do unpolarized electrons affect the polarization of a stored proton beam?

Mit

glie

d d

er

Helm

holt

z-G

em

ein

sch

aft

Do unpolarized electrons affect the polarization of a stored proton beam?

How to produce polarized antiprotons - and what to use them for?

October 7, 2008 | Frank Rathmann (for the ANKE and PAX collaborations)

SPIN 2008 (Charlottesville, Virginia, USA)

October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 2

Introduction

~ 3 years ago, we proposed a method to polarize antiprotons

by „spin-filtering“


Introduction

New initiative, driven by the FAIR-project at GSI


Introduction

(How) is it possible to provide polarized antiproton beams

in HESR ?

High Energy Storage Ring (HESR)

for a beam of antiprotons


Plan of talk

The (long) road to polarized antiprotons:

Proposals, ideas, calculations, … Experiments

Depolarization studies at COSY

FILTEX (TSR)

Spin-filtering at COSY (see talk by A. Nass)

Spin-filtering at AD/CERN Summary, Conclusion

… taken on by the PAX-collaboration Spokespersons: F. Rathmann (Jülich), P. Lenisa (Ferrara)


Two Methods: Loss versus spin flip

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


Proposed methods (1): Some history …

EPAC 1988

Stern-Gerlach splitting never tried (huge effort)


Proposed methods (2): Recent paper

Need for an experimental test of this idea !


Depolarization Studies at COSY: Idea

• Use proton beam and co-moving electrons

• Turn experiment around: p e p into p e p

i.e. observe depolarization of a polarized proton beam

COSY electron cooler (detuned)

Velocity mismatch


Depolarization Studies at COSY: Principle (1)

p

e-coolerANKE 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


Depolarization Studies at COSY: Principle (2)

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

f

fvv

5

7R

R

Rpp

vp/ ve~0.03


Depolarization Studies at COSY: Cycle setup

26850

time (s)

Target off Target on

0 200 400 600 800

Num

ber

of

Bea

m P

artic

les

+245

27095

Tdetuned

50·5 s

Tnominal

50·5 s1000

4 108

2 108Eco

ole

r V

olta

ge (

V)

0 200 400 600 800 1000

tuned cycle detuned cycle

Tnominal

50·5 s

Telectron-off

50·5 s

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


Depolarization Studies at COSY: Super CycleB

eam

cu

rren

t

0

Ptuned Pdetuned

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


Depolarization Studies at COSY: Polarimetry (Experiment carried out in March 2008)

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

p D2

Deuteron identification

d

p


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

iza

tion

Tuned and detuned beam polarizations



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/P

tune

d



Vdetuned (Volt) Th(keV) (10-3 c) -426 -3 2.71 ± 0.17 0.951

0 0 0.74 ± 0.04 0.500

245 1 1.74 ± 0.24 0.886

301 1.5 2.00 ± 0.23 0.914

348 2 2.24 ± 0.21 0.931

426 3 2.68 ± 0.17 0.950

Weight functions and (1- ) from 3D Maxwellian electron

velocity distributions

barn10

C

Lvnt2

P

Pln

)v()1()v( 24

2rel

R

Ceuneddet

tuned

uneddet

||

P||v

Pv

e||

e

Thermal transverse motion of electrons in the ecooler:

experiment measures mixture

)eV2.0kT(m

kT

e

measured

v



No effect observedmeasured cross section at least 6 orders-of-magnitude smaller than predicted 1013 b

0

4107

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

dep

ol (

barn

)Nominal proton energy in electron rest frame (keV)

Preliminary

0 1 2 3

0 110-3 210-3 310-3

2107

-2107

-4107


Depolarization Studies at COSY: Results (5)Systematic errors

• Total measurement error dominated by statistics.

Uncertainty fromFractional contribution to total error

average electron velocity < 0.15

ring circumference < 2·10-4

10-4 uncertainty of HV power supply < 10-2

longitudinal motion of protons < 4·10-6

characteristic transverse velocity of electrons < 7·10-3

Prel

imin

ary

• Systematic errors of polarization determination in progress.


Depolarization Studies at COSY: New calc´s

No effect expected !

(NIM B)10.1016/JNIMB.2008.04.010

~ 1 mb


Spin-filtering:

Polarization build-up of an originally unpolarized particle beam by repeated interaction with polarized hydrogen target, e.g. in a storage ring:

Spin-filtering is known to work („FILTEX“)


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

Spin filtering works for protons

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


Spin-filtering at COSY: Optimize, understand FILTEX

p

pp = 0.3… GeV/c

Superconducting quadrupole

(new)

ABS + storage cell, Si-tracking det´s

(HERMES)

Need a „low-ß section“ in

COSY


Spin-filtering at COSY: Low-ß Section

Need superconducting quadrupoles

0

5

10

15

20

25

30

35

40

45

50

16.8 17.3 17.8 18.3 18.8 19.3 19.8 20.3 20.8 21.3 21.8 22.3 22.8

Length [m]

Bet

a fu

nctio

ns [m

]

1 2 3 4 Target: Storage cell

Polarimeter


Spin-filtering at CERN/AD: pp and pd scattering

Measurement of effective p polarization build-up cross section

First measurement of spin-correlations in above reactions

• Target (equipment used, tested at COSY)

• Electron cooler (upgrade of existing AD-cooler)

• Snake (also longitudinal; new)


Expectations for AD

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

• Cooled 2 beam emittance = 1 m

• Realistic calculation of acc(mrad) using AD lattice functions from Pavel Belochitsky 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)

dcell (mm) acc(mrad)

10 7.4 ± 1.5

12 8.9 ± 1.5

14 10.5 ± 1.5

16 12.0 ± 1.5


Expectations for AD (Filtering for two beam lifetimes)

100 200 3000

0.05

0.1

0.15

10 mm, 7.4 mrad12 mm, 8.9 mrad14 mm, 10.5 mrad16 mm, 12.0 mrad10 mm, 25 mrad10 mm, 50 mrad

longitudinal

Pol

ariz

atio

n (2

·b)

100 200 3000

0.02

0.04

0.06

0.08

0.1transverse

100 200 3000

0.05

0.1

0.15

Beam kinetic energy (MeV)

100 200 3000

0.01

0.02

A

D


Spin-filtering at COSY: Milestones, timeline

COSY: determine / optimize beam lifetime: needed for large filtering time (beamtime in II/2008)

SC quadrupoles – design almost ready; companies have been contacted (order in 2008)

COSY: set up HERMES-ABS and recoil detectors (2009)

COSY: implement set-up in ring (2010-11), perform sf-measurements

CERN/AD: LoI full proposal; move equipment and repeat with anti-protons (~ 2011-12)

By 2012/13 know how best to do spin-filtering with p!! Design the APR (antiproton polarizer ring)


Summary:

p e

p e+

p p

p p

long. trans.

WAKBJ: gigantic ???

MSS: small small

1016


Summary:

p e

p e+

p p

p p

long. trans.

WAKBJ: gigantic ???

MSS: small small

No depolarization of polarized protons


Summary:

p e

p e+

p p

p p

long. trans.

WAKBJ: gigantic ???

MSS: small small

No depolarization of polarized protons

Spin-filtering works:

p (FILTEX) COSY

p CERN/AD


Conclusion:

The road towards polarized antiprotons is long …

But: - clear roadmap

- commitment by PAX-collaboration

- first measurements/achievements

We appreciate any help!

Note:

Now and here (expertise)

or „never“ (not in a very long time)!


Spares


Hadron Physics „Dream Machine“ for FAIR:

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

using HESR, CSR and APR


Quark Transversity Distribution in Drell-Yan:

Double transverse spin asymmetry:

llqq *

First direct measurement: No competitive processes


Cooler on and off


Spin-filtering at TSR: „FILTEX“

TSR … Test Storage Ring at MPI Heidelberg

FILTEX … Filter Experiment (1992)

do unpolarized electrons affect the polarization of a stored proton beam?

Documents