1. PAX Polarized Antiproton EXperiment
dr. Paolo Lenisa
Universita’ and INFN - Sezione di Ferrara
PAX Polarized Antiproton EXperiment
PAX Collaboration
Spokespersons:
Frank Rathmann
Paolo Lenisa

2. PAX Collaborators Ma Bo-Qiang
Department of Physics, Beijing, P.R. China
Klaus Goeke, Andreas Metz, and Peter Schweitzer
Institut für Theoretische Physik II, Ruhr Universität Bochum, Germany
Jens Bisplinghoff, Paul-Dieter Eversheim, Frank Hinterberger, Ulf-G. Meißner, and Heiko Rohdjeß
Helmholtz-Institut für Strahlen- und Kernphysik, Bonn, Germany
Sergey Dymov, Natela Kadagidze, Vladimir Komarov, Anatoly Kulikov, Vladimir Kurbatov, Vladimir Leontiev, Gogi Macharashvili, Sergey Merzliakov, Valerie Serdjuk, Sergey Trusov, Yuri Uzikov, Alexander Volkov, and Nikolai Zhuravlev
Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russia
Igor Savin, Vasily Krivokhizhin, Alexander Nagaytsev, Gennady Yarygin, Gleb Meshcheryakov, Binur Shaikhatdenov, Oleg Ivanov, Oleg Shevchenko, and Vladimir Peshekhonov
Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna, Russia
Wolfgang Eyrich, Andro Kacharava, Bernhard Krauss, Albert Lehmann, David Reggiani, Klaus Rith, Ralf Seidel, Erhard Steffens, Friedrich Stinzing, Phil Tait, and Sergey Yaschenko
Physikalisches Institut, Universität Erlangen-Nürnberg, Germany
Guiseppe Ciullo, Marco Contalbrigo, Marco Capiluppi, Paola Ferretti-Dalpiaz, Alessandro Drago, Paolo Lenisa, Michelle Stancari, and Marco Statera
Instituto Nationale di Fisica Nucleare, Ferrara, Italy
Nicola Bianchi, Enzo De Sanctis, Pasquale Di Nezza, Delia Hasch, Valeria Muccifora, Karapet Oganessyan, and Patrizia Rossi
Instituto Nationale di Fisica Nucleare, Frascati, Italy

3. (continued)
Stanislav Belostotski, Oleg Grebenyuk, Kirill Grigoriev, Peter Kravtsov, Anton Izotov, Anton Jgoun, Sergey Manaenkov, Maxim Mikirtytchiants, Oleg Miklukho, Yuriy Naryshkin, Alexandre Vassiliev, and Andrey Zhdanov
Petersburg Nuclear Physics Institute, Gatchina, Russia
Dirk Ryckbosch
Department of Subatomic and Radiation Physics, University of Gent, Belgium
David Chiladze, Ralf Engels, Olaf Felden, Johann Haidenbauer, Christoph Hanhart, Andreas Lehrach, Bernd Lorentz, Nikolai Nikolaev, Siegfried Krewald, Sig Martin, Dieter Prasuhn, Frank Rathmann, Hellmut Seyfarth, Alexander Sibirtsev, and Hans Ströher
Forschungszentrum Jülich, Institut für Kernphysik Jülich, Germany
Ashot Gasparyan, Vera Grishina, and Leonid Kondratyuk
Institute for Theoretical and Experimental Physics, Moscow, Russia
Alexandre Bagoulia, Evgeny Devitsin, Valentin Kozlov, Adel Terkulov, and Mikhail Zavertiaev
Lebedev Physical Institute, Moscow, Russia
N.I. Belikov, B.V. Chuyko, Yu.V. Kharlov, V.A. Korotkov, V.A. Medvedev, A.I. Mysnik, A.F. Prudkoglyad, P.A. Semenov, S.M. Troshin, and M.N. Ukhanov
High Energy Physics Institute, Protvino, Russia
Mikheil Nioradze, and Mirian Tabidze
High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia
Mauro Anselmino, Vincenzo Barone, Mariaelena Boglione, and Alexei Prokudin
Dipartimento di Fisica Teorica, Universita di Torino and INFN, Torino, Italy
Norayr Akopov, R. Avagyan, A. Avetisyan, S. Taroian, G. Elbakyan, H. Marukyan, and Z. Hakopov
Yerevan Physics Institute, Yerevan, Armenia

4. Outline The Future GSI Facility Physics Case Transversity SSA
Electromagnetic Form Factors
Antiproton Polarizer
Polarized Internal Target
Polarization Buildup
Beam lifetimes
Requirements for HESR
Detector Concept
Forward Spectrometer
Large Acceptance Spectrometer
Physics Performance
Conclusion

5. Future Int. Accelerator Facility at GSI
SIS100/300
HESR:
PANDA and PAX
FLAIR:
(Facility for very Low energy Anti-protons and fully stripped Ions)
CR-Complex
NESR

6. The Antiproton Facility
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 ~ (stochastic-cooling)
High resolution mode
Δp/p ~ (8 MV HE e-cooling)
Luminosity = 1031 cm-2s-1
HESR
Gas Target and Pellet Target:
cooling power determines thickness
Super
FRS
NESR CR
RESR
Cooling – e- and/or stochastic
2MV prototype e-cooling at COSY
Antiproton Production Target
Antiproton production similar to CERN
Production rate 107/sec at 30 GeV
Energy = GeV/c

7. The Central Physics Issue
Twist-2 distribution functions
Spin-average
Helicity-difference
Helicity-flip

8. Status of knowledge Transversity, Remains still unmeasured
Well known and well modeled
Known, but poorly modeled
Remains still unmeasured
Poorly modeled
Transversity,
A review in:
Barone, Drago,Ratcliffe,
Phys. Rep. 359 (2002) 1

9. Transversity Chiral-odd: requires another chiral-odd partner
Probes relativistic nature of quarks
No gluon analog for spin-1/2 nucleon
Different evolution than
Sensitive to valence quark polarization
Properties:
Chiral-odd: requires another chiral-odd partner

10. Transversity in Drell-Yan processesqL q l+ l-
q2=M2 qT
PAX: Polarized antiproton beam → polarized proton target (both transverse)
M invariant Mass
of lepton pair
Elementary QED process
θ: polar angle of lepton
in l+l- rest frame
: azimuthal angle
w.r.t. proton polarization

11. ATT in the Drell-Yan production at PAX
RHIC: τ=x1x2=M2/s~10-3
→ Exploration of the sea quark content (polarizations small!)
ATT very small (~ 1 %)
PAX: M2~10 GeV2, s~30-50 GeV2, τ=x1x2=M2/s~
→ Exploration of valence quarks (h1q(x,Q2) large)
xF=x1-x2
0.2
0.4
0.6
0.15
0.25
Anselmino, Barone, Drago, Nikolaev
(hep-ph/ v1)
T=22 GeV
T=15 GeV
0.3
ATT/aTT > 0.3
Models predict |h1u|>>|h1d|
Main contribution to Drell-Yan events
at PAX from x1~x2~τ
deduction of x-dependence of h1u(x,M2)!

12. Single Spin Asymmetries
Several experiments have observed unexpectedly large single spin asymmetries in pbar-p at large values of xF ≥ 0.4 and moderate values of pT (0.7 < pT < 2.0 GeV/c)
E704 Tevatron FNAL 200GeV/c π+
Large asymmetries originate from valence quarks: sign of AN related to u and d-quark polarizations π- xF

13. Gauge Link structure: Universality violation?
Gauge invariant definition of T-odd distribution function in
DIS contains a future pointing Wilson line, whereas in
Drell-Yan (DY) it is past pointing
DIS DY
Collins, PLB 536 (2002) 43
Requires experimental checks

14. Proton Electromagnetic Formfactors
Measurement of relative phases of magnetic and electric FF in the time-like region
Possible only via SSA in the annihilation pp → e+e-
Double-spin asymmetry
independent GE-Gm separation
test of Rosenbluth separation in the time-like region

15. Polarized internal target
Interaction Region
point-like
5-10 mm
free jet
low density
1012 cm-2
extended mm
storage cell
high density
1014 cm-2

16. Example: The HERMES target

17. The HERMES target
Atomic Beam Source
NIM A 505, (2003) 633

18. The HERMES target Atomic Beam Source Pz+ = |1> + |4>
NIM A 505, (2003) 633
Pz+ = |1> + |4>
Pz- = |2> + |3>

19. The HERMES target Atomic Beam Source Storage cell Diagnostics:
NIM A 505, (2003) 633
Storage cell
NIM A 496, (2003) 277
Diagnostics:
Target Gas Analyzer
NIM A 508, (2003) 265
Breit-Rabi Polarimeter
NIM A 482, (2002) 606

20. Target polarization Relation to measured quantities:
PT = total target polarization
a0 =atomic fraction in absence of recombination
ar =atomic fraction surviving recombination
Pa = polarization of atoms
Pm = polarization of recombined molecules
Relation to measured quantities:
Sampling corrections
ar = ca arTGA
Pa = cP PaBRP

21. Target performance Longitudinal Polarization (B=335 mT)
Hydrogen
Deuterium
Pt = ± 0.028

22. Target performance Longitudinal Polarization (B=335 mT)
Hydrogen
Deuterium
Pt = ± 0.028

23. Target performance Tranverse Polarization (B=297 mT) 2002 - … Hydrogen
PT =  0.033

24. Principle of Spin Filter Method( ) k P if , 2 1
tot Q = × s +
P beampol.
Q targetpol.
k || beam
For initially equally populated
spin states:  (m=½)
 (m=-½) Q 1
tot × s =
Expectation
Target
Beam  
For low energy pp scattering:
1<0  tot+<tot-

25. Filter Test at TSR with protons
Results
F. Rathmann. et al.,
PRL 71, 1379 (1993)
T=23 MeV
Experimental Setup

26. Puzzle from FILTEX Test
Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1
Expected build-up: P(t)=tanh(t/τ1),
1/τ1=σ1Qdtf=2.4x10-2 h-1
 about factor 2 larger!
σ1 = 122 mb (pp phase shifts)
Q = 0.83 ± 0.03
dt = (5.6 ± 0.3) x 1013cm-2
f = MHz
Three distinct effects:
Selective removal through scattering beyond θacc=4.4 mrad σR=83 mb
Small angle scattering of target protons into ring acceptance σS=52 mb
Spin transfer from polarized electrons of the target atoms to the stored protons
σE=-70 mb
Horowitz & Meyer, PRL 72, 3981 (1994)
H.O. Meyer, PRE 50, 1485 (1994)

27. Spin transfer from electrons to protons
Horowitz & Meyer, PRL 72, 3981 (1994)
H.O. Meyer, PRE 50, 1485 (1994)
α fine structure constant
λp=(g-2)/2= anomalous magnetic moment
me, mp rest masses
p cm momentum
a0 Bohr radius
C02=2πη/[exp(2πη)-1] Coulomb wave function
η=-zα/ν Coulomb parameter (neg. for anti-protons)
v relative lab. velocity between p and e
z beam charge number

28. Beam lifetimes in HESR The lifetime of a stored beam is given by
(Target thickness =
dt=5·1014 atoms/cm2)
400
800
1200
T (MeV) 2 4 6 8
beam lilfetime τb (h)
Ψacc = 1 mrad
5 mrad
10 mrad 10
20 mrad
In order to achieve highest polarization in the antiproton beam, acceptance angles around Ψacc = 10 mrad are needed.

29. Polarization Build-up
Exploit spin transfer process σE
works also if hadronic polarizing cross sections σR and σSturn out to be small
N(t)=N0exp(-t/τb)
τb=(fdtσL)-1
I(t)=N(t) f
P(t)=1-exp(-t/τ1)~ σEdtfQt
Optimum filtering time: t=2τb (from d(P2I)/dt=0)
 P(2τb )=2Q (σE/σL)
Estimate for σL from Indiana Cooler
σL=4.75 107 T-2 mb , (Note: σE~T-1)
R.E. Pollock et al.,
NIM A 330, 380 (1993)

30. Antiproton Polarizer antiproton Polarization (%) Expected Buildup
t (h) 5 10 15 20 8 6 4 2
T=500 MeV
T=800 MeV
dt=5·1014 atoms/cm2
Pelectron=0.9
Goal
spin-transfer cross section
(electrons to antiprotons) 10
100
1000
T (MeV)
e (mbarn) 1

31. Polarization Conservation in a Storage Ring
Indiana Cooler
H.O. Meyer et al.,
PRE 56, 3578 (1997)
HESR design must allow for storage of polarized particles!

32. Spin Manipulation in a Storage Ring
(A. Krisch et. al)
Frequent spin-flips reduce systematic errors
Spin-Flipping of protons and deuterons by artifical resonance
RF-Dipole
Applicable at High Energy Storage Rings (RHIC, HESR)
Stored protons:
P(n)=Pi()n
 =(99.3±0.1)%

33. Polarimetry Different schemes to determine target and beam polariz.
Suitable target polarimeter (Breit-Rabi or Lamb-Shift) to measure target polarization
At lower energies ( MeV) analyzing power data from PS172 are available.
Therefrom a suitable detector asymmetry can be calibrated
→ effective analyzing power
Beam and target analyzing powers are identical
measure beam polarization using an unpolarized target
Export of beam polarization to other energies
target polarization is independent of beam energy

34. Detector Concept Two complementary parts:
Forward detector (±8o acceptance) a la HERMES
Identify unambiguously leading particles
Measure precisely their momenta
Central Large Acceptance Detector
Measure angles and energies of medium energy electromagnetic particles (Drell-Yan)

35. Forward Detector

36. Large Acceptance Detector

37. Physics Performance Luminosity
Spin-filtering for two beam lifetimes: P > 5%
N(pbar) = 5·1011 at fr~6·105 s-1
dt = 5·1014 cm-2
Time-averaged luminosity is about factor 3 lower
beam loss and duty cycle
Experiments with unpolarized beam
L factor 10 larger

38. only non-resonant J/Ψ contribution included
Count rate estimate
Uncertainty in ATT depends on target and beam polarization ( |P|>0.05, |Q|~0.9)
Note: Conservative estimate since hadronic buildup effect might be large as well
T = 15 GeV
T = 22 GeV
240 days
only non-resonant J/Ψ contribution included

39. Extension of the “safe” region
h1q(x,Q2) not confined to „safe“ region M > 4 GeV!
unknown vector coupling,
but same Lorentz
and spinor structure
as other two processes
Unknown quantities cancel in the ratios for ATT, but helicity structure remains!
Cross section increases by two orders from M=4 to M=3 GeV
→ Drell-Yan continuum enhances sensitivity of PAX to ATT
Anselmino, Barone, Drago, Nikolaev
(hep-ph/ v1)

40. Conclusion
Challenging opportunities and new physics accessible with PAX at HESR
unique access to a wealth of new fundamental physics observables
polarized antiprotons (P>5%)
Central physics issue: h1q (x,Q2) of the proton in DY processes
Other issues:
Electromagnetic Formfactors
Polarization effects in Hard and Soft Scattering processes
differential cross sections, analyzing powers, spin correlation parameters
Machine design (more beam!)
Need separate target station
HESR must be capable to store polarized antiprotons
Polarization buildup requires large acceptance angle (10 mrad)
Storage cell target requires low-β section
Slow ramping of beam energy needed to optimize pol. build-up

41. PAX: The next steps Jan.2004 LOI submitted
Formation of an advisory committee at GSI
Apr.-May 2004 Evaluation of LOI’s
(If approved)
Techn. Report (with Milesones)
Evaluations & Green Light for Construction
Technical Design Reports (for Milestones)
2012 Commissioning of HESR