Atomic Physics with Ultra-slow Antiprotons p. 1E. Widmann

Atomic Physics with Ultra-Slow Antiprotons　

E. WidmannASACUSA 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 @ CERNPrecision spectroscopy of

antiprotonic helium (3-body system, well advanced) antihydrogen (2-body system, very early stage)

Extension towards ultra-low energy antiprotons: MUSASHI @ ADOutlook

Atomic Physics with Ultra-slow Antiprotons p. 2E. 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 Templeby Utagawa Hiroshige (1797-1858)

Atomic Spectroscopy And Collisions Using Slow Antiprotons

~ 40 members

Atomic Physics with Ultra-slow Antiprotons p. 3E. 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

Atomic Physics with Ultra-slow Antiprotons p. 4E. 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

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

AD & Experiments

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

Antiprotonic Helium

Atomic Physics with Ultra-slow Antiprotons p. 7E. 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

Atomic Physics with Ultra-slow Antiprotons p. 8E. Widmann

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

0 / en M m

Angular Momentum

Energy

Atomic Physics with Ultra-slow Antiprotons p. 9E. Widmann

CPT Test for Antiproton Charge and Mass

Resonance scansShift of line centerwith density

Zero-density values compared to state-of-the-art three-body QED calculations AD 2000: absolute accuracy of

~ 1.3x107 reached For narrow transitions (<50

MHz) exp. and theory agree to ~ 5x107

This sets a new CPT limit of 6x108 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 resultM. Hori et al., PRL 87 (2001) 093401

Atomic Physics with Ultra-slow Antiprotons p. 10E. Widmann

–

e B eg s

[ ( ) ( ) ]p s p l p Ng p s g p l

p el s

“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:

p ej l s

p p e pJ j s l s s

–

HF ~ 10 … 15 GHz Bakalov & Korobov

SHF ~ 50 … 150 MHz PRA 57 (1998) 1662

Atomic Physics with Ultra-slow Antiprotons p. 11E. 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

( ) with 2p

l p N Np

Qg p l

M

Atomic Physics with Ultra-slow Antiprotons p. 12E. 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!

–

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

Antihydrogen

Atomic Physics with Ultra-slow Antiprotons p. 14E. 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)

Atomic Physics with Ultra-slow Antiprotons p. 15E. Widmann

n=1

n=2

Bohr Dirac Lamb HFS

j=1/2

j=3/2

2P1/2

2P3/2

2S1/2

F=0F=1

1s-2s2 photon=243 nm

Ground statehyperfinesplittingf = 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 103

1S-2S spectroscopy needs antihydrogen trapped in a neutral atom trap

GS-HFS can be done with atomic beams

Atomic Physics with Ultra-slow Antiprotons p. 16E. 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!

Zemach

d

LNM

OQPz2

11

2

3

4

2 2Z m p

p

G p G pe E M( ) ( )

exp

exp

. .

th 3 5 0 9 ppm

Atomic Physics with Ultra-slow Antiprotons p. 17E. 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

Atomic Physics with Ultra-slow Antiprotons p. 18E. Widmann

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)

Atomic Physics with Ultra-slow Antiprotons p. 19E. 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

Atomic Physics with Ultra-slow Antiprotons p. 20E. 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)

Atomic Physics with Ultra-slow Antiprotons p. 21E. 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