GPDs. -- status of measurements -- a very brief introduction prerequisites and methods DVCS & DVMP: selected results on the way to an EIC

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1 Delia Hasch GPDs -- status of measurements -- a very brief introduction prerequisites and methods & DVMP: selected results on the way to an EIC see additional slides for results not covered POETIC 01, Bloomington, Indiana-USA, 0 - Aug, 01

2 why GPDs? proton helicity flipped while quark helicity is conserved requires orbital angular momentum 0 q E ),, ( ),, ( 1 t q q q t x E t x H xdx J [X. Ji (1996)] spin puzzle q g z q z g q z L g L q J J s % zero

while quark helicity is conserved q E J q 0 1 1 1 requires orbital

Ji (1996)] nucleon imaging: FT (GPD) impact parameter space b :

3 why GPDs? 1 q g 1 spin puzzle q sz J J q L q z g L g z proton helicity flipped while quark helicity is conserved q E J q requires orbital angular momentum xdx 30% zero H q ( x,, t) E q ( x,, t) t0 [X. Ji (1996)] nucleon imaging: FT (GPD) impact parameter space b : spatial distribution in T transverse plane (transverse distance from proton center of momentum) [M. Burkardt(001), M. Diehl(00)] [fig: courtesy C. Weiss]

4 how to constrain GPDs? Q Q >>, t<< appear in factorisation theorem for hard exclusive processes x x t H( x,, t) x ~ x Bj x Bj

5 how to constrain GPDs? Q Q >>, t<< appear in factorisation theorem for hard exclusive processes x x t H( x,, t) x ~ x Bj x Bj spin ½ target: 4 leading-tw, chiral even q & g GPDs: H, H conserve nucleon helicity E, E involve nucleon helicity flip + 4 chiral odd ( transversity ) GPDs, which flip the parton helicity H T related to transversity ~ ~

6 how to constrain GPDs? Q Q >>, t<< appear in factorisation theorem for hard exclusive processes x x t H( x,, t) x ~ x Bj x Bj : most clean process, (some) flavour dependent information from p & n target OR: evolution ~ ~ H, H, E, E

7 how to constrain GPDs? Q Q >>, t<< appear in factorisation theorem for hard exclusive processes x x t H( x,, t) x ~ x Bj x Bj : most clean process, (some) flavour dependent information from p & n target OR: evolution DVMP: flavour decomposition & gluons ~ ~ H, H, E, E VM H, E ~ ~ ~ ~ PS H, E, H T, E T

8 how to constrain GPDs? Q Q >>, t<< appear in factorisation theorem for hard exclusive processes x x t H( x,, t) x ~ x Bj x Bj : most clean process, (some) flavour dependent information from p & n target OR: evolution DVMP: flavour decomposition & gluons ~ ~ ~ PS H, E, H T, E T

9 how to constrain GPDs? Q Q >>, t<< appear in factorisation theorem for hard exclusive processes x x t H( x,, t) x ~ x Bj x Bj : most clean process, (some) flavour dependent information from p & n target OR: evolution DVMP: flavour decomposition & gluons BUT factorisation only for s L meson distribution amplitude needed large NLO & power corrections ~ ~ ~ PS H, E, H T, E T

link GPDs & observables x x complex amplitude

(integrated over), needs deconvolution apart

directly accessible extrapolation t 0 model

asymmetry ~ Re(T ): integral of GPDs over x

10 link GPDs & observables x x complex amplitude Compton Form Factor (CFF) x is mute variable (integrated over), needs deconvolution apart from cross over trajectory (x ± ) GPDs not directly accessible extrapolation t 0 model dependent cross section & beam charge asymmetry ~ Re(T ): integral of GPDs over x beam or target spin asymmetries ~ Im(T ), i.e., x= ±ξ

11 link GPDs & observables x x complex amplitude Compton Form Factor (CFF) x is mute variable (integrated over), needs deconvolution apart from cross over trajectory (x ± ) GPDs not directly accessible extrapolation t 0 model dependent cross section & beam charge asymmetry ~ Re(T ): integral of GPDs over x beam or target spin asymmetries ~ Im(T ), i.e., x= ±ξ x scan of GPDs: double : JLab1 (?) Q evolution: EIC

12 the ideal experiment for measuring hard exclusive processes Q >>, t<< Q high & variable beam energy ensure hard regime wide kinematic range L/T separation for ps meson prod. t high luminosity small cross sections fully differential analysis hermetic detectors ensure exclusivity

13 the ideal experiment for measuring hard exclusive processes Q >>, t<< Q high & variable beam energy ensure hard regime wide kinematic range L/T separation for ps meson prod. t high luminosity small cross sections fully differential analysis hermetic detectors ensure exclusivity doesn t exist (yet)

14 experimental prerequisites polarised 7GeV e+/e unpolarised 90GeV p full event reconstruction HERA till 007 polarised 7GeV e+/e long+transv polarised p, d targets unpolarised nuclear targets missing mass technique 006/7 data taken with recoil det.

15 experimental prerequisites polarised 7GeV e+/e unpolarised 90GeV p full event reconstruction HERA till 007 polarised 7GeV e+/e long+transv polarised p, d targets unpolarised nuclear targets missing mass technique 006/7 data taken with recoil det. CEBAF Hall-A highly polarised, high lumi 6GeV e long polarised effective p, n targets CLAS: full event reconstruction Hall-A: missing mass/energy technique

unpolarised nuclear targets missing mass technique 006/7 data taken with recoil det.

CLAS: full event reconstruction Hall-A: missing mass/energy technique highly polarised,

16 experimental prerequisites polarised 7GeV e+/e unpolarised 90GeV p full event reconstruction HERA till 007 polarised 7GeV e+/e long+transv polarised p, d targets unpolarised nuclear targets missing mass technique 006/7 data taken with recoil det. CEBAF Hall-A highly polarised, high lumi 6GeV e long polarised effective p, n targets CLAS: full event reconstruction Hall-A: missing mass/energy technique highly polarised, 160GeV m long+transv polarised effective p, d targets missing mass/energie technique CERN COMPASS-II with recoil det.

amplitudes ~ ~ ps meson production H, E, role of transverse photons, power corrections & chiral-odd GPDs ~

17 results on /off the menu data over wide kinematic range: HERA-collider (COMPASS) HERMES JLab VM production H, E low x: gluon imaging high x: quarks & gluons; role of NLO contributions low W data from Jlab SDMEs / amplitudes ~ ~ ps meson production H, E, role of transverse photons, power corrections & chiral-odd GPDs ~ ~ H, E, H, E... the golden channel & most rich plate nuclear modification of amplitudes: HERMES hunting the OAM

18 VM x energy dependence probes transition from soft to hard regime ds/dt ~ e b t

19 VM x energy dependence probes transition from soft to hard regime,, J/, ds/dt ~ e b t universality of b slope parameter point like configurations dominate

20 gluon imaging: J/ energy dependence probes hard regime; FT average impact parameter ds/dt ~ e b t FT average impact parameter b ( x Bj distance between active quark/gluon and proton center of momentum ) [M. Burkardt(001), M. Diehl(00)] T [fig: courtesy C. Weiss]

21 gluon imaging: J/ energy dependence probes hard regime; FT average impact parameter [Frankfurt, Strikman, Weiss (011)] ds/dt ~ e b t FT average impact parameter b ( x Bj distance between active quark/gluon and proton center of momentum ) [M. Burkardt(001), M. Diehl(00)] T T [fig: courtesy C. Weiss]

22 VM production: from low high x NLO corrections to VM production are kinematics of COMPASS/ HERMES/ CLAS1 [M. Diehl, W. Kugler (007)]... despite, LO GPD model (handbag fact.; DD ansatz): [S. Goloskokov, P. Kroll (007, 010)] + power corrections W = 90 GeV W = 75 GeV 0 Zeus H1 LO GPD + power correction

23 VM production: from low high x NLO corrections to VM production are kinematics of COMPASS/ HERMES/ CLAS1 [M. Diehl, W. Kugler (007)]... despite, LO GPD model (handbag fact.; DD ansatz): [S. Goloskokov, P. Kroll (007, 010)] + power corrections 0 Zeus H1 Compass Hermes W = 90 GeV W = 10 GeV W = 5 GeV...does NOT work for low W of CLAS

24 VM production: from low high x NLO corrections to VM production are kinematics of COMPASS/ HERMES/ CLAS1 [M. Diehl, W. Kugler (007)]... despite, LO GPD model (handbag fact.; DD ansatz): [S. Goloskokov, P. Kroll (007, 010)] + power corrections 0 Zeus H1 dominance of gluon exchange contrib. H1, ZEUS E665 HERMES CLAS Compass Hermes W = 90 GeV W = 10 GeV W = 5 GeV Q = 3.8 GeV

25 ps meson production -- role of power corrections & longitudinal-transverse transitions -- ep n 0 ep p Hall-A

26 ps meson production -- role of power corrections & longitudinal-transverse transitions -- * p n [PLB659(008)]

27 ps meson production -- role of power corrections & longitudinal-transverse transitions -- * p n [PLB659(008)] Regge model [Laget(008)] s tot... s L need of L/T separation, especially for lower Q, higher t

28 ps meson production -- role of power corrections & longitudinal-transverse transitions -- ep n sin( S ) A UT arises from pure s L contribution NLO/power corrections cancel to large extend in asymmetry [PLB68(010)] curves: GPD model [GK(009)]

29 ps meson production -- role of power corrections & longitudinal-transverse transitions -- ep n sin( S ) A UT arises from pure s L contribution NLO/power corrections cancel to large extend in asymmetry [PLB68(010)] curves: GPD model [GK(009)] significant contribution from L/T interference, need to go beyond leading-tw description

30 ps meson production -- role of power corrections & longitudinal-transverse transitions -- 0 ep p sin A LU any non-zero beam-spin asymmetry indicates L-T interference [PRC77(008)] ep n [PLB68(010)] significant contribution from L/T interference, need to go beyond leading-tw description

31 ps meson production -- role of transversity GPDs -- 0 ep p cross sections vs t s T parametrized employing transversity GPDs (and assuming factorization) [Goldstein etal.(011), Goloskokov and Kroll (011)] s L + e s T s LT s TT [arxiv: ] curves: GPD model calc.s with dominant contributions from transversity GPDs [Goloskokov Kroll(011)] [Goldstein etal.(011)]

32 Deeply virtual Compton Scattering Bethe-Heitler ~ ~ H, H, E, E dσ ( * * ) bilinear in GPDs linear in GPDs

33 Deeply virtual Compton Scattering Bethe-Heitler ~ ~ H, H, E, E dσ ( * * ) bilinear in GPDs linear in GPDs LO sea quarks + NLO gluons

34 extracted transverse size (as before for VM) [H1, PLB659(008)] b T ( ) x B =10-3 <Q >=8.0 GeV

35 Bethe-Heitler ~ ~ H, H, E, / JLab << Bethe-Heitler dσ ( * * ) bilinear in GPDs linear in GPDs, information about phase access to Re and Im parts of CFFs

36 Bethe-Heitler ~ ~ H, H, E, / JLab << Bethe-Heitler dσ ( * * ) bilinear in GPDs linear in GPDs, information about phase isolate interference term: different beam charges: e + e polarisation observables: s UT beam target U, L U, L, T Unpolarised, Longitudinally, Transversely polarised

Hall-A interference term dσ ( * * ) different beam charges: e + e only @HERA, upcoming @COMPASS

37 Hall-A interference term dσ ( * * ) different beam charges: e + e polarisation observables: s UT (, S,...) beam target U, L U, L, T Unpolarised, Longitudinally, Transversely polarised

38 Hall-A interference term dσ ( * * ) cross section in full glory: [M. Diehl] beam charge longitudinal beam polarisation Longitudinal or transverse target polarisation

39 Hall-A interference term dσ ( * * ) cross section in full glory: [M. Diehl] beam charge longitudinal beam polarisation Longitudinal or transverse target polarisation

40 Hall-A interference term dσ ( * * ) cross section in full glory: [M. Diehl] fourier coefficients c n and s n provide experimenal constrain on CFFs example: I ds LU

41 Hall-A interference term dσ ( * * ) cross section in full glory: [M. Diehl] fourier coefficients c n and s n provide experimenal constrain on CFFs example: I ds LU accessible linear combinations of CFFs, hence GPDs : dσ I LU xbj ~ t F1 H ( F1 F ) H F E... x 4M Bj dominant contribution for proton for neutron F 1, F... Pauli & Dirac FF

42 first signals -- interference term -- A LU ~ ()*Im()*sin ( + ) [PRL87(001), 18001] [PRL87(001), 1800] A LU sin dependence indicates dominance of handback contribution

43 Hall-A call for high statistics dσ ( * * ) s UU [PRL97(006)] [GPD model: VGG(1999)]

44 Hall-A call for high statistics dσ ( * * ) s UU [PRL97(006)] s LU [GPD model: VGG(1999)]

45 call for high statistics beam-spin asymmetry [PRL100(008)] A LU ~ ()*Im()*sin ( + ) A LU a sin 1 ccos

46 call for high statistics beam-spin asymmetry [PRL100(008)] 3D analysis in x, Q, t <-t> = 0.18 GeV <-t> = 0.30 GeV <-t> = 0.49 GeV <-t> = 0.76 GeV A LU a sin 1 ccos

47 call for new analysis methods dσ ( * * combined analysis of charge & polarisation observables separation of Interference & amplitudes )

48 call for new analysis methods dσ ( * * combined analysis of charge & polarisation observables separation of Interference & amplitudes e.g., beam-spin asymmetry: s LU LU I ( ; P, e ) s ( ) 1 P A ( ) e P A ( ) e A ( ) l l UU l l l LU ) l C

49 call for new analysis methods dσ ( * * combined analysis of charge & polarisation observables separation of Interference & amplitudes e.g., beam-spin asymmetry: s LU LU I ( ; P, e ) s ( ) 1 P A ( ) e P A ( ) e A ( ) l l UU l l l LU ) l C charged-averaged beam-spin asymmetry: ALU ( s s ) ( s )/ ( ) s s1 sin

50 call for new analysis methods dσ ( * * combined analysis of charge & polarisation observables separation of Interference & amplitudes e.g., beam-spin asymmetry: s LU LU I ( ; P, e ) s ( ) 1 P A ( ) e P A ( ) e A ( ) l l UU l l l LU ) l C charged-averaged beam-spin asymmetry: A LU ( s s ) ( s )/ ( ) s s1 sin charge-difference beam-spin asymmetry: ALU ( s s ) ( s )/ ( ) s n 1 s I n sin( n) Im(CFF)

51 call for new analysis methods dσ ( * * combined analysis of charge & polarisation observables separation of Interference & amplitudes e.g., beam-spin asymmetry: s LU LU I ( ; P, e ) s ( ) 1 P A ( ) e P A ( ) e A ( ) l l UU l l l LU ) l C charged-averaged beam-spin asymmetry: A LU ( s s ) ( s )/ ( ) s charge-difference beam-spin asymmetry: A LU ( s s ) ( s )/ ( ) s s1 sin n 1 I s sin( n) Im(CFF) n beam-spin averaged charge asymmetry: A C ( s s ) ( s )/ ( ) s 3 n 0 c I n cos( n) Re(CFF)

52 call for new analysis methods dσ ( * * combined analysis of charge & polarisation observables separation of Interference & amplitudes s LU LU I ( ; P, e ) s ( ) 1 P A ( ) e P A ( ) e A ( ) l l UU l l l LU ) l C s1 [JHEP07(011] sin n 1 I 3 sn sin( n) n 0 c I n cos( n) [JHEP07(001]

53 call for completeness charge asymmetry Re (H) Hall-A beam-spin asymmetry Im (H) transverse target spin asymmetry Im (H-E) transverse-target double-spin Re (H-E) longitudinal target spin asymm. ~ Im (H) longitudinal-target double-spin ~ Re (H)

54 hunting the OAM lattice results: [P. Hägler etal.(011)] 1 1 0,,, ),, ( ),, ( 1, 1 t g q g q g q g q t x E t x H xdx J J J

55 1 1 0,,, ),, ( ),, ( 1, 1 t g q g q g q g q t x E t x H xdx J J J hunting the OAM lattice results: [P. Hägler etal.(011)] GPD model tuned to VM: [Goloskokov, Kroll(008)] variants for GPD E

56 hunting the OAM sensitivity to GPD E (@fixed target exp. kinematics) ),, ( ),, ( 1 t q q q t x E t x H xdx J GPD models: J q free parameter in ansatz for E p: A UT HERMES n: A LU Hall A meson prod. A UT : 0 HERMES, COMPASS...also w,,, K *0

57 hunting the OAM -- p : transverse target-spin asymmetry -- GPD models: J q free parameter in ansatz for E [JHEP06(008)] [VGG]

58 hunting the OAM -- n : beam-spin cross section difference -- GPD models: J q free parameter in ansatz for E [PRL99(007)] [VGG] Hall-A

59 hunting the OAM model dependent [VGG(1999)] constrain of J u vs J d lattice GPD & TMD models [figure taken from Bachetta&Radici, PRL107(011)]

conclusions 10-3 10-1 0.-0.5 HERA collider COMPASS HERMES / JLab 10-4 < x B < 0.0 0.0 < x B < 0.4 / 0.1 < x B < 0.

60 conclusions HERA collider COMPASS HERMES / JLab 10-4 < x B < < x B < 0.4 / 0.1 < x B < 0.6 x B sea quarks & gluons, VM (gluons) (valence) quarks, (mesons) increasing amount and precision of experimental data large variety of different observables (however, many still with limited precision) progress in model calculations, plenty of room for more work...

61 conclusions & perspectives HERA collider HERMES / JLab x B Compass-II JLab1GeV EIC increasing amount and precision of experimental data large variety of different observables (however, many still with limited precision) progress in model calculations, plenty of room for more work... bright future for GPD studies: JLab1: in valence kinematic region COMPASS-II with recoil: & VM in transition kinematic region

62 [ Volker Burkert, Enrico Fermi physics school, Varenna, Italy, July 011 ] 1 GeV Approved Experiments by Physics Topics [ Topic Hall A Hall B Hall C Hall D Total The Hadron spectra as probes of QCD (rated) (GlueX and heavy baryon and meson spectroscopy) 1 1 The transverse structure of the hadrons (rated) (Elastic and transition Form Factors) The longitudinal structure of the hadrons (rated) (Unpolarized and polarized parton distribution functions) 4 8 The 3D structure of the hadrons (unrated) (Generalized Parton Distributions and Transverse Momentum (*) Distributions) Hadrons and cold nuclear matter (rated) (Medium modification of the nucleons, quark hadronization, N-N correlations, hypernuclear spectroscopy, few-body experiments) Low-energy tests of the Standard Model and Fundamental Symmetries (rated) 1 3 TOTAL Current PAC approved experiments represent over 6 years of running at 35 weeks/year (*) 3 new approved proposals on the B since then

63 @CLAS1 [014+] [ fully differential analysis watch requirement t << Q

64 @Hall A [014+] 11 GeV [ fully differential analysis watch requirement t << Q

65 @COMPASS-II 014+ ~ < x < 0.3

66 @COMPASS-II 014+ cross section: slope parameter b: ds/dt ~ e b t [ COMPASS projections

67 @COMPASS-II 014+ beam helicity & charge asymmetry A ( t, cos C x B ) 0.005<x COMPASS projections x<0.3 [

68 conclusions & perspectives HERA collider HERMES / JLab x B Compass-II JLab1GeV EIC increasing amount and precision of experimental data large variety of different observables (however, many still with limited precision) progress in model calculations, plenty of room for more work... bright future for GPD studies: JLab1: in valence kinematic region COMPASS-II with recoil: & VM in transition kinematic region EIC: mapping GPDs from Q evolution of & from meson production

69 additional slides

70 the HERA collider experiments hermetic detector p escapes through beam pipe LPS: p tagged control sample

71 the HERA collider experiments LPS: p tagged data sample e-sample: control sample e+e-, J/ bg-sample -sample: + (+) -

72 the HERA collider experiments full data sample e-sample: control sample e+e-, J/ bg-sample -sample: + (+) -

73 exclusivity fixed target: via missing mass / energy (ep e X) part of the signal subtracted very well understood

74 exclusivity fixed target: via missing mass / energy (ep e X) with p detection & + ID: transition GPDs

75 exclusivity fixed target: via missing mass / energy (ep e X) part of the signal subtracted very well understood Hall-A

76 exclusivity: HERMES with recoil

77 exclusivity: HERMES with recoil

78 exclusivity: HERMES with recoil

79 HERMES target spin asymmetries

80 HERMES target spin asymmetries

81 HERMES VM SDMEs

82 HERMES VM SDMEs

83 HERMES VM SDMEs

84 HERMES VM SDMEs

85 VM x W & t dependences: probe transition from soft to hard regime soft hard expect d to increase from ~0. to ~0.8 b to decrease from ~10 to ~4-5 GeV

86 VM x W dependence: probe transition from soft to hard regime J/Y U two ways to set a hard scale: large Q mass of produced VM universality: and at large Q +M similar to J/Y, Y

87 VM production from low high x HERA-collider COMPASS / HERMES / Jlab g+(sea) g+(sea)+q v (,w) q v (,w) x B NLO corrections to VM production are large: [M. Diehl, W. Kugler (007)] 0 cross kinematics of COMPASS / HERMES / JLab1

Deeply Virtual Compton Scattering cross sections @ low x ~ ~ H, H, E, E dσ I

88 Deeply Virtual Compton Scattering cross low x ~ ~ H, H, E, E dσ I ds dt e b t t slope provides absolute normalisation FT average impact parameter

89 cross section [PLB659(008)] t slope measurement provides absolute normalisation ds dt e b t

90 cross section [PLB659(008)] t slope measurement provides absolute normalisation Zeus (p tagged events) [JHEP05(009)] ds dt e b t universality of slope parameter: pointlike configurations dominate

91 cross section [PLB659(008)] t slope measurement provides absolute normalisation Zeus (p tagged events) [JHEP05(009)] ds dt e b t universality of slope parameter: pointlike configurations dominate FT average impact parameter b T ( ) x B =10-3 <Q >=8.0 GeV [courtesy of C. x B =10-3

92 sea quark & gluon imaging remember J/ universality of slope parameter: pointlike configurations dominate FT average impact parameter b T ( ) x B =10-3 [courtesy of C. x B =10-3 <Q >=8.0 GeV

93 call for high statistics beam-spin asymmetry [PRL100(008)] Im( F 1 H)

94 hunting the OAM -- 0 : transverse target-spin asymmetry -- after the full glory of SDME extractions [PLB679(009)] [formalism by M. Diehl (007)] * ( L 0 ) : L 0 ' n mm ' * μ,ν 0, 1 long.pol: 0 transv.pol: ±1

95 hunting the OAM -- 0 : transverse target-spin asymmetry -- after the full glory of SDME extractions [formalism by M. Diehl (007)] [PLB679(009)] * ( L 0 ) : L [GPD model: Ellighaus et al. (004)] 0 ' n mm ' * μ,ν 0, 1 long.pol: 0 transv.pol: ±1 more data coming: COMPASS, JLab1 with transv. Target more models: Goloskokov, Kroll

97 towards GPDs recent developments (beyond VGG(1999)...) Goloskokov, Kroll (007): LO GPD model using DD, regge t dep., power corrections fit to exclusive meson production data

98 towards GPDs recent developments (beyond VGG(1999)...) Goloskokov, Kroll (007): LO GPD model using DD, regge t dep., power corrections fit to exclusive meson production data Kumericki, Müller (010): partial wave expansion of GPDs, regge t dep., dispersion relations fit to data

99 towards GPDs recent developments (beyond VGG(1999)...) Goloskokov, Kroll (007): LO GPD model using DD, regge t dep., power corrections fit to exclusive meson production data Kumericki, Müller (010): partial wave expansion of GPDs, regge t dep., dispersion relations fit to data Goldstein, Hernandez,Liuti (010): quark-diquark model of GPDs, Regge ansatz for low x region & t dep. fit to data

100 towards GPDs recent developments (beyond VGG(1999)...) Goloskokov, Kroll (007): LO GPD model using DD, reggezised t dep., power corrections fit to exclusive meson production data Kumericki, Müller (010): partial wave expansion of GPDs, reggezised t dep., dispersion relations fit to data Goldstein, Hernandez,Liuti (010): Guidal 011 VGG 1999 quark-diquark model of GPDs, Regge ansatz for low x region & t dep. fit to data talk by S. Liuti [tomorrow] Guidal (011): model independent extraction of CFF (GPD extr. requires model ansatz) kinematic fitting of data (per experiment)

101 towards global analysis of GPDs (slide from K. Kumericki, Photons11)

102 towards global analysis of GPDs -- employ all available exclusive data ( & meson production) -- GK (007) comparison to KM09,10

hunting the OAM Delia Hasch a very brief review of the spin sum rule observables of OAM some attempts to quantify OAM conclusion

hunting the OAM Delia Hasch a very brief review of the spin sum rule observables of OAM some attempts to quantify OAM conclusion INT workshop on gluons and the quark sea at high energies, INT Seattle, Sep-Nov, 2010 Delia Hasch hunting the OAM a very brief review of the spin sum rule observables of OAM some attempts to quantify OAM