Space detectors TUS/KLYPVE for Study of Cosmic Rays in Energy Range of the GZK Energy Limit. TUS/KLYPVE collaboration: SINP MSU, JINR (Dubna), CSCB “Progress”, RSC “Energia”, Universities of Korea and Mexico B.A. Khrenov D.V.Skobeltsyn Institute of Nuclear Physics of the Moscow State University D.V.Skobeltsyn Institute of Nuclear Physics of the Moscow State University GZK40 Workshop 18 May 2006

40 years old problem: Is there the cut off in cosmic ray energy spectrum? P+γ=P+hadrons E γ =2E ph E p /M p c 2 E ph = eV (T=2.75K) In proton rest frame photon energy E γ >100 MeV for E p >10 20 eV. ρ ph =500 cm -3 Cross-section of interaction is σ= cm 2 Interaction free path L=1/ σ ρ ph =70 Mpc G.T. Zatsepin, 1968 Greisen-Zatsepin-Kuzmin made the first estimates of the effect and find the energy limit for protons E GZK =5x10 19 eV.

When the GZK problem was formulated the best CR experimentalists opened the new approach to measuring of the highest energy EAS- by registering fluorescence of the atmosphere A.E. Chudakov and K. Suga- idea of the fluorescence detector K. Greisen and A. Bunner- start to build the FD. Then the Utah group made the Fly’ Eye.

1980- J. Linsley- idea of looking on EAS from the space. 90’s-Development of space projects: OWL, KLYPVE L. Scarsi –EUSO as a ESA project. Meanwhile: HiRes collaboration made the new ground detector and has measured the CR spectrum in the GZK region. In Argentina the Pierre Auger hybrid array on the ground started measurements in the GZK region. Telescope Array collaboration is preparing the hybrid array in the Northern Hemisphere.

Energy calibration is the main reason of difference in spectra from different experiments. The calorimetric data from the atmosphere fluorescence light are decisive for surface detector arrays. Recent experimental data on the energy spectrum of Extreme Energy Cosmic Rays (EECR) Pune ICRC, 2005Today

If we use only data of the arrays that measured energy by the calorimetric method (“Proton” satellite data and Cherenkov-TUNKA data) or at least by the electron size method (MSU data) we find steeper spectrum at energy 3 PeV<E<1 EeV (Khrenov&Panasyuk, 2006, Priroda, #2,p ) which better meets the Auger spectrum. Absolute energy and intensity is well measured at the knee energy range. V. Prosin et al, EASTOP+Cherenkov I(>3 PeV)=2.3± m -2 s -1 sr -1

One of the most important issue in analysis of the experimental data of EECR is a search for correlation of EECR arriving direction with the known astrophysical objects capable to accelerate particles to extreme energies. AGASA+Yakutsk data (E>40EeV), HiRes data in the Northern Hemisphere give evidence for correlation with BL Lac sources (Gorbunov&Troitsky; HiRes collaboration) Map of BL sourcesMap of AGASA EECR events

Today the Pierre Auger observatory in the Southern hemisphere is the largest EECR array. But it does not cover an important part of the “local” source map available for observation by the array in the Northern Hemisphere (inside the green curve). J. Cronin

The fluorescence probe space detectors (TUS and KLYPVE) with integral aperture of the Auger scale will look for EECR sources in a full sky observation. Later (in ) larger aperture space detector will open the study of Cosmic Rays beyond the GZK energy limit.

Assets and difficulties of the space experiment. 1. Looking down we have better atmosphere transparence and a relatively constant distance to EAS. 2. One detector covers a large atmosphere area. 3. One and the same detector collect data over the whole sky. But 1. Average background UV light is higher than in the special regions where the ground FD’s are operating. 2. UV background is changing on-route of the orbital detector. 3. Signal is much less than in the ground measurements and the FD design meets new technological problems.

In the TUS-type detector a simple mirror optics with a comparatively narrow FOV is suggested- the “telescope” option of the space detector. Advantages of this design: 1. Simple optics has been already tested in several ground arrays. 2. A large mirror (area of ~10 m 2 ) will allow us to start measurements with a “low” energy threshold (~10 19 eV). With this threshold it will be possible to look for cosmological neutrinos- products of the EECR protons interaction with CBMW photons. It means that we will able to look beyond Greisen-Zatsepin-Kuzmin energy limit. 3.In future the mirror area enlarged up to 1000 m 2 (adaptive optics has to be applied) will allow us to register EECR at very large area of the atmosphere (10 7 km 2 ) with the help of a telescope at the geostationary orbit. 4.TUS detector as the pilot mirror telescope has to approve the technology of large mirror telescopes for the EECR research.

The TUS detector will be launched on a new platform separated from the main body of the “Foton” satellite (RosCosmos project, Samara enterprise, launching in ). Satellite limits for the scientific instrument are: mass 60 kg, electric power 60 Wt, orientation to nadir ±3 o. Preliminary TUS design: 1- in the transportation mode, 2 – in operation. 12 Mirror area 1.5 m 2, pixels cover 4000 km 2 of the atmosphere (orbit height 400 km).

Detector larger than TUS- with mirror area ~10 m 2 may be accommodated on the Russian Segment of ISS (KLYPVE project). Detector mass – 200 kg, Electric power Wt

Proposing large mirror in space we have to consider the segmented mirror- concentrator design. In the TUS telescope it consists of 7 Fresnel type mirror segments. Proposing large mirror in space we have to consider the segmented mirror- concentrator design. In the TUS telescope it consists of 7 Fresnel type mirror segments.  The mirror- concentrator mass is less than 20 kg for the mirror area 2 m 2.  Accuracy in mirror ring profiles  mm.  Stability of the mirror construction in the temperature range from –60 o to + 60 o C.  The mirror segments should make a plane with the angular accuracy less than 1 mrad. Diameter of the mirror 1.8 m, focal distance- 1.5 m

In the KLYPVE detector the mirror area is planned equal to 10 m 2 (diameter of the mirror and focal distance is 3 m). Number of Segments is 37.

The mechanism of mirror development has been designed (Consortium Space Regatta)

A sample of the mirror segment.

The TUS Photo Receiver, comprising 256 PM tubes. The TUS Photo Receiver, comprising 256 PM tubes. Photo receiver is consisted of 16 pixel rows and columns. Every pixel is a PM tube (Hamamatsu R1463, 13 mm diameter multialcali cathode) with a square window mirror light guide. 16 PM tubes (a row) has a common voltage supply and are controlled by one data acquisition unit. UV filter cover all pixel windows.

Registration Electronics. 256 photo receiver pixels are grouped in 16 clusters. In every cluster the PM tube analog signal is transmitted to one ADC with the help of multiplexer (20 MHz frequency). Every 0.8 µsec the digital signal is recorded in the FPGA memory. The digital information is also coming to the trigger system. The final trigger is worked out in the TUS FPGA where the map of triggered pixels is analyzed. Energy consumption per a channel is 10 mWt. The TUS energy consumption is less than 60 Wt. 16 channels module of the TUS electronics

UV detector based on the pixel design of the TUS telescope is measuring UV from the atmosphere on board the “Universitetsky- Tatiana” satellite. Polar orbit height-950 km. Measurements started from January It is an educational satellite, see Web site

UV light intensity, measured by the “Tatiana” detector- moonless night side of the Earth. Peaks are lights from large cities (α-Mexico City, β- Houston, γ- Los-Angeles.

UV intensity at the South High Latitudes. Moonless night. The peak is Aurora lights.

UV intensity on the night side of the Earth at full moon.

Average UV intensity per circulation (at the night side) during one moon month. Dashed line is the moon phase. In 8 days of the moon month the average UV intensity is more than 10 times higher than at moonless night.

UV flashes registered by the “Tatiana” detector. Oscilloscope trace 4 ms. UV energy in the atmosphere kJ.

UV flashes registered by the “Tatiana” detector. Oscilloscope trace- 64 ms. UV energy in the atmosphere 0.1-1MJ.

UV flash distribution over the world map. 50 of 83 registered flashes are in the equatorial belt 10 o N- 10 o S.

Important issue is the absolute energy calibration. Today several new experiments are checking the fluorescence yield as a function of atmosphere density, temperature, composition. In Figure the data of Kakimoto et al are presented, full circles-summer atmosphere (T=296K, sea level), Open circles- winter atmosphere. Recent data of Stanford group at sea level give 4.4±0.7 ph/m electron in agreement with the previous data. At altitudes 6-15 km where EAS maximum expected for EECR events of zenith angle >60 o the yield 5 ph/m±0.7 is a reliable value.

Simulation of EECR registration E 0 =100 ЕeV, θ 0 =75°, φ 0 =25°, Moonless night; σE 0 / E 0 ~ 10 %, σθ 0 ~ 1.5°, σφ 0 ~ 1°. Example of the EAS, “registered” by the KLYPVE detector In the near horizontal tracks the scattered Cherenkov light from the atmosphere is negligible to compare with fluorescence. The Cherenkov scattered from the clouds or ground is a strong signal.

Inclined EAS’s (zenith angles >50 o ) develop high in atmosphere- above the clouds- and are effectively registered by the space fluorescence detector. The Cherenkov light scattered from the clouds gives the absolute scale of height in the atmosphere in observation from the satellite. The cloud height has to be measured by a special device (Lidar) immediately after the EAS event registration.

Expected temporal profile of EAS signal in TUS pixels. Time samples 0.8 microsecond. Primary energy 100 EeV. Zenith angle 75 o.

The following features of the detector are taken into account in the simulation: 1.Reflectivity of the aluminum mirror (could be done 0.9). 2.Increasing of the focal spot with off- axis angle (in average 2 pixels are registering signal at the TUS detector FOV edge). 3. Light collection by the square pixel light guide (in average 0.75 of light coming to the pixel is guided to the PM tube). 4. Quantum efficiency of the PM tube Efficiency of the registering signal in ADC time samples t s =0.8 µs by front- end electronics with RC= ts. 6.Event selection system operating in 2 steps: signal threshold in one pixel and n-fold coincidences of the neighbor pixels. Today an area and quality of mirror is a key technological point in getting a good S/N ratio. We should look also for a new photo detector with higher quantum efficiency.

Unique feature of future space detectors might be a possibility to register the residual shower developing in the ocean. The light absorption in ocean water is of the order of shower path (10 m) and a fast (~50 ns) ocean signal could be selected from the longer EAS signal.

Selected for TUS PM tubes and the pixel electronics will allow to operate the detector at moon nights (with higher energy threshold). Energy threshold for TUS and KLYPVE detectors as a function of the background UV intensity is presented below. At the threshold E thr the signal in the shower maximum is equal to 3sigma of the background and 3-fold coincidence of pixels were taken. TUSKLYPVE

Arrival equatorial coordinates of the isotropic radiation for the range of zenith angles 60 o -90 o. ISS orbit, one year of observation by TUS. Red points are BL sources due to S. Troitsky (its N/S assymetry might be due to poor knowledge of the Southern sky). P. Klimov and S. Sharakin

The TUS/KLYPVE space detectors will be used for other researches: 1.For observation of the UV atmosphere flashes with resolution in time 0.8 µs and in space 2-4 km. Due to large mirror aperture the sensitivity of the detector will allow to observe the beginning of the discharge in the atmosphere and to reveal the origin of the flashes. 2.For observation of the micro meteors with the kinetic energy threshold of about 100J (solar system meteors of size ~mm). 3. For a search of sub-relativistic dust grains (velocity ~ cm/s ) not observed yet by other methods.

Development of the flash in video (observed, left) and in TUS pixels (expected).

Simulation of the micro meteor registration by TUS The meteor threshold kinetic energy – 100J. Expected rate- 100 per day.

Expected signal profile from the sub-relativistic (velocity cm/s) dust grain. Energy 20J.

Conclusion 1. The space experiments will give an independent evidence for EECR particles and their rate. The space observation has the advantage of whole sky coverage by one and the same detector. 2. The main goal of the first TUS experiment is to approve the new method of space observation of EECR and its techniques. 3. Other phenomena of fluorescence light in the atmosphere (UV flashes in the atmosphere electric discharges, UV light from micro meteors and sub-relativistic dust grains) could be studied by the TUS- type detectors. 4. In international collaboration the next more sophisticated detectors could be developed with a major goal to cover the atmosphere area up to 10 7 km 2 needed for exploring Cosmic Rays beyond the GZK energy limit. International Workshop on June (Italy)