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The Search for Color Transparency @ 12 GeV

The Search for Color Transparency @ 12 GeV. Dipangkar Dutta Duke University / TUNL. May 19, 2006. Color Transparency. CT refers to the vanishing of the h-N interaction for h produced in exclusive processes at high Q. Original concept of CT introduced by Mueller and Brodsky in 1982.

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The Search for Color Transparency @ 12 GeV

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  1. The Search for Color Transparency@ 12 GeV Dipangkar Dutta Duke University / TUNL May 19, 2006

  2. Color Transparency CT refers to the vanishing of the h-N interaction for h produced in exclusive processes at high Q Original concept of CT introduced by Mueller and Brodsky in 1982 • At high Q , the hadron involved fluctuates to a small transverse size – called the PLC (quantum mechanics) • The PLC remains small as it propagates out of the nucleus (relativity). • The PLC experiences reduced attenuation in the nucleus – it is color screened ( nature of the strong force). A.H.Mueller in Proc. of 17th recontre de Moriond, Moriond, p13 (1982) S.J.Brodsky in Proc. of 13th intl. Symposium on Multiparticle Dynamics, p963 (1982)

  3. in other words it still remains to be answered Does QCD matter in the “real” world? Why? Three decades and a Nobel prize after the development of QCD; understanding nucleons & nuclei in terms of quarks and gluons is still one of the important unsolved problem of the Standard Model of nuclear and particle physics. Look for clues in the parton-hadron transition

  4. Exclusive Processes Nuclei Nucleons • Quark counting rules • Hadron helicity conservation • Color transparency • Nuclear filtering The Parton-Hadron Transition Exclusive processescan be used to look for signatures for the transition from quark-gluon degrees of freedom of QCD to the nucleon-meson effective degrees of freedom. CT is totally unexpected in a strongly interacting hadronic picture. But it is quite natural in a quark-gluon framework. It is very good indicator of a transition from hadron to quark dof.

  5. Correlated quark momentum and helicity distributions in transverse space - GPDs Generalized Parton Distribution GPDs allow simultaneous determination of longitudinal momentum and transverse position of partons, they correlate different partonic configurations in the hadron Proton form factors, transverse charge & current densities Structure functions, quark longitudinal momentum & helicity distributions

  6. Connecting GPDs & CT Recent theoretical work identifies connections between GPDs and CT. M. Burkardt and G. Miller (hep-ph/0312190) have derive the effective size of a hadron in terms of GPD’s:The existence of color transparency would place constraints on the analytic behavior and would provide testable predictions for GPD’sS. Liuti and S. K. Taneja (PRD 70,07419 (2004)) have explored structure of GPD in impact parameter space to determine characteristics of small transverse-separation componentsNuclei can be used as filters to map the transverse components of hadron wave function: i.e.a new source of information on GPD’s

  7. Factorization in deep-exclusive meson production Meson distribution amplitude Hard amplitude, calculable in pQCD GPDs Factorization is not rigorously possible without the onset of CT. - Strikman, Frankfurt, Miller and Sargsian CT & Factorization Factorization theorems have been derived for deep-exclusive processes and are essential for the access to GPDs. It is still uncertain at what Q2 value reaches the factorization regime

  8. Past Color Transparency Searches CT refers to the vanishing of the h-N interaction for h produced in exclusive processes at high Q + h can be : qq system (e e in QED) qqq system (unique to QCD) • Color Transparency inA(p,2p) BNL • Color Transparency inA(e,e’ p) SLAC,JLab • Color Transparency inA(l,l’ r) FNAL,HERMES,JLab • Color Transparency in di-jet production FNAL • Color Transparency inA(g,p p), A(e,e’ p)JLab

  9. Transparency in A(p,2p) Reaction First experiment to look for color transparency Glauber calculation Results inconsistent with CT but explained in terms of nuclear filtering or charm resonance states.

  10. Constant value fit for Q2> 2 (GeV/c)2 has c2 /df @ 1 A(e,e’p) Results Q2 dependence consistent with standard nuclear physics calculations Solid Pts – JLab Open Pts -- other N. C. R. Makins et al. PRL 72, 1986 (1994) G. Garino et al. PRC 45, 780 (1992) D. Abbott et al. PRL 80, 5072 (1998) K. Garrow et al. PRC 66, 044613 (2002)

  11. qqq vs qq systems • There is no unambiguous, model independent, evidence for CT in qqq systems. • Small size is more probable in 2 quark system such as pions than in protons. • Onset of CT expected at lower Q2 in qq system. • Formation length is ~ 10 fm at moderate Q2 in qq system. - B. Blattel et al., PRL 70, 896 (1993)

  12. diffractive dissociation cross-section fit to: • > 0.76 unlike the pion-nucleus total cross-section. s = s0Aa A(p, dijet) Data from FNAL Coherentp+diffractive dissociation with 500 GeV/c pions on Pt and C. p + A  (2 jets) + A’ Aitala et al., PRL 86 4773 (2001)

  13. Pion-photoproduction Hall A Experiment E94-104 700 pion C.M. angle 900 pion C.M. angle D. Dutta et al. PRC 68, 021001R (2003) H. Gao et al. PRC 54, 2779 (1996)

  14. The A(e,e’p) Reaction 12C e + A  e + p + X 56Fe 197Au These predictions are consistent with existing data and independent calculations of: G. Miller et al. B. Kundu et al. PRD 62, 113009 (2000) • Two different quark distributions predict effects > 40 % at • Q2 between 1 – 5 (GeV/c)2 for Gold nucleus. JLab Experiment E01-107: A(e,e’ p) on H, D, C, Cu, Au Spokespersons: Thesis Student: D. Dutta, R. Ent & K. Garrow Ben Clasie (MIT)

  15. Preliminary Results Systematic uncertainty Model dependent uncertainty Several reaction mechanism related issues need to be addressed in the model used here. analysis in progress by Ben Clasie (MIT)

  16. Future Experiments A detailed study of the parton-hadron transition region is an essential part of the planned upgrade of JLab to 12 GeV. …understanding the mechanisms at work in this transition region is of primary importance to our understanding of the rich variety and structure and phases that emerge out of QCD….. -Science Review of the proposed 12 GeV upgrade A thorough search for an unambiguous evidence for CT is an important part of the physics driving the 12 GeV upgrade.

  17. A(e,e’p) at 12 GeV A(e,e’p) on 1H and 12C with 8.8 and 11.0 GeV beam Q2 range covered 8.0 – 16.0 (18.0) (GeV/c)2 Targets: 4.2 cm (0.5%) liq. 1H and 2.5% solid 12C HMS: electron arm, Pe ~ 1.4 – 4.5 GeV/c qe ~ 25.9 – 65.3 deg PID e-/p- separation upto 4.5 GeV/c SHMS: hadron arm, Pp~ 5.1 – 10.5 GeV/c qp~ 7.0 – 22.7 deg PID p/p+/K+ separation upto 10.5 GeV/c Proton K.E. – 4.3 – 9.6 GeV

  18. PID in SHMS and HMS

  19. A(e,e’p) at 12 GeV Kinematics Table

  20. A(e,e’p) at 12 GeV Rates (50 mA on 1H and 90mA on 12C) 12C(e,e’p) S/N ~ 0.5 – 0.2 (for 0.5 ns coincidence time resoln.)

  21. 275 hrs (1H + 12C ) 360 hrs A(e,e’p) at 12 GeV Projected Results With HMS and SHMS @ 12 GeV

  22. A(e,e’p) at 12 GeV A(e,e’p) on 1H,2H and 12C with 8.8 beam Q2 range covered 5.0 – 9.5 (11.0) (GeV/c)2 Targets: 4.2 cm (0.5%) liq. 1H, 2H and 2.5% solid 12C HMS: electron arm, Pe ~ 1.8 – 4.2 GeV/c qe ~ 21.3 – 46.0 deg PID e-/p- separation upto 4.2 GeV/c SHMS: hadron arm, Pp~ 4.3 – 6.3 GeV/c qp~ 9.5 – 17.1 deg PID p/p+/K+ separation upto 6.3 GeV/c W fixed at 2.14 GeV, |t| 0.72-1.8 GeV2, kp0.9 –1.9 GeV

  23. A(e,e’p) at 12 GeV Kinematics Table

  24. A(e,e’p) at 12 GeV Rates (50 mA on 1H, 2H and 90mA on 12C) 12C(e,e’ p)

  25. Pion electroproduction @ 12 GeV Projected Results 235 hrs (1H,2H & 12C )

  26. Summary • Exclusive processes are crucial in studying the • transition from the nucleon-meson to the quark-gluon • picture. • By comparing exclusive processes on both nucleons • and nuclei, one of the signatures of this transition – • namely color transparency can be studied. • - Recent theoretical work identifies connections between • GPDs and CT. • Proton transparency data can be well described • by conventional nuclear physics. • Meson production data from JLab show hints of • QCD dynamics and provide some useful clues about • the transition region.

  27. With the proposed upgrade of JLab to 12 GeV along with the results obtained at 6 GeV we should be able to make significant progress in identifying the energy threshold for the transition from quarks to nuclei. Summary

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