Towards next generation fundamental precision measurements with muon

1. Towards next generation fundamental precision measurements with muon All my work is supported by the SNSF grant 129600 and 146902. Kim Siang Khaw Precision Physics at Low Energy group Institute for Particle Physics (IPP) ETH Zurich PSI, 8th July 2014

2. How did I end up in Switzerland? CERN ETH & PSI Osaka Tokyo Kyoto Penang

3. What is muonium and what can we do with it? Motivations

4. What is muonium (Mu)? • Pure leptonic bound-state of μ+ and e-, 2.2 μs lifetime • The1S-2S transition frequency and the ground state HFS were measured to very high precision (4 ppb and 12 ppb) • Being used since 1960s extensively to • study μ-e interactions • test QED bound state theory • determine and extract fundamental constants (mμ/me, μ magnetic moment, qμ/qe) • probe physics beyond standard model (LFV, mirror world, etc ...) Courtesy K. Jungmann Hydrogen-like atom!

5. Motivation • Improve fundamental precision measurements with muon (μ+) and muonium (Mu), which are mostly limited by statistics and beam quality. Two straight forward ways available are: • Optimizing μ+ to Mu conversion rate [Antognini, PRL 108] • Porous silica material • Developing a high quality slow muon beam line [Bao, PRL 112] • Phase space compression of 1010 • Sub-eV energies • Sub-mm beam size • High efficiency (10-3) • Several next generation experiments can be conceived with new μ+ and Mu beams • Higher precision Mu spectroscopy, search for Mu-antiMu oscillations • μEDM, (g-2)μ, etc …… or even antimatter gravity! • Can probe energy scales of up to 1000 TeV (complementary to HEP)

6. Optimizing μ+ to Mu conversion rate using porous silica Muonium production 6

7. Low Energy Muon (LEM) at PSI 590 MeV Cyclotron I = 2 mA (1.2 MW) μE4 beam line positron counters LEμSR spectrometer

8. Muonium production – Porous silica • Bulk silica - high Mu production rate but no emission outside the target (Mu in vacuum is needed!) • Silica with structured pore-network (porous silica) - lower formation rate but high fraction of Mu diffuses out • Measurements done at LEM@PSI with 4000 μ+ /s on sample • Muon spin rotation technique to extract Mu formation probability • Positron shielding technique (PST) to extract Mu emission into vacuum

9. Muon Spin Rotation technique (μSR) • Monitor the evolution of μ+ spin after implantation, under external magnetic field • Larmor precession frequency of Mu = 103 times of μ+ • Can distinguish if an implanted μ+ remains unbound and forms Mu • Decay positron emitted preferentially in the direction of μ+ spin due to the parity violation of weak interaction • With a segmented positron detectors, Mu formation rate can be determined from the precession amplitude B = 100 G

10. Results from μSR technique • The time spectra measured in each individual segment is given by • The Mu formation probability can be calculated by comparing μ+ precession amplitude, Aμ of different samples. • We obtained 60% Mu formation proability for porous silica.

11. Positron shielding technique (PST) • No Mu emission into vacuum → exponential decay • Mu emission into vacuum → deviation from exponential function for the downstream detectors • Increase in count rate when Mu decaying outside of the sample • GEANT4 simulation for 0% (F0) and 100%(F100) • Fit the data with Ffit = aF100 + (1-a)F0 Al coated copper plate

12. Emission of Mu into vacuum • Optimization of emission of Mu into vacuum • measurements with different pore sizes and temperatures • extract emission probabilitiesand velocity distributions • best results so far (5 nm pore size, 20% at 100 K and 40% at 250 K, Boltzmann velocity distribution) • More than 10 times improvement of Mu 1S-2S with current systems(μ+ beam, Mu yield in vacuum, CW laser)

13. Towards Mu 1S-2S – a trapping cell • To increase the laser-Mu interaction time • Different spectra when Mu is bouncing inside • Beam time in summer 2014 NOW!

14. Developing a high quality slow muon beam line Phase space compression 14

15. Slow muon beam program at PSI D. Taqqu, PRL 97 • position-dependent μ+ drift velocity in helium gas (density gradient) • Phase space compression (1010), sub-mm size and sub-eV energy • 3 stages of compression : transverse compression, longitudinal compression and extraction of the μ+ beam • Estimated efficiency of about 10-3

16. Testing longitudinal compression at PSI • Feasibility test done at πE1 at PSI (2 × 104μ+/s @ 10 MeV/c) • 30 μm thick plastic scintillator (S1 – start) • PCB with metallic strips to define potential (-550 V to + 550 V) • 2 scintillators to tag e+ from μ+ decay (P1, P2 – stop) • Helium gas pressure was varied from 5 mbar to 12 mbar

17. Raw data • The histograms are scaled with et/τ to remove μ+ decay effect • The prompt peaks are coming from high energy μ+ decaying in flight • -HV: μ+ are being attracted to P1 and P2 • +HV: μ+ are being pushed away from P1 and P2

18. Results Y. Bao, PRL 112 • Implementation of low energy μ+ elastic collision physics and Mu formation in He gas into GEANT4 down to 0.1 eV energy • Good agreements between MC and data • Starting from an approximately flat stop distribution, the muons are compressed in the center in less than 2 μs feasible!

19. Testing transverse compression Proposed test of transverse compression at PSI in December 2014 Expected time spectra when the E or B field is switched off or without gas density gradient

20. Neutron radiography of 3He gas density Courtesy A. Eggenberger, F. Piegsaand G. Wichmann

21. Summary • Muonium production • Ongoing efforts to increase μ+ and laser interaction time • Measurement of the muonium 1S-2S is possible within 5 years. • Muon beam phase space compression • Transverse compression will be tested by end of this year. • Full compression scheme could be realized within the next 5 years. • Together with my colleagues and collaborators, we are opening up new possibilities in the next generation muon and muonium precision measurements.

22. All my works would not be possible without the supports from my lovely colleagues and collaborators! And more ……

23. BACKUPs 23

24. Overview of my PhD work • I have been working on the development of a novel muon beam and a new muonium source in the past 3 years. • I am involved heavily in the simulation and analysis works of the group (COMSOL multiphysics, GEANT4 and ROOT) and also in setting up DAQ system, etc. • I contribute significantly to the muonium production experiment (proposal, simulation, beam time, analysis, internal reports). • I contribute significantly to the phase space compression of muon beam experiment (proposal, simulation, DAQ, beam time, analysis, detectors). • I am also working as a demonstrator for the IPP’s advanced undergraduate lab (plastic scintillating fiber and MPPC). All my work is supported by the SNSF grant 129600 and 146902.

25. PSI Experimental hall πE1 beam line Phase space compression of muon beam μE4 beam line Muonium production from porous silica

26. Details of LEM

27. Target for muonium 1S-2S spectroscopy Target geometry for muonium 1S-2S measurement and possible detection scheme of the excited atoms. SiN 3x3 mm2, 30 nm thick window mounted in the Ps experiment

28. Muonium production in superfluid helium D. Kaplan et al., arXiv:1308.0878 R. Abela et al., JETP Lett. 57 (1993) 157 • Implant slow μ+ into superfluid helium • Production of Mu at 0.5 K measured 30 years ago • No measurement yet on Mu yield in vacuum • monoenergetic Mu will be emitted from the surface verticallywith velocity 6.3 × 103 m/s (chemical potential) • Could realize interferometer but many R&Ds are needed

29. Testing antimatter gravity with Mu • The mass is dominated by anti-muon almost antimatter • Could test the gravitational interaction of 2nd generationparticle (antihydrogen, positronium – 1st generation) • Well studied and can be produced at very high rates • Test of Mu's gravitational interaction is possible in 2 ways #1 - Annual modulation of 1S-2S transition frequency#2 - Mach Zehnder three-grating atom interferometer 2nd generation! Repulsive? Attractive?

30. #1: 1S-2S spectroscopy (not to scale) • Measure the gravitational redshift when the earth revolves around the sun (dH = 5 x 106 km) • νshift = [dU(rmax)-dU(rmin)]/c ～3.2 x 10-10 S.G. Karshenboim, arXiv/0811.1008 • Precision level of about 0.1 ppb is needed (current = 4 ppb)→ 40 times improvement! • This improvement will require: • high slow μ+ rate (currently 4000/s at LEM@PSI) • high μ+ → slow Mu conversion rate (Porous silica) • high power CW laser (Ps 1S-2S at ETH, P. Crivelli) • a better reference line (I2 at Taiwan) Credited to K. Jungmann 30

31. #2: Mach Zehnder interferometer L.M. Simons, priv. comm., 1995 T. Philipps, Hyp. Int. 109(1997)357 K. Kirch, arXiv:physics/0702143 D. Kaplan et al., arXiv:1308.0878 • Neutral atom interferometer for gravity measurements • Measurements on g have reached precision of 1010 • No measurement done yet on antimatter • To have enough statistics and measurable deflection • separation between gratings ~ 2.2 μs • grating pitch ~ 100 nm • 105monoenergeticMu/s • precision ~ 0.3g/ sqrt(#days)

32. Helium gas density gradient • Leak-proof cylinder made of copper (top, bottom) and stainless steel (sides) • Resistors to heat up the cell and sensors to measure the temperatures • Helium gas pressure - 0.01 mbar to 50 mbar • Copper plate temperatures - 3 K to 50 K • Good agreement between COMSOL simulations and measurements (also tested with neutron radiography method) • Implementation of effective density gradient in GEANT4 simulation

33. Courtesy A. Eggenberger

34. Courtesy G. Wichmann

35. Courtesy G. Wichmann

36. Advanced student lab at IPP ETH