Spin Filtering Studies at COSY and AD

Alexander Nass for the collaboration

University of Erlangen-Nürnberg

SPIN 2008, Charlottesville,VA,USA, October 8, 2008

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 h1q (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

HESRPAX Polarized

Antiprotons

Principle of Spin Filtering

P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot

longitudinal case:

Q)( ||0tot

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

Polarized H target

Unpolarizedp/p beam

Principle of Spin Filtering

P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot

longitudinal case:

Q)( ||0tot

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

Polarized H target

Polarizedp/p beam

Spin Filtering Tests at TSR (MPI Heidelberg)

Experimental SetupExperimental Setup ResultsResults

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

T=23 MeV

Interpretations of the result

Observed polarization cross section: σ = 72.5 ± 5.8 mb

Current interpretation: 2001, Milstein and Strakhovenko + Nikolaev and Pavlov: selective removal through scattering off nuclei beyond the acceptance angle => σ = 85.6 mb

Experimental tests to disentangle the effects of electrons and nuclei Experiments with protons at COSY (Jülich):

No data to predict polarization for filtering antiprotons Spin Filtering measurements with antiprotons at AD (CERN)

Depolarization measurements done (talk of F. Rathmann)

Spin Filtering experiments with polarized target

Requirements for Spin Filtering

Highly polarized internal gaseous target with areal densities up to 1014 atoms/cm2 Storage cellPassing of the stored p/p beam through this cell and high acceptance Low beta section Ability to produce and measure nuclear polarization of H and D target gas with xyz-target holding fields

Atomic Beam Source and polarimeterLongitudinal spin filtering Siberian snake Detection of recoil particles Silicon detectors

Experimental Overview

ABS

BRP

COSY-Quadupoles

Low--Quadrupoles

Target chamberw storage celland detectors

The Polarized Atomic Beam Source

Former HERMES ABS rebuilt with modified vacuum system New cabling for fast installation and removal and new interlock systemConstruction of an analysis chamber with QMS and compression tubeFirst intensity measurements done (intensities up to 6 x 1016 atoms/s)Tests with a new alcohol cooled microwave dissociator on the way

Storage Cell and Holding field

Filtering requires 1014 atoms/cm2 storage cell

Walls of Teflon foil to let recoils pass and suppress depolarization and recombination

Openable cell to allow injected uncooled AD beam to pass

First cell prototype built and to be tested soon

Weak holding field coils at the outside of the target chamber to provide quantization axis for the spins of the target atoms

Cell cross section 10 x 10 mm

Storage Cell

The Breit-Rabi Polarimeter

Former HERMES BRP rebuilt with modifications due to new configuration

Tracking calculations modified sextupole magnet configuration for 300 K effusive H / D beam

New strong field transition cavity for hydrogen and deuterium

New cabling and interlock system are installed, start-up on the way

The low--section

Increase of luminosity and acceptance to reach reasonable polarization build-up times and polarization

Calculations show that 4 (6) additional quadrupoles are necessary for COSY (AD)

COSY AD

Cell Size

The low--section

Superconducting quadrupoles needed to reach the necessary pole-tip fields

Design of the coils and cryostats on the way, first prototype will be produced in 2009

Inside of cryostat will be used as cryopump

Magnets in cryostat for COSY

Beam Line Vacuum at the Target

Flow limiters to reduce gas flow into the adjacent sections

Pump with cold surfaces of the superconducting quadrupoles

Silicon Detectors

Measurements of beam polarization using pp (pp)-elastic scattering at COSY (AD)

Good azimuthal resolution (up/down asymmetries)

Low energy recoils (<8 MeV) detected by silicon telescopes

Transverse & Longitudinal FilteringUse of the WASA and electron cooler solenoid to form a Siberian snake at COSY for long. filtering

Implementation of a Siberian snake into AD

target

Planned measurements

2010/11: Filtering measurements at COSY with nuclear polarized hydrogen target in a weak magnetic holding field using a proton beam to produce polarized protons and commission the experiment for AD.2011/12: Filtering measurements at AD with nuclear polarized hydrogen and deuterium target in a weak magnetic holding field and an antiproton beam to show the ability of the method to produce polarized antiprotons.