Towards Polarized Antiprotons at FAIR - fz-juelich.decollaborations.fz-juelich.de/ikp/pax/public_files/usual_event/2006... · Towards Polarized Antiprotons at FAIR. 2 ... • Different

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Frank RathmannInstitut für Kernphysik

Forschungszentrum Jülich

Kyoto, October 3, 2006

http://www.fz-juelich.de/ikp/pax

Towards Polarized Antiprotons Towards Polarized Antiprotons at FAIRat FAIR

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Frank Rathmann Towards Polarized Antiprotons at FAIR 2 of 30

Outline

• PAX physics program• Accelerator configuration for FAIR• Towards polarized antiprotons

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Central PAX Physics Case:Central PAX Physics Case:Transversity distribution of the nucleon in Drell-Yan:

→ FAIR as successor of DIS physics– last leading-twist missing piece of the QCD description

of the partonic structure of the nucleon– observation of h1

q (x,Q2) of the proton for valence quarks (ATT in Drell-Yan >0.2)

– transversely polarized proton beam or target ( )– transversely polarized antiproton beam ( )

HESR

QCD Physics at FAIR (CDR): unpolarized Antiprotons in HESR

PAX → Polarized Antiprotons

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PAX Physics Program

• Transversity• Electromagnetic Form Factors• Hard Scattering Effects• SSA in DY, origin of Sivers function• Soft Scattering

– Low-t Physics– Total Cross Section– pp interaction

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Leading Twist Distribution Functions

1/2 1/2

L L+f1(x)

h1(x)

proton proton’

quark quark’

u↑ = 1/√2(uR + uL)u↓ = 1/√2(uR - uL)

No probabilistic interpretation in the helicity base (off diagonal)

Probabilistic interpretation in helicity base:

q(x) spin averaged(well known)

∆q(x) helicity diff.(known)

δq(x) helicity flip(unknown)

1/2 1/2

R R

1/2 1/2

L L-

1/2 1/2

R R

g1(x)

Transversitybase

1/2 -1/2

R L

-↑ ↑

↑ ↑

↓ ↓

↓ ↓

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Transversity

2Q

- Probes relativistic nature of quarks- No gluon analog for spin-1/2 nucleon- Different evolution than - Sensitive to valence quark polarization

PropertiesProperties::

q∆

ChiralChiral--odd: requires another chiralodd: requires another chiral--odd partnerodd partner

Impossible in DIS Direct Measurement

p↑p↑→l+l-X ep↑→e’h⊥X

Indirect Measurement:Convolution of with

unknown fragment. fct.

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Transversity in Drell-Yan processes

p pqL

q

l+

l-q2=M2

qT

Polarized antiproton beam → Polarized proton target (both transverse)

)M,x(q)M,x(qe

)M,x(h)M,x(hea

ddddA 2

2q

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2q

22

q1

q

21

q1

2q

TTTT ∑∑

=σ+σσ−σ

≡↑↓↑↑

↑↓↑↑,...d,d,u,uq =

M invariant Massof lepton pair

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Proton Electromagnetic Formfactors

• Measurement of relative phases of magnetic and electric FF in the time-like region– Possible only via SSA in

the annihilation pp → e+e-

• Double-spin asymmetry– independent GE-Gm

separation– test of Rosenbluth

separation in the time-like region

-0.4

-0.2

0

0.2

0.4

5 10 15 20 25 30 35 40

1/Q fit

(log2 Q2) /Q2 fit

impr. (log2 Q2) /Q2 fitIJL fit

Pol

ariz

atio

n P

y (fo

r θ

= 4

5°)

q2 (GeV2)

( )[ ]2p

2

2E

22M

2M

*E

y

m4/q

/|G|)(sin|G|)(cos1)GGIm()2sin(A

=τ

ττθ+θ+⋅⋅θ

=

S. Brodsky et al., Phys. Rev. D69 (2004)

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Facilty for Antiproton and Ion Research(GSI, Darmstadt, Germany)

-Proton linac (injector)-2 synchrotons (30 GeV p)-A number of storage rings

Parallel beams operation

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PAX Collider Setup

PAX Collider Luminosity> 1031 cm-2s-1

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Polarized AntiprotonsIntense 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)

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

• 5/2006 (Th. Walcher et al.) polarized electron beamSee Talk by K. Aulenbacher (9A, Fr)

Spin filtering is the only succesfully tested technique

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Principle of spin-filteringP beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ⊥·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot ⋅σ±σ=σ ⊥±

longitudinal case:

Q)( ||0tot ⋅σ+σ±σ=σ ⊥±

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

Unpolarized anti-p beam

Polarized H target

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P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ⊥·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot ⋅σ±σ=σ ⊥±

longitudinal case:

Q)( ||0tot ⋅σ+σ±σ=σ ⊥±

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

Unpolarized anti-p beam

Polarized H target

Polarizedanti-p beam

Principle of spin-filtering

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1992 Filter Test at TSR with protons

Experimental SetupExperimental Setup

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1992 Spin Filter Test at TSR with protons

Experimental SetupExperimental Setup ResultsResults

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

T=23 MeV

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Two 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 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 effect1. Selective removal through scattering beyond θacc=4.4 mrad (σR⊥=85.6 mb)No 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

Spin filtering works! But how?

(-> more in next talk by N.N. Nikolaev)

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Spin Filtering: Present Status

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

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Spin Filtering studies at COSY

Goal: • Understanding the spin filtering mechanism:• Disentangle electromagnetic and hadronic contributions to

the polarizing cross section

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Polarizing cross sections from the two models

… only hadronic (Budker-Jülich)

- electromagnetic + hadronic (Meyer-Horowitz)

TSR

A measurement of σeff to 10% precision requirespolarization measurement with ∆P/P = 10%.

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How to disentangle hadronic and electromagnetic contributions to σeff ?

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)

strong (3kG)longitudinal

transv. + longit.

only elm.

only had.

Elm. + had.

Interaction

weak (20 G)

Holding field

0+1|1> + |2>

+10|1> + |4>

+1+1|1>

PzPeInj. states

AD Experiments require both transverse and longitudinal (weak) fields.

AD Experiments will be performed also with D target.

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

- Snake necessary

Target polarimetry requires BRP for pure electron and D polarization.

Method 1: Polarization build-up experiments

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Experimental setup

• Low-beta section• Polarized target (former HERMES target)• Detector• Snake• Commissioning of AD setup

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βx,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 (more details in A. Nass’ 9A, Fr)

LowLow beta beta sectionsection

S.C. quadrupoles necessary for AD experiment

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ANKE ANKE vsvs new IP: Acceptance and Lifetimenew 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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FigureFigure of of MeritMerit at at newnew IPIP

Topt ~ 55 MeV

Calculation based on Budker-Jülich

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1.5x103 s-1

2.2x104 s-1

5x10 s-1

7.5x102 s-1

Total rate

New IP

ANKE

PIT

< 1 s42 %5τ = 13 h

1 s16 %2τ = 5 h

26 min3.5 %5τ = 42 h

44 min1.2 %2τ = 16 h

Meas. Time (∆P/P=10%)Polar.Filter. time

ANKE ANKE vsvs new IP: Polarizationnew IP: Polarization

New IP

ANKEPolariza

tion

[%]

Expectations based on Budker-Jülich:

• T = 40 MeV

• Ninj=1.5x1010 protons

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Detector concept• 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

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Hans-Otto Meyer’s idea“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 target: • Large analyzing power• Large counting rates

• Distinguish electron effect fromnormal depolarization in COSY

• Prerequisites:•Large beam lifetime•Large polarization lifetime

4Heempty

Prediction for ANKE/COSY (4 weeks)

New Proposal for COSY turned in this week

4He

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AD ring at CERN

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 cross-sectionBoth transverse and longitudinalVariable acceptance at targetPolarized D target

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

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Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Case)

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

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yxFall 2006 Submission of proposal to COSY-PACBeam depolarization studies(Beam lifetime studies)

Spring 2007 Submission of FP 7 applicationFall 2007 Technical proposal to COSY-PAC for spin filtering

Technical proposal to SPSC for spin filtering at AD2006-2007 Design and construction phase2008-2009 Spin-filtering studies at COSY

Commissioning of AD experiment2009 Installation at AD2009-2010 Spin-filtering studies at AD

Quite a challenge in front of us:

Young (and less young) polarization enthusiasts are welcome!

Documents

Towards Polarized Antiprotons at FAIR - fz-juelich.decollaborations.fz-juelich.de/ikp/pax/public_files/usual_event/2006... · Towards Polarized Antiprotons at FAIR. 2 ... • Different