Quark Structure of the Proton –The Horizons Broaden!

On behalf of the HERMES collaboration

H. E. Jackson

highlights

H. E. Jackson,QNP092GeVe ebeam ofHERAepcollider

H. E. Jackson, QNP093

The HERMES SpectrometerThe 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 dNk±(x)/dx for D target

Strange q’s isoscalar - Sp(x) = Sn(x)

Only Assumptions Isospin symmetry between p and n

Charge conjugation symmetry in fragmentation

dNk±(x)/dx strongly constraints pdf’s and D(z)’s

H. E. Jackson, QNP095

Extraction of S(x)=s(x)+sbar(x)Extraction of S(x)=s(x)+sbar(x)

Dotted: CTEQ6 + fitted ∫DS(z)dz

Dashed: Q(x)∫DQ(z)dz

Dashed-dotted: S(x)∫DS(z)dz

Solid: S(x)=x-a1 e-x/a2 (1-x)

Q(x): CTEQ6L +∫DQ(z)dzextr.

H. E. Jackson, QNP096

Extraction of S(x) (cont’d)Extraction of S(x) (cont’d)

∫DS (z)dz taken from

De Florian et al.

PRD75, 114010

(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 polarizationStrange Sea polarization

From longitudinal inclusive & kaon spin asymmetries for the deuteron:

Strange quark contribution to helicity sum rule ½=Jz =½∆Σ+∆G+Lpart ?

∆Σ=∆Q+∆S

∆Q≡∫01 Q(x)dx

Data Confirm conclusion that sea quark polarizations are ≈ 0

H. E. Jackson, QNP098

Azimuthal asymmetries in SIDIS at HERMESAzimuthal 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 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 HERMESAzimuthal 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 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 HERMESAzimuthal 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 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 HERMESAzimuthal 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 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 LOProton Spin Structure in LO

3 PDF’s = complete description of the nucleon at leading twist –

(integrated over quark kt )

transversityh1 - chiral odd - DIS – can be studied by measuring azimuthal asymmetries in SIDIS

∫h1(x)dx measures nucleon tensor charge

No coupling to gluons – all valence object

H. E. Jackson, QNP0913

Transversity and Collins AsymmetriesTransversity and Collins Asymmetries

SIDIS cross section for transversely polarized target:

Transversity with chiral-odd Collins fragmentation function generate the Collins asymmetry – 2<sin(φ+φS)>UT.

Extraction process – maximum likehood fit to the SIDIS data alternately in x, z, and ph┴, but unbinned in φ and φS.

H. E. Jackson, QNP0914

Collins Amplitudes for π’s and K’sCollins 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 h1(x)≈∆(x) since ∆u(x) is positive and ∆d(x) negative

Large negative moment for π─ a signal for H1

fav ≈ -H1unfav ?? 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 H1

fav ≈ ─H1unfav

(Efremov et al., PRD73, 094025, 2006)

H. E. Jackson, QNP0915L. Pappalardo at DIS2009L. Pappalardo at DIS2009

Also M. Anselimo, et al. arXiv:0807.0173

H. E. Jackson, QNP0916

The Sivers Effect – companion to Collins AsymmetriesThe Sivers Effect – companion to Collins Asymmetries

Sivers signature -azimuthal asymmetry – 2<sin(φ-φS)>UT.

Arises from correlation between kT and Starget .

Lq is needed for an observable Sivers effect.

Gauge link (soft gluon exchange) provides the phase for the interference required to allow a time-odd f1T

┴ .

2<sin(φ─φS> extracted with same maximum likehood fit to SIDIS data as Collins analysis.

H. E. Jackson, QNP0917

Sivers Amplitudes for π’s and K’sSivers Amplitudes for π’s and K’s

Amplitudes >0 increasing with z=Eh /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 ρ0 decay

H. E. Jackson, QNP0918

Distribution and fragmentation functions in SIDIS Distribution and fragmentation functions in SIDIS

H. E. Jackson, QNP0919

Cahn and Boer-Mulders Effects in SIDIS Cahn and Boer-Mulders Effects in SIDIS

H. E. Jackson, QNP0920

Cos(φ) moment in unpolarized SIDIS Cos(φ) moment in unpolarized SIDIS

H. E. Jackson, QNP0921

Cos(2φ) moment in unpolarized SIDIS Cos(2φ) moment in unpolarized SIDIS

H. E. Jackson, QNP0922

Deep virtual Compton scattering (DVCS) at HERMES 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 Charge dependence of DVCS

NEW

beam spin asymmetry: HERMES preliminarybeam charge asymmetry: HERMES preliminary

H. E. Jackson, QNP0925

Nuclear mass dependence of DVCS 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 τDVCS

Effects predicted for

J=0,1/2 nuclei

H. E. Jackson, QNP0926

Concluding remarks 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