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
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...