E. Widmann, Antihydrogen GS-HFS, p. 1 LEAP03, Yokohama, March 4, 2003

Measurement of the Hyperfine Structure of AntihydrogenE. Widmann, R.S. Hayano, M. Hori, T. Yamazaki

ASACUSA collaboration

LEAP03, Yokohama, March 4, 2003

CPT Symmetry and other fundamental symmetriesGround-state hyperfine structureMeasurement using atomic beams

LOI submitted to AD: SPSC-I-226

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 violation

1956 Theory: Lee & Young1957 ß-decay Wu et al. π -> µ -> e decay

100 %

CP violation 1964 K0 decays: Kronin and Fitch

2001 B decays: BELLE, BaBar

ε ~2.3 x 10–3

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

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)

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

Precision Spectroscopy of Hydrogen and CPT

Sensitivities1S-2S

Electron mass Proton mass proton charge

radius Rp2S-2P

RpGS-HFS

Proton magnetic moment µp

µe Proton magnetic

radius RMTheory

Rp and RM

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 νHF = 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!

Zemach

d

LNM

OQPz2

11

2

3

4

2 2Z m p

p

G p G pe E M( ) ( )

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–

1950 4 x 10–8

1960-70Hydrogen 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. 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

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

solenoid 1 solenoid 2

Sextupole 1 length 1.25 m (not to scale!)

positron plasma diameter 4 mm (radius not on scale)

y

z

mesh electrodeelectrodes

solid material in central part to block trajectory in region where field is too small

40mm

neutral atomtrajectory

30mm

400mm

200mm

compensation coils

66mm

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 setupBUT: Many open questions

Simultaneous confinement Loading of Paul traps from

outside Cooling method Heating of particles by applied

RF

Needs lots of R&DM.Hori & W. Pirkl

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(rmax) = 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

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, B1 = 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

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

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 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