1. Alba Cappa Universita’ and INFN Torino Čerenkov Light Measurements for the EUSO Experiment Rencontres de Moriond – Very High Energy Phenomena in the Universe La Thuile, March 12-19, 2005

2. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 2 CONTENTS:  the ULTRA experiment for EUSO  the ULTRA detector  simulated and collected data  data analysis  conclusions

3. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 3 EUSO : an UHECRs observatory UHECRs spectrum EUSO will provide to solve some problems of Fundamental Physics and HE astrophysics: investigation of the highest energy processes in the Universe through the detection and investigation of the Extreme Energy component of the cosmic radiation (EECRs / UHECRs with E > 5×10 19 eV); arrival direction and small-scale clustering will provide informations on the origin of EECRs and magnetic fields; HE neutrino astronomy will probe the boundaries of the extreme Universe and the nature and distribution of EECRs sources. do the GZK cut-off exist?

4. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 4 The EUSO project EUSO geometrical design EUSO focal surface EUSO will look downwards to the Earth atmosphere. It will see the fluorescent UV traces isotropically produced by the charged secondary particles along the EAS development. EUSO will detect also the Cherenkov light emitted in a narrow cone centered on the shower axis and hitting the Earth surface, where it’s partially diffused. image of a shower from a UHE primary on the EUSO focal surface: fluorescent and Cherenkov signals. Cherenkov signal

5. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 5 ULTRA facility in the EUSO framework reflection/diffusion coefficient ? ULTRA UV Light Transmission and Reflection in the Atmosphere ULTRA goals: measurement of the EAS characteristics and associated Cherenkov light diffused by various surfaces.

6. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 6 ULTRA : a supporting activity for the EUSO project ULTRA : hybrid system UVscope ETscope UV optical unit for Cherenkov light detection EAS telescope, scintillator’s array ETscope detector: characterization of the triggering EAS (shower size, arrival direction, core position) and comparison with the results of the simulations. UVscope and ETscope work in coincidence to detect the EAS and the Cherenkov light generated and reflected/diffused back by the Earth surface.

7. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 7 ETscope @ Mont Cenis 1970 m a.s.l. - 805 g/cm 2 ETscope @ LPSC Grenoble 216 m a.s.l. - 990 g/cm 2 The ULTRA setup 2003/2004 Experimental Setup 4+1 counting stations distance between modules = 35/54 m standard NIM & CAMAC electronics / ACQ by Labview 4-fold coincidence 150 ns threshold: 0.3 VEM 2 couples of “Belenos” (Cherenkov light detectors) near to the central station, pointing to zenith and nadir. L=54 m ST3 ST4 ST1 ST5 ST2 B-UPB-DW

8. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 8 Scintillator NE102A 80x80 cm 2 x 4 cm Expected Light Yield ~40 p.e./m.i.p. 2 PMTs High/Low Gain HG pmt Saturation ~40 VEM / 0.64 m 2 LG pmt Saturation ~400 VEM / 0.64 m 2 Procedures for the triggering events: event by event for each station the following characteristics are known: - arrival time - deposited energy in the scintillator (number of VEMs) - position of the detectors RECONSTRUCTION arrival direction (  ) shower size N e (E o ) core position The ETscope detector

9. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 9 SIMULATIONS (I) Procedures for the simulated events: event by event for each station the following characteristics are known: - deposited energy in the scintillator (number of VEMs) - position of the detectors - true values for size and core position RECONSTRUCTION of the internal events shower size N e (E o ) core position resolution in the reco very important also for the reconstruction of the real data the ones having the core inside the array: UVscope FOV is limited to the dimensions of ETscope area

10. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 10 SIMULATIONS (II)  = 0 o, energy (eV)  = 20 o, energy (eV) 5*10 13 1*10 14 3*10 14 5*10 14 1*10 15 3*10 15 5*10 15 1*10 16  primary particles type: protons;  2000 events for each energy and primary inclination;  two observation levels: 0m asl, 2000m asl. EAS simulation: CORSIKA simulations of EAS with QGSJET hadronic interaction model:

11. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 11 SIMULATIONS (III) detector simulation: a Monte Carlo program simulate the detector response to the showers generated by CORSIKA, for different geometrical configurations (the experimental conditions used in the measurement campaigns @ Grenoble, @ Mont-Cenis, @ Capo Granitola). From the simulations we can predict the detector side that is required to have the best measurement conditions @ the observation level of interest. study of the effective area optimization of the detector: calculation of the threshold energy measurement of the expected counting rate

12. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 12 Grenoble (winter 2004-05 campaign) : Mont-Cenis (2004 campaign) : Capo Granitola (spring-summer 2005 campaign) : SIMULATIONS (IV) Some results for: - effective area for internal events - effective area - convolution between the effective area and the CR spectrum E(GeV) A eff (m 2 ) A int (m 2 ) A eff AE -γ (m 2 )

13. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 13 Čerenkov light measurement (I) Tyvec Refecting- Diffusing Surface 2+2 optical units (Belenos-up & down) located near to the ETscope central station (1.5 cm Ø pmt + fresnel lens) / triggered by EAS events FOV = 30 o bottom oriented unit top oriented unit 2004 CAMPAIGN in this measurement campaign, we are interested to the detect em component in coincidence with diffused Cherenkov light. For this reason (and due to high beckground in Grenoble), we used a surface with a very high reflectivity coefficient.

14. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 14 The ETscope data @ LPSC 937 events collected in 38.4 hours TRIGGER CONDITIONS: Data selected requiring the triggering of the central detector and the Belenos-up or the Belenos-down. Requiring a signal over threshold on the Belenos-up high energy shower are selected, and even higher requiring the Belenos-down. Measurement campaigns: 2004 (Mont-Cenis, Grenoble) winter 2004-2005 (Grenoble) I will show the data analysis of the 2004 campaign @ Grenoble

15. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 15 5.25±0.02 5.65±0.04 6.26±0.20 23.1±0.4 11.6±0.7 16.7±3.2 LPSC size spectrum Cherenkov light measurement (II) green: trigger of central station + Belenos-up red: trigger of Belenos-down LPSC zenith angle

16. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 16 blue points: Cherenkov l.d.f. obtained from events with core located within 20 meters to central station (absolute single-pe calibration used) background level: 3000 photons /(m 2 ns sr) (10 x Mont-Cenis background) green line: CORSIKA Simulation for 10 16 eV proton, with wavelength in 300- 400 nm band. Cherenkov light measurement (III)

17. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 17 UP Oriented Unit (1) vs Event Number UP Oriented Unit (2) vs Event Number Twilight Cherenkov light measurement (IV) The signal measured by the Belenos-up shows the excellent correlation between the two detectors. Yellow points are the twilight, well visible at the end of two measurement nights.

18. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 18 Reflection coefficient measurement Data: May-June 2004, 6 events selected Due to low ADC gain and wrong ADC calibration in May only June data are available: 2 surviving events in  t=17 h used to a very preliminary estimation on the reflected light. -background level used -top/bottom units relative normalization applied run no.event no.Log(size)  (°)reflectivity % 130175.82623 134536.92822 compatible with tyvec reflectivity and detector acceptance

19. 13/03/2005Alba Cappa - Very High Energy Phenomena in the Universe 19 CONCLUSIONS 2004 campaigns (Mont-Cenis @ 1970m asl, Grenoble @ 200m asl), measured: em component; direct Cherenkov light; 2 events of diffuse Cherenkov light; background evaluation; winter 2004-2005 (Grenoble): more statistics, analysis of the events is still in progress; UVscope characterization; spring/summer 2005 (Capo Granitola @ sea level- Sicily): final measurements with UVscope; direct Cherenkov light detection.