First Detection of Cherenkov Light from Air Showers

First Detection of Cherenkov Light from Air Showers with Si. PM Nepomuk Otte 1, 4 A. Biland 2, I. Britvitch 2, E. Lorenz 1, 2, F. Pauss 2, D. Renker 3, U. Rösler 2 1 MPI für Physik, München 2 ETH, Zürich 3 PSI, Villigen 4 Humboldt Universität, Berlin

Outline • • What this study is all about G-APDs / Si. PMs 3 Tests Conclusions

what this study is all about astrophysics in an unexplored energy window between 10 and 100 Ge. V • extragalactic background light studies • gamma ray bursts • dark matter • test of quantum gravity • pulsars • …

One example: Pulsars PSR B 1951+32 No detection >100 Ge. V indicates strong cutoff

PSR B 1951+32 ground based experiments Satellite domain This is the interesting energy range not covered by experiments where is the cutoff and what is its shape?

γ-ray astrophysics from ground Possible by detecting Cherenkov light from air showers Imaging technique very successful! high sensitivities >200 Ge. V MAGIC telescope

PSR B 1951+32 Pushing from this sides requires: • larger light collectors • high efficiency photon detectors currently ~20% QE

The G-APD / Si. PM a promising photon detector concept advantages • detectors with ~60% efficiency become available • internal gain ~105 -106 • compact and robust • … disadvantages • small sizes • optical crosstalk • high dark rates • … Otte et al. , IEEE TNS. 53 (2006) 636. P. Buzhan et al. http: //www. slac-stanford. edu/pubs/icfa/fall 01. html

from latest Hamamatsu data sheet can hope for factor >2 increased detection sensitivity

Test 1 16 Photonique SSPM_0606 BG 4 MM • grouped 4 x 4 • each sensor area 4. 4 mm 2 • peak sensitivity @ 580 nm Setup mounted in the focal plane of MAGIC trigger on one group record signal of remaining groups

Test 1 50 nsec well defined timing and narrowness of signals detection of Cherenkov light

Test 2 4 groups of blue sensitive devices from Hamamatsu sensitive area of one group 9 mm² just viewing the sky • trigger: - 2 PMTs (ET 9114) - Winston cones limit Fo. V to 1 steradian - trigger threshold 8 phe - coincidence window 5 nsec average over 10 signals Select air showers with photo density of ≥ 26 photons/cm² e. g. cosmic rays with > 500 Te. V trigger rate 1 per 5 min (50% accidentals 50% showers) matches former Airobicc measurements

Test 3 same setup as in Test 2 but: placed in the focal plane of a solar light concentrator at the Paul-Scherrer-Institut. PMTs G-APDs planar mirror 120 m² parabolic mirror 8. 5 m Ø only 15 m² used because of limited acceptance

Test 3 PMT signals G-APD signals 50 nsec Signal readout by Domino Ring Sampler 2 Gs/sec

Test 3

Test 3

Conclusions • detection of Cerenkov light from air showers by GAPDs in 3 different tests. • Estimate a factor >2 increased sensitivity compared to vacuum photomultipliers • The intrinsic noise rate of the blue sensitive G-APDs (Hamamatsu) was below the level of the background light no cooling needed! Stay tuned!