1. Big Gravitational Trap for neutron lifetime measurements
A. Fomin
Project leader: A. Serebrov
PNPI, Gatchina, Russia
Physics of fundamental Symmetries and Interactions - PSI2013
PSI, Switzerland
8-12 September 2013

2. Gravitrap  Big Gravitrap
Increasing of “wide” trap volume is 5.3.
Increasing of “narrow” trap volume is 18.
Statistical accuracy 0.7 s → 0.2 s;
Vacuum correction 0.4 s → 0.04 s;
Measurement in two positions without disassembling;
Improvement of loss factor ? 210-6 → 10-6 ?
Expected accuracy: statistical ~ 0.2 s
systematical < 0.1 s
878.5 ± 0.7stat ± 0.3sys s
Phys. Lett. B 605, 72 (2005)
Phys. Rev. C 78, (2008)

3. The method of neutron lifetime measurement
with gravitationally trapped ultracold neutrons

4. Russian traditions
Tsar Bell
Tsar Cannon
Tsar Gravitrap

5. Scheme of Big Gravitational Trap
insert
measurements without insert
UCN trap
UCN
valve
detector
measurements with insert
axis of trap and insert rotation
UCN

6. Design of Big Gravitrap

7. Manufacturing of Big Gravitrap

8. Manufacturing of Big Gravitrap

9. MC simulation of neutron lifetime experiments
MC simulation, data analysis:
measured value nm
initial value n0
nm  n0 =?
MC code A.K. Fomin, PhD Thesis, PNPI, Gatchina, 2006
Gravitrap
Phys. Lett. B 605, 72 (2005)
Phys. Rev. C 78, (2008)
MAMBO I
JETP Lett. 90, 555 (2009)
Phys. Rev. C 82, (2010)
KI experiment
JETP Lett. 92, 40 (2010)
Big Gravitrap
Technical Physics 11 (2013)

10. High precision Monte Carlo simulation
PNPI computing clusters:
1. ITAD cluster - photo
2. PC Farm
6.41011 neutron histories
1.5 year of statistics accumulation

11. Time diagram of measurement cycle
t, s
, degree
Etrap, neV
filling
300
180
monitoring
500 15
60.1
holding
300; 2000
78.5
emptying 1
200 19
55.2
emptying 2 24
49.3
emptying 3 33
39.1
emptying 4

12. UCN spectrum for each of 4 emptyings

13. Extrapolation to neutron lifetime
with insert
without insert
nm  n0, s
without insert
0.05 ± 0.54
with insert
–0.16 ± 0.32
joint
–0.05 ± 0.10

14. Thermal screens
Thermal screen “mushroom” near the bottom of the trap does not slow down emptying process.

15. Inserts of different heighta b a c d e f b
wrong spectrum  syst 0.05 s (with insert)
No systematic because corresponding
MC spectra will be used for  calculation.

16. Stiffening angle wrong spectrum  syst 0.01 s (without insert)
No systematic because corresponding MC spectra will be used for  calculation.

17. Extrapolation to neutron lifetime
with insert
without insert
nm  n0, s
without insert
0.05 ± 0.54
with insert
–0.16 ± 0.32
joint
–0.05 ± 0.10

18. Plan of Big Gravitational Trap position at PF2 MAM at ILL
EDM spectrometer
Big Gravitational Trap
UCN turbine

19. Conclusion
Monte-Carlo model of Big Gravitrap is built. The systematic uncertainty connected with a method of calculation of effective frequency of UCN collisions in the trap is defined with value of 0.1 s.
Manufacture of the setup is almost completed. Vacuum tests are done. Now cryogenic tests are planned.