Spin Filtering at COSY and Perspectives for PAX

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Spin Filtering at COSY and Perspectives for PAX

September 17, 2012 | Alexander Nass

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Polarize antiprotons by „spin-filtering“

September 17, 2012

Our 1st Proposal on Spin Filtering (2005)

SPIN2012, Dubna, Russia

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3September 17, 2012

PAX Proposal to FAIR (2005)


High Energy Storage Ring (HESR) for a

beam of antiprotons

178 Collaborators36 Institutions

(15 EU, 21 Non-EU)

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4September 17, 2012

Quark structure of the nucleon


transversely polarisedquarks and nucleons

q

longitudinally polarisedquarks and nucleons

q

unpolarised quarksand nucleons

q

nxqxqxqx T1

55LTw2Corr Sγγ)(γ)(S)(

21)(

Well known Known Less known

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5September 17, 2012

Physics with Polarized Antiprotons


Polarized antiprotons will pave the way to novel double (and single) spin observables: • Proton-spin structure:

Complete map of transversity Flavour separation

• Electromagnetic Form FactorsIndependent extraction of moduli of GE-GM in Time-Like regionTest of the Rosenbluth separation in Time-Like regionMeasurement of the phase

• Hard p-pbar scatteringAdditional measurement in one of the most intriguing puzzles of

Hadron Physics • Hadron spectroscopy • Low-t pbar-p scattering

Spin and isospin dependence of nucleon-antinucleon interaction at low energy

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6September 17, 2012

Access to transversity through Drell-Yan


llqq *

q q

q qqqqqTTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dddd

21212

211121112

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7September 17, 2012

Phase I: Fixed target experiments in CSR


direction ofantiprotons

Physics: EMFF pbar-p elastic

Independent from HESR running

pol./unpol. antiprotons in CSR 0.2 GeV/c<p<2.5 GeV/cpolarized internal proton target

(antiprotons)

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8September 17, 2012

Phase II: Asymmetric Proton-Antiproton Collider


direction ofprotons

direction ofantiprotons

polarized antiprotons in HESR (p=15 GeV/c)polarized protons in CSR (p=3.5 GeV/c)

Physics: Transversity EMFF pbar-p elastic

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9September 17, 2012

Antiproton Polarizer Ring (APR)


Ring ParameterBeam energy 250 MeV

Number of antiprotons

1012

Ring acceptance 250 mm mrad

Betatron ampl. at IP < 0.3m

Ring circumference 86,5 m

Snake strength 2.4 Tm

Target

Electron Cooler Snake

Ion-optics at IPAtomic Beam Source (ABS) parameter

ABS flow in feeding tube

1,5·1017 /s

Storage cell length 40 cmFeeding tube diameter length

1 cm 15 cm

Long. holding field 300 mTNuclear polarization 0.9Cell temperature 100 K

Injection/Extraction

Final configuration after spin-filtering studies

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10September 17, 2012

Evaluation by QCD-PAC (March 2005)


… the PAC would like to stress again the uniqueness of the program with polarized anti-protons and polarized protons that could become available at GSI.

Recommendation of the STI of FAIR (Sept. 2005)The STI (Scientific and Technical Issues) requests R&D work to be continued on the proposed asymmetric collider experiment with both polarized anti-protons and protons:

- to demonstrate that the required luminosity for decisive measurements can be reached ( accomplished)

- to demonstrate that a high degree of anti-proton polarisation can be reached

The STI believes that PAX should become part of the FAIR core research program based on its strong scientific merit once the open problems are convincingly solved.

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Luminosity Considerations for Collider Mode


Particle speciesMomentum / GeV/cNumber of bunchesTotal number of particlesBeam lifetime / hPeak luminosity / cm-2 s-1

CSR HESRproton

s antiproton

3.65 1510 30

1012 3·1011

~ 45 ~ 8001.6·1030

CSR HESRantiproton

s proton

3.65 15- -

5·1011 1012

~ 1500 ~ 3001.2·1031

“old”

“new”

Antiprotons in HESR -> protonsBunched beams -> coasting

L>1031s-1cm-2

2006: I. milestone for PAX

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Polarized Antiprotons


Intense beam of polarized antiprotons was never produced:• Conventional methods (ABS) not applicable

• Polarized antiprotons from anti-lambda decay • I < 1.5 10∙ 5 s-1 (P ≈ 0.35)

• Antiproton scattering off liquid H2 target• I < 2 10∙ 3 s-1 (P ≈ 0.2)

Small polarization from pbar-C scattering experiments at LEAR• Stern-Gerlach spin separation in a beam (never tested, theoretically

unlikely to work)

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Production of polarization in a stored BeamTwo Methods: Loss versus spin flip


For an ensemble of spin ½ particles with projections + () and – ()

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A new idea (2007)


Eur. Phys. J. A 34, 447 (2007)

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ep spin flip studies at COSY (2008)


• Use proton beam and co-moving electrons • Turn experiment around: p e → p e into p e → p e i.e. observe depolarization of a polarized proton beam

COSY electron cooler

(detuned)

Velocity mismatch

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Principle of the Depolarization Measurement


Nominal CoolerVoltage

Tnominal = 100 s

Detuned CoolerVoltage

Tdetuned= 50 s

D2 Target onEcool on

D2 Target offEcool on/detuned

2TT

uneddet

alminno

Eh = 0.001 MeVΔV = 235 V

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ep spin flip cross section at COSY


No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than predicted 1013 b

0

4107

|Relative velocity of electrons in proton rest frame| (c)

dep

ol (b

arn)

Nominal proton energy in electron rest frame (keV)0 1 2 3

0 110-3 210-3 310-3

2107

-2107

-4107

D.Oellers et al., Physics Letters B 674 (2009) 269

Meanwhile, Mainz group discovered numerical problems in the calculation → two errata.

2008: II. milestone for PAX

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18September 17, 2012 SPIN2012, Dubna, Russia

Production of polarization in a stored BeamTwo Methods: Loss versus spin flip

For an ensemble of spin ½ particles with projections + () and – ()

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Spin Filtering


Polarization build-up of a circulating particle beam by interaction with a polarized gas target

Unpolarized anti-p beam

Polarized target

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Spin Filtering


Polarization build-up of a circulating particle beam by interaction with a polarized gas target

Unpolarized anti-p beam

Polarized target

Polarized anti-p beam

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Filter Test at TSR with protons (FILTEX, 1992)


Experimental Setup

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

T=23 MeV

Low energy pp scattering

1<0 tot+<tot-

Expectation

Target Beam

PAX submitted new proposal to find out how well does spin filtering work 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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Plan for PAX at AD / CERN (2009)


PAX target section

Electron cooler

Siberian snake

Status in 2009:• Spin-filtering only viable option• Spin-dependence of pbar-p

interaction unknown• “Warm” solution for AD lattice

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Spin dependence of the pbar-p interaction


Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991).

Model OBEPF: J. Haidenbauer, K. Holinde, A.W. Thomas, Phys. Rev. C 45, 952 (1992).

Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995).

• Measurement of the polarization buildup equivalent to the determination of σ1 and σ2

• Once a polarized antiproton beam is available, spin-correlation data can be measured at AD (50-500 MeV)

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Additional calculations


Cross sections

Projected polarizations

PLB 690 (2010)

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Stages of installation at AD

SPIN2012, Dubna, Russia2010 2011 2012

Installation of six magnets for the low-β insertion

Spin-filtering measurements up to 70 MeV with transverse beam

polarization

Installation of the target chamber: Machine acceptance

studies. Stacking studies

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PAX gets acknowledgement in the community:EU-Grants

• 2008-2011 – I3HP2 WP25 (PolAntiP)• Depolarization studies• Transverse spin-filtering at COSY

• 2012-2014 – I3HP3 WP25 (PolAntiP)• Longitudinal spin-filtering at COSY

• 2010-2015 – Advanced Resarch Grant POLPBAR

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Spin Filtering at COSY (2008-2011)

WASAe-cooler

ANKE

PAX

SPIN2012, Dubna, RussiaSeptember 17, 2012

Main purpose:1. Commissioning of the experimental setup for CERN/AD2. Quantitative understanding of the machine parameters

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Commissioning (2008-2011)


ABS

Breit-Rabi

polarimeter

• 2008-11: Installation and commissioning of the HERMES pol. target

p D2

• 2008-11: Installation and commissioning of the ANKE beam polarimeter

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Commissioning (2008-2011)


• 2009-10: Installation and commissioning of the low-β section

• 2010-11: Studies of beam-lifetime limitations

(t: 300 s 8000 s)

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Spin Filtering at COSY (2011)

p

cluster targ. + STT (beam

polarimetry)

polarized target

COSY ring

Spin-flipper

2011: III. milestone for PAX

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Conclusion: Spin Filtering

• Antiproton polarization:• Spin filtering only viable mechanism • Complete understanding of spin filtering

with p• Data on spin-dependence of pbar-p

interaction needed•Polarized antiprotons remain a missing and unique tool for hadron physics

(More about in the talk of G.Ciullo)

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Conclusion: Physics case for pol. antiprotons

• ATT in Drell-Yan production remains the unique direct way to access h1• pbar-p, pbar-d, p-p, p-d collider remains a unique machine to perform

the flavour decomposition of transversity

• Interest in Transverse Momentum dependent effect has increased• PAX physics case should be updated with the novel transverse

momentum distributions (TMD)

• Interest in proton EMFF has developed:• Different Space-Like experiments addressing two-photon

contribution• Still no individual determination yet of FF in the Time-Like region• Necessity of a complete space-time description

Documents

Spin Filtering at COSY and Perspectives for PAX