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PAX Polarized Antiproton Experiments
http//www.fz-juelich.de/ikp/pax
Paolo Lenisa Università and INFN Ferrara,
ITALY
Trento, July 6th 2006
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PAX Collaboration

• 180 physicists
• 35 institutions (15 EU, 20 NON-EU)

TIMELINE Jan. 04 Letter of Intent for
FAIR May 04 QCD-PAC meeting at GSI Aug.
04 Workshop on polarized antiprotons at GSI Jan.
05 Technical Proposal for FAIR Mar.
05 QCD-PAC meeting at GSI Nov. 05 LoI to
CERN-SPSC to perform spin-filtering experiments
with antiprotons at the AD ring Apr. 06 LoI
to COSY-PAC for spin filtering experiments with
protons at COSY
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Evaluation by QCD-PAC (March 2005)
the PAC would like to stress again the
uniqueness of the program with polarized
anti-protons and polarized protons that could
become available at GSI.
Recommendation of the STI of FAIR (Sept. 2005)

• The STI requests RD work to be continued on the
  proposed asymmetric collider experiment with both
  polarized anti-protons and protons
• t o demonstrate that a high degree of
  anti-proton polarization can be reached
• The STI believes that PAX should become part of
  the FAIR core research program based on its
  strong scientific merit once the open problems
  are convincingly solved.

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Physics Motivations
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Physics with polarized antiprotons at GSI-PAX
Transversity via Drell-Yan processes
High Energy
direct access to transversity
Transverse Single Spin Asymmetries
QCD theorem (Sivers)D-Y (Sivers)DIS
Elastic processes
spin mysteries like in pp ?
Low Energy
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h1 from pbar-p Drell-Yan at GSI
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Precision in h1 measurement
1 year of data taking at 153.5 GeV collider
L 21030 cm-2s-1
(L1031 reachable)
10 precision on the h1u (x) in the valence
region
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What about p-p?
Barone, Calarco, Drago Martin, Schäfer,
Stratmann, Vogelsang
RHIC tx1x210-3 ? sea quarks
(ATT 0.01 )
JPARC/U70 tx1x210-1 ? valence and sea
(ATT 0.1 )
PAX tx1x210-1 ? valence and sea
(ATT 0.1 )
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DY in p-p ATT
A. Drago

• Aymmetry is large at PAX energy (gt 0.1)
• Sign of the asymmetry will distinguish between
  the two models.
• It will give indications about calculation of sea
  distributions.

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DY events distribution (vs15 GeV)
p-p
p-pbar
Extraction of h1u for xgt0.2
p-pbar p-p -gt complete map of transversity
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DY in p-p ALL

• Large asymmetries expected
• Test of the assumptions of the fits

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Physics with polarized antiprotons at GSI-PAX
High Energy
Transverse Single Spin Asymmetries
QCD theorem (Sivers)D-Y (Sivers)DIS
Elastic processes
spin mysteries like in pp ?
Low Energy
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Single Spin Asymmetries (and their partonic
origin)
p
Pq
k-
Collins effect fragmentation of polarized quark
depends on Pq (pq x k-)
pq
q
P
k-
Sivers effect number of partons in polarized
proton depends on P (p x k-)
p
Pq
q
Boer-Mulders effect polarization of partons in
unpolarized proton depends on Pq (p x k-)
k-
p
Collins chiral-odd Sivers chiral-even Boer-Mulde
rs chiral-odd
These effects may generate SSA
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BNL-AGS vs 6.6 GeV 0.6 lt pT lt 1.2 p?p
E704 vs 20 GeV 0.7 lt pT lt 2.0 p?p
STAR-RHIC vs 200 GeV 1.1 lt pT lt 2.5 p?p
E704 vs 20 GeV 0.7 lt pT lt 2.0 p?p
SSA, pp ? pX
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Physics with polarized antiprotons at GSI-PAX
High Energy
Transverse Single Spin Asymmetries
QCD theorem (Sivers)D-Y (Sivers)DIS
Elastic processes
spin mysteries like in pp ?
Low Energy
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pp Elastic Scattering from ZGS
Spin-dependence at large-P? (90cm) Hard
scattering takes place only with spins ??.
T10.85 GeV
Similar studies in pp elastic scattering
D.G. Crabb et al., PRL 41, 1257 (1978)
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Physics with polarized antiprotons at GSI-PAX
High Energy
Transverse Single Spin Asymmetries
QCD theorem (Sivers)D-Y (Sivers)DIS
Elastic processes
spin mysteries like in pp ?
Time-like e.l.m. form factors
Low Energy
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Proton Electromagnetic Formfactors

• Single-spin asymmetry in pp ? ee-
• Measurement of relative phases
• of magnetic and electric FF in
• the time-like region
• Double-spin asymmetry in pp ? ee-
• independent GE-Gm separation
• test of Rosenbluth separation in the time-like
  region

S. Brodsky et al., Phys. Rev. D69 (2004)
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Experimental setup
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PAX Accelerator Setup

• Antiproton Polarizer Ring (APR)
• Asymmetric Antiproton-Proton Collider (CSR)
• High Energy Synchrotron Ring (HESR)

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Antiproton Polarizer Ring
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Staging Phase I (PAX_at_CSR)
Physics EMFF pbar-p elastic
Experiment pol./unpol. pbar on internal
polarized target
Independent from HESR running
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Staging Phase II (PAX_at_HESR)
Physics Transversity
EXPERIMENT Asymmetric collider polarized
antiprotons in HESR (p15 GeV/c) polarized
protons in CSR (p3.5 GeV/c)
Second IP with minor interference with PANDA
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Parameters
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Symmetric collider
Luminosity
Asymm. collider
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PAX Detector Concept
Physics h1 distribution sin2q
EMFF sin2q pbar-p elastic
high t
Azimuthally Symmetric BARREL GEOMETRY LARGE
ANGLES
Experiment Flexible Facility
ee-
Detector Extremely rare DY signal (10-7
p-pbar) Maximum Bjorken-x coverage
(M interval) Excellent PID
(hadron/e rejection 104) High
mass resolution (2 ) Moderate lepton
energies (0.5-5 GeV)
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Kinematics for Drell-Yan processes
CERN NA51 450 GeV/c
Q2gt4 GeV2
QCD corrections might be very large at smaller
values of M, for cross-sections, not for ATT
K-factor almost spin-independent
H. Shimizu, G. Sterman, W. Vogelsang and H.
Yokoya, hep-ph/0503270 V. Barone et al., in
preparation
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PAX Detector Concept
Physics h1 distribution sin2q
EMFF sin2q pbar-p elastic
high t
Azimuthally Symmetric BARREL GEOMETRY LARGE
ANGLES
Experiment Flexible Facility
ee-
Detector Extremely rare DY signal (10-7
p-pbar) Maximum Bjorken-x coverage
(M interval) Excellent PID
(hadron/e rejection 104) High
mass resolution (2 ) Moderate lepton
energies (0.5-5 GeV)
Magnet Keeps beam polarization vertical
Compatible with Cerenkov Compatible
with polarized target
TOROID NO FRINGE FIELD
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PAX Detector Concept
GEANT simulation
(200 mm)
Cerenkov
(20 mm)
Designed for Collider but compatible with fixed
target
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The (long) way towards a polarized antiproton
collider
Phase 0 2006-2010
Pol. buildup measurements _at_ COSY and CERN
2011-2013 APR final design and construction
Phase I 2014-2017 APRCSR _at_ GSI Physics EMFF,
p-pbar elastic with fixed target.
Phase II 2018 - HESRCSR asymmetric
collider Physics h1
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Antiproton and Proton accelerators scheme
Energy
proton
HESR
SIS18
HESR
antiproton
RESR
CSR
CSR
HESR
CSR
CSR
time
APR
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Higher energy p-p machine
V. Barone, T. Calarco and A. Drago Phys. Rev. D
56 (1997) 527

• s ?
• Asymmetry ?
• vs _at_ PAX ideal

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Transverse sea
CQSM
CDM
V. Barone, T. Calarco and A. Drago Phys. Lett. B
390 (1997) 287
M. Wakamatsu and T. Kubota Phys. Rev. D 63 (1999)
034020

• The two models predict different sign for
  (with comparable amplitude).

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Longitudinal sea
M. Glück et al. Phys. Rev. D 63 (2001) 094005