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 Vision Space Science for Europe 2015-2025
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. 2
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, on 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 of a large part of the UHECP physicists community, in a coordinated effort. Alessandro Petrolini - Phys. Dept. University of Genova and INFN, Italy. 3
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. 4
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. 5
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 ≃ 10 19 eV , θ z ≃ 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. 6
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: I Aε ≈ 150 = ⇒ ∆ E /E ≈ 0 . 1 (statistical error only). • Apparent time duration: T ≈ 80 µ s . • 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. 7
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 · 10 11 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 · 10 5 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. 8
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 on a pixel-by-pixel (or so) basis is unavoidable to go at E ≈ 10 19 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. 9
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 m 3 ), 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. 10
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. 11
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