1. Study of VHE Cosmic Ray Spectrum by means of Muon Density Measurements at Ground Level I.I. Yashin Moscow Engineering Physics Institute, IIYashin@mephi.ru Vulcano 2008, 26th-31st May

2. A.G. Bogdanov, R.P. Kokoulin, G. Mannocchi, A.A. Petrukhin, O. Saavedra, V.V. Shutenko, G. Trinchero, I.I. Yashin A.G. Bogdanov, R.P. Kokoulin, G. Mannocchi, A.A. Petrukhin, O. Saavedra, V.V. Shutenko, G. Trinchero, I.I. Yashin Contents 1. Motivation 2. Local muon density phenomenology 3. DECOR data VS simulation 4. Conclusions Moscow Engineering Physics Institute, Russia Istituto Nazionale di Astrofisica, Sezione di Torino Universita di Torino, Italy Vulcano 2008, 26th-31st May

3. Motivation Motivation In EAS data interpretation, primary spectrum, composition, interaction characteristics, and their energy dependence are unknown. To solve the problem involving several unknown functions, measurements of different EAS observables are necessary. In this talk, phenomenology and recent data on a new EAS observable – local muon density distributions in a wide range of zenith angles – are considered. Vulcano 2008, 26th-31st May

4. Local muon density phenomenology Local muon density phenomenology If the size of the detector is small compared to typical distances of substantial changes of muon LDF, the detector may be considered as a point-like probe. In a muon bundle event, the local muon density D (in a random point of the shower) is estimated: D = (number of muons) / (detector area); [D] = particles / m 2. Collection area rapidly increases with zenith angle (~ 1 km 2 at 80  ) Vulcano 2008, 26th-31st May

5. Local muon density phenomenology Local muon density phenomenology Without considering fluctuations, spectrum of events in local density may be written as [Kokoulin at al., 2005] where N (> E) - primary spectrum, E is defined by the equation: [ events / (s sr)] For a nearly scaling LDF around some energy E 0 For a nearly scaling LDF around some energy E 0 and power type primary spectrum Vulcano 2008, 26th-31st May

6. General view of NEVOD-DECOR complex Side SM:8.4 m 2 each σ x  1 cm; σ ψ  1° Coordinate-tracking detector DECOR (~115 m 2 ) Cherenkov water detector NEVOD (2000 m 3 ) Vulcano 2008, 26th-31st May

7. A typical muon bundle event in Side DECOR X-projection X-projection Y-projection Y-projection Vulcano 2008, 26th-31st May

8. Muon bundle event (geometry reconstruction) Vulcano 2008, 26th-31st May

9. DECOR data summary Muon bundle statistics 2002 - 2007 (*) For zenith angles < 75°, only events in limited intervals of azimuth angle (with DECOR shielded by the water tank) are selected. Vulcano 2008, 26th-31st May m  Live time (hr) No. events  3 30 - 60 120   < 160; 200   < 240 75818137  5 30 - 60 120   < 160; 200   < 240 12968864  10 30 - 60 120   < 160; 200   < 240 26803272  3  60120   < 160; 200   < 240 15524109  5  60120   < 160; 200   < 240 101026786  10  60120   < 160; 200   < 240 199222013  10  750   < 360 19922395

10. DECOR data summary Distribution in multiplicity Vulcano 2008, 26th-31st May

11. DECOR data summary Distribution in zenith angle Vulcano 2008, 26th-31st May α ~ (4.5 - 4.8); β ~ (1.9 - 2.3)

12. Procedure of the analysis Procedure of the analysis Muon bundle experimental distributions N ev (m, θ, φ) Deconvolution accounting for S eff (θ,φ), Poisson fluctuations, trigger and selection conditions CORSIKA simulation of LDF for different A, E and θ Convolution with primary spectrum and composition model Local muon density spectrum dF (D, θ)/dD (detector independent) Vulcano 2008, 26th-31st May

13. Calculation details Primary “all-particle” spectrum: Power type spectrum with the knee at 4 PeV Below the knee: dN/dE = 5.0 (E, GeV)  2.7 cm -2 s -1 sr -1 GeV -1 ; After the knee: steepening to (   1) = 3.1. CORSIKA simulation of 2D muon LDF: CORSIKA 6.200 – 6.600 QGSJET 01c + GHEISHA 2002; SIBYLL 2.1 + FLUKA 2003.1b Set of fixed zenith angles, fixed primary energies Primary protons and Iron nuclei EMF Vulcano 2008, 26th-31st May

14. Effective primary energy range Effective primary energy range Lower limit ~ 10 15 eV (limited by DECOR area). Upper limit ~ 10 19 eV (limited by statistics). Vulcano 2008, 26th-31st May

15. Low angles: around the “knee” Vulcano 2008, 26th-31st May

16. θ = 50 º : 10 16 – 10 17 eV θ = 50 º : 10 16 – 10 17 eV Vulcano 2008, 26th-31st May

17. θ = 65 º : 10 16 – 10 18 eV Vulcano 2008, 26th-31st May

18. Combined estimator of primary energy Vulcano 2008, 26th-31st May Event-by-event analysis: for every event with some set of observables (m, θ, φ) it is possible to attribute a certain effective primary energy. Densities: (0.05 - 2.0 м -2 ); zenith angles: (40º - 80º); E ~ (10 16 - 10 18 эВ)

19. Combined estimator of primary energy Vulcano 2008, 26th-31st May

20. Combined estimator of primary energy Vulcano 2008, 26th-31st May

21. Large angles: around 10 18 eV Vulcano 2008, 26th-31st May

22. Conclusions 1 LMDS method 1.A new approach based on local muon density spectrum phenomenology provides possibility to study PCR in a very wide energy range (from 10 15 to 10 19 eV) by means of a single, not large detector. 2.Local muon density spectra are sensitive to primary spectrum and composition and forward region of hadronic interactions. 3.Analysis of local muon density spectra together with data of experiments on other EAS observables will allow putting new constraints on combinations of spectrum, composition and interaction models. Vulcano 2008, 26th-31st May

23. Conclusions 2 DECOR data analysis Conclusions 2 DECOR data analysis are in a reasonable agreement with expectation in the knee energy region; favor an increase of the effective primary mass at approaching energies 10 17 eV; indicate an increase of local muon density spectrum slope at effective primary energy around 10 17 eV. Within the frame of the considered spectrum and interaction models, DECOR data: Vulcano 2008, 26th-31st May

24. Thank you for the attention! Vulcano 2008, 26th-31st May