Spin Physics with Polarized Antiprotons at HESR (FAIR GSI) E. Steffens 1, P. Lenisa 2 *, Frank Rathmann 3 *, P. Ferretti-Dalpiaz 2, M. Contalbrigo 2, A. Kacharava 1,3, D. Reggiani 1, S. Yashchenko 1,3 for the PAX Collaboration 1 Physik. Inst., Univ. of Erlangen-Nürnberg, 2 Univ. of Ferrara and INFN, 3 Inst. für Kernphysik, FZ Jülich * Spokespersons PAX Collaboration Introduction Spin filtering in the APR PAX experiment FILTEX test experiment at the TSR Heidelberg (1992) Conclusions E. Steffens DPG Berlin 2005 1
Introduction New opportunities at FAIR for the study of antiprotonproton interactions High-energy storage ring HESR: LEAR data can be extended to high energies The Study of spin dependence of pp requires polarized antiprotons Proposal by PAX collaboration to add a dedicated Antiproton Polarizer Ring (APR) to FAIR Design of a low-energy APR in progress: P>30% possible! Note: in PAX-LoI (Jan.04) without APR we assumed P=5-10% E. Steffens DPG Berlin 2005 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 in a unique way via the double transverse spin asymmetry A TT in the Drell-Yan production of lepton pairs theoretical expectations for A TT in DY, 30-40% transversely polarized antiprotons transversely polarized proton target definitive observation of h 1q (x,q 2 ) of the proton for the valence quarks E. Steffens DPG Berlin 2005 3
Other Physics Topics Single-Spin Asymmetries Electromagnetic Form Factors Hard Scattering Effects Soft Scattering Low-t Physics Total Cross Section p-p interaction E. Steffens DPG Berlin 2005 4
Polarized Antiprotons Proposal to polarize p s stored in LEAR, with Ecool and storage cell target: E. St., et al, LEAR-WS Tignes 1985 Experimental test in the Heidelberg TSR by the FILTEX Collaboration in 1992: build-up of proton pol. measured! 01/04: PAX LoI on spin physics at HESR submitted to FAIR 07/04: QCD-PAC requested the design of a world class facility for polarized antiprotons Techn. Proposal (TP) submitted by PAX in Jan.05, plus recent addendum: see at www.fz-juelich.de/ikp/pax E. Steffens DPG Berlin 2005 5
Spin Filter Method E. Steffens, B. Povh, Th. Walcher et al, 3rd LEAR Workshop, Tignes (1985) σ tot = σ 0 + σ P Q + σ (P k)(q k) P beam polarization Q target polarization k beam direction τ I I beam τ + pol (t) (t) For initially equally populated spin states: (m=+½) and (m=-½) = = = = ( σ σ I0 2 I0 2 σ 0 pol e e transverse case: tot ± τ τ c 1 Q d t t beam t beam = σ 1 + σ ) d f t rev e e 0 f τ + τ rev t pol t pol ± σ Q P(t) I(t) longitudinal case: ( σ + σ ) Q E. Steffens DPG Berlin 2005 6 = = σ tot ± + + + + + = σ = 0 ± Time dependence of P and I I I I I I I t = tanh τ I 0 e τ t beam pol t cosh τ pol
Polarization Buildup: Optimum Interaction Time Measuring time t to achieve a certain error is inversely prop. to Figure of Merit FOM = P2 IP Optimimum time for Polarization Buildup given by maximum of FOM(t) t filter = 2 τ beam I/I 0 0.8 0.6 0.4 FOM =P 2 I Beam Polarization P 0.2 0 2 4 6 t/τ beam E. Steffens DPG Berlin 2005 7
Experimental Results from Filter Test Protons, T=23 MeV F. Rathmann. et al., PRL 71, 1379 (1993) Observed build-up: dp/dt = ± (1.24 ± 0.06) % h -1 Expected build-up: P(t) (t/tpol) pp phase shifts: σ 1 = 122mb 1/τ pol = σ 1 Qd t f = 2.4 % h -1 about factor 2 larger! Low energy pp scattering σ 1 <0 σ tot+ <σ tot- Expectation Target Beam E. Steffens DPG Berlin 2005 8
Experimental Results from Filter Test Protons, T=23 MeV F. Rathmann. et al., PRL 71, 1379 (1993) Horowitz & Meyer, PRL 72, 3981 (1994) H.O. Meyer, PRE 50, 1485 (1994) Refined analysis: Three effects! *Selective removal through scattering beyond Ψacc=4.4 mrad: σ R =83 mb *Small angle scatt. of target protons into ring acceptance: σ S =52 mb *Spin Spin transfer from polarized electrons of the target atoms to the stored protons: σ EM =70 mb (-) Low energy pp scattering σ 1 <0 σ tot+ <σ tot- Correction: σ eff = (83+52-70)mb = 65mb Theory: 1/τ pol = 1.28%/h Experiment: (1.24±0.06)%/h EM spin transfer confirmed! E. Steffens DPG Berlin 2005 9
Exploitation of Spin Transfer PAX will employ spin-transfer from polarized electrons of the target to antiprotons r r p + e p + QED Process: calculable! e Hydrogen gas target: 1+2 in strong field (300 mt) P e =0.993 P p =0.007 σ EM (mb) 600 500 400 300 200 100 Atomic Electrons σ EM = 2 σ EM Free Electrons 1 10 100 T (MeV) E. Steffens DPG Berlin 2005 10
Dedicated Antiproton Polarizer (APR) σ EM = 2 σ EM r Q Injection p Injection B B Siberian Snake Siberian Snake CSR ESR e-cooler Electron Cooler ABS ABS AP APR 100 m Polarizer Target Polarizer Target β=0.2 m d b =ψ acc β 2 d t =d t (ψ acc ) q=1.5 10 17 s -1 l b =40 cm (=2 β) T=100 K d f =1 cm, l f =15 cm Longitudinal pol. (B guide = 300 mt) Extraction Extraction e-cooler Electron Cooler Internal Experiment Experiment PAX Polarization Buildup in AP parallel to measurement in CSR and/or HESR F. Rathmann et al., PRL 94, 014801 (2005) E. Steffens DPG Berlin 2005 11
FOM after t=2τ beam 15 Optimum Beam Energies for Buildup in APR APR Space charge limit ψ acc = 50 mrad Ψ acc (mrad) Maximum FOM at T opt τ beam (h) 10 1.2 20 30 40 2.2 4.6 9.2 P(2τ beam ) T opt (MeV) 0.19 163 0.29 88 0.35 61 0.39 47 10 40 mrad 50 16.7 0.42 38 5 30 mrad 20 mrad 10 mrad 1 10 100 T (MeV) E. Steffens DPG Berlin 2005 12
Performance of Polarized Internal Targets Example: HERMES (Stored Positrons) Hydrogen P T = 0.795 ± 0.033 HERMES Transverse Field (B = 297mT) Similar performance for IUCF and COSY targets Targets work very reliably (many months of stable operation) E. Steffens DPG Berlin 2005 13
Transversity in Drell-Yan processes at PAX Polarized Antiproton Beam Polarized Proton Target (both transversely polarized) Q l + Q T l - Q 2 =M 2 p Q L p 2 q 2 q 2 e h (x, M )h (x, M ) q 1 1 1 2 A dσ dσ q TT = â TT 2 2 dσ + dσ e q(x, M )q(x, M 2 ) q q 1 2 q = u, u,d, d,... M invariant Mass of lepton pair E. Steffens DPG Berlin 2005 14
A TT for PAX kinematic conditions PAX: M 2 ~10 GeV 2, s~30-50 GeV 2, x 1 x 2 =M 2 /s ~ 0.2-0.3 Exploration 22 GeV/c of fixed valence target quarks 15 GeV/c fixed [h 1q (x,q 2 ) large] A TT /a TT up to 0.3 Models predict h 1u >> h 1d u 2 u 2 h (x,m )h (x,m ) A = 1 1 1 1 TT â TT 2 2 u(x,m )u(x, M ) (where q 1 p = q p 1 = q) Fixed Target vs Asymmetric Collider A TT /â TT 0.3 0.2 0.1 15 fixed 15+3.5 collider 15 + 15 collider 30 1000 22 fixed 45 80 200 400 Main contribution to Drell-Yan events at PAX from x 1 ~x 2 : deduction of x-dependence of h 1u (x,m 2 ) s = 10000 0 0 0.2 0.4 0.6 0.8 1 x F Anselmino et al. PLB 594,97 (2004) E. Steffens DPG Berlin 2005 15
A TT for PAX kinematic conditions PAX: M 2 ~10 GeV 2, s~30-50 GeV 2, x 1 x 2 =M 2 /s ~ 0.2-0.3 Exploration 22 GeV/c of fixed valence target quarks 15 GeV/c fixed [h 1q (x,q 2 ) large] Fixed Target vs Asymmetric Collider A TT /â TT 0.3 0.2 15 fixed 15+3.5 collider 30 22 fixed 45 80 Collider Options for Transversity measurement: 15 GeV/c + 15 GeV/c s = 1000 GeV 2, too high 15 GeV/c + 3.5 GeV/c s = 220 GeV 2, ideal 0.1 15 + 15 collider 1000 s = 10000 200 400 0 0 0.2 0.4 0.6 0.8 1 x F Anselmino et al. PLB 594,97 (2004) E. Steffens DPG Berlin 2005 16
Towards an Asymmetric Polarized pp Collider I. CSR at FAIR (3.5 GeV/c) a. Formfactor measurement pp e + e - - unpolarized antiproton beam on polarized internal proton target HESR p p injection p CSR PAX PANDA E. Steffens DPG Berlin 2005 17
Towards an Asymmetric Polarized pp Collider I. CSR at FAIR (3.5 GeV/c) a. Formfactor measurement pp e + e - - unpolarized antiproton beam on polarized internal proton target b. CSR + AP: p p elastic HESR p p injection p Injector p CSR AP PAX PANDA E. Steffens DPG Berlin 2005 18
Towards an Asymmetric Polarized pp Collider I. CSR at FAIR (3.5 GeV/c) a. Formfactor measurement pp e+e- - unpolarized antiproton beam on polarized internal proton target b. CSR + AP: p p elastic II. Asymmetric Collider p p : 3.5 GeV/c protons + 15 GeV/c antiprotons (also fixed target experiment possible) HESR p p injection p Injector p CSR AP PAX PANDA E. Steffens DPG Berlin 2005 19
Conceptual Detector Design ~3 m E. Steffens DPG Berlin 2005 20
Expected precision of the h 1 measurement One year of data taking at 50 % eff. (180 d), A TT /a TT =0.3 Safe region (M > 4 GeV)! Collider mode: 5 10 30 cm -2 s -1 Fixed Target: 2.7 10 31 cm -2 s -1 Anselmino et al. PLB 594,97 (2004); Efremov et al., Eur.Phys.J. C35,207 (2004) J/Ψ region can be included! Cross section increases by two orders from M=4 to M=3 GeV E. Steffens DPG Berlin 2005 21
Conclusions Polarized Antiprotons lead to new physics at HESR Unique access to a wealth of new observables Central physics issue: h q 1 (x,q 2 ) of the proton measured in DY Note: High statistics by inclusion of J/Ψ region! 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 Projections for HESR fed by a dedicated APR: P beam > 0.30 5.6 10 10 polarized antiprotons Luminosity: - Fixed target: L 2.7 10 31 cm -2 s -1 - Collider: L 2 10 30 cm -2 s -1 (first estimate ) E. Steffens DPG Berlin 2005 22
170 PAX Collaborators, 27 Institutions (17 EU, 17 non-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 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 Unternehmensberatung und Service Büro (USB), Gerlinde Schulteis & Partner GbR, Langenbernsdorf, Germany 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 E. Steffens University DPG of Wisconsin, Berlin 2005 Madison, USA 23 Department of Physics, University of Virginia, Virginia, USA