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The PAX Project Spin Physics at GSI

The PAX Project Spin Physics at GSI. P olarized A ntiproton E x periments www.fz-juelich.de/ikp/pax. Central Physics Issue. Transversity distribution of the nucleon: last leading-twist missing piece of the QCD description of the partonic structure of the nucleon

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The PAX Project Spin Physics at GSI

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  1. The PAX ProjectSpin Physics at GSI PolarizedAntiprotonExperiments www.fz-juelich.de/ikp/pax 5th Workshop on the Scientific Cooperation between German Research Centres and JINR

  2. Central Physics Issue Transversity distribution of the nucleon: • last leading-twist missing piece of the QCD description of the partonic structure of the nucleon • directly accessible uniquely via the double transverse spin asymmetry ATT in the Drell-Yan production of lepton pairs • theoretical expectations for ATT in DY, 30-40% • transversely polarized antiprotons • transversely polarized proton target • definitive observation of h1q(x,Q2) of the proton for the valence quarks

  3. Leading Twist Distribution Functions R L L R L R R L quark quark’ 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 proton proton’ R L 1/2 -1/2     -     Probabilistic interpretation in helicity base: + f1(x) q(x) spin averaged (well known) - Dq(x) helicity diff. (known) g1(x) No probabilistic interpretation in the helicity base (off diagonal) h1(x) u = 1/2(uR + uL) u = 1/2(uR - uL) Transversity base dq(x) helicity flip (unknown)

  4. Evaluation by QCD Program Advisory Committee (July 2004) • STI Report: • Your LoI has convinced the QCD-PAC • that Polarization must be included into the design of FAIR from the beginning, and • that the presently proposed scheme is not optimized as to the physics. You […] are invited and encouraged to design a world-class facility with unequalled degree of polarization of antiprotons. • Common Report: • […] The PAC considers the spin physics of extreme interest and the building of an antiproton polarized beam as a unique possibility for the FAIR Project. • […] The unique physics opportunities, made possible with polarized antiproton beams and/or polarized target are extremely exciting, especially in double spin measurements. • […] It would be very unfortunate if decisions about the facility, made now, later preclude the science.

  5. σEM|| (mb) Atomic Electrons 600 500 Pure Electrons 400 300 200 100 T (MeV) 1 10 100 Exploitation of Spin Transfer PAX will employ spin-transfer from polarized electrons of the target to antiprotons (QED Process:calculable) Hydrogen gas target: ①+② in strong field (300 mT) Pe=0.993 Pz=0.007

  6. Ψacc=50 mrad EM only 0.4 40 30 0.3 20 Beam Polarization P(2·τbeam) 0.2 10 0.1 5 0 1 10 100 T (MeV) Filter Test: T = 23 MeV Ψacc= 4.4 mrad Antiproton Beam Polarization Buildup in HESR (800 MeV) F. Rathmann et al., PRL 94, 014801 (2005)

  7. M invariant Mass of lepton pair Transversity in Drell-Yan processes Polarized Antiproton Beam → Polarized Proton Target (both transversely polarized) l+ Q2=M2 l- Q QT p p QL

  8. ATT for PAX kinematic conditions 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~0.2-0.3 →Exploration ofvalence quarks(h1q(x,Q2) large) 0.3 ATT/aTT > 0.3 Models predict |h1u|>>|h1d| 0.25 0.15 T=15 GeV (s=5.7 GeV) T=22 GeV (s=6.7 GeV) 0.10 Anselmino et al. PLB 594,97 (2004) Main contribution to Drell-Yan events at PAXfrom x1~x2~τ: deduction of x-dependence of h1u(x,M2) 0 0.6 0.4 0.2 xF=x1-x2 xF=x1-x2 Similar predictions by Efremov et al., Eur. Phys. J. C35, 207 (2004)

  9. Towards an Asymmetric Polarized Hadron Collider • CSR (COSY-like) at FAIR(3.5 GeV/c) • Formfactor measurement pp → e+e- • unpolarized antiproton beam on polarized internal target • CSR + AP: pp elastic • Asymmetric Collider pp: : 3.5 GeV/c protons + 15 GeV/c antiprotons (also fixed target experiment possible)

  10. Towards an Asymmetric Polarized Hadron Collider • CSR at FAIR (3.5 GeV/c) • Formfactor measurement pp → e+e- • unpolarized antiproton beam on polarized internal target • CSR + AP: pp elastic • Asymmetric Collider pp: : 3.5 GeV/c protons + 15 GeV/c antiprotons (also fixed target experiment possible)

  11. Towards an Asymmetric Polarized Hadron Collider • CSR at FAIR (3.5 GeV/c) • Formfactor measurement pp → e+e- • unpolarized antiproton beam on polarized internal target • CSR + AP: pp elastic • Asymmetric Collider pp:3.5 GeV/c protons + 15 GeV/c antiprotons(also fixed target experiments possible)

  12. ATT for PAX kinematic conditionsFixed Targetvs Collider 22 GeV/c fixed target 22 GeV/c 15+3.5 collider 15+3.5 15 + 15 collider Anselmino et al. PLB 594,97 (2004) Similar predictions by Efremov et al., Eur. Phys. J. C35, 207 (2004) • Collider Options for Transversity measurement: • 15 GeV/c + 15 GeV/c  s=1000 GeV2, too high • 15 GeV/c + 3.5 GeV/c  s=220 GeV2,ideal

  13. Conceptual Detector Design ~3 m

  14. Time schedule Jan. 04 LOI submitted 15.06.04 QCD PAC meeting at GSI 18-19.08.04 Workshop on polarized antiprotons at GSI 15.09.04Additional PAX document on Polarization at GSI: • F. Rathmann et al., PRL 94, 014801 (2005) 15.11.04 Additional PAX document: Number of IP’s at HESR 21.12.04 Additional PAX document: Asymmetric Collider 15.01.05Technical Report (with Milestones) • Design and Construction of APR at IKP of FZJ . . . . . Evaluations & Green Light for Construction 2005-2008Technical Design Reports (for Milestones) >2012Commissioning of HESR

  15. Conclusion • Challenging opportunities and new physics accessible at HESR • Unique access to a wealth of new fundamental physics observables • 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 • Asymmetric Collider: • 15 GeV/c + 3.5 GeV/c • ideal conditions for Transversity measurements • Calculation of Intrabeam and Beam-Beam Scattering (Meshkov/Sidorin using BETACOOL) • Projections for HESR fed by a dedicated AP: • Pbeam > 0.30 • 5.6·1010 polarized antiprotons • Luminosity: Fixed target: L  2.7 ·1031 cm-2s-1 • Collider: L  1030 cm-2s-1 (first estimate)

  16. ~170 PAX Collaborators, 34 Institutions (17 inside, 17 outside EU) Yerevan Physics Institute, Yerevan, Armenia Department of Subatomic and Radiation Physics, University of Gent, Belgium University of Science & Technology of China, Beijing, P.R. China Department of Physics, Beijing, P.R. China Centre de Physique Theorique, Ecole Polytechnique, Palaiseau,France High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia Nuclear Physics Department, Tbilisi State University, Tbilisi, Georgia Forschungszentrum Jülich, Institut für Kernphysik Jülich, Germany Institut für Theoretische Physik II, Ruhr Universität Bochum, Germany Helmholtz-Institut für Strahlen- und Kernphysik, Bonn, Germany Physikalisches Institut, Universität Erlangen-Nürnberg, Germany Unternehmensberatung und Service Büro (USB), Gerlinde Schulteis & Partner GbR, Langenbernsdorf, Germany Department of Mathematics, University of Dublin, Dublin,Ireland University del Piemonte Orientale and INFN, Alessandria, Italy Dipartimento di Fisica, Universita di Cagliari and INFN, Cagliari,Italy Instituto Nationale di Fisica Nucleare, Ferrara, Italy Dipartimento di Fisica Teorica, Universita di Torino and INFN, Torino, Italy Instituto Nationale di Fisica Nucleare, Frascati, Italy Dipartimento di Fisica, Universita di Lecce and INFN, Lecce, Italy Soltan Institute for Nuclear Studies, Warsaw,Poland Petersburg Nuclear Physics Institute, Gatchina, Russia Institute for Theoretical and Experimental Physics, Moscow, Russia Lebedev Physical Institute, Moscow, Russia Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Russia Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russia Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna, Russia Budker Institute for Nuclear Physics, Novosibirsk, Russia High Energy Physics Institute, Protvino, Russia Institute of Experimental Physics, Slovak Academy of Sciences and P.J. Safarik University, Faculty of Science, Kosice,Slovakia Department of Radiation Sciences, Nuclear Physics Division, Uppsala University, Uppsala, Sweden Collider Accelerator Department, Brookhaven National Laboratory,USA RIKEN BNL Research Center, Brookhaven National Laboratory,USA University of Wisconsin, Madison,USA Department of Physics, University of Virginia, Virginia, USA

  17. Outline WHY?Physics Case HOW?Polarized Antiprotons WHERE?FAIR Project at Darmstadt WHAT? Transversity Measurement WHEN?Time Schedule Conclusion

  18. Transversity Properties: • Probes relativistic nature of quarks • No gluon analog for spin-1/2 nucleon • Different evolution than • Sensitive to valence quark polarization Chiral-odd: requires another chiral-odd partner epe’hX ppl+l-X Indirect Measurement: Convolution with unknown fragment. fct. Impossible in DIS Direct Measurement

  19. Other Physics Topics • Single-Spin Asymmetries • Electromagnetic Form Factors • Hard Scattering Effects • Soft Scattering • Low-t Physics • Total Cross Section • pbar-p interaction

  20. 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 S. Brodsky et al., Phys. Rev. D69 (2004)

  21. Study onset of Perturbative QCD p (GeV/c) • High Energy • small t: Reggeon Exchange • large t: perturbative QCD • Pure Meson Land • Meson exchange • ∆ excitation • NN potential models • Transition Region • Uncharted Territory • Huge Spin-Effects in pp elastic scattering • large t: non- and perturbative QCD

  22. pp elastic scattering from ZGS Spin-dependence at large-P (90°cm): Hard scattering takes place only with spins . T=10.85 GeV Similar studies in pp elastic scattering at PAX D.G. Crabb et al., PRL 41, 1257 (1978)

  23. Outline WHY? Physics Case HOW?Polarized Antiprotons WHERE? FAIR Project at Darmstadt WHAT? Transversity Measurements WHEN? Time Schedule Conclusion

  24. For initially equally populated spin states:  (m=+½) and  (m=-½) transverse case: longitudinal case: Spin Filter Method P beam polarization Q target polarization k || beam direction σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k) Time dependence of P and I

  25. I/I0 0.8 Beam Polarization 0.6 0.4 0.2 0 2 6 4 t/τbeam Polarization Buildup: Optimum Interaction Time statistical error of a double polarization observable (ATT) Measuring time t to achieve a certain error δATT ~ FOM = P2·I (N ~ I) Optimimum time for Polarization Buildup given by maximum of FOM(t) tfilter = 2·τbeam

  26. Experimental Results from Filter Test Results Experimental Setup T=23 MeV F. Rathmann. et al., PRL 71, 1379 (1993) Low energy pp scattering 1<0  tot+<tot-

  27. 1992 Filter Test at HD-TSR with protons

  28. Puzzle from FILTEX Test Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1 • Expectedbuild-up: P(t)=tanh(t/τpol), • 1/τpol=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 = 1.177 MHz Three distinct effects: • Selective removal through scattering beyond Ψacc=4.4 mradσR=83 mb • Small angle scattering of target protons into ring acceptanceσS=52 mb • Spin transfer from polarized electrons of the target atoms to the stored protons σEM=70 mb (-) Horowitz & Meyer, PRL 72, 3981 (1994) H.O. Meyer, PRE 50, 1485 (1994)

  29. 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=1.793 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 (negative for antiprotons) v relative lab. velocity between p and e z beam charge number

  30. B Dedicated Antiproton Polarizer (AP) Injection Siberian Snake HESR AP 440 m e-cooler e-cooler Internal Experiment 150 m Extraction ABS Polarization Buildup in AP parallel to measurement in HESR Polarizer Target F. Rathmann et al., PRL 94, 014801 (2005) db=ψacc·β·2dt=dt(ψacc) lb=40 cm (=2·β) df=1 cm, lf=15 cm β=0.2 m q=1.5·1017 s-1 T=100 K Longitudinal Q (300 mT)

  31. ψacc(mrad) 40 10 8 6 beam lilfetime τbeam (h) 30 25 4 20 2 10 10 100 1000 T (MeV) Beam lifetimes in the AP Beam Lifetime Coulomb Loss Total Hadronic

  32. Optimum Beam Energies for Buildup in AP ψacc= 50 mrad FOM AP Space charge limit 15 40 mrad 10 5 30 mrad 20 mrad 10 mrad T (MeV) 10 100 1

  33. Space-Charge Limitation in the AP Before filtering starts: Nreal = 107 s-1 · 2τbeam Nind. 1013 1012 1011 ψacc= 50 mrad 40 mrad 1010 30 mrad Nreal 20 mrad 10 mrad 109 10 mrad 10 100 T (MeV) 1

  34. B Transfer from AP to HESR and Accumulation Injection Siberian Snake HESR AP 440 m e-cooler e-cooler Internal Experiment 150 m Extraction ABS COSY Polarizer Target

  35. 10 mrad 20 mrad 30 mrad 40 mrad 50 mrad 8·1010 6·1010 4·1010 2·1010 0 20 40 60 80 t (h) Accumulation of Polarized Beam in HESR PIT: dt=7.2·1014 atoms/cm2 τHESR=11.5 h Number accumulated in equilibrium independentof acceptance Npbar No Depolarization in HESR during energy change

  36. σEM|| (mb) Atomic Electrons 600 500 Pure Electrons 400 300 200 100 T (MeV) 1 10 100 How about a Pure Polarized Electron Target? Maxiumum σEM|| for electrons at rest: (675 mb ,Topt = 6.2 MeV): Gainfactor ~15 over atomic e- in a PIT • Density of an Electron-Cooler fed by 1 mA DC polarized electrons: • Ie=6.2·1015 e/s • A=1 cm2 • l=5 m • dt = Ie·l·(β·c·A)-1 = 5.2·108 cm-2 • Electron target density by factor ~106 smaller, • no match for a PIT (>1014 cm-2)

  37. Longitudinal Field (B=335 mT) Dz PT = 0.845 ± 0.028 Dzz HERMES H PT = 0.795  0.033 HERMES Performance of Polarized Internal Targets HERMES: Stored Positrons PINTEX: Stored Protons H Fast reorientation in a weak field (x,y,z) Transverse Field (B=297 mT) Targets work very reliably (many months of stable operation)

  38. Outline WHY? Physics Case HOW? Polarized Antiprotons WHERE?FAIR Project at Darmstadt WHAT? Transversity Measurement WHEN? Time Schedule Conclusion

  39. NEW Facility • An“International Accelerator Facility for Beams of Ions and Antiprotons”: • Top priority of German hadron and nuclear physics community (KHuK-report of 9/2002) and NuPECC • Favourable evaluation by highest German science • committee (“Wissenschaftsrat” in 2002) • Funding decision from German government in • 2/2003 – staging and at least 25% foreign funding • to be build at GSI Darmstadt; • should be finished in > 2011 (depending on start) • FAIR • (Facility for Antiproton and Ion Research)

  40. FAIR – Prospects and Challenges • FAIR is a facility, which will serve a large part of the nuclear physics community (and beyond): • Nuclear structure  Radioactive beams • Dense Matter  Relativistic ion beams • Hadronic Matter  Antiprotons, (polarized) • Atomic physics • Plasma physics • FAIR will need a significant fraction of the available man-power and money in the years to come: • 1 G€  10 000 man-years = 100 “man” for 100 years • or (1000 x 10) • FAIR will have a long lead-time (construction, no physics) •  staging (3 phases)

  41. Facilty for Antiproton and Ion Research (GSI, Darmstadt, Germany) • Proton linac (injector) • 2 synchrotons (30 GeV p) • A number of storage rings •  Parallel beams operation

  42. The FAIR project at GSI SIS100/300 50 MeV Proton Linac HESR: High Energy Storage Ring: PANDA (and PAX) CR-Complex FLAIR: (Facility for very Low energy Anti-protons and fully stripped Ions) NESR

  43. 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 ~ 10-4 (stochastic-cooling) High resolution mode • Δp/p ~ 10-5 (8 MV HE e-cooling) • Luminosity = 1031 cm-2s-1 SIS100/300 HESR Super FRS CR Gas Target and Pellet Target: cooling power determines thickness NESR Antiproton Production Target Beam Cooling: e- and/or stochastic 2MV prototype e-cooling at COSY • Antiproton production similar to CERN • Production rate107/sec at 30 GeV • T = 1.5 - 15 GeV/c(22 GeV)

  44. LoI‘s for Spin Physics at FAIR SIS100/300 External:ASSIA Extracted beam on PET (Compass-like) Internal:PAX in HESR Polarized antiprotons + PIT

  45. The New Polarization Facility HESR AP+COSY • Conceptual Design Report for FAIR did not include Spin Physics: • Jan. ’04: 2 Letters of Intent for Spin Physics • ASSIA (R. Bertini) • PAX (P. Lenisa, FR)

  46. Outline WHY? Physics Case HOW? Polarized Antiprotons WHERE? FAIR Project at Darmstadt WHAT? Transversity Measurement at PAX WHEN? Time Schedule Conclusion

  47. M invariant Mass of lepton pair Transversity in Drell-Yan processes at PAX Polarized Antiproton Beam → Polarized Proton Target (both transversely polarized) l+ Q2=M2 l- Q QT p p QL

  48. dt = areal density frev = revolution frequency Npbar = number of pbar stored in HESR L= dtxfrevxNpbar Estimated Luminosity for Double Polarization Polarized Internal Target in HESR In equilibrium: Qtarget = 0.85 Pbeam = 0.3 σtot(15 GeV) = 50 mb (factor >70 in measuring time for ATT with respect to beam extracted on solid target)

  49. l+ Q2=M2 l- Q QT p p QL 1) Count rate estimate. Signal Estimate Polarized Antiproton Beam → Polarized Proton Target (both transversely polarized) 2) Angular distribution of the asymmetry.

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