Do unpolarized electrons affect the polarization of a stored proton beam?
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Transcript of Do unpolarized electrons affect the polarization of a stored proton beam?
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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“
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 3
Introduction
New initiative, driven by the FAIR-project at GSI
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 4
Introduction
(How) is it possible to provide polarized antiproton beams
in HESR ?
High Energy Storage Ring (HESR)
for a beam of antiprotons
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 5
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)
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 6
Two Methods: Loss versus spin flip
For an ensemble of spin ½ particles with projections + () and - ()
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 7
Proposed methods (1): Some history …
EPAC 1988
Stern-Gerlach splitting never tried (huge effort)
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 8
Proposed methods (2): Recent paper
Need for an experimental test of this idea !
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 9
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 10
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 11
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 12
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 13
Depolarization Studies at COSY: Super CycleB
eam
cu
rren
t
0
Ptuned Pdetuned
Determine Ptuned and Pdetuned from identical cycles, except for detuned cooler
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 14
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 15
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 16
Depolarization Studies at COSY: Results (2)
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 17
Depolarization Studies at COSY: Results (3)
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 18
Depolarization Studies at COSY: Results (4)
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 19
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.
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 20
Depolarization Studies at COSY: New calc´s
No effect expected !
(NIM B)10.1016/JNIMB.2008.04.010
~ 1 mb
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 21
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“)
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 22
Spin-filtering at TSR: „FILTEX“ – proof-of-principle
Spin filtering works for protons
F. Rathmann. et al., PRL 71, 1379 (1993)
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 23
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 24
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 25
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)
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 26
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 27
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 28
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)
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 29
Summary:
p e
p e+
p p
p p
long. trans.
WAKBJ: gigantic ???
MSS: small small
1016
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 30
Summary:
p e
p e+
p p
p p
long. trans.
WAKBJ: gigantic ???
MSS: small small
No depolarization of polarized protons
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 31
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 32
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)!
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 33
Spares
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 34
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
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 35
Quark Transversity Distribution in Drell-Yan:
Double transverse spin asymmetry:
llqq *
First direct measurement: No competitive processes
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 36
Cooler on and off
October 7, 2008 Institut für Kernphysik (IKP) , Jülich Center for Hadron Physics (JCHP) 37
Spin-filtering at TSR: „FILTEX“
TSR … Test Storage Ring at MPI Heidelberg
FILTEX … Filter Experiment (1992)