1. E. Widmann, Antihydrogen GS-HFS, p. 1 LEAP03, Yokohama, March 4, 2003 Measurement of the Hyperfine Structure of Antihydrogen E. Widmann, R.S. Hayano, M. Hori, T. Yamazaki ASACUSA collaboration LEAP03, Yokohama, March 4, 2003  CPT Symmetry and other fundamental symmetries  Ground-state hyperfine structure  Measurement using atomic beams LOI submitted to AD: SPSC-I-226

2. E. Widmann, Antihydrogen GS-HFS, p. 2 LEAP03, Yokohama, March 4, 2003 History of Violations of Fundamental Symmetries  Historically it was believed that nature would conserve symmetries of space  Observed symmetry violations in weak interaction Size and pattern of CPT violation? Size of effect Parity violation1956 Theory: Lee & Young 1957 ß-decay Wu et al. π -> µ -> e decay 100 % CP violation1964 K 0 decays: Kronin and Fitch 2001 B decays: BELLE, BaBar ε ~2.3 x 10 –3 T violation1998 K 0 decays: CPLEARA ~ 7 x 10 –3

3. E. Widmann, Antihydrogen GS-HFS, p. 3 LEAP03, Yokohama, March 4, 2003 Verifications of CPT Symmetry: Comparison of particle – antiparticle properties  simple comparison of dimensionless numbers misleading  pattern of CPT violation unknown (P: weak interaction, CP: K, B mesons)

4. E. Widmann, Antihydrogen GS-HFS, p. 4 LEAP03, Yokohama, March 4, 2003 Precision Spectroscopy of Hydrogen and CPT Sensitivities 1S-2S  Electron mass  Proton mass  proton charge radius R p 2S-2P  R p GS-HFS  Proton magnetic moment µ p  µ e  Proton magnetic radius R M Theory  R p and R M

5. E. Widmann, Antihydrogen GS-HFS, p. 5 LEAP03, Yokohama, March 4, 2003 Ground-State Hyperfine Structure of (Anti)Hydrogen  One of the most accurately measured quantities in physics  hydrogen maser, Ramsey  ν HF = 1.420405751766(9) GHz  spin-spin interaction positron - antiproton  Leading: Fermi contact term  magnetic moment of pbar  only known to 0.3%  Fermi contact term differs from experiment by about 32 ppm  Zeemach corrections  magnetic and electric form factors of (anti)proton  Evaluation for Hydrogen: 3 ppm deviation theory-exp. remains  GS-HFS also contains information on form factors (structure) of (anti)proton!

6. E. Widmann, Antihydrogen GS-HFS, p. 6 LEAP03, Yokohama, March 4, 2003 History of Hydrogen HFS Measurements 1936Simple atomic beams ~ 5 % 1947Atomic beams plus 4 x 10 –6 discovery of anomalous microwave resonance magnetic moment of e – 19504 x 10 –8 1960-70Hydrogen maser6 x 10 –13 not possible for antimatter N.B. HFS spectroscopy of trapped antihydrogen does not lead to high precision due to the inhomogeneous magnetic field inside the trap

7. E. Widmann, Antihydrogen GS-HFS, p. 7 LEAP03, Yokohama, March 4, 2003 Layout to measure HFS using atomic beams  Production from trapped antiprotons and positions  atoms “evaporate” from formation region  No neutral-atom trap needed !!  use atomic beam method  focusing and spin selection by sextupole magnets  spin-flip by microwave radiation  low-background high-efficiency detection of antihydrogen through annihilation

8. E. Widmann, Antihydrogen GS-HFS, p. 8 LEAP03, Yokohama, March 4, 2003 Antihydrogen Formation  ATHENA, ATRAP 2002:  Nested Penning traps  GS-HFS: access needed  Mesh electrodes  Split solenoid  Other methods (better access)  Paul (RF) trap  “cusp” trap (magnetic bottle)  Important parameters  Production rate  Velocity (temperature)  Fraction of 1S population  Not yet known!  Recombination mechanisms  Radiative: -> ground state  3-body:-> Rydberg states Nested Penning traps, split solenoid

9. E. Widmann, Antihydrogen GS-HFS, p. 9 LEAP03, Yokohama, March 4, 2003 Antihydrogen Formation using Paul traps  Small size (no superconducting magnet needed)  Small source dimensions  1 mm^3  Compact setup BUT:  Many open questions  Simultaneous confinement  Loading of Paul traps from outside  Cooling method  Heating of particles by applied RF Needs lots of R&D M.Hori & W. Pirkl

10. E. Widmann, Antihydrogen GS-HFS, p. 10 LEAP03, Yokohama, March 4, 2003 Monte-Carlo simulation of Hbar trajectories  typical production parameters  Temp. 15 K  B(r max ) = 1.2 T Trajectories (x and z scale different!!)  S2 rotated by 180 degrees w.r.t S1  m=1 -> -1: defocusing  atoms w/o spin flip blocked in S2  microwave cavity between S1,S2  spin-flip -> S2 focuses Result: ~ 10 –4 of all Hbar arrive at detector

11. E. Widmann, Antihydrogen GS-HFS, p. 11 LEAP03, Yokohama, March 4, 2003 Achievable Resolution  Transitions in zero field  measure directly HF  Line width determined by transition time  Velocity ~ 300 – 400 m/s  L = 20 cm, B 1 = 5x10 –4 Gauss  FWHM of resonance curve:  ~ 2 – 3 kHz:  / ~ 2x10 –6  line can be split to higher precision  Typical velocity spectrum after double sextupole beam line

12. E. Widmann, Antihydrogen GS-HFS, p. 12 LEAP03, Yokohama, March 4, 2003 Production rates with RFQD  between 5x10 -5 and 2x10 -4 of formed Hbar atoms can be detected after S2  200 Hbar/s in ground state -> 0.5 – 2.5 events / min  Possible with measured production rates + RFQD  2 million antiprotons/AD shot typically captured  One resonance scan per day

13. E. Widmann, Antihydrogen GS-HFS, p. 13 LEAP03, Yokohama, March 4, 2003 Summary  Hyperfine structure measurement is complementary to 1S-2S laser spectroscopy  Addresses different topics  Magnetic moment: improvement of factor 10 3 feasible  Structure of the proton / antiproton  CPT test in the hadronic sector  Experimental constraints  Antihydrogen production parameters crucial (Temperature, Rate)  Feasible with 200 antihydrogens/s @ 15 K evaporating from formation region  Antihydrogen beam preferable (-> Cusp trap? Y. Yamazaki)  Time scale  Evaluate formation schemes until 2004  Experiments at AD from 2006

14. E. Widmann, Antihydrogen GS-HFS, p. 14 LEAP03, Yokohama, March 4, 2003 Conditions for atomic beam experiments  Velocity distribution depends on temperature of formed antihydrogen

15. E. Widmann, Antihydrogen GS-HFS, p. 15 LEAP03, Yokohama, March 4, 2003 HFS Measurements in a neutral atom trap  Neutral atom traps use force of magnetic field gradient on magnetic moment of atom  “depth” typically < 1 K (50 µeV)  Constant holding-field B z,0 to avoid spin flips  Typical configuration  Trapped hydrogen  Cesar et al., PRL 77, 255 (1996)  T ~ 25 mK  Thermal radius of atom cloud r ~ 0.05 mm - 1 mm  B ~ 0.002 - 0.04 T  Breit-Rabi energy of (1,1) state:  0.028 - 0.56 GHz shifted  Strong broadening of HFS line by thermal motion of trapped H Only low accuracy achievable

16. E. Widmann, Antihydrogen GS-HFS, p. 16 LEAP03, Yokohama, March 4, 2003 Velocity distribution in nested Penning traps  pbar stop, thermalize, diffuse in positron plasma  positron plasma rotates  caused by radial electric field x B  frequency depends on density  10 8 e + /cm 3 : f = 100 kHz  10 9 e + /cm 3 : f = 400 kHz  Example for velocity distribution  antiprotons also rotate with approximate same frequency  formation is governed by internal temperature of the cloud  neutral atoms get boost by rotation  Radius of plasma ~ 2 mm

17. E. Widmann, Antihydrogen GS-HFS, p. 17 LEAP03, Yokohama, March 4, 2003 Antihydrogen Formation using Paul traps  Small size (no superconducting magnet needed)  Small source dimensions  1 mm^3  Compact setup BUT:  Many open questions  Simultaneous confinement  Loading of Paul traps from outside  Cooling method  Heating of particles by applied RF Needs lots of R&D M.Hori & W. Pirkl

18. E. Widmann, Antihydrogen GS-HFS, p. 18 LEAP03, Yokohama, March 4, 2003 Antihydrogen for Spectroscopy  High-precision spectroscopy for CPT tests  Recent successes for the formation of cold antihydrogen  Method: nested Penning traps  Velocity distribution unknown  Reported production rates:  Few atoms/second for 10 4 antiprotons per mixing Time to think about spectroscopy! ATHENA 15 K temperature Most likely formation by radiative recombination Predominantly ground-state antihydrogen produced ATRAP 4 K Three-body recombination Rydberg states

19. E. Widmann, Antihydrogen GS-HFS, p. 19 LEAP03, Yokohama, March 4, 2003 Ground-state (anti)hydrogen in magnetic field Breit-Rabi diagram Magnetic moment Numerical values of hydrogen

20. E. Widmann, Antihydrogen GS-HFS, p. 20 LEAP03, Yokohama, March 4, 2003 The ultimate “Fundamental” Symmetry: CPT  C charge conjugationparticle  antiparticle  Pparity (space inversion)  Ttime reversal  Consequences : particles/antiparticles have  same masses, lifetimes, g-factors, |charge|, etc.  CPT invariance is a mathematical theorem:  consequence of Lorentz-invariance  local interactions  point-like particles  Lüders, Pauli, Bell and Jost, 1955  QED, standard model are all CPT invariant  Assumptions are invalid in string theory

21. E. Widmann, Antihydrogen GS-HFS, p. 21 LEAP03, Yokohama, March 4, 2003 Possible problems with CPT: Baryogenesis  Antimatter absence in the universe  Standard scenario for Baryogenesis (Sakharov 1967)  Baryon-number non-conservation  C and CP violation  Deviation from thermal equilibrium  Currently known CP violation not large enough  Other source of baryon asymmetry?

22. E. Widmann, Antihydrogen GS-HFS, p. 22 LEAP03, Yokohama, March 4, 2003 First Cold Antihydrogen 2002 @ AD ATHENA Nature 419 (2002) 456 ATRAP

23. E. Widmann, Antihydrogen GS-HFS, p. 23 LEAP03, Yokohama, March 4, 2003 Recombination Mechanisms Low temperature (4 K) High temperature (15 K)

24. E. Widmann, Antihydrogen GS-HFS, p. 24 LEAP03, Yokohama, March 4, 2003 Atoms in sextupole field Breit-Rabi diagram  B = 0 at r = 0  Low-field seekers are focused  Spin selection  Increase of solid angle

25. E. Widmann, Antihydrogen GS-HFS, p. 25 LEAP03, Yokohama, March 4, 2003 ASACUSA plans with RFQD (1) MUSASHI  RFQD + catching trap + extraction  10 eV – 1000 eV antiproton beam  Slow extraction possible  Status  Extraction successful, but efficiency still too low  Efforts to improve under way  Physics topics  Atomic collision physics (atom formation, ionization)  ASACUSA proposal  Nuclear physics  Protonium X-ray  Nuclear periphery (n-halo)  ASACUSA status report 2001  Monoenergetic Ultra Slow Antiproton Source for High-precision Investigations

26. E. Widmann, Antihydrogen GS-HFS, p. 26 LEAP03, Yokohama, March 4, 2003 ASACUSA plans with RFQD (2)  Antihydrogen ground- state hyperfine structure  Measurement in atomic beam  10 K atoms evaporating from formation region useful  No trapping needed  Low transport efficiency: ~ 10 –4  High antihydrogen production rate needed: ~ 200 / s  Only feasible at AD with RFQD  Trap 10 6 pbar / shot  Evaluate formation schemes until 2004  Experiments at AD from 2006