1 E.C. Aschenauer Recent results from lepton proton scattering on the spin structure of the nucleon

2 E.C. Aschenauer The contemporary experiments Beam: 27.5 GeV e ± ; % polarization Target: (un)-polarized gas targets; polarization Beam: 160 GeV  ; 75% polarization Target: 6 LiD; 50% polarization Two high-resolution 4 GeV spectrometers Hall A Large acceptance spect. electron/photon beams Hall B 7 GeV spectrometer, 1.8 GeV spectrometer, large installation experiments Hall C Beam: ≤6 GeV e - ; 85% polarization Target: polarized targets 3 He, 6 LiD, NH 3

3 E.C. Aschenauer News on the spin structure of the nucleon Naïve parton model BUT 1989 EMC measured  = ± ± Spin Puzzle Unpolarised structure fct. Gluons are important ! Sea quarks  q s GGGG Full description of J q and J g needs orbital angular momentum

4 E.C. Aschenauer Deep Inelastic Scattering q Important kinematic variables: cross section: DF FF Spin 1

5 E.C. Aschenauer How to measure Quark Polarizations Virtual photon  * can only couple to quarks of opposite helicity Virtual photon  * can only couple to quarks of opposite helicity Select q + (x) or q - (x) by changing the orientation of Select q + (x) or q - (x) by changing the orientation of target nucleon spin or helicity of incident lepton beam target nucleon spin or helicity of incident lepton beam Asymmetry definition: inclusive DIS: only e’ info used semi-inclusive DIS: e’+h info used

6 E.C. Aschenauer World data on inclusive DIS New data from COMPASS, New data from COMPASS, HERMES & JLab very precise HERMES & JLab very precise high x-behaviour consistent with high x-behaviour consistent with A  1 with x  1 A  1 with x  1 A 1 d consistent with zero A 1 d consistent with zero for x < 0.05 for x < 0.05 ProtonDeuterium CLAS PLB 641, 11 (2006) A 1 n from 3 He (Hall-A) COMPASS PRD75(2007)012007

7 E.C. Aschenauer World data on inclusive DIS Combine p and d to get n: or 3 He What can we learn on the PDFs What can we learn on the PDFs Compass: hep-ex/ Hermes: hep-ex/

8 E.C. Aschenauer HERMES: Integrals Q 2 =5 GeV 2, NNLO in MS scheme Saturation in deuteron integral is assumed use only deuterium use only deuterium From hyperon beta decay a 8 =0.586±0.031 From neutron beta decay a 3 =1.269±0.003 COMPASS: COMPASS:

9 E.C. Aschenauer CLAS:  q Using: Using:

10 E.C. Aschenauer Polarised quark distributions Correlation between detected hadron and struck q f “Flavor – Separation” “Flavor – Separation” Inclusive DIS: Semi-inclusive DIS: In LO-QCD:

11 E.C. Aschenauer COMPASS: Valence PDFs For LO: For LO: Assuming: Assuming:  v is 2.5  stat away from flavour symmetric sea scenario symmetric sea scenario

12 E.C. Aschenauer Polarised quark distributions Correlation between detected hadron and struck q f “Flavor – Separation” “Flavor – Separation” Inclusive DIS: Semi-inclusive DIS: Extract  q by solving: In LO-QCD: MC

13 E.C. Aschenauer good agreement with NLO-QCD Polarised opposite to proton spin Polarized Quark Densities  u(x) > 0 First complete separation of First complete separation of pol. PDFs without assumption on pol. PDFs without assumption on sea polarization sea polarization Polarised parallel to proton spin  d(x) < 0 ~ 0  u(x),  d(x) ~ 0 No indication for< 0 No indication for  s(x) < 0 In measured range (0.023 – 0.6) In measured range (0.023 – 0.6)

14 E.C. Aschenauer SIDIS data improves description of all  q, especially light sea Kretzer FF favor SU(3) symmetric sea, not so for KKP  ~30% in all cases D. De Florian et al. hep-ph/ Q 2 =10 GeV 2 Kretzer KKP   DIS   SIDIS uvuv uu dvdv dd ss gg                  NLO FIT to DIS & SIDIS Data

15 E.C. Aschenauer Several more fits using mainly only inclusive data or a combination of inclusive and using mainly only inclusive data or a combination of inclusive and some semi-inclusive data some semi-inclusive data Results for  G still completely all over the place Results for  G still completely all over the place Need a consistent approach for fit and uncertainty determination Need a consistent approach for fit and uncertainty determination with all world data taken into account with all world data taken into account  G<0  G>0  G<0  G>0 Lets measure  G more directly

16 E.C. Aschenauer The golden channels Idea: Direct measurement of  G Isolate the photon gluon fusion process (PGF) Open Charm production Open Charm production Reaction: Reaction: LO-MC: Aroma

17 E.C. Aschenauer The golden channels Idea: Direct measurement of  G Isolate the photon gluon fusion process detection of hadronic final states with high p T detection of hadronic final states with high p T high p T pairs of hadrons high p T pairs of hadrons single high p T hadrons single high p T hadrons h±h±h±h±h±h±h±h± h±h±h±h± less sub-processes contributing less sub-processes contributing more sub-processes contributing  higher statistics higher statistics less sub-processes contributing less sub-processes contributing more sub-processes contributing  higher statistics higher statistics Several possible contributions to the measured asymmetry MC needed to determine R and a LL q g q g qg Important at Q2<0.1

18 E.C. Aschenauer COMPASS Results Channel: Channel: h±h±h±h±h±h±h±h± x F > 0.1 z > 0.1 m(h 1,h 2 ) > 1.5 GeV 10% of statistics R PGF = /  2 (scale) ~ 3 GeV 2 ~ 0.13 Q 2 > 1 GeV 2 Cuts: Cuts: Q 2 < 1 GeV 2 used for  g/g extraction &  g/g=0.016±0.058(stat.)±0.055(syst.)  2 =3.0GeV 2

19 E.C. Aschenauer HERMES Results Channels: Channels: h ± h ±, h ± Subprocess Asymmetries (using GRSV std.) Subprocess Fractions

20 E.C. Aschenauer World Data on  G/G Long way to go till  g(x) x

21 E.C. Aschenauer The Hunt for L q Study of hard exclusive processes leads to a new class of PDFs Generalized Parton Distributions possible access to orbital angular momentum exclusive: all products of the reaction are detected missing energy (  E) and missing Mass (M x ) = 0 missing energy (  E) and missing Mass (M x ) = 0 from DIS: ~0.3

22 E.C. Aschenauer GPDs Introduction What does GPDs charaterize? unpolarized polarized conserve nucleon helicity flip nucleon helicity not accessible in DIS DVCSDVCSDVCSDVCS quantum numbers of final state select different GPD pseudo-scaler mesons vector mesons A C,A LU, A UT, A UL A UT,   + A UT,  

23 E.C. Aschenauer HERMES / JLAB kinematics: BH >> DVCS DVCS two experimentally undistinguishable processes: DVCS Bethe-Heitler (BH) p +  isolate BH-DVCS interference term non-zero azimuthal asymmetries

24 E.C. Aschenauer  UT ~ sin  ∙Im{k(H - E) + … }  C ~ cos  ∙Re{ H +  H +… } ~  LU ~ sin  ∙Im{H +  H + kE} ~  UL ~ sin  ∙Im{H +  H + …} ~ polarization observables:  polarization observables:  UT beam target kinematically suppressed H H H, E ~ different charges: e + e -  different charges: e + e - H DVCS ASYMMETRIES  = x B /(2-x B ),k = t/4M 2

25 E.C. Aschenauer CLAS: DVCS - BSA Integrated over t = 0.18 GeV 2 = 0.30 GeV 2 = 0.49 GeV 2 = 0.76 GeV 2 Accurate data in a large kinematical domain

26 E.C. Aschenauer A way to E and J u -J d Hermes DVCS-TTSA: Hall A nDVCS-BSA: x=0.36 and Q 2 =1.9GeV 2 Neutron obtained combining Neutron obtained combining deuterium and proton deuterium and proton F 1 small u & d cancel in F 1 small u & d cancel in

27 E.C. Aschenauer Can we constrain (J u - J d ) first model dependent extraction of J u - J d possible first model dependent extraction of J u - J d possible VGG-Code: GPD-model: LO/Regge/D-term=0 VGG-Code: GPD-model: LO/Regge/D-term=0

28 E.C. Aschenauer Access to L q in semi-inclusive scattering New structure function accessible with SSA New structure function accessible with SSA std. FF Sivers DFF Side view Front view right left photon NOTE: QCD tells us that the FSI has to be attractive, since quark and remnants form a color antisymmetric state right left photon right left proton quarks  A distortion in the distribution of quarks in transverse space can give rise to a nonzero Sivers function A distortion in the distribution of quarks in transverse space can give rise to a nonzero Sivers function The presence of spin can distort the distribution of quarks in transverse space (orbital angular momentum of quarks is required) The presence of spin can distort the distribution of quarks in transverse space (orbital angular momentum of quarks is required)

29 E.C. Aschenauer HERMES & COMPASS Measuremnets Deuterium Proton Proton: Proton: Sivers moment: Sivers moment:  + > 0  - ~ 0 K + > 0 K - ~ 0 K + > 0 K - ~ 0 K + >  + K + >  + sea quarks important sea quarks important Deuterium ~ 0 Deuterium ~ 0 u and d quark cancel u and d quark cancel

30 E.C. Aschenauer Results from theory QCDSF/UKQCD Collab. (hep-ph/ ) Lattice QCD: Sivers negative for up quarks positive for down quarks Anselmino et al., hep-ph/ [20] Anselmino et al., PRD72 (05) [21] Vogelsang, Yuan, PRD72 (05) [23] Collins et al., hep-ph/ Pheno. analysis from data:

31 E.C. Aschenauer Summary qqqq GGGG LgLgLgLg LqLqLqLq qqqq qqqq GGGG LgLgLgLg LqLqLqLq qqqq

32 E.C. Aschenauer Spin is fascinating Thank you for your attention

33 E.C. Aschenauer BACKUP SLIDES

34 E.C. Aschenauer angle of hadron relative to initial quark spin (Sivers) angle of hadron relative to final quark spin (Collins) (Sivers) (Collins) Azimuthal angles and asymmetries chiral-even naïve T-odd DF related to parton orbital momentum violates naïve universality of PDF peculiarity of f  1T different sign of f  1T in DY