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Measurement of the Ground-State Hyperfine Structure of

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					         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


E. Widmann, Antihydrogen GS-HFS, p. 1                           LEAP03, Yokohama, March 4, 2003
History of Violations of Fundamental Symmetries
             it was believed that nature would conserve
 Historically
  symmetries of space
 Observed symmetry violations in weak interaction


                                                                      Size of effect
Parity violation 1956 Theory: Lee & Young                             100 %
                 1957 ß-decay Wu et al.
                      π -> µ -> e decay
CP violation                 1964 K0 decays: Kronin and Fitch         ε ~2.3 x 10–3
                             2001 B decays: BELLE, BaBar

T violation                  1998 K0 decays: CPLEAR                   A ~ 7 x 10–3

                                   Size and pattern of CPT violation?

 E. Widmann, Antihydrogen GS-HFS, p. 2                           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)

    E. Widmann, Antihydrogen GS-HFS, p. 3           LEAP03, Yokohama, March 4, 2003
   Precision Spectroscopy of Hydrogen and CPT
Sensitivities
1S-2S
   Electron mass
   Proton mass
   proton charge
    radius Rp
2S-2P
   Rp
GS-HFS
   Proton magnetic
    moment µp
   µe
   Proton magnetic
    radius RM
Theory
   Rp and RM

 E. Widmann, Antihydrogen GS-HFS, p. 4   LEAP03, Yokohama, March 4, 2003
           Ground-State Hyperfine Structure of
                     (Anti)Hydrogen
 Oneof the most accurately              Fermi contact term differs from
 measured quantities in physics           experiment by about 32 ppm
    hydrogen maser, Ramsey              Zeemach corrections
    νHF = 1.420405751766(9) GHz               magnetic and electric form factors
 spin-spininteraction positron -               of (anti)proton
  antiproton
                                                                      L                         O
 Leading: Fermi contact term            Zemach 
                                                      2Zme
                                                       2     z  d3 p GE ( p 2 )GM ( p 2 )
                                                                 p4
                                                                      M
                                                                      N     1 
                                                                                           1   P
                                                                                                Q
                                               Evaluation for Hydrogen: 3 ppm
                                                deviation theory-exp. remains
                                         GS-HFS   also contains information
 magnetic        moment of pbar          on form factors (structure) of
      only known to 0.3%                 (anti)proton!




E. Widmann, Antihydrogen GS-HFS, p. 5                         LEAP03, Yokohama, March 4, 2003
        History of Hydrogen HFS Measurements

1936 Simple atomic beams                ~5%
1947 Atomic beams plus                  4 x 10–6    discovery of anomalous
     microwave resonance                            magnetic moment of e–
1950                                    4 x 10–8
1960-70 Hydrogen maser                  6 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

E. Widmann, Antihydrogen GS-HFS, p. 6                      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




 E. Widmann, Antihydrogen GS-HFS, p. 7   LEAP03, Yokohama, March 4, 2003
                              Antihydrogen Formation
 ATHENA,           ATRAP 2002:                Nested Penning traps, split solenoid
      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
E. Widmann, Antihydrogen GS-HFS, p. 8                         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

E. Widmann, Antihydrogen GS-HFS, p. 9       LEAP03, Yokohama, March 4, 2003
     Monte-Carlo simulation of Hbar trajectories
       production
 typical                                   S2   rotated by 180 degrees w.r.t S1
 parameters                                     m=1 -> -1: defocusing
     Temp. 15 K                            atoms w/o spin flip blocked in S2
     B(rmax) = 1.2 T                       microwave cavity between S1,S2
                                                spin-flip -> S2 focuses


 Result:
 ~ 10–4 of all Hbar
 arrive at detector

Trajectories
    (x and z scale
    different!!)




  E. Widmann, Antihydrogen GS-HFS, p. 10                            LEAP03, Yokohama, March 4, 2003
                                  Achievable Resolution

 Transitions  in zero field                  Typicalvelocity spectrum after
    measure directly HF                     double sextupole beam line
 Line width determined by
  transition time
    Velocity ~ 300 – 400 m/s
    L = 20 cm, B1 = 5x10–4 Gauss
 FWHM of resonance curve:

   d ~ 2 – 3 kHz: d / ~ 2x10–6
     can be split to higher
 line
 precision




E. Widmann, Antihydrogen GS-HFS, p. 11                    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




 E. Widmann, Antihydrogen GS-HFS, p. 12         LEAP03, Yokohama, March 4, 2003
                                         Summary

 Hyperfine structure measurement is complementary to
  1S-2S laser spectroscopy
 Addresses different topics
      Magnetic moment: improvement of factor 103 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



E. Widmann, Antihydrogen GS-HFS, p. 13             LEAP03, Yokohama, March 4, 2003

				
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