1. Muon Capture on the Deuteron The MuSun Experiment
PSI Experiment R-08-01
physics update
overview run 2011
analysis progress
systematics of
impurities
beam request 2012
Claude Petitjean
μ-stop signals showing pileup of fusion events
BV43, Feb 22, 2012

2. physics update
μ- + d  ν + n + n measure rate Λd in μd() atom to <1.5%
simplest weak interaction process in a nucleus allowing for precise theory & experiment
nucleon FF (GP) from MuCap
ab initio QCD calculations with effective field theory
close relation to neutrino/astrophysics
solar fusion reaction p+p  de+
ν+d scattering in SNO exp.
model independent connection to μd by a single Low Energy Constant (LEC)
μ + d determines this LEC in clean
2 N system  “Calibrates the Sun”

3. recent calculations of ΛD
ΛD year authors method
[sec-1]
Ando et al., P. Lett. B533, EFT*
416± Ricci et al., N.P. A837, SNPA/EFT*
392.0± Marcucci et al., P.Rev.C83: EFT*
399.0± Marcucci, arXiv: [nucl-th] EFT
Adam, arXiv:1110:3183 [nucl-th] EFT
SNPA … Standard Nuclear Physics Approach (Potential Model + MEC)
EFT* … Hybrid Eff. Field Theory Calculation (Pot. Model, EFT op.)
EFT … full Effective Field Theory Calculation

4. experimental update Λd = 1/τμ-d - 1/τμ+ use lifetime method
≥ μ→eνν decays
measure τμ-d to 10ppm
Λd = 1/τμ-d - 1/τμ+
low temperature ~34K
D2 gas, density φ ~ 6%
spin state & hf transition
observable via
ddμ3He+n fusion reaction
new Cryo-TPC with ultra-pure deuterium gas at high density
full WFD readout to cope with small signals and fusion reactions
purity requirements ~ 1 ppb

5. the upgraded Cryo TPC vertical drift field 11 kV/cm
Vdrift = 5mm/μs h = 72 mm
D2 density 6.4% of lq.H2
(5.6 bar)
liquid Neon cooling circuit T ~34K
HV -80kV
grid -3 kV
0.4 mm
Be window
48 anode pads (Au-plt)
12 x 9 cm2

6. setup of MuSun at the πE3 beamline
e detector & n counters
cold box lq. Neon cooling
TPC
wfd‘s HV
D2 circulation & cleaning system

7. beam rates (kHz) with kicker
overview of run 2011
12 weeks incl. setup & tests
4.8 x 109 good μ- stops in fiducial vol.
with decay electron & 4 x 108 μ+ stops
21.2 TB μ- & 2.5 TB μ+ of clean data
improvements since run 2010b:
upgraded cryo-TPC op. at T = 34K-50K
produced new hydrogen-depleted
deuterium gas (cp < 10-4)
stable HV at 80 kV (no sparks)
better frontend electronics
gas chromatography w. online sampling
new X-ray detectors (Ge, NaJ)
clean neutron spectra by liq. detectors
new on-/offline analyzer programs 
new analysis framework („roadmap“)
drifttime effect  impurity control
beam rates (kHz) with kicker
μSC scint. Trigger
μSC & μPC pileup-protected
@ good TPC stop in fiducial vol. 5.6
@ good decay-electron track

8. MuSun analysis roadmap

9. muon beam μ→ z-x stopping distribution in TPC
beamspot
μSC & μPC
only 
beamspot
μSC & μPC
&TPC track 
1 pixel ~ 2 mm
z-x stopping distribution in TPC
8x6 pixels, first two used for
muon track identification  μ→

10. the accoustic problem in 2010 was solved with base line restorer
TPC signals
the accoustic problem in 2010 was solved with base line restorer
typical example of a muon stop event
the pulses are fitted
with a template close
to a Gaussian 

11. ES is a measurement of signal strength!
energy spectra of muon signals
red: muon energy of preceeding anode to stop (Eo)
blue: muon energy of stopping anode (E1)
black: S-energy ES = Eo + 2 E1  very important!
ES is a measurement of signal strength!

12. fusion events fusion channels in deuterium
ddμ → 3He(0.82 MeV) + μ + n(2.5 MeV) 88% R3He = 0.18 mm E3Heobs ~ 0.40 MeV
ddμ → 3Heμ(0.80 MeV) + n(2.5 MeV) 12% R3Heμ = 0.6 mm E3Heμobs~ 0.64 MeV
ddμ → p(3.0 MeV) + t(1.0 MeV) + μ Rp = 16 mm, Rt = 1 mm Etotobs ~ 3.7 MeV
total fusion yield ~5% at density φ = 0.06 (well known from former μCF exp.)
μ + separated 3He-fusion μ + separated hor. / vert. (p+t)-fusion
examples of muon stop events followed by dd fusion (separated in drift time)

13. fit of separated 3He fusion-recoils
 calibration of pads
E ~ 1.6 keV/ch
energy resolution
of TPC & analysis
σE ~ 50 keV
3He↑ ↑μ3He

14. energy depositions on stopping anode
many p+t fusions overlap with μ signal on stop anode!

15. fit of ~1 shift of μ- (μ+) data shows clean spectra (no bad stops)
lifetime spectra
fit of ~1 shift of μ- (μ+) data shows clean spectra (no bad stops)

16. Cs137 calibration spectrum
neutron spectra
liquid scint.
detector w.
improved magn. shield
Cs137 calibration spectrum
neutron time distribution at 2 diff. densities
slope shows depopulation of μdF=3/2 hf state
8 liquid scint. detectors with PSD electronics
PSD spectrum

17. spectra of muonic X-rays
germanium time spectra:
black: μSC trigger
red: μ-stop in fid. volume
germanium energy spectra (time prompt to the μSC):
black: requirement of a delayed electron
red: no electron requested (allows high-Z stops)

18. systematics: the problem with impurities
the distorting effect on the lifetime allows only ppb admixtures:
Element λdZ ΛdZ (s-1) Δλ (s-1)
N x 1011s cZ/ppb cZ/ppb
O x 1011s cZ/ppb cZ/ppb
vapor pressures of calculated equilibrium concentrations
selected elements of N2 & O2 gases vs temperature

19. drift time effect ES drops with drift time slope temperature dependent
chromatography
at 50K: 5 ppb N2
0.6 ppb O2 ↓
drift time effect
S-energy vs drift time at 50K
ES drops with drift time
slope temperature dependent
reduced after gas cleaning!
 handle on impurities
drift time effect vs temperature

20. search for optimal TPC condition
P-T diagram of cryogenic deuterium
higher density  higher P,T  more impurities ↔ faster spinflip
smaller density  smaller P,T  less impurities ↔ slower spinflip

21. work plan & beam request 2012
2012 is analysis and commissioning year:
further development of analysis programs
and Monte Carlo.
analyze run 2011.
repair and upgrade electron wire chamber system.
overhaul CHUPS circulation system.
improve cryo-TPC system - remove heat leaks.
new & improved frontend electronics.
prepare setup and beam tests in new (extended) πE1 area.
2 weeks (end September 2012) for πE1 commissioning.
2012 beam time request:
one 4-week cycle (October 2012) in πE1 area.
study impurity issues
test upgrades of apparatus.
final production runs in 2013/2014

22. top view of extended πE1 area (ready in fall 2012)
old πE1
Dolly
muSR