The CERN Antiproton Physics Programme -

The Antiproton Decelerator (AD) & ELENA

Dániel Barna

Wigner Research Centre for Physics, Budapest, Hungary

● The CERN antiproton facilities● Experiments, their programmes and results

The CERN Antiproton Decelerator● Deceleration: 3.57 GeV/c →

100 MeV/c (Ekin=5.3 MeV)

● Stochastic and electron cooling

● 1 bunch (~107 P) / 100 s (beam steering is painfully slow...)

ELENA – The future of antiprotons @ CERN● ELENA = Extra Low ENergy Antiproton ring – under construction!● Extension to the Antiproton Decelerator, 30.4 m circumference● Further decelerate antiprotons to 100 keV to improve

efficiency of experiments● Allow simultaneous running of multiple experiments

The ELENA Ring

electroncooler

ELENA: electrostatic beamlines

p/H- source for commissioning and quick beamline setup

ELENA: electrostatic beamlines

p/H- source for commissioning and quick beamline setup

pin p

out

The ELENAIon Switch

Installed and commissioned with 100 keV H- beam

ELENA: electrostatic beamlines

Quick electrostatic switches distribute beam to 4 experiments running parallel

4 bunches (1 μs) per shot:4 experiments can run in parallel

ELENA: electrostatic beamlines

Static spherical deflectors where no quick switching is needed

Quick switches and deflectors

Spherical electrostatic deflector giving 33o deflection

Fast deflector (<1 μs) giving220 mrad kick (J. Borburgh et.al.)

Fast deflector (<1 μs) giving220 mrad kick (J. Borburgh et.al.)

ELENA: electrostatic beamlines

Straight sections: electrostatic quadrupoles - FODO transport

Quadrupole doublet + steerer unit

The antiproton physics programme at CERN

Running and planned experiments at the AD & ELENA

● ATRAP (Antihydrogen TRAP)H laser spectroscopy (to come), p magnetic moment & q/m

● ALPHA (Antihydrogen Laser PHysics Apparatus)H laser & mw spectroscopy, gravity (to come)

● Asacusa (Atomic Spectroscopy And Collisions Using Slow Antiprotons)H mw spectroscopy, p-He laser spectroscopy (m

p/m

e),

antiproton dE/dx, σannihil

in matter

● BASE (Baryon Antibaryon Symmetry Experiment)p magnetic moment & q/m

● AEGIS (Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy)H gravity

● GBAR (Gravitational Behaviour of Antihydrogen at Rest)Future, with ELENA: H gravity

● ACE (Antiproton Cell Experiment)cancer therapy, finished

Running and planned experiments at the AD & ELENA

● ATRAP (Antihydrogen TRAP)H laser spectroscopy (to come), p magnetic moment & q/m

● ALPHA (Antihydrogen Laser PHysics Apparatus)H laser & mw spectroscopy, gravity

● Asacusa (Atomic Spectroscopy And Collisions Using Slow Antiprotons)H mw spectroscopy, p-He laser spectroscopy (m

p/m

e),

antiproton dE/dx, σannihil

in matter

● BASE (Baryon Antibaryon Symmetry Experiment)p magnetic moment & q/m

● AEGIS (Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy)H gravity

● GBAR (Gravitational Behaviour of Antihydrogen at Rest)Future, with ELENA: H gravity

● ACE (Antiproton Cell Experiment)cancer therapy, finished

Trap-b

ased exp

eriments

The antiproton physics programme● Most experiments want to compare proton-

antiproton properties: test CPT● ... which works very well so far. Need to find

very tiny differences. High-precision physics.● Antiproton physics is interesting: these

experiments are the highlight visit targets when LHC is running...

● ... it produces important physics results as well!

Antiproton physics is on the headlines

ALPHA experiment

Antiproton physics is on the headlines

ATRAP experiment

Antiproton physics is on the headlinesASACUSA experiment

Antihydrogen beam!

Antiproton physics is on the headlinesASACUSA experiment

Assuming CPT, antiprotonic helium results contribute to the official value of proton/electron

mass ratio

Antiproton physics is on the headlinesASACUSA experiment

ACEAntiproton Cell Experiment

Antiproton Cell Experiment

● Goal: highest localised energy deposition in the tissues, without damaging the surroundings

photonscharged particles(protons)

antiprotons

Simulation

Antiprotons can be more efficient

● Until they stop, they deposit about the same energy as protons

● Annihilation: ~ 30 MeV strongly localised energy deposition

np

p np

ππ

π

π

phot

on

np

ππ

π

π

Relativistic pions have small energy deposition

Nucleus recoil:slow, low range Fission

fragmentsslow, short range

Antiproton Cell Experiment

50 MeV antiproton beam

Target: cells suspended in gelSliced after irradiation to measure survival rate

Antiproton Cell Experiment

Depth Depth

Protons Antiprotons

Sur

viva

l pro

bab

ility

Targeted zone: smaller survival rate

non-targeted zone: higher survival rate

Antiproton Cell Experiment

ALPHASynthesis of antihydrogen

Laser & MW spectroscopy, gravity

SuperconductingPenning trap

e+ source

Production and trapping of antihydrogen for laser spectroscopy

p (5.3 MeV)

1) Capturing antiprotons

Penning-Malmberg trap (=multiring trap)

Longitudinal magnetic field

1) Capturing antiprotons2) Cooling by electrons in the same trap

Production and trapping of antihydrogen for laser spectroscopy

3) To capture oppositely charged positrons in the same trap: modify the potential

positrons

antiprotons

V1 V2 V3 V7

Production and trapping of antihydrogen for laser spectroscopy

4) Antihydrogen synthesis

positrons

antiprotons

Antiprotons need to get in contact with positrons, at low velocities

Production and trapping of antihydrogen for laser spectroscopy

● Excite axial motion of antiprotons...● ...in an anharmonic potential (frequency is a function of amplitude)● Use a frequency-chirped excitation (frequency is function of time) to

precisely control the oscillation amplitude...● ...and align the 'turnover' point of antiprotons (v=0) with positrons● Autoresonant excitation (C.Amole, et.al., Phys. Plasmas 20, 043510

(2013))

5) Trap antihydrogen for laser spectroscopy

H

The neutral antihydrogen escapes the Penning-Malmberg trap immediately.

Add a multipole magnetic field (“Ioffe-Pritchard” trap) with minimal magnetic field at the centre.

The “low field seeking” spin-states of H can be trapped if initial kinetic energy < trap depth (for more than 1000 s!)

Production and trapping of antihydrogen for laser spectroscopy

Nature 7 (2011), 558

resonant MW on

time [s]

Alpha achievements● H synthesized and trapped routinely (1 trapped H per attempt

(20min) & 104 p), practically arbitrarily long (Nature 7 (2011), 558)

● Shining on-resonance MW ontotrapped H induced spin-flip and escape from trap (yes-no experiment, no spectroscopy yet)(Nature 483(2012), 439)Will be improved in future

● Quickly switch off magnetic trapand observe “free fall” (annihilationposition)-65 < mH,grav / mH,inertial < 75(95% conf.lev)Dedicated setup (vertical trap) is planned in the future

● 1s-2s laser spectroscopy is coming this summer, probably.

Spectroscopy of antihydrogen

TODAY:

ALPHA:~ 1 trapped H per attempt(104 p )

ATRAP:~ 5 trapped H per attempt(106 p, 2 heures)

FUTURE (probably this year): laser spectroscopy of trapped antihydrogen

H 1s-2s laser spectroscopy with a single atom?

Laser

● H has a finite oscillation in the trap

● Overlap with the focussed laser beam?

● Need long interaction time. Cosmic background would exceed the signal over a long period (remember: there is probably just 1 H in the trap)

● After a 1s --> 2s transition a second photon from the same laser ionizes the H

● Keep the charged-particle trap ON as well, which captures p after the ionization

● Integrate over a long time

● Then suddenly switch off the trap and detect if there was a p

ATRAPAntihydrogen synthesis and laser

spectroscopy, p q/m and μ

Antihydrogen production by Cesium (ATRAP)

Cs

Cs (excited)

Cs+

e-e-

e+e+

e-e-

e+e+

e-e-

e+e+

e-e-

e+e+

Antihydrogen production by Cesium (ATRAP)

e-e-

e+e+pp

H (excited)

Possible to control H state by the laser energy

Antihydrogen production by Cesium (ATRAP)

Magnetic moment of antiproton:ATRAP

B~5.7 Tesla

-V

-V

+V

+V

p

Penning trap

Oscillation in longitudinal electric potential

Magnetic moment of antiproton:ATRAP

-V

-V

+V

+V

Penning trap + magnetic bottle

p

Magnetic moment of antiproton:ATRAP

-V

-V

+V

+V

Slower oscillation

Penning trap + magnetic bottle

p

Magnetic moment of antiproton:ATRAP

-V

-V

+V

+V

Faster oscillation

● Measure frequency to determine spin-state

● Induce spin flips via MW

● Determine spin-flip probability vs. MW frequency

Penning trap + magnetic bottle

p

Magnetic moment of antiproton:ATRAP

J. DiSciacca, et.al., PRL 110(2013), 130801

Resonance

Line shape due to p sampling the inhomogeneous B field of the trap

p

Magnetic moment of antiproton:ATRAP

Precision:μ

p = μ

p (5 ppm)

J. DiSciacca, et.al., PRL 110(2013), 130801

BASEBaryon Antibaryon Symmetry

Experiment

antiproton & proton: q/m & μ

Antiproton charge-to-mass ratio● Measure cyclotron frequencies of a p and a H-

alternatingly in the same trap

● (q/m)p – (q/m)p = 1 ± 7·10-11

BASE - S.Ulmer, et.al., Nature 524 (2015), 196

Magnetic moment of antiprotonDouble-trap: BASE

Try to make spin-flip via MW excitation

Magnetic bottle – detect spin-state

Magnetic moment of antiprotonDouble-trap: BASE

Try to make spin-flip via MW excitation

Magnetic bottle – detect spin-state

Today: Δμ/μ = 3 x 10-9 with a single protonRepeat with a single antiproton!(A. Mooser, et.al.: Nature 509 (2014), 596)

Asacusa experimentAntihydrogen group

MW spectroscopy of H/H (Asacusa)RFQ decelerator (100 keV)

Positron source

Positron accumulator

Synthesis trap

Superconducting Penning trap – capture and cooling

Synthesis trap. Its magnetic trap focuses the low-field-seeking states of H

MW cavity – try to make a transition to a high-field-seeking state

MW spectroscopy of H/H (Asacusa)

Synthesis trap. Its magnetic trap focuses the low-field-seeking states of H

MW cavity – try to make a transition to a high-field-seeking state

MW spectroscopy of H/H (Asacusa)

Sextupole filter: focuses only if no transition occured

Detector

TODAY: ● 80 H detected (without the MW cavity)● Relative precision of 10-7 reached with a hydrogen beamFUTURE: MW spectroscopy of H (needs a lot of H !!)

MW spectroscopy of H/H (Asacusa)

M.Diermaier,et.al., Hyperfine Interactions 233(2015), 35

ν-ν0 [kHz]

rate

at

dete

ctor

[H

z]

With hydrogen beam!

magnetic field [T]

fre

quen

cy [

GH

z]

Gravity experiments

AEGIS

Antimatter & gravity - AEgIS

pp

e+e+

SiO2

Antimatter & gravity - AEgIS

e-e-

e+e+

Laser(excite the positronium)

pp

e+e+

SiO2

Antimatter & gravity - AEgIS

e+e+

SiO2

e-e-

H

H

H

HH emission in 4π

Stark acceleration

Antimatter & gravity - AEgIS

The periodic pattern is displaced due to gravity

Detector: emulsion !(Gives best spatial resolution; no time resolution is needed)

Moiré deflectometer

GBARGravitational Behaviour of

Antihydrogen at Rest

Antimatter& gravity:GBAR

electron linac e+ productiontarget

Antimatter& gravity:GBAR

e+ productiontarget

Laser (excite Ps)

e-e-e+e+

Antimatter& gravity:GBAR

● H+ trapped together with Be+

● Be+ cooled by laser

● H+ cooled by Be+ down to ~20 μK (~1 m/s)

● Ionisation by laser: H+ → H (neutral, starts falling)

● Mesure the time-of-flight

H+ trap

Asacusa experiment

antiprotonic helium spectroscopy group

Trapping antiprotons?

● All experiments so far used Penning traps (or variants of it) to trap antiprotons and make precise measurements on it, or create antihydrogen

● Is this the only way?

P stops in material – replaces an electron in an atomic orbit – cascades down immediately (and annihilates)

Emitted radiation: X-ray. Spectrum → mP (precision: 5 x 10-5)

Antiprotonic helium – a unique exotic atom P replaces one electron:

nucleus + P + electronin high Rydberg state (n~38, l~n-1)

~3% in metastable states (lifetime: 3-4 μs, enough for experimenting)

antiproton's atomic transitions are in the visible range(laser spectroscopy, high precision)

Simple enough for 10-9 calculations, or better(Master of it: V. Korobov)

Time [μs]

# o

f a

nn

ihila

tion

s [a

.u.]

97%

3% metastable

An alternative way to trap antiprotons – exotic atoms

An exotic atom is a Nature-made trap, free from man-made imperfections

Principle of laser spectroscopy of pHe

P principal quantum number

P orbital quantum number

Principle of laser spectroscopy of pHe

P principal quantum number

P orbital quantum number

Why metastable?● In high-L states, negligible overlap

with the nucleus● Electron removes degeneracy,

protects from collisions● Due to large ionization

potential: Auger decaywould require transitionswith large Dn, which would require large DL (suppressed)

Principle of laser spectroscopy of pHe

Laser-induced population transfer

Principle of laser spectroscopy of pHe

Laser-induced population transfer

H-like ion withdegenerate levels

Principle of laser spectroscopy of pHe

Laser-induced population transfer

Collisions: Stark mixing

p

p

p

Principle of laser spectroscopy of pHe

Laser-induced population transfer

p

p

p

Collisions: Stark mixing

TIME [ns]

What exactly can we learn from P-He spectroscopy?

● Measure atomic transition frequencies of antiprotonic helium: νexp

● Compare it to theoretical 3-body calculations: νth

[V.I. Korobov, for example: Phys. Rev. A77 (2008) 042506]

● Interpretation:

Frequency is function of many constants: νth(mHe, q, me, mP)Use this hydrogen-like parametrization:

Let νth(mP/me) ≡ νexp mP/me – a dimensionless constant

νn , l→n ' ,l '=Rcm p̄*

meZ eff2(n , l , n ' , l ' )(

1n2

−1n ' 2

)

Screening by electron; use QED to calculate

Known to extremely high precision

●2-photon spectroscopy (overcome Doppler-limit)●Better cryostat at 1.5 K

AD, no RFQ decelerator:high density target needed to stop pcollisional shiftsLEAR

decelerating-RFQ, pbar stops in low-density targetlaser linewidth

Pulse-amplified CW laser, frequency combDoppler-width @ T=10K

Long history, continuously increasing precision

Experimental layout40-100 keV

RFQ Decelerator(100 keV)

Target: helium gas,T=1.5 K

Asacusa:laser spectroscopyof p-He

The Asacusa pHe beamline & exp.

Measured resonance profiles with 2-photon spectroscopy

-1 0 1Laser frequency offset [GHz]

P 4He (36,34) → (34,32)

P 4He (33,32)→(31,30)

-1 0 1Laser frequency offset [GHz]

-1 0 1Laser frequency offset [GHz]

P 3He (35,33)→(33,31)

Fractional precision of frequency:2.3-5 x 10-9

Precision of antiproton/electron mass ratio: 1.3 x 10-9

Agreement with proton within errorbars

CODATA is using these results for proton/electron mass ratio (assuming CPT)

[Nature 475 (2011) 484]

Hyperfine lines caused by the interaction betweenS

e lP (S

3He)

(Anti)proton-electron mass ratio

CODATA 2010

{Indirect (spin-flip measurements)

Summary

● CERN has an intensive antiproton programme● Will continue for the coming 10-15 years with

ELENA (under construction)● Low-energy, high-precision experiments● Measuring fundamental constants, testing

symmetries● Antiproton physics is interesting, it has produced

– and is expected to produce headline news...