Antiproton-Proton Scattering Experiments with Polarization. PAX Collaboration

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1 Antiproton-Proton Scattering Experiments with Polarization PAX Collaboration Spokespersons: Paolo Lenisa Frank Rathmann

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 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 CR-Complex NESR FLAIR: (Facility for very Low energy Anti-protons and fully stripped Ions)

6 The Antiproton Facility HESR (High Energy Storage Ring) Length 442 m Bρ = 50 Tm N = 5 x antiprotons HESR High luminosity mode Luminosity = 2 x cm -2 s -1 p/p ~ 10-4 (stochastic-cooling) Antiproton Production Target CR Super FRS NESR High resolution mode p/p ~ 10-5 (8 MV HE e-cooling) Luminosity = cm -2 s -1 Gas Target and Pellet Target: cooling power determines target thickness Antiproton production similar to CERN Production rate 10 7 /sec at 30 GeV Anti-Proton Beam = GeV/c Cooling - electron and/or stochastic 2MV prototype 2 MV e-cooling at COSY

7 The 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 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 antiproton spin-filtering rate and luminosity of HESR at PAX

8 Transversity in Drell-Yan processes PAX: Polarized antiproton beam polarized proton target (both transverse) l + l - q 2 =M 2 q q T p q L p e h (x,m )h (x,m 2 q 2 q 2 q A dσ dσ q TT = â TT 2 2 dσ + dσ e q(x,m )q(x,m 2 q 1 2 ) q ) q = u, u,d, d,... M invariant Mass of lepton pair Elementary QED process qq l + l 2 sin θ = cos 2φ 1+ cos θ â TT 2 θ: polar angle of lepton in l + l - rest frame ϕ: azimuthal angle w.r.t. proton polarization

9 A TT in the Drell-Yan production at PAX Measurement of A TT also planned at RHIC, but τ=x 1 x 2 =M 2 /s~10-3 Exploration of the sea quark content (polarizations small!) at RHIC A TT very small (a percent or less) For PAX, typical kinematics M 2 ~10 GeV 2, s~30-50 GeV 2 τ=x 1 x 2 =M 2 /s~ , only quarks with large x contribute! Valence quarks for which h 1q (x,q 2 ) large! A TT /a TT > 0.3 Models predict h 1u >> h 1d u 2 u 2 A = h1 (x1,m )h1 (x1,m ) TT â TT 2 u(x,m )u(x, M 2 ) (where q p 1 = q p = q) Main contribution to Drell-Yan events at PAX from x 1 ~x 2 ~ τ deduction of x-dependence of h 1u (x,m 2 )! A â TT TT T=15 GeV T=22 GeV Anselmino, Drago, Nikolaev x F =x 1 -x 2

10 Extension of the safe region The determination of h 1q (x,q 2 ) is not confined to the safe region M > 4 GeV! qq qq qq J / Ψ γ * e + e unknown vector coupling, but same Lorentz and spinor structure as other two processes Unknown quantities cancel in the ratios for A TT, 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 A TT

11 Single Spin Asymmetries Several experiments have observed unexpectedly large single spin asymmetries in pbar-p at large values of x F 0.4 and moderate values of p T (0.7 < p T < 2.0 GeV/c) E704 Tevatron FNAL 200GeV/c π + A N = 1 P beam N N + N N π - Large asymmetries originate from valence quarks: sign of A N related to u and d-quark polarizations x F

12 SSA in Drell-Yan Processes PAX will allow studies of new non-perturbative spin properties of the proton: non-vanishing T-odd correlation functions, like the Sivers Function Theoretical Prediction: Collins, PLB 536 (2002) 43 T f = f 1 DY 1T DIS

13 Proton Electromagnetic Formfactors Measurement of the relative phase of magnetic and electric FF in the time-like region This phase can only be measured via SSA in the annihilation pp e + e - double-spin asymmetry independent G E -G m separation test of the Rosenbluth separation in the time-like region

14 Principle of a polarized internal target Target Source Detector Beam Storage Cell Polarimeter point-like 5-10 mm Interaction Region free jet low density cm -2 extended mm storage cell high density cm -2

15 Principle of Spin Filter Method σ tot = σ 0 + σ 1 P Q For initially equally populated spin states: (m=½) (m=-½) + σ I 2 M MK ( M ) ML = 0, if P k = 0 ( P k ) ( Q k ) σ tot ± = σ 0 P beampol. Q targetpol. k beam ± σ 1 Q For low energy pp scattering: σ 1 <0 σ tot+ <σ tot- Expectation Target Beam

16 Filter Test at TSR (1992)

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

18 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/τ 1 ), 1/τ 1 =σ 1 Qd t f= =2.4x10-2 h -1 about factor 2 larger! σ 1 = 122 mb (pp phase shifts) Q = 0.83 ± 0.03 d t = (5.6 ± 0.3) x cm -2 f = MHz Meyer and Horowitz identified three distinct effects to explain exactly the observed build-up! 1. Selective removal through scattering beyond θ acc =4.4 mrad σ R =83 mb 2. Small angle scattering of target protons into ring acceptance σ S =52 mb 3. Spin transfer from polarized electrons of the target atoms to the stored protons =-70 mb σ E Horowitz & Meyer, PRL 72, 3981 (1994) H.O. Meyer, PRE 50, 1485 (1994)

19 Polarization Build-up up Exploit spin transfer process σ E works also if hadronic polarizing cross sections σ and σ R S turn out to be small N(t)=N 0 exp(-t/τ b ) τ b =(f d t σ L ) -1 I(t)=N(t) f P(t)=1-exp(-t/τ 1 )~ σ E d t f Q t Optimum filtering time t=2 τ b (from d(p 2 I)/dt=0) P(2τ b )=2 Q (σ E /σ L ) Estimate for σ L from Indiana Cooler σ L = T -2 mb, (Note: σ E ~T -1 ) R.E. Pollock et al., NIM A 330, 380 (1993)

20 Spin transfer from electrons to protons p + e p + e ( 1+ λ ) p me ν 2α ln( 2pa ) 2 1 4πα 2 0 σe = C0 sin 2 2 p mp 2α ν Horowitz & Meyer, PRL 72, 3981 (1994) H.O. Meyer, PRE 50, 1485 (1994) α λ p =(g-2)/2=1.793 m e, m p p a 0 C 2 0 =2πη/[exp(2πη)-1] η=-zα/ν v z fine structure constant anomalous magnetic moment rest masses cm momentum Bohr radius Coulomb wave function Coulomb parameter (neg. for anti-protons) relative lab. velocity between p and e beam charge number

21 Antiproton Polarizer Expected Buildup spin-transfer cross section (electrons to antiprotons) d t = atoms/cm 2 P electron =0.9 σ e (mbarn) σ etr ( T) antiproton Polarization (%) Polarization P2( t, 800) P2( t, 500) 6 4 I( t, ) T=500 MeV Goal T=800 MeV T T (MeV) t 3600 beam lifetime [h] t (h) 30

22 Beam lifetimes in HESR The lifetime of a stored beam is given by σ C = θ max dσ dω 4 e dω = 2πε m 1 2ψ v 2 θ Ruth. 0 p acc min τ b = ( σ C 1 + σ 0 ) d t f σ0 = σ tot (pp) Calculation assumes a target thickness of d t = atoms/cm 2 In order to achieve highest polarization in the antiproton beam, acceptance angles around Ψ acc = 10 mrad are needed. beam lifetime [h] beam lilfetime τ b (h) τ T, τ T, τ T, τ T, mrad 20 mrad T (MeV) 1 T kinetic energy [MeV] 5 mrad Ψ acc = 1 mrad

23 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!

24 Spin Manipulation in a Storage Ring SPIN@COSY (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)=P i (η) n η=(99.3±0.1)% Ferrite Rf-dipole higher Bdl=0.58 T mm stored deuterons flipped also efficiency η>0.9

25 Polarimetry PAX will employ different schemes to determine beam and target polarization 1. A suitable target polarimeter (Breit-Rabi or Lamb- Shift) allows one to determine the target polarization 2. 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

26 Detector Concept Two complementary parts: 1. Forward detector (±8 0 acceptance) a la HERMES a) Identify unambiguously leading particles b) measure precisely their momenta 2. Central Large Acceptance Detector a) measure angles and energies of medium-energy electromagnetic particles (Drell-Yan)

27 Forward Detector

28 Large Acceptance Detector

29 Luminosity Physics Performance Spin-filtering for two beam lifetimes: P > 5% N(pbar) = at f r ~ s -1 d t = cm -2 L(t = 0) = 1 10 N p f r d t = cm 2 s 1 Time-averaged Luminosity is about factor 3 lower beam loss and duty cycle For experiments with unpolarized beam L is factor 10 larger

30 Count rate estimate Uncertainty of Double-spin asymmetry A TT depends on polarization of beam and target ( P >0.05, Q ~0.9) δ A TT = 1 P Q N 22 N Note: Conservative estimate since hadronic buildup effect might be large as well 240 days T = 15 GeV T = 22 GeV only nonresonant J/Ψ contribution included

31 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: h 1q (x,q 2 ) 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

32 PAX: The next steps 2004 LOI on its way! Formation of an advisory committee at GSI in progress: Evaluation of LOI s available within a couple of weeks If approved, Technical Report (with Milesones) by ! followed by Evaluations & Green Light for Construction Technical Design Reports (for Milestones) 2012 Commissioning of HESR

PAX Polarized. Antiproton. EXperiment. PAX Collaboration. Paolo Lenisa. Universita and INFN - Sezione di Ferrara.

PAX Polarized. Antiproton. EXperiment. PAX Collaboration. Paolo Lenisa. Universita and INFN - Sezione di Ferrara. dr. Paolo Lenisa Universita and INFN - Sezione di Ferrara PAX Polarized Antiproton EXperiment PAX Collaboration www.fz-juelich.de/ikp/pax Frank Rathmann Paolo Lenisa Spokespersons: f.rathmann@fz-juelich.de