Status of the Experiment Polarizing antiprotons E. Steffens
University of Erlangen-Nrnberg for the PAX Collaboration
http://www.fz-juelich.de/ikp/pax/ E. Steffens - DSPIN2009 1 PAX
Experiment
Slide 2
Introduction We have proposed a method to polarize antiprotons
by spin-filtering 2 PAX ExperimentE. Steffens - DSPIN2009
Slide 3
Is it possible, and how, to provide polarized antiproton beams
in HESR ? High Energy Storage Ring (HESR) for a beam of antiprotons
3 PAX ExperimentE. Steffens - DSPIN2009 Introduction New
initiative, driven by the FAIR-project at GSI
Slide 4
Introduction Our knowledge about pp interaction is limited:
Lack of polarization data! Restricted to single-spin (A 0n00, A
000n ) 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 E.
Steffens - DSPIN2009PAX Experiment 4
Slide 5
E. Steffens - DSPIN2009PAX Experiment 5 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 h 1 q (x,Q 2 ) of
the proton for valence quarks (A TT in Drell-Yan >0.2)
transversely polarized proton beam or target ( ) transversely
polarized antiproton beam ( ) + many polarization observables in pp
scattering PAX Polarized Antiprotons
Slide 6
Quark Transversity Distribution in Drell-Yan Double transverse
spin asymmetry: First direct measurement: No competitive processes
6 PAX ExperimentE. Steffens - DSPIN2009
Slide 7
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 COSY
Spin-filtering at AD/CERN Spin-filtering at COSY Conclusion Task
taken on by the PAX Collaboration: ~100 members 16 institutions
Spokespersons: P. Lenisa (Ferrara), F. Rathmann (Jlich) 7 PAX
ExperimentE. Steffens - DSPIN2009
Slide 8
Two Methods: Spin-dependent loss versus spin flip For an
ensemble of spin particles with projections + ( ) and ( ) 8 PAX
ExperimentE. Steffens - DSPIN2009
Slide 9
Proposed methods: Spin flip Need for an experimental test of
this idea! 9 PAX ExperimentE. Steffens - DSPIN2009
Slide 10
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 10 PAX ExperimentE.
Steffens - DSPIN2009
Slide 11
ep spin flip studies at COSY: Tools p e-cooler ANKE cluster
target & STT T p = 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 D
2 -cluster target of ANKE 11 PAX ExperimentE. Steffens -
DSPIN2009
Slide 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 v e = 1.510
-3 c f R = 40 Hz in 5 s: v p / v e ~0.03 12PAX ExperimentE.
Steffens - DSPIN2009
Slide 13
ep spin flip studies at COSY: Polarimetry pd elastic
scattering: detection in two (L-R) symmetric Silicon Tracking
Telescopes p D2D2 Deuteron identification d p 13 PAX ExperimentE.
Steffens - DSPIN2009
Slide 14
ep spin flip cross section at COSY: Result No effect observed:
measured cross sections at least 6 orders-of-magnitude smaller than
the predicted 10 13 b. 14 PAX ExperimentE. Steffens - DSPIN2009 0 4
10 7 |Relative velocity of electrons in proton rest frame| (c)
depol (barn) Nominal proton energy in electron rest frame (keV)
0123 0 1 10 -3 2 10 -3 3 10 -3 2 10 7 -2 10 7 -4 10 7 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!
Slide 15
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: 15 PAX ExperimentE.
Steffens - DSPIN2009
Slide 16
P beam polarization Q target polarization k || beam direction
tot = 0 + 1 PQ + 2 (Pk)(Qk) transverse case:longitudinal case: For
initially equally populated spin states: (m=+) and (m=-)
Unpolarized anti-p beam Polarized target Polarization Buildup E.
Steffens - DSPIN200916PAX Experiment
Slide 17
P beam polarization Q target polarization k || beam direction
tot = 0 + 1 PQ + 2 (Pk)(Qk) transverse case:longitudinal case: For
initially equally populated spin states: (m=+) and (m=-)
Unpolarized anti-p beam Polarized target Polarized anti-p beam
Polarization Buildup E. Steffens - DSPIN200917PAX Experiment
Slide 18
E. Steffens - DSPIN2009PAX Experiment 18 statistical error of a
double polarization observable (A TT ) Measuring time t to achieve
a certain error ATT t ~ FOM = P 2 I Figure of Merit and optimum
filtering time (N ~ I) Optimimum time for polarization buildup
given by maximum of FOM(t) t filter = 2 beam 02 4 6 t/ beam I/I 0
0.2 0.4 0.6 0.8 Beam Polarization
Slide 19
Spin-filtering at TSR: FILTEX proof-of-principle Spin filtering
works for protons F. Rathmann et al., PRL 71, 1379 (1993) 19 PAX
ExperimentE. Steffens - DSPIN2009 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: exp =73
6 mb Average theoretical value: theo =86 2 mb Good agreement: ~2
discrepancy Brief summary in: D. Oellers et al., Phys. Lett. B 674,
269 (2009).
Slide 20
20 pp interaction models E. Steffens - DSPIN2009PAX
Experiment
Slide 21
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 1 and 2 Once a polarized
antiproton beam is available, spin-correlation data can be measured
at AD (50-500 MeV)
Slide 22
PAX at the AD (the only place worldwide) E. Steffens -
DSPIN2009PAX Experiment 22 PAX target section Electron cooler
Siberian snake
Slide 23
E. Steffens - DSPIN2009PAX Experiment 23 Experimental Setup
Atomic Beam Source Six additional quadrupoles Breit-Rabi
Polarimeter Target chamber: Detector system + storage cell
Slide 24
Polarized Target E. Steffens - DSPIN2009 PAX Experiment 24 Q x
Q y Q z : 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 x y z
Slide 25
ABS Target chamber Breit-Rabi polarimeter Electric power
Cooling water Atomic Beam Source and Breit-Rabi Polarimeter E.
Steffens - DSPIN2009 PAX Experiment 25 COSY/AD beam axis
Slide 26
Atomic Beam Source and Breit-Rabi Polarimeter E. Steffens -
DSPIN2009PAX Experiment26 BRP vacuum HFT QMAs ABS/TC vacuum
Bake-out Coils power
Slide 27
Target chamber, cell and detector system E. Steffens -
DSPIN2009PAX Experiment27 Storage cell: jet density 100 Silicon
strip detectors Atomic beam Stored beam Guide field coils (x, y, z)
movable flow limiter
Slide 28
E. Steffens - DSPIN2009PAX Experiment28 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
Slide 29
Openable storage cell E. Steffens - DSPIN2009PAX Experiment29
closedopened AD beam envelope at injection requires openable
storage cell P. Belochitsky - CERN
Slide 30
AD optics (P. Belochitsky - CERN) E. Steffens - DSPIN2009PAX
Experiment30 At injectionSqueezed 1.Beam is injected with low-
section moderately powered on. 2.At experiment energy (T
Expected polarizations after filtering for two lifetimes 32 PAX
ExperimentE. Steffens - DSPIN2009 Model A: Production of
longitudinal polarization acc > 13 mrad P(2 b ) changes only
marginally 88.6 1010.8 1213.0 Limit
Slide 33
Main phases of installation at AD E. Steffens - DSPIN2009 33
PAX Experiment 200920102011 Phase 1 Phase 2 Phase 3 Installation of
six magnets for the low- insertion Spin-filtering measurements up
to 70 MeV with transverse beam polarization Installation of the
target chamber: Machine acceptance studies. Stacking studies
Slide 34
Time plan for AD E. Steffens - DSPIN2009PAX Experiment 34
PhaseTimeDescription 1Shutdown 2009/10 2010 2 weeks 3 weeks
Installation of six magnets for the low- insertion. Commissioning
of the low- section: demonstrate compatibilty with AD users PAX
optics implementation 2a 2b Shutdown 2010/11 2 weeks in 2011 3
weeks in 2011 Shutdown 2011/12 2 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. 36 weeks
in 2012Spin-filtering measurements using H and D target up to 70
MeV with transverse beam polarization. 4Shutdown 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. 56 weeks in
2013Spin-filtering measurements using H and D target up to 430 MeV
with transverse beam polarization. 6Shutdown 2013/14Implementation
of the Siberian snake. 78 weeks in 2014Spin-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- section into the AD end of this year!
Slide 35
E. Steffens - DSPIN2009PAX Experiment 35 Phase 1: All AD
magnets remain in place Installation of six magnets for the low-
insertion. Commissioning of the low- 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
Slide 36
Spin-filtering studies at COSY ABS BRP COSY-Quadupoles Low-
quadrupoles Target chamber with storage cell and detector system E.
Steffens - DSPIN2009 36 PAX Experiment Main purpose: 1.Repeat
spin-filtering with protons. No surprises expected 2.Commissioning
of the experimental setup for AD Proposal to COSY PAC submitted in
July 2009 Low- magnet installation at COSY
Slide 37
Time plan for COSY PhaseTimeBeam timeDescription 1Summer 2009
Fall 20092 weeks Installation of four magnets for the low
insertion. Commissioning of the low section and machine acceptance
measurement. 2Summer 2010 20101 week 21 week 4 weeks Installation
of the target chamber, ABS, BRP and a detection system for
spinfiltering. 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. 3Summer
2011 20114 weeks Installation of the complete AD detector.
Commissioning of the installed equipment. 4Summer 2012 2012 1 week
4 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. 5Summer 2013 20133 weeks Implementation of the AD
Siberian snake. Commissioning of the AD Siberian snake. E. Steffens
- DSPIN2009PAX Experiment 37
Slide 38
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 38 PAX
ExperimentE. Steffens - DSPIN2009 Now and here or never!
Slide 39
Spare transparencies E. Steffens - DSPIN2009PAX Experiment
39
Slide 40
Hadron Physics Dream Machine an asymmetric (double-polarized)
proton (15 GeV/c) antiproton (3.5 GeV/c) collider using HESR, CSR
and APR 40 PAX ExperimentE. Steffens - DSPIN2009 p p
Slide 41
PAX Experiment 41 h 1u from p -p Drell-Yan at PAX PAX : s=x 1 x
2 ~0.02-0.3 valence quarks (A TT large ~ 0.2-0.3 ) u-dominance |h
1u |>|h 1d | 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 h 1u (x) in the valence region P p =10% P p
=30%
Slide 42
Proposed methods: Some history EPAC 1988 Stern-Gerlach
splitting never tried (huge effort) 42 PAX ExperimentE. Steffens -
DSPIN2009
Slide 43
PAX Experiment 43 of 19 statistical error of a double
polarization observable (A TT ) Measuring time t to achieve a
certain error ATT t ~ FOM = P 2 I Figure of Merit and optimum
filtering time (N ~ I) Optimimum time for polarization buildup
given by maximum of FOM(t) t filter = 2 beam 02 4 6 t/ beam I/I 0
0.2 0.4 0.6 0.8 Beam Polarization
Slide 44
ep spin flip studies at COSY: Principle (1) p e-cooler ANKE
cluster target & STT T p = 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 D 2 -cluster target of ANKE 44 PAX
ExperimentE. Steffens - DSPIN2009
Slide 45
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 v e = 1.510
-3 c f R = 40 Hz in 5 s: v p / v e ~0.03 45PAX ExperimentE.
Steffens - DSPIN2009
Slide 46
ep spin flip studies at COSY: Cycle setup 26850 time (s) Target
offTarget on 0200400600800 Number of Beam Particles + 245 27095 T
detuned 495 s T nominal 495 s 1000 4 10 8 2 10 8 Ecooler Voltage
(V) 0200400600800 1000 tuned cycledetuned cycle T nominal 495 s T
electron-off 495 s Compare cycle-by-cycle: No electrons to detuned
electrons 46 PAX ExperimentE. Steffens - DSPIN2009
Slide 47
Beam current 0 P tuned P detuned Determine P tuned and P
detuned from identical cycles, except for detuned cooler 47 PAX
ExperimentE. Steffens - DSPIN2009 ep spin flip studies at COSY:
Super Cycle
Slide 48
Depolarization Studies at COSY: Results (1) pd elastic
scattering: detection in two (L-R) symmetric silicon tracking
telescopes p D2D2 -4-3-201234 0 0.2 0.4 0.6 tuned cooler detuned
cooler Proton kinetic energy in electron rest frame (keV) Beam
Polarization Tuned and detuned beam polarizations 48 PAX
ExperimentE. Steffens - DSPIN2009
Slide 49
ep spin flip studies at COSY: Results (1) pd elastic
scattering: detection in two (L-R) symmetric silicon tracking
telescopes p D2D2 Measured ratio of polarizations vs Proton Kinetic
energy in electron rest frame -4-3-201234 0.8 1 1.2 Nominal proton
kinetic energy in electron rest frame (keV) P detuned /P tuned 49
PAX ExperimentE. Steffens - DSPIN2009
Slide 50
ep spin flip studies at COSY: New calcs ~ 1 mb No effect
expected! 50 PAX ExperimentE. Steffens - DSPIN2009
Slide 51
Atomic Beam Source and Breit-Rabi Polarimeter E. Steffens -
DSPIN2009PAX Experiment51 BRP vacuum HFT QMAs ABS/TC vacuum
Bake-out Coils power
Slide 52
Development of cryopump for target chamber E. Steffens -
DSPIN2009 52 PAX Experiment Task taken on by Gatchina group TPH
1600 Gate valves Active baffles 8 K Shield 75 K Cryo chamber Cold
head
Slide 53
Question 15: Vacuum System for Spin Filtering at AD E. Steffens
- DSPIN2009PAX Experiment 53 Intensity of ABS = 6x10 16 H/s (2 HFS)
Q = 3x10 16 H 2 /s = 1.24x10 -3 mbarl/s Effusive flow out of one
side of the target cell into the acceptance angle of the flow
limiter FL with diameter d FL : Q cell = 1.5x10 16 (1-cos 2 FL ) H
2 /s Direct flow out of the target chamber through the flow
limiters Q TC =p TC x C Conductance of the flow limiter: C=302
(134) l/s for d FL =30 (20) mm Pressure in the adjacent beam line p
BL = (Q cell +Q TC )/2500 l/s (NEG) Cryopump S=20000 l/s p TC = Q/S
= 6.2x10 -8 mbar p TC
Slide 54
Crucial: Vacuum system E. Steffens - DSPIN2009PAX
Experiment54
Slide 55
pp and np scattering experiments at LEAR E. Steffens -
DSPIN2009PAX Experiment 55
Slide 56
E. Steffens - DSPIN2009PAX Experiment 56 np cross sections
Slide 57
E. Steffens - DSPIN2009PAX Experiment 57 pp integrated cross
sections
Slide 58
E. Steffens - DSPIN2009PAX Experiment 58 pp differential cross
sections
Slide 59
E. Steffens - DSPIN2009PAX Experiment 59 pp differential cross
sections
Slide 60
E. Steffens - DSPIN2009PAX Experiment 60 pp analyzing
powers
Slide 61
E. Steffens - DSPIN2009PAX Experiment 61 pp nn differential
cross sections
Slide 62
E. Steffens - DSPIN2009PAX Experiment 62 pp nn differential
cross sections
Slide 63
E. Steffens - DSPIN2009PAX Experiment 63 pp nn differential
cross sections
Slide 64
E. Steffens - DSPIN2009PAX Experiment 64 pp nn analyzing
powers
Slide 65
Depolarization parameter D 0n0n E. Steffens - DSPIN2009PAX
Experiment 65
Slide 66
Novosibirsk Model predictions for the antiproton beam
polarization after filtering for two beam lifetimes with Hydrogen
target E. Steffens - DSPIN2009PAX Experiment66 V.F. Dmitriev et
al., NIM B 266, 1122 (2008)
Slide 67
E. Steffens - DSPIN2009PAX Experiment 67 of 19 First
Measurement of Polarization Lifetime at T p = 45 MeV (Nov.
2007)
Slide 68
Expected antiproton beam polarization AD machine acceptance: A
x =180 m, A y =200 m Cooled 2 beam emittance = 1 m Realistic
calculation of acc (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) 68PAX ExperimentE. Steffens - DSPIN2009
Storage cell radius (mm) Acceptance angle (mrad) 8
Slide 69
Beam lifetime E. Steffens - DSPIN2009PAX Experiment69 88.6
1010.8 1213.0 Single-Coulomb scattering at the target dominates
beam loss
Slide 70
Polarization buildup cross section E. Steffens - DSPIN2009PAX
Experiment70
Slide 71
COSY low- section cell Storage cell at COSY is not required to
be openable E. Steffens - DSPIN2009 71 PAX Experiment
Slide 72
Time plan for COSY PhaseTimeBeam timeDescription 1Summer 2009
Fall 20092 weeks Installation of four magnets for the low
insertion. Commissioning of the low section and machine acceptance
measurement. 2Summer 2010 20101 week 21 week 4 weeks Installation
of the target chamber, ABS, BRP and a detection system for
spinfiltering. 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. 3Summer
2011 20114 weeks Installation of the complete AD detector.
Commissioning of the installed equipment. 4Summer 2012 2012 1 week
4 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. 5Summer 2013 20133 weeks Implementation of the AD
Siberian snake. Commissioning of the AD Siberian snake. E. Steffens
- DSPIN2009PAX Experiment 72 No way to measure P z with an
unpolarized target P z Q z A zz
Slide 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! 73 PAX ExperimentE. Steffens - DSPIN2009 Georg Christoph
Lichtenberg (1742-1799) If you want to see something new, you have
to create something new.