Review of Cherenkov Imaging Devices in Astroparticle Physics Experiments

1. REVIEW OF CHERENKOV IMAGING DEVICES IN • ASTROPARTICLE PHYSICS EXPERIMENTs • (currently running, under construction or planned) • E. Lorenz, MPI for Physics, Munich and ETH Zurich • OVERVIEW • INTRODUCTION, THE MAIN AREAS OF ASTROPARTICLE PHYSICS (APP) RESEARCH • THE IMPORTANCE OF CHERENKOV LIGHT IN MANY EXPERIMENTS • AREAS IN APP EXPERIMENTS WHICH RELY MOSTLY/PARTLY ON CHERENKOV LIGHT DETECTION • A) GROUND BASED GAMMA-RAY ASTRONOMY • B) THE HIGHEST ENERGY EXPERIMENTS • C) NEUTRINO EXPERIMENTS • CONCLUSIONS

2. ASTROPARTICLE PHYSICS IS A RAPIDLY EXPANDING • FIELD OF FUNDAMENTAL RESEARCH • AREAS OF ASTROPARTICLE PHYSICS (APP) • (IN THE US: PREFER THE NAME PARTICLE ASTROPHYSICS) • GAMMA-RAY (g) ASTRONOMY • n ASTRONOMY (LOW AND HIGH ENERGY) • STUDY OF THE HIGHEST ENERGY (> 1019 eV) COSMIC PARTICLES • STUDY OF THE CHEMICAL COMPOSITION OF COSMIC RAYS ABOVE 1012 eV • NUCLEAR ASTROPHYSICS • DARK MATTER SEARCHES (WIMPS) • (GRAVITATIONAL WAVE PHYSICS) • BOUNDARIES NOT ALWAYS CLEARLY DEFINED • ULTIMATE GOAL: CONTRIBUTE TO UNDERSTAND OUR UNIVERSE COMPLETELY • PARTICLES AS INFORMATION CARRIERS FROM OUR UNIVERSE = MESSENGERS • SEARCH FOR PARTICLE PHYSICS (EXAMPLE: WIMPS, NEUTRALINO. TOPOLOGICAL • DEFECTS, RELIC PARTICLES.?GRAVITON?) • LINKS TO CLASSICAL ASTRONOMY

3. THE EXPERIMENTAL CHALLENGES IN HIGH ENERGY ASTROPARTICLE PHYSICS (as viewed from the instrument side) • OBSERVATIONAL SCIENCE • INITIAL PARAMETERS NOT UNDER CONTROL AS IN HEP • ENERGY , TIME, (PATRICLE TYPE), (DIRECTION) • FLUXES ARE VERY LOW -> NEEDS ULTRA-LARGE DETECTOR VOLUMES • HIGH ENERGY -> CALORIMETRIC DETECTORS TO CONVERT INITIAL ENERGY • INTO OBSERVABLE QUANTITIES • INITIAL PARTICLE->INTERACTION IN CALORIMETER MATERIAL -> SHOWER-> • -> OBSERVABLES -> PHOTONS,CHARGE CARRIERS IN SUITABLE • MATERIALS • (-> RADIO WAVES ???) • (->ACOUSTICAL SIGNALS ???) • ->IONISATION -> TRACKING, COUNTING, (TAIL CATCHER) CALORIMETERS • nearly all based on light detection in solid devices (gaseous det. have some operation probl.)

4. CALORIMETER MATERIALS: COST AN ISSUE: USE FROM NATURE (EXAMPLE: n DETECTOR FOR ASTRONOMY MUST BE > 109 TONS, FOR SUN n LESS VOLUME) POSSIBLE NATURAL CALORIMETER MATERIALS (MUST BE TRANSPARENT FOR MEASURABLE PHOTONS): ATMOSPHERE, WATER, ICE ALL HAVE THEIR SPECIFIC PROBLEMS ‘EXOTIC’ MATERIALS: PURIFIED AND ACTIVATED OIL (LIQUID SCINTILLATOR) LIQUID PURIFIED ARGON, (XENON) (MAINLY IONISATION BUT ALSO SCINTILLATION, BECOMES IMPORTANT FOR LARGER VOLUMES) PROCESSES GENERATING PHOTONS CHERENKOV RADIATION IN AIR, WATER, ICE SCINTILLATION IN AIR (N2 FLUORESCENCE)

5. NEARLY ALL EXPERIMENTS IN APP RELY ON PHOTON DETECTION (QUITE DIFFERENT COMPARED TO THE NEEDS OF HEP EXPERIMENTS) SIDE COMMENT: BETTER PHOTON DETECTORS WILL MAKE BETTER PHYSICS WILL ALLOW NEW EXPERIMENTS UP TO NOW IMPOSSIBLE APP IS NOW A DRIVING FORCE FOR NEW PHOTON DETECTORS NEED FOR LARGE ACTIVE AREA SINGLE PHOTON SENSORS (UNO, HYPERK 50-100 K LARGE PMTS) NEED FOR LARGE NR AT LOW COST SENSORS (CTA 100-1000 K PIXELS) NEED FOR HIGHER QE/PDE PHOTON DETECTOR PERFORMANCES WERE NORMALLY RATED BY THE QUANTUM EFFICIENCY (QE), MORE RECENTLY IT WAS FOUND THAT THE PHOTON DETECTION EFFICIENCY (PDE) IS A BETTER PARAMETER TO QUALIFY/QUANTIFY SENSORS

7. SOME SPECIFIC PROBLEMS COMMON TO NEARLY ALL APP EXPERIMENTS • THE YIELD OF SCINTILLATION OR CHERENKOV LIGHT YIELD IS • EXTREMLY LOW. ORDER 10-5 TO 10-3 OF TOTAL PRIMARY ENERGY • (EXCEPTION IN L-Ar,Xe, LIQUID SCINTILLATOR) • -> THERE IS A NEED OF VERY LARGE PHOTON DETECTORS. • OPTICAL CONCENTRATOR ELEMENTS HELP BUT ARE ALSO NOT CHEAP: • MIRRORS, FRESNEL LENSES, WINSTON CONE CONCENTRATORS • FLUORESCENT FLUX CONCENTRATORS • NEED OF PIXELIZED SENSORS TO OVERCOME VARIOUS BACKGROUNDS • g-HADRON SEPARATION IN g ASTRONOMY • TO REJECT BACKGROUND LIGHT • TO DETERMINE DIRECTION OF SHOWERS • NEED OF FAST PHOTON DETECTORS • nsec TIME RESOLUTION FOR CHERENKOV TYPE DETECTORS • 10 - FEW 100 nsec TIME RESOLUTION FOR SCINT. LIGHT DETECTORS • EARTH ROTATES: CALORIMETER AND PHOTON DETECTORS MUST COPE • WITH ROTATION (TELESCOPES, 4p UNIDIRECTIONAL READOUT..)

8. WHAT MAKES THE CHERENKOV EFFECT SO ATTRACTIVE ? THERE EXIST NATURAL TRANSPARENT MEDIA WITH REASONABLY HIGH TRANSMISSION IN CLEAR AIR (l =500 nm) : 10-20 km (density dep.) asl IN CLEAR WATER (l =500 nm) : 60-80 m (in pure ICE larger, results not consistent, scattering problems) LOSSES: ABSORPTION (EXAMPLE O3, CO2 IN AIR...) SCATTERING: RAYLEIGH, MIE CHERENKOV EMISSION IST PROMPTAND SHORT BUT LIGHT PATHES CAN BE LARGE (DISPERSION) CHERENKOV EMISSION IS DIRECTIONAL IN AIR : 0.3 TO 1.4 ° OFF THE INITIAL PARTICLE DIRECTION (ß =1) IN WATER(ICE): 41.° (ß=1) SOMETIMES THIS CAN BE A PROBLEM IN WATER DETECTORS: USE OF DIFFUSE REFLECTORS GAIN OF MORE LIGHT IN WATER: ADD WAVELENGTH SHIFTER (MAKES LIGHT EMISSION ≈ 4p) CHERENKOV LIGHT IN AIR,WATER,ICE WELL MATCHTE WITH SPECTRAL SENSITIVITY OF MOST PMTS NOTE: NEARLY ALL HIGH ENERGY SHOWERS IN AIR,WATER,ICE HAVE DOMINANTLY e+.e- (ß≈1) AS SHOWER PARTICLES

9. THE AREA OF GROUND-BASED g ASTRONOMY Currently one of the most productive section of APP Window was opened 1989 by discovery of gs from the CRAB Nearly all discoveries made by Cherenkov light detectors (> 95%) Imaging Air Cherenkov Telescopes Water pond detectors Wide angle open PMT arrays

10. KIFUNE PLOT 44 SOURCES (13 AGNs) (NOW(FALL07) 70 SOURCES) 2006) Mkn180 PG1553 NOT ALL SOURCES IN INNER GALACTIC PLANE SHOWN ALL SOURCES HAVE SPECTRA EXTENDING ABOVE 1 TEV, RARELY SPECTRA EXTEND ABOVE 10 TEV (CRAB->80 GEV)MANY AGNS HAVE A SOFT SPECTRUM

13. THE NEW GENERATION OF HIGH SENSITIVITY CHERENKOV TELESCOPES MAGIC(Germany, Italy & Spain) 20031 telescope 17 meters Ø VERITAS(USA & England)20074 telescopes10 meters Ø Whiple obs. Base camp Arizona Roque delos Muchachos, Canary Islands CANGAROO III(Australia & Japan) 20044 telescopes 10 meters Ø Komas land, Namibia HESS(Germany & France) 20024 telescopes 12 meters Ø Woomera, Australia

14. THE NEXT IACTS, ALREADY UNDER CONSTRUCTION MAGIC-II MAGIC-I HESS II IN CENTER OF HESS 2007-9, 27mØ, 600 Tons MACE PROJECT, HENLE, INDIA 2 IACTS (21 m Ø) MAGIC II to be completed Spring/summer 2008

15. NEW AIR CHERENKOV TELESCOPE PROJECTS Aim for higher sensitivity (factor 10 increase), lower threshold (<- 50 GeV) European initiative: CTA (Cherenkov telescope array) US Project: AGIS Both in the 100-150 M€ price range, 50-100 telescopes + quite a few other smaller projects: GAW (Gama Air Watch, large W, EUSO upside- down), LEA (Low Energy Array),Ten-Ten... CTA 2(3) types of telescopes for low/ high energy range Proven technology (-> safe construction) PMTs with new high QE cathodes? Alternatice camera sensors: high PDE G-apds 2x higher pde than PMTs First tests very encouraging

16. AGIS TELESCOPE DESIGN FOR WIDE ANGLE OBSERVATION A new approach to the telescope optics CURRENTLY DESIGN OPTIMISATION AND POSSIBLE PRODUCTION AT ARGONNE NAT. LAB

17. VERY WIDE ANGLE CHERENKOV DETECTORS ARRAY OF OPEN PMTS (WITH LIGHT CATCHERS TO INCREASE COLL. AREA AND ≈1 STERAD ACC.) SAMPLE LIGHT FRONT WITH HIGH TIMING PRECISION, ANGULAR RESOLUTION X 0.05-0.3°, ENERGY RESOLUTION: 15-5%. SOME COARSE CHEMICAL COMPOSITION ANALYSIS POWER ORIGINAL CONCEPT : WEGA, AIROBICC

18. THE TUNKA -133 AIR CHERENKOV DETECTOR ARRAY PROJECT

20. WATER CHERENKOV DETECTORS The Pool approach to detect shower tail particles (mostly for g-astronomy) 100% up-time, wide angle Caveat: poor angular resolution, poor energy resolution strong rise in theshold as function of Zenith angle T(Q) = A(cos (Q)-(5-6) )

22. THE MILAGRO TAIL CATCHER WATER’ARRAY’ ≈100% ACTIVE COVERAGE AT SHOWER END PM ARRANGEMENT VIEW FROM OUTSIDE, LIGHT SEAL COVER

24. A FUTURE REALISTIC POND DETECTOR: HAWC MILAGRO DERIVATIVE -> HIGH MOUNTAIN LARGER AREA IMPROVED CONFIGUTATION (WALLS BETWEEN CELLS)

26. OBSERVATION OF HIGHEST ENERGY COSMIC RAYS BY A GROUND-BASED ARRAY OF WATER TANKS BY FLUORESCENCE LIGHT+ CHERENKOV LIGHT PARTLY AN UNWANTED BACKGROUND

27. STILL A PROJECT 2014, 200k km2

30. Water Cherenkov Detector • 12 m³ ultrapure water • duty cycle: 100% • angular resolution ≤ 1.1° • energy resolution ≈ order (10%) • PMT signals: • shape and • time information • 25 ns intervals • ⇒distinction between muonic and electromagnetic component

31. Fluorescence Telescopes – Stereo Measurement Δ energy ~ 6% Δ direction ~ 0,6 o Δ X max ~ 10 g/cm 2 cosmic ray extensive air shower fluorescence light Station II Station I

33. EECR detection EUSO will detect EAS light from above: Fluorescence photonsisotropically produced at different depths image the shower longitudinal profile Cherenkov photonscollimated with the shower are detected when reflected/diffuse in a surface Both types of photons contain information on the energy, direction and nature of the incoming particle The Earth atmosphere is both the detector and the propagation medium. It affects the signal production, propagation and the Acceptance

34. NEUTRINO ASTRO PHYSICS, NEUTRINO ASTRONOMY • n’s : • OCCUR IN MANY HIGH ENERGY PROCESSES • MESSENGERS OF LEPTONIC PROCESSES • FLY STRAIGTH-> CAN BE EXTRAPOLATED TO ORIGIN, • IF ENERGY HIGH ENOUGH • BASICALLY UNABSORBED (NOT LIKE g’s OF CERTAIN ENERGY) • CAN SEE(IN PRINCIPLE) THROUGH ENTIRE UNIVERSE • FLUX OF HIGH ENERGY n’s VERY SMALL • INTERACTION CROSS SECTION VERY SMALL • -> NEEDS ULTRA-LARGE DETECTORS • NOT ALL n PARAMETERS KNOWN: MASSES… • FIRST DETECTED n SOURCES: SUN, SN 1987 A. • FIRST HINTS FROM AMANDA OF AN AGN (1ES1959)

35. REQUIREMENTS, PROBLEMS OF n-DETECTION FROM COSMIC SOURCES • ULTRA-LARGE DETECTOR VOLUMES NEEDED, RATES NEVERTHELESS VERY SMALL • INDIRECT DETECTION THROUGH NEUTRAL /CHARGED CURRENT REACTIONS • CHERENKOV LIGHT FROM CHARGED SECONDARY PARTICLES IN LARGE WATER(ICE) VOLUMES • (SCINTILLATION LIGHT IN LARGE LIQUID SCINTILLATOR DETECTORS POSSIBLE FOR MeV n) • SHIELDING PROBLEMS -> DETECTORS DEEP UNDERGROUND • FOR LOWER ENERGY: NEED OF LOW BACKGROUND MATERIALS • DUE TO EARTH ROTATION 4p LIGHT DETECTOR COVERAGE • CALIBRATION A PROBLEM • DETECTORS MIGHT BE ALSO USEFUL FOR OTHER FUNDAMENTAL PHYSICS STUDIES • (Proton decay)

36. DETECTORS FOR MeV/GeV n‘s SUPERKAMOKANDE (AMANDA, ANTARES) NEW PROJECTS BASED ON CHERENKOV EFFECT UNO, DUE, TRES (funding limitations only one at most) COMPETITION BY LIQUID ARGON DETECTOR (100 kT PROJECT RUBBIA) SCINTILLATOR DETECTORS (LENA, HANO-HANO)

37. THE TEMPLATE DETECTOR FOR ALL LARGE VOLUME WATER DETECTORS SUPERKAMIOKANDE m n

38. THE BASIC CHERENKOV PHOTON DETECTION ELEMENT IN n DETECTORS A LARGE AREA PHOTOMULTIPLIER WITH SINGLE PHOTON DETECTION EFFICIENCY IN A PRESSURE VESSEL QE PDE correlated TIME RESOLUTION

39. DUE Hyper-Kamiokande ≡ TRE HYPER KAMIOKANDE HOMESTAKE MINE FREJUS TUNNEL MEMPHIS

40. DETECTORS FOR HIGH ENERGY n ASTRONOMY

41. Antares detector 42° 50’ N 6° 10’ E Atlas Equipped volume 0.1 km2 x 0.4 km (=800 x SuperK)

42. 5 STRINGS INSTALLED AND FIRST DATA RECORDED, SEE TALK G. HALLEWELL

43. CURRENTLY 22 STRINGS RUNNING (ARRAY TO BE COMPLETED ≈2012) AMANDA Clear ice, Cherenkov detector)

45. DETECTORS RUNNING, UNDER CONSTRUCTION OR PLANNING LAKE BAIKAL (running) AMANDA(running), ICECUBE (partially running) at Southpole ANTARES (assembling),NESTOR, NEMO, KM3NET in the mediterrenian FINAL AIM TO BUILD A ≈ 1km3 SIZE DETECTOR COMBINATION SPOLE+ MED.SEA DETECTORS SHOULD COVER ENTIRE SKY JUST AT THE DETECTION LIMIT OF STRONGEST PRED. n SOURCES MIGHT NEED ≥ 10 km3 VOLUME(needs better-higher PDE- sensors and lower costs)

46. THE LAKE BAIKAL DETECTOR

47. Future directions in VHE n detectors • Combined efforts of ANTARES, NEMO,NESTOR -> KM3NET • Extension of LAKE BAIKAL EXPERIMENT-> 0.2 to 1 km3 • May be: denser insert into ICECUBE • May be acoustic or radio detectors can replace/complement current • detectors • Module spacing <-> costs, threshold • Higher PDE PMTs • Improved readout • Lower costs/string • Next steps have to wait for the outcome of the 1. Generation km3 det. • (or convincing results from acoustic or radio detectors)

48. HAD TO SKIP QUITE A FEW MORE PROVEN APPLICATIONS WATER CHERNKOV COUNTERS AS VETO DETECTORS (BOREXINO, SUPER-K,OUTRIGGER TANKS MILAGRO.... AEROGEL CHERENKOV DETECTORS IN SATELLITE AND BALOON BORNE DETECTORS FOR NUCLEARASTROPHYSICS APPL.

49. CONCLUSIONS MOST OF THE HEP-APP EXPERIMENTS IN g-ASTRONOMY AND n ASTRONOMY RELY ON THE CHERENKOV EFFECT AND EFFICIENT DETECTION OF CHERENKOV PHOTONS WATER TANK DETECTORS BASED ON CHERENKOV LIGHT DETECTION ARE A VERY COST EFFECTIVE ALTERNATIVE TO SCINTILLATION COUNTERS IN APP DETECTORS ONE OBSERVES RARELY RESOLVABLE RINGS, MORE OFTEN CLUSTERS OF UNRESOLVED PHOTONS OR SINGLE PHOTONS WITH PHOTON DETECTOR OF BETTER PDE WE CAN EXPECT A QUANTUM JUMP IN SENSITIVITY AND SIGNIFICANTLY BETTER PHYSICS WITHOUT THE CHERENKOV EFFECT AND APPROPRIATE PHOTON DETECTORS OUR UNDERSTANDING OF THE RELATIVISTIC UNIVERSE WOULD BE FAR BEHIND THE CURRENT STATUS.

50. IN WATER