nearly
horizontal direction (HAS) or as upward-going air
showers (UAS) [10]. UAS is produced by the
decay of a tau-particle emitted by the interaction
in the earth's crust by the interaction of an earth-
skimming or earth-penetrating tau-neutrino.
Neutrino-hadron cross-section data at the highest
accelerator energy was given by the Electron
Positron collider experiments at HERA, Cr N —2
X 10-34CM2 at Nrs=314GeV. According to the
standard QCD predictions and cosmogenic GZK
neutrino flux calculations, JEM-EUSO is predict-
ed to observe 1-10 neutrino events. Extra-
dimensional models [11] predict varieties of
cross-sections. The'-predicted event rate is at least
100 times larger than the Standard QCD rate
(Figure 2), and it is testable by JEM-EUSO.
Cosmogenic neutrinos are expected to be
observed at least for a few events in JEM-EUSO.
If top-down scenario for '' super-GZK particles
(blue and green lines) is the valid case, dozens of
events are expected with the standard QCD cross
section. On the other hand, if JEM-EUSO does
not observe significant neutrino events exceeding
a few events, it would exclude most of the top-
down models, as well as the extra-dimensional
models. By its three-plus-years of operation of the
tiled mode, JEM-EUSO can set an upper-limit of
neutrino flux significantly lower than the Wax-
man-Bahcall limit [12] in the energy range of
1020eV and above (Figure 3).
i67
tog
105 	'
103
102
i0a	 10$	 10i0	 1012
E„ (GeV)
Fig.2 Neutrino cross-sections. Dotted: Standard
QCD. Color lines: extra-dimension prediction for
On =1 (yellow) to 7 (black).
IF
SN W,c	 4ceGu>a
X03
tOz
	 assn-PUSOW,i)
"E
usom^
	
WSUm
w 10 eusatoxea)
w
I [ ;-r	 \
o.,II...I....	 \00e
 ...
17	 18	 19	 20	 21
	
zz	 23
log(E/W
Figure 3 (Preliminary) flux-sensitivity of JEM-
EUSO of l event/energy-decade/year. An obser-
vational efficiency of 25 % is assumed. Red Thick
Line: EUSO (min); Blue Thick Line: JEM-EUSO
Nadir; Green Thick Line: JEM-EUSO-Tilt.
3.2 Super-LHC Physics
SHORT TITLE
The center of mass energy of an extreme energy
particle and a target nucleus interaction in the
atmosphere exceeds the energy reachable by
Large Hadron Collider (LHC) more than three
orders of magnitudes. In this extreme energy
frontier, many new physics that may change
around the trans-GZK energies have been pro
-
posed and seriously discussed. JEM-EUSO can
examine the Lorentz Invariance at very high Lor-
entz factors (y-10 1 1). Special relativity has been
undoubted at lower energies so that the GZK
cutoff is expected to be imminent. In this sense
gamma ray mean free path in vacuum is shorter
than 100 kpc by interactions with CMB unless
strong quantum gravity effect prohibits yy^e+e:'
process; and hence, no gamma ray events are
expected for EHECRs in standard physics. How-
ever, if GZK-process itself would not appear as
expected, it could imply some limitations of local
Lorentz Invariance in the presence of external
fields. These EHECRs offer a high-precision
experimental testing of the theory of relativity
and quantum gravity.
The standard quantum physics also predicts that
EAS should suffer a large fluctuation of cascade
development because
	 of the
	 Landau-
Pomeranchuk-Migdal (LPM) effect. It will be-
come considerable above 5x1020 eV for protons
and above 5xl021eV from iron nuclei. JEM-
EUSO can observe this fluctuation.
3.3. Global Earth Observation
JEM-EUSO is also expected to observe atmos-
pheric luminous phenomena such as lightning,
nightglow, and meteors. In the upper atmosphere
of the thunderstorm, many luminous transient
events have been observed, such as, sprite, blue
jet, and elves. These are believed to be a secon-
dary discharge caused by the electric field from
the redistribution of electric charge of the light-
ning. 'Gamma rays were also observed associated
with lightning [13]. These are explained by
streamer discharge [14]. If this is the case,
streamer formation must be preceded by the main
discharge. Furthermore, some satellites detected
several gamma-ray bursts probably associated
with lightning from the earth [15]. Such runaway
electrons produced by cosmic-rays might be ac-
celerated by the quasi-static electric field of the
discharge associated with lightning. JEM-EUSO
would keep monitoring both EHECR tracks and
runaway phenomena to see whether there is any
recognizable relationship. Other exotic atmos-
pheric phenomena . such as surface-glow of the
earth are also included in the mission studies.
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