Precision measurement of the muon mass by 1S-2S laser ...
Transcript of Precision measurement of the muon mass by 1S-2S laser ...
Precision measurement of the muon mass by 1S-2S laser spectroscopy of muonium
Takahiro Hiraki (on behalf of the collaboration)
MAC/MuSAC 2019
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Collaboration list- T. Hiraki, H. Hara, Y. Imai, T. Masuda, Y. Miyamoto,
S. Uetake (PI), S. Yamamoto, K. Yoshimura
- Y. Ikedo, N. Kawamura, A. Koda, T. Mibe, Y. Miyake, Y. Oishi,M. Otani, S. Patrick, K. Shimomura, K. Suzuki, T. Yamazaki, M. Yoshida
- C. Zhang, Y. Mao
- K. Ishida
- S. Kamal
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Okayama university
KEK
Peking university
Riken
University of British Columbia
introduction 3
12𝑆𝑆1/2
22𝑆𝑆1/2
𝐹𝐹 = 1
𝐹𝐹 = 0
𝐹𝐹 = 0𝐹𝐹 = 1
• Muonium (Mu: μ+e-): pure leptonic two-body bound state- possible to precisely calculate transition frequencies
between states such as Mu 1S-2S and hyperfine structure (HFS)- Mu transition frequencies can be written as:
• Mu transition frequencies depends on precisely-measuredfundamental parameters and muon mass (𝑚𝑚𝜇𝜇)
- Current muon mass precision comes from HFS measurement
introduction 4
• goal of this project:measure Mu 1S-2S transition frequency with a precision of 100 kHz
- ~100 improvement from the previous experiment ➡ muon mass precision: 120 ppb→~10 ppb- contribution to CODATA (and PDG) from Japan
• Current theoretical precision of HFS is dominated by muon mass precision
• If this precision is achieved by Mu 1S-2S measurement,theoretical precision of Mu HFS will be 515 Hz → ~40 Hz
- Hadronic vacuum polarization (233 Hz), electroweak effect (65 Hz) can be confirmed with measurement of HFS (by MuSEUM experiment)
M. I. Eides, Phys. Lett. B 795, 113 (2019)
history of muonium 1S-2Syear Japan abroad1987 First laser Mu 1S-2S exp.
S. Chu, A.P. Mills, Jr. A.G. Yodh,K. Nagamine, Y. Miyake, T. Kuga
1999 Mu 1S-2S exp. at RAL- Current best precision
2009 J-PARC start operation- high intensity muon
source available
before 2017 no proposal of Mu 1S-2Sexperiment
new Mu1S-2S project started at PSI
late 2018 this project started2019 budget proposal approved
(科研費基盤S, S. Uetake (PI), K. Shimomura, M. Yoshida,T. Yamazaki, M. Yoshimura)
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preparation
past Mu 1S-2S experiment 6
V. Meyer et al., Phys. Rev. Lett. 84, 1136 (2000)
• usage of pulse laser causes broad spectra (limit precision)- narrow-linewidth CW laser will greatly improve precision- lower excitation rate is covered by using MLF intense μ beam
244 nm
244 nm
• Current best result was obtained in RAL ~20 years ago
Mu 1S, F=1
Mu 2S, F=1 detuning
Δν1S2S = 2455528941.0 (9.8) MHz
μ++e-detection
to reduce Doppler shift 7
1st order 2nd order
• 2nd order Doppler shift can not be canceled even in the case of counter-propagating excitation
- largest systematic source in our experiment→ It is important to use slow muonium
aerogel target • room-temperature muonium available• We will use laser-ablated aerogel target- Studies have been done by J-PARC μ g-2 group
G. A. Beer et al., PTEP 2014 091C01
𝜇𝜇+
• 1st order Doppler shift can be completely cancelled out by counter-propagating excitation with an optical cavity
mirror mirror
experimental principle 8
• Mu 1S → 2S (CW laser) → μ+ (high-power pulsed laser)• Ionized μ+ guided by slow muon beam line (SMBL)- used in past test experiments in MLF MUSE- now SMBL is at KEK and used for laser ionization test of H atom
244 nmCW laser
cavity
electrostaticmirror
Bendingmagnet
MCPscintillatorlensSOA lens
355 nmpulse laser
schedule 9
Another Mu 1S-2S experiment in PSI ・Different experimental principle- DC μ beam, 2S Mu detection scheme- 2-Phase experiment
P. Crivelli
FY 2019 FY 2020 FY 2021 FY 2022-Hydrogen gas exp. Phase-0 exp.
Phase-1 exp.target: 1 MHz
Phase-2 exp.target: 100 kHz
application tohigh intensity ultra slow muon
Mu distribution study
high-power CW laser development
244 nm pulse laserconstruction
244 nm CW laserconstruction
S2 construction
high-power pulse laser development
MLF S1-type proposal was submitted last year- technical review in 2019 Dec., PAC in 2020 Jan.
experimental area 10
• S2 area (under construction, plan to start in 2020 Nov.)• After initial commissioning studies, Phase-0 exp. will start
J-PARC MLF MUSE
laser system 11
Phase-0
976 nmECDL
Ti:Scavity
SHG CLBO
TaperedAmp.
488 nm 244 nm532 nmNd:YAG
CW→pulse
• backup: dye laser (already available) etc.
Ti:Samp
SHG LBO
25 Hz
976 nm
• pulse laser system- linewidth is broad and this laser cannot be used for
precise measurement of Mu 1S-2S transition- excitation probability is much higher than CW laser and
muonium 1S-2S ionization signal can be quickly confirmed
Setup (plan)
CW
laser system 12
976 nmECDL(+TA)
SHG cavityLBO crystal
SHG cavityCLBO crystal
Mu chambercavity
Yb-dopedfiber amplifier 488 nm 244 nm
frequency comb
Phase-1, Phase-2• continuous-wave (CW) laser system - Compared to usual spectroscopy experiments,
number of Mu is limited and it is important to construct high-power CW laser cavity
- we plan to construct ~30 W (Phase-2) deep UV cavity• Accuracy of laser frequency is also important, and
optical frequency comb will also be used (~2 kHz precision)Setup (under construction)
expected resonance curve 13
500 kW24 h/point
1 MW96 h/point
Phase-1 Phase-2
• statistic uncertainty: ~600 kHz in Phase-1, ~70 kHz in Phase-2• (2nd-order) Doppler shift: 500-600 kHz- If target temperature is controlled with a precision of 5 K,
Doppler shift uncertainty of ~30 kHz can be achieved
summary• Precision frequency measurement of Mu 1S-2S transition• Significant improvement can be achieved by usinghigh-intensity muon beam at MLF MUSE and recent development of laser techniques
- Phase-1 FY2020-2021, f1S2S precision:1 MHz- Phase-2 FY2022-, f1S2S precision:100 kHz• If ~100 kHz precision is achieved,
muon mass precision is improved from 120 ppb to ~10 ppb
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Backup
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theory 16
C. Frugiuele et al., Phys. Rev. D 100, 015010 (2019)
Spin-independent force
electron g-2 +muon g-2
Ps 1S-2S
Mu Lamb shift
Mu 1S-2S(1.4 MHz)
Mu 1S-2S(3 kHz)
Due to new particle mediation, binding potential of muonium is modified
new physics using Mu?• If 𝑚𝑚𝜇𝜇 precision of ~ 10 ppb is achieved by this project,
theoretical precision of Mu HFS can be reducedfrom 515 → ~40 Hz
- better than electroweak effect (65 Hz) and new physicseffect might be observed (with MUSEUM experiment)
• If new physics effect would be observed, this might be related to muon g-2 anomaly.
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M. I. Eides, Phys. Lett. B 795, 113 (2019)
updated analysis of RAL 18
V. Meyer et al., Phys. Rev. Lett. 84, 1136 (2000)
• In the RAL experiment, laser frequency was calibrated by usinga hyperfine component of an R-branch line in 127I2
• Later, those lines were re-calibrated by using an optical frequency comb
Δν1S2S = 2455528941.0 (9.1)(3.7) MHzI. Fan et al., Phys. Rev. A 89, 032513 (2014)Δν1S2S = 2455528940.6 (9.1)(3.7) MHz
V. Meyer et al., Phys. Rev. Lett. 84, 1136 (2000)
- uncertainty of this re-calibration (0.6 MHz) is smaller than muonium statistics and residual Doppler effect of RAL exp.
simulation overview1. S2 area beam injection
- beamline simulation by G4 beamline- absolute flux is estimated by S1 data
2. muonium formation in aerogel- based on past studies by muon g-2 group
3. laser simulation- solve optical Bloch simulation- the same method was used in H 1S-2S experiments
4. downstream beam line transportation and detection- muon transport simulation by using geant4- validated by past experiments
• Background rate will be estimated in Phase-0 experiment
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S2 flux estimation 20
SSL1 [mm×mm]
SSL2[mm×mm]
Collimator efficiency muon flux(500 kW)
note
100×40 40×40 In 5.7×10-4 1.9×105/s current S1100×40 40×40 Out 5.9×10-4 1.9×105/s100×40 240×240 Out 7.2×10-3 2.4×106/s use this setting240×240 240×240 Out 1.1×10-3 3.5×106/s
• The SSL1 slit is common for S1 and S2
• beam widthin the S2beamline
• muon absolute flux at S2:estimate based on S1 data
- 1.2-2.4×106/s (500 kW, w/o slit)• beam profile before injection:- σx=33.2 mm, σy=12.7 mm
• muonium diffusion inside aerogelis simulated by a diffusion model
- This model is validated by pastbeam experiments in TRIUMF
- ~2% muon forms muonium and emit from the aerogel target
S2 beamline simulation 21
emit fromaerogel
total
0mm
2468
simulation by Ce(Peking univ.)
P. Bakule et al., Prog. Theor. Exp. Phys. 2013, 103C01 (2013)
Mesh
Mu profile (S2-line) 22
time
XY X YAerogel target: ~ 78 mm Φ
• Muonium emit from aerogel gradually
• Narrow beam in Y direction is preferablebecause the laser passes through Y=0
• calculate excitation and ionization probability using optical-Bloch equations.
laser simulation 23
Mu 1S
Mu 2S
ionized
244 nm
244 nm
μ++e-
⟩|𝑔𝑔
⟩|𝑒𝑒
aerogel
For each particle, track informationbased on muonium diffusioninside the aerogel is used
laser simulation• Settings
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efficiency table 25
efficiencystopping inside target 0.47muonium formation 0.52emit out of target 0.082muonium angular momentum for excitation 𝐹𝐹 = 1
0.75
laser ionization 2.0×10-8 (Phase-1)1.8×10-7 (Phase-2)
mesh transmission 0.85muon transportation 0.77MCP detection 0.90analysis selection 0.33
lineshape width better precision of center frequency
is achievable by narrower lineshape
possible systematic sources• Laser linewidth- In RAL experiment, pulsed 244 nm laser was used.- inevitable lineshape uncertainty (~1 MHz)- CW laser and optical frequency comb will be used and < 1 kHz possible
• Residual Doppler effect- largest syst. source in RAL experiment - can be removable by using CW optical cavity
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mirror mirror
lineshape width better precision of center frequency
is achievable by narrower lineshape
possible systematic sources• DC Stark shift: DC electric field shifts Δν1S2S
- “pulsed” DC field necessary• AC Stark shift: laser field also shifts Δν1S2S
- proportional to 244 nm laser intensity- should be estimated by simulation• Laser power stability: monitor laser power• muon lifetime : principle limitation- width: 72.4×2~145 kHz (FWHM)
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other systematic sources• DC Stark shift: proportional to 𝐸𝐸2- largely reduced by applying DC fieldafter the pulse laser pass through
- shift uncertainty: ~0.05 kHz (Residual electric field: 0.1 V)
• AC Stark shift: proportional to CW laser intensity- monitor laser power during data taking- estimated shift size: ~30 (3) kHz (Phase-2)• laser frequency stability: 2 kHz
• They are smaller than statistic uncertainty and Doppler shift uncertainty
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Mu ionization comparison 29
Mu 1S
Mu 2S
ionized
244 nm
244 nm
244 nm
μ++e-
Mu 1S
Mu 2P
ionized
122 nm
355 nm
μ++e-
threshold threshold
• There exists ways to generate ultraslow muon by ionizing Mu
• Currently, Lyman α laser (1S-2P excitation) is used in U-line andis planned to use in E34 (muon g-2) experiment
• Very high-power 244 nm pulse laser is an alternative way togenerate high-intensity ultraslow muon
• From simulation, laser ionization rate with 200 mJ 244 nmpulse laser (with a mirror) seems to be slightly larger than that of 5 μJ 122 nm laser (without a mirror)
Mu ionization comparison 30
Parameters 1S-2P (122 nm, 355 nm) 1S-2S (244 nm pulse)laser intensity 5 μJ (122 nm),
300 mJ (355 nm)200 mJ
laser linewidth 100 GHz (122 nm) narrow (FT-limited)laser duration(FWHM)
1 ns (122 nm)5 ns (355 nm)
5 ns
laser spatial width (D4σ)(at beam waist)
20 mm (xy direction)2 mm (z direction)
20 mm (xy direction)2 mm (z direction)
beam injection position z = 4 mm z = 4 mmmirror position not installed x = 100 mmionization probability 0.0056 0.0066
beamline: S2, target: aerogel
aerogelz
y• For 244 nm pulse laser, it is important toput a mirror for increasing ionization rate
- In the counter-propagating excitationDoppler effect is largely reduced
Laser room 31
• Movable by using a crane• container-type simple room (with interlocks)
External cavity diode laser
• ECDL in Littrow config.• Diffracted light whichback to the DL oscillate
• control temperature byPeltier device
• linewidth:~MHz• power:~40 mW
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laser diode
grating
Piezo actuator
collimator lens
p
n
diode laser (DL)+
-eh
Tapered Amplifier 33
American Journal of Physics 82, 805 (2014)
25 mW ➡~1W
Yb-doped fiber amplifier 34
976 nmECDL
isolatorASE
Wavelength Division Multiplexing (WDM)
915 nmpump
combinerundopedfiber
Yb-doped fiber
combiner
Yb-doped fiber
ASE rejection
amplified976 nm
30 mW
setup (under construction)
• In order to reduce ASE, only 915 nm and 976 nm component are selected outside the fiber and couple them to fibers again
976 nm laser system 35
fiber fusion 36
• edge of fibers are polished• normal fiber and Yb-doped
fiber is connected by using a fiber splicer
after polish connected area
• We found fiber fusion work is difficult due to bad fiber polish, bad fiber connection etc.
LBO cavity 37
LBO crystal
Similar type cavity will be used
244 nm CW laser cavity 38
x
y
5-pass
aerogel• It is known from past laser studies
deep-uv laser easily damage mirrors- mirrors quickly degrades due to
lack of oxygen gas or hydrocarbon contamination
- flow high purity oxygen gasaround at least cavity mirrors
- The beamline is operated in vacuum, separation by windowor differential pumping is necessary.
• multi-pass CW cavity- Increase Mu excitation rate
PSI 39
P. Crivelli
S2 area plan 40
experimental area 41
Laser room will be constructedaround here (common space with E34 (g-2) group?)
Laser
test experiment using H• 1S-2S ionization experiment of hydrogen atom- similar atom system with muonium
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Mu 1S
Mu 2S
ionized
244 nm
244 nm
244 nm
μ++e-
pulse
pulse
pulse H 1S
H 2S
243 nm
243 nm
243 nm
H++e-
pulse
pulse
pulse
muonium hydrogen atom
• 1S-2S frequency of hydrogen atom is known precisely (~10Hz)and can be used as a frequency standard
• this can also be used as a downstream beamline test
ionized
Hydrogen test@Okayama 43
Acknowledgement:Kentaro Kawaguchi (Okayama univ.), Kouzo Hakuta (UEC)
discharge ON
• see H+ ionization signal with changing laser frequency
If microwave dischargecontinues successfully,red light (hydrogen Balmer α, 656.5 nm) can be seen.
Hydrogen test@Okayama• preparatory experiment: 1S-2S ionization of H atom
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Setup
• H atom is generated by the microwave discharge system• 243 nm laser is generated by using a dye laser (SHG) • Quartz (tube) and Al (nozzle) are used in order to reduce
recombination of H atom
energymeter
H2 gas Microwavecavity
Microwave generator
gasbottle
flowmeter
pressuregauge
nozzle
pressuregauge
Quartztube amplifier oscillo
scope
HV
243 nm
Hydrogen test@Okayama 45
discharge ONdischarge OFF
HV: -50 Vaveraged pulse height (oscilloscope)
stray light background
H 1S
H 2S
243 nm
243 nm
detuning
observed 1S-2S ionization peak
laser power : ~0.5 mJ
test experiment using H
• Microwave cavity generate H atom from H2 gas• Differential pumping enables us to connect H sourceto the target chamber (pressure < 10-4 Pa)
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pinhall H2
pump(differential pumping)
laser
microwavecavitytarget
chamber
another laser plan• M.Yoshida (KEK) is developing a pulse laser systemwhich can be used as a backup of the ionization laser forthe E34 experiment
• This laser ionize Mu via 1S-2S transition and so can beused as a laser for our experiment(Phase0, Phase1)
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976 nmCW SOA
488 nm 244 nm
SHG SHG
• Arbitrary temporal shaping of the 976 nm laser pulse isgenerated by using semiconductor optical amplifier (SOA)
- Linewidth is expected to be narrow
Setup multi-passamplifier