Quark Structure of the Proton – The Horizons Broaden! On behalf of the HERMES collaboration H. E. Jackson highlights

H. E. Jackson,QNP092  GeV  e   e   beam of  HERA  ep  collider

H. E. Jackson, QNP093 The HERMES Spectrometer

H. E. Jackson, QNP094 Quark Sea in the Nucleon – Origin and Nature Detection of s quarks and effects on proton structure has been difficult HERMES has precise data on SIDIS multiplicities of π ± ’s and K ± ’s useful in study of strange quark properties. Open issues – gluon splitting versus non-perturb. processes –polarization ?? – measureable presence of s quarks. Strange q’s are pure sea – a useful probe of the sea

HERMES dN k± (x)/dx for D target Strange q’s isoscalar - S p (x) = S n (x) Only Assumptions Isospin symmetry between p and n Charge conjugation symmetry in fragmentation dN k± (x)/dx strongly constraints pdf’s and D(z)’s H. E. Jackson, QNP095 Extraction of S(x)=s(x)+sbar(x) Dotted: CTEQ6 + fitted ∫D S (z)dz Dashed: Q(x)∫D Q (z)dz Dashed-dotted: S(x)∫D S (z)dz Solid: S(x)=x -a1 e -x/a2 (1-x) Q(x): CTEQ6L +∫D Q (z)dz extr.

H. E. Jackson, QNP096 Extraction of S(x) (cont’d) ∫D S (z)dz taken from De Florian et al. PRD75, (2007) S(x)≠k(ubar+dbar) S(x) is softer in shape than light isoscalar sea. Data shape should be important in constructing non-perturbative models of generation of sea quarks. S(x) ≈ 0 for x > 0.1 Implications important for measurements of charm production at high energy (e.g. NuTeV)

H. E. Jackson, QNP097 Strange Sea polarization From longitudinal inclusive & kaon spin asymmetries for the deuteron: Strange quark contribution to helicity sum rule ½=J z =½∆Σ+∆G+L part ? ∆Σ=∆Q+∆S ∆Q≡∫ 0 1 Q(x)dx Data Confirm conclusion that sea quark polarizations are ≈ 0

H. E. Jackson, QNP098 Azimuthal asymmetries in SIDIS at HERMES Polarization/charge dependent A(φ)’s of mesons and photons in SIDIS access a broad range of interesting physics topics

H. E. Jackson, QNP099 Azimuthal asymmetries in SIDIS at HERMES transversity Polarization/charge dependent A(φ)’s of mesons and photons in SIDIS access a broad range of interesting physics topics

H. E. Jackson, QNP0910 transversity Azimuthal asymmetries in SIDIS at HERMES Polarization/charge dependent A(φ)’s of mesons and photons in SIDIS access a broad range of interesting physics topics

H. E. Jackson, QNP0911 transversity Azimuthal asymmetries in SIDIS at HERMES Polarization/charge dependent A(φ)’s of mesons and photons in SIDIS access a broad range of interesting physics topics

H. E. Jackson, QNP0912 Proton Spin Structure in LO 3 PDF’s = complete description of the nucleon at leading twist – (integrated over quark k t ) transversity h 1 - chiral odd - DIS – can be studied by measuring azimuthal asymmetries in SIDIS ∫h 1 (x)dx measures nucleon tensor charge No coupling to gluons – all valence object

H. E. Jackson, QNP0913 Transversity and Collins Asymmetries SIDIS cross section for transversely polarized target: Transversity with chiral-odd Collins fragmentation function generate the Collins asymmetry – 2 UT. Extraction process – maximum likehood fit to the SIDIS data alternately in x, z, and p h┴, but unbinned in φ and φ S.

H. E. Jackson, QNP0914 Collins Amplitudes for π’s and K’s Moments for π + & K + ≈ same - signal of dominance of u(x) fragmentation Moments for π ─ & K ─ ≠, but K ─ has no valence quarks in common with the target proton Difference in sign for π + & π ─ plausible – if h 1 (x)≈∆(x) since ∆u(x) is positive and ∆d(x) negative Large negative moment for π ─ a signal for H 1 fav ≈ -H 1 unfav ?? String models of fragmentation suggest such behavior Effects of transversity are large! BEWARE – Effects in “disfavored” fragmentation can be of opposite sign and not necessarily small! Global analysis of early HERMES, and BELLE data gave H 1 fav ≈ ─H 1 unfav (Efremov et al., PRD73, , 2006)

H. E. Jackson, QNP0915 L. Pappalardo at DIS2009 Also M. Anselimo, et al. arXiv:

H. E. Jackson, QNP0916 The Sivers Effect – companion to Collins Asymmetries Sivers signature -azimuthal asymmetry – 2 UT. Arises from correlation between k T and S target. L q is needed for an observable Sivers effect. Gauge link (soft gluon exchange) provides the phase for the interference required to allow a time-odd f 1T ┴. 2 extracted with same maximum likehood fit to SIDIS data as Collins analysis.

H. E. Jackson, QNP0917 Sivers Amplitudes for π’s and K’s Amplitudes >0 increasing with z=E h /hν u-quark dominance + positive amplitudes implies large negative Sivers Function K + > π + ?? sea quarks may contribute π + ─ π ─ amp. >0 – asymmetries not due to π’s from ρ 0 decay

H. E. Jackson, QNP0918 Distribution and fragmentation functions in SIDIS

H. E. Jackson, QNP0919 Cahn and Boer-Mulders Effects in SIDIS

H. E. Jackson, QNP0920 Cos(φ) moment in unpolarized SIDIS

H. E. Jackson, QNP0921 Cos(2φ) moment in unpolarized SIDIS

H. E. Jackson, QNP0922 Deep virtual Compton scattering (DVCS) at HERMES Generalized parton distributions (GPDs) accessible in DVCS from beam charge and azimuthal dependences via interference term in DVCS Moments of GPDs constrain Jq via Ji relation

H. E. Jackson, QNP0923 Only a feasibility demonstration - model does not fit all data! [JHEP06(2008)] suppressed

H. E. Jackson, QNP0924 Charge dependence of DVCS NEW beam spin asymmetry: HERMES preliminary beam charge asymmetry: HERMES preliminary

H. E. Jackson, QNP0925 Nuclear mass dependence of DVCS NEW Select for each target 2 samples (t cutoffs): ►coherent enriched (65% coherent fraction) ► incoherent enrich. (60% incoherent fraction) H, He, N, Ne, Kr, Xe No nuclear mass dependences of BSA and BCA within uncertainties ►No enhancement of τ DVCS Effects predicted for J=0,1/2 nuclei

H. E. Jackson, QNP0926 Concluding remarks Next generation results for DVCS soon with improved exclusivity ─ Recoil detector For more details and additional topics see talks on Tuesday afternoon : Avertisyan – exclusive mesons Yu – DVCS at HERMES Miyachi – TMDs studies