Paolo Lenisa, Kolya Nikolaev, Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich L.D.Landau Institute, Chernogolovka Future QCD Spin-physics with Polarized Antiprotons at FAIR

2 Facilty for Antiproton and Ion Research (GSI, Darmstadt, Germany)

3 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  (polarized) Antiprotons -Atomic physics -Plasma physics FAIR will need a significant fraction of the available man-power and money in the years to come: 1 G€  man-years = 100 “man” for 100 years or (1000 x 10) FAIR will have a long lead-time (construction, no physics)  staging (3 phases)

4 HESR Antiproton Production Target HESR (High Energy Storage Ring) Length 442 m Bρ = 50 Tm N = 5 x antiprotons High luminosity mode Luminosity = 2 x cm -2 s -1 Δp/p ~ (stochastic-cooling) High resolution mode Δp/p ~ (8 MV HE e-cooling) Luminosity = cm -2 s -1 The Antiproton Facility Antiproton production similar to CERN Production rate 10 7 /sec at ~30 GeV/c T = GeV/c (22 GeV) Gas Target and Pellet Target: cooling power determines thickness Super FRS NESR CR Beam Cooling: e - and/or stochastic 2MV prototype e-cooling at COSY SIS100/300

5 High-Energy Storage & Cooler Ring (HESR) und Detector electron cooler universal detector PANDA p-injection circumference 442 m max. bending power 50 Tm HESR p detector features: measurement and identification of , e ,  ,  , K , p, p high rate capability fast trigger scheme

6 Central PAX Physics Case: Transversity distribution of the nucleon in Drell-Yan:  FAIR as successor of DIS physics –last leading-twist missing piece of the QCD description of the partonic structure of the nucleon –observation of h 1 q (x,Q 2 ) of the proton for valence quarks (A TT in Drell-Yan >0.2) –transversely polarized proton beam or target ( ) –transversely polarized antiproton beam (  ) HESR QCD Physics at FAIR (CDR): unpolarized Antiprotons in HESR PAX  Polarized Antiprotons

7 W. Pauli N. Bohr  Even they were puzzled by spin…

8 Where do we stand? the (spin) structure of the nucleon … H1, ZEUS,++ HERMES, ++ HERMES: first glimpse HERMES COMPASS CERN RHIC SLAC

9 Where do we stand? the (spin) structure of the nucleon … H1, ZEUS,++ HERMES, ++ HERMES: first glimpse HERMES COMPASS CERN RHIC SLAC ? UPCOMING: HERMES JLab ? Transversity h 1, d q

10 Leading Twist Distribution Functions 1/2 L L + f 1 (x) h 1 (x) proton proton’ quarkquark’ u  = 1/  2(u R + u L ) u  = 1/  2(u R - u L ) No probabilistic interpretation in the helicity base (off diagonal) Probabilistic interpretation in helicity base: q(x) spin averaged (well known)  q(x) helicity diff. (known)  q(x) helicity flip (unknown) 1/2 R R L L - R R g 1 (x) Transversity base 1/2 -1/2 R L -        

11 Georg Christoph Lichtenberg ( ) “Man muß etwas Neues machen, um etwas Neues zu sehen.” “You have to make something new, if you want to see something new”

12 PAX Physics Transversity Electromagnetic Form Factors Hard Scattering Effects SSA in DY, origin of Sivers function Soft Scattering –Low-t Physics –Total Cross Section – pp interaction

13Transversity -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 Impossible in DIS Direct Measurement ppl+l-Xppl+l-X ep   e’h  X Indirect Measurement: Convolution of with unknown fragment. fct.

14 PAX: s~ GeV 2, M 2 ~ GeV 2,  =x 1 x 2 =M 2 /s~ → Exploration of valence quarks (h 1 q (x,Q 2 ) large) A TT for PAX kinematic conditions A TT /a TT > 0.2 Models predict |h 1 u |>>|h 1 d | RHIC: √s = 200 GeV, M 2 ≤100 GeV2 τ=x 1 x 2 =M 2 /s ≤2x10 -3 → Exploration of the sea quark content (polarizations small!) A TT very small (~ 1 %), luminosity problems ? A. Efremov et al. Eur. Phys. J. C 35 (2004) 207

15 Proton Electromagnetic Formfactors JLAB E835 Similar new data from ISR events at BABAR

16 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 G E -G m separation –test of Rosenbluth separation in the time-like region S. Brodsky et al., Phys. Rev. D69 (2004)

17 pp Elastic Scattering from ZGS/AGS Spin-dependence at large-P  90° cm ): Spin-dependence at large-P  (90° cm ): Hard scattering takes place only with spins  Similar studies in pp elastic scattering, 90°cm including angles > 90°cm A. Krisch, Sci. Am. 257 (1987) “The results challenge the prevailing theory that describes the proton’s structure and forces” D.G. Crabb et al., PRL 41, 1257 (1978) T=10.85 GeV

physicists 35 institutions (15 EU, 20 Non-EU) PAX Collaboration Spokespersons: Paolo Lenisa Paolo Frank Rathmann Frank Rathmann

19 The PAX proposal: Jan.04 LOI submitted 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.

20 The STI requests R&D work to be continued on the proposed asymmetric collider experiment with both polarized anti-protons and protons,  to demonstrate that the required luminosity for decisive measurements can be reached.  to demonstrate that a high degree of anti-proton polarisation can be reached. Recommendations of the STI WG on FAIR (August 2005) The PAX proposal: Jan.04 LOI submitted 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.

21 Principle of Spin Filter Method P beam polarization Q target polarization k || beam direction σ tot = σ 0 + σ  ·P·Q + σ || ·(P·k)(Q·k) transverse case:longitudinal case: For initially equally populated spin states:  (m=+½) and  (m=-½) Unpolarized p beam Polarized H target

Filter Test at TSR with protons Experimental Setup Results F. Rathmann. et al., PRL 71, 1379 (1993) T=23 MeV Expectation TargetBeam   For low energy pp scattering:  1 <0   tot+ <  tot-

PAX Accelerator Setup Antiproton Polarizer Ring (APR) + Cooler Storage Ring (CSR, COSY-like): 3.5 GeV/c + HESR: 15 GeV/c  Asymmetric Double-Polarized Antiproton-Proton Collider HESR

Phase I: PAX at CSR Physics:Electromagnetic Form Factors pp elastic scattering Experiment: polarized/unpolarized p on polarized target Independent of HESR experiments HESR

EXPERIMENT: Asymmetric Collider: Polarized Antiprotons in HESR (15 GeV/c) Polarized Protons in CSR (3.5 GeV/c) Physics: Transversity Second IP with minor interference with PANDA Phase II: PAX at CSR HESR

26 Spin transfer from electrons to protons Horowitz & Meyer, PRL 72, 3981 (1994) H.O. Meyer, PRE 50, 1485 (1994) α fine structure constant λ p =(g-2)/2=1.793anomalous magnetic moment m e, m p rest masses Can one exploit spin-transfer from polarized electrons of the target to antiprotons ? Physics Polarization Staging Signals Timeline Principal technique for precision Ge/Gm separation at JLAB by measuring the recoil proton polararization

27 Spin Transfer Cross Section T (MeV)  EM  (mbarn) Physics Polarization Staging Signals Timeline

28 Puzzle from FILTEX Test Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x h -1 Expected build-up: P(t)=tanh(t/τ pol ), 1/τ pol =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 Three distinct effects: 1.Selective removal through scattering beyond Ψ 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 σ EM  =70 mb (-) Horowitz & Meyer, PRL 72, 3981 (1994) H.O. Meyer, PRE 50, 1485 (1994)

29 Milstein & Strakhovenko & Nikolaev & Pavlov  FILTEX result can be almost explained without EM spin transfer More precisely: elastic pe scattering is entirely within the ring acceptance angle -----> nearly exact cancellation of filtering by transmission and EM spin transfer  still ~2σ deviation Recent Development σ 1 Theory [mb]StrakhovenkoNikolaev/Pavlov SAID FILTEX reanalyzed:

30

31 Beam Polarization (Hadronic Interaction: Longitudinal Case) Experimental Tests required: Repetition of Filtex with protons at COSY Final Design of APR: Filter test with p at AD of CERN Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) T (MeV) T (MeV) P P 2 beam lifetimes Ψ acc =10-50 mrad 3 beam lifetimes Ψ acc =20 mrad

32 PAX: M 2 ~ GeV 2, s~ GeV 2,  =x 1 x 2 =M 2 /s~ → Exploration of valence quarks (h 1 q (x,Q 2 ) large) A TT for PAX kinematic conditions RHIC: τ=x 1 x 2 =M 2 /s~10 -3 → Exploration of the sea quark content (polarizations small!) A TT very small (~ 1 %)

33 Cerenkov PAX detector and signal Large angular acceptance Sensibility to electron pairs Toroid magnet

34 Cerenkov PAX detector and signal 1 year of data taking L=2x10 30 cm -2 s -1, P=0.3, Q=0.8

35 Beam (MeV/c) (GeV 2 )  e+e- (nbarn)* L (cm -2 s -1 ) Days DS Days SS x x x N pbar = 1x10 11 f=L CSR /  c d t =1x10 14 cm -2 Q=0.8 (p pol) P=0.3 (pbar pol)  =0.5 Estimated signal for EMFF (Phase I) PS170 and E835 PAX could run down to 200 MeV/c with double polarization Running days to get  O = 0.05

36 BNL E838 Estimated Signal for pp elastic (Phase I) Cross section estimation for p=3.6 GeV/c,  =120° Event rate (  t=0.1 GeV 2 ): 2 hours to get N  10

37 Dream Option: Collider (15 GeV) L > cm -2 s -1 to get comparable rates M>4 GeV M>2 GeV ___ 22 GeV ___ Collider (15 GeV+15GeV) 22 GeV 15 GeV Collider 15 GeV+15 GeV

38 Phase 0: APR design and construction. Physics: buildup COSY and CERN Phase I: GSI Physics: EMFF, p-pbar elastic with fixed target. Phase II: … HESR+CSR asymmetric collider Physics: h 1 Timeline Timeline

39 Facility Layout (September 2005)

40 Conclusions Challenging opportunities accessible with polarized p’s Unique access to a wealth of new fundamental physics observables Central physics issue: h 1 q (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 param. Staged approach Filter Tests Experiments with protons (COSY) and antiprotons (CERN) Projections for double polarization experiments: P beam > 0.20 Collider: L> 1.6 ·10 30 cm -2 s -1 Fixed Target: L  2.7 ·10 31 cm -2 s -1 Detector concept: Large acceptance detector with a toroidal magnet  unbunched beams 2 ·10 31 cm -2 s -1 possible

41

42 Estimated signal for h 1 (Phase II) 1 year of data taking Collider: L=2x10 30 cm -2 s -1 Fixed target: L=2.7x10 31 cm -2 s -1

43 PAX Integrated Luminosities for Physics Cases pb -1 fb -1 Integrated Luminosity EMFF, DSA, s=3.76 GeV 2 ppbar elastic, DSA, t=4 GeV 2 Phase-I: L=1.5·10 31 cm -2 s -1 Antiproton Beam Polarization P pbar =0.3, Proton Polarization P p =0.8 Phase-II: L=2·10 30 cm -2 s -1 EMFF, DSA, s=9 GeV 2 Absolute Error Δ DSA =0.05 h 1, DSA, M>2 GeV, Δ=10% h 1, DSA, M>4 GeV, Δ=20% (1 y) (4 y) (1 y)

44 0% 50% 100% Radioactive Beams Nucleus-Nucleus Collisions Antiprotons Plasma-Physics 100 Tm Ring 300 Tm Ring Collector & Storage Ring High-Energy Storage Ring Nucleus-Nucleus 100 sec Radioactive Beams Plasma Physics Antiprotons Duty-Cycles of the Accelerator Rings Duty-Cycles of the Physics Programs Parallel Operation SIS300

Beam Polarization P(2·τ beam ) 10 T (MeV)100 EM only Ψ acc =50 mrad 0 1 Filter Test: T = 23 MeV Ψ acc = 4.4 mrad Buildup in HESR (800 MeV) Beam Polarization (Electromagnetic Interaction)

46 Precision of h 1 measurement 1 year of data taking GeV/c Collider L = 2∙10 30 cm -2 s -1 hundreds of events/day 10 % precision on the h 1 u (x) in the valence region

47 A TT asymmetry: angular distribution Needs a large acceptance detector (LAD) Asymmetry is largest for angles =90 ° Asymmetry varies like cos(2 f ). Physics Polarization Staging Signals Timeline

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49 Background to Drell-Yan e + e - Background to Drell-Yan e + e - ½ hour experiment: 2∙10 8 p-pbar interactions several DY events combinatorial +charm bckg Background 1:1 to signal after PID, E>300 MeV, conversion veto, mass cut * the combinatorial component can be subtracted (wrong-sign control sample) * the charm can be reduced (vertex decay) & --

50 Precision of h 1 measurement 1 year of data taking GeV/c Collider L = 2∙10 30 cm -2 s -1 hundreds of events/day 10 % precision on the h 1 u (x) in the valence region

51 A TT asymmetry: angular distribution Needs a large acceptance detector (LAD) Asymmetry is largest for angles =90 ° Asymmetry varies like cos(2 f ).

52 Theoretical prediction T=22 GeV T=15 GeV x F =x 1 -x Magnitude of Asymmetry Angular modulation Forward Part (FWD): q lab < 8° Large Acceptance Part (LAD): 8° < q lab < 50° Beam and Target Polarization:P=Q=1 LAD

53 Estimated signal 120k event sample 60 days at L=2.1 × cm 2 s -2, P = 0.3, Q = 0.85 Events under J/y can double the statistics.  Good momentum resolution required LAD A TT =(4.3  0.4)·10 -2

54 Is PANDA suitable for Drell-Yan? Is PANDA suitable for Drell-Yan? Muons: * classical approach but with absorbers * p contamination in PANDA like set-up (TOPAZ) * punch-through at 1 and 2 GeV/c (CLEO studies) * M ll >4 GeV/c 2 due to poor resolution Detector: not compatible with polarized target compatible with TRD plus excellent Calo PID * challenging PID * more material * complicate trigger Program : fixed target experiment with low s (p‹15 GeV/c) unpolarized target lower energy and resonance studies high luminosity beam

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

A TT for PAX Kinematic Conditions s~200 GeV 2 ideal: Large range in x F Large asymmetry, (h 1 u /u) 2 ~ A TT RHIC RHIC: τ=x 1 x 2 =M 2 /s~10 -3 → → Exploration of sea quark content: A TT small (~ 1 %) PAX PAX: M 2 ~10 GeV 2, s~200 GeV 2  =x 1 x 2 =M 2 /s~0.05 → → Exploration of valence quarks h 1 q (x,Q 2 ) large A TT /a TT > 0.2 Models predict |h 1 u |>>|h 1 d | x F =x 1 -x 2 Anselmino et al., PLB 594,97 (2004) Efremov et al., EPJ C35, 207 (2004)

57 PAX Detector Concept PAX Detector Concept Physics:h 1 distribution sin 2  EMFF sin2  pp-p elastic high |t| Magnet: no precession of beam polarization Compatible with Cerenkov Compatible with polarized target Detector: Extremely rare DY signal (10 -7 p-pbar) Maximum Bjorken-x coverage (M interval) Excellent PID (hadron/e rejection ~ 10 4 ) High mass resolution (≤2 %) Moderate lepton energies (0.5-5 GeV) Azimuthal Symmetry: BARREL GEOMETRY LARGE ANGLES Experiment: Flexible Facility TOROID NO FRINGE FIELD e+e-e+e-

58 Designed for Collider but compatible with fixed target Cerenkov (200  m) (20  m) GEANT simulation PAX conceptional Detector Design

59 Outline WHY? Physics Case HOW? Polarized Antiprotons WHAT?Staging Detector and signal estimate WHEN? Timeline

60 Results on g 1 Results on g 1 u d u d u d u d u d u d

61 EMC (‘88) DS =0.123 ±... Spin Puzzle gluons are important ! don’t forget the orbital angular momentum! SLAC, CERN, DESY: Where is the proton spin? “… the proton is an object we thought we knew so well, but which reveals another face when it spins.” J. Ellis QPM:

62 … 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. Evaluation by QCD-PAC (March 2005) …the PAC considers it is essential for the FAIR project to commit to polarized antiproton capability at this time and include polarized transport and acceleration capability in the HESR, space for installation of the APR and CSR and associated hardware, and the APR in the core project We request the PAX collaboration to: 1) Commit to the construction and testing of the APR 2) Explore all options to increase the luminosity to the value of cm -2 s -1 3) Prepare a more detailed physics proposal and detector design for each of the proposed stages. These stages may include: a) 3.5 GeV/c polarized antiprotons on a polarized proton target b) 15 GeV/c polarized antiprotons with the PANDA detector (for single spin asymmetries) c) 15 GeV/c polarized antiprotons on a polarized proton target in a dedicated detector d) Collisions of 15 GeV/c antiprotons with 3.5 GeV/c polarized protons.

63 …the PAC considers it is essential for the FAIR project to commit to polarized antiproton capability at this time and include polarized transport and acceleration capability in the HESR, space for installation of the APR and CSR and associated hardware, and the APR in the core project We request the PAX collaboration to: 1) Commit to the construction and testing of the APR 2) Explore all options to increase the luminosity to the value of cm -2 s -1 3) Prepare a more detailed physics proposal and detector design for each of the proposed stages. These stages may include: a) 3.5 GeV/c polarized antiprotons on a polarized proton target b) 15 GeV/c polarized antiprotons with the PANDA detector (for single spin asymmetries) c) 15 GeV/c polarized antiprotons on a polarized proton target in a dedicated detector d) Collisions of 15 GeV/c antiprotons with 3.5 GeV/c polarized protons. 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.

64 PAX Part of the basic research program as defined by the CDR– Part of the core experimental facility of FAIRno The STI requests R&D work to be continued on the proposed asymmetric collider experiment with both polarized anti-protons and protons,  to demonstrate that the required luminosity for decisive measurements can be reached.  to demonstrate that a high degree of anti-proton polarisation can be reached.  to advance the studies of the APR and the CSR. The experiment is invited to contribute to the TDR. 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. Recommendations of the STI Working Group on FAIR (Preliminary, August 2005)

65 p (GeV/c) Study onset of 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 High Energy small t: Reggeon Exchange large t: perturbative QCD