The CERN Antiproton Physics Programme - The Antiproton Decelerator (AD...
Transcript of The CERN Antiproton Physics Programme - The Antiproton Decelerator (AD...
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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
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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...)
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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
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The ELENA Ring
electroncooler
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ELENA: electrostatic beamlines
p/H- source for commissioning and quick beamline setup
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ELENA: electrostatic beamlines
p/H- source for commissioning and quick beamline setup
pin p
out
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The ELENAIon Switch
Installed and commissioned with 100 keV H- beam
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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
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ELENA: electrostatic beamlines
Static spherical deflectors where no quick switching is needed
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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.)
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ELENA: electrostatic beamlines
Straight sections: electrostatic quadrupoles - FODO transport
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Quadrupole doublet + steerer unit
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The antiproton physics programme at CERN
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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
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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
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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!
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Antiproton physics is on the headlines
ALPHA experiment
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Antiproton physics is on the headlines
ATRAP experiment
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Antiproton physics is on the headlinesASACUSA experiment
Antihydrogen beam!
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Antiproton physics is on the headlinesASACUSA experiment
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Assuming CPT, antiprotonic helium results contribute to the official value of proton/electron
mass ratio
Antiproton physics is on the headlinesASACUSA experiment
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ACEAntiproton Cell Experiment
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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
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● 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
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50 MeV antiproton beam
Target: cells suspended in gelSliced after irradiation to measure survival rate
Antiproton Cell Experiment
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Depth Depth
Protons Antiprotons
Sur
viva
l pro
bab
ility
Targeted zone: smaller survival rate
non-targeted zone: higher survival rate
Antiproton Cell Experiment
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ALPHASynthesis of antihydrogen
Laser & MW spectroscopy, gravity
SuperconductingPenning trap
e+ source
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Production and trapping of antihydrogen for laser spectroscopy
p (5.3 MeV)
1) Capturing antiprotons
Penning-Malmberg trap (=multiring trap)
Longitudinal magnetic field
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1) Capturing antiprotons2) Cooling by electrons in the same trap
Production and trapping of antihydrogen for laser spectroscopy
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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
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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))
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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
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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.
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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
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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
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ATRAPAntihydrogen synthesis and laser
spectroscopy, p q/m and μ
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Antihydrogen production by Cesium (ATRAP)
Cs
Cs (excited)
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Cs+
e-e-
e+e+
e-e-
e+e+
e-e-
e+e+
e-e-
e+e+
Antihydrogen production by Cesium (ATRAP)
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e-e-
e+e+pp
H (excited)
Possible to control H state by the laser energy
Antihydrogen production by Cesium (ATRAP)
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Magnetic moment of antiproton:ATRAP
B~5.7 Tesla
-V
-V
+V
+V
p
Penning trap
Oscillation in longitudinal electric potential
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Magnetic moment of antiproton:ATRAP
-V
-V
+V
+V
Penning trap + magnetic bottle
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p
Magnetic moment of antiproton:ATRAP
-V
-V
+V
+V
Slower oscillation
Penning trap + magnetic bottle
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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
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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
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p
Magnetic moment of antiproton:ATRAP
Precision:μ
p = μ
p (5 ppm)
J. DiSciacca, et.al., PRL 110(2013), 130801
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BASEBaryon Antibaryon Symmetry
Experiment
antiproton & proton: q/m & μ
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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
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Magnetic moment of antiprotonDouble-trap: BASE
Try to make spin-flip via MW excitation
Magnetic bottle – detect spin-state
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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)
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Asacusa experimentAntihydrogen group
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MW spectroscopy of H/H (Asacusa)RFQ decelerator (100 keV)
Positron source
Positron accumulator
Synthesis trap
Superconducting Penning trap – capture and cooling
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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)
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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
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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]
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Gravity experiments
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AEGIS
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Antimatter & gravity - AEgIS
pp
e+e+
SiO2
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Antimatter & gravity - AEgIS
e-e-
e+e+
Laser(excite the positronium)
pp
e+e+
SiO2
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Antimatter & gravity - AEgIS
e+e+
SiO2
e-e-
H
H
H
HH emission in 4π
Stark acceleration
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Antimatter & gravity - AEgIS
The periodic pattern is displaced due to gravity
Detector: emulsion !(Gives best spatial resolution; no time resolution is needed)
Moiré deflectometer
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GBARGravitational Behaviour of
Antihydrogen at Rest
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Antimatter& gravity:GBAR
electron linac e+ productiontarget
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Antimatter& gravity:GBAR
e+ productiontarget
Laser (excite Ps)
e-e-e+e+
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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
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Asacusa experiment
antiprotonic helium spectroscopy group
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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?
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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
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Principle of laser spectroscopy of pHe
P principal quantum number
P orbital quantum number
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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)
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Principle of laser spectroscopy of pHe
Laser-induced population transfer
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Principle of laser spectroscopy of pHe
Laser-induced population transfer
H-like ion withdegenerate levels
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Principle of laser spectroscopy of pHe
Laser-induced population transfer
Collisions: Stark mixing
p
p
p
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Principle of laser spectroscopy of pHe
Laser-induced population transfer
p
p
p
Collisions: Stark mixing
TIME [ns]
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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
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●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
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Experimental layout40-100 keV
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RFQ Decelerator(100 keV)
Target: helium gas,T=1.5 K
Asacusa:laser spectroscopyof p-He
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The Asacusa pHe beamline & exp.
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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)
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(Anti)proton-electron mass ratio
CODATA 2010
{Indirect (spin-flip measurements)
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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...