Astroparticle physics with high-energy photons II – Techniques & Instruments

1. Astroparticle physicswith high-energy photonsII – Techniques & Instruments Alessandro de Angelis Lisboa 2003 http://wwwinfo.cern.ch/~deangeli

2. The subject of these lectures…(definition of terms) • Detection of high-energy photons from space • High-E X/g: probably the most interesting part of the spectrum for astroparticle • Point directly to the source • Nonthermal above 30 keV • What are X and gamma rays ? Arbitrary ! (Weekles 1988) X 1 keV-1 MeV X/low E g 1 MeV-10 Me medium 10-30 MeV HE 30 MeV-30 GeV VHE 30 GeV-30 TeV UHE 30 TeV-30 PeV EHE above 30 PeV No upper limit, apart from low flux (at 30 PeV, we expect ~ 1 g/km2/day)

3. Outline of these lectures 0) Introduction & definition of terms 1) Motivations for the study high-energy photons 2) Historical milestones 3) X/g detection and some of the present & past detectors 4) Future detectors

4. The problem - I

5. The problem - II

6. 3) Detection of a high E photon • Above the UV and below “50 GeV”, shielding from the atmosphere • Below the e+e- threshold + some phase space (“10 MeV”), Compton/scintillation • Above “10 MeV”, pair production • Above “50 GeV”, atmospheric showers • Pair <-> Brem

7. Consequences on the techniques • The earth atmosphere (28 X0 at sea level) is opaque to X/g Thus only a satellite-based detector can detect primary X/g • The fluxes of h.e. g are low and decrease rapidly with energy • Vela, the strongest g source in the sky, has a flux above 100 MeV of 1.3 10-5 photons/(cm2s), falling with E-1.89 => a 1m2 detector would detect only 1 photon/2h above 10 GeV => with the present space technology, VHE and UHE gammas can be detected only from atmospheric showers • Earth-based detectors, atmospheric shower satellites • The flux from high energy cosmic rays is much larger

8. Sat Satellite-based and atmospheric: complementary, w/ moving boundaries • Flux of diffuse extra-galactic photons Atmospheric

9. Satellite-based detectors:figures of merit • Effective area, or equivalent area for the detection of g Aeff(E) = A x eff. • Angular resolution is important for identifying the g sources and for reducing the diffuse background • Energy resolution • Time resolution

10. X detectors • The electrons ejected or created by the incident gamma rays lose energy mainly in ionizing the surrounding atoms; secondary electrons may in turn ionize the material, producing an amplification effect • Most space X- ray telescopes consist of detection materials which take advantage of ionization process but the way to measure the total ionization loss differ with the nature of the material Commonly used detection devices are... • gas detectors • scintillation counters • semiconductor detectors

11. X detection (direction-sensitive)

12. X detection (direction-sensitive) Unfolding is a nice mathematical problem !

13. g satellite-based detectors: engineering • Techniques taken from particle physics • g direction is mostly determined by e+e- conversion • Veto against charged particles by an ACD • Angular resolution given by • Opening angle of the pair m/E ln(E/m) • Multiple scattering (20/pb) (L/X0)1/2 (dominant) => large number of thin converters, but the # of channel increases (power consumption << 1 kW) • If possible, a calorimeter in the bottom to get E resolution, but watch the weight (leakage => deteriorated resolution) Smart techniques to measure E w/o calorimeters (AGILE)

14. Satellite-based detectors in the ‘70s • Two satellites in the ‘70s : SAS-2 in 1972, COS-B in 1975 • SAS-2 (Derdeyn et al. 1972) • Prototype • COS-B (Bignami et al. 1975) • thin W plates with wire chambers • range 50 MeV - 2 GeV • Scintillators for trigger • Energy measured by a CsI calorimeter 4.7 X0 thick • Effective area ~ 0.05 m2 • Angular resolution ~ 3 deg • Energy resolution ~50%

15. EGRET • High Energy g detector • 20 MeV-10 GeV on the CGRO (1991-2000) • thin tantalium plates with wire chambers • Scintillators for trigger • Energy measured by a NaI (Tl) calorimeter 8 X0 thick • Effective area ~ 0.15 m2 @ 1 GeV • Angular resolution ~ 1.2 deg @ 1 GeV • Energy resolution ~20% @ 1 GeV • Scientific success • Increased number of identified sources, AGN, GRB, sun flares...

16. g detectors on satellite:comparison with X-ray detectors X-ray TelescopeGamma-ray (EGRET) Detection technology CCD, Ge e+e- pair creation tracking Sensitivity a few micro-Crab ~ ten milli-Crab Angular resolution < 1 arc-second<1 degree No. of Sources detected >>106~300

17. INTEGRAL/CHANDRA • INTEGRAL, the International Gamma-Ray Astrophysics Laboratory is an ESA medium-size (M2) science mission • Energy range 15 keV to 10 MeV plus simultaneous X-ray (3-35 keV) and optical (550 nm) monitoring • Fine spectroscopy (DE/E ~ 1%) and fine imaging (angular resolution of 5') • Two main -ray instruments: SPI (spectroscopy) and IBIS (imager) • Chandra, from NASA, has a similar performance

18. Earth-based detectorsProperties of Extensive Air Showers • We believe we know well the g physics up to EHE… Predominant interactions e.m. • e+e- pair production dominates • electrons loose energy via brem • Rossi approximation B is valid • Maximum at z/X0 ln(E/e0); e0 is the critical energy ~80 MeV in air; X0 ~ 300 m at stp • Cascades ~ a few km thick • Lateral width dominated by Compton scattering ~ Moliere radius (~80m for air at STP) • Note: lhad ~ 400 m for air => hadronic showers will look ~ equal to e.m., apart from having 20x more muons and being less regular

20. Hadron rejection : Small field-of-view makes protons look like gammas.

21. Earth-based detectors • An Extensive Air Shower can be detected • From the shower particles directly (EAS Particle Detector Arrays) • By the Cherenkov light emitted by the charged particles in the shower (Cherenkov detectors)

22. Cherenkov (Č) detectorsCherenkov light from g showers • Člight is produced by particles faster than light in air • Limiting angle cos qc ~ 1/n • qc ~ 1º at sea level, 1.3º at 8 Km asl • Threshold @ sea level : 21 MeV for e, 44 GeV for m Maximum of a 1 TeV g shower ~ 8 Km asl 200 photons/m2 in the visible Duration ~ 2 ns Angular spread ~ 0.5º

23. Cherenkov detectorsPrinciples of operation • Cherenkov light is detected by means of mirrors which concentrate the photons into fast optical detectors • Often heliostats operated during night • Problem: night sky background On a moonless night ~ 0.1 photons/(m2 ns deg) Signal  A fluctuations ~ (AtW)1/2 => S/B1/2 (A/tW)1/2

24. Č detectorsAnalysis features • Rejection of cosmic ray background: from shape or associated muon detectors • Wavefront timing: allows rejection and fitting the primary direction as well

25. Whipple-10m since 1969 100 PMT’s by 1990 HEGRA 1994-2002 5 telescopes / stereoscopy La-Palma Canaries CANGAROO since 1994 Australia STACEE Since 2000 Albuquerque • CAT • Thémis (French Pyrénées) • first light summer 1996, • fine camera : 600 pixels

26. Extensive Air Shower Particle Detector Arrays • Built to detect UHE gammas small flux => need for large surfaces, ~ 104 m2 • But: 100 TeV => 50,000 electrons & 250,000 photons at mountain altitudes, and sampling is possible • Typical detectors are arrays of 50-1000 scintillators of ~1m2/each (fraction of sensitive area < 1%) • Possibly a m detector for hadron rejection • Direction from the arrival times, dq can be ~ 1 deg • calibrated from the shadow from the Moon • Thresholds rather large, and dependent on the point of first interaction

27. EAS Particle Detector ArraysPrinciple • Each module reports: • Time of hit (10 ns accuracy) • Number of particles crossing detector module • Time sequence of hit detectors -> shower direction • Radial distribution of particles -> distance L • Total number of particles -> energy

28. EAS Particle Detector ArraysAn example: CASA-MIA (< 1996) • CASA: 0.25 km2 air array which detects the em showers produced by gamma rays and cosmic rays at 100 TeV and above; 1089 stations • A second array, the Michigan Anti Mu (MIA), is made of 2500 square meters of buried counters in 16 patches. MIA measures the muon content of the showers, which allows to reject > 90% of the events as hadronic background

29. EAS Particle Detector ArraysAnother (less standard) example • Milagro in New Mexico

30. Air fluorescence detectors • The flux of EHE photons is very low ~2/(Km2 week sr) > 1 PeV => need for huge effective volume use the atmosphere as converter • Luckily, excited N2 emits fluorescence photons (~5 photons/m/electron ~ as for Č, but not beamed) • Fly’s Eye : 67 x 1.5 spherical mirrors seen by PMs (1981-) A second detector added in 1986 • Superior in shower imaging

31. 4) The future • Satellite-based: EGRET had a large success • But: disposables (gas for 5 refills) => Room for improvement • Higher sensitivity would be very useful... • Very near future: Improvement in air Cherenkov telescopes • Flux sensitivity • Better angular & time resolutions • Lower energy thresholds • Larger mirrors and higher quantum-efficiency detectors • Improvement in EAS Particle Detector Arrays • Higher altitude • Increased sampling • New concept (EUSO, OWL)

32. GLAST Tracker • g telescope on satellite for the range 20 MeV-300 GeV • hybrid tracker + calorimeter • International collaboration US-France-Italy-Japan-Sweden • Broad experience in high-energy astrophysics and particle physics (science + instrumentation) • Timescale: 2006-2010 (->2015) • Wide range of physics objectives: • Gamma astrophysics • Fundamental physics Calorimeter A HEP / astrophysics partnership

33. GLAST: the instrument • Tracker Si strips + converter • Calorimeter CsI with diode readout (a classic for HEP) • 1.7 x 1.7 m2 x 0.8 m height/width = 0.4  large field of view • 16 towers  modularity

34. Si strips + converter High signal/noise Rad-hard Low power 4x4 towers, of 37 cm  37 cm of Si 18 x,y planes per tower 19 “tray” structures 12 with 2.5% Pb on bottom 4 with 25% Pb on bottom 2 with no converter Electronics on the sides of trays Minimize gap between towers Carbon-fiber walls to provide stiffness GLAST: the tracker

35. GLAST performance (compared to EGRET)

36. Geminga Radio-Quiet Pulsars Geminga Crab PKS 0528 +134 GLAST performance two examples of application • Cosmic ray production • Facilitate searches for pulsations from millisecond pulsars

37. AGILE (the GLAST precursor) To be launched in 2005 Lifetime of 3 years

38. But despite the progress in satellites… • The problem of the flux (~1 photon/day/km2 @ ~30 PeV) cannot be overcomed • Photon concentrators work only at low energy • The key for VHE gamma astronomy and above is in earth-based detectors • Also for dark matter detection…

39. Ground-based detectorsImprovements in atmospheric Č • Improving flux sensitivity • Detect weaker sources, study larger sky regions S/B1/2 (A/tW)1/2 • Smaller integration time • Improve photon collection, improve quantum efficiency of PMs • Use several telescopes • Lowering the energy threshold • Close the gap ~ 100 GeV between satellite-based & ground-based instruments • Use solar plants

40. Major projects in atmospheric ČAiming at lower threshold (~20 GeV) • STACEE (past and future…) • US, heliostats in Albuquerque (NM) • CAT/CELESTE (European, lead by France) • Solar plant in Pyrenees • MAGIC (European, lead by Germany) • large parabolic dish (17m), automatic alignment control, technique at the state of the art • Canary Islands, 2003

41. Major projects in atmospheric ČAiming at improved flux sensitivity • CANGAROO (past and future…) • Australia; Japan is building new telescopes • HESS (European, lead by Germany) • 4 x 110 m2 telescopes in Namibia, > 2003 • VERITAS (US, Arizona) • 7 x Whipple-like 100 m2 telescopes in Arizona, > 2005

42. Č detectorsOverview of next detectors MAGIC(Germany, Italy & Spain)Winter 20031 telescope 17 meters Ø WHIPPLE/ VERITAS(USA & England)now/2005?7 telescopes10 meters Ø Montosa Canyon, Arizona Roque delos Muchachos, Canary Islands CANGAROO III(Australia & Japan)Spring 20044 telescopes 10 meters Ø Windhoek, Namibia HESS(Germany & France)Summer 20024 (16) telescopes 10 meters Ø Woomera, Australia

43. Ground-based detectorsImprovements in EAS PDAs • Higher altitude • Tibet (past and future) => TibetII • Increased sampling • Larger density • Better sensitive elements (scintillators at present) ARGO in Tibet (Italy/China): full coverage detector of dimension ~5000 m2 ARGO

44. But also the generic CR detectors... • Auger Southern Observatory in Argentina • When completed, world's largest cosmic ray observatory with 1600 detectors spread over 3000 km2 - A complementary observatory is planned for the northern hemisphere • The detectors are water tanks equipped with PMs, which detect Č radiation • Fluorescence detectors as well

45. Sky coverage in 2003

46. An armada of detectorsat different energy ranges

47. …some are coming now MAGIC 2003

48. Sensitivity

49. A new concept: EUSO (and OWL) • The Earth atmosphere is the ideal detector for the Extreme Energy Cosmic Rays and the companion Cosmic Neutrinos. The new idea of EUSO (2009-) is to watch the fluorescence produced by them from the top

50. The EeV and ZeV energies and EUSO • EUSO can open a new energy frontier at the ZeV scale...