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Spin Experiments Technological challenges and selected physics highlights

Spin Experiments Technological challenges and selected physics highlights. Klaus Rith University of Erlangen-Nürnberg & DESY. 18th International Spin Physics Symposium, Charlottesville, VA – Oct. 6-10, 2008. N. Bohr. W. Pauli. Spin experiments. University of Lund, 31.5.1951.

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Spin Experiments Technological challenges and selected physics highlights

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  1. Spin Experiments Technological challenges and selected physics highlights Klaus Rith University of Erlangen-Nürnberg & DESY 18th International Spin Physics Symposium, Charlottesville, VA – Oct. 6-10, 2008

  2. N. Bohr W. Pauli Spin experiments University of Lund, 31.5.1951 K. Rith 2

  3. N. Bohr W. Pauli Spin experiments • are fascinating • enhancesmall signals • provide new observables • often generate surprises K. Rith 2

  4. Prerequisites - Technological achievements strained GaAspolarizede--sources with pe 0.8 longitudinal polarization of 27.6 GeV stored e-/e+ beam with pe 0.6– spin rotators internal storage cellpolarizedH, D, 3He gas targets with no dilution (f=1), pTH,D 0.8 large polarizedkryogenic targets(NH3, ND3, LiD) polarized stored proton beams (presently up to 100 GeV) with pp 0.6– Siberian snakes Fast and precise polarimeters J. Clarke Challenges: - polarized positron sources(for ILC) - polarizedantiprotons with pB0.2 E. Steffens K. Rith 3

  5. Strained GaAs polarized e-sources Early ´90s @SLAC: Overcome GaAs limit of pe= 0.5 by strained GaAs K. Rith 4

  6. AfLR from SLD Highlight 1 SLD achievements: Unique data on AfLR = = Statistically most precise single determination of sin2W sin2W(MZ) = 0.23098  0.00026 g2L,f – g2R,f2gV,f/gA,f g2L,f + g2R,f1 +g2V,f/g2A,f gV,e-/gA,e- = 1 – 4 sin2W,f K. Rith 5

  7. Strained GaAs polarized e-sources Now ‚standard equipment‘ at all electron facilities: (AMPS, BATES), ELSA, JLAB, MAMI, JPARC,…….. Example: SLAC E158 –Run 3 Sophisticated surface structure to overcome charge limit and achieve high polarisation (gradient-doped strained superlattice) Precise control of beam helicity at source K. Rith 6

  8. E158 – PV in Møller-scattering First PV experiment in e-L,R e- e- e- End of SLAC fixed target programme Pe = 0.89  0.04, Ebeam = 45 & 48 GeV (spinrotation by extra  due to g-2) E‘  13-24 GeV, Q2  0.026 GeV2 Challenge: Control of beam-helicity related systematic errors

  9. E158 – PV in Møller-scattering Highlight 2  Z0 + Electroweak interference: e- e- e-L,R e-L,R APV = - A(Q2,y)[1-4sin2Weff(Q)]= [-1.310.14 (stat)0.10 (sys)]10 -7 sin2Weff(Q)= 0.23970.00100.008 P.L. Anthony et al., PRL 95 (2005) 081601 Limit on SO(10) MZ’ 1.0 TeV Limit on l.h. contact interaction LLL ~ 7 or 16 TeV 6.2  Limit on lepton flavor violating coupling ~ 0.01GF K. Rith 8

  10. PV in eN  eN SAMPLE/BATES A4/MAMI G0/JLAB HAPPEX/JLAB K. Rith 9

  11. Nucleon Strange Form Factors Highlight 3 Very small asymmetries: O(10-6) J. Liu et al., Phys. Rev. C76 (2007) 025202 D.S. Armstrong et al., PRL 95 (2005) 092001 K. Rith 10

  12. Precise determination of GEn Highlight 4 Tool: double-polarization experiments D(e,e‘n) with polarized D target 2D(e,e‘n) with LD2 target and nrecoil polarimeter 3He(e,e‘n) with polarized3He target E. Geis et al. (BLAST), PRL 101 (2008) 042501 K. Rith 11

  13. Polarized muon beam – EMC, SMC, COMPASS Myon beam: 100 - 200 GeV    ,- - Advantage: ‘Natural‘ beampolarization:    J=0 Disadvantage: low beam currents – I  1 pA Require high-mass polarized target, N  1024 nucleons/cm2 NH3 (f 3/17), ND3 (f 6/20), LiD (f 4/8),…… f = fraction of polarizable nucleons W. Meyer K. Rith 12

  14. Polarized target - COMPASS World‘s largest kryogenic polarized target 180 mrad K. Rith 13

  15. COMPASS spectrometer 50 m K. Rith 14

  16. Polarized e beam in storage ring– LEP, HERA Mechanism:Spin flip by emission of synchrotron radiation  1 / 1010 - 1011 emissions (Sokolov-Ternov) Degree of polarization: depends critically on machine energy and magnet alignement Example: LEP – mZ = 91.1874  0,0021 GeV Beam energy dominant error of 1.7 MeV Measurement by resonant depolarization of transversely polarized beam Influence of tide, TGV leaving airport station etc. Longitudinal polarization: requires spin rotators Polarization measurement: Compton backscattering of circularly polarized laser light K. Rith 15

  17. Polarized e beam in HERA e beam: E = 27.6 GeV, Ie < 50 mA K. Rith 16

  18. Polarized e beam in HERA e beam: E = 27.6 GeV, Ie < 50 mA 2002-2007 3 spinrotators 1995-2000 1 spinrotator After ´high –luminosity upgrade‘: depolarization by beam-beam interactions K. Rith 17

  19. Total polarized CC cross section Highlight 5 L R W- W+ e-L q e+R q e- CCep (Pe) = (1  Pe)CCep (Pe=0) R No sign of r.h currents W- e-R q Chiral structure of SM confirmed e+ Convert to 90% CL on heavy WR: mW,R > 208 GeV (H1) K. Rith 18

  20. Internal polarized storage-cell gas targets K. Rith 19

  21. Internal polarized storage-cell gas targets Principle: Stern-Gerlach separation of HF-states + RF-transitions Target polarisation: PT 0.85, Dilution factor:f=1 Ideal for storage rings: IUCF, COSY, BATES.. K. Rith 19

  22. Asymmetries in polarized pp scattering Highlight 6 Example: PINTEX at IUCF: p p  p p Precise measurement of spin correlation parameters F. Rathmann et al., Phys. Rev. C58 (1998) 658 before after Test and improvement of NN potential models K. Rith 20

  23. Polarized proton collider - RHIC RHIC pC Polarimeters Absolute Polarimeter (H jet) PHOBOS BRAHMS Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Partial Snake Pol. H- Source LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS pC Polarimeter Strong AGS Snake Masterpiece of accelerator physics May 2006 May 2006 Ep = 100 GeV Ep = 100 GeV T. Roser K. Rith 21

  24. Polarized proton collider - RHIC PHOBOS BRAHMS PHENIX STAR Pol. H- Source LINAC BOOSTER AGS K. Rith 22

  25. Asymmetries in polarized pp collisions K. Rith 23

  26. Nucleon Spin ½ = ½ + G + Lq + Lg (Quark spins) (Gluon spins) (Orbital angular momenta) EMC (1987):  = 0,12 0,090,14 K. Slifer K. Rith 24

  27. Dg2 DgDq Dq2 Nucleon Spin - Tools Polarised DIS  or jet production inpp l‘ = l = Hard Scattering Process =E - E‘, Q2= -q2=-(l – l ‘)2 x=Q2/(2M) = fraction ofnucleon‘s longitudinal momentum carried by struck quark q(x) = quark number density W -production Drell-Yan ( ) X X p p l + l + qv * d W+ qv u X l X p l - p K. Rith 25

  28. Highlight 7 Asymmetries in polarized DIS beamtarget From W. Vogelsang eq2q(x) g1(x) L.O. -  q  A1(x)  eq2q(x) F1(x) +  q K. Rith 26

  29. Highlight 7 g1(x),  g1(x) = ½zq2q(x) q q(x) = q (x) – q (x) HERMES  = 0,330 ± 0,025 ± 0,011 ± 0,028 (from 1d) MS (exp) (theory) (evol.) q = q(x) dx COMPASS  = 0,30 ± 0,01 ± 0,02 (from NLO QCD fit) MS (stat) (evol.) 1 = g1(x) dx   q q K. Rith 27

  30. Quark helicity distributions from SIDIS Leading hadronoriginates with large probability from struck quark Dqh(z):= Fragmentation function (FF) z = Eh/ zq2q(x)Dqh(z) A1h(x,z) = zq2 q(x)Dqh(z) Measurehadronasymmetries Measure hadron asymmetries Targets: H, D ; h =±, K±, p K. Rith 28

  31. Highlight 8 Quark helicity distributions HERMES, PRL 92 (2004) 012005, PRD 71 (2005) 012003 HERMES, PLB 666 (2008) u > d ? S = 0.037  0.019(stat.)  0.027(syst.) s < 0 ? (inclusive data and SU(3): S = - 0.085  0.013(stat.) 0.012(syst.)) x K. Rith 29

  32. Highlight 8 Valence-quark helicity distributions L.O. L.O. COMPASS, PLB 660 (2008) 458 u + d = 31N - ½1v + a8/12 Flavor asymmetric polarized sea (u = - d) favoured K. Rith 30

  33. N Highlight 9 Gluon helicity distribution Photon-gluon fusion e‘ e L.O. analyses E. Rondio K. Rith 31

  34. Highlight 9 G from pp 0 (jet) X A. Adare et al. (PHENIX); arXiv:0810.0694  De Florian et al.: hep-ph/0804.0422 gseems to be rather small!! jets NLO analysis (without data from previous slide) K. Rith 32

  35. Spin budget Origin of nucleon spin still unclear: Where do the missing 65% come from? X. Ji:‚Dark Spin‘ Is there a substantial contribution of g and/or qatvery low x? EIC What is the contribution of orbital angular momenta Lq, Lg ??? K. Rith 33

  36. Transversity q(x) For a complete description of momentum and spin distribution of the nucleon at leading-twist: 3 distribution functions (DF) Transversity DF Unpolarised DF Helicity DF q(x) q(x) q(x) known well known unknown before HERMES, COMPASS K. Rith 34

  37. Azimuthal angular distributions Amplitude has 2 components: TransversityDF 2sin( + S)hUT ~q(x)H1q(z) CollinsFragmentation Function U: unpol. e-beam T: transv. pol. Target Unpolarised FF z = Eh/ : conv. integral over pT and KT 2sin( - S)hUT~ f1Tq(x)D1q(z) (Requires non-vanishing orbital angular momentaLq of quarks) SiversDF N. Makins, M. Anselmino K. Rith 35

  38. Collins amplitudes (proton) Highlight 10 2sin( + S)hUT ~ q(x) H1q(z) M. Diefenthaler @ DIS07, hep-ex 0707.0222 (also HERMES, P. R. L. 94 (2005) 012002) First measurement of non-zero Collins effect Both Collinsfragmentation function and transversity distribution function are sizeable Surprisingly large - asymmetry Possible source: large contribution (with opposite sign) from unfavored fragmentation, i.e. u - H1,disf - H1,fav K. Rith 36

  39. Collins amplitudes (d ) +p Highlight 10 COMPASS, hep-ex/0802.2160 deuteron Different from zero, Compatible with HERMES Compatible with zero information about d N. Makins, M. Anselmino K. Rith 37

  40. Sivers amplitudes (p) Highlight 11 2sin( - S)hUT ~ f1Tq(x) D1q(z) M. Diefenthaler @ DIS07, hep-ex 0706.2242 (also HERMES, P. R. L. 94 (2005) 012002) First observationof non-zeroSiversdistribution functioninDIS Experimental evidence for orbital angular momentum Lqof quarks But: Quantitative contributionofLqtonucleon spin stillunclear K. Rith 38

  41. Sivers ampl. (d ) +p Highlight 11 COMPASS, hep-ex/0802.2160 deuteron Compatible with zero Still compatible with zero K. Rith 39

  42. AN for identified hadrons in p p Highlight 12 E 704 Possible origins: Collins FF, Sivers DF, Twist-3 Combinations of above Important data for test of theoretical models K. Rith 40

  43. q and f1T in p p Drell-Yan Future qis chiral-odd. Its measurement requires anotherchiral-odd object! Semi-Inclusive DIS:Collins fragmentation function.(Requires additional input e.g. fromBELLE) p p Drell-Yan: Combination of qv and qv E. Steffens QCD prediction: f1T(x)SIDIS = -f1T(x)DY q  q qq    l+l- anti-lensing  green quark green quark anti-green anti-quark anti-green remnant anti-green remnant K. Rith 41

  44. Determination of Lq - GPDs Tool: Generalised Parton Distributions Formfactors: PDFs: GPDs: Fouriertransform of e.g. a radial charge distribution Number density of quarks with longitudinal momentum fraction x Generalised description in 2+ 1 dimensions C. Weiss K. Rith 42

  45. Q2 t Determination of Lq Ji relation: Jq=1/2 + Lq= lim dx x [H(x,,t) + E(x,,t)] H(x,,t), E(x,,t): Generalised Parton Distributions (GPDs) t  0 Access: exclusive processes Final state sensitive to different GPDs Vector mesons (, , ) H, E Pseudoscalar mesons(,) H, E DVCS () H, E, H, E     E. Voutier K. Rith 43

  46. Hard exclusive processes - Lq Calorimeter and superconducting magnet within CLAS torus HERMES/Recoil Detector, (2006 – 2007) dedicated calorimeter (424 PbWO4 crystals) detect photons from 5o CLAS12 JLab/Hall A, (2004 – 2005) HRS + PbF2 H(e,e’gp), D(e,e’gN) K. Rith 44

  47. Azimuthal asymmetries DVCS: Beam-spin asymmetry HERMES,PRL 87 (2001) 182001 CLAS,PRL 87 (2001) 182002 JLAB/HALL A,PRL 97 (2006) 262002 d4 - d4 CLAS,PRL 97 (2006) 072002 DVCS: Longitudinal target-spin asymmetry K. Rith 45

  48. Hard exclusive processes - Lq Highlight 13 Pioneermeasurements DVCS: Beam charge asymmetry HERMES, JHEP 0806 (2008) 66 DVCS: Transv. target spin asymmetry (SA) DVCS: Long. target SA 0: Transv. target SA K. Rith 46

  49. Highlight 13 Determination of Jq First model dependent attempt: HERMES, JHEP 06 (2008) 066; JLAB/HALL A, PRL 99 (2007) 242501 Lattice: Ld  -L u  0.2 !?? K. Rith 47

  50. Conclusion Spin physics is exciting We are looking forward to see plenty of new results at this conference and from the next generation of high precision spin experiments K. Rith 48

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