Search for diffuse gamma - radiation with energy E γ >100TeV at the “Carpet-3” array

1. Search for diffuse gamma - radiation with energy Eγ>100TeV at the “Carpet-3” array A.U. Kudzhaev,D.D. Dzhappuev, V.B. Petkov, A.S. Lidvansky,V.I.Volchenko, G.V. Volchenko, E.A. Gorbacheva, I.M. Dzaparova, N.F.Klimenko, A.N. Kurenya, O.I.Mikhailova, K.V. Pticina, M.M. Hadzhiev, A.F.Ynin Baksan Neutrino Observatory, INR of RAS

2. Dependenceof integralflux of gamma-rayfromenergy thresholdone [Yu.A. Fomin, arXiv:1410.2599v2 [astro-ph.HE] 10 Oct 2014 ] Estimates of the integral gamma-ray flux: Detection claims by Tien Shan (gray open circle) and Lodz (gray solid circle) and EAS-MSU (dark red squares and error bars). Gray triangles, squares and diamonds are for EAS-TOP, CASA-MIA, and KASCADE, respectively. Black open symbols: triangles (Yakutsk), diamonds (Pierre Auger), small squares (AGASA, large squares (Telescope Array). The curve represents a theoretical prediction for the model in which photons and neutrinos are produced in cosmic-ray collisions with the hot gas surrounding our Galaxy, assuming the best IceCube observed neutrino spectrum.

3. Baksan Neutron Monitor Large Area Muon Detector The central part of Carpet Outside detector

4. The “Carpet-2” air shower array

5. The “Carpet“ array (400 detectors)

6. Passing of muons and hadrons through an absorber of MD

7. 1ststage of the Muon Detector, 175 m2, inoperationsince 1999 year

8. The trigger of MD for record of events

9. Experimental data In order to definition energy EAS, used measured experimental value it is the total number of relativistic particles(Ne) in “Carpet” and for definition of number muons in shower, nμ– number of muons with threshold energy registered in MD. The “Carpet” array and MD are working independently each other and have different dead times of registered electronics. But time marks of events in MD and “Carpet” are made at the same clock and it give possibility to conduct an identification of coincidence events in time interval Δt=1msec. For this analyses using a data from array in period 1999-2011years are recorded. In data processing are included an events satisfied to next conditions: 1. an axis of showers are in “Carpet”(200 m2); 2. zenith angles of showers θ<40°; 3.No≥ 104 in “Carpet” ; 4. a number of nonzero detectors is more 300 in “Carpet”; After such selection are remained 130000 of showers, stored information in 3390 days.

10. Simulation of experiment For simulation of showers used the package of program CORSIKA v. 6720 (QGSJET01C FLUKA 2006). There was simulated of 5400 showersfromprimary protonswith energyin the interval (0.316 - 31.6) PeV, the 3665 of showersfrom nuclear iron with energiesin interval (0.316 - 31.6) РеV and 3360 of showersfrom gamma-rayswith energiesin the interval (0.316 – 31.6) PeV . By results of simulation was obtained: correlationdistributionnμ – Ne, wherenμ – number of muonsinMD, with 175 m2area, Ne- totalnumberof relativistic particles in Carpet; an averaged dependence of energy for primary protonsandgamma – raysfrom valueNe: Ep [GeV] =174•Nе.0.48 Eγ [GeV] =138•Nе.0.65

11. The limitation at the flux of diffuse gamma-radiation For separation of showers of primary gamma-rays from background ordinary EAS have been carried out the analysis of correlation dependence in plane nμ– Ne of detected and simulation of events. In this work we analyse the re- gion with Ne>106 in which for used the method of processing of experimental data must separate model gamma rays from ordinary EAS. For estimation of efficiency selection of gamma-rays at Ne≥106 and Ne≥5∙106 on plane nμ-Ne is distinguished the region an arrangement only simulation of gamma-rays without detected of EAS. At figure the boundary of this region is distinguish by broken line. The relation of number simulation of gamma-rays is situated in this region to it total number at Ne≥106 and Ne≥5∙106 are by efficiency εγ of it detection. The calculated this way the values for two intervals on Ne equals0.6 and 0.8 accodingly.

12. Distribution nμ - Ne

13. As in the distinguish region are absent the detected an events (absent a background), must used the next formula for valuation of upper limit for flux of primary gamma-rays at 90% confidence: Iγ=2.3/(S∙T∙εγ), where S=196m2 – the area of detected axes EAS, T – the pure time selec- tion of information and εγ – the efficiency of detection of showers from primary gamma-rays. The upper limits for Eγ≥1.3∙1015(Ne≥106) and for Eγ≥3.2∙1015(Ne≥5∙106), using for received the values of efficiency were obtained.

14. The estimationof integralflux of gamma-showersby“Carpet-2” data.Time an accumulation: 3390days

15. Distribution ofnμ - Nefor EAS with axes in“Carpet”with different areas[calculations]

16. Detection efficiency for gamma-ray showers with axes inside the “Carpet” [calculation]

17. “Carpet-3”experiment The preparation of the experiment is assumed step-by-step an increasing of continuous area MD at first to 410 m^2 and later to 615 m^2 one. For increasing of area detection of axes EAS will be placed 20 modules additionaly in wich are arranged in 9 of scintillator counters by area 0.92m^2 each. At present at underground tunnels are placed already 410 plastic scintillator counters with total continuous area 410m^2 that are completed by electronics.The calculations of efficiency of selection gamma-rays and sensitivity of different configurations of shower array from primary gamma rays were carried out.

18. Carpet-3 Carpet-3: planned to operate since 2018 Muon Detector 410 m2 2017 Additional 20 modules of surface detectors of 8.3 m2area (9 scintillation counters of area of 0.92 m2 in each module) December 2017

19. 2-d stage of the Muon Detector, 205 m2205 detectors are placed in the first tunnel

20. Carpet-3 sensitivity to the flux of diffuse cosmic gamma rays At next figure are shown the expectation limitations in flux of cosmic diffuse gamma-radiation for two of configurations of “Carpet-3 ”array and for two values of time collections of information. As seen, with area MD 410m^2 the new array will hase the best sensitivity to flux of primary gamma-rays with energy in the interval 100TeV-1PeV.

21. Estimates of the integral gamma-ray flux

22. Current situation with Carpet-3 construction Two underground tunnels are filled with scintillation counters of total continuous area of 410 m2 . The detectors are totally equipped with electronics and will be tuned together with data acquisition system at the end of 2016. Full-scale operation of 410 m2MD is planned to be started in the first quarter of 2017. 20 additional shower detectors will be installed to extend the array during 2017 with a total area of 180 m2 . Every such detector contains 9scintillation counters of 1 m2 area each.

23. Conclusion 1. The Carpet-3 air shower array is under construction at the Baksan Neutrino Observatory by step-by-step upgrade and extension. The aim is to study diffuse gamma-ray background at energy above 100 TeV. 2. After final accomplishment of this array it can be competitive in its class and will have a chance to get the world-best limit on the flux of gamma rays of cosmic origin. 3. This will allow one to solve the problem of origin of high-energy astrophysical neutrinos detected by IceCube.