EUSO The E xtreme U niverse S pace O bservatory

EUSOThe Extreme Universe Space

Observatory

Marco PallaviciniINFN Genova, Italy

Nestor Insitute, Pilos, Jun. 05-10, 2002 M. Pallavicini - INFN Genova 2

Talk Overview

Scientific case and Science Goals

The observational approach

The detector on the ISS

The detector optics

Detector expected performances


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.


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 ( ~ 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)


Today’s knowledge: spectrum

•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

ICRC2001

•Present data is interesting and challenging•Not consistent fluxes among measurements•GKZ cut off ? •Energy scales ?


Today’s knowledge: Direction

Arrival direction of 59 events with energies above 4 1019 eV

observed by AGASA

No large scale anisotropyIndication of point like sources(1 triplet, 6 doublets, Prob. 0.07%)Triplet in the direction of interacting galaxy VV141


Today’s knowledge: Direction (II)


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 )?

AGASA is almost completeHiRES will go on for 5 years


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) ?


Top-Down and Bottom-Up scenarios

Bottom - upBottom - 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.

Top - downTop - down


Bottom-Up: Cosmic accelerators


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.


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


Euso observational approach

Nitrogen SpectrumPhotons per m

EUSO

Columbus

Euso Area vs Auger

EUSO

Pierre-Auger


Geometry

30°

EUSO on ISS

230 km

380

km

Earth surface

EUSO Geometry

Detector distance 380 km380 km

Total field of view 60°60°

Geometrical factor 5 5 10 1055 km km22srsr

Target air mass2 2 10 101212 tons tons

Pixel size(.8 (.8 .8) km .8) km22


The instrument

Fresnel lens Iris

Focal surface

Focal surface

support structure

System electronics

Monocular and Compact


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


Optics: Fresnel lenses

1.5 Fresnel lens prototype

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 (%) 60C

<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)

400 490~770

Total weight < 200 KgSmall chromatic aberrationSpace environmentSmall F/# < 1.25Small point-spread functionMechanical strength for launch±30° field of view

Requirements

Possible materials


Optics: structure16:16:09

f/1.25, 7mm pixel, 2.8m EPD, Dmax < 3.75 Scale: 0.03 DJL 06-Jan-00

735.29 MM

• 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 Polymer•12 metering struts with 11 cross braces, 20% Contingency 60 kg

•

6 mm

10 mm

50 mm

10 mm

20 mm

15 mm

Ring and Rib Detail Strut Detail

rings

ribs

struts and cross braces


Optics: performance

De-focussing

Acceptance

UV Filter


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.


Focal surface

Hamamatsu R7600-M64

Light Guide or Lens

Focal surface is not a planeThe FS is logically divided into macrocellsDetailed structure is under studyTrade off among efficiency, weight, feasibility, mechanichal stability

“Macrocell”


Photodetectors

Hamamatsu R7600-03-M64

Pmts will be arranged in “microcells”, i.e. units of 4 pmts hold by a single PCB

Possible option:Weakly focused R8520

Better uniformityNeed additional RD5x5 maybe


Optical adaptors (I): Lens

Problem: Hamamatsu R7600-M64 has a large dead area

Option 1: Lens

FeaturesGood collection efficiency and angular acceptance

DrawbacksWeight


Optical adaptors (II): Light guides

2.8cmUV filter

LightGuide

2cm

2.57cm

2cm

Entrance Surface of Light Guide

Surface of R7600-M16

7mm

4mm

2.57cm

0.3m

m


Optical adaptors: comparison


Electronics

MC

_TR

IGG

ER

From

other MCs

SYSTEM TRIGGER

SA

VE

_FR

AM

E

EUSO CONTROL &

DATA HANDLING

UNIT LEVEL

K A

PMT

PIXEL

Inco

min

g U

V

ph

oton

M=M+1

M_thr Co

mp

are

X &

Y+

PH

_C

NT

RIN

GM

EM

OR

IES

MCellX

Y

From other pixels

MACROCELL DIGITAL

ELECTRONICS LEVEL

MC-level Dig.

Thrsh

From other pixels

Analog Threshold

N=N+1

N_thr

Co

mp

are

Pixel-level Digital Thrsh

ASIC

X

Y

Enable

ASIC DIGITAL/ANALOG

ELECTRONICS LEVEL

ANALOGmemories


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


Background

Background is mostly due to:

Nightglow (~400 m-1 s-1 sr-1 over sea)Man madeAtmospheric phenomena


Event reconstruction

X projection

TU

TU

Yprojection

A

B

C

to receiver

CR1

2 21

tan

2 tan

x

y

x y

c t


NeutrinosProtons & Nuclei

Expected Performances

Angular resolution vs energy

Events in 1 yearProton vs neutrino separation


Schedule (a sort of)

Phase A (preliminary study): 2002-2003

Phase B (project): 2003-2004

Phase C-D (construction): 2005-2008

Phase E (operation): 2009 ?


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

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EUSO The E xtreme U niverse S pace O bservatory

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