Introduction

Status of the ExperimentPolarizing antiprotonsE. Steffens – University of Erlangen-Nürnberg

for the PAX Collaborationhttp://www.fz-juelich.de/ikp/pax/

E. Steffens - DSPIN2009

Introduction

We have proposed a method to polarize antiprotons by

„spin-filtering“


Is it possible, and how, to provide polarized antiproton beams in

HESR ?

High Energy Storage Ring (HESR)

for a beam of antiprotons


Introduction

New initiative, driven by the FAIR-project at GSI

Introduction

• Our knowledge about pp interaction is limited: • Lack of polarization data!

Restricted to single-spin (A0n00, A000n) data.No spin-correlation data!

• Attempts at LEAR (1983-1996) to produce polarized stored antiprotons were unsuccessful!

• Revival of ideas about stored polarized antiprotons: → PAX experiment at FAIR (see PAX TP hep-ex/0505054)

• Polarized antiprotons: A missing tool • Nucleon-antinucleon scattering at the parton level • Hadron spectroscopy• Nucleon-antinucleon scattering at low energy



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

Last leading-twist missing piece of the QCD description of the partonic structure of the nucleon

Direct measurement 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 ()

+ many polarization observables in pp scattering

PAX → Polarized Antiprotons

Quark Transversity Distribution in Drell-Yan

Double transverse spin asymmetry:

llqq *

First direct measurement: No competitive processes


Plan of talk

Polarizing antiprotons … Proposals, ideas, calculations, … Present status of pp interaction models Experiments

FILTEX (TSR)e p spin flip cross section measurement at COSYSpin-filtering at AD/CERNSpin-filtering at COSY

Conclusion

Task taken on by the PAX Collaboration: ~100 members 16 institutions

Spokespersons: P. Lenisa (Ferrara), F. Rathmann (Jülich)


Two Methods: Spin-dependent loss versus spin flipFor an ensemble of spin ½ particles with projections + () and – ()


Proposed methods: Spin flip

→ Need for an experimental test of this idea!


ep spin flip studies at COSY: Idea

• 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


PAX Experiment 11

ep spin flip studies at COSY: Tools

p

e-cooler ANKE cluster target & STT

Tp = 49.3 MeV

• Use (transversely) polarized proton beam circulating in COSY• Switch on (detuned) electron cooler to depolarize proton beam• Analyze proton polarization with internal D2-cluster target of

ANKE


PAX Experiment 12

ep spin flip studies at COSY: Feasibility

Detuning e-cooler for 5 s only ensures that proton momentum stays fixed.

After detuning, proton energy slowly follows electron energy: U = 245 V ve = 1.5·10-3 cfR = 40 Hz in 5 s:

c104

107.8f

ffv

v

5

7R

R

Rpp

vp/ ve~0.03


ep spin flip studies at COSY: Polarimetry

pd elastic scattering:detection in two (L-R) symmetric Silicon Tracking Telescopes

p D2

Deuteron identification

d

p


ep spin flip cross section at COSY: Result

No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than the 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. Analytical calculation by Novosibirsk group (Strakhovenko et al): Spin flip negligible!

Spin-dependent loss: Spin-filtering

Polarization build-up of an initially unpolarized particle beam by repeated passage through a polarized hydrogen target in a storage ring:


P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ1·P·Q + σ2·(P·k)(Q·k)

transverse case:

Qtot 10 longitudinal case:

Qtot )( 210

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

Unpolarized anti-p beam

Polarized target

Polarization Buildup

E. Steffens - DSPIN2009 16PAX Experiment

P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ1·P·Q + σ2·(P·k)(Q·k)

transverse case:

Qtot 10 longitudinal case:

Qtot )( 210

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

Unpolarized anti-p beam

Polarized target

Polarized anti-p beam

Polarization Buildup

E. Steffens - DSPIN2009 17PAX Experiment

PAX ExperimentE. Steffens - DSPIN2009 18

statistical error of a double polarization observable (ATT)

NQP1

TTA

Measuring time t to achieve a certain error δATT

t ~ FOM = P2·I

Figure of Merit and optimum filtering time

(N ~ I)

Optimimum time for polarization buildup given by maximum of FOM(t)

tfilter = 2·τbeam

0 2 4 6 t/τbeam

I/I0

0.2

0.4

0.6

0.8

Bea

m P

olar

izat

ion

Spin-filtering at TSR: „FILTEX“ – proof-of-principle

→ Spin filtering works for protons

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


PAX submitted new proposal to find out how well spin filtering works for antiprotons: Measurement of the Spin-Dependence of the pp Interaction at the AD Ring

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

Polarization build-up process quantitatively understood!

• TSR spin filtering with protons:σexp=73 ± 6 mb

• Average theoretical value:σtheo=86 ± 2 mb

• Good agreement: ~2 σ discrepancy• Brief summary in: D. Oellers et al.,

Phys. Lett. B 674, 269 (2009).

PAX Experiment 20

pp interaction models


Spin-dependence of the pbar-p interaction

E. Steffens - DSPIN2009 PAX Experiment 21

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)

PAX at the AD (the only place worldwide)


PAX target sectionElectron cooler

Siberian snake


Experimental Setup

Atomic Beam Source

Six additional quadrupolesBreit-Rabi

Polarimeter

Target chamber:Detector system + storage cell

Polarized Target


Qx Qy Qz: Quantization axis is reoriented by a weak magnetic guide field of 10 G

Injected hyperfine states from ABS

BRP measures occupation numbers of different HFS

+ corrections → Target Polarization

xy z

ABS

Targetchamber

Breit-Rabipolarimeter

Electric power Cooling

water

Atomic Beam Source and Breit-Rabi Polarimeter


COSY/ADbeam axis



BRP vacuum HFT

QMAs

ABS/TC vacuum

Bake-out

Coils power

Target chamber, cell and detector system


Storage cell:jet density 100 Silicon strip detectors

Atomic beam

Stored beam

Guide field coils(x, y, z)

movable flow limiter


12 x 2 HERMES recoil detectors + 12 x 1 PAX STT detectors

Full system consisting of 36 Detectors

Target cell + Detectors with cooling system and shielding

Detectors surrounding the openable storage cell

1 PAX Layer

2 HERMES1 PAX STT

Detector System

Openable storage cell


closedopened

AD beam envelope at injection requires openable storage cell

P. Belochitsky - CERN

AD optics (P. Belochitsky - CERN)


At injection “Squeezed”

1. Beam is injected with low-β section moderately powered on.2. At experiment energy (T<450 MeV), β-functions are „squeezed“ by fully

powering on low-β magnets.3. Then storage cell is closed and gas is injected.

Expected polarizations after filtering for two lifetimes


Model A: Production of longitudinal polarizationθacc > 13 mrad → P(2∙τb) changes only marginally

d (mm) Θacc (mrad)

8 8.610 10.812 13.0

Limit

Main phases of installation at AD


2009 2010 2011

Phase 1

Phase 2

Phase 3

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

Time plan for AD


Phase Time Description

1 Shutdown 2009/1020102 weeks3 weeks

Installation of six magnets for the low-β insertion.Commissioning of the low-β section:

• demonstrate compatibilty with AD users• PAX optics implementation

2a

2b

Shutdown 2010/112 weeks in 20113 weeks in 2011Shutdown 2011/122 weeks in 2012

Installation of the target chamber. Machine acceptance studies. Stacking studies (split in sessions).Installation of ABS, BRP, and detector system.Measurement of H target polarization with antiproton beam.

3 6 weeks in 2012 Spin-filtering measurements using H and D target up to 70 MeV with transverse beam polarization.

4 Shutdown 2012/13

4 weeks in 2013

Shutdown possibly extended up to six months. Implementation and commissioning of electron cooler upgrade to 300 keV.Commissioning of the electron cooler with beam.

5 6 weeks in 2013 Spin-filtering measurements using H and D target up to 430 MeV with transverse beam polarization.

6 Shutdown 2013/14 Implementation of the Siberian snake.

7 8 weeks in 2014 Spin-filtering measurements with H and D target up to 430 MeV with longitudinal beam polarization.

PAX ready to set sequence into motion by installing low-β section into the AD end of this year!


Phase 1:

• All AD magnets remain in place• Installation of six magnets for the low-β insertion.• Commissioning of the low-β section

• Central quad taken out only after commissioning• Same performance of machine as before

• Layout of vacuum system, based on suggestions by the CERN group(→ NEG works)

• Pumping crosses• Turbo pump 200 l/s• Ion getter pump 400 l/s• 2 x SAES GP500 NEG pump 1900 l/s

Spin-filtering studies at COSY

ABS

BRP

COSY-Quadupoles

Low-β quadrupoles

Target chamber with storage cell

and detector system


Main purpose:1. Repeat spin-filtering with protons. No surprises expected2. Commissioning of the experimental setup for AD

Proposal to COSY PAC submitted in July 2009

Low-β magnet installation at COSY

PAX Experiment 37

Time plan for COSYPhase Time Beam time Description1 Summer 2009

Fall 2009 2 weeksInstallation of four magnets for the low–β insertion.Commissioning of the low–β section and machine acceptance measurement.

2 Summer 2010

2010 1 week2×1 week 4 weeks

Installation of the target chamber, ABS, BRP and a detection system for spin–filtering.Measurement of the acceptance angle at the target position.Measurement of the target polarisations in dp and pd.Spin filtering at COSY with transverse beam polarisation.

3 Summer 20112011 4 weeks

Installation of the complete AD detector.Commissioning of the installed equipment.

4 Summer 2012

20122012

1 week4 weeks

Implementation of the two additional solenoids in the injection beam line, ANKE ABS and detectors.Commissioning of the Siberian snake. Spin filtering at COSY with longitudinal beam polarisation.


Implementation of the AD Siberian snake.Commissioning of the AD Siberian snake.


Conclusions

Polarized antiprotons: a missing tool for spin physics

First measurement of the spin-dependence of pbar-p interaction

AD unique machine! Commissioning of equipment at COSY Clear strategy and commitment by PAX

Collaboration


Now and here or never!

Spare transparencies


Hadron Physics „Dream Machine“

… an asymmetric (double-polarized) proton (15 GeV/c) – antiproton (3.5 GeV/c) collider

using HESR, CSR and APR


pp


h1u from p-p Drell-Yan at PAX

PAX : M2/s=x1x2~0.02-0.3 valence quarks (ATT large ~ 0.2-0.3 )

)()()()(ˆ

21

2111

xuxuxhxhaA uu

TTTT

q q

q qqqqqTTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dddd

21212

211121112

• u-dominance• |h1u|>|h1d|

Similar predictions by Efremov et al., Eur. Phys. J. C35, 207 (2004)

Anselmino et al. PLB 594,97 (2004)

1year run: 10 % precision on the h1u(x) in the valence region

Pp=10% Pp=30%

Proposed methods: Some history …

EPAC 1988

Stern-Gerlach splitting never tried (huge effort)


E. Steffens - DSPIN2009 43 of 19

statistical error of a double polarization observable (ATT)

NQP1

TTA

Measuring time t to achieve a certain error δATT

t ~ FOM = P2·I

Figure of Merit and optimum filtering time

(N ~ I)

Optimimum time for polarization buildup given by maximum of FOM(t)

tfilter = 2·τbeam

0 2 4 6 t/τbeam

I/I0

0.2

0.4

0.6

0.8

Bea

m P

olar

izat

ion

ep spin flip studies at COSY: Principle (1)

p

e-cooler ANKE cluster target & STT

Tp = 49.3 MeV

• Use (transversely) polarized proton beam circulating in COSY• Switch on (detuned) electron cooler to depolarize proton beam• Analyze proton polarization with internal D2-cluster target of

ANKE


ep spin flip studies at COSY: Feasibility

Detuning e-cooler for 5 s only ensures that proton momentum stays fixed.

After detuning, proton energy slowly follows electron energy: U = 245 V ve = 1.5·10-3 cfR = 40 Hz in 5 s:

c104

107.8f

ffv

v

5

7R

R

Rpp

vp/ ve~0.03


ep spin flip studies at COSY: Cycle setup

26850

time (s)

Target off Target on

0 200 400 600 800

Num

ber o

f Bea

m P

artic

les

+245

27095

Tdetuned

49·5 s

Tnominal

49·5 s1000

4 108

2 108Eco

oler

Vol

tage

(V)

0 200 400 600 800 1000

tuned cycle detuned cycle

Tnominal

49·5 s

Telectron-off

49·5 s

Compare cycle-by-cycle: No electrons to detuned electrons


Bea

m c

urre

nt

0

Ptuned Pdetuned

Determine Ptuned and Pdetuned from identical cycles, except for detuned cooler


ep spin flip studies at COSY: Super Cycle

Depolarization Studies at COSY: Results (1)

pd elastic scattering:detection in two (L-R) symmetric silicon tracking telescopes

p D2

-4 -3 -2 -1 0 1 2 3 40

0.2

0.4

0.6

tuned coolerdetuned cooler

Proton kinetic energy in electron rest frame (keV)

Bea

m P

olar

izat

ion

Tuned and detuned beam polarizations


ep spin flip studies at COSY: Results (1)

pd elastic scattering:detection in two (L-R) symmetric silicon tracking telescopes

p D2

Measured ratio of polarizations vs Proton Kinetic energy in electron rest frame

-4 -3 -2 -1 0 1 2 3 4

0.8

1

1.2

Nominal proton kinetic energy in electron rest frame (keV)

Pde

tune

d/Ptu

ned


ep spin flip studies at COSY: New calc´s

~ 1 mb → No effect expected!




BRP vacuum HFT

QMAs

ABS/TC vacuum

Bake-out

Coils power

Development of cryopump for target chamber


Task taken on by Gatchina group

TPH 1600

Gate valves

Active baffles 8 K

Shield 75 K

Cryo chamber

Cold head

Question 15: Vacuum System for Spin Filtering at AD


• Intensity of ABS = 6x1016 H/s (2 HFS)Q = 3x1016 H2/s = 1.24x10-3 mbarl/s

• Effusive flow out of one side of thetarget cell into the acceptance angle of the flow limiter qFL with diameter dFL:Qcell = 1.5x1016 (1-cos2 qFL) H2/s

• Direct flow out of the target chamber through the flow limiters QTC=pTC x CConductance of the flow limiter: C=302 (134) l/s for dFL=30 (20) mm

• Pressure in the adjacent beam line pBL = (Qcell+QTC)/2500 l/s (NEG)

dFL

[mm]Qcell

[H2/s]QTC

[H2/s]Qcell+QTC

[H2/s] pBL

[mbar]Qcell+QTC

(2 HFS)

[mbar l/s]

Qcell+QTC

(1 HFS)

[mbar l/s]

Days until regeneration in normal ABS operation (1 HFS

injected) [days]

20 3.7x1013 2.0x1014 2.4x1014 4.0x10-9 9.9x10-6 5x10-6 16.730 8.4x1013 4.5x1014 5.3x1014 8.9x10-9 2.2x10-5 1.1x10-5 7.5

CryopumpS=20000 l/s

pTC = Q/S = 6.2x10-8 mbar

pTC

Crucial: Vacuum system


pp and np scattering experiments at LEAR



np cross sections


pp integrated cross sections


pp differential cross sections


pp differential cross sections


pp analyzing powers


pp → nn differential cross sections






pp → nn analyzing powers

Depolarization parameter D0n0n


Novosibirsk Model predictions for the antiproton beam polarization after filtering for two beam lifetimes with Hydrogen target


V.F. Dmitriev et al., NIM B 266, 1122 (2008)

E. Steffens - DSPIN2009 67 of 19

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

Expected antiproton beam polarization

• AD machine acceptance: Ax=180 m, Ay=200 m

• Cooled 2 beam emittance = 1 m

• Realistic calculation of qacc(mrad) using AD lattice functions and triangular density distribution in storage cell

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

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

PAX ExperimentE. Steffens - DSPIN2009

0 2 4 6 8 100

10

20

Storage cell radius (mm)

Acc

epta

nce

angl

e (m

rad)

8

Beam lifetime


d (mm) Θacc (mrad)

8 8.610 10.812 13.0

Single-Coulomb scattering at the target dominates beam loss

Polarization buildup cross section


COSY low-b section

cell

Storage cell at COSY is not required to be openable


Time plan for COSYPhase Time Beam time Description1 Summer 2009

Fall 2009 2 weeksInstallation of four magnets for the low–β insertion.Commissioning of the low–β section and machine acceptance measurement.

2 Summer 2010

2010 1 week2×1 week 4 weeks

Installation of the target chamber, ABS, BRP and a detection system for spin–filtering.Measurement of the acceptance angle at the target position.Measurement of the target polarisations in dp and pd.Spin filtering at COSY with transverse beam polarisation.


Installation of the complete AD detector.Commissioning of the installed equipment.

4 Summer 2012

20122012

1 week4 weeks

Implementation of the two additional solenoids in the injection beam line, ANKE ABS and detectors.Commissioning of the Siberian snake. Spin filtering at COSY with longitudinal beam polarisation.


Implementation of the AD Siberian snake.Commissioning of the AD Siberian snake.


No way to measure Pz with an unpolarized target → Pz ∙ Qz ∙ Azz

PAX Experiment 73

Conclusions

Polarized antiprotons: a missing tool for spin physics First measurement of the spin-dependence of pbar-p interaction AD unique machine! Commissioning of equipment at COSY Clear strategy and commitment by PAX Collaboration

Now and here or never!


Georg Christoph Lichtenberg(1742-1799)

If you want to see something new, you have to create something new.

Introduction

Documents

polarized proton beam

spinfiltering2pax experimente

spin flipfor

proton energy

proton polarization

spin flip need

ep spin flip studies

spincorrelation data