Quark Structure of the Proton

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Quark Structure of the Proton The Horizons
Broaden!
highlights

• On behalf of the HERMES collaboration

H. E. Jackson
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(No Transcript)
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The HERMES Spectrometer
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Quark Sea in the Nucleon Origin and Nature

• Open issues gluon splitting versus non-perturb.
  processes polarization ?? measureable presence
  of s quarks.
• Strange qs are pure sea a useful probe of the
  sea

• Detection of s quarks and effects on proton
  structure has been difficult
• HERMES has precise data on SIDIS multiplicities
  of ps and Ks useful in study of strange quark
  properties.

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

• HERMES dNk(x)/dx for D target
• Strange qs isoscalar - Sp(x) Sn(x)
• Only Assumptions
• Isospin symmetry between p and n
• Charge conjugation symmetry in fragmentation
• dNk(x)/dx strongly constraints pdfs and D(z)s

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.
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Extraction of S(x) (contd)
?DS (z)dz taken from De Florian et al. PRD75,
114010 (2007)

• S(x)?k(ubardbar) 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 gt 0.1 Implications important for
  measurements of charm production at high energy
  (e.g. NuTeV)

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Strange Sea polarization
Strange quark contribution to helicity sum rule
½Jz ½?S?GLpart ?
From longitudinal inclusive kaon spin
asymmetries for the deuteron
?S?Q?S ?Q?01 Q(x)dx
Data Confirm conclusion that sea quark
polarizations are 0
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Azimuthal asymmetries in SIDIS at HERMES
Polarization/charge dependent A(f)s of mesons
and photons in SIDIS access a broad range of
interesting physics topics
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Azimuthal asymmetries in SIDIS at HERMES
Polarization/charge dependent A(f)s of mesons
and photons in SIDIS access a broad range of
interesting physics topics
transversity
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Azimuthal asymmetries in SIDIS at HERMES
Polarization/charge dependent A(f)s of mesons
and photons in SIDIS access a broad range of
interesting physics topics
transversity
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Azimuthal asymmetries in SIDIS at HERMES
Polarization/charge dependent A(f)s of mesons
and photons in SIDIS access a broad range of
interesting physics topics
transversity
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Proton Spin Structure in LO
3 PDFs complete description of the nucleon at
leading twist (integrated over quark kt )

• h1 - 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

transversity
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Transversity and Collins Asymmetries
SIDIS cross section for transversely polarized
target

• Transversity with chiral-odd Collins
  fragmentation function generate the Collins
  asymmetry 2ltsin(ffS)gtUT.
• Extraction process maximum likehood fit to the
  SIDIS data alternately in x, z, and ph-, but
  unbinned in f and fS.

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Collins Amplitudes for ps and Ks

• Moments for p K same - signal of dominance
  of u(x) fragmentation
• Moments for p- K- ? , but K- has no valence
  quarks in common with the target proton
• Difference in sign for p p- plausible if
  h1(x)?(x) since ?u(x) is positive and ?d(x)
  negative
• Large negative moment for p- a signal for H1fav
  -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 H1fav -H1unfav (Efremov et al.,
  PRD73, 094025, 2006)

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Also M. Anselimo, et al. arXiv0807.0173
L. Pappalardo at DIS2009
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The Sivers Effect companion to Collins
Asymmetries

• Sivers signature -azimuthal asymmetry
  2ltsin(f-fS)gtUT.
• 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- .
• 2ltsin(f-fSgt extracted with same maximum likehood
  fit to SIDIS data as Collins analysis.

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Sivers Amplitudes for ps and Ks

• Amplitudes gt0 increasing with zEh /h?
• u-quark dominance positive amplitudes implies
  large negative Sivers Function
• K gt p ?? sea quarks may contribute
• p - p- amp. gt0 asymmetries not due to ps from
  ?0 decay

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Distribution and fragmentation functions in SIDIS
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Cahn and Boer-Mulders Effects in SIDIS
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Cos(f) moment in unpolarized SIDIS
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Cos(2f) moment in unpolarized SIDIS
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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
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suppressed
JHEP06(2008)
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Charge dependence of DVCS
NEW
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Nuclear mass dependence of DVCS
No nuclear mass dependences of BSA and BCA within
uncertainties ?No enhancement of tDVCS Effects
predicted for J0,1/2 nuclei
NEW
H, He, N, Ne, Kr, Xe
Select for each target 2 samples (t cutoffs)
?coherent enriched (65 coherent fraction)
?incoherent enrich. (60 incoherent fraction)
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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