Technische Universität München PENeLOPE (Precision Experiment on the Neutron Lifetime Operating on Proton Extraction) D. Gaisbauer a , W. Gebauer a , E. Gutsmiedl a , F. Haas a , F.J. Hartmann a , M. Losekamm a , D. Margiotta a , S. Materne a , J. Nitschke a , S. Paul a , R. Picker b , D. Renker a , T. Pöschl a , S. Ritt c , W. Schreyer a , A. Senft a , D. Steffen a , R. Stoepler a , C. Tietze a , F. Wiest a a Technische Universität München, Physik Department, Germany b California Institute of Technology, Pasadena, USA c Paul Scherrer Institut, CH-5323 Villigen, Switzerland
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Technische Universität München
PENeLOPE (Precision Experiment on the Neutron Lifetime Operating on Proton Extraction) D. Gaisbauera, W. Gebauera, E. Gutsmiedla, F. Haasa, F.J. Hartmanna, M. Losekamma, D. Margiottaa, S. Maternea, J. Nitschkea, S. Paula, R. Pickerb, D. Renkera, T. Pöschla, S. Rittc, W. Schreyera, A. Senfta, D. Steffena, R. Stoeplera, C. Tietzea, F. Wiesta aTechnische Universität München, Physik Department, Germany bCalifornia Institute of Technology, Pasadena, USA cPaul Scherrer Institut, CH-5323 Villigen, Switzerland
Technische Universität München Spin flip suppression
• spin flip: – systematic studies possible varying the central current – around 2-3 % of dep. UCN reach UCN detector MC simulations: – spin-flip loss time τSF > 109 s – systematic effect: ∆τn < 0.01 s
Technische Universität München Electrons or protons ???
35
𝐸𝑝 < 750 𝑒𝑒 𝐸𝑒 < 780 𝑘𝑒𝑒
⇒ electrostatic manipulation of p possible ⇒ detector on HV ⇒ electrons are repelled by magnetic mirror effect
30 kV
Electrons protons
collection efficiency: 35 % 70 %
z [m
]
r [m]
Technische Universität München Particle detection
• requirements on proton detector – low energy < 30 keV – low temperature < 77 K – large area > 0.2 m2
– strong magnetic field > 0.5 T – high vacuum < 2 x 10-8 mbar – affordable << magnet costs
• various concepts were explored – thin pure CsI + APD columnar structure – bulk CsI + APC light at APD marginal – gas detector gas diffusion to high – MCPs not stable enough – direct APD detection bingo! – bulk CsI + SiPM very hip these days, under investigation
Technische Universität München Avalanche Photodiodes
15.03.2012
• Reverse-biased p-n-junction • Primary photo electron
accelerated in electric field and multiplied in an avalanche
• large gain, but proportional • Operable at large magnetic field
and low temperature (~77K)
37
5 mm
Technische Universität München APD as direct Proton Sensor
15.03.2012 38
• several hundreds of electron-hole pairs are produced • illumination with 30 keV protons from “paff”-accelerator at 77K
Technische Universität München APD as direct Proton Sensor
15.03.2012 39
• several hundreds of electron-hole pairs are produced • illumination with 30 keV protons from “paff”-accelerator • even 5 keV protons can be observed • costs are pretty steep • >1000 channels
• 2004 - physics solution for magnet found • 2007 - first prototype coil tested: partial failure... • after further setbacks: change of contractor 2009
Technische Universität München Coil revision 2010
- topology unchanged - bigger coil distances - less coils 44 ⇒ 28 - max. field in conductor 6.1 ⇒ 5.5 T
# of cycles necessary to reach 0.1 s in both detection schemes
610
time necessary 37 days
⇒ BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
NLFS: number of low field seekers - fM: fraction of marginal UCN - τn: beta decay lifetime -τM: storage lifetime of marginal UCN NHFS: number of high-field seekers - τHFS: storage lifetime of HFS - B: const background
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 55
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 0.7s
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 56
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 0.7s
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 57
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 30s
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 58
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s
⇒
Technische Universität München Rest gas interaction
• rest gas interaction: – for efficient proton collection: p < 10-7 mbar – n absorption (nitrogen) and upscattering (hydrogen): p < 3 · 10-8 mbar – mass spectrometry to examine partial pressures
H2 partial pressure
⇒
Technische Universität München Experiment phases (1) Magnet off, filling in polarized
neutrons (200 s)
storage volume
UC
N guide
r-z plot x-y-z plot
detector for decay particles
n absorbing rings spectrum cleaning
Technische Universität München Experiment phases (1) Magnet off, filling in neutrons
(200 s) (2) spectrum cleaning
(160 s) (3) ramping up magnet
(50-200 s) (4) cleaning high-field seekers
(ca 100 s) (5) neutron storage, counting
of protons and depolarised UCN (up to 8000 s)
E: 0-115 neV magnets on filling tube closed detector open protons: 106 x slower electron: 109 x slower
Technische Universität München Exp. phases: 5 - ramp-down, UCN counting
(1) Magnet off, filling in neutrons (100 s)
(2) spectrum cleaning (160 s)
(3) ramping up magnet (50-200 s)
(4) cleaning high-field seekers (ca 100 s)
(5) neutron storage, counting of protons and depolarised UCN (up to 3000 s)
(6) ramping down magnet (50-200 s)
(7) UCN counting (250 s)
neutron counting collection efficiency around 75 %
E: 0-108 neV ramping down in 10 s filling tube closed detector open
storage volume
UC
N guide
Technische Universität München Systematic effects
• spin flip: – around 5 % of dep. UCN reach UCN detector – spin-flip lifetime τSF > 109 s systematic effect: ∆τn < 0.01 s
• UCN energy distribution – proton collection efficiency is space- and energy dependent – time-evolving effects may change efficiencies – not expected, but may be examined through energy shaping:
• absorber movable • magnetic trap depth adjustable • “U” before experiment
Is our absorber design capable of removing high energy neutrons
sufficently?
⇒ test of different absorber materials down to temperatures of 10 K ⇒ energie selective measurement
UCN valves
10.11.2012 Physik Department E18 64
„UCN plug“
Technische Universität München Statistical experiment simulation
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
NLFS: number of low field seekers fM: fraction of marginal UCN τn: beta decay lifetime τM: storage lifetime of marginal UCN NHFS: number of high-field seekers τHFS: storage lifetime of HFS B: const background
Technische Universität München High-field seeker cleaning II
• influence of waiting time on measured lifetime???
• proton detector sees lower storage time of high-field seekers
• Why not neutron detector?
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅+
⋅+= 1064404-880 e125.0e10 e(t)
measured neutron lifetime for fixed absorber
NLFS: number of low field seekers fM: fraction of marginal UCN τn: beta decay lifetime τM: storage lifetime of marginal UCN NHFS: number of high-field seekers τHFS: storage lifetime of HFS B: const background
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅+
⋅+= 1064404-880 e125.0e10 e(t)
measured neutron lifetime for fixed absorber
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅⋅+
⋅+= − 10834404-880 e104.2e10 e(t)
measured neutron lifetime for lowered absorber
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
⇒ better, but not good enough
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
measured neutron lifetime for lowered absorber
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
⇒ better, but not good enough
⇒ spin filter is needed ⇒ 90 % polarization is
enough
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
measured neutron lifetime for lowered abs + spin filter
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅⋅+
⋅+= − 10844404-880 e104.2e10 e(t)
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
⇒ better, but not good enough
⇒ spin filter is needed ⇒ 90 % polarization is
enough
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅⋅+
⋅+= − 10844404-880 e104.2e10 e(t)
measured neutron lifetime for lowered abs + spin filter
Technische Universität München Coil bumpiness... consequences