1 dr. paolo lenisa università di ferrara and infn – italy on behalf of the pax-collaboration...
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dr. Paolo LenisaUniversità di Ferrara and INFN – ITALY
on behalf of the PAX-Collaboration
Perspectives for Polarized Antiprotons
Polarized AntiprotonsP.Lenisa
XIV International Workshop on Polarized Sources, Targets and PolarimetrySt. Petersburg, 13.09.2011
Motivation:Missing tool for Hadron Physics
2Polarized AntiprotonsP.Lenisa
Polarized Antiprotons
Polarized Antiprotons 3
transversely polarisedquarks and nucleons
q
longitudinally polarisedquarks and nucleons
q
unpolarised quarksand nucleons
q
Quark structure of the nucleon
nxqxqxqx T1
55LTw2Corr Sγγ)(γ)(S)(
2
1)(
P.Lenisa
Well known Known Less known
Polarized Antiprotons 4
Inclusive DIS Semi-inclusive DIS Drell-Yan
HERMES,COMPASS,JLab
transversely polarisedquarks and nucleons
q
longitudinally polarisedquarks and nucleons
q
unpolarised quarksand nucleons
q
nxqxqxqx T1
55LTw2Corr Sγγ)(γ)(S)(
2
1)(
Quark structure of the nucleon
P.Lenisa
Accesso to transversity through Drell-Yan
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llqq *
q q
q qqqqq
TTTT xqxqxqxqe
xhxhxhxheaA
)()()()(
)()()()(ˆ
dd
dd
21212
211121112
Polarized AntiprotonsP.Lenisa
Asymmetric (double-polarized)
proton (15 GeV/c) – antiproton (3.5 GeV/c) collider
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pp
A double polarized pbar-p collider for FAIR
Polarized AntiprotonsP.Lenisa
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1 year run -> 10 % precision on the h1u (x) in the valence region
Pp=30%
Pp=10%
Polarized AntiprotonsP.Lenisa
q q
q qqqqq
TTTT xqxqxqxqe
xhxhxhxheaA
)()()()(
)()()()(ˆ
dd
dd
21212
211121112
h1u from p-p Drell-Yan at PAX
• u-dominance• |h1u|>|h1d|
)()(
)()(ˆ
21
2111
xuxu
xhxhaA uuTTTT
Polarized Antiprotons 8
Polarization
Rosenbluth
Space-Like FFs: proton data
Study of the Proton Electromagnetic Form-Factors
JLab results dramatically changed picture of the Nucleon:
- GEp/GM
p decreases with Q2
- data suggest GEp crosses 0 at Q2 8
GeV2
Time-Like FFs: proton data
Expected Q2 behaviour reached quite early, however ...... there is still a factor of 2between timelike and spacelike.
Additional and more precise measurements needed
P.Lenisa
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•Most contain moduli GE, GM• Independent GE-GM separation• Test of Rosenbluth separation in the time-like region
•Access to GE-GM phase•Very sensitive to different models
Double polarized pbar-p annihilation:
E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005)
Polarized AntiprotonsP.Lenisa
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Polarization and Models in T.L. Region
VDM : IJL
Ext. VDM
‘QCD inspired’
R
Ay Axx Ayy
AxzAzz
E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005)
Polarized AntiprotonsP.Lenisa
Method:The mechanism of spin-filtering
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Polarized Antiprotons
P. Lenisa PAX Status Report 12
Polarized antiprotons
Intense beam of polarized pbar never produced:
• Synchr. radiation ~ (4/R) -> pol ~107 y in 20 TeV pbar ring
• Conventional methods (ABS) not applicable
• Polarized pbar from antilambda decay• I< 1.5∙105 s-1 (P ≈ 0.35)
• Pbar scattering off liquid H2 target• I< 2∙103 s-1 (P ≈ 0.2)
Production of polarization in a stored beam
Two Methods: Loss versus spin flip
For an ensemble of spin ½ particles with projections + () and – ()
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Spin-filtering
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Polarization build-up of a circulating particle beam by interaction with a polarized gas target
Polarized Antiprotons
Unpolarized anti-p beam
Polarized target
Polarization Buildup
P.Lenisa 15
S beam-particle spinQ target polarizationk || beam direction
)ˆ)(ˆ()( 210 kQkSQStot
)/tanh()(
tNN
NNtP
fdQ t
1
~1
fQdt)~~(
1
1
||
Polarized Antiprotons
Unpolarized anti-p beam
Polarized target
Polarized anti-p beam
P.Lenisa 16
Polarization BuildupS beam-particle spinQ target polarizationk || beam direction
)ˆ)(ˆ()( 210 kQkSQStot
)/tanh()(
tNN
NNtP
fdQ t
1
~1
fQdt)~~(
1
1
||
Polarized Antiprotons
Optimum (black curve) after 2 lifetimes filtering
Spin-filtering at TSR: „FILTEX“ – proof-of-principle
Spin filtering works for protons
F. Rathmann et al., PRL 71, 1379 (1993)
17Polarized AntiprotonsP.Lenisa
PAX@AD/CERN:Antiproton polarization
PAX@COSY :Proton polarization
PAX@FAIR:Eexperiments with
pol. pbar
P.Lenisa 18Polarized Antiprotons
Polarized AntiprotonsExperimental program:
Measurements with pbar at AD-Ring
P.Lenisa 19
PAX target section
Measurements at AD (CERN)•Aim: 1st measurement of the spin-dependence of the pbar-p cross section•Method: measurement of polarization build-up by spin-filtering
Polarized Antiprotons
Spin-dependence of the pbar-p interaction
P.Lenisa 20
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).
Polarized Antiprotons
Expected polarizations after filtering for two lifetimes
transverse
A
D
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longitudinal
Polarized AntiprotonsP.Lenisa
• Measurement of the polarization buildup allows determination of σ1 and σ2
• Once pbar polarization available, spin-correlation coefficients accessible
Polarized Antiprotons 22
More recent calculations…
PLB 690 (2010)
P.Lenisa
Cross sections
Projected polarizations
PAX@AD/CERN:Antiproton polarization
PAX@COSY :Proton polarization
PAX@FAIR:Experiments with pol. pbar
P.Lenisa 23Polarized Antiprotons
Polarized AntiprotonsExperimental program
Measurements with p at COSY-Ring (Germany)
WASA
e-cooler
ANKE
PAX
Spin-filtering at COSY
Main purpose:1. Commissioning of the experimental setup for CERN/AD2. Quantitative understanding of the machine parameters
P.Lenisa 24Polarized Antiprotons
Installation of low-β section (2009)
•Beam has to fit through storage cell target (dt=5x1013 atoms/cm2)•Increase acceptance angle at target position
P.Lenisa 25Polarized Antiprotons
• Model in good agreement with measurement: β ~ 0.3m -> beam fits through the cell!
• No negative impact on the COSY operation
Commissioning of the experimental setup (2010)I. Machine studies: Low- section
P.Lenisa 26Polarized Antiprotons
In case intra-beam scattering poses a limitation, increase of beam emittance should increase lifetime! (Touschek)
• Increase of beam emittance by tilting of electron cooler beam• Beam emittance measured with ionisation profle monitor
P.Lenisa 27Polarized Antiprotons
Commissioning of the experimental setup (2010)I. Machine studies: Studies of beam-lifetime
limitations
ABSABS
Breit-Rabipolarimeter
Breit-Rabipolarimeter
Spin filtering requires >1013 atoms/cm2 → ABS + openable storage cell
Analysis of target polarization by Breit-Rabi polarimeter (BRP) and a target gas analyzer (TGA)
Commissioning of the experimental setup (2010)II. Polarized Target
P.Lenisa 28Polarized Antiprotons
P.Lenisa Polarized Antiprotons 29
BRP: Continous monitoring of the target polarization
p D2
pd elastic scattering:detection in two (L-R) symmetric Silicon Tracking Telescopes
Commissioning of the experimental setup (2010)III. Beam Polarimeter
P.Lenisa 30Polarized Antiprotons
Deuteron identification
d
p
P.Lenisa Polarized Antiprotons 31
Commissioning of the experimental setup (Aug. 2011)
IV. Installation of NEG pump (12000 l/s)
In an ideal machine Single-Coulomb scattering at the target dominates beam loss
COSY beam
movable frame system
September 2011 ongoing beamtime:I Measurement of ring acceptance
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September 2011 ongoing beamtime:II Ring polarization studies
P.Lenisa 33Polarized Antiprotons
I. Measurement of polarization lifetime: P>105sII. Measurement of spin-flip efficiency: =0.987
Spin-filtering cycle
P.Lenisa 34Polarized Antiprotons
PolarizationdP/dt 0.18%/h
Cycle
COSY measurement
revtpolpol
revtc0beam
fdQ
1
fd)(
1
P.Lenisa Polarized Antiprotons 35
To be continued ….
Ferrara - Castello EstenseSebastiano Filippi: “The spinning top game" – XVI cent.
Additional slides
P.Lenisa 36Polarized Antiprotons
pp interaction models
P.Lenisa 37Polarized Antiprotons
Nuclear polarization of the hydrogen target determined with the Breit-Rabi polarimeter after opening and closing of the storage cell a few times
Nuclear polarization of the hydrogen target determined with the Breit-Rabi polarimeter after opening and closing of the storage cell a few times
closed open
0penable storage cell•Atomic beam source provides polarized hydrogen target•Storage cell target to reach dt=5x1013 atoms/cm2
P.Lenisa 38Polarized Antiprotons
Polarisation buildup cross sections
Folie 34
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Polarized antiprotons on fixed target
(PAX-Phase I)
EXPERIMENT:Fixed target experiment:
polarized antiprotons protons in CSR (p>200 MeV/c)fixed polarized protons target
P.Lenisa