The “Carpet-3” shower array for search of diffuse gamma radiation with energy Eγ>100TeV

1. The “Carpet-3” shower array for search of diffuse gamma radiation with energy Eγ>100TeV A.U. Kudzhaev for “Carpet-3” collaboration Institute for Nuclear Research, Russian Academy of Sciences, Moscow MOSCOW - 2017

2. CARPET-2

3. The “Carpet-2” shower array The layout of the “Carpet-2” multipurpose air shower array: 1-6 – outdoor huts with scintillators, 7 – the “Carpet”, 8 – the muon detector, 9 – a liquid scintillator detector, 10 – a plastic scintillator detector, 11 – a neutron monitor. The layout of the “Carpet-2” multipurpose air shower array: 1-6 – outdoor huts with scintillators, 7 – the “Carpet”, 8 – the muon detector, 9 – a liquid scintillator detector, 10 – a plastic scintillator detector, 11 – a neutron monitor. The layout of the “Carpet-2” multipurpose air shower array: 1-6 – outdoor huts with scintillators, 7 – the “Carpet”, 8 – the muon detector, 9 – a liquid scintillator detector, 10 – a plastic scintillator detector, 11 – a neutron monitor.

4. EXPERIMENT Two triggers of the Carpet array and the proper MD trigger formed by the coincidence scheme upon the actuation of any three out of five MD modules are used to record information. The Carpet and MD operate independent of each other and have different dead times of recording electronics. But time markers of events in the MD and Carpet are produced by one and the same clock, so that coincident events are reliably identified within a time interval Δt=1ms. The total number of relativistic particles within the Carpet (Nr.p.) and the number nμof muons recorded by the MD are experimentally measured quantities used to determine the energy of EAS and the total number of muons in it, respectively. The events satisfying the following conditions are included into processing: 1. Shower size are well within the “Carpet”; 2. Zenith angles of showers θ<40o; 3. Nr.p. >2·104; 4. The number of nonzero detectors is more than 300. After such a selection about 1.3·105 showers survived from all showers detecting during the period since 1999 to 2011.

5. Net time of data accumulation is equal to 3390 days(~9.2 years). For modeling showers the CORSIKA code v.6720 was used (model QGSJET01C for higher energy and FLUKA 2006 for low energy . 5400 showers from primary protons and 6597 showers from primary iron nuclei were simulated within the energy interval (0.316-31.6)PeV, as well as 815 showers from primary gamma rays in the range (0.3-9)PeV. As a result of modeling, the following averaged relations were obtained: Ep[GeV]=174·Ne0.48; Eγ[GeV]=138·Ne0.65 .

6. “Carpet” [196m2]

7. 2d tunnel ofMD(205 detectors)

8. The flux upper limits for diffuse cosmic gamma rays In order to distinguish showers from primary gamma rays against the background ordinary showers, the analysis of correlated dependence in the nμ- Ne plane of detected and simulated events has been carried out. In this work we analyze the region with Ne>6·105, in which one can separate the simulated gamma rays from ordinary EAS for the used method of processing experimental data. In order to evaluate the efficiency of selection of gamma rays at Ne>6·106 on the plane nμ- Ne it is necessary to isolate the region where only simulated gamma ray showers exist without any detected EAS. In this figure the boundary of this region is shown by a broken line. The ratio of the number of gamma-ray showers in this region to the total number at Ne>6· 106 is the detection efficiency εγ. The value of εγfor this interval of Ne estimated in this way, is equal to 0.96.

9. Since no detected events are present in this region (there is no background) one can use the following formula for estimation of the flux upper limit for primary gamma rays at the 90% confidence level: where S=200m2 is the area on which EAS axes are detected, T is the net time of data accumulation, and εγis 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 with energies Eγ>9.3·1014 eV (Ne>7.9·105), Eγ>1.4·1015eV (Ne>1.5·106), Eγ>2.2·1015 eV, Eγ>2.2·1015(Ne>106) were obtained. These fluxes are equal to Iγ=4·10-15[cm-2·s-1·sr-1], Iγ=5.1·10-15[cm-2·c-1·sr-1], and Iγ=3.8·10-15eV, respectively.

10. Dependence of nμfrom Ne in EAS for galaxy disc and out of one Black points – the events out of Galaxy disc, <nμ>=18.5±23.7 Read points - the events in Galaxy disc, (|b|<5o, 50o<l<200o, <nμ>=18±23.3 Such method of searching of gamma rays from Galaxy disc give not of positive effect. For positive effect it is necessary in order to the <nμ> of Galaxy must be less than of out Galaxy in 5 times. In further we are planned to investigate are known the points sources in our Galaxy.

11. The Carpet-3 experiment Realization of the experiment suggests that continuous area of MD should be increased at first up to 410m2 and then up to 615m2. Also, 20 additional shower detectors will be installed to extend the array. Every such detector will contain 18 scintillation detector of 0.5 m2 area each. At the present stage 410 scintillation detectors with total continuous area are installed in the MD underground tunnels, and they are totally equipped with electronics. The work on adjusting the electronics of scintillation detectors and on constructing data acquisition system for the given configuration of MD is in progress. The efficiency of selection of gamma ray showers and the array sensitivity to their detection are calculated for different configuration of the array.

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

13. Limits on the integral flux of gamma rays versus their energy This figure shows the expectation limits for flux of cosmic diffuse gamma rays for two configurations of the “Carpet-2” air shower array and for two values of data accumulation time. As is seen, even at the MD area of 410 m2 the new array will have the best sensitivity to the flux of primary gamma rays with energies in the range 100TeV-1PeV.

14. 1st tunnel ofMD(205 detectors)

15. New modules on the surface of the muon detectors

16. The new liquid scintillator detector for modules of ground part of “Carpet-3” shower array For modules “Carpet-3” shower array the liquid detector with scintillator in wrapping plastic have been constructed. The detector is represented the container by size 66x74x30cm3 made from thick layer veneer by thickness 10mm. AT the bottom of the detector 10 wrapping plastic are placed. A wrapping is represented itself a plastic bottle by size 14x14x31 cm3, in which is flooded scintillator on the basis reactive fuel T-6 with density 0.82g/cm3. In the capacity of light reflected of surface new detector was used an layer of white paint in one case, put on surface, and in another case a glued to surface an aluminium foil with the help sticky tape.

17. Appearance of the new detector. Disposition of plastic wrapping with liquid scintillator at the bottom of the detector . Disposition of plastic wrapping with liquid scintillator at the bottom of the detector .

18. The amplitude spectra from new detector • Comparison of the amplitude spectra on single muons, when • inner surface of the new detector is coated with • white paint; • aluminium foil Spectra have been received with the help of oscillograph LECROY WaveJet in voltage divider of detector U=-1700v. As seen of this picture the maximum of first spectrum corresponds to 8.5v and the second maximum corresponds to 12.5v. That is in second case the efficiency of light collection at 32% more then in the first case. Whence it follows that in the capacity of reflection photons in the new detector follow use an aluminium foil.

19. The characteristics of new scintillation detector 1. Amplitude signal from anode – 12mv; 2. Inhomogeneity of detector – 27%; 3. Total number of photoelectrons at the photocathode – 360; 4. Energey resolution – 45%.

20. Conclusion Search of local sources gamma-radiation with energy higher than 100TeV at the “Carpet” shower array of Baksan Neutrino Observatory for INR of RAS in 1980-s was carried out. From Crab Nebula have been detected the flare of gamma-radiation with energy higher 100TeV while for such sources, as CygnusX-3,HerX-1,Geminga, and 4U115+63 were obtained only upper limits of flux for its was Iγ=(1-5)·10-14[cm-2·c-1]. The predicted the flux of diffuse gamma-radiation of galaxy origin in our work, is closed to existed experimental limits in field lower than 5PeV and with improve sensitivity of “Carpet-3” gives possibility to detect or at least to obtain the best result of upper limit. The constructed liquid detector at “Carpet-2” array will be used in modules of “Carpet-3” which increase an area of location axes of showers, and thereby allow to increase a statistic of detected events, and to lower an energy threshold of primary spectrum of cosmic rays.