Experiment on search for neutron- antineutron oscillations using a projected UCN source at the WWR-M reactor A. Fomin Project leader: A. Serebrov PNPI, Gatchina, Russia International Workshop "Probing Fundamental Symmetries and Interactions with UCN“ 1 Mainz, Germany, April 11-15, 2016
Baryon Asymmetry 2
ILL beam experiment 3
ESS beam experiment 4
NNbar via UCN muon veto calorimeter pressure, magnetic shield tracker N t 2 – discovery potential Storage trap: height 2.5 m, v boundary = 6.8 m/s, diffusion 90 %, abs. in walls 3 10 -5 5
Progress of UCN sources 5 10 PNPI project [17] present 4 10 first test experiments SD 2 pulse mode 3 10 projects with superfluid He LANL-PNPI [8] [15-16] 2 10 ILL [4] ILL [13] -3 ILL [12] 1 UCN density, cm 10 PNPI [3] SD 2 Mainz [9] 0 PNPI 10 PSI-PNPI PNPI [10] PNPI [5] PNPI [6] -1 project 10 ILL first test SD 2 reactor SD 2 in pulse mode SRIAR -2 PNPI experiment test experiment 10 PNPI with SD 2 IAE -3 10 TUM PNPI -4 10 IAE -5 10 -6 10 JINR -7 10 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 years 6
MCNP neutron flux calculation results and heat generation in thermal column of WWR-M reactor at 15 MW Ф=4.5∙10 12 n/( с m 2 s) Ф( =9 А)=3∙10 10 n/( с m 2 sA) Q He =6 W He Т=1.2 К 19 W LD 2 Т=20 К Al, Q Al =13 W C Т= 30 0 К Pb Т=300 К LD 2 , Q LD2+Al =100 W C, Q C =700 W Pb, Q Pb =15 к W Ф=10 14 n/(cm 2 s) Q=15 MW 7 7
Project of UCN source at reactor WWR-M (PNPI, Gatchina) 8
MC model of the source 6 1 5 2 4 3 ( 1 ) source chamber; ( 2 ) neutron guide; ( 3 ) UCN trap; ( 4 ) membrane in front of the inlet to the UCN trap;( 5 ) pipe for filling the chamber; ( 6 ) pipeline for evacuation of the chamber (UCN gravitational shutter) 9
UCN density 6 10 source -3 UCN density, cm 5 10 trap 35 l 4 10 trap 350 l 3 10 0,7 0,8 0,9 1,0 1,1 1,2 1,3 1,4 1,5 T, K He II , s 6.7 100 23.3 600 10 Production of the source 10 8 UCN/s.
What is the probability for UCÑ to be reflected? 2 U 0 1 1 (1 i ) E R U 0 1 1 (1 ) i E W U U iW 0 U 0 11
We can consider two cases: R 0 1. (pessimistic case) R R ( . ) . 0 2 0 8 2. (optimistic case) U iW for n 0 U iW for n 0 12
Reflection coefficient for UCÑ 1,0 0,9 ~ ~ 0,8 E /U 0 =0.1 ~ ~ E /U 0 =0.15 0,7 ~ ~ E /U 0 =0.25 0,6 0,5 ~ R ~ ~ E /U 0 =1 0,4 0,3 0,2 ~ =0.2 0,1 0,0 0 1 2 3 4 5 6 7 8 9 10 ~ 13
UCN number in the trap for different storage trap radius 10 5x10 10 4x10 number of UCN in the trap 10 3x10 10 2x10 10 1x10 0 0 1 2 3 4 5 6 storage trap radius, m Storage trap: height 2.5 m, v boundary = 6.8 m/s, diffusion 90 %, abs. in walls 3 10 -5 14
UCN density for different storage trap radius 7000 maximum UCN density near the bottom 6000 5000 3 of the storage trap, n/cm 4000 3000 2000 1000 0 0 1 2 3 4 5 6 storage trap radius, m Storage trap: height 2.5 m, v boundary = 6.8 m/s, diffusion 90 %, abs. in walls 3 10 -5 15
UCN time of flight for different storage trap radius 600000 1 m 2 m density of distribution, arb. un. 500000 3 m 4 m 5 m 400000 6 m 300000 200000 100000 0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 t, s Storage trap: height 2.5 m, v boundary = 6.8 m/s, diffusion 90 %, abs. in walls 3 10 -5 16
N t 2 for different storage trap radius 11 1,6x10 11 1,4x10 11 1,2x10 11 1,0x10 2 , n·s 10 8,0x10 N·t 10 6,0x10 10 4,0x10 10 2,0x10 0,0 0 1 2 3 4 5 6 storage trap radius, m Storage trap: height 2.5 m, v boundary = 6.8 m/s, diffusion 90 %, abs. in walls 3 10 -5 17
Oscillation period 2 ( ) N t T nn N ~ 3 T years 0.9 N ( at 90% CL) 0 2.3 (1 2) 10 s (90% CL) 9 nn 18
UCN facilities at reactor WWR-M (preliminary) n , Gravitrap nEDM n , magnetic trap n ñ n n 19
UCN facilities at reactor WWR-M (preliminary) 20
Conclusion 1. Optimal size of the storage trap for NNbar oscillation experiment at reactor WWR-M: height 2.5 m, radius 3 m. 2. Increase of the experiment sensitivity is about 20 80 times to ILL level. 3. Oscillation period for 3 years: (1 2) 10 s (90% CL) 9 nn 21
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