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Current source of low-energy antiprotons: AD @ CERN Precision spectroscopy of

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

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Current source of low-energy antiprotons: AD @ CERN Precision spectroscopy of

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  1. Atomic Physics with Ultra-Slow AntiprotonsE. WidmannASACUSA collaboration, University of TokyoInternational Workshop on Nuclear and Particle Physics at 50-GeV PSTsukuba, 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. ASACUSA collaboration @ CERN-AD Atomic Spectroscopy And Collisions Using Slow Antiprotons • 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 Asakusa Kannon Temple by Utagawa Hiroshige (1797-1858) Spokesman: R.S. Hayano, University of Tokyo ~ 40 members

  3. 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 Antiproton Production at CERN

  4. 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. AD & Experiments

  6. Antiprotonic Helium

  7. – 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 ms

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

  9. CPT Test for Antiproton Charge and Mass • AD 2000: absolute accuracy of ~ 1.3x10-7 reached • For narrow transitions (G<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*Q2 • 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 Zero-density values compared to state- of-the-art three-body QED calculations Shift of line center with density Resonance scans M. Hori et al., PRL 87 (2001) 093401

  10. 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: “Hyperfine” structure of pHe+ – – nHF ~ 10 … 15 GHz Bakalov & Korobov nSHF ~ 50 … 150 MHz PRA 57 (1998) 1662

  11. 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. 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 Dn=Dl=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! Outlook - 2-photon transitions in pHe+ –

  13. Antihydrogen

  14. 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) Antihydrogen and CPT

  15. Leading term: Fermi contact term a measurement of nHF 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 One of the most accurately measured quantities in physics hydrogen maser, Ramsey (Nobel price 1989) spin-spin interaction electron - (anti)proton Ground-State Hyperfine Structure of (Anti)Hydrogen 2S1/2 j=3/2 2P3/2 n=2 j=1/2 2P1/2 Ground state hyperfine splitting f = 1.4 GHz 1s-2s 2 photon l=243 nm F=1 n=1 F=0 Bohr Dirac Lamb HFS

  16. 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! (Anti)hydrogen GS-HFS and Theory, CPT

  17. 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 Possible experiment with atomic beams

  18. Ultra-Low Energy Antiprotons: MUSASHIMonoenergetic 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. 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 First antiprotons trapped & cooled by ASACUSA trap group

  20. 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. 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

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