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Transcript of FNAL, Jan 25, 2008 Road to Polarized Antiprotons: Depolarization Studies and Spin Filtering...
FNAL, Jan 25, 2008
Road to Polarized Antiprotons:Depolarization Studies
and Spin Filtering Experiments at COSY and
AD
Frank RathmannInstitut für Kernphysik
Forschungszentrum Jülich
Frank Rathmann Road to polarized Antiprotons 2 of 19
Intense beam of polarized antiprotons was never produced:
•Conventional methods (ABS) not appliable
•Polarized antiprotons from antilambda decay • I < 1.5∙105 s-1 (P ≈ 0.35)
•Antiproton scattering off liquid H2 target• I < 2∙103 s-1 (P ≈ 0.2)
Little polarization from pbarC scattering exp’ts at LEAR
•Stern-Gerlach spin separation in a beam (never tested)
•6/2007 Walcher/Arenhoevel: polarized electrons/positronsSpin filtering is the only succesfully tested technique
Polarized Antiprotons
Frank Rathmann Road to polarized Antiprotons 3 of 19
Experimental SetupExperimental Setup ResultsResults
F. Rathmann. et al., PRL 71, 1379 (1993)
T=23 MeV
Low energy pp scattering
1<0 tot+<tot-
Expectation
Target Beam
1992 Filter Test at TSR with protons
Frank Rathmann Road to polarized Antiprotons 4 of 19
1994 Meyer and Horowitz: three distinct effects1. Selective removal through scattering beyond θacc=4.4 mrad (σR=83 mb)
2. Small angle scattering of target prot. into ring acceptance (σS=52 mb)
3. Spin-transfer from pol. el. of target atoms to stored prot. (σE=-70 mb)
σ1= σR+ σS + σE = 65 mb
2005 Milstein & Strakhovenko + Nikolaev & Pavlov: only one effectOnly pp elastic scattering contributesNo contribution from other two effects σ1 = 85.6 mb
Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1
P(t)=tanh(t/τ1), 1/τ1=σ1Qdtf
σ1 = 72.5 ± 5.8 mb
Two interpretations of FILTEX result
Frank Rathmann Road to polarized Antiprotons 5 of 19
… only hadronic (Budker-Jülich)
- electromagnetic + hadronic (Meyer-Horowitz)
TSR
… FILTEX does not provide the answer
Effective Polarizing cross sections
Frank Rathmann Road to polarized Antiprotons 6 of 19
Spin Filtering works, but:
1. Controversial interpretations of FILTEX experiment• Further experimental tests necessary
• Which role do electrons play?• How does spin filtering work?
Tests with protons at COSY
2. No data to predict polarization from filtering with antiprotons Measurements with antiprotons at AD/CERN
Spin Filtering: Present Status
Frank Rathmann Road to polarized Antiprotons 7 of 19
arXiv:0706.3765v3 [physics.acc-ph] 14Nov 2007
Frank Rathmann Road to polarized Antiprotons 8 of 19
Principle of the Depolarization Measurement
using co-moving electrons of the e-cooler
Nominal CoolerVoltage
Tnominal = 100 s
Detuned CoolerVoltage
Tdetuned= 50 s
D2 Target onEcool on
D2 Target offEcool on/detuned
2T
T
uneddet
alminno
Eh = 0.001 MeVΔV = 235 V
Frank Rathmann Road to polarized Antiprotons 9 of 19
Switch off ecooler
Machine Test for Depolarization Measurements(Nov. 2007)
Detuned ecooler ΔU=150 V
Machine-wise, experiment is feasible
Frank Rathmann Road to polarized Antiprotons 10 of 19
New Low Energy Polarimeter for COSY (Nov. 2007)
ANKE Target Chamber
Two Silicon Tracking Telecopes
Frank Rathmann Road to polarized Antiprotons 11 of 19
Performance of New Low Energy Polarimeter (Nov. 2007)
Frank Rathmann Road to polarized Antiprotons 12 of 19
Polarimetry 45 MeV
Frank Rathmann Road to polarized Antiprotons 13 of 19
First Measurement of Polarization Lifetime at Tp = 45 MeV (Nov. 2007)
Experimental determination of the depolarizing ep cross ~ March 2008
Frank Rathmann Road to polarized Antiprotons 14 of 19
Goal: •Complete understanding of the spin filtering mechanism
•Disentangle electromagnetic and hadronic contributions to the polarizing cross section
1. Low-beta section
2. Polarized target (former HERMES target)
3. Detector (partially former HERMES Silicon recoil)
Commissioning of AD setup
Spin Filtering studies at COSY
Frank Rathmann Road to polarized Antiprotons 15 of 19
x,ynew = 0.3 m -> large increase in target density•Shorter buildup time, higher rates•Larger polarization buildup rate due to larger acceptance
Superconducting quadrupoles necessary
Low-β section
Frank Rathmann Road to polarized Antiprotons 16 of 19
Target Snake
E-cooler
T= 5 - 2.8 GeV Np = 3·107
Study of spin filtering in pbar-p (pbar-d) scattering
Measurement of effective polarization buildup cross-section• Both transverse and longitudinal• Variable acceptance at target• Test also polarized D target
First ever measurement for spin correlations in pbar-p (and pbar-D)
Spin Filtering at AD of CERN
Frank Rathmann Road to polarized Antiprotons 17 of 19
e-CoolerAPRABS
Polarizer Target
InternalExperiment
Siberian Snake
BInjection
150 m
F. Rathmann et al., PRL 94, 014801 (2005)
Extractione-Cooler
Small Beam Waist at Target β=0.2 mHigh Flux ABS q=1.5·1017 s-1
Dense Target T=100 K, longitudinal Q (300 mT)
beam tube db=ψacc·β·2dt=dt(ψacc), lb=40 cm
(=2·β)
feeding tube df=1 cm, lf=15 cm
Large Acceptance APR
World-First: Antiproton Polarizer Ring (APR)
Frank Rathmann Road to polarized Antiprotons 18 of 19
Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995)
Model A: T. Hippchen et al., Phys. Rev. C 44, 1323
(1991)
50 100 150 200 250 T (MeV) 50 100 150 200 T (MeV)
0.05
0.10
0.15
0.20
P
0.05
0.10
0.15
0.20
P
2 beam lifetimesΨacc=10-50 mrad
3 beam lifetimesΨacc=20 mrad
Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering)
Frank Rathmann Road to polarized Antiprotons 19 of 19
Fall 2007 Submission of proposal to COSY-PAC
- Beam depolarization studies
- Beam and polarization lifetime studies
Spring 2008 Technical proposal to COSY-PAC for spin filtering
Technical proposal to SPSC for spin filtering at AD
2008-2009 Design and construction phase
2009 Spin-filtering studies at COSY
Commissioning of AD experiment
Then Installation at AD
Spin-filtering studies at AD
Quite a challenge in front of us:
Young (and less young) polarization enthusiasts are welcome!
Outlook until ~2012
Design of the APR
Frank Rathmann Road to polarized Antiprotons 20 of 19
Intense beam of polarized antiprotons was never produced:
•Conventional methods (ABS) not appliable
•Polarized antiprotons from antilambda decay • I < 1.5∙105 s-1 (P ≈ 0.35)
•Antiproton scattering off liquid H2 target• I < 2∙103 s-1 (P ≈ 0.2)
•Little polarization from pbarC scattering exp’ts at LEAR
•Stern-Gerlach spin separation in a beam (never tested)
•6/2007 Walcher/Arenhoevel: polarized electrons/positrons
Spin filtering is the only succesfully tested technique
Polarized Antiprotons
Frank Rathmann Road to polarized Antiprotons 21 of 19
Topics
• IntroductionIntroduction
• Depolarization Studies using unpolarized Depolarization Studies using unpolarized ElectronsElectrons
• Testing the Arenhoevel/Walcher PredictionsTesting the Arenhoevel/Walcher Predictions
• Upper Limit of the Depolarizing Cross SectionUpper Limit of the Depolarizing Cross Section
• Spin Filtering Studies at COSY and ADSpin Filtering Studies at COSY and AD
Frank Rathmann Road to polarized Antiprotons 22 of 19
Experimental Setup at TSR (1992)
Frank Rathmann Road to polarized Antiprotons 23 of 19
1994 Meyer and Horowitz: three distinct effects1. Selective removal through scattering beyond θacc=4.4 mrad (σR=83 mb)
2. Small angle scattering of target prot. into ring acceptance (σS=52 mb)
3. Spin-transfer from pol. el. of target atoms to stored prot. (σE=-70 mb)
σ1= σR+ σS + σE = 65 mb
2005 Milstein & Strakhovenko + Nikolaev & Pavlov: only one effectOnly pp elastic scattering contributesNo contribution from other two effects σ1 = 85.6 mb
Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1
P(t)=tanh(t/τ1), 1/τ1=σ1Qdtf
σ1 = 72.5 ± 5.8 mb
Two interpretations of FILTEX result
Frank Rathmann Road to polarized Antiprotons 24 of 19
Spin filtering works, but:
1. Controversial interpretations of FILTEX experiment• Further experimental tests necessary
• How does spin filtering work?• Which role do electrons play?
Tests with protons at COSY
2. No data to predict polarization from filtering with antiprotons Measurements with antiprotons at AD/CERN
Spin Filtering: Present Status
Frank Rathmann Road to polarized Antiprotons 25 of 19
Spin Filtering studies at COSY
Goal: •Understanding the spin filtering mechanism:
•Disentangle electromagnetic and hadronic contributions to the polarizing cross section
Frank Rathmann Road to polarized Antiprotons 26 of 19
Experimental setup
• Low-beta section • Polarized target (former HERMES
target)• Detector• Snake• Commissioning of AD setup
Frank Rathmann Road to polarized Antiprotons 27 of 19
x,ynew = 0.3 m -> increase in density with respect to ANKE: factor
30•Shorter buildup time, higher rates•Larger polarization buildup rate due to larger acceptance•Use of former HERMES target and Breit-Rabi Polarimeter
Superconducting quadrupoles necessary
Low-β section
Frank Rathmann Road to polarized Antiprotons 28 of 19
Acceptance @ ANKE
Cross sections
Acceptance @ new-IP
Lifetimes… only hadronic - electromagnetic + hadronic
__ COSY average ψacc = 1 mrad….. ψacc = 2 mrad
ANKE vs new IP: Acceptance and Lifetime
Frank Rathmann Road to polarized Antiprotons 29 of 19
PIT Filter. time Polar. Total rate Meas. Time (P/P=10%)
ANKE 2= 16 h 1.2 % 7.5x102 s-1 44 min
5 = 42 h 3.5 % 5x10 s-1 26 min
New IP 2= 5 h 16 % 2.2x104 s-1 1 s
5= 13 h 42 % 1.5x103 s-1 < 1 s
New IP
ANKE
Pola
riza
tion
[%
]
Expectations based on Budker-Jülich:
• T = 40 MeV
• Ninj=1.5x1010 protons
ANKE vs new IP: Polarization
Frank Rathmann Road to polarized Antiprotons 30 of 19
Injection of different combinations of hyperfine states• Different electron and nuclear polarizations• Null experiments possible:
•Pure electron polarized target (Pz = 0), and•Pure nuclear polarized target (Pe=0)
Inj. states Pe Pz Interaction Holding field
|1> +1 +1 Elm. + had. transv. + longit. weak (20 G)
|1> + |4> 0 +1 only had.longitudinal strong (3kG)
|1> + |2> +1 0 only elm.
Strong fields can be applied only longitudinally (minimal beam interference)
- Snake necessaryTarget polarimetry requires BRP for pure electron and nuclear polarization.
Method 1: Polarization build-up experiments
How to disentangle hadronic and electromagnetic contributions to eff ?
Frank Rathmann Road to polarized Antiprotons 31 of 19
Target Snake
E-cooler
T= 5 - 2.8 GeV Np = 3·107
Study of spin filtering in pbar-p (pbar-d) scattering
Measurement of effective polarization buildup cross-section• Both transverse and longitudinal• Variable acceptance at target• Test also polarized D target
First ever measurement for spin correlations in pbar-p (and pbar-D)
AD ring at CERN
Frank Rathmann Road to polarized Antiprotons 32 of 19
Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995)
Model A: T. Hippchen et al., Phys. Rev. C 44, 1323
(1991)
50 100 150 200 250 T (MeV) 50 100 150 200 T (MeV)
0.05
0.10
0.15
0.20
P
0.05
0.10
0.15
0.20
P
2 beam lifetimesΨacc=10-50 mrad
3 beam lifetimesΨacc=20 mrad
Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering)
Frank Rathmann Road to polarized Antiprotons 33 of 19
Depolarization Studies using unpolarized Depolarization Studies using unpolarized ElectronsElectrons
• Use electrons in ecooler instead of target electrons to observe depolarization
Rough extraction for numerical estimates
Frank Rathmann Road to polarized Antiprotons 34 of 19
Ecooler Settings for Tp=45 MeV
Typical parameters of COSY Cooler
• Electron Current 240 mA• Cross section 5 cm2
• Length 2 m• Nominal Voltage 24.5 kV
Electron target thickness seen by the protons
Frank Rathmann Road to polarized Antiprotons 35 of 19
Estimated Polarization Lifetime
revtp fd
1
Frank Rathmann Road to polarized Antiprotons 36 of 19
Energy Resolution of Protons in Electron Rest System
TT1
p
p
to electron
rest system Tp = 65, 45, 30 MeV
Frank Rathmann Road to polarized Antiprotons 37 of 19
Polarimetry
Frank Rathmann Road to polarized Antiprotons 38 of 19
Polarimetry
Frank Rathmann Road to polarized Antiprotons 39 of 19
Beam Polarization with detuned cooler
Eh = 0.001, 0.002, 0.003 MeV
D2 Target onEcool on
D2 Target offEcool on/detuned
Frank Rathmann Road to polarized Antiprotons 40 of 19
Counting statistics• With
– 109 stored protons at T = 45 MeV– Target thickness dt(D2) = 2·1014 cm-2
– Injected Beam Polarization P = 0.8– Detector system as shown– After 1 cycle (250 s): ΔP = 0.108
15 cycles (~1 h): ΔP = 0.03150 cycles (~10h): ΔP = 0.009
Eh (MeV) ΔV (V) τp(A-W) (s) P(t=250 s)
0.001 234 0.04 0
0.002 332 25 0.10
0.003 407 2000 0.78
Frank Rathmann Road to polarized Antiprotons 41 of 19
Estimated Precision of Polarization Lifetime based on Counting Statistics in
Polarimeter
revt
in
out
fdt
)PP
ln(
Eh = 0.001, 0.01, 0.1 MeV
Measuring time per point: ~14 h
Frank Rathmann Road to polarized Antiprotons 42 of 19
Measuring time per point: ~14 h
Eh = 0.002 MeV
Estimated Precision of Polarization Lifetime based on counting statistics
Frank Rathmann Road to polarized Antiprotons 43 of 19
Phase 0: present -2012
Physics: buildup measurements @ COSY and CERN
APR design and construction
Phase I: 2015-2019
APR+CSR @ GSI
Physics: EMFF, p-pbar elastic with fixed target
Phase II: 2020 - …
HESR+CSR asymmetric collider
Physics: h1
Outlook beyond 2012
Antiproton Facility spares
Frank Rathmann Road to polarized Antiprotons 45 of 19
HESR
Antiproton Production
Target
HESR (High Energy Storage Ring)• Length 442 m• Bρ = 50 Tm• N = 5 x 1010 antiprotons
High luminosity mode• Luminosity = 2 x 1032 cm-2s-1
• Δp/p ~ 10-4 (stochastic-cooling)
High resolution mode• Δp/p ~ 10-5 (8 MV HE e-cooling)• Luminosity = 1031 cm-2s-1
•Antiproton production similar to CERN
•Production rate 107/sec at 30 GeV•T = 1.5 - 15 GeV/c
Gas Target and Pellet Target: cooling power determines thickness
SuperFRS
NESR
CR
Beam Cooling: e- and/or stochastic2MV prototype e-cooling at COSY
SIS100/300
The Antiproton Facility
Spin Filtering spares
Frank Rathmann Road to polarized Antiprotons 47 of 19
e-CoolerAPRABS
Polarizer Target
InternalExperiment
Siberian Snake
BInjection
150 m
F. Rathmann et al., PRL 94, 014801 (2005)
Extractione-Cooler
Small Beam Waist at Target β=0.2 mHigh Flux ABS q=1.5·1017 s-1
Dense Target T=100 K, longitudinal Q (300 mT)
beam tube db=ψacc·β·2dt=dt(ψacc), lb=40 cm
(=2·β)
feeding tube df=1 cm, lf=15 cm
Large Acceptance APR
World-First: Antiproton Polarizer Ring (APR)
Frank Rathmann Road to polarized Antiprotons 48 of 19
statistical error of a double polarization observable (ATT)
NQP
1TTA
Measuring time t to achieve a certain error
δATT
t ~ FOM = P2·I
Polarization Buildup: General Features IV
(N ~ I)
Optimimum time forPolarization Buildup
given by maximum of FOM(t)tfilter = 2·τbeam
0 2 4 6 t/τbeam
I/I 0
0.2
0.4
0.6
0.8
Beam
Pola
riza
tion
Frank Rathmann Road to polarized Antiprotons 49 of 19
Figure of Merit at new IP
Topt ~ 55 MeV
Calculation based on Budker-Jülich
Frank Rathmann Road to polarized Antiprotons 50 of 19
• Will measure beam polarization by using the polarization observables:
•p-p elastic (COSY)•pbar-p elastic (AD)
• Good azimuthal resolution (up/down asymmetries)• Low energy recoil (<8 MeV)
•Silicon telescopes•Thin 5μm Teflon cell needed
• Angular resolution for the forward particle for p-pbar at AD• AD experiment will require an openable cell
Detector concept
Frank Rathmann Road to polarized Antiprotons 51 of 19
Beam Polarization in a dedicated Antiproton Polarizer
0.1
0.2
0.3
0.4
Beam
Pola
riza
tion P
(2·τ
beam)
01 10 T (MeV)100
Polarisation buildup through spin transfer
5030
ψacc(mrad)
10
epep Horowitz & Meyer, PRL 72, 3981
(1994)H.O. Meyer, PRE 50, 1485 (1994)
PAX will exploit spin-transfer to polarize antiprotons and to go after transversity
Frank Rathmann Road to polarized Antiprotons 52 of 19
“If polarized electrons polarize an initially unpolarized beam, then, unpolarized electrons should depolarize an initially polarized beam!”
Method 2: Depolarization experiments
Electrons in 4He storage cell or D cluster-jet target:
• Large analyzing power• Large counting rates
• Distinguish electron effect from normal depolarization in COSY
• Prerequisites:•Large beam lifetime•Large polarization lifetime
4Heempty
Prediction for ANKE/COSY (4 weeks)
Approved new Proposal for COSY
4He
Hans-Otto Meyer’s suggestion
Frank Rathmann Road to polarized Antiprotons 53 of 19
Polarization Buildup:
P beam polarizationQ target polarizationk || beam direction
σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)
polbeam
polbeam
tt
0
tt
0
ee2
I)t(I
ee2
I)t(I
transverse case:
Q0tot
longitudinal case:
Q)( ||0tot
For initially equally populated spin states: (m=+½) and (m=-½)
revtpolpol
revtc0beam
fdQ
1
fd)(
1
)t(I)t(P)t(FOM
tcosheIII)t(I
ttanh
II
II)t(P
2
pol
t
0
pol
beam
Time dependence of P, I, and FOM
Frank Rathmann Road to polarized Antiprotons 54 of 19
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)
Unpolarized anti-p beam
Polarized H target
Polarization Buildup:
Frank Rathmann Road to polarized Antiprotons 55 of 19
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)
Unpolarized anti-p beam
Polarized H target
Polarized anti-p beam
Polarization Buildup:
Frank Rathmann Road to polarized Antiprotons 56 of 19
Experimental SetupExperimental Setup ResultsResults
F. Rathmann. et al., PRL 71, 1379 (1993)
T=23 MeV
Low energy pp scattering
1<0 tot+<tot-
Expectation
Target Beam
1992 Filter Test at TSR with protons
Frank Rathmann Road to polarized Antiprotons 57 of 19
Rate EstimateFür 1*E9 Protonen mit einer Polarisation von 0.8.
Target sind 2E14/cm2 d und die Strahlenergie beträgt 45MeV.
Die Plots findest du angehängt.
Weitere Zahlen:
Totale Zählraten L:5.8/s R:8.1/s
Error of Polarization after 1s: 0.86
(Die 0.13 waren bei 100s E7 Teilchen, aber 30mal....)
Integriert man über 100s (Strahllebensdauer ebenfalls 100s) dann erhält
man (100 -100/e)=63.2 -fache Statistik also einen Fehler von
0.86/sqrt(63.2)=0.108. Dies ist leider deutlich schlechter als die
erhofften 0.02, aber sicherlich kein Showstopper.
Dauer eines Zyklus:
10s für Injektion
100s für E-Cooler-Spielerei
100s für Polarisationsmessung
5s für Extraktion
==============================
215s = 4Min(240s)
In einer Stunde hätten wir also 15 Zyklen also einen Fehler von 0.03.
Nach 10h: 0.009. Wir sollten also ohne Probleme an einem Tag sowohl die
Injektionspolarisation, sowie die Polarisation nach E-Cooler-Spielerei
messen können.
Frank Rathmann Road to polarized Antiprotons 58 of 19
“If polarized electrons polarize an initially unpolarized beam, then, unpolarized electrons should depolarize an initially polarized beam!”
Electrons in 4He storage cell or D cluster-jet target:
• Large analyzing power• Large counting rates
• Distinguish electron effect from normal depolarization in COSY
• Prerequisites:•Large beam lifetime•Large polarization lifetime
4Heempty
Prediction for ANKE/COSY (4 weeks)
Approved new Proposal for COSY
4He
Depolarization Study at COSY
Explore also option with co-moving electrons in cooler