1. Atomic Physics with Ultra-slow Antiprotons p. 1 E. Widmann Atomic Physics with Ultra-Slow Antiprotons E. Widmann ASACUSA collaboration, University of Tokyo International Workshop on Nuclear and Particle Physics at 50-GeV PS Tsukuba, December 10, 2001  Current source of low-energy antiprotons: AD @ CERN  Precision spectroscopy of  antiprotonic helium (3-body system, well advanced)  antihydrogen (2-body system, very early stage)  Extension towards ultra-low energy antiprotons: MUSASHI @ AD  Outlook

2. Atomic Physics with Ultra-slow Antiprotons p. 2 E. Widmann ASACUSA collaboration @ CERN-AD  University of Tokyo, Japan  RIKEN, Saitama, Japan  Tokyo Institute of Technology, Japan  University of Tsukuba, Japan  Institute for Molecular Science, Okazaki, Japan  Tokyo Metropolitan University, Japan  CERN, Switzerland  University of Aarhus, Denmark  University of Wales Swansea, UK  KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary  University of Debrecen, Hungary  KVI, Groningen, The Netherlands  PSI Villigen, Switzerland  Ciril -Lab. Mixte CEA-CNRS, Caen Cedex, France  GSI, Darmstadt, Germany  Institut für Kernphysik, Iniversität Frankfurt  Universität Freiburg, Germany  St. Patrick's College, Maynooth, Ireland  The Queen’s University of Belfast, Ireland Spokesman: R.S. Hayano, University of Tokyo Asakusa Kannon Temple by Utagawa Hiroshige (1797-1858) Atomic Spectroscopy And Collisions Using Slow Antiprotons ~ 40 members

3. Atomic Physics with Ultra-slow Antiprotons p. 3 E. Widmann Antiproton Production at CERN  26 GeV protons from CERN PS impinge onto solid target  Proton-antiproton pair production  Capture in storage ring  LEAR area until 1996:  3 rings for capture, accumulation, extraction (AC, AA, LEAR)  AD: low cost all-in-one solution

4. Atomic Physics with Ultra-slow Antiprotons p. 4 E. Widmann Antiproton Decelerator (AD) at CERN  Started operation July 6th, 2000  Antiproton production at 3.5 GeV/c, capture, deceleration, cooling (no accumulation)  100 MeV/c (5.3 MeV)  Pulsed extraction  4 x 10^7 antiprotons per pulse of 200 ns length (in 2001)  1 pulse / 2 minutes  Topics: antiprotonic atom formation and spectroscopy incl. antihydrogen (ATRAP, ATHENA) Antiproton production ASACUSA experimental area

5. Atomic Physics with Ultra-slow Antiprotons p. 5 E. Widmann AD & Experiments

6. Atomic Physics with Ultra-slow Antiprotons p. 6 E. Widmann Antiprotonic Helium

7. Atomic Physics with Ultra-slow Antiprotons p. 7 E. Widmann pHe + “Atomcule” – a naturally occurring trap for antiprotons – - 3-body system - 2 heavy “nuclei” with Z=1 and Z=-1 -electron can be treated by Born-Oppenheimer approximation -~ 3% of stopped antiprotons survive with average lifetime of ~ 3  s

8. Atomic Physics with Ultra-slow Antiprotons p. 8 E. Widmann Observed transitions in 4 He  Spectroscopy method: forced annihilation by laser transition meta-stable to short-lived state  LEAR: 10 transitions in 4 He, 3 in 3 He observed  First experimental proof that exotic particle is captured around  AD: 8 new transitions in 4 He, 4 new in 3 He  Last transitions in v=0, 1 (UV) and v=4 cascade observed  Systematic studies possible Angular Momentum Energy

9. Atomic Physics with Ultra-slow Antiprotons p. 9 E. Widmann CPT Test for Antiproton Charge and Mass Resonance scans Shift of line center with density Zero-density values compared to state- of-the-art three-body QED calculations  AD 2000: absolute accuracy of ~ 1.3x10  7 reached  For narrow transitions (  <50 MHz) exp. and theory agree to ~ 5x10  7  This sets a new CPT limit of 6x10  8 between mass & charge of proton and antiproton  We determine M*Q 2  Q/M was determined at LEAR to 9 x 10 -11 (G. Gabrielse)  Factor 300 improvement over X-ray measurements  10 over LEAR PS205 result M. Hori et al., PRL 87 (2001) 093401

10. Atomic Physics with Ultra-slow Antiprotons p. 10 E. Widmann – “Hyperfine” structure of pHe +  interactions of magnetic moments:  electron:  pbar:  Dominant splitting: “Hyperfine”:  sizeable because of large l of pbar.  “ Superhyperfine” splitting  Interaction antiproton spin with other moments  Spin coupling scheme: – HF ~ 10 … 15 GHz Bakalov & Korobov SHF ~ 50 … 150 MHz PRA 57 (1998) 1662

11. Atomic Physics with Ultra-slow Antiprotons p. 11 E. Widmann First Observation of 2-laser MW Triple Resonance (PRELIMINARY online data 2001)  HF transitions are sensitive to orbital magnetic moment of antiproton  Relationship between particle charge and orbital angular moment  First measurement for (anti)proton  HF transitions are indirectly sensitive to antiproton (spin) magnetic moment  Experimentally known to only 3x10 -3  Further increase in accuracy may reach this level  Direct but very difficult:  SHF transitions  HFS resolved  Exp. accuracy ~ 1.5x10 -5  Good agreement with latest theory values: < 5x10 -5 (=theoretical uncertainty

12. Atomic Physics with Ultra-slow Antiprotons p. 12 E. Widmann Outlook - 2-photon transitions in pHe +  Current precision (50 – 100 MHz) seems limit for pulsed laser system  pulse-amplified cw-laser needed  Go to ultra-low density using RFQD:  antiprotons with 10 - 100 keV to be stopped in ~mbar helium gas done  Elimination of collisional shift and broadening  Doppler-free two-photon spectroscopy   n=  l=2 transitions ­ virtual intermediate state close to real one  state of the art: 10 MHz  Gives 1 ppb for CPT test of M and Q  Proton mass only known to 2.1 ppb! –

13. Atomic Physics with Ultra-slow Antiprotons p. 13 E. Widmann Antihydrogen

14. Atomic Physics with Ultra-slow Antiprotons p. 14 E. Widmann Antihydrogen and CPT  Tests of particle – antiparticle symmetry properties  Neutral form of antimatter  Hydrogen is most accurately known atom  Some of most accurately measured physical quantities are  1S-2S transiton: ~ 10 -14 relative  Ground state hyperfine splitting: ~ 10 -12 relative  Very high precision reachable, but  Challenge:  Formation at ultra-cold antihydrogen for precision spectroscopy  Strategy: use penning traps to trap & cool pbar, positrons  Recombination by overlapping clouds  No progress so far (2 years)

15. Atomic Physics with Ultra-slow Antiprotons p. 15 E. Widmann n=1 n=2 BohrDiracLambHFS j=1/2 j=3/2 2 P 1/2 2 P 3/2 2 S 1/2 F=0 F=1 1s-2s 2 photon =243 nm Ground state hyperfine splitting f = 1.4 GHz Ground-State Hyperfine Structure of (Anti)Hydrogen  One of the most accurately measured quantities in physics  hydrogen maser, Ramsey (Nobel price 1989)  spin-spin interaction electron - (anti)proton  Leading term: Fermi contact term  a measurement of HF will directly give a value for the magnetic moment of pbar  only known to 3 x 10  3  1S-2S spectroscopy needs antihydrogen trapped in a neutral atom trap  GS-HFS can be done with atomic beams

16. Atomic Physics with Ultra-slow Antiprotons p. 16 E. Widmann (Anti)hydrogen GS-HFS and Theory, CPT  Fermi contact term in agreement with experimental value by about 32 ppm  higher-order corrections  Zeemach corrections  depend on magnetic and electric form factors of proton  Zeemach corrections ­ ~ - 41.1(7) ppm  remaining discrepancy (incl. Polarizability)  Comparison of experimental accuracies and CPT tests with hydrogen  GS-HFS also tests form factors (structure) of (anti)proton!

17. Atomic Physics with Ultra-slow Antiprotons p. 17 E. Widmann Possible experiment with atomic beams  Monte-Carlo of trajectories  x and z scales different!  Follow early stage of hydrogen HFS spectroscopy  Spin selection and focusing by magnetic field gradient (sextupole magnets)  No neutral atom trap needed  Transport of Hbar escaping from recombination region  Critical question  Velocity distribution of Hbar  Small solid angle but high detection efficiency  MC indicates feasibility if Hbar formation rate ~ 200/s  Possible resolution <10 -6

18. Atomic Physics with Ultra-slow Antiprotons p. 18 E. Widmann Ultra-Low Energy Antiprotons: MUSASHI Monoenergetic Ultra Slow Antiproton Source for High-precision Investigations Inject 100 keV beam from RFQD into a 5 T solenoid magnet Degrade by a foil to 10 keV Trap, electron cool to a few eV and compress Extract at desired energy (10-1000 eV) fast and slow extraction Transport to experimental region (high pressure, low field) Y. Yamazaki et al., U Tokyo (Komaba)

19. Atomic Physics with Ultra-slow Antiprotons p. 19 E. Widmann First antiprotons trapped & cooled by ASACUSA trap group  Combination of RFQD (deceleration efficiency ~ 40 %) and large catching trap allows capture of 300’000 antiprotons and more from a single AD shot  Cooling of antiprotons successfully achieved  Extraction of antiprotons at energies down to 10 eV demonstrated in 2001

20. Atomic Physics with Ultra-slow Antiprotons p. 20 E. Widmann Physics with MUSASHI  10 – 1000 eV antiproton beam useful for  Formation of antiprotonic atoms (protonium, …)  Ionization in single collision by slow antiprotons ­ Ionization chamber to be installed at AD in October  Many other applications, e.g using continuous beam ­ Protonium X-ray spectroscopy (PS207, D. Gotta) ­ Probing neutron and proton distribution in nuclei (PS209, J.Jastrzebski)

21. Atomic Physics with Ultra-slow Antiprotons p. 21 E. Widmann Summary & Outlook  Fundamental atomic physics with ultra-slow antiprotons provides important contributions to  Advances of three-body QED calculations  high-precision tests of CPT  Long-lasting program  Antiproton source is needed also in the future  AD @ CERN was built after the closure of LEAR as a low-cost interim solution  Majority of construction cost of AD was provided by Japan  JHF would be natural place for continuation