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

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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

Frank Rathmann Observables in Antiproton-Proton Interactions 24

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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