the aegis experiment · the ﬁrst experiment planned in aegis to probe the validity of the weak...

Andreas Knecht / CERN

on behalf of the AEgIS collaboration

LEAP 2013, 10/6/2013

The AEgIS Experiment

Measuring the Gravitational Interaction of Antimatter

Andreas Knecht LEAP 2013, 10/6/2013

AEgIS Collaboration

2

University of Oslo and University of Bergen, NorwayCERN, Switzerland

INFN Genova, ItalyINFN Bologna, Italy

Kirchhoff Institute of Physics, Heidelberg, Germany

Max-Planck-Insitut für Kernphysik Heidelberg, Germany

INFN, Università degli Studi andPolitecnico Milano, Italy

INFN Pavia-Brescia, Italy

INR Moscow, Russia

Université Claude Bernard, Lyon, France

Czech Technical University,Prague, Czech Republic

INFN Padova-Trento, Italy

ETH Zurich, Switzerland

Laboratoire Aimé Cotton, Orsay, France

University College, London, United Kingdom

Stefan Meyer Institut, Vienna, Austria

University of Bern, Switzerland


Motivation

First direct test of the Weak Equivalence Principle involving antimatterDirect tests so far only for matter systemsValidity for antimatter inferred from heavily debated indirect argumentsTheory could accommodate differences (e. g. through potential including gravivector and graviscalar)

3

Nieto and Goldman, Phys. Rep. 205, 221 (1991)Amole et al., Nat. Comm. 4:1785 (2013)


Motivation

4

And quite generally:Experimental test of the gravitational interaction in a new sector - one for the textbooks (and for the public)!


AEgIS Experimental Goal

Primary goal:Measurement of gravitational acceleration g for antihydrogen with 1% accuracy

Secondary goals:Spectroscopy of antihydrogenStudy of Rydberg atomsPositronium physics: formation, excitation, spectroscopy

5

Figure 3.5: Schematic view of the AEGIS Moiré deflectometer (not to scale). The cylinders represent theelectrodes of the trap for charged particles in which the antihydrogen will be produced. The first cloudrepresents the antihydrogen before the acceleration and the second one the cloud at the time t0 when theaccelerating electric field is switched o↵. The two gratings and the detector are shown.

3.5 The first AEGIS gravity measurement: a classical Moirédeflectometer coupled to a position sensitive detector

The first experiment planned in AEGIS to probe the validity of the weak equivalence principle for anti-hydrogen is the g measurement with a classical Moiré deflectometer. Such an apparatus was built andoperated by M. K. Oberthaler et al., in 1996 [64] and we are proposing an upgraded design of it (M. K.Oberthaler is member of AEGIS).

A classical deflectometer is usually made of three gratings, but the slit widths are su�ciently largethat di↵raction can be neglected. Referring to relation 3.5 for L = 0.1 m, a = 40 µm and for L = 1m, a = 120 µm. As already anticipated, the motion of the atoms in the Moiré deflectometer is purelyclassical. The presence of the first two gratings at distance L produces a periodical structure in thenumber of the atoms N(x) arriving at distance L from the second grating. Here x is the coordinate inthe direction of the gravity force. In the experiment described in [64] the atomic density modulation wasdetected, as in the case of the interferometer experiments, by using the third grating as filter: the thirdgrating is moved in the vertical direction by a fraction �x of the grating period and the total number ofatoms passing through is detected vs �x.The number of atoms N(�x) is a periodical function of �x with period keff = 2⇡/a.The comparison of N(�x) with and without including the gravity force shows that the fall of the atoms

19

Produce ultra cold antiprotonsForm positronium by interaction of positrons with a porous target (pulsed)Laser excite Ps to get Rydberg Ps (pulsed)Form Rydberg cold antihydrogen (pulsed) byStark accelerate the antihydrogen with inhomogeneous electric fields

→ Pulsed production of a cold beam of antihydrogen

Measure the gravitational accelerationin a classical moiré deflectometer


AEgIS Experimental Strategy

6

Chapter 4

Antihydrogen production by chargeexchange

The production of antihydrogen in AEGIS is based on the charge exchange reaction between antiprotonsand Rydberg positronium

Ps⇤ + p! H⇤ + e� (4.1)

The use of this reaction was proposed some time ago [150] and recently demonstrated by the ATRAPcollaboration [91]. The method by which the antihydrogen production will be implemented in AEGIShowever significantly di↵ers from that of ATRAP.

Charge exchange reactions between Rydberg atoms and ions are largely studied in atomic physics:we only recall here the main physical features of this process.

The main reasons that make this reaction interesting for the AEGIS design are

• the large cross section which is of the order of a0n4 where a0 = 0.05 nm is the Bohr radius and nis the principal quantum number of the Ps;

• the expected distribution of the quantum states of the produced antihydrogen. The antiatomsare produced in Rydberg states with a predictable state population strictly related to that of theincoming positronium. The range of final quantum states is reasonably narrow. Thanks to thesensitivity to electric field gradients of these Rydberg atoms a beam can be formed by acceleratingthe atoms with a time dependent inhomogeneous electric field.

• the possibility to experimentally implement the reaction in such a way that very cold antihydrogencan be produced. To maximize the e�ciency in the use of the antihydrogen and the quality of thebeam it is in fact important that the transverse velocity be as low as possible.

In order to best understand the formation process under the experimental conditions of AEGIS, andin order to optimize the production rate of useful antihydrogen atoms, we have implemented a completecalculation of the charge exchange process using a classical trajectories Monte Carlo (section 4.2).

4.1 Kinematics

The conservation of energy and momentum in the charge exchange reaction sets the constraints on theminimum energy of the resulting antihydrogen. Figure 4.1 defines the coordinate system: we call xp thedirection of the antiproton velocity before the recombination; ✓Ps the angle between the positroniumand antiproton velocity and ✓H the angle formed by the emerging antihydrogen velocity and the xp axis.After some calculations it is straightforward to find that the antihydrogen velocity v2H in the laboratoryreference satisfies

v2H

+ v2p + 2✓

me+mp

◆2v2Ps � 4

me+mp

vHvPscos(✓H � ✓Ps)� 2vpvPscos(✓Ps)� 2me+mp

Q

mp= 0 (4.2)

AEGIS collaboration

Storry et al., PRL 93, 263401 (2004)Vliegen and Merkt, J. Phys. B: At. Mol. Opt. Phys. 39, L241 (2006)


Antihydrogen Formation

Positronium charge exchange technique:Large cross-section, scales as n4Narrow and defined final state distributionAntihydrogen production from antiprotons at rest

7

grating 1 grating 2

position-sensitivedetector

L Latomicbeam

Ps

laser excitation

antiproton trap

positronium converter

e+

Ps

Ps*Ps*

H*

H*H beamH*

accelerating electric field

Schematic overview

Physics goals: measurement of the gravitational interaction betweenmatter and antimatter, H spectroscopy, ...

_

Schematic overview

Chapter 4

Antihydrogen production by chargeexchange

The production of antihydrogen in AEGIS is based on the charge exchange reaction between antiprotonsand Rydberg positronium

Ps⇤ + p! H⇤ + e� (4.1)

The use of this reaction was proposed some time ago [150] and recently demonstrated by the ATRAPcollaboration [91]. The method by which the antihydrogen production will be implemented in AEGIShowever significantly di↵ers from that of ATRAP.

Charge exchange reactions between Rydberg atoms and ions are largely studied in atomic physics:we only recall here the main physical features of this process.

The main reasons that make this reaction interesting for the AEGIS design are

• the large cross section which is of the order of a0n4 where a0 = 0.05 nm is the Bohr radius and nis the principal quantum number of the Ps;

• the expected distribution of the quantum states of the produced antihydrogen. The antiatomsare produced in Rydberg states with a predictable state population strictly related to that of theincoming positronium. The range of final quantum states is reasonably narrow. Thanks to thesensitivity to electric field gradients of these Rydberg atoms a beam can be formed by acceleratingthe atoms with a time dependent inhomogeneous electric field.

• the possibility to experimentally implement the reaction in such a way that very cold antihydrogencan be produced. To maximize the e�ciency in the use of the antihydrogen and the quality of thebeam it is in fact important that the transverse velocity be as low as possible.

In order to best understand the formation process under the experimental conditions of AEGIS, andin order to optimize the production rate of useful antihydrogen atoms, we have implemented a completecalculation of the charge exchange process using a classical trajectories Monte Carlo (section 4.2).

4.1 Kinematics

The conservation of energy and momentum in the charge exchange reaction sets the constraints on theminimum energy of the resulting antihydrogen. Figure 4.1 defines the coordinate system: we call xp thedirection of the antiproton velocity before the recombination; ✓Ps the angle between the positroniumand antiproton velocity and ✓H the angle formed by the emerging antihydrogen velocity and the xp axis.After some calculations it is straightforward to find that the antihydrogen velocity v2H in the laboratoryreference satisfies

v2H

+ v2p + 2✓

me+mp

◆2v2Ps � 4

me+mp

vHvPscos(✓H � ✓Ps)� 2vpvPscos(✓Ps)� 2me+mp

Q

mp= 0 (4.2)

AEGIS collaboration

Figure 4.4: Mean value of the principal quantum number nH of the produced Has a function of the initialnPs state. Di↵erent conditions are evaluated:⌅ fixed lPs,• mixed lPs [0;n-1]N lPs = 2 with di↵erent values of kv

n(H)0 10 20 30 40 50 60 70 80

prob

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

n (H) distribution

l (H)0 10 20 30 40 50 60 70

prob

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

l (H) distribution

k (H)-100-80 -60 -40 -20 0 20 40 60 80

prob

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0.0018

0.002

k (H) distribution

Figure 4.5: Distribution of final states obtained with 3000 anti-hydrogen atoms; from left to right, thethree plots show the distribution of nH , lH and kH . The initial state of the positronium used to simulatethe charge exchange process was: nPs = 35 and lPs = 2.

35

nPs = 35


Moiré Deflectometer

8

grating 1 grating 2

position-sensitivedetector

L Latomicbeam

Ps

laser excitation

antiproton trap

positronium converter

e+

Ps

Ps*Ps*

H*

H*H beamH*

accelerating electric field

Schematic overview

Physics goals: measurement of the gravitational interaction betweenmatter and antimatter, H spectroscopy, ...

_

Schematic overview

x

GratingGratingunitsunits

v =600 m/s

v =250 m/s

δ = ―gt²a

with gravity

Gravitational deflection & Moiré deflectometer

Classical deflectometer (shadow mask)Third grating replaced by position-sensitivedetector


Moiré Deflectometer

9

time (s)0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 0.0018 0.002 0.0022

Phas

e (ra

d)

0

0.5

1

1.5

2

2.5

3

With Real Detector resolution

0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 0.0018 0.002 0.0022

0

0.5

1

1.5

2

2.5

3

With Infinite Detector resolution

Figure 3.14: Phase shift as a function of the time-of-flightp

< T 2 >(sec) between the two gratings of theMoiré interferometer. Top plot: assuming a 10µm detector resolution; Bottom plot: assuming perfectdetector resolution.

A proper magnetic shielding has to be designed around the grating system. Again, atoms in thefundamental state are preferred over Rydberg states with high m.

• Systematic errors can be controlled by comparison of the gravity induced shift with that obtainedwhen taking data with the gratings rotated by 900 degrees. In this case the e↵ect of gravity iscanceled.

• The design of the deflectometer can still be optimized: it is possible that having the same openingfraction in the two gratings is not the optimum solution.

• to cross-check our results, we are evaluating the possibility of carrying out the charge symmetricexperiment (producing hydrogen atoms, rather than antihydrogen atoms, by using protons, ratherthan antiprotons), but this requires enhancing the position sensitive detector with a scheme thatcan ionize ground state Hydrogen atoms.

3.6 Additional measurements with the antihydrogen beam

The availability of a beam of antihydrogen o↵ers the possibility to perform additional measurementsaiming to study antihydrogen properties. We simply mention here the possibility to perform Rydberg

28

Phase shift as a function of time (velocity of antihydrogen) gives gravitational acceleration: Δz ~ gt2


Experimental Apparatus

10

p from AD_

Positron accumulator5T magnet 1T magnet

Layout of the zone


Location

11


Experimental Installation

12

Zone early 2011 Zone late 2012


5T Catching Traps

13

HV

HV

HV

1

2

3


1T Formation Traps

14


Central Antihydrogen Detector

Scintillating fibre detector operating at 4K800 channels readout by SiPM200 MHz readout detecting hit pattern

15


Positron System

16

800 MBq 22Na sourceSolid neon moderator

Positron trap

Positron accumulatorBuffer gas cooling

Pulsed transfer line ~0.1T


Positron System

Ongoing work to increase rates and efficiencies

17

Number of stored e+ and lifetime

0 200 400 600 800

0 20 40 60 80 100 120

Time (s)

Lifetime = 29+/-2 sfill time = 120 s

7-8 106 e+

3 106 e+ Lifetime = 12+/-1 sfill time = 38 s

5 106 e+

6 106 e+

coun

ts (a

.u.)

Pulse number

Lifetime = 25+/-2 sfill time = 100 s

1 pulse from trap 5-6 104 e+

Dump intensity 7-8 106 e+

Lifetime ~30 s

Fill time ~120 s

5-6 x 104 e+ from trap

Conclusion

M o d e r a t i o n - Tr a n s p o r t efficiency ~ 2.5 10-2

Spot dimension 4-5 mm

Spot dimension 1-2 mm

Trapping-dumping efficiency ~ 0.14

Permanent diagnostic systems tested and calibrated

e+

Dump intensity 7-8 106

Lifetime ~30 s

Fill time ~120 s Transport efficiency ~80-90 %

Improvements for increasing the accumulator dump intensity (aim 108) Improvements for optimization of the beam transport and diagnostic in 5 T region


Commissioning Results

Trapping, cooling

18

Trapping voltage [kV]1 2 3 4 5 6 7 8 9

]5A

ntip

roto

ns c

augh

t [ x

10

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Antiproton catching vs applied high voltage

Antiproton cooling time [s]0 5 10 15 20 25 30 35 40

Col

d / h

ot a

ntip

roto

n fr

actio

n

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Cold and hot antiproton fractions vs. electron cooling time



19

Lifetime ~500 s

Storing

sec0 50 100 150 200 250 300

Tra

pped

ant

ipro

tons

0

20

40

60

80

100

120

140

310×

Hot antiprotons storage time9 KV

Cold antiproton storage



Manipulations

20



Positron transfers through transfer line and 5T into 1T magnet

21

Extraction pulsefrom accumulator

Scintillator pulsesfrom positron annihilation in 1T


Detector Tests

22

Parasitic tests:

Silicon detectors (strip, pixel) MCP Emulsions

Explore different candidate technologies for the (downstream) antihydrogen detector

See poster by O. Karamyshev


Silicon Detectors

3D pixel sensor designed for the ATLAS upgradeAlso tested: strip sensor, Mimotera

23

+ Installation of the detector in the six cross chamber

3D pixel detector mounted on the flange

p_

[MeV]totE

Prob

abilit

y

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14 FTFChipsData

[MeV]totE0 5 10 15 20 25 30

DAT

A/N

SIM

N 0

1

2

Analyses andresults on the

MIMOTERA data

A. Gligorova,N. Pacifico,G. Bonomi,C. Riccardi,A. Magnani,H. Sandaker,M. Caccia

Short reminder ofthe MIMOTERAdetectorInstallation in testbeam in May-June2012Features of theMIMOTERA

Analyses andResultsCalibrationSignal and NoiseClustering AlgorithmPotential BackgroundSourceTracks produced byannihilation productsComparison betweenMonte Carlo models(CHIPS and FTF)and data

Conclusions

ClusteringI Clustering was performed after applying the above

mentioned cut on the single pixels.I Clusters were defined as conglomerates of pixels

neighbouring in the horizontal, vertical and diagonaldirection.

I To avoid overlapping of clusters, only frames with apixel occupancy < 10% and less than 150 clusters perframe were accepted for analysis.

Energy [keV]1 10210 310 410

Cou

nts

210

310

410

510

Raw signalNoiseNoise subtracted

Distribution of the signal in single pixelsafter subtraction of the noise fitted witha normal distribution.

X0 20 40 60 80 100

Y

0

20

40

60

80

100

0

1000

2000

3000

4000

5000

6000

7000

Sample of a triggered frame afterapplying the noise cut


Mimotera Detector

112 x 112 silicon pixel detector, 153 μm x 153 μm, 15 μm active depth

Detailed comparison of data vs simulation

Test of Monte Carlo treatment of antiproton annihilations on bare silicon

24

Publication forthcoming!

Preliminary


Emulsions

25

Exposure of emulsionDevelopment in dark roomScanning on automated microscopes

Offline track and vertex finding algorithms1 μm vertex resolution

See talk by J. StoreyFriday @ 9:55 am

Glass%base%1%mm%

Emulsion)layer))(50)micron))

Focus&

an#proton(

Base (glass or plastic)(several 100 μm)


First Test of Moiré Deflectometer

26

Mini-Deflectometer

CERN 2013: Philippe Bräunig

emul

sion

deflectometer (353 hits)

reference grating (296 hits)

• ~100keV antiprotons• 7 hours exposure time• deflectometer and emulsion in the OVC• no seperation foil

~100 keV antiprotons7 hour exposureBare emulsion behind deflectometer


First Test of Moiré Deflectometer

Antiproton fringes observed

Alignment of gratings using light and single grating

Promising results!

27

Publication forthcoming!

Rotation (rad)-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Perio

d39

39.2

39.4

39.6

39.8

40

40.2

40.4

40.6

40.8

20

40

60

80

100

Cross-correlation method

Preliminary


Conclusions and Outlook

Installation of apparatus largely completed and commissioned

Parasitic measurements essential in converging to an optimal deflectometer/detector layout

Next steps:Install proton source, hydrogen detectorCommission Rydberg positronium formationWork on hydrogen formation/characterization

Goal: Be ready for antihydrogen beam formation in summer 2014!

28


Backup

29

Positronium target - parameters

Ultracold antiprotons

Antiprotons in the trap cannot be directly cooled to 100 mK

Cool antiprotons by collisions with a partner particle stored in the same trap that can be cooled

e- antiproton

L C

electronsResistive cooling with a resonant tuned circuit + radiation cooling

Laser cooling of La_

Ultimate temperature: 240 nK

Negative ions: La-

A demonstration of laser cooling of negative ions is needed Experiment in progress at MPI (members of AEGIS)

antiprotonsEmbedded electron cooling, adiabatic cooling, evaporative cooling, ...

Harmonic Generator

n=1 → n=3 205 nm Transition saturation energy: ~2 µJ

n=3 → Rydberg 1650-1700 nm Transition saturation energy: ~0.2 mJ

Nd:YAG 1064 nm

650 mJ, 5 ns

4th

2nd

1st

OPG

OPG + OPA SUM

OPA

894 nm

1650-1700 nm

266 nm

532 nm

1064 nm

Laser source and harmonic generator: Tender will start within December 2010 (?) Expected arrive in March - April 2011 Goal of the apparatus:

About 10 times the saturation energy

Rydberg excitation via a simultaneous two step incoherent process: 1 → 3 → Rydberg (wavelengths: 205 nm and 1650 - 1700 nm)

Main effects of level broadening: 1 → 3: Doppler effect (~0.04 nm) due to velocity distribution of Ps3 → Rydberg: Motional Stark effect (makes a quasi-continuum from n=17, each level is broadened to many nm) due to Ps movement in a strong B field

Lasers

components delivered in April 2011(pumping laser delivered in autumn 2011)

Laser system: power tests

required level = 2μJ required level = 200μJ

Moiré deflectometer: first tests

SolidWorks StudentenlizenzNur für akademische Zwecke

Faraday cup(detects integral

of incomingatom beam)

smalldistance

for highercontrast

small prototypegrating structures

loadingflange

last gratingis used to scanfringe pattern

v1

Moiré deflectometer: 6” (full size) grating prototype

the aegis experiment · the ﬁrst experiment planned in aegis to probe the validity of the weak...

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