Towards Polarized Antiprotons
Frank RathmannInstitut für Kernphysik
Forschungszentrum Jülich
Workshop on „Observables in Antiproton-Proton Interactions“
Trento, July 3-7, 2006
Frank Rathmann Observables in Antiproton-Proton Interactions 2
Polarized AntiprotonsPolarized AntiprotonsIntense beams of polarized pbar never produced
• Conventional methods (ABS) not appliable
• Polarized pbar from antilambda decay- I< 1.5∙105 s-1 (P ≈ 0.35)
• Pbar scattering off liquid H2 target- I< 2∙103 s-1 (P ≈ 0.2)
• Stern-Gerlach spin separation of a stored beam- untested
• 15.05.2006 (Walcher et al.): Use polarized electron beam
Spin-filtering is the only succesfully tested technique
Frank Rathmann Observables in Antiproton-Proton Interactions 3
P beam polarizationQ target polarizationk || beam direction
σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)
polbeam
polbeam
tt0
tt0
ee2I)t(I
ee2I)t(I
transverse case:
Q0tot
longitudinal case:Q)( ||0tot
For initially equally populated spin states: (m=+½) and (m=-½)
revtpolpol
revtc0beam
fdQ1
fd)(1
pol
t
0
pol
tcosheIII)t(I
ttanhIIII)t(P
beam
Time dependence of P and I (removal only)
Spin Filter MethodSpin Filter Method
Frank Rathmann Observables in Antiproton-Proton Interactions 4
statistical error of a double polarization observable (ATT)
NQP1
TTA
Measuring time t to achieve a certain error δATT ~ FOM = P2·I
Optimum Interaction Time
(N ~ I)
Optimimum 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
Beam
Pol
ariza
tion
Frank Rathmann Observables in Antiproton-Proton Interactions 5
1992 Filter Test at TSR with protons1992 Filter Test at TSR with protonsExperimental SetupExperimental Setup
Frank Rathmann Observables in Antiproton-Proton Interactions 6
Polarized Atomic Beam SourcePolarized Atomic Beam Source
mmjj = = ++1/21/2
mmjj = = --1/21/2
mmii=-=-1/21/2
mmii=-=-1/21/2mmii=+1/=+1/22
mmii=+1=+1/2/2
1|1>|2>
|3>|4>
ee-
pp|1>
Atoms with mAtoms with mjj=+=+½ ½ focused focused
in sextupole magnetsin sextupole magnets
RF transitions select HFS
Frank Rathmann Observables in Antiproton-Proton Interactions 7
1992 Filter Test at TSR with 1992 Filter Test at TSR with protonsprotons
Experimental SetupExperimental Setup ResultsResults
F. Rathmann. et al., PRL 71, 1379 (1993)
T=23 MeV
Low energy pp scattering
1<0 tot+<tot-
ExpectationTarget Beam
Frank Rathmann Observables in Antiproton-Proton Interactions 8
Two interpretations of FILTEX resultTwo interpretations of FILTEX result
1994: Meyer and Horowitz: three distinct effects1. Selective removal through scattering beyond θacc=4.4 mrad (σR=83 mb)2. Small angle scattering of target protons into ring acceptance (σS=52 mb)3. Spin-transfer from polarized e- of H atoms to stored protons (σE=-70 mb)
σ1= σR+ σS + σE = 65 mb
2005: Milstein & Strakhovenko + Nikolaev & Pavlov: only one effect1. Selective removal through scattering beyond θacc=4.4 mrad (σR=85.6 mb)
No contribution from other two effects (cancellation of scattering and transmission)
σ1 = 85.6 mb
Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1
P(t)=tanh(t/τ1), 1/τ1=σ1Qdtf σ1 = 72.5 ± 5.8 mb
Spin-filtering works! But how?
Details in Nikolaevs Talk
Frank Rathmann Observables in Antiproton-Proton Interactions 9
Spin-Filtering: Present SituationSpin-Filtering: Present Situation
Spin Filtering works, but:1. controversial interpretations of TSR result2. no experimental data base for antiprotons
experimental tests needed with 1. Protons at COSY2. Antiprotons at AD of CERN
Frank Rathmann Observables in Antiproton-Proton Interactions 10
Spin-filtering studies at COSY
Objective: •Understanding of spin-filtering mechanism:•Disentangle electromagnetic and hadronic contributions
to the polarizing cross section
Frank Rathmann Observables in Antiproton-Proton Interactions 11
Polarizing cross sections from the two models
… only hadronic - electromagnetic + hadronic
TSR
A measurement of eff to 10% precision requires polarization measurement with P/P = 10%.
Frank Rathmann Observables in Antiproton-Proton Interactions 12
How to disentangle hadronic and electromagnetic contributions to eff ?
Injection of different combinations of hyperfine states• Different electron and nuclear polarizations• Null experiments possible:
•Pure electron polarized target (Pz = 0), and•Pure nuclear polarized target (Pe=0)
Inj. states Pe Pz Interaction Holding field|1> +1 +1 Elm. + had. transv. + longit. weak (20 G)
|1> + |4> 0 +1 only had. longitudinal strong (3kG)|1> + |2> +1 0 only elm.
AD Experiments require both transverse and longitudinal (weak)fields.
Strong fields can be applied only longitudinally (minimal beam interference)
- Snake necessaryTarget polarimetry requires BRP for pure electron polarization.
Frank Rathmann Observables in Antiproton-Proton Interactions 13
Experimental setup
• Low-beta section • Polarized target (former HERMES target)• Detector• Snake• Commissioning of AD setup
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x,ynew = 0.3 -> increase in density with respect to ANKE: factor 30•Lower buildup time, higher rates•Larger polarization buildup rate due to higher acceptance•Use of HERMES target (already in Jülich)
Low beta section
S.C. quadrupole development applicable to AD experiment
Frank Rathmann Observables in Antiproton-Proton Interactions 15
ANKE vs new IP: Acceptance and Lifetime
Acceptance @ ANKE
Cross sections
Acceptance @ new-IP
Lifetimes… only hadronic - electromagnetic + hadronic
__ COSY average ψacc = 1 mrad….. ψacc = 2 mrad
Frank Rathmann Observables in Antiproton-Proton Interactions 16
Figure of Merit at new IP
Topt ~ 55 MeV
Calculation based on Budker-Jülich
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PIT Filter. time Polar. Total rate Meas. Time (P/P=10%)
ANKE 2= 16 h 1.2 % 7.5x102 s-1 44 min5 = 42 h 3.5 % 5x10 s-1 26 min
New IP 2= 5 h 16 % 2.2x104 s-1 1 s5= 13 h 42 % 1.5x103 s-1 < 1 s
ANKE vs new IP: Polarization
New IP
ANKE
Pola
riza
tion
[%
]
Expectations based on Budker-Jülich for:
• T = 40 MeV • Ninj=1.5x1010 protons
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Present Status
Low-beta sectionto be designed and constructed (with AD in mind)
Polarized targetbeing setup at IKP/FZJ (from HERMES)
DetectorUse of ANKE STT developmentAdditional forward detector needed for AD
Siberian snake for longitudinal running needed
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Timeline
Fall 2006 Submission of full proposal to COSY2006-2007 Design and construction phase2008 Spin-filtering studies at COSY
Commissioning of AD experiment2009 Installation at AD2009-2010 Spin-filtering studies at AD
Antiproton Polarizer Ring (APR)Antiproton Polarizer Ring (APR)
e-CoolerAPRABS
Polarizer Target
InternalExperiment
Siberian SnakeB
Injection
150 m
F. Rathmann et al., PRL 94, 014801 (2005)
Extractione-Cooler
Small Beam Waist at Target β=0.2 mHigh Flux ABS q=1.5·1017 s-1
Dense Target T=100 K, longitudinal Q (300 mT) beam tube db=ψacc·β·2dt=dt(ψacc), lb=40 cm
(=2·β) feeding tube df=1 cm, lf=15 cm
Large Acceptance APR
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Beam lifetimes in the APR
10 100 1000 T (MeV)
40
3025
ψacc(mrad)
20102
4
6
8
beam
lilfe
time
τ bea
m (h
)
10
Beam Lifetime
Coulomb LossTotal Hadronic )T()T(
m4)T(s1
)m4)T(s()T(sm4)m2)T(s(
4ddd),T(
pptot0
2p
2acc
22p
2
2p
22p2
.RuthaccC
max
min
)T(f)(d))T(),T((1),T(
revacct0accCaccbeam
Frank Rathmann Observables in Antiproton-Proton Interactions 22
Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Case)
Experimental Study required:•Repetition of Filtex with protons at COSY•Final Design of APR: Filter studies with p at AD of CERN
Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995)
Model A: T. Hippchen et al., Phys. Rev. C 44, 1323
(1991)
50 100 150 200 250 T (MeV) 50 100 150 200 T (MeV)
0.05
0.10
0.15
0.20P
0.05
0.10
0.15
0.20P
2 beam lifetimesΨacc=10-50 mrad
3 beam lifetimesΨacc=20 mrad
Frank Rathmann Observables in Antiproton-Proton Interactions 23
A Pure Polarized Electron Target?A Pure Polarized Electron Target?
1 10 100 T (MeV)
σ EM
|| (m
b)100200300400500600
EM||EM 2
Pure Electrons
Atomic Electrons
Maxiumum σEM|| for electrons at rest: (675 mb ,Topt = 6.2 MeV):Gainfactor ~15 over atomic e- in a PIT
Density of an Electron-Cooler fed by 1 mA DC polarized electrons:
•Ie=6.2·1015 e/s•A=1 cm2
•l=5 mdt = Ie·l·(β·c·A)-1 = 5.2·108 cm-2
Electron target density by factor ~106 smaller, no match for a PIT (>1014 cm-2)
New calculations for smaller relative energies Talk by Walcher
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Conclusions•Outstanding physics potential of polarized antiprotons
•Different proposals for polarizing antiprotons, but only one successfull experimental method (spin-filtering)
•Understanding of spin-filtering process still incomplete
•COSY will play a fundamental role in understanding the spin filtering process and in commissioning for the decisive experiment with antiprotons at AD
•Once hadronic buildup mechanism is verified Filtering Studies at AD to determine σ1 and σ2 of pbarp scattering to optimize APR design
Frank Rathmann Observables in Antiproton-Proton Interactions 25
Spares
Frank Rathmann Observables in Antiproton-Proton Interactions 26
Detector concept•Reactions: •p-p elastic (COSY)•p-pbar elastic (AD)
•Good azimuthal resolution (up/down asymmetries)•Low energy recoil (<8 MeV)
•Silicon telescopes•Thin 5μm Teflon cell needed
•Angular resolution for the forward particle for p-pbar•AD experiment will require an openable cell
Frank Rathmann Observables in Antiproton-Proton Interactions 27
Models A and D
Calculations by Johann Haidenbauer
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