JEM-EUSO is a science mission to explore extremes of the Universe. It observes the dark-side of the Earth and detects UV photons emitted from the extensive air shower caused by an extreme energy particle (about 10(exp 20) eV). Such a particle arrives almost straightly through our Milky Way Galaxy and is expected to allow us to trace the source location by its arrival direction. This will open the door to the new astronomy with charged particles. In its five years operation including the tilted mode, JEM-EUSO will detect at least 1,000 events with E>7 X 10(exp 19) eV and determine the energy spectrum of trans-GZK region with a statistical accuracy of several percent. JEM-EUSO is planned to be transported with HTV (H2 Transfer Vehicle) and attached to the Japanese Experiment Module/ Exposure Facility (JEM/EF) of International Space Station. JAXA has selected JEM-EUSO for one of the mission candidates of the second phase utilization of JEM/EF for the launch of early 2010s. One year-long phase-A study will be carried out under JAXA

Adams, J.H.

Christl, M.J.

Watts, J.W.

NASA Technical Reports Server

rAuthors:	 J. Collaboration
Title:	 The JEM-EUSO Mission
Publication:	 Proceedings of the International Cosmic Ray Conference 2007; Merida, Mexico; July 3 -
11, 2007
Refereed:	 No
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Type:	 Conference Proceedings
Organization:	 VP62
Abstract:
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	 5/30/2007
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30TH INTERNATIONAL COSMIC RAY CONFERENCE
ICDCN7
Merida,M6dco
The JEM-EUSO Mission
JEM-EUSO COLLABORATION
ebisu@postman.riken.jp
Abstract: JEM-EUSO is a science mission to explore extremes of the Universe. It observes the
dark-side of the Earth and detects UV photons emitted from the extensive air shower caused by an ex-
treme energy particle (about 10 20 eV). Such a particle arrives almost straightly through our Milky
Way Galaxy and is expected to allow us to trace the source location by its arrival direction. This will
open the door to the new astronomy with charged particles. In its five years operation including the
tilted mode, JEM-EUSO will detect at least 1,000 events with E>7 X 10 19 eV and determine the en-
ergy spectrum of trans-GZK region with a statistical accuracy of several percent. JEM-EUSO is
planned to be transported with HTV (H2 Transfer Vehicle) and attached to the Japanese Experiment
Module/ Exposure Facility (JEM/EF) of International Space Station. JAXA has selected JEM-EUSO
for one of the mission candidates of the second phase utilization of JEM/EF for the launch of early
2010s. One year-long phase-A study will be carried out under JAXA.
1. Mission Overview
JEM-EUSO (Extreme Universe Space Observa-
tory on Japanese Experiment Module) is anew
type of observatory that uses the whole earth as a
detector including the International Space Station
(ISS) where a remote sensor is located. It ob-
serves transient luminous phenomena taking
place in the earth's atmosphere caused by parti-
cles and waves coming from space. The sensor is
a super wide-field telescope that detects extreme
energy particles with energy above 10 20eV. This
remote-sensing instrument orbits the earth every
— 90 minutes on board International Space Station
(ISS) at the altitude of — 430 km (Figure 1). An
extreme energy particle collides with a nucleus in
the earth's atmosphere and produces an Extensive
Air Shower (EAS) that consists of numerous
electrons, positrons, and photons. JEM-EUSO
captures the moving track of the fluorescent UV
photons and reproduces the development of EAS.
The JEM-EUSO telescope has a super-wide
Field-of-View (±30°) with two double sided
curved Fresnel lenses and records 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). These time-segmented images allow
determining the energies and directions of the
particles.
Figure 1 JEM-EUSO telescope
JEM-EUSO instrument can reconstruct the in-
coming direction of the extreme energy particles
with accuracy better than several degrees. Its
observational aperture of the ground area is a
circle with 250 km radius and its atmospheric
volume above it with a 60-degree field-of-view is
about 1 tera-ton or more. The target volume for
upward neutrino ,events exceeds 10 tera-tons. The
instantaneous aperture of JEM-EUSO is larger
than the Pierre Auger Observatory by a factor of
Figure 2 Observational Aperture of JEM-EUSO
Vertical Mode
	 Tilted Mode
Figure 3 JEM-EUSO attached to ISS
2. Science Objectives
SHORT TITLE
systematic survey of nearby sources;
and
• separate gamma rays and neutrinos
from nucleons and nuclei, which al-
lows testing of the Super-Heavy-
Particle (SHP) . models that assume
long-lived particles produced in the
early era of the universe.
• The extreme energy particles can be
traced back to the origin in the
measured arrival direction with accu-
racy better than a few degrees.
AGASA experiments [3] reported
small-scale anisotropy (cluster) and
some correlation existed in the arri-
val direction of extreme energy par-
ticles with AGNs/Blazars. Hi-Res [4]
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. Nearby point sources
can bear several dozens of events.
2.1. Main Objective: Straight Line Astron-
omy by Particle Chanel at Energy >1020eV
JEM-EUSO is designed to detect more than 1,000
events with energy higher than 7x 10 19eV in a
few years of operation. This number of events
exceeds the critical value to observe all the
sources at least once within several hundred Mpc
even when the'Greisen-Zatsepin-Kuz'min (GZK)
cutoff [1] is at work. Hence, JEM-EUSO may
initiate a new astronomy with these charged parti-
cles (10 19eV<E<1021 eV). This experiment can
• possibly identify the particle and en-
ergy sources using the arrival direc-
tion, and study acceleration mecha-
nisms with the observed events;
• clarify the 'trans-GZK intensity pro-
file [2] of distant sources and make a
Figure 4 Arrival direction expected from JEM-
EUSO
In a global anisotropy analysis, arrival directions
are integrated for spherical harmonics. Such an
analysis should reveal the source distributions of
Extreme energy particles. 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 uniform expo-
sure for all sky. If the extreme energy particles
come from cosmological distances as those of
30TH INTERNATIONAL COSMIC RAY CONFERENCE 2007
gamma-ray bursts and active galactic nuclei,
these point sources might indicate global isotropy.
Decays or annihilation of a super-heavy particle
(SHP; in 1022-2s eV/c) can also produce ex-
treme energy particles. If extreme energy particle
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 Sagitta-
rius, too. If they belong to clusters of galaxies,
they may show the enhancement at nearby clus-
ters [5].
When the point sources are seen for events above
1020eV, other member events of these sources at
different energies could also be identified.
Changes in apparent point-spread-function de-
pending on energy, magnitude and direction, and
they can help determining the galactic magnetic
field [6].
2.2. Exploratory Objectives
2.2.1. Detection of extreme energy neutrino
can constrain the extra-dimension theory
Cosmogenic neutrinos may steadily be produced
in universe in the GZK process in which an ex-
treme energy proton looses its energy through the
collisions with 2.7K microwave backgrounds.
Many authors already pointed out the possibility
that they are also produced during acceleration at
high-energy objects such as AGNs or gamma-ray
bursts.
Neutrino-hadron cross-section data at the highest
accelerator energy was given by the Electron
Positron collider experiments at HERA at the
center of mass energy of 314 Gev, which corre-
sponds to 52 TeV of such fixed target collision as
that of cosmic-ray experiments. According to the
standard QCD predictions and cosmogenic GZK
neutrino flux calculations, JEM-EUSO is pre-
dicted to observe 1-10 neutrino events [7]. Extra-
dimensional models [8] predict varieties of cross-
sections. The predicted event rate is at least 100
times larger than the Standard QCD rate, and it is
testable by JEM-EUSO.
103
102
m
w 10
w
1
0.1
17	 18	 19	 20	 21	 22	 23
log(E/eV)
Figure 4 The flux-sensitivity of JEM-EUSO of 1
event/energy-decade/year •, an observational effi-
ciency of 25% is assumed. Red Thick Line: ESA-
EUSO (min); Blue Thick Line: JEM-EUSO Na-
dir; Green Thick Line: JEM-EUSO-Tilt. As for
Ice cube (Pink line), a few events/energy-
decade/10years is assumed. Black Line denotes
the Waxman-Bahcall limit.
Neutrino events can clearly be distinguished by
JEM-EUSO from those of gamma-ray, protons
and nuclei in terms of the shower maximum X,,,.
[9]•
By its three-years of operation of the tiled mode,
JEM-EUSO can set an upper-limit of neutrino
flux significantly lower than the Waxman-Bahcall
limit [10] in the energy range of 10 20eV and
above. 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, at least
several events are expected in a year. 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.
2.2.2. Super-LHC Physics
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-
SHORT TITLE
posed and seriously discussed. For example,
JEM-EUSO can examine the Lorentz Invariance
at very high Lorentz factors (y-10 11 ). If GZK-
process itself would not appear as expected [11],
it could imply some limitations of local Lorentz
Invariance in the presence of external fields. The
standard quantum physics also predicts that EAS
suffers large fluctuations of cascading from Lan-
dau-Pomeranchuk-Migdal (LPM) effect [12]. It
becomes considerable from 5x10 20 eV for protons
and from 5x10 21 eV from iron nuclei. JEM-EUSO
can observe this fluctuation with a high statistics.
2.2.3. Global Earth Observation
JEM-EUSO will also observe atmospheric lumi-
nous 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 secondary dis-
charge caused by the electric field from the redis-
tribution of electric charge of the lightning [14].
Gamma rays were also observed associated with
lightning [15]. Runaway electrons produced by
cosmic-rays might be accelerated by the quasi-
static electric field of the discharge associated
with lightning.
3. Conclusions
JAXA has selected JEM-EUSO for one of the
mission candidates of the second phase utilization,
of JEM/EF for the launch of early 2010s. One
year-long phase-A study will be carried out under
JAXA. Its expected versatile performances on
orbit for several years to a decade will be helpful
in observing extremely high energy universe and
exploring fundamental physics beyond the LHC
energies
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