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Contents. Introduction (motivation of precise measurements of neutron lifetime, history of experimental accuracy improvement). a. Result of neutron lifetime measurements with gravitational trap of ultracold neutrons.

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  1. Contents • Introduction (motivation of precise measurements of neutron lifetime, history of experimental accuracy improvement). • a. Result of neutron lifetime measurements with gravitational trap of ultracold neutrons. • b. Preliminary result of neutron lifetime with magnetic trap of ultracold neutrons. • Neutron lifetime data for Standard Model and cosmology. • Conclusion.

  2. Neutron decay and Standard Model CKM mixing matrix: W.Marciano A.Sirlin PRL 96, 032002 (2006) Required experimental accuracy for n and A has to be about 10-3 and better.

  3. Neutron decay and (V-A) test of Standard Model

  4. A-asymmetry measurements (history of experimental results)

  5. Neutron lifetime measurements (history of experimental results) n=6.5

  6. Recent neutron lifetime experiments PNPI with collaborators • Result of neutron lifetime measurements with gravitational trap of UCN (878.50.8) s (PNPI-ILL-JINR) • Preliminary result of neutron lifetime with magnetic trap of UCN (874.6+4.0-1.6) s (PNPI-ILL-TUM)

  7. Neutron lifetime measurements with gravitational trap of ultracold neutrons PNPI-ILL-JINR Setup for the measurement of n-lifetime at ILL (Grenoble, France)

  8. Scheme of “Gravitrap”, the gravitational UCN storage system • 1 – neutron guide from UCN Turbine; • 2 – UCN inlet valve; • 3 – beam distribution flap valve; • 4 – aluminium foil (now removed); • 5 – “dirty” vacuum volume; • 6 – “clean” (UHV) vacuum volume; • 7 – cooling coils; • 8 – UCN storage trap; • 9 – cryostat; • 10 – mechanics for trap rotation; • 11 – stepping motor; • 12 – UCN detector; • 13 – detector shielding; • 14 – evaporator

  9. Deposition of LTF on the trap surface • The chemical formula of LTF contains only C, O and F. • Molecular weight - 2354 • Density at r.t. 1.825 g/ml • Vapour pressure at r.t. • 1.5*10-3 mbar • Fermi potential 102.8 neV • Calculation based on cold neutron transmission data predicts for LTF at 190K h=2*10-6( Yu.N.Pokotilovski, JETP 96, 2003) LTF evaporator is heated to +1400C Vacuum Trap surface is cooled to about -1500C

  10. Time diagram of measuring cycle

  11. Method of n-lifetime measurement Total probability of UCN losses: Probability of losses in trap walls:

  12. Calculation of loss weighted wall collision frequency

  13. Extrapolation to n- lifetime ( joint energy and size extrapolation) • The result of joint (size and energy) extrapolation: • The result of energy extrapolation: 13 s 5 s • The result of size extrapolation: 7 s • Size extrapolation has rather weak dependence on m(E) and we take it as the most reliable. The most close extrapolation to neutron lifetime (5 s only) is reached in this experiment!

  14. Final result and list of systematic corrections and uncertainties tn [s] = 878.5 ± 0.7stat ± 0.3syst

  15. Neutron storage bottle (made of permanent magnets) PNPI-ILL-TUM Preliminary measurement of neutron lifetime does not confirm world average value and is more close to measurements with gravitational trap.

  16. Neutron decay and Standard Model (status in 2003)

  17. Data analysis with the most precise measurements of neutron decay nVud ΔVud=2.4σ 00Vud Δ=2.4σ The improvement of the accuracy of A-measurements (factor of 3 or more) is extremely important.

  18. Future projects for correlation coefficients D.Dubbers TPFNP, University of South Carolina (USA), October 14-15, 2005

  19. Future neutron lifetime projects P.Geltenbort TPFNP, University of South Carolina (USA), October 14-15, 2005

  20. Neutron decay and cosmology G. J. Mathews, T. Kajino, T. Shima, Phys. Rev. D 71, 021302(R) (2005) n, world average n, “Gravitrap” result New n=(878.50.8) s confirms nb/n from CMB.

  21. Conclusion • The most precise measurement of neutron lifetime with gravitational trap of UCN (878.50.8) s is in the contradiction with world average value (885.70.8) s - n=6.5 standard deviation. • Preliminary measurement of neutron lifetime with magnetic trap (874.6+4.0-1.6) sdoes not confirm world average value and is more close to result of measurement with gravitational trap. • The most precise measurements of n and A-asymmetry are in better agreement with unitarity test of CKM. • New n=(878.50.8) s confirms nb/n from CMB. • The future improvement of =GA/GV measurement is extremely important for V-A test of Standard Model on the level 5∙10-4 of nVud. • There are the prospects to reach the level 5∙10-4.

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