Upload
dangminh
View
216
Download
0
Embed Size (px)
Citation preview
OVERVIEW OF RECENT WORK ON LASER
EXCITATION OF POSITRONIUM FOR THE
FORMATION OF ANTIHYDROGEN
Pauline Yzombard(1), on behalf of the AEgIS(2) collaboration
(1) Laboratoire Aimé Cotton, Bâtiment 505, Orsay, France(2) AD-6: AEgIS, C.E.R.N. Route de Meyrin 385, 1217 Meyrin, Switzerland
g ?
Anti-Apple
Earth
g ?
OUTLINE
I. AEgIS experiment
II. Positron and laser systems
III. Recent works
Ps(n=3) laser excitation
Ps Rydberg
IV. Future works: toward a colder 𝐻 beam
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
2
CERN
Czech Technical
University
ETH Zurich
University of
Genova
University of
Milano
University of
Padova
University of
Pavia
University College
London
Politecnico di
Milano
Max-Planck Institute
Heidelbert
Institute of Nuclear
Research of the
Russian Academy
of Science
University of
Bergen
University of
Bern
University of
Brescia
Heidelberg
University
University of
Trento
University of
Paris Sud
University of
Oslo
University of Lyon 1
INFN sections of:
Genova, Milano,
Padova, Pavia,
Trento
Stefan Meyer Institute
I. AE IS COLLABORATIONg
I. AEGIS
ANTIMATTER EXPERIMENT: GRAVITY, INTERFEROMETRY, SPECTROSCOPY
Main goal: Measurement of g with 1% precision on antihydrogen.
Challenges:
- Production of a bunched cold beam of antihydrogen
- Measurement of vertical beam deflection (10 μm drop over 1 m)
via moiré deflectometer.
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
4
g ?
Anti-
Apple
Earth
moiré
deflectometer
e+
Ps convertor
p trap
Cf. Talk of Daniel Krasnicky
Overview of latest results from AEgIS
Aghion, S. and al. Nat. Commun vol 5 4538 (2014)
I. AEGIS - PRINCIPLE
Anti-hydrogen formation via Charge exchange process with Ps*
Principle demonstrated by ATRAP collaboration
Ps* produced via Cs* collisions on positrons trapped plasma
C. H. Storry et al., Phys. Rev. Lett. 93 (2004) 263401] 93 (2004) 263401
Interests:
Pulsed H production (time of flight – Stark acceleration)
Narrow and well-defined H n-state distribution
Colder production than via mixing process expected
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
5
Rydberg Ps*
Long lifetime + large cross section
σ≈ 𝑎0𝑛4
→ H formation enhanced
II. POSITRON AND LASER SYSTEMS - POSITRON SYSTEM
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
6
AEgIS zone
Positron system
Efficient transfer of positrons into the main traps - cfTalk of Daniel Krasnicky Overview of latest results from AEgIS
Studying positrons and Positronium physics in a dedicated test chamber
II. POSITRON AND LASER SYSTEMS - POSITRONIUM FORMATION
7Mariazzi S et al., Phys. Rev. B 2010, 81, 235481
PbWO4
Sketch of the e+ system - parameters given for 2015
22Na 11mCi
3 104 e+ / 0.15s
7 108 e+ / 3min 3.3keV e+
bunch implanted
SEM image: Silica-based nano- porous target
II. POSITRON AND LASER SYSTEMS - POSITRONIUM FORMATION
8
SSPALS (single shot positron
annihilation lifetime spectroscopy)(*)
measurements –
Average of 10 single shots.
S. Aghion et al. Nucl. Instru. Meth. in
Phy. Res Sect. B 362:86 92, 2015.
(*)Cassidy D B et al., NIMB 2007, 580, 1338
Production of Ps in the test chamber
3.3keV
Ps formation sketch
τ = 142ns
II. POSITRON AND LASER SYSTEMS - LASER SYSTEM
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
9
~1700 nm
Ps
Internal
energy
n=1
n=2
n=3
n Rydberg
≈ 15 − 20
continuum
205 nm
A dedicated laser system:conceived to be broadband σ ~110GHz
- to cover Doppler broadening and
magnetic mixing (Zeeman effect, at 1 T)
inside the main trap
In front of the test chamber:
Energy 60µJ, pulse 2ns, waists 6mmx8mm
In front of the test chamber:
Energy 1.3mJ, pulse 4ns, waist 10mm
III. RECENT WORKS- POSITRONIUM = 3 LASER EXCITATION
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD10
n
S(%)=(Area laser OFF−Area laser ON)
Area laser OFF
1064 n
m
Ps
Internal
energy
n=1
n=2
n=3
continuum
205 nm
Aghion S et al., PRA, submitted Feb.2016
Test chamber
photo-
ionization
n=3 excitation + photoionization
EM conditions:
B = 250 Gauss
E = - 600 V/cm
e+
Gamma detector
Si02 nano-
porous targeto-Ps
cloud
preliminary
III. RECENT WORKS- POSTRONIUM = 3 LASER EXCITATION
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
11
n
Scan of the n=3 transition
-3P excitation line centered
at 205.05±0.02 nm
- excitation-ionization
S(%) laser at resonnace ≈ 15.5%
Aghion S et al., PRA, submitted Feb.2016
- From this measurement:
We extrapolate an average
temperature of the excited
o-Ps : T ~1300K ± 200 K
(Doppler broadening)
- e+ implantation energy 3.3keV
- Target at room temperature
preliminary
Predicted: 205.0474 nm
III. RECENT WORKS- POSITRONIUM RYDBERG EXCITATION (VIA =3 STATE)
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
12
n
Scan of the Rydberg transitionsRydberg excitation(n=1 →n=3 → 𝑛 = 15 transition)
Ps
Internal
energy
n=1
n=2
n=3
205 nm
1680 nm
-
1710 nm
n Rydberg
≈ 15 − 20
Aghion S et al., PRA, submitted Feb.2016
preliminary
preliminary
continuum
n=15n=16
n=17
IV. FUTURE WORK –TOWARD COLDER 𝐻
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
13
- Sympathetic Cooling of 𝑝 with laser cooled anions
Atomic anions studied: Os-, La
-
An alternative project: laser cooling of molecular anions, as C2-
P. Yzombard et al. Phys. Rev. Lett. 114, 213001
IV. FUTURE WORK - TOWARD A POSITRONIUM LASER COOLING ?
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD
14
- Focusing Ps beam – via Doppler cooling
Laser focusing
Improving the 𝐻 formation = having a better solid angle
IV. FUTURE WORK - TOWARD A POSITRONIUM LASER COOLING ?
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD15
- Focusing Ps beam – via Doppler cooling
Ps
Internal
energy
n=1
n=2
n=3
continuum
243 nm
1S
2P
Challenge: short Ps lifetime (~142ns)
Interest: lightest atom (µ =2 me)
implies a huge recoil energy for each scattered
photon (~1500m/s or 0.3 K)
Laser development: a long pulse 243nm has to
be implemented
(pulse ~30ns to 200ns)
Probing time
Probing time
Probing time
Probing time
IV. FUTURE WORK - TOWARD A POSITRONIUM LASER COOLING ?
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD 16
-1D Doppler cooling ?
Ps
Internal
energy
n=1
n=2
n=3
continuum
243 nm
1S
2P
Simulations:
Ps 1D velocities distributions,
probed for different timing
during laser cooling – B = 0 T.
Ps velocities distributions (m/s) – 1D
PL wL ΓL δL T 3D(Ps
cloud)
5000W 7mm 50GHz 2.5cm-1 1000 K
Simulation parameters
Velocities range
excited by laser
Legend:
CONCLUSION AND OUTLOOK
Recent works in Ps physics:
First measurements of n=3 Ps laser excitation
Proof of Rydberg excitation with our dedicated laser system – major step to form 𝐻via charge exchange process
Future developments for laser works:
getting a colder 𝑝 plasma (sympathetic cooling via cold anions)
or/and focusing Ps beam (Doppler cooling)
MARCH 9 - LEAP 2016 - PAULINE YZOMBARD 17
Algorithm - simulations
PHYSICAL REVIEW A 69, 063806 (2004)
Absorption-emission processes calculated using rate equations
-> taking account : Laser detuning d, linewidth Glaser, saturation and
Doppler effects.
G= 1/lifetime = natural linewidth
Glaser (FWMH) Total linewidth Gtot = G+ Glaser+Gf+Ge
d
WRabi
(h/2p)WRabi=-<e|qer|f>Elaser
r
I = e0c Elaser2/2=2 Power/(p waist2)
f
e
Einstein Rate equations
Rate
Absorption
Ge
Gf Lf
Le
=> Kinetic Monte Carlo + Verlet
Solve exactly the rate equations.
Better than standard (Metropolis)
Monte Carlo P(t+dt)~P(t)+G dt
Verlet algorithm to drive the particles motion
Internal state (population) KMC
External state (position) Verlet
-All levels and transitions needed (n=1->n=2)
-gravity, magnetic field and recoil photons
-Dipole moment aligned on local field local laser polarization.
Algorithm - simulations
Anions cooling ?
Cooling Os- ?
Cooling La- ?
=> Heidelberg, Ger.
A. Kellerbauer
Cooling C2- ?
22
C2-