Meziani final

Fundamental Structure of Hadrons: 

Fundamental Structure of Hadrons Zein-Eddine Meziani April 06, 2005 DOE Science Review for JLab 12 GeV Upgrade

The Science Problem ?: 

The Science Problem ? Quantum Chromodynamics (QCD) in the confinement regime: How does it work? What do we know? QCD works in the perturbative (weak) regime Many experimental tests led to this conclusion, example: Nucleon as a laboratory Proton is not pointlike (Nobel Prize: Hofstadter); Elastic electron scattering Quarks and gluons/Partons are the constituents; Deep Inelastic electron Scattering (Nobel prize: Friedman, Kendall and Taylor, 1991). Theory celebrated recently Asymptotic freedom (Nobel prize: Gross, Politzer and Wilczek, 2004). but Confinement in QCD is still a puzzle and among the 10 top problems in Physics! (Gross, Witten,.…) Strings 2000

Why Jlab 12 GeV?: 

Why Jlab 12 GeV? Transition from pQCD to Strong QCD needs data with high precision for a quantitative understanding of confinement What quantities do we measure? Nucleon structure functions: [System responds incoherently] Determine the helicity-dependent and -independent parton distributions at large x with flavor decomposition Determine higher moments of structure functions to compare to Lattice QCD Hadron form factors : pion, nucleon [System responds coherently]

Slide5: 

0 1 10 ∞ Q2 GDH Sum Rule IGDH (0) Generalized GDH Integral IGDH (Q2 ) Bjorken Sum Rule G1p-n Higher twists & color Polarizabilities d2(Q2) , f2 (Q2) Lattice QCD pQCD

Slide6: 

Unpolarized structure functions F1(x,Q2) and F2(x,Q2) Proton & neutron measurements provide d/u distributions ratio Polarized structure functions g1(x,Q2) and g2(x,Q2) Proton & neutron measurements combined with d/u provide the spin-flavor distributions Du/u & Dd/d Q2 :Four-momentum transfer x : Bjorken variable ∫ : Energy transfer M : Nucleon mass W : Final state hadrons mass L T U

12 GeV upgrade kinematical reach: 

12 GeV upgrade kinematical reach Access to very large x (x > 0.4) Clean region No strange sea effects No explicit hard gluons to be included Quark models can be a powerful tool to investigate the structure of the nucleon Comparison with lattice QCD is possible for higher moments of structure functions. n = 2,4,..

The tools: 

The tools A high duty cycle, high current, polarized 12 GeV electron beam A high luminosity Hall. A large acceptance Hall. Polarized targets

Slide9: 

Understand the nucleon structure in the valence quark region What is required? Complete knowledge of parton distribution functions (PDFs). Unpolarized, helicity-dependent Theoretically large x exposes valence quarks - free of sea effects x->1 behavior – sensitive test of spin-flavor symmetry breaking important for higher moments of PDFs - compare with lattice QCD intimately related with resonances, quark-hadron duality

Slide10: 

In the large x region (x>0.5) the ratio F2n/F2p is not well determined due to the lack of free neutron targets Impact: determine valence d quark momentum distribution extract helicity dependent quark distributions through inclusive DIS high x and Q2 background in high energy particle searches. construct moments of structure functions

Slide11: 

Mirror symmetry of A=3 nuclei Extract F2n/F2p from ratio of 3He/3H structure functions Super ratio R = ratio of ”EMC ratios” for 3He and 3H Calculated to within 1% Most systematic and theoretical uncertainties cancel Nearly free neutron target by tagging low-momentum proton from deuteron at backward angles Small p (70-100 MeV/c) Minimize on-shell extrapolation (neutron only 7 MeV off-shell) Backward angles (qpq> 110o) Minimize final state interactions Spectator tagging DIS from A=3 nuclei

Slide12: 

Unpolarized Neutron to Proton Ratio Hall C 11 GeV with HMS HallB 11 GeV with CLAS12

Slide13: 

Proton Neutron

Slide15: 

A1n at 11 GeV A1p at 11 GeV

Slide16: 

Spin-flavor decomposition of valence and sea quarks by tagging hadron (e.g. π, K) in current fragmentation region D(z) quark--> hadron fragmentation function unpolarized or polarized beam and target mass of unobserved X system, Wx > 2 GeV

Slide17: 

Berger criterion Dh>2 to avoid contamination from target fragmentation (z > 0.4) Factorization of current and target fragmentation ep -> e’ p+ X ( Ee =5.7 GeV, MX > 1.1)

Slide18: 

At RHIC with W production At JLab 12 GeV with SIDIS

Flavor decomposition (2): 

Flavor decomposition (2) Asymmetry measurements with different hadrons (p+,p-) and targets (p,n) allow flavor separation Ee =11 GeV NH3 and 3He

Slide20: 

First data from HERMES  0 Predictions: Instantons (QSM):

Quark-gluon correlations and g2: 

Quark-gluon correlations and g2

g2 at JLab with 11 GeV: 

g2 at JLab with 11 GeV

Color “Polarizabilities”: 

Color “Polarizabilities”

Slide24: 

Both d2 and f2 are required to determine the color polarizabilities To extract f2, d2 needs to be determined first. target mass correction term dynamical twist-3 matrix element dynamical twist-4 matrix element

d2 with 11 GeV at JLab : 

d2 with 11 GeV at JLab

Slide26: 

Nucleon Form Factors charge proton neutron magnetization

Proton Charge Form Factor @ 12GeV: 

Proton Charge Form Factor @ 12GeV Transverse quark momentum allows for a spin-flip amplitude, thus orbital momentum plays a role and ln-2(Q2/L2)Q2F2/F1  constant (Ji) Here shown as ratio of Pauli & Dirac Form Factors F2 and F1

Slide28: 

GEp with the 12 GeV upgrade

Charged Pion Electromagnetic Form Factor: 

Charged Pion Electromagnetic Form Factor HMS+SHMS (11 GeV) projection Where does the dynamics of the q-q interaction make a transition from the strong QCD (confinement) to the pQCD regime? It will occur earliest in the simplest systems the pion form factor Fp(Q2) provides a good starting system to determine the relevant distance scale experimentally In asymptotic region, F  8s ƒ  Q-2

Conclusion: 

Conclusion JLab at 12 GeV is a unique facility to determine the nucleon large x quark distributions. Semi-inclusive DIS will allow an unprecedented flavor decomposition for valence quarks at large x First quantitative insights into the effect of the color E and B fields in the nucleon structure by the measurement of d2 and f2. Proton charge/magnetic (coherent) response will be explored at very short distances. Charged Pion (coherent) response will be investigated to link our understanding to the pQCD regime. This program will have a clear and comprehensive impact on our understanding of QCD within the first 5 years