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