Imaging Sea Quarks and Gluons at an EIC Tanja Horn The 19 th Particles and Nuclei International Conference Cambridge, MA, 28 July 2011 (PANIC 2011) Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, Tanja Horn, CUA Colloquium 1 PANIC 2011, Cambridge, MA
Internal Landscape of the Nucleon • Hadrons in QCD are relativistic many-body systems – Fluctuating number of elementary quark and gluon constituents – Rich structure of the wave function • Components probed in ep scattering: Accessible range of energies and resolution, Q 2 , for – JLab 12 GeV: valence region probing components of the hadron wave function – EIC: probes sea quark and gluon components [Weiss 09] • Key physical interests – Transverse spatial distribution x – Correlations: transverse, longitudinal, and nuclear modifications – Tests of reaction mechanism non-pert. sea radiative valence quarks/gluons gluons/sea quarks/gluons Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, 2 PANIC 2011, Cambridge, MA
Nucleon Structure through Exclusive Processes e’ Q 2 >>R -2 • Exclusive processes at sufficiently high Q 2 e π , K, γ , etc. allow access to Generalized Parton Q 2 Distributions (GPDs) – Factorization theorem: non-perturbative physics factorizes from perturbative QCD processes for hard pointlike longitudinal photons GPD Δ T • N’ GPDs are a tool for transverse imaging of N the nucleon – Encode information on correlations and Transverse Fourier x- x’ distribution of partons in transverse space [Burkhardt 00] – Moments, Form factor of local twist-2 spin-n operators: EM tensor, angular momentum [Ji 96, Polyakov 02] • Tests of reaction mechanism – Model-independent features of small-size regime ξ =0 x< ξ – Finite-size corrections q q Transverse density correlations Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, 3 PANIC 2011, Cambridge, MA
Imaging Example: DVCS Interference with BH gives access to DVCS amplitude LT Im( DVCS ) ~ H ( x , ; t ) H ( x , ; t ) Re( DVCS ) ~ dx x t- dependence allows Fourier x=0.45 transform in ξ =0 limit H(x= ξ ,t)/F 1 (t) x=0.35 x=0.25 x b (fm) |t| (GeV 2 ) Projected results for GPD H( ξ ,x= ξ ,t) Transverse spatial image of proton obtained extracted from beam spin asymmetry by Fourier transforming the measured GPD Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, 4 PANIC 2011, Cambridge, MA
Transverse Imaging through GPDs at EIC Exclusive Reactions: * N M B pointlike? π , ρ , J/ Ψ , φ , long. only ρ , γ K, K* Δ T • Nucleon structure described by 4 GPDs: ~ E ~ J/ Ψ , φ – gluon H, E (unpolarized), , (polarized) H ρ º, γ gluon + singlet quark • Mesons select definite charge, spin, flavor component of GPD ρ + , K* non-singlet q π , K, η non-singlet Δ q • DVCS (flavor blind) probes GPD H and provides additional information on singlet quarks EIC enables a comprehensive program of Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, transverse imaging of gluons and sea quarks PANIC 2011, Cambridge, MA 5
Gluon Imaging with J/ Ψ • Transverse spatial distributions from exclusive J/ ψ , and φ at Q 2 >10 GeV 2 – Transverse distribution directly from Δ T dependence – Reaction mechanism, QCD description studied at HERA [H1, ZEUS] • Physics interest – Valence gluons, dynamical origin – Chiral dynamics at b~1/M π [ Strikman, Weiss 03/09, Miller 07 ] – Diffusion in QCD radiation • Existing data – Transverse area x<0.01 [HERA] – Larger x poorly known [FNAL] [Weiss INT10-3 report] Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, 6 PANIC 2011, Cambridge, MA
Gluon Imaging: Valence-like Gluons • Transverse imaging of valence-like valence-like gluons gluons through: * N J / N • Imaging requires – Full t-distribution for Fourier transform ~100 days, ε = 1.0, L =10 34 s -1 cm -2 – Non-exponential? Power-like at |t|>1 GeV 2 ? – Electroproduction with Q 2 >10 GeV 2 : test reaction mechanism, compare different channels, control systematics • Experimentally need: – Recoil detection for exclusivity, wide coverage in t with high resolution – Luminosity ~ 10 34 , electroproduction, 0< t <2 GeV 2 √ s~30 GeV Hyde, Weiss „09 First gluon images of the [Weiss INT10-3 report] nucleon at large x! Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, 7 PANIC 2011, Cambridge, MA
Singlet Quark Imaging with ~365 days, ε = 1.0, L =10 34 s -1 cm -2 DVCS d σ (ep→γ p)/dt (nb/sr) [Fazio 10+, INT report] • DVCS cross section and beam charge asymmetry allow accessing GPD H √ s~140 GeV – Additional information on singlet quarks t (GeV 2 ) ~100 days, ε = 0.5, L =10 34 s -1 cm -2 d d A LU = d + d √ s~140 GeV • DVCS beam spin asymmetry linked to imaginary part of Compton Form Factor H – Complementary to unpolarized cross sections and beam charge asymmetry – Using L and T target asymmetries can also 3<Q 2 <6 GeV 2 1.6E-3 < x B < 2.5E-3 access other GPDs [Geraud, Moutarde, Sabatie 10+, INT10-3 report] Measurements of DVCS with different combinations of beam and target polarizations over a wide kinematic range with high precision/luminosity Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, allows access to sea quark GPDs directly and indirectly to gluon GPDs 8 PANIC 2011, Cambridge, MA
Gluon vs. singlet quark size • Do singlet quarks and gluons have the same transverse distribution? – Hints from HERA: Area q q Area ( g ) – Dynamical models predict difference: pion cloud, constituent quark picture [Strikman, Weiss 09] – No difference assumed in present pp MC generators for LHC! ~30 days, ε = 1.0, L =10 34 s -1 cm -2 • EIC: gluon size from J/ ψ , singlet quark size from DVCS – x-dependence: quark vs. gluon diffusion in wave function – Detailed analysis: LO NLO [Mueller et al.] √ s=100 GeV Detailed differential image of nucleon‟s partonic structure [Sandacz, Hyde, Weiss 08+] Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, 9 PANIC 2011, Cambridge, MA
Imaging of non-singlet sea quarks ep → e' π + n • New territory for collider! • Do strange and non-strange sea quarks have the same spatial distribution? ep → e‘ K + n – π N or K Λ components in nucleon – QCD vacuum fluctuations ep → e'K + Λ ~100 days, ε = 1.0, L =10 34 s -1 cm -2 – Nucleon/meson structure √ s~30 GeV • Lower and more symmetric energies essential to ensure exclusivity – t -distributions, Fourier transform Imaging of strange sea quarks! Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, [Horn et al. 08+, INT10-3 report] 10 PANIC 2011, Cambridge, MA
Beyond transverse imaging • Longitudinal correlations in nucleon – GPDs at x’ ≠ x: correlated qqbar pairs in nucleon – QCD vacuum structure, relativistic nature of nucleon – EIC: reveal correlations through exclusive meson, γ at x>0.1 , Q 2 dependence • Orbital motion of quarks/gluons – Transverse spin asymmetry A UT in f , J/ Y production – Constrain gluon helicity flip GPD E g – Transverse Momentum Distributions (TMDs) and orbital motion from SIDIS – Imaging in momentum space, major component of EIC program – Connection with GPDs – Unintegrated distributions, Ji sum rule • L/T separated cross sections in non-perturbative regime (non-diff.) – Data taken at different beam energies (Rosenbluth) – Sufficiently large Δε (to control systematic uncertainty in the separation) Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 11 2011, Cambridge, MA
Transverse polarization example Transverse spin • Deformation of transverse distribution by transverse polarization of nucleon slower – Helicity flip GPD E, cf. Pauli ff x quarks move • EIC: exclusive ρ and φ production with faster transversely polarized beam – Excellent statistics at Q 2 >10 GeV 2 – Transverse polarization natural for collider Asymmetry x [Horn, Weiss 09] Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, 12 PANIC 2011, Cambridge, MA
Image the Transverse Momentum of the Quarks Swing to the left, swing to the right: A surprise of transverse-spin experiments [NSAC LRP07] The difference between the p + , p – , and K + asymmetries reveals that quarks and anti-quarks of different flavor are orbiting in different ways within the proton. d h ~ S e q 2 q(x) d f D f h (z) Sivers distribution Tanja Horn, Imaging Sea Quarks and Gluons at 13 an EIC, PANIC 2011, Cambridge, MA
EIC: π + projections with proton target ~30 days, ε = 0.5, L =10 34 s -1 cm -2 √ s~140 GeV √ s~50 GeV √ s~15 GeV [Huang 10+] Tanja Horn, Imaging Sea Quarks and Gluons at 14 an EIC, PANIC 2011, Cambridge, MA
Image the Transverse Momentum of the Quarks [Prokudin, Qian, Huang] Only a small subset of the (x,Q 2 ) landscape has been mapped here: terra incognita Gray band: present “knowledge” Red band: EIC (1 ) (dark gray band: EIC (2 )) [Prokudin] Exact k T distribution presently unknown! “Knowledge” of k T distribution at large k T is artificial! (but also perturbative calculable limit at large k T ) An EIC with good luminosity & high transverse polarization is the optimal tool to to study this! Tanja Horn, Imaging Sea Quarks and Gluons at 15 an EIC, PANIC 2011, Cambridge, MA
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