2-8 July 2017 KBR, Terskol (BNO); KChR, Nizhnij Arkhyz (SAO) The International Conference  SN 1987A, Quark Phase Transition in Compact Objects and Multimessenger Astronomy 2-8 July 2017 KBR, Terskol (BNO); KChR, Nizhnij Arkhyz (SAO)

Institute for Nuclear Research, Russian Academy of Sciences, Moscow Search for diffuse gamma radiation with energy Eγ > 100 TeV at the Carpet-3 experiment. D.D. Dzhappuev Institute for Nuclear Research, Russian Academy of Sciences, Moscow

Introduction Early experiments that tried to implement this idea: The idea to search for high-energy gamma rays by way of detecting muon-poor showers belongs to Maze and Zawadski (1960). This seemed to be the simplest way of distinguishing gamma-ray induced showers from ordinary EAS. Early experiments that tried to implement this idea: Lodz group (Gawin et al., 1968) Yakutsk (Glushkov et al., 1985) Tien Shan (Nikolsky et al., 1987) Mt. Chacaltaya (Suga et al., 1988) Some of these experiments pretended to detect gamma rays in the energy region (10^14 - 5.10^17) eV. However, their results were of limited statistical significance and were not confirmed later.

More recent experiments in the range 3.10^14 - 5.10^16 eV EAS-TOP (Aglietta et al., 1996) CASA-MIA (Chantell et al., 1997) KASCADE (Schatz et al., 2003) for the energy region 5.10^15 - 2.10^17 eV MSU (Fomin et al, 2013, 2014) KASCADE-Grande(D. Kang et al, 2015 ). at energies higher than 10^18 eV Haverah Park (Ave et al., 2000) AGASA (Shinozaki et al., 2002; Risse et al., 2005;Rubtsov et al.,2006) Yakutsk (Glushkov et al., 2007, 2010) PierreAuger (Abraham et al., 2008, Abreu et al., 2011)

Limits on the integral gamma-ray flux from PeV to ZeV . Full boxes (red online): MSU; open triangles (EAS-TOP) , open boxes (CASA-MIA ), open diamonds (KASCADE ), gray diamonds(KASCADEGrande full triangles (Yakutsk), full diamonds (Pierre Auger) full circles (AGASA ), large full boxes (Telescope Array). Only upper limits were obtained in these experiments, being considerably lower than previously announced detections.

A new impetus to interest in this problem was given by publications of the IceCube results on detection of high-energy astrophysical neutrinos (Aartsen et al., 2013). Neutrinos produced in decays of charged pions should be accompanied by gamma rays produced in decays of neutral pions. This is the motivation for new specialized experiments with more precise measurements of the flux of diffuse gamma rays at energies higher than 100 TeV.

The diffuse cosmic photon integral flux versus the photon minimal energy [data of experiments]

“Andyrchy” EAS array “Carpet-2” EAS array BUST Tunnel entrance

CARPET-2 air shower array

The Carpet array (400 detectors)

1st stage of the Muon Detector, 175 m2 , in operation since 1999

Simulation of the experiment The CORSIKA code v. 6720 (QGSJET01C FLUKA 2006) was used. 5400 showers from primary protons with energy in the interval (0.316 - 31.6) PeV were simulated; 3665 showers from iron nuclei, and 3360 showers from primary gammas. As a result, correlation plots nμ – Ne were obtained, where nμ is the number of muons in the MD of area of 175 m2 , and Ne is the total number of relativistic particles in the Carpet; average energies of primary protons and gamma as functions of Nr.p : Ep [GeV] =174•Nе.0.48 Eγ [GeV] =138•Nе.0.65

Nμ - Ne distribution for EAS with axes well inside the Carpet at an infinite MD area [calculation]

nμ - Ne distribution for EAS with axes well inside the Carpet SМD = 175 m2 [simulation]

Experimental data Energy threshold for muons is 1 GeV. The period of data is 1999 – 2011. The events satisfying the following conditions were selected : 1) shower axes within the Carpet (200 m2) ; 2) zenith angles θ < 40° ; 3) Nr.p in the Carpet ≥ 104 ; 4) number of nonzero detectors in the Carpet greater than 300. 130000 such showers for 3390 days of array operation.

nμ – Ne distribution: experiment and CORSIKA gammas

The upper limits on the integral flux of diffuse cosmic gamma rays , Since no detected events are present in this region (there is no background) one can use the following formula for estimation of the upper limit on the integral flux of primary gamma rays at the 90% confidence level: where S = 200 м2 is the area on which EAS axes are detected, T is the net time of data accumulation, and εγ is the detection efficiency for showers from primary gamma rays. Using the derived values of efficiency the upper limits for the flux of diffuse cosmic gamma rays were obtained. Ne Eγ[eV] NB εγ log10(Eγ Iγ(>E) [eV cm-1s-1 str-1]) ≥ 6×105 ≥ 9.3×1014 0.95 0.61 ≥ 106 ≥ 1.3×1015 0.99 0.85 ≥ 5×106 ≥ 3.2×1015 1.0 0.92

Upper limits on the integral flux of diffuse gamma rays

Detection efficiency for gamma-ray showers with axes inside the Carpet [calculation] 

Layout of the Carpet-3 air shower array Carpet-3: planned to operate since 2018 Muon Detector 410 m2 December 2017 Additional 20 modules of surface detectors of 9 m2 area (18 scintillation counters of area of 0.5 m2 in each module) 2017-2018 1-7 are the outdoor huts with scintillators, 8 is the Carpet, 9 is neutron monitor, and 10 is the muon detector, red squares represent new modules with scintillation detectors.

Carpet-3 sensitivity to the flux of diffuse cosmic gamma rays

Conclusions 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.