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Many exciting old ideas with antiprotons, pre LEAR 1977 - 1984Revival for FAIR / FLAIR
Trap experiments active at AD/CERN
pp →YY with S = ±1, ±2, ±3 (possibly YY atomic effects)CP violation test: αΛ – αΛ = 0 Compare decay asymmetry of Λ and Λ
ELENA: cooled p beams down to 100keV (best stop experim.) Walter Oelert 10.6.10
S=-2 hadronic states (B=1, 2, 3,…) via p stop. Recoilless! Highest precisionp stop and coincident channeling (dynamic unit cell tomography)Annihilat. dynamics p+9Be→{αα}380keV
Breeding of cooled d beams in double ring collider. Max. rate, max. qualityProduction of polarised p with filter method in cooler ring
…and more
Ideas get lost after a scientific lifetime
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• Production of antiprotons• Spin filter method• Antihyperon decay• Polarised production• Comparison
Ways to make polarised antiproton beamsDieter Grzonka, Kurt Kilian, Walter Oelert, IKP FZ-Jülich
MESON2010 10.–17. 6. 2010 Krakow
Monday 14.6.2010
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Production of antiprotonsConvert collision energy into particle-antiparticle pairs
energy → p + p (in 3S1- ?)
Quasifree production
p + p → p + (3p)0<ε<max
Symmetric in cm system
At 26 GeV/c beam
0 < ε <3360 MeV
2914 MeV/c > pcm > 0
If pcm < 150 MeV/c
then S wave production
D. Dekkers CERN PS 1968
K. Kilian et al.1977 pre LEAR memo to PSCC
26 GeV/c beam
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pp→p+(3p)
Assumption of quasifree nucleon-nucleon interaction is reasonable.
Simple kinematical situation
At maximum (3.65 GeV/c) antiprotons are collected, cooled and piled up in storage synchrotrons. From there extremely dense beams are delivered.
At CERN (26 GeV) one gets one useful antiproton from 106 beam protons
Average p flux I0 = 107 s-1
p lab. Momentum MC simulation
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Spin filter methodSuggested for the future ISR: P.L.Csonka, Nucl. Instr. Meth. 63 (1968) 247
If singlet and triplet cross sections are different, then an internal polarised target depletes one of the stored spin components faster than the other. Polarisation rises on the expense of intensity.
σ = σH + ΔσCb
Spin filtering for polarised antiprotons works only with cooling
avoids beam blow up and losses by multiple scattering
K.Kilian 1980, Pol. Conf. Lausanne, K.Kilian & D.Moehl 1982, Erice LEAR workshop
Filtering below 1 GeV/c →Important ΔσCb
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Spin-filtering at TSR: „FILTEX“ – proof-of-principle
→ Spin filtering works for protons
F. Rathmann et al., PRL 71, 1379 (1993)
6Spin-filtering studies at COSY and ADFrank Rathmann
PAX submitted new proposal to find out how well spin filtering works for antiprotons: Measurement of the Spin-Dependence of the pp Interaction at the AD Ring
(CERN-SPSC-2009-012 / SPSC-P-337)
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statistical error of a double polarization observable (ATT)
NQP
1TTA
Measuring time t to achieve a certain error δATT
t ~ FOM = P2·I
Polarization Buildup: Figure of Merit
(N ~ I)
Optimum time forPolarization Buildup given by maximum of FOM(t)tfilter = 2·τbeam
0 2 4 6 t/τbeam
I/I0
0.2
0.4
0.6
0.8
Bea
m P
olar
izat
ion
P2Τ
σ↑↑ : σ↓↑ P2Τ
1 : 0.5 21%
1 : 0.8 7%
ΔσCb → will
dilute effect
2T > 4 days
?Ask F.R.
Other spin dependent processes? E.g. B. Schoch: scatter polarised photons
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Λ → p + π+
p
plab
(p)
pcm
π+
plab
(π+)
Antihyperon decay
Decay makes p with helicity h = - 0.64. Lorentz boost creates transverse vector polarisation.
First and so far only experiment with polarised 200 GeV p at Fermilab. Λ production with primary proton beam. At the end an average of 104 polarised p s-1
A. Bravar et al. Phys. Rev. Lett. 77, 2626 (1996)
Decay momentum in cm syst. is 101 MeV/c
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FNAL experiment: A. Bravar et al. P.R.L.77,2626,(1996)
NB: decay polarisation tagging below 0.5 mrad ! Experiment ~ km long
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Useful antihyperon source in the GeV range (FAIR)
pp → ΛΛ → pπ+ pπ-
Decay direction of the hyperon defines the polarisation direction of the baryon.
The two decay V are tags and spectrometers for each other
Most important is geometrical reconstruction of all tracks
Will not work with internal target (miserable multi track reconstruction, miserable trigger condition)
Branching ratio σΛΛ /σtot = 10-3
cτΛ = 7.89 cm
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Active sandwich target, tracker, baryon number identifier
pp target efficiency ~ 10-2
Insert a flat target for
p secondary scattering
(done for Λ and Λ scattering)
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CP violation test
P. D. Barnes et al., PR C54 1877 (1996)105 pair events (at 1.642 and 1.918 GeV/c)
[ A ] = 0.013 ± 0.022 (most precise so far)
100 times smaller error allows relevant CP testNeeds 109 pair events or 2x1014 beam p (200 days)
As byproduct: “beam” of 109 polarised decay p
A = (αΛ + αΛ ) / (αΛ - αΛ ) = 0
ΛΛ production >95% triplet
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Use the antiproton factory (nearly) as usual.
Cut out kinematical regions in the antiproton production spectrum which would dilute vector polarisation
• Avoid pure s wave antiprotons• Cut one side in the horizontal angular distribution• Cut up and down angles• In addition avoid depolarisation in the cooler synchrotron
Polarised production
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y
x
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Red lines: angular and momentum acceptance of AD
S wave region
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y
x
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Clean cuts may need a “pointlike” source, means a shorter production target
Reduction 1/5
Cuts in kinematics
Reduction 1/5
I/I0 ~ 1/25
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p production and transport to AD-
Necessary cuts in p distribution easily made in the existing beam line
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Existing AD for p stop experiments
Acceptance H, V (π mm mrad) 200/180
Acceptance Δp/p (%) ±3.2%
Number of p injected 5 107 per cycle
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AD tune diagram and
Limit of spin stability
(red lines)
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CNI polarimeter reaction (coulomb-nuclear interference) allows to check if polarised p come out
A = 4.5% maximum
at t = - 0.0037 (GeV/c)2
corresponds to 38 mrad
for p+p scattering at 3.5 GeV/c
Polarisation test at CERN PS
Cu (lH2 ) target on external beam
1.5 Tm dipole, 10 cm gap
Straw tracker stacks before and after an lH2 analyser target on the p exit side. Adapted to 3.3 to 3.7 GeV/c p
Trigger szintillators
All in vacuum
(Target and detectors exist at COSY TOF)
A
2mb polarim. react.
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Measurement of antiproton polarisationdetector components in vacuum
1 m
PT < 150 MeV/c( s-wave )
PT < 700 MeV/c
AD acceptance
straw tubes( track resolution ~ 100 μm )
Cerenkovdetectorn=1.03
liquid hydrogenanalyser target
24 GeV/cprotonbeam
antiprotonproductiontarget1 cm W
dipole magnet1.6 T
38 mrad
scintillatorhodoscope
P = 3.4 – 3.6 GeV/c
beam dump
2% precision in p polarisation with 4 10^16 primary protons on 8mm W target
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Comparison
Filter methode Λ decay Polarised production
P 0 – 40% ?? >45% ! 0 - 40% ??
I/I0 10-1 – 10-2 ? 10-3 x 10-2 x .2 ~ 2 10-
6 0.2 x 0.2 ~ 4 10-2
P2 I < 1.6 10-2 4 10-7 < 6.4 10-3
T0 ~ 2 days (hadronic)
Reduced duty factor ?
Polarisation dependence of filter reactions ?
(not spin transfer)
Sibirian snake needed
Proof with protons ok
External target for Λ productionDecay spectrometer and –polarimeter
Pol. p scattering parasitic with CP test?
Has been used (FNAL)
Numbers are known
Is there p polarisation?
Test experiment on external PS beam
Would be by far simplest solution
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Comparison
Filter methode Λ decay Polarised production
P 0 – 40% ?? >45% ! 0 - 40% ??
I/I0 10-1 – 10-2 ? 10-3 x 10-2 x .2 ~ 2 10-
6 0.2 x 0.2 ~ 4 10-2
P2 I < 1.6 10-2 4 10-7 < 6.4 10-3
T0 ~ 2 days (hadronic)
Reduced duty factor ?
Polarisation dependence of filter reactions ?
(not spin transfer)
Sibirian snake needed
Proof with protons ok
External target for Λ productionDecay spectrometer and –polarimeter
Pol. p scattering parasitic with CP test?
Has been used (FNAL)
Numbers are known
Is there p polarisation?
Test experiment on external PS beam
If p not polarised, use polarised 26 GeV proton beam
Would be by far simplest solution
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Thank you for your attention
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polarisation dependent interactions
Spin filter idea with cooling (K. Kilian & D. Moehl 1980 Lausanne Pol. Conf., 1982 Erice LEAR workshop) Stimulated activities.
Most successful: E. Steffens and the FILTEX collaboration at the TSR in MPI Heidelberg. Proof that it works with protons. F. Rathmann PRL 71 1379 (1993)
Idea of spin transfer at very low energy e↑ + p → e + p↑ in beam – beam interaction. PAX collaboration at COSY showed that there is no effect
D. Oellers et al. Phys. Lett. B674 (2009) 269
Certainly polarisation dependent is interaction of circularly polarised photons with p
γ + p → n + π B. Schoch, EPJ 2010
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Intensity loss - polarisation gain - FOM
With a storage cell target (3 1013 pol. prot. cm-2 )
T0 ~ 2 days (hadronic)
K.K. & D.M. Erice 1982
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Geometry spectrometer (PS185 at LEAR)
A stack of 23 wire chambers
Decay spectrometer and polarimeter with full acceptance and very high precision
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