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Franco Bradamante Trieste University and INFN

The Spin Structure of the Nucleon: a phenomenological introduction and the most recent results. Franco Bradamante Trieste University and INFN. Jefferson Lab, May 18, 2012. historical introduction the QCD structure Longitudinal Transverse the experiments

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Franco Bradamante Trieste University and INFN

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  1. The Spin Structure of the Nucleon:a phenomenological introduction and the most recent results Franco Bradamante Trieste University and INFN Jefferson Lab, May 18, 2012

  2. historicalintroduction the QCD structure Longitudinal Transverse the experiments results on transversity Siverseffects outlook Jefferson Lab, May 18, 2012 F. Bradamante

  3. Frisch and Stern (1933) spin should be 0 NB: the small anomaly of the electron Kusch and Foley (1947) vertex effect Schwinger (1948) Magnetic moments the nucleon is not a Dirac particle (point-like particle)  per-se indication of internal structure the question on the existence of the antiproton only solved in 1955 in Berkeley understood in terms of radiation effects  QED Jefferson Lab, May 18, 2012 F. Bradamante

  4. assuming thep in P-state for a dissociation probability of ~ 1/3 Anomalus Magnetic Moments of the Nucleons the similar size and opposite sign suggestpion cloudeffect Jefferson Lab, May 18, 2012 F. Bradamante

  5. THE QUARK MODEL Jefferson Lab, May 18, 2012 F. Bradamante

  6. Major Breakthrough hadron spectoscopy theQUARK MODEL(1964) SU(6) magnetic moments: Jefferson Lab, May 18, 2012 F. Bradamante

  7. Major Breakthrough hadron spectoscopy theQUARK MODEL(1964) SU(6) magnetic moments: assuming u and d Dirac particles with similar agreement for all baryons Jefferson Lab, May 18, 2012 F. Bradamante

  8. The Constituent Quark Model in this model the spin of the nucleon is given by the spin of the quarks probability of finding a quark in a given state of polarization Jefferson Lab, May 18, 2012 F. Bradamante

  9. The Constituent Quark Model in this model the spin of the nucleon is given by the spin of the quarks probability of finding a quark in a given state of polarization the existence of quarks and their properties firmly established in DEEP INELASTIC SCATTERING SLAC Friedmann and Kendell (1969) Bjorken, Feynman Jefferson Lab, May 18, 2012 F. Bradamante

  10. HOW IS DS MEASURED? Jefferson Lab, May 18, 2012 F. Bradamante

  11. Deep Inelastic Scattering key role in the study of the partonic structure of the nucleon valence quarks sea quarks gluons Q2 >> M2 W2=(P+q)2 >> M2 Inclusive DIS: only the incident and scattered leptons are measured Semi-Inclusive DIS: the incident and scattered leptons, and at least one final state hadron are measured Jefferson Lab, May 18, 2012 F. Bradamante

  12. Deep Inelastic Scattering key role in the study of the partonic structure of the nucleon valence quarks sea quarks gluons Q2 >> M2 W2=(P+q)2 >> M2 Inclusive DIS: only the incident and scattered leptons are measured Semi-Inclusive DIS: the incident and scattered leptons, and at least one final state hadron are measured NB: COMPLEMENTARY APPROACH @ RHIC (will not mention) Jefferson Lab, May 18, 2012 F. Bradamante

  13. F2(x) = 2x·F1(x)Callan-Gross in the parton model Structure Functions and PDFs: q(x) Inclusive DIS: unpolarised Jefferson Lab, May 18, 2012 F. Bradamante

  14. measured at CERN, HERA, SLAC Structure Functions and PDFs: q(x) Inclusive DIS: unpolarised F2(x) = 2x·F1(x)Callan-Gross in the parton model Jefferson Lab, May 18, 2012 F. Bradamante

  15. measured at CERN, HERA, SLAC Structure Functions and PDFs: q(x) Inclusive DIS: unpolarised F2(x) = 2x·F1(x)Callan-Gross in the parton model  q(x) from global analysis of DIS and hard scattering data (QCD fits) Jefferson Lab, May 18, 2012 F. Bradamante

  16. Structure Functions and PDFs: q(x) Inclusive DIS: unpolarised F2(x) = 2x·F1(x)Callan-Gross in the parton model  q(x) from global analysis of DIS and hard scattering data (QCD fits) Jefferson Lab, May 18, 2012 F. Bradamante

  17. Parton Distribution Functions Jefferson Lab, May 18, 2012 F. Bradamante

  18. Parton Distribution Functions Jefferson Lab, May 18, 2012 F. Bradamante

  19. Dq’s can be extracted from the DIS cross-section asimmetry Δσ for parallel and antiparallel lepton and nucleon spins Helicity PDFs Jefferson Lab, May 18, 2012 F. Bradamante

  20. Inclusive DIS: beam and target longitudinally polarized beam/target helicity g1measured at SLAC, EMC, SMC, HERMES, COMPASS g2suppressed by a factor g20.01 at 100 GeV (SMC, SLAC) Structure Functions and Helicity PDFs Jefferson Lab, May 18, 2012 F. Bradamante

  21. Inclusive DIS: beam and target longitudinally polarized beam/target helicity Structure Functions and Helicity PDFs g1measured at SLAC, EMC, SMC, HERMES, COMPASS g2suppressed by a factor g20.01 at 100 GeV (SMC, SLAC) Jefferson Lab, May 18, 2012 F. Bradamante

  22. Inclusive DIS: beam and target longitudinally polarized beam/target helicity in the parton model Structure Functions and Helicity PDFs g1measured at SLAC, EMC, SMC, HERMES, COMPASS g2suppressed by a factor g20.01 at 100 GeV (SMC, SLAC) DSSV 2009 Jefferson Lab, May 18, 2012 F. Bradamante

  23. in polarised DIS one measures using complementary information from the WEAK DECAY CONSTANTS of the BARYONS EMC 1988 G1p= 0.123  0.013  0.019DS = 0.12  0.17 The Quark Contribution to the Nucleon Spin one can get Du, Dd, Ds and then DS  SPIN CRISIS Jefferson Lab, May 18, 2012 F. Bradamante

  24. EMC 1988 G1p= 0.123  0.013  0.019DS = 0.12  0.17 The Quark Contribution to the Nucleon Spin  SPIN CRISIS Jefferson Lab, May 18, 2012 F. Bradamante

  25. LATEST RESULTS: HERMES  = 0.330 ± 0.025 ± 0.011 ± 0.028 (from 1d) (exp) (theory) (evol.) COMPASS  = 0.30 ± 0.01 ± 0.02 (from NLO QCD fit) (stat) (evol.) DS: latest results Jefferson Lab, May 18, 2012 F. Bradamante

  26. THE SPIN PUZZLE: WAYS OUT • contribution from GLUON SPIN in inclusive DIS Dq and DG mix up in g1(DGLAP equations) spin sum-rule NECESSITY OF A DIRECT MEASUREMENT OF DG → SIDIS experiments (HERMES and COMPASS) • contribution from ORBITAL ANGULAR MOMENTUM of quarks and gluons Jefferson Lab, May 18, 2012 F. Bradamante

  27. QCD fit + direct measurements conclusion: ΔG SMALLand unlikely to account for the missing spin note: NLO fits, LO data same conclusion from RHIC experiments Jefferson Lab, May 18, 2012 F. Bradamante

  28. Experiments a worldwide effort since decades Jefferson Lab, May 18, 2012 F. Bradamante

  29. Experiments SPIN CRISIS E80 E130 E142/3 E154/5 EMC SMC COMPASS HERMES CLAS/HALL-A Phenix/Star a worldwide effort since decades Jefferson Lab, May 18, 2012 F. Bradamante

  30. The Players, today HERMES @ DESY pure H and D target COMPASS @ CERN high energy m-beam JLAB Experiments very high luminosity Jefferson Lab, May 18, 2012 F. Bradamante

  31. luminosity: ~5 . 1032 cm-2 s-1 beam intensity: 2.108m+/spill (4.8s/16.2s) beam momentum: 160 GeV/c longitudinally polarised muon beam longitudinally or transversely polarised target calorimetry particle identification LHC SPS N

  32. 160 GeVμ SM2 SM1 6LiD Target COMPASS Trigger hodoscopes ECal & HCal μFilter 50 m RICH MWPC Straws TWO STAGE SPECTROMETER: Gems Drift chambers Polarized beam and target Micromegas SAT, LAT, PID Silicon SciFi 0.003 < x < 0.5 10-3 < Q2 < 10 GeV2 F. Bradamante

  33. COMPASS the target system 3He – 4He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) solid state target operated in frozen spin mode 2002-2004: 6LiD (polarised deuteron, L&T) dilution factor f = 0.38 polarization PT = 50% two 60 cm long cells with opposite polarisation (systematics) during data taking with transverse polarisation, polarisation reversal in the cells after ~ 4-5 days F. Bradamante

  34. COMPASS the target system solid state target operated in frozen spin mode 2002-2004: 6LiD (polarised deuteron, L&T) dilution factor f = 0.38 polarization PT = 50% two 60 cm long cells with opposite polarisation (systematics) • 2006: • PTM replaced with the large acceptanceCOMPASS magnet (180 mrad) • 2 target cells 3 target cells • 6LiD (L) 2007:NH3 (polarised protons, L&T) dilution factor f = 0.14 polarization PT = 90% 2010:NH3 (T) 2011:NH3 (L) Jefferson Lab, May 18, 2012 F. Bradamante

  35. Jefferson Lab, May 18, 2012 F. Bradamante

  36. JLab experiments Jefferson Lab, May 18, 2012 F. Bradamante

  37. THE QCD STRUCTURE LONGITUDINAL TRANSVERSE Jefferson Lab, May 18, 2012 F. Bradamante

  38. Since many years intriguing evidence of large transverse spin effects at high energy hyperon polarization high pt effects in hadronic interactions asymmetries in hadron production STAR Puzzles in hadronic reactions RUN6 PRL 101 (2008) 222001 Jefferson Lab, May 18, 2012

  39. Since many years intriguing evidence of large transverse spin effects at high energy hyperon polarization high pt effects in hadronic interactions asymmetries in hadron production STAR Puzzles in hadronic reactions RUN6 PRL 101 (2008) 222001 Hope to find solutions at the quark level (DTq(x) …) Jefferson Lab, May 18, 2012

  40. i.e. Puzzles in hadronic reactions Jefferson Lab, May 18, 2012 F. Bradamante

  41. Puzzles in hadronic reactions i.e. in hadronic reactions like with a transversely polarized proton, the spin asymmetry in leading twist perturbative QCD is expected to vanish THE DATA STRONGLY CONTRADICT THIS! Jefferson Lab, May 18, 2012 F. Bradamante

  42. in the collinear case, three distribution functions are necessary to describe the structure of the nucleon at LO: Parton Distribution Functions Jefferson Lab, May 18, 2012 F. Bradamante

  43. in the collinear case, three distribution functions are necessary to describe the structure of the nucleon at LO: Parton Distribution Functions Jefferson Lab, May 18, 2012 F. Bradamante

  44. in the collinear case, three distribution functions are necessary to describe the structure of the nucleon at LO: Parton Distribution Functions Jefferson Lab, May 18, 2012 F. Bradamante

  45. in the collinear case, three distribution functions are necessary to describe the structure of the nucleon at LO: Parton Distribution Functions ALL OF EQUAL IMPORTANCE ! Jefferson Lab, May 18, 2012 F. Bradamante

  46. HELICITY and TRANSVERSITY are different have different properties are measured in different ways HELICITY vs TRANSVERSITY thus one has to deal differently the situations when the target spins are LONGITUDINAL and TRANSVERSE Jefferson Lab, May 18, 2012 F. Bradamante

  47. HOW to MEASURE TRANSVERSITY Jefferson Lab, May 18, 2012 F. Bradamante

  48. HOW to MEASURE TRANSVERSITY DTq(x)is chiral-odd  cannot be measured in inclusive DIS it can be measured in SIDIS: the observable is the so- called“Collins asymmetry”, the convolution of DTq(x) with another chiral-odd quantity, the “Collins” function, which describes a possible left-right asimmetry of the hadrons in the hadronization process of a transverselypolarized quark Jefferson Lab, May 18, 2012 F. Bradamante

  49. C Collins asymmetry in SIDIS off transversity polarised nucleons amplitude of the sinFCmodulation in the azimuthal distribution of the final state hadrons FC = fh + fS - pfh azimuthal angle of the hadron, fS azimuhtal angle of the nucleon spin transversity “Collins FF” both unknown ! today the most promising way to access transversity Jefferson Lab, May 18, 2012 F. Bradamante

  50. The conjecture was right !! Jefferson Lab, May 18, 2012 F. Bradamante

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