1. Yu.V. Stenkin, 32 ICRC. Beijing'20111 The PRISMA project and the cosmic ray knee problem Yuri V. Stenkin Institute for Nuclear Res. of RAS, Moscow, Russia

2. Yu.V. Stenkin, 32 ICRC. Beijing'20112 The Project aims Why PRISMA? PRImary Spectrum Measurement Array The main goal is: TO SOLVE THE “KNEE PROBLEM” Other aims: –cosmic rays spectra and mass composition –cosmic ray sources –applied Geophysical measurements

3. Yu.V. Stenkin, 32 ICRC. Beijing'20113 History & Motivation Why do we need a new project? 1. The “knee problem” is a milestone of the cosmic ray physics. 2. Very few experiments have been designed specially for that. (KASCADE and Tibet AS are the best ones). 3. The problem still exists.

4. Yu.V. Stenkin, 32 ICRC. Beijing'20114 The “knee problem” The “knee problem” The problem is more than 50-years old! 1. Astrophysical explanation. In 1958 there was published a paper (G.V. Kulikov & G.B. Khristiansen) claiming the knee existence in cosmic ray energy spectrum. They observed a sharp change of slope in EAS size spectrum and proposed a model describing this effect as an evidence of existence of 2 sources of c. r.: Galactic and Metagalactic ones. 2. Nuclear-physical explanation. But, from the beginning and up to now there exist alternative explanations of this effect by dramatic change of particle interactions at these energies (S.I.Nikolsky, Kazanas & Nikolaidis, A.A.Petrukhin). Very few people know that there exist one more explanation.

5. Yu.V. Stenkin, 32 ICRC. Beijing'20115 3. Phenomenological explanations The knee in electromagnetic component can be explained by a break of equilibrium between the EAS components at energy of ~ 100 TeV / nucleon when the number of cascading hadrons is close to 0. Proposed in: Yu. Stenkin. Mod. Phys. Lett. A, 18, 1225 (2003)

6. Yu.V. Stenkin, 32 ICRC. Beijing'20116 When the break occurs? At E~100 TeV / nucleon For p: ~100 TeV For Fe: ~5 PeV (just the knee region) For details see: Yu. Stenkin, Phys. of Atom. Nucl., 71 (2008), 99 This figures are sequences of : L int = 90 g/cm 2 in air the Earth’s atmosphere thickness =1030 g/ cm 2 (depending on altitude)

7. Yu.V. Stenkin, 32 ICRC. Beijing'20117 Experiments Experiments Tibet AS vs KASCADE Both gave many interesting results. BUT, their results contradict each other and they did not answer the question on the knee origin and thus, the knee problem is still open! Moreover, the problem became even less clear…. (see G. Schatz. Proc. 28th ICRC, Tsukuba, (2003), 97; Yu. Stenkin. Proc. 29th ICRC, Pune (2005), v.6, 621; M.Amenomori et al. Astrophys. J, (2008), v.678, 1165)

8. Yu.V. Stenkin, 32 ICRC. Beijing'20118 to make a device based on new principles and on novel experimental approaches How the problem could be solved? On my opinion the only way is:

9. Yu.V. Stenkin, 32 ICRC. Beijing'20119 PRISMA could be the solution PRISMA Prism (Yu. Stenkin. ArXiv: 0902.0138v1 [Astro-ph.IM])

10. Yu.V. Stenkin, 32 ICRC. Beijing'201110 New principles The main EAS component is: hadrons Therefore, let us concentrate mostly on the hadronic component Bun, instead of huge and expensive hadron calorimeter of fixed area, let us make simple, inexpensive and of unlimited area detector. How this could be done?

11. Yu.V. Stenkin, 32 ICRC. Beijing'201111 New Methods New method has been developed in our Lab. in 2001. The method is based on thermal neutron “vapour” accompanying EAS. (See Hamburg Conference). Later we developed special detector for this purpose - en-detector.

12. Yu.V. Stenkin, 32 ICRC. Beijing'201112 The en-detector design 6 Li(n,a) 3 H+4.8 MeV 160,000 photons per capture ZnS(Ag) is a unique scintillator for heavy particles detection: Scintillator: ZnS(Ag)+ 6 LiF Similar to that using in neutron imaging technique 1 -PE water tank,  =72 cm, h=57 cm 2 -lid  =30 см 3 - 6’’ PMT 4 - scintillator, s=0.35 м 2 5 - reflecting cone Detection efficiency ~ 20%

13. Yu.V. Stenkin, 32 ICRC. Beijing'201113 en-detector design

14. Yu.V. Stenkin, 32 ICRC. Beijing'201114 N-carpet: 400*1m 2 en- detectors grid with spacing of 5 m Central muon detector: 400*1m 2 plastic scinillators Muon detector tunnels: 1200*1m 2 plastic scintillators Outer trigger detectors: 4*25*1m 2 plastic scintillators

15. Yu.V. Stenkin, 32 ICRC. Beijing'201115 Main features: Range in primary energy: from ~10 TeV to ~30 PeV energy resolution: ~ 15 - 20 % angular resolution: ~ 1 o core location:< 1.0 m capability to measure EAS size independently in: e, n and  capability to select AS with equal E/nucleon

16. Yu.V. Stenkin, 32 ICRC. Beijing'201116 EAS size distribution in different components

17. Yu.V. Stenkin, 32 ICRC. Beijing'201117 A prototype of PRISMA (the ProtoPrisma array, see poster 22 HE1.4, ID 1136 ) 16 en-detectors Location: on 4th floor inside building in MEPhi, Moscow

18. Yu.V. Stenkin, 32 ICRC. Beijing'201118 The ProtoPrisma schematic view

19. Yu.V. Stenkin, 32 ICRC. Beijing'201119 e n Big EAS event example. Ne=(4.5  0.8)10 6, s =1.15, x = 15 m; y =23m Nn = 106

20. Yu.V. Stenkin, 32 ICRC. Beijing'201120 Location Collaboration Institutions budget high altitude is preferable Tibet would be the best location It depends on: Our plans...

21. Yu.V. Stenkin, 32 ICRC. Beijing'201121 1. The PRISMA project R&D 2. Expand the ProtoPrisma up to 32 en-detectors (2011) 3. Developing and construction of high-altitude prototype in collaboration with Chinese physicists (2012) 4. Collaboration with LHAASO project 5. Geophysical researches

22. Yu.V. Stenkin, 32 ICRC. Beijing'201122 Large High Altitude Air Shower Observatory LHAASO Project: γ-astronomy and origin of CR Core Detector Array PRISMA? (from Zhen Cao report)

23. Yu.V. Stenkin, 32 ICRC. Beijing'201123 PRISMA YBJ prototype (2012) (from Zhen Cao report)

24. Yu.V. Stenkin, 32 ICRC. Beijing'201124 Involved Institutions: 1. Institute for Nuclear Research, Moscow 2. MEPhI, Moscow 3. Skobeltsyn Institute, MSU, Moscow 4. IHEP, Beijing, China 5....

25. Yu.V. Stenkin, 32 ICRC. Beijing'201125 Thank you!

26. Yu.V. Stenkin, 32 ICRC. Beijing'201126 Depth in atmosphere No of particles From Hayakawa manual on cosmic ray physics EAS components equilibrium Break of equilibrium Break in attenuation “knee” in N e spectrum