UHE Cosmic Particles studies from space: super-EUSO: a possible - - PowerPoint PPT Presentation

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Villa Mondragone - Frascati (Roma) / May 14, 2009 UHE Cosmic Particles studies from space: super-EUSO: a possible next-generation experiment ? Alessandro Petrolini Universit` a di Genova and INFN sezione di Genova BR-247 Cosmic Vision Cosmic

SLIDE 1

Villa Mondragone - Frascati (Roma) / May 14, 2009

UHE Cosmic Particles studies from space: super-EUSO: a possible next-generation experiment ?

Alessandro Petrolini

Universit` a di Genova and INFN sezione di Genova

BR-247

Space Science for Europe 2015-2025

Cosmic Vision Cosmic Vision

SLIDE 2

My Framework (for this talk...) Frascati / May 14, 2009

My Framework (for this talk...)

I am not discussing any science issue:

they are extensively discussed elsewhere and I leave them to people more qualified than I am.

I restrict myself to discuss the conception and design of a space-based experiment

for observation of UHE Cosmic Particles from space in the post Pierre Auger Observatory (PAO) era. I am assuming that: – the present: Auger-south; – .......... the (hopefully) near future: Auger-south plus Auger-north; – .................... the (hopefully not too far) far future: a space-based experiment ???

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 3

Beyond the Pierre Auger Observatory from space ??? Frascati / May 14, 2009

Beyond the Pierre Auger Observatory from space ???

Exceeding the PAO performance requires a huge experiment,
n a long time-scale,

requiring a large amount of preliminary R&D and ancillary studies.

The challenging goal of a big experiment from space requires intermediate steps,

some of which are on the way: JEM-EUSO, ... Other intermediate steps include some path-finder and/or technological model (see later...).

What we are learning from PAO will help to tune the future scientific objectives.
A tuning of the scientific objectives is mandatory because

the Experiment-For-Everything is, most likely, impossible: a choice of scientific objectives will be needed, to drive trade-offs and choices on the performance.

Such a challenging enterprise would require the involvement
f a large part of the UHECP physicists community, in a coordinated effort.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 4

Beyond the Pierre Auger Observatory from space ??? Frascati / May 14, 2009

Science will be, obviously, the driving force.

However, after a careful assessment of the predictable status of science in some ten/fifteen years from now, we need to consider a realistic implementation of possible Experimental Apparata, to avoid dreams which will never become a reality, at least on the time-scale of a human life...

Most new big projects have a long time duration

and require a long time for conception, design, commissioning (plus getting funds...). Therefore we must start right now to think about concrete proposals for realistic implementations of post PAO :=(south+north) experiments. High Energy Physicists, for instance, are already thinking of post-LHC experiments, since years, even before LHC has started taking data.

It is not too early!

Some ten years are certainly necessary to design and build such an apparatus...

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 5

The apparatus required for space-based UHECP observation Frascati / May 14, 2009

The apparatus required for space-based UHECP observation

The required apparatus is an Earth-watching

large aperture, large FoV, fast and highly pixelized digital camera for detecting near-UV single photons superimposed on a huge background capable of (at least!) five years operation in space.

It is (see Marco’s talk on JEM-EUSO) made of:

– a main optics, collecting photons and focusing the EAS image onto the FS; – the Photo-Detector on the FS, registering the EAS image which is made of: sensors, f/e electronics, b/e electronics, triggering and data analysis systems; – ancillary instrumentation ??? (to be evaluated...): ∗ LIDAR for atmospheric monitoring (?); ∗ IR camera (?); ∗ a suitable radio-detection system (?). – system instrumentation.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 6

Order of magnitude estimates: the EAS signal Frascati / May 14, 2009

Order of magnitude estimates: the EAS signal Hadron-induced EASes and a huge space-based apparatus

Hadron-induced EAS:

E ≃ 1019 eV, θz ≃ π/4, and φ = π/2.

Apparatus:

H ≃ 400 km height, entrance pupil diameter D ≃ 5 m, half-angle FoV γ = 20◦ and total apparatus detection efficiency ε ≈ (0.1 ÷ 0.2). See: http://xxx.lanl.gov/abs/0810.5711 .

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 7

Order of magnitude estimates: the EAS signal Frascati / May 14, 2009

How does the EAS appear in our digital camera ?

Time-integrated signal reaching the apparatus (irradiance):

I ≈ 50 photons · m−2: a large entrance pupil is required.

This irradiance implies a total number of detected photons from the EAS:

IAε ≈ 150 = ⇒ ∆E /E ≈ 0.1 (statistical error only).

Apparent time duration: T ≈ 80 µs.
The typical (angular) length is: ∆ξ ≈ 1.5◦:

a fine granularity of the photo-detector is needed (better than ≈ 0.1◦ × 0.1◦) to get ∆θ ≈ 1◦; this and the large FoV implies a large number of channels.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 8

Order of magnitude estimates: night-glow background Frascati / May 14, 2009

Order of magnitude estimates: night-glow background

In the real world background makes the previous estimations too optimistic...
Reference background in the 330 nm ÷ 400 nm wavelength range:

B ≈ 5·1011 photons · m−2 · s−1 · sr−1. Current estimates: it can be up to a factor two larger. Its detailed space-time structure is poorly known.

Total background rate intercepted (on the whole entrance pupil and full FoV): ≈ 4 THz.
Total background rate detected on the PD per pixel

(pixel size: 0.1◦ × 0.1◦ for a total of N = 1.2·105 pixels): 3 MHz/pixel. This gives: – one order of magnitude more background than signal photons superimposed on the typical EAS (all space-time length). – roughly the same number of signal and background photons near the EAS maximum.

One needs to find a way to cope with this huge background ...

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 9

Extraction of the EAS signal from the background Frascati / May 14, 2009

Extraction of the EAS signal from the background

The previous figures show that it is a real challenge...

In order to extract the EAS from the background a precise knowledge of the properties of the background is required, at the space-time level of the EAS kinematics.

A continuos monitoring (and subtraction) of the average background
n a pixel-by-pixel (or so) basis is unavoidable to go at E ≈ 1019 eV.
The acceptable background level also depends on the energy of the EAS.

In order to allow for background dependent observations a precise knowledge of the Instrument sensitivity as a function of the background is required, which requires a precise Instrument calibration.

In order to face the background a clever and powerful triggering and data-handling scheme

needs to be invented.

Many other types of backgrounds, in addition to the night-glow, exist...

Most of them appear not to be dangerous (kinematics very different from an EAS)...but?

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 10

EUSO: some history Frascati / May 14, 2009

EUSO: some history

EUSO was proposed to the European Space Agency (ESA) as a free-flyer with:

– optics diameter: ≃ 3.5 m; – orbit height and inclination as a free parameter to be tuned; – mass, volume, power, telemetry and other budgets: largely unconstrained.

ESA recommended to consider the accommodation on the ESA Columbus module on the ISS:

many constraints had to be taken into account, including: – fixed orbit height; – limits on mass, volume, power, telemetry and other budgets. – The accommodation had to be made compatible with the ISS/Columbus resources including: mass (1.5 ton), volume (2.5 × 2.5 × 4.5 m3), power (1 kW), telemetry (180 Mbit/orbit). – volume limited by the envisaged accommodation on the Shuttle, not by its capabilities... Many constraints, mainly due to the ISS, limited the final EUSO performance

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 11

The heritage of EUSO projected into the future Frascati / May 14, 2009

The heritage of EUSO projected into the future

EUSO, an European-led project of the European Space Agency,

underwent a detailed phase-A study.

We have learnt a lot from the EUSO phase-A studies

about space-based observation of UHECP.

The EUSO heritage is exceedingly precious: many lessons were learnt...

and we must use what we learnt from EUSO, to develop a second generation experiment.

We can consider EUSO as our prototype exercise: we have possibly done mistakes!

One needs a safe design margin on the expected performance at design stage ! Aim (dream of ?) to an experiment with much better performance than EUSO...

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 12

From EUSO to super-EUSO ??? Frascati / May 14, 2009

From EUSO to super-EUSO ???

EUSO: the efficiency plateau was reached at ≈ (1 ÷ 2)·1020 eV:
ne needs to gain a factor (10 ÷ 20) - at least - in the energy threshold...
More collected photons improve the energy resolution and angular resolution on the UHECP.
Increasing the entrance pupil also increases the background rate:

it is not enough to enlarge the entrance pupil to improve the performance; energy threshold: at some point the EAS will fade away in the background.

Optics: reduce the FoV to get better optical efficiency: assume γM = (20◦ ÷ 25◦) (half-angle).

Aim to improve the average optical efficiency. Recover the instantaneous geometrical aperture by higher orbits.

Number of channels: assume a maximum of ≈ one Mega (it is already very challenging).

This implies angular granularity of 0.06 degrees (one mrad). One needs to account for a higher orbit, that is smaller pixels.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 13

From EUSO to super-EUSO ??? Frascati / May 14, 2009

Optimisation of the orbital parameters

Free-flyer: many more degrees of freedom in the choice of the orbit than from the ISS.

One may also think to change the orbit during the mission. Changing the orbit height actually shifts up/down the observational energy range (that is the working point). – Tune the orbit: either elliptic orbit or orbit altitude change. – Baseline: elliptical orbit with perigee at 400 km and apogee at 1100 km.

Tilting is not required; if it were useful: no problem to tilt.
Repetitive passes above specified locations at the Earth

(calibration sources, Auger sites for cross-calibration...).

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 14

Technical Developments: from EUSO to super-EUSO Frascati / May 14, 2009

Technical Developments: from EUSO to super-EUSO

Deployable catadioptic optics (much larger optics is possible).
GAPD (the so-called SiPM): lightweight, no VHV, easily shaped....
Low-power: sensors, f/e electronics, ...(new space-qualified technologies).
...

All of them are interesting for many other applications.....funding for R&D is possible! Being inside a technological road-map might help to push the scientific objectives

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 15

Provided suitable technologies are successfully developed ... Frascati / May 14, 2009

Provided suitable technologies are successfully developed ...

Area and instantaneous geometrical aperture (depends on orbit and FoV):

– ≈ 0.8·106 km2 observed area (at aphelion); – ≈ 2·106 km2 · sr instantaneous geometrical aperture (at aphelion). Duty cycle not included! What the duty cycle is going to be? Measurements required...

Threshold energy: depends on the optics entrance pupil and Photo-Detector Efficiency (PDE).

– the optics aperture is the only sizeable parameter, to within the external constraints; – PDE can realistically improve by a factor two or so...(it is the only factor ≪ 1); – a lot of other factors affect the overall efficiency (all of them ≈ 0.9). Guess-estimate: with D ≈ 6 m and PDE doubled with respect to EUSO

ne can think to reach: E ≈ 1019 eV with ∆E /E ≈ 0.1 (statistical only).

But background subtraction is not trivial and must be worked out !

Can expect ∆θ ≈ 1◦ on the reconstructed primary particle direction:

limited by the EAS visible track-length and by the affordable number of channels. See all details in: http://xxx.lanl.gov/abs/0810.5711 .

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 16

The main super-EUSO baselines parameters and design goals Frascati / May 14, 2009

The main super-EUSO baselines parameters and design goals

Main physical Parameters Operating Wavelength Range (WR) {330 nm λ 400 nm} Background (in WR) 1 (3 ÷ 15)·1011 photons m−2 s−1 sr−1 Average atmospheric transmission (in WR) Katm 0.4 Orbital Parameters Orbit perigee rP ≃ 800 km Orbit apogee rA ≃ 1100 km Orbit inclination i ≈ (50◦ ÷ 60◦) Orbital period T0 ≃ 100 min Velocity of the ground track vGT ≃ 7.5 km/s Pointing and pointing accuracy Nadir to within ∆ξ ≃ 3◦ Satellite Parameters Satellite envelope shape Frustum of a cone Diameters DMAX ≃ 11 m and DMIN ≃ 7 m. Length L ≃ 10 m Operational Lifetime (5 ÷ 10) years

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

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The main super-EUSO baselines parameters and design goals Frascati / May 14, 2009

Main instrument parameters and requirements Type Deployable catadioptric system Main mirror DM ≃ 11 m Entrance pupil and corrector plate DEP ≃ 7 m Angular granularity ∆ℓ ≈ 0.7 km at the Earth Optics throughput εO 0.7 f/# ≈ 0.6 Optics spot size diameter on the FS 3 mm ÷ 5 mm Instrument Field of View (FoV), half-angle: γM = 20◦ ÷ 25◦ Total length of the optics ≈ 9 m Focal Surface size (diameter) ≈ 4 m PDE εPDE 0.25 Number of detector channels ≈ 1.2 million Size of the pixels on the PD ≈ 4 mm Photo-Sensor GAPD Power consumption less than 2 mW per channel Main Performance Parameters and requirements Low Energy Threshold Eth ≈ 1019 eV. Instantaneous geometrical aperture AG ≈ 2.0·106 km2sr Statistical error on the energy measurement ∆E/E ≈ 0.1 @ E ≈ 1019 eV Angular resolution on the primary direction ∆χ ≈ (1◦ ÷ 5◦) Observation Duty cycle η ≈ (0.1 ÷ 0.2) Main budgets (at the present level of knowledge) Mass 5 ton Power 5 kW Telemetry 20 Gbit/orbit

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 18

Main intrisic critical issues of space-base observation Frascati / May 14, 2009

Main intrisic critical issues of space-base observation

The large distance implies that: the signal is faint, angular resolution is not excellent and the

transverse extent of the EAS is not observable.

Non-random plus random (night-glow) backgrounds...

Total background larger than from ground.

Huge background: online subtraction is required for triggering (HW implementation ?):

to be conceived.

Orbit optimisation: man-made background, atmospheric phenomena, day-night..
Stray-light control with such a large FoV and sensitive apparatus.
Atmospheric monitoring: critical and important item.

The observed FoV is continuously changing: a continuous monitoring is needed and parameter recording is required.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 19

Main technological critical issues of space-base observation Frascati / May 14, 2009

Main technological critical issues of space-base observation

Large deployable optics.
Architecture, design and engineering of the Photo-Detector (one Mega-channel):

front-end electronics (design, power); trigger.

Detector calibration: need to calibrate ≈ one million channels on-orbit.
Power consumption; mass.
A suitable (huge) launcher vehicle.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 20

A large experiment for the ESA Cosmic Vision program (2015-2025) Frascati / May 14, 2009

A large experiment for the ESA Cosmic Vision program (2015-2025)

One possible opportunity to dream for a large future mission:

the ESA Cosmic Vision program (2015-2025).

Two out of the four main themes of the ESA road-map are relevant to Particle Astrophysics:

– What are the fundamental physical laws of the Universe? – How did the Universe originate and what is it made of? The study of UHECP from space entered the ESA road-map (so many other themes too...).

A new call for missions due for implementation in the period 2015-2025 will go out in 2010.
The previous selection (2007) judged the super-EUSO proposal a scientifically valuable one

but technological readiness was judged very low.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 21

A large experiment for the ESA Cosmic Vision program (2015-2025) Frascati / May 14, 2009 Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 22

A large experiment for the ESA Cosmic Vision program (2015-2025) Frascati / May 14, 2009 Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 23

Critical points detected by ESA Frascati / May 14, 2009

Critical points detected by ESA

All critical points detected by ESA were well known to us.
They point out that a lot of work is required in order to prepare a new proposal.
A lot of work requires a lot of people.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 24

Critical points detected by ESA Frascati / May 14, 2009

Design does not fit the Ariane 5 fairing. This is not critical (generally low maturity of the proposal) but it must

be studied.

A pathfinder is discussed in the proposals. Why a precursor? To do what? What are the critical items that the

precursor should address? What agencies are going to fund this precursor?

The optics appears a very critical item. It has been classified TRL=2. Design is very preliminary. Feasibility is

not shown. Manufacturing problems are not discussed. Deployability is very critical too. Never, a study for such a challenging mirror has been performed. Baffling (and shutter) system not discussed in details. It looks very immature.

GAPD were also classified TRL=2. Response in the UV is not yet acceptable or demonstrated (other issues as

well).

The Focal Surface photo-detector is large and complex.
Data Handling System (DHS) with 1 Mega-channel is considered critical (TRL=3).
Calibration appears critical and not properly addressed in the proposal.
The re-use of the Herschel platform is only stated and not discussed. It does not seem a viable solution.
Thermal aspects appear critical.
Power budget (5 kW) in umbra is challenging.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 25

The road-map and the intermediate steps Frascati / May 14, 2009

The road-map and the intermediate steps

Demanding requirements: impact on resources.
Careful experiment optimisation: collect as much as possible information at a preliminary stage.
A well defined road-map with intermediate steps is required.

The challenging goal of a big space experiment requires intermediate steps, some of which are on the way: JEM-EUSO, ... Intermediate steps might include:

balloon flights to test/measure some low-energy CR;
technological tests via stratospheric airplane flights;
support activities, including: fluorescence yield and Cherenkov albedo measurements;
one (or a few?) small missions on a micro-satellite;
...

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.

SLIDE 26

The road-map and the intermediate steps Frascati / May 14, 2009

Step 1: background measurement

A detailed measurement/characterisation of the background,
n the space-time scales characteristics of the EAS development is required

to improve our knowledge of it and possibly exploit it to improve background rejection. A low-cost micro-satellite (a few MEuro) to characterise the background is a fundamental step to prepare such a mission. Moreover: Duty cycle estimation? Stray light control? Measure far-off nadir. Test radio? Design tuned to s-EUSO preparation but interesting measurements for geo-physics...

Step 2: a technological model

A small technological model for validation of the chosen technologies, later on.

– perform functional tests on critical parts of the apparatus (optics deployment not-to-scale, for instance); – qualify the observational approach (watching, for instance, laser shoots at the Earth); – test some technological items. In the meantime JEM-EUSO will provide useful information.

Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy.