Date post: | 31-Dec-2015 |
Category: |
Documents |
Upload: | damon-wilkinson |
View: | 224 times |
Download: | 3 times |
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