Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich

FNAL, Jan 25, 2008

Road to Polarized Antiprotons:Depolarization Studies

and Spin Filtering Experiments at COSY and

AD

Frank RathmannInstitut für Kernphysik

Forschungszentrum Jülich

Frank Rathmann Road to polarized Antiprotons 2 of 19

Intense beam of polarized antiprotons was never produced:

•Conventional methods (ABS) not appliable

•Polarized antiprotons from antilambda decay • I < 1.5∙105 s-1 (P ≈ 0.35)

•Antiproton scattering off liquid H2 target• I < 2∙103 s-1 (P ≈ 0.2)

Little polarization from pbarC scattering exp’ts at LEAR

•Stern-Gerlach spin separation in a beam (never tested)

•6/2007 Walcher/Arenhoevel: polarized electrons/positronsSpin filtering is the only succesfully tested technique

Polarized Antiprotons


Experimental SetupExperimental Setup ResultsResults

F. Rathmann. et al., PRL 71, 1379 (1993)

T=23 MeV

Low energy pp scattering

1<0 tot+<tot-

Expectation

Target Beam

1992 Filter Test at TSR with protons


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 prot. into ring acceptance (σS=52 mb)

3. Spin-transfer from pol. el. of target atoms to stored prot. (σE=-70 mb)

σ1= σR+ σS + σE = 65 mb

2005 Milstein & Strakhovenko + Nikolaev & Pavlov: only one effectOnly pp elastic scattering contributesNo contribution from other two effects 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

Two interpretations of FILTEX result


… only hadronic (Budker-Jülich)

- electromagnetic + hadronic (Meyer-Horowitz)

TSR

… FILTEX does not provide the answer

Effective Polarizing cross sections


Spin Filtering works, but:

1. Controversial interpretations of FILTEX experiment• Further experimental tests necessary

• Which role do electrons play?• How does spin filtering work?

Tests with protons at COSY

2. No data to predict polarization from filtering with antiprotons Measurements with antiprotons at AD/CERN

Spin Filtering: Present Status


arXiv:0706.3765v3 [physics.acc-ph] 14Nov 2007


Principle of the Depolarization Measurement

using co-moving electrons of the e-cooler

Nominal CoolerVoltage

Tnominal = 100 s

Detuned CoolerVoltage

Tdetuned= 50 s

D2 Target onEcool on

D2 Target offEcool on/detuned

2T

T

uneddet

alminno

Eh = 0.001 MeVΔV = 235 V


Switch off ecooler

Machine Test for Depolarization Measurements(Nov. 2007)

Detuned ecooler ΔU=150 V

Machine-wise, experiment is feasible


New Low Energy Polarimeter for COSY (Nov. 2007)

ANKE Target Chamber

Two Silicon Tracking Telecopes


Performance of New Low Energy Polarimeter (Nov. 2007)


Polarimetry 45 MeV


First Measurement of Polarization Lifetime at Tp = 45 MeV (Nov. 2007)

Experimental determination of the depolarizing ep cross ~ March 2008


Goal: •Complete understanding of the spin filtering mechanism

•Disentangle electromagnetic and hadronic contributions to the polarizing cross section

1. Low-beta section

2. Polarized target (former HERMES target)

3. Detector (partially former HERMES Silicon recoil)

Commissioning of AD setup

Spin Filtering studies at COSY


x,ynew = 0.3 m -> large increase in target density•Shorter buildup time, higher rates•Larger polarization buildup rate due to larger acceptance

Superconducting quadrupoles necessary

Low-β section


Target Snake

E-cooler

T= 5 - 2.8 GeV Np = 3·107

Study of spin filtering in pbar-p (pbar-d) scattering

Measurement of effective polarization buildup cross-section• Both transverse and longitudinal• Variable acceptance at target• Test also polarized D target

First ever measurement for spin correlations in pbar-p (and pbar-D)

Spin Filtering at AD of CERN


e-CoolerAPRABS

Polarizer Target

InternalExperiment

Siberian Snake

BInjection

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

World-First: Antiproton Polarizer Ring (APR)


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

0.20

P

0.05

0.10

0.15

0.20

P

2 beam lifetimesΨacc=10-50 mrad

3 beam lifetimesΨacc=20 mrad

Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering)


Fall 2007 Submission of proposal to COSY-PAC

- Beam depolarization studies

- Beam and polarization lifetime studies

Spring 2008 Technical proposal to COSY-PAC for spin filtering

Technical proposal to SPSC for spin filtering at AD

2008-2009 Design and construction phase

2009 Spin-filtering studies at COSY

Commissioning of AD experiment

Then Installation at AD

Spin-filtering studies at AD

Quite a challenge in front of us:

Young (and less young) polarization enthusiasts are welcome!

Outlook until ~2012

Design of the APR


Intense beam of polarized antiprotons was never produced:

•Conventional methods (ABS) not appliable

•Polarized antiprotons from antilambda decay • I < 1.5∙105 s-1 (P ≈ 0.35)

•Antiproton scattering off liquid H2 target• I < 2∙103 s-1 (P ≈ 0.2)

•Little polarization from pbarC scattering exp’ts at LEAR

•Stern-Gerlach spin separation in a beam (never tested)

•6/2007 Walcher/Arenhoevel: polarized electrons/positrons

Spin filtering is the only succesfully tested technique

Polarized Antiprotons


Topics

• IntroductionIntroduction

• Depolarization Studies using unpolarized Depolarization Studies using unpolarized ElectronsElectrons

• Testing the Arenhoevel/Walcher PredictionsTesting the Arenhoevel/Walcher Predictions

• Upper Limit of the Depolarizing Cross SectionUpper Limit of the Depolarizing Cross Section

• Spin Filtering Studies at COSY and ADSpin Filtering Studies at COSY and AD


Experimental Setup at TSR (1992)


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 prot. into ring acceptance (σS=52 mb)

3. Spin-transfer from pol. el. of target atoms to stored prot. (σE=-70 mb)

σ1= σR+ σS + σE = 65 mb

2005 Milstein & Strakhovenko + Nikolaev & Pavlov: only one effectOnly pp elastic scattering contributesNo contribution from other two effects 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

Two interpretations of FILTEX result


Spin filtering works, but:

1. Controversial interpretations of FILTEX experiment• Further experimental tests necessary

• How does spin filtering work?• Which role do electrons play?

Tests with protons at COSY

2. No data to predict polarization from filtering with antiprotons Measurements with antiprotons at AD/CERN

Spin Filtering: Present Status


Spin Filtering studies at COSY

Goal: •Understanding the spin filtering mechanism:

•Disentangle electromagnetic and hadronic contributions to the polarizing cross section


Experimental setup

• Low-beta section • Polarized target (former HERMES

target)• Detector• Snake• Commissioning of AD setup


x,ynew = 0.3 m -> increase in density with respect to ANKE: factor

30•Shorter buildup time, higher rates•Larger polarization buildup rate due to larger acceptance•Use of former HERMES target and Breit-Rabi Polarimeter

Superconducting quadrupoles necessary

Low-β section


Acceptance @ ANKE

Cross sections

Acceptance @ new-IP

Lifetimes… only hadronic - electromagnetic + hadronic

__ COSY average ψacc = 1 mrad….. ψacc = 2 mrad

ANKE vs new IP: Acceptance and Lifetime


PIT Filter. time Polar. Total rate Meas. Time (P/P=10%)

ANKE 2= 16 h 1.2 % 7.5x102 s-1 44 min

5 = 42 h 3.5 % 5x10 s-1 26 min

New IP 2= 5 h 16 % 2.2x104 s-1 1 s

5= 13 h 42 % 1.5x103 s-1 < 1 s

New IP

ANKE

Pola

riza

tion

[%

]

Expectations based on Budker-Jülich:

• T = 40 MeV

• Ninj=1.5x1010 protons

ANKE vs new IP: Polarization


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.

Strong fields can be applied only longitudinally (minimal beam interference)

- Snake necessaryTarget polarimetry requires BRP for pure electron and nuclear polarization.

Method 1: Polarization build-up experiments

How to disentangle hadronic and electromagnetic contributions to eff ?


Target Snake

E-cooler

T= 5 - 2.8 GeV Np = 3·107

Study of spin filtering in pbar-p (pbar-d) scattering

Measurement of effective polarization buildup cross-section• Both transverse and longitudinal• Variable acceptance at target• Test also polarized D target

First ever measurement for spin correlations in pbar-p (and pbar-D)

AD ring at 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

0.20

P

0.05

0.10

0.15

0.20

P

2 beam lifetimesΨacc=10-50 mrad

3 beam lifetimesΨacc=20 mrad

Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering)


Depolarization Studies using unpolarized Depolarization Studies using unpolarized ElectronsElectrons

• Use electrons in ecooler instead of target electrons to observe depolarization

Rough extraction for numerical estimates


Ecooler Settings for Tp=45 MeV

Typical parameters of COSY Cooler

• Electron Current 240 mA• Cross section 5 cm2

• Length 2 m• Nominal Voltage 24.5 kV

Electron target thickness seen by the protons


Estimated Polarization Lifetime

revtp fd

1


Energy Resolution of Protons in Electron Rest System

TT1

p

p

to electron

rest system Tp = 65, 45, 30 MeV


Polarimetry


Polarimetry


Beam Polarization with detuned cooler

Eh = 0.001, 0.002, 0.003 MeV

D2 Target onEcool on

D2 Target offEcool on/detuned


Counting statistics• With

– 109 stored protons at T = 45 MeV– Target thickness dt(D2) = 2·1014 cm-2

– Injected Beam Polarization P = 0.8– Detector system as shown– After 1 cycle (250 s): ΔP = 0.108

15 cycles (~1 h): ΔP = 0.03150 cycles (~10h): ΔP = 0.009

Eh (MeV) ΔV (V) τp(A-W) (s) P(t=250 s)

0.001 234 0.04 0

0.002 332 25 0.10

0.003 407 2000 0.78


Estimated Precision of Polarization Lifetime based on Counting Statistics in

Polarimeter

revt

in

out

fdt

)PP

ln(

Eh = 0.001, 0.01, 0.1 MeV

Measuring time per point: ~14 h


Measuring time per point: ~14 h

Eh = 0.002 MeV

Estimated Precision of Polarization Lifetime based on counting statistics


Phase 0: present -2012

Physics: buildup measurements @ COSY and CERN

APR design and construction

Phase I: 2015-2019

APR+CSR @ GSI

Physics: EMFF, p-pbar elastic with fixed target

Phase II: 2020 - …

HESR+CSR asymmetric collider

Physics: h1

Outlook beyond 2012

Antiproton Facility spares


HESR

Antiproton Production

Target

HESR (High Energy Storage Ring)• Length 442 m• Bρ = 50 Tm• N = 5 x 1010 antiprotons

High luminosity mode• Luminosity = 2 x 1032 cm-2s-1

• Δp/p ~ 10-4 (stochastic-cooling)

High resolution mode• Δp/p ~ 10-5 (8 MV HE e-cooling)• Luminosity = 1031 cm-2s-1

•Antiproton production similar to CERN

•Production rate 107/sec at 30 GeV•T = 1.5 - 15 GeV/c

Gas Target and Pellet Target: cooling power determines thickness

SuperFRS

NESR

CR

Beam Cooling: e- and/or stochastic2MV prototype e-cooling at COSY

SIS100/300

The Antiproton Facility

Spin Filtering spares


e-CoolerAPRABS

Polarizer Target

InternalExperiment

Siberian Snake

BInjection

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

World-First: Antiproton Polarizer Ring (APR)


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: General Features IV

(N ~ I)

Optimimum time forPolarization Buildup

given by maximum of FOM(t)tfilter = 2·τbeam

0 2 4 6 t/τbeam

I/I 0

0.2

0.4

0.6

0.8

Beam

Pola

riza

tion


Figure of Merit at new IP

Topt ~ 55 MeV

Calculation based on Budker-Jülich


• Will measure beam polarization by using the polarization observables:

•p-p elastic (COSY)•pbar-p 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 at AD• AD experiment will require an openable cell

Detector concept


Beam Polarization in a dedicated Antiproton Polarizer

0.1

0.2

0.3

0.4

Beam

Pola

riza

tion P

(2·τ

beam)

01 10 T (MeV)100

Polarisation buildup through spin transfer

5030

ψacc(mrad)

10

epep Horowitz & Meyer, PRL 72, 3981

(1994)H.O. Meyer, PRE 50, 1485 (1994)

PAX will exploit spin-transfer to polarize antiprotons and to go after transversity


“If polarized electrons polarize an initially unpolarized beam, then, unpolarized electrons should depolarize an initially polarized beam!”

Method 2: Depolarization experiments

Electrons in 4He storage cell or D cluster-jet target:

• Large analyzing power• Large counting rates

• Distinguish electron effect from normal depolarization in COSY

• Prerequisites:•Large beam lifetime•Large polarization lifetime

4Heempty

Prediction for ANKE/COSY (4 weeks)

Approved new Proposal for COSY

4He

Hans-Otto Meyer’s suggestion


Polarization Buildup:

P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)

polbeam

polbeam

tt

0

tt

0

ee2

I)t(I

ee2

I)t(I

transverse case:

Q0tot

longitudinal case:

Q)( ||0tot

For initially equally populated spin states: (m=+½) and (m=-½)

revtpolpol

revtc0beam

fdQ

1

fd)(

1

)t(I)t(P)t(FOM

tcosheIII)t(I

ttanh

II

II)t(P

2

pol

t

0

pol

beam

Time dependence of P, I, and FOM


Principle of spin-filtering


σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot

longitudinal case:

Q)( ||0tot


Unpolarized anti-p beam

Polarized H target




σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot

longitudinal case:

Q)( ||0tot


Unpolarized anti-p beam

Polarized H target

Polarized anti-p beam



Experimental SetupExperimental Setup ResultsResults

F. Rathmann. et al., PRL 71, 1379 (1993)

T=23 MeV

Low energy pp scattering

1<0 tot+<tot-

Expectation

Target Beam

1992 Filter Test at TSR with protons


Rate EstimateFür 1*E9 Protonen mit einer Polarisation von 0.8.

Target sind 2E14/cm2 d und die Strahlenergie beträgt 45MeV.

Die Plots findest du angehängt.

Weitere Zahlen:

Totale Zählraten L:5.8/s R:8.1/s

Error of Polarization after 1s: 0.86

(Die 0.13 waren bei 100s E7 Teilchen, aber 30mal....)

Integriert man über 100s (Strahllebensdauer ebenfalls 100s) dann erhält

man (100 -100/e)=63.2 -fache Statistik also einen Fehler von

0.86/sqrt(63.2)=0.108. Dies ist leider deutlich schlechter als die

erhofften 0.02, aber sicherlich kein Showstopper.

Dauer eines Zyklus:

10s für Injektion

100s für E-Cooler-Spielerei

100s für Polarisationsmessung

5s für Extraktion

==============================

215s = 4Min(240s)

In einer Stunde hätten wir also 15 Zyklen also einen Fehler von 0.03.

Nach 10h: 0.009. Wir sollten also ohne Probleme an einem Tag sowohl die

Injektionspolarisation, sowie die Polarisation nach E-Cooler-Spielerei

messen können.


“If polarized electrons polarize an initially unpolarized beam, then, unpolarized electrons should depolarize an initially polarized beam!”

Electrons in 4He storage cell or D cluster-jet target:

• Large analyzing power• Large counting rates

• Distinguish electron effect from normal depolarization in COSY

• Prerequisites:•Large beam lifetime•Large polarization lifetime

4Heempty

Prediction for ANKE/COSY (4 weeks)

Approved new Proposal for COSY

4He

Depolarization Study at COSY

Explore also option with co-moving electrons in cooler

Documents

Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich