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New results in lepton - nucleon spin physics

New results in lepton - nucleon spin physics. K. Rith, DIS04, 14.4.2004. Spin -dependent SF g 1 (x), g 2 (x). Quark helicity distr. q f (x). Gluon polarisation g(x)/g(x). Transversity distribution q f (x). The HERMES spectrometer.

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New results in lepton - nucleon spin physics

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  1. New results in lepton-nucleonspin physics K. Rith, DIS04, 14.4.2004 Spin-dependent SFg1(x), g2(x) Quark helicity distr. qf(x) Gluon polarisation g(x)/g(x) Transversity distribution qf(x)

  2. TheHERMESspectrometer HERAe+/e- beam of 27.6 GeV, I~50 10 mA, beam-pol~55% kinematics: 0.02<x<0.6, 1.0<Q2<15 GeV2 tracking: p/p~2%, <0.6 mrad, 40-220 mrad PID: Calorimeter, Preshower, TRD, RICH

  3. HERMESinternal target Pure polarised gas targets: H, D, 3He, target polarisation: pT(H,D)  85% Luminosity: 4*1030 cm-2 s-1(H @ 10 mA)  6*1033 cm-2 s-1 (D2@ 50 mA) spin reversal every 120 sec

  4. HERMES data taking Long. TargetPolarisation Transv. TargetPolarisation

  5. COMPASS at CERN E = 160 GeV, pB -76% 2.8*108/spill (4.8 s/16.2 s) polarized LiD-target , pT 50% Luminosity:  5*1032 cm-2 s-1 50 m

  6. 3He – 4He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) two 60 cm long Target-Containers with opposite polarization COMPASS polarized LiD target 4 possible spin combinations: 1 2 reversed every 8 hours or: 3 4 SMC PT magnet: present acceptance 70 mrad instead of 180 mrad reduced acceptance for x > 0.1 reversed once a week Polarization: ~50%

  7. GB COMPASS data taking 2002: 260 TByte 2003 Event reconstruction: 500 TB raw data  500 000 Batch jobs ( 1 GByte ~ 8 hours) Process in parallel as much as possible (presently: ~1000 CPUs) • 2002 & 2003: • 500 TByte Data • 1010Events long. pol. • 3.109 Events transv. pol. • 0.1% with Q²>1(GeV/c)²

  8. Experiments @JLAB CEBAF Large Acceptance Spectrometer E < 6 GEV, Luminosity < 1036 cm-2s-1, pB 0.7, pT  0.35 Luminosity < 1034 cm-2s-1

  9. Spin-dependent Deep-Inelastic Lepton-Nucleon Scattering Nucleon Nucleon     Quarks Quarks 1/2~q+  3/2~q-  Helicity distr.: q(x):=q+(x)-q-(x) g1(x) := ½ q zq2q(x) 1/2- 3/2g1 Asymmetry: A1=  F1(x) := 1/2+ 3/2F1 ½ q zq2q(x) f = 1 for H, D f < 0.5 for LiD f < 0.33 for 3He f < 0.17for NH3 Dilutions: Aexp (fpTDpB) A1 A1 ~ (fpTDpBN)-1

  10. A1g1/F1 - Proton andDeuteron  g1p/F1p well known for x10-3 Excellent agreement between all experiments g1p/F1p(within errors) independent of Q2;Q2 dependence ofg1 and F1very similar <Q2> = f(x) Extrapolationtox0for Q2 =Q02 ? HERMES errors will increase at low and high x due to unfolding corr.

  11. First A1d from COMPASS 2002 data only:6.5 Million DIS events Q2 > 1 (GeV/c)2, 0.1 < y < 0.9 expect *4 statistics by end of 2004 Details  M. Leberig, WG F

  12. A1n from Jlab E99-117 Phys. Rev. Lett. 92, 012004 (2004) In addition: 1n(Q2), g2n(x,Q2), 2n(Q2), d2(Q2) 12 GeV upgrade: more data at higher x Details  N.Liyanage, WG F

  13. xg1(x) - world data Integrals at Q02 = 2,5 GeV2, QCD analysis of Q2 dependence and SU(3): ? =u+d+s  0,20  0,04 .. ? GluonsG Rest? Orbital angular momentaLq,g

  14. NLOQCD(MS) fit • Assumptions: • Helicity distribution of sea quarks flavour symmetric • - uv and dv constraint by F and D (SU(3) symmetry) • Results for Q02= 4 GeV2: • uv  0.73 .....0.86 (0.10) • dv -0.40...-0.46 (0.10) • qs -0.04 ...-0.09 •   0.14 ...0.20 • G  0.68 ...1.26 BB: Blümlein, Böttcher hep/ph 0203155 LSS: Leader et al., hep/ph 0111267 GRSV: Glück et al., hep/ph 0011215 AAC: Goto et. Al., hep/ph 0001046

  15. NLOQCD(MS) fit Concern: uv and dv constraint by F and D (SU(3) symmetry) ga/gv = 1.0 instead of 1.254 give same quality of fit in measured region All the difference is shifted to the unmeasured low-x region low-x extrapolation and results for moments questionable HERMES will only state partial moments over measured region

  16. Quark helicity distributions from semi-inclusive asymmetries =E - E‘ z = Eh/ Leading hadron originates with large probability from struck quark D(z):= Fragmentation function

  17. Semi-inclusive asymmetries-1 In leading order: P.L. B 464 (1999) 123 zq2q(x)Dqh(z) A1h(x,z) = zq2q(x)Dqh(z) zq2q(x)Dqh(z) q(x) = zq‘2q‘(x)Dq‘h(z)q(x) Quark-‘Purity‘ Phq Different targets and hadrons h: Solve linear system for Q with A = (A1,p, A1,d, A1,p, A1,d, A1,pK ) A = PQ

  18. Semi-inclusiveasymmetries-Deuteron ,K, p asymmetries identified with RICH PionsKaons P.R.L.92 (2004) 012005 Statistics sufficient for 5-parameter-fit Q(x) = (u(x)/u(x), d(x)/d(x), u(x)/u(x), d(x)/d(x), s(x)/s(x) )

  19. Extracted quark helicitydistributions P.R.L.92 (2004) 012005 u > d ? The HERMES data are consistent with flavour symmetry of sea quarkhelicity distributions d(x) - 0.4 u(x) (!?) What is the dynamics behind this?? Data with much higher statistical accuracy urgently needed s < 0 ? Details  M. Leberig, WG F x

  20. ThegluonpolarisationG/G Method: Photon-Gluon-Fusion q q t  h/2mq  Charm-production (Hard scale: mass of c-quark) e+, + e-, - D J/ * * c pt c c c g c g c D  Pairs of hadrons h+h- with high transverse momenta (Hard scale: pT ) h2 * g () h1

  21. G/G from high-pT hadron pairs 3 main contributions to *p  h+h- X : h2 h2 h2 * q q * * q V q g p g q q h1 h1 QCDC VMD PGF h1 AVDM +0.5 q/q AVDM = 0 APGF -1G/G Relative contributions: Monte Carlo simulation - PYTHIA(5) But: applicable at HERMES (COMPASS) kinematics? Resolved photons? Intrinsic kT? ? Tuned PYTHIA6 givesmuchsmaller fPGF

  22. G/G from high-pT hadron pairs P.R.L. 84 (2000) 2584 Quasi-real photoproduction Proton target 0.06 < x < 0.28 <Q2> = 0.06 (GeV/c)2 Asymmetry is negative A= - 0.28  0.12  0.02 G/G= 0.41  0.18  0.03

  23. High-pT hadron pairs: COMPASS Cuts: 0.4 < y < 0.9, z > 0.1, xF > 0.1 no Q2 cut, logQ2  -1 pT1, pT2 > 0,7 GeV/c p2T1 + p2T2 > 2.5 GeV2/c2 m(h1h2) > 1.5 GeV/c2 (removes VM) Result: A||/D = - 0.065  0.036(stat)  0.01(syst) Error for asymmetry already very small projected stat. error (incl. 2003/04): 0.018 But: data dominated by low pT

  24. G/G from high-pt hadron pairs A = - 0.133  0.058 A = - 0.040  0.042 1996 – 2000 data A = - 0.039  0.028

  25. G/G from high-pT hadron pairs: SMC E = 190 GeV Cuts: as COMPASS exception: Q2 > 1 GeV2/c2 DIS regime optimization offPGF:pT-cuts and neural network -(NN) fPGF 0.3 hep-ex/0402010 Result: Asymmetry is positive ! ? Proton plus deuteron data, NN classification: G/G= -0.20  0.28  0.10

  26. D0 D* Charm production: COMPASS J/ Details  F.H. Heinsius, WG F Signal seen, but limited statistics, (remind dilution factors !) Still some way to go for G/G 2002: mostly “elastic“ background 2003: dedicated trigger (2*yield) - study diffractive and elastic processes

  27. chiral odd FF: Collins FF single helicity flip double helicity flip ‘Transversity‘ h1 Complete description of nucleon in leading order QCD: 3 DF f1 = Quark momenta,  q q , V g1 = - longitudinal quark spin, , q   5q, A h1 = - transverse quark spin, , q 5 q, T h1 is chiral odd, measurement requires other chiral odd DF (e.g. Drell-Yan), or FF (SIDIS) like the Collins FF H1(z)

  28. Azimuthal asymmetries: CollinsvsSiverseffect 2 different possible sources for azimuthal asymmetry:  product of chiral-odd transversity distribution h1(x) and chiral-odd fragmentation function H1(z)(Collins)  product of naive time-reversal odd distribution function f1T and familiar unpolarised fragmentation function D1(z) (Sivers) (requires orbital angular momentum of quarks) Longitudinally polarised target: Collins and Sivers effect indistinguishable Transversely polarised target: 2 azimuthal angles, Collins andSivers effect distinguishable AUTsin( + s ) AUTsin( - s )

  29. Single Spin Asymmetries (SSA) ep(d)e‘hX N+() -N-() AUL() = N+() +N-() U: unpol. e-beam L: long. pol. Target Fit sin() to asymmetries AULsin() transverse spin component: ST sin  (15% - 20%) (for HERMESkinematics)

  30. SSA from long. polarized target Deuteron Proton P.L. B 562 (2003) 182 + P.R. D 64 (2001) 097101. o o + - - K+ - + 0  - +  0 2.4 M DIS 8.9 M DIS

  31. AULsin() from long. polarized target P.L. B 562 (2003) 182 + HERMES CLAS + o Furthermore: ALUsin() (~ e(x)) - K+ Details  E. Avetisyan, M. Khandaker, WG F

  32. AULsin() from longitudinally polarized target + AULsin  SL(M/Q) za2 x [hLa(x) H1a(z) - x h1La(x) Ha(z)/z + ..] - ST za2 x h1a(x) H1a(z) SL >> ST Collins fragmentation function o Theory predictions seem to explain the data well A.V. Efremov et al., Eur. Phys. J. C 24 (2002) 47 B. Ma et al., P.R. D66 (2002) 094001 but contain a lot of assumptions: magnitude of H1/D1 4 ...12% only part of Twist-3 contribution taken into account no Sivers contribution taken into account - K+

  33. AUTsin() from transv. pol. H target Simultaneous fit to sin( + s) and sin( - s) „Collins“ moments Unexpected pattern: expect A+  Ao 0 and A- 0 and smaller in magnitude Data show A+  0 but Ao  A-  0 and larger in magnitude Possible source: H1,disf - H1,fav?

  34. AUTsin() from transv. pol. H target Simultaneous fit to sin( + s) and sin( - s) „Sivers“ moments First measurement of Siversasymmetry Sivers function nonzero  orbital angular momentum ofquarks Details  R. Seidl, WG F Sivers flavor separation possible and underway HERMES 2002-2005 data: Hope for factor of 4-9 in statistics

  35. Collins asymmetryfromCOMPASS 2002 data Details  H. Fischer, WG F 2002 data COMPASS 2002-2004 data: ~ factor of 4 in statistics

  36. Stay tuned … New exiting results will come soon ! Conclusions Plenty of new data from COMPASS, HERMES, JLAB, SMC Rather precise results on asymmetries, spin-dependentSF and quark helicity distributions. Furtherimprovementsonmeasurementofsea quark polarisation desirable G/G results puzzling, we still wait for a clean and precise experimental determination First results on Transversity andSiverseffect very promising Special thanks to H. Fischer and Z.-E. Meziani

  37. g2(x) ~ ~ g2(x,Q2) = - g1(x,Q2) + g1(z,Q2) dz/z + g2(x,Q2) = g2WW(x,Q2) + g2(x,Q2) Quark-Gluon Correlation (Twist-3 Operator) E155x, Phys. Lett. B 553 (2003) 18 Further improvement by HERMES and COMPASS very unlikely

  38. Test of Burkhardt-Cottingham SR • valid at all Q2 • Many scenarios of g2’s low x behavior which would invalidate the sum rule are discussed in the literature. Courageous extrapolations to high and low x Conclusion of authors: BC-sum rule fullfilled within errors Details  N.Liyanage, WG F

  39. AT, b1and b2- deuteron Deuteron is spin-1 target V = Pz= p+ - p- , Pz1 T = Pzz= p+ + p- -2p0 , -2 Pz z +1 More structure functions meas = u [1 + PbVA + ½TAT] A  g1/F1 [ 1 +½ TAT] AT  2/3b1/F1 Proton Deuteron F1½ zq2 [q+ + q-] 1/3 zq2 [q+ + q-+ q0] F2 2xF1 2xF1 g1½ zq2 [q+ - q-] ½ zq2 [q+ - q-] b1½ zq2 [2q0 - (q+ + q-)] b2 2xb1

  40. The HERMESpolarised internal gas target

  41. AT, b1and b2- deuteron First measurement, only possible with atomic gas target Model: K. Bora, R.L. Jaffe, PRD 57 (1998) 6906

  42. AT, b1and b2- deuteron See e.g.: - P. Hoodboy et al., N.P. B312 (89) 571 - R.L. Jaffe & A. Manohar N.P. B321 (89) 343 - X. Artru & M. Mekhfi, Z. Phys. C45 (90) 669 - N.N. Nikolaec & W. Schäfer, P.L. B398 (97) 245 - J. Edelmann et al., Z. Phys. A357 (97) 129, P.R. C57 (98) 3392 - K. Bora & R.L. Jaffe, P.R. D57 (98) 6906 - - Deuteron is spin-1 target AT  10-2 little impact on det. of g1 b1dis sizeable ! and interesting by itself related to - nuclear binding - D-stateadmixture - diffractive nuclear shadowing - nuclear excess pions inD - VMD+ double scattering - -

  43. Purities (Probability that observed hadron originates from quark of type f) Kaons have about 10% sensitivity to the strange sea Adequate degree of orthogonality: Shaded bands: systematic uncertainties

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