Transcript Borexino Trigger System

EUSO
The Extreme Universe Space
Observatory
Marco Pallavicini
INFN Genova, Italy
Talk Overview
 Scientific case and Science Goals
 The observational approach
 The detector on the ISS
 The detector optics
 Detector expected performances
Nestor Insitute, Pilos, Jun. 05-10, 2002
M. Pallavicini - INFN Genova
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Euso
An Innovative Space Mission
doing astronomy
by looking downward from the Space Station
at the Earth Atmosphere
 Euso is devoted to the exploration from space of the highest energy
processes present and accessible in the Universe:
The extreme energy cosmic rays ( E > 4 1019 eV)
 They are directly related to the extreme boundaries of the physical
world.
Nestor Insitute, Pilos, Jun. 05-10, 2002
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Scientific motivations
 Why should we study the Extreme Energy Cosmic Radiation (EECR)

From the Astroparticle Physics point of view, the EECRs have energies only a few decades
below the Grand Unification Energy (1024 - 1025 eV), although still rather far from the
Planck Mass of 1028 eV.

If protons, they show the highest Lorentz factor observed in nature (g ~ 1011).

What is the maximum Cosmic Ray energy, if there is any limit?

There is no compelling evidence for identification of EECR sources with objects known in
any astronomical channel.

They may be a unique probe for Grand Unification theories and cosmological models

Neutrino astronomy from the deep space (no GZK cut off)
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Today’s knowledge: spectrum
ICRC2001
•Energy spectrum decreases like ~ E-3
•The spectrum extends above 1020 eV
•At these extreme energies, flux is of the
•order of Km-2 century-1
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•Present data is interesting and challenging
•Not consistent fluxes among measurements
•GKZ cut off ?
•Energy scales ?
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Today’s knowledge: Direction
Arrival direction of 59 events
with energies above 4 1019 eV
observed by AGASA
No large scale anisotropy
Indication of point like sources
(1 triplet, 6 doublets, Prob. 0.07%)
Triplet in the direction of interacting
galaxy VV141
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Today’s knowledge: Direction (II)
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Experimental problem ?
 HiRes and AGASA measurements are barely compatible. Is there a problem ?
The number of events detected by AGASA above 1020 eV is quite larger than that
detected by HiRES (10 events vs 2 events) for equivalent exposure.
 The position of the “ankle” in the Cosmic Ray spectrum for AGASA is at energies a
factor 2–3 larger than the one shown by HiRES ( 1019 eV vs 3x1018 eV).

GZK: Is this a measurement of
the effect or discovery of its non
existence (AGASA, 2.6 s)?
AGASA is almost complete
HiRES will go on for 5 years
Nestor Insitute, Pilos, Jun. 05-10, 2002
M. Pallavicini - INFN Genova
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Today’s ignorance
 How the cosmic rays reach such huge energies ?

Acceleration mechanisms ?
 Decay from super-heavy relic particles ?
 What are they ?

Protons ?
 Nuclei ?
 Neutrinos ?
 If accelerated, from where ?


Galactic sources?
Extragalactic? Why GZK is not there (if AGASA is right) ?
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Top-Down and Bottom-Up scenarios
Bottom - up
“Bottom-up”: with acceleration in rapidly evolving processes
occurring in Astrophysical Objects with an extreme case in this
class being represented by the Gamma Ray Bursts (GRBs). The
observation of “direction of arrival and time coincidences”
between the optical-radio transient and Extreme Energy Neutrinos
could provide a crucial identification of the EECR sources.
“Top-down”: processes with the cascading of ultrahigh
energy particles from the decay of Topological Defects;
these are predicted to be the fossil remnants of the Grand
Unification phase in the vacuum of space. They go by
designations, such as cosmic strings, monopoles, walls,
necklaces and textures. Inside a topological defect the
vestiges of the early Universe may be preserved to the
present day.
Nestor Insitute, Pilos, Jun. 05-10, 2002
M. Pallavicini - INFN Genova
Top - down
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Bottom-Up: Cosmic accelerators
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Euso Scientific goals
 Extension of the measurament of the energy spectrum of the Cosmic
Radiation beyond the GZK conventional limit (EGZK  5 x 1019 eV).


How does the Cosmic Ray spectrum continues beyond the existing data?
Is there a maximum energy (Emax) ?
 All sky survey of the arrival direction of EECRs.

Point sources? We want to identify their optical counter-part.
 Observation of a possible flux of High Energy Cosmic Neutrinos.

Neutrinos can arrive from very distant sources!
 Systematic sounding of the Atmosphere with respect to cloud
distribution and UV light absorption/emission characteristics.

Investigation of Atmospheric Phenomena such as Meteors and Electrical
Discharges.
Nestor Insitute, Pilos, Jun. 05-10, 2002
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The Euso experiment
 Experiments carried out by means of ground-based observatories,
Auger (hybrid) and HiRes – Telescope Array (fluorescence), are
limited by practical difficulties connected to the relatively small
collecting area (up to 3000 Km2!!) still marginal for the extremely low
flux involved (order of 1 particle/100 Km2/sr/year for a Primary of 1020
eV).
To overcome these difficulties, an adequate solution is
provided by observing the atmosphere UV induced
fluorescence from space which allows to exploit up to
millions Km2 /sr
Nestor Insitute, Pilos, Jun. 05-10, 2002
M. Pallavicini - INFN Genova
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Euso observational approach
Columbus
Nitrogen Spectrum
Photons per m
Euso EUSO
Area vs Auger
Pierre-Auger
EUSO
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Geometry
EUSO Geometry
EUSO on ISS
Detector distance
380 km
Total field of view
60°
30°
380
km
Geometrical factor
5  105 km2sr
Target air mass
2  1012 tons
Pixel size
(.8  .8) km2
Nestor Insitute, Pilos, Jun. 05-10, 2002
230 km
Earth surface
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The instrument
Monocular and Compact
System electronics
Focal surface
support structure
Focal surface
Iris
Fresnel lens
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Euso parameters
Field of View
± 30° around Nadir
Lens Diameter
2.5 m
Entrance Pupil Diameter
 2.0 m
F/#
< 1.25
Operating wavelengths
300-400 nm
Angular resolution (for event direction of
arrival)
~ 1°
Pixel diameter (and spot size)
~ 5 mm
Pixel size on ground
~0.8 x 0.8 km2
Number of pixels
~ 2.5 x 105
Track time sampling (Gate Time Unit)
833 ns (prog.)
Operational Lifetime
3 years
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Optics: Fresnel lenses
1.5 Fresnel lens prototype
Possible materials
Property
ZEONEX
TPX
CYTOP
PMMA
Refractive index
1.525
1.463
1.346
1.49
Abbe’s number
56
90
55
Transmittance
(400 nm) 3 mm
92%
92 ~ 93%
92%
86%
Linear expansion
coefficient /C
6.0E-5
1.17E-4
7.4E-5
8.0E-5
Water absorption
rate (%) 60C
<0.01
<0.01
<0.01
0.3
Density g/cm3
1.01
0.833
2.03
1.20
Tensile strength
kg/cm2
600
>235 (at
yield)
400
490~77
0
Nestor Insitute, Pilos, Jun. 05-10, 2002
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Requirements
Total weight < 200 Kg
Small chromatic aberration
Space environment
Small F/# < 1.25
Small point-spread function
Mechanical strength for launch
±30° field of view
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Optics: structure
16:16:09
• Mass of each Lens
• 20 mm PMMA 125 kg
• 20 mm TPX 90 kg
• 20 mm CYTOP 215 kg
• 20 mm Zenoex 105 kg
• 3 support rings, 24 ribs/lens,
•
20%Contingency 90 kg
•
• Mass of Optical Structure
• Graphite Fiber Re-enforced
735.29
f/1.25, 7mm pixel, 2.8m EPD, Dmax < 3.75 Scale:
Polymer
•12 metering struts with 11 cross
braces, 20% Contingency 60 kg
10 mm
0.03
DJL
MM
struts and
cross braces
06-Jan-00
rings
15 mm
6 mm
10 mm
50 mm
Ring and Rib Detail
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20 mm
Strut Detail
ribs
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Optics: performance
UV Filter
De-focussing
Acceptance
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Focal surface design
 Sensitivity to single photons in the wave length region between 300
nm and 400 nm
 Fast response (  10 ns ), to be able count single photons and
reconstruct the EAS direction from a single observation point by using
photons time distribution
Each pixel must see roughly 1 Km2 at ground level
 1 Km  3 ms; at 1021 eV you expect up to about 100 photons per ms on a
single pixel
 The system must be able to count photons at ( peak, max ) 100 MHz in a
continuous background of about 1 MHz per pixel (from night glow 3 1011
photons m-2 s-1 sr-1)

 A few mm2 spatial resolution on the focal plane


Optics point spread function size is a few mm2.
We do not want to be worse than that.
Nestor Insitute, Pilos, Jun. 05-10, 2002
M. Pallavicini - INFN Genova
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Focal surface
“Macrocell”
Focal surface is not a plane
The FS is logically divided into
macrocells
Detailed structure is under study
Trade off among efficiency, weight,
feasibility, mechanichal stability
Light Guide
or Lens
Hamamatsu
R7600-M64
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Photodetectors
Hamamatsu
R7600-03-M64
Possible option:
Weakly focused R8520
Pmts will be arranged in
“microcells”, i.e. units of
4 pmts hold by a single
PCB
Better uniformity
Need additional RD
5x5 maybe
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Optical adaptors (I): Lens
Problem: Hamamatsu R7600-M64 has a large dead area
Option 1: Lens
Features
Good collection
efficiency and angular
acceptance
Drawbacks
Weight
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Optical adaptors (II): Light guides
2.8cm
UV filter
2cm
2.57cm
Entrance Surface of
Light Guide
7mm
0.3m
m
4mm•
Surface of
R7600-M16
2cm
Light
Guide
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2.57cm
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Optical adaptors: comparison
COLLECTION EFFICIENCY
1.1
1.0
0.9
refracting light pipe
0.8
0.7
0.6
refletting light pipe
0.5
0.4
0
10
20
30
40
50
max (deg.)
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PIXEL
From
other
pixels
MACROCELL
DIGITAL
ELECTRONICS
LEVEL
Compare
From
other
pixels
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SYSTEM
TRIGGER
RING
MEMORIES
X&Y
X
+ PH_CNT
Y
Y
X
Compare
A
K
Enable
Analog
Threshold
EUSO
CONTROL &
DATA
HANDLING
UNIT LEVEL
From
other
MCs
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SAVE_FRAME
Incoming UV
photon
Electronics
The natural detector
 The atmosphere is required to produce a shower.

Two source of signal for Euso:
 Fluorescence
 Cerenkov

The amount of light is proportional to the energy of the primary particle
 The shape of the shower and the depth of its maximum gives information
about primary particle type
 Both signal intensity and shape are affected by atmospheric conditions





Rayleigh scattering
Aerosol (Mie scattering)
Ozone
Water vapor and cloud reflection and absorption
Ground albedo
Euso needs night-time monitoring of these variables
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Background
Background is mostly due to:
Nightglow (~400 m-1 s-1 sr-1 over sea)
Man made
Atmospheric phenomena
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Event reconstruction
Y
p
r
o
je
ct
io
n
TU
X projection
to receiver
1  x 
  tan  
 y 
2
2



x


y
1
  2 tan 

 ct 
Nestor Insitute, Pilos, Jun. 05-10, 2002
CR
T
U
A

C
B
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Expected Performances
Events in 1 year
Free flyer; <h>=500 km
lens o =3.5 m
1000
100
10
GZK spectral structure
Expected Events / Year
Proton vs neutrino separation
Neutrinos
Protons & Nuclei
ISS; <h>=380 km
lens o =2.5 m
1020
1021
Energy (eV)
Angular
resolution vs energy
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Schedule (a sort of)
Phase A (preliminary study): 2002-2003
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Phase B (project):
2003-2004
Phase C-D (construction):
2005-2008
Phase E (operation):
2009 ?
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Conclusion
 The study of EECR may lead to important discoveries in fundamental
physics and astrophysics
 EUSO is an innovative mission that will collect thousands of events
above 1020 eV
 The phase A has been approved by ESA and financial support has been
provided by INFN and other institutions
 Launch is foreseen in this decade
Nestor Insitute, Pilos, Jun. 05-10, 2002
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