Measuring the Gravitational Acceleration of
Antimatter: The AEgIS Experiment
Torkjell Huse (for Nicola Pasifico) – University of Oslo
On behalf of the AEgIS collaboration
1
CIPANP 2015
22/05/2015
Outline
Motivation of the AEgIS experiment
AEgIS overview







Antihydrogen production
Antiproton cooling
Positron system
Traps
Charge exchange reaction with positronium
The FACT detector and gravity module



Antihydrogen detector
Gravity module


Deflectometer
Free fall detector
Conclusions

2
CIPANP 2015
22/05/2015
A E g I S collaboration
CERN
Czech Technical
University
ETH Zurich
University of
Milano
University of
Padova
University of
Pavia
Politecnico di
Milano
University College
London
Stefan Meyer Institute
University of
Genova
Institute of Nuclear
Research of the
Russian Academy
of Science
University of
Bergen
University of
Lyon 1
3
INFN sections of:
Genova, Milano,
Padova, Pavia,
Trento
Max-Planck Institute
Heidelbert
University of
Bern
University of
Oslo
University of
Brescia
University of
Paris Sud
CIPANP 2015
22/05/2015
Heidelberg
University
University of
Trento
Scientific motivation
General relativity is a classic (non quantum) theory
EEP violations may appear in some quantum theories
New quantum scalar and vector fields are allowed in some models (Kaluza
Klein…)
Einstein field:
Tensor graviton (spin 2)
+ Gravi – vector (spin 1)
+ Gravi – scalar (spin 0)
These fields may mediate interactions violating the equivalence principle
(M. Nieto and T. Goldman - Phys. Rep. 205, 5 221-281 (1992)
Scalar: “charge” of particle equal to “charge” of antiparticle (attractive
force)
Vector: charge of particle opposite to charge of antiparticle
(repulsive/attractive force)
Cancellation between vector and scalar components is possible for matter!








4
CIPANP 2015
22/05/2015
Einstein Equivalence Principle
The Einstein Equivalence Principle is summarised by the
following 3 principles



Weak Equivalence Principle (mi=mg) +
For any non-gravitational experiment


Lorentz Local Invariance (independence from any free falling frame of
reference) +
Local Position Invariance (independence from position in the
universe)
Verified e.g. through gravitational red shift

5
CIPANP 2015
22/05/2015
WEP and matter


6
Verification of the WEP for
matter attained to 10-13
No precise verification to
date for antimatter.
CIPANP 2015
22/05/2015
We cannot build an tension pendulum made
of antimatter
We have to “borrow” another way of doing the WEP
measurement from atomic physics

Split and recombine the atomic wave
function in presence of gravity
Quantum interference if
Dfg = kgT 2
dg >> lDB L
Very cold atoms are needed with a very collimated beam
A. Peters et al, Nature 400 (1999) 849
7
CIPANP 2015
22/05/2015
The AEgIS way

We cannot get to μK / nK temperatures required for
quantum interference


Using classical interference:



8
Difficult to have good collimation
Use a two grating configuration with classical interferometry
(grating pitch ~ 40 um)
Aiming at an initial accuracy of 1%
Good collimation of the beam is not necessary for physics
(only for statistical reasons)
CIPANP 2015
22/05/2015
Measurement sensitivity



9
1% sensitivity
achievable with ~ 600
annihilations
Measurement
resolution ~ 3 um
Cold antihydrogen
necessary for bigger
deflection and lower
beam divergence.
CIPANP 2015
22/05/2015
AEgIS experiment layout
Aims:
 Measure the gravitational acceleration
for antihydrogen in Earth’s
gravitational field
 Hyperfine Spectroscopy of
antihydrogen
 Spectroscopy of 1s->2s transition
10
CIPANP 2015
22/05/2015
Antihydrogen production in a glance




11
5.3 MeV antiprotons
energy-degraded down
to few keV
Trapping in a PenningMalmberg trap
Antihydrogen
production through
charge-exchange
reaction with Rydbergstate positronium (see
next slide)
1st ever attempt at
producing a pulsed
antihydrogen beam!
CIPANP 2015
22/05/2015
Antiproton cooling



1)
2)
3)
4)
12
Bring the traps to 100 mK through
dilution cooling (exploiting a phase
separation of a He3-He4 mixture)
Electrons cooled down by a
resonant circuit subtracting axial
energy from the electrons
Other forms of cooling under
consideration are evaporative
cooling, ion cooling, sysiphus cooling
(currently being researched by AEgIS
collaboration members) [see New. J.
Phys 8 45 (2006) and Phys. Rev. A 89,
043410 (2014)] .
Kinetic energy potential energy
Dissipative ”Sisyphus transfer step”
Molecule back in position
Original internal state
CIPANP 2015
22/05/2015
Positron system






Surko-type accumulator:
radioactive source,
solid neon moderator
buffer gas
Source activity (now)=
14 mCi
we expect 1.2 108 e+
with 50 mCi source
e+ first trap
13
CIPANP 2015
22/05/2015
e+ accumulator
Charge exchange and Stark acceleration
Positrons incoming from a β+ source hit
a silicon microporous target, where
they capture an electron and
Positronium (Ps) is created.
Positronium is excited in Rydberg
states with laser light (Ps*)


First production ever
of pulsed antiH beam!!!
Antiprotons coming at ~5 MeV are
slowed down by degraders to ~100 keV
and a fraction is trapped in a penning
trap.
Several bunches can collected in the
trap to increase the spatial density.
Antiprotons in the trap take the
positrons from Ps* through chargeexchange reaction and form Rydberg
anti-H
Antihydrogen is then accelerated
forward through Stark acceleration




14
CIPANP 2015
22/05/2015
The trap system
Off-axis
trap (positrons)
Ps
Production
target
On-axis
trap (antiprotons)
Hbar
production
trap
15
CIPANP 2015
22/05/2015
The Fast Annihilation Cryogenic Tracking
(FACT) detector
•
•
•
•
•
•
•
•
Purpose: detect antihydrogen
annihilations in the trap (proof of
antihydrogen formation)
800 scintillating fibers (4 layers 1mm
diameter)
coupled to clear fibers
z sensitivity (beam formation): 2.1 mm
resolution
Read out by Multi Pixel Photon
Counters (MPPC)
Operated at 4 K, 1 Tesla, dissipation
10W
Volume with vacuum separated from
the main trap vacuum
Counts thousands annihilations in
about 1ms
J. Storey et al (AEgIS Coll.) NIMA 732 437 (2013)
16
CIPANP 2015
22/05/2015
The gravity module
17
Readout ASICs
77 (or 4) K vessel
Emulsion
Low energy antihydrogen @ 4K/100mK
Scintillating fiber
Detector
~0.5 m
moire
deflectometer
Strip detector (25 um pitch, 50 um thickness)
CIPANP 2015
22/05/2015
Probing the deflectometer with antimatter



Measuring forces using “slow” antiprotons (~ 100 keV)
Deflectometer prototype on small distances, using emulsions for detecting
antiprotons
Force measured from deflection of antiproton fringe pattern from light fringe
pattern
18
CIPANP 2015
22/05/2015
Silicon detector





19
First ever use of silicon to detect
direct on-sensor annihilations
Cryogenic operation, vacuum
separation window (UHV to OVC)
Strip detector with 50 um thickness,
25 um strip pitch. Resolution down
to ~7 um
Sensors produced by SINTEF,
Norway
Custom self-triggering readout ASIC
from IDE AS - Norway
CIPANP 2015
22/05/2015
Detector tests


20
A secondary beamline has
been dedicated to detector
tests (silicon and emulsions)
and deflectometer studies
The annihilation events can be
identified as “star shaped”,
where the prongs derive from
the annihilation products.
CIPANP 2015
22/05/2015
Conclusions





AEgIS is in commissioning phase. Trap systems are ready.
Work is in progress to improve antihydrogen cooling
The deflectometer has successfully been tested for the first
time with antimatter beams. Further tests are foreseen this
year
Detector tests were successful. Design of the gravity module
to be started soon.
Positronium spectroscopy studies can be started immediately
21
CIPANP 2015
22/05/2015