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Spin Filtering at COSY and Perspectives for PAX. September 17, 2012 | Alexander Nass. Our 1st Proposal on Spin Filtering (2005). Polarize antiprotons by „ spin-filtering “. PAX Proposal to FAIR (2005). 178 Collaborators 36 Institutions (15 EU, 21 Non-EU).

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Spin Filtering at COSY and Perspectives for PAX

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Spin Filteringat COSY andPerspectivesfor PAX

September 17, 2012 | Alexander Nass

Our 1st Proposal on Spin Filtering (2005)

Polarizeantiprotonsby „spin-filtering“

SPIN2012, Dubna, Russia

PAX Proposalto FAIR (2005)

178 Collaborators

36 Institutions

(15 EU, 21 Non-EU)

High Energy Storage Ring (HESR) for a beam ofantiprotons

SPIN2012, Dubna, Russia

Quark structureofthenucleon

transversely polarised

quarks and nucleons

unpolarised quarks

and nucleons

longitudinally polarised

quarks and nucleons

Less known

Well known


SPIN2012, Dubna, Russia

PhysicswithPolarized 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 Factors

Independent extraction of moduli of GE-GM in Time-Like region

Test of the Rosenbluth separation in Time-Like region

Measurement of the phase

• Hard p-pbar scattering

Additional measurement in one of the most intriguing puzzles of

Hadron Physics

• Hadron spectroscopy

• Low-t pbar-p scattering

Spin and isospindependence of nucleon-antinucleoninteractionatlowenergy

SPIN2012, Dubna, Russia

Access totransversitythroughDrell-Yan

SPIN2012, Dubna, Russia

Phase I: Fixed targetexperiments in CSR

pol./unpol. antiprotonsin CSR 0.2 GeV/c<p<2.5 GeV/c

polarizedinternalproton target

direction of




pbar-p elastic

Independent from HESR running

SPIN2012, Dubna, Russia

Phase II: Asymmetric Proton-Antiproton Collider

polarizedantiprotons in HESR (p=15 GeV/c)

polarizedprotons in CSR (p=3.5 GeV/c)

direction of


direction of




pbar-p elastic

SPIN2012, Dubna, Russia

Antiproton Polarizer Ring (APR)



Finalconfigurationafter spin-filteringstudies

Electron Cooler


Ion-optics at IP

SPIN2012, Dubna, Russia

Evaluation by QCD-PAC (March 2005)

Recommendationofthe STI of FAIR (Sept. 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.

  • 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.

SPIN2012, Dubna, Russia

LuminosityConsiderationsforCollider Mode




Antiprotons in HESR -> protons

Bunched beams -> coasting

2006: I. milestone for PAX

SPIN2012, Dubna, Russia

Polarized Antiprotons

  • Intense beam of polarizedantiprotonswasneverproduced:

  • Conventionalmethods (ABS) notapplicable

  • Polarizedantiprotons from anti-lambda decay

    • I < 1.5∙105 s-1 (P ≈ 0.35)

  • Antiprotonscattering off liquid H2 target

    • I < 2∙103 s-1 (P ≈ 0.2)

  • Small polarization from pbar-C scatteringexperimentsat LEAR

  • Stern-Gerlach spin separation in a beam (nevertested, theoreticallyunlikely to work)

SPIN2012, Dubna, Russia

Productionofpolarization in a stored Beam

TwoMethods: Loss versus spinflip

For an ensembleofspin ½ particleswithprojections+() and– ()

SPIN2012, Dubna, Russia

A newidea (2007)

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

SPIN2012, Dubna, Russia

epspinflipstudiesat COSY (2008)

  • Use protonbeam 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

Velocity mismatch

COSYelectron cooler(detuned)

SPIN2012, Dubna, Russia

Detuned Cooler


Tdetuned= 50 s

Nominal Cooler


Tnominal = 100 s


Eh = 0.001 MeV

ΔV = 235 V

D2 Target on

Ecool on

D2 Target off

Ecool on/detuned

SPIN2012, Dubna, Russia

epspinflipcrosssectionat COSY

Nominal protonenergy in electronrestframe (keV)






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


depol (barn)








|Relative velocityofelectrons in protonrestframe| (c)

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

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

2008: II. milestone for PAX

SPIN2012, Dubna, Russia

Productionofpolarization in a stored Beam

TwoMethods: Loss versus spinflip

For an ensembleofspin ½ particleswithprojections+() and– ()

SPIN2012, Dubna, Russia

Unpolarized anti-p beam


Spin Filtering

Polarization build-up of a circulating particle beam

by interaction with a polarized gas target

SPIN2012, Dubna, Russia

Polarizedanti-p beam

Unpolarized anti-p beam

Spin Filtering

Polarization build-up of a circulating particle beam

by interaction with a polarized gas target

Polarized target

SPIN2012, Dubna, Russia

Filter Test at TSR withprotons (FILTEX, 1992)

Experimental Setup

T=23 MeV

F. Rathmann. et al.,

PRL 71, 1379 (1993)

Low energy

pp scattering

1<0  tot+<tot-

PAX submitted new proposal to find out how well does spin filtering work for antiprotonsMeasurement ofthe Spin-Dependenceofthe pp Interaction atthe AD Ring

(CERN-SPSC-2009-012 / SPSC-P-337)

SPIN2012, Dubna, Russia

Plan for PAX at AD / CERN (2009)

  • Status in 2009:

    • Spin-filtering only viable option

    • Spin-dependence of pbar-p interaction unknown

  • “Warm” solution for AD lattice


PAX target section


SPIN2012, Dubna, Russia

Spin dependenceofthepbar-p interaction

  • Measurement of the polarization buildup equivalent to the determination of σ1andσ2

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

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).

SPIN2012, Dubna, Russia

Additional calculations

PLB 690 (2010)

Cross sections

Projected polarizations

SPIN2012, Dubna, Russia

Stages ofinstallationat AD

Installation of six magnets for the low-β insertion

Installation of the target chamber: Machine acceptance studies. Stacking studies

Spin-filtering measurements up to 70 MeV with transverse beam polarization




SPIN2012, Dubna, Russia

PAX getsacknowledgement in thecommunity:


  • 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

SPIN2012, Dubna, Russia

Spin Filteringat COSY (2008-2011)

Main purpose:

1. Commissioning of the experimental setup for CERN/AD

2. Quantitative understanding of the machine parameters





SPIN2012, Dubna, Russia



Commissioning (2008-2011)


  • 2008-11: Installation andcommissioningofthe HERMES pol. target



  • 2008-11: Installation andcommissioningofthe ANKE beam polarimeter

SPIN2012, Dubna, Russia

Commissioning (2008-2011)

  • 2009-10: Installation andcommissioningofthelow-βsection

  • 2010-11: Studies of beam-lifetimelimitations

  • (t: 300 s  8000 s)

SPIN2012, Dubna, Russia

cluster targ. + STT (beam polarimetry)


Spin Filteringat COSY (2011)

COSY ring


polarized target

2011: III. milestone for PAX

SPIN2012, Dubna, Russia

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)

SPIN2012, Dubna, Russia

Conclusion: Physicscasefor 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

SPIN2012, Dubna, Russia

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