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Theory Introduction to Semi-Inclusive Physics

Theory Introduction to Semi-Inclusive Physics. Jianwei Qiu Brookhaven National Laboratory. Jefferson Lab ( Jlab ) 2014 Joint Hall A/C Summer Meeting JLab , Newport News, VA, June 4-5, 2014. DIS vs. SIDIS. Inclusive DIS – one scattering plane:. Localized probe: .

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Theory Introduction to Semi-Inclusive Physics

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  1. Theory IntroductiontoSemi-InclusivePhysics Jianwei Qiu Brookhaven National Laboratory Jefferson Lab (Jlab) 2014 Joint Hall A/C Summer Meeting JLab, Newport News, VA, June 4-5, 2014

  2. DIS vs. SIDIS • Inclusive DIS – one scattering plane: • Localized probe: • Two independent variables:  E • Semi-inclusive DIS (SIDIS) – two scattering planes: E’ • Leptonic plane: • Hadronic plane: • Path of the color flow • Angle between two planes:

  3. Semi-inclusive DIS • Naturally, two scales: • high Q – localized probe • To “see” quarks and gluons • Low pT– sensitive to confining scale • To “see” their confined motion • Theory – QCD TMD factorization Confined motion • Spin-motion correlation: 4 spin combinations Needs 4 spin combinations Various TMDs: vector, axial vector, tensor

  4. TMDs – role of spin and motion • Rich quantum correlations: 8 leading power (twist) quark TMDs: Similar for gluons

  5. Quantum correlation between hadron and parton • Collins effect – between parton spin and hadronization: • Sivers effect – between hadron spin and parton motion: Siversfunction Collins function Observed particle Hadron spin influences parton’s transverse motion Parton’s transverse spin influence its hadronization Transversity o Observed particle JLab12, COMPASS, and low energy EIC for valence, EIC@US covers the sea and gluon!

  6. SIDIS – the best for probing TMDs • Naturally, two planes: • Separation of TMDs: Collins frag. Func. from e+e- collisions Very hard, if not impossible, to separate TMDs in hadronic collisions Using a combination of different observables (not the same observable): jet, identified hadron, photon, …

  7. QCD corrections • Sources of partonkT at the hard collision: Gluon shower Emerge of a hadron hadronization • Parton kT generated by the shower caused by the collision: Confined motion • Has very little to do with the kT in hadron wave function – hadron structure • At large Q2 and collision energy (large phase space), • the shower generated kT could be perturbative • Q2 – evolution of the cross section • “True” parton structure: • Input distribution for the Q2evolution - nonperturbative

  8. Factorization for SIDIS TMD fragmentation • Leading power contribution: Soft factors TMD parton distribution • Low PhT – TMD factorization: • High PhT – Collinear factorization: • PhT Integrated - Collinear factorization:

  9. Modified Universality of TMDs • TMD distributions with non-local gauge links: • Parity + Time-reversal invariance: The sign change is a critical test of TMD factorization approach

  10. Evolution of TMDs • Evolution in the b-space – Fourier transform of kT: • RG equations: Boer, 2001, 2009, Idilbi, et al, 2004 Aybat, Rogers, 2010 Kang, Xiao, Yuan, 2011 Aybat, Collins, Qiu, Rogers, 2011 Sun, Yuan, 2013 … • Evolution equations for Sivers function: CS: RGs:

  11. Numerical “prediction” for evolution • Aybat, Prokudin, Rogers, 2012: Huge Q dependence • Sun, Yuan, 2013: Smaller Q dependence No disagreement on evolution equations! Issue: extrapolation to non-perturbative large b-region choice of the Q-dependent “form factor” – more work needed!!!

  12. World effort on TMDs BNL FNAL JPARC electron pion positron pion EIC lepton lepton proton lepton proton pion proton antilepton SIDIS Drell-Yan BESIII Partonic scattering amplitude Fragmentation amplitude Distribution amplitude Test of the sign change! e–e+ to pions

  13. Transition from low pT to high pT • TMD factorization to collinear factorization: Two factorization are consistent in the overlap region where TMD Collinear Factorization • Quantum interference – high pT region (integrate over all kT): Single quark state quark-gluon composite state interfere with (Spin flip) Non-probabilistic quark-gluon quantum correlation Kang, Yuan, Zhou, 2010

  14. Twist-3 correlation functions Kang, Qiu, PRD, 2009 • Twist-2parton distributions: • UnpolarizedPDFs: • Polarized PDFs: • Two-sets Twist-3 correlation functions: Role of color magnetic force!

  15. Evolution of twist-3 correlation functions Kang, Qiu, 2009 • Closed set of evolution equations (spin-dependent): Plus two more equations for: and

  16. Sample scale dependence of twist-3 correlations Kang, Qiu, 2009 • Follow DGLAP at large x • Large deviation at low x (stronger correlation) Matching between low pT (resum) and high pT (fixed) Kang, Xiao, Yuan, 2011

  17. Single-spin asymmetry in hadronic collisions • Consistently observed for over 35 years! ANL – 4.9 GeV BNL – 6.6 GeV FNAL – 20 GeV BNL – 62.4 GeV BNL – 200 GeV • Definition:

  18. Do we understand it? Kane, Pumplin, Repko, PRL, 1978 • Early attempt: Cross section: 2 Asymmetry: Too small to explain available data! • QCD factorization at twist-3: Qiu and Sterman, NPB, 1991 Sivers - type Collins - type

  19. A sign “mismatch” if keeps only Sivers-type • Sivers function and twist-3 correlation: Kang, Qiu, Vogelsang, Yuan, 2011 + UVCT • “direct” and “indirect” twist-3 correlation functions: Calculate Tq,F(x,x) by using the measured Sivers functions indirect indirect direct direct Metz & Pitonyak, 2013 Important role of Collins’ effect to single pion production – twist-3 FFs SIDIS – separate two effects by difference in angular distribution

  20. Flavor structure of the proton sea • The proton sea is not SU(3) symmetric! Confirmed by Drell-Yan exp’t Violation of Gottfried sum rule Why ? Why does change sign?

  21. Challenges for d(x) – u(x) • All known models predict no sign change! Chiral-quark soliton model Meson cloud Statistic model • Future experiments: Fermilab E906 Very important non-perturbative physics What is the ratio as x increases?

  22. Asymmetry between strange and up/down sea? • LO and NLO QCD global fitting to DIS data: for x > 0.1 with • New LHC data on W/Z data: • HERMES data: Does not follow the shape of u(x) + d(x)? Why strange sea behave so different? Need FFs • PT-integrated SIDIS:

  23. Hadronization puzzle • Strong suppression of heavy flavors in AA collisions: • Emergence of hadrons: How do hadrons emerge from a created quark or gluon? How is the color of quark or gluon neutralized? • Need a femtometer detector or “scope”: Nucleus, a laboratory for QCD Evolution of partonic properties

  24. Nucleus as a “detector” The “vertex” detector At a fermi scale Nucleus in SIDIS is an ideal “vertex” detector Need a good control of the kinematics of fragmenting parton Almost impossible for a hadron machine

  25. Color neutralization – energy loss • Unprecedented νrange at EIC: D0 Control of ν and medium length! • Heavy quark energy loss: π semi-inclusive DIS • Mass dependence of fragmentation pion Need the collider energy of EIC for heavy flavors D0

  26. PT broadening of leading hadron in SIDIS • Definition:

  27. Color fluctuation – azimuthal asymmetry • Preliminary low energy data: Hicks, KEK-JPAC2013 Contain terms in cos(φpq) and cos(2φpq) only statistical uncertainties shown • Classical expectation: Any distribution seen in Carbon should be washed out in heavier nuclei • Surprise: Azimuthal asymmetry in transverse momentum broadening Spin-”orbital” correlation + soft multiple scattering Qiu & Pitonyak In preparation

  28. SIDIS’ role in probing the gluon saturation • Strong suppression of dihadron correlation in eA@EIC: Theory Simulation ϕ12 • Never been measured! • Directly probe Weizsacker-Williams (saturated) gluon distribution • in a large nucleus • A factor of 2 suppression of away-side hadron-correlation! • No-sat: Pythia + nPDF (EPS09)

  29. Summary • SIDIS in eP offers many more better controlled observables to probe QCD’s confining features and hadron’s partonic structure From 3D confined motion to quantum interference of different parton states Best channel for probing TMDs • SIDIS in eA collision is ideal for probing “hadronization”, • “color neutralization”, QCD energy loss, … • JLab12 is excellent for the valence region, while a future • EIC will cover the sea and gluon • A future EIC@US could help continue to keep the US’s leadership position in nuclear physics and … Thanks!

  30. Electron-Ion Collider (EIC) • A giant “Microscope” To “see” quarks and gluons • A sharpest “CT” To “cat-scan” nucleons and nuclei

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