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Kees de Jager Jefferson Lab Quarks in Hadrons and Nuclei Erice September 16-24, 2007

Thomas Jefferson National Accelerator Facility. Page 1. Recent Experimental Results from JLab Neutron Charge Form Factor Deeply Virtual Compton Scattering. Kees de Jager Jefferson Lab Quarks in Hadrons and Nuclei Erice September 16-24, 2007. Aerial View of CEBAF. Arc. Linac. Linac.

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Kees de Jager Jefferson Lab Quarks in Hadrons and Nuclei Erice September 16-24, 2007

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  1. Thomas Jefferson National Accelerator Facility Page 1 Recent Experimental Results from JLab Neutron Charge Form Factor Deeply Virtual Compton Scattering Kees de Jager Jefferson Lab Quarks in Hadrons and Nuclei Erice September 16-24, 2007

  2. Aerial View of CEBAF Arc Linac Linac Arc 3 End Stations

  3. 6 GeV CEBAF

  4. CEBAF Actual Parameters • Primary Beam: Electrons • Beam Energy: 6 GeV • 10 >  > 0.1 fmnucleon  quark transitionbaryon and meson excited states • 100% Duty Factor (CW) Beam • coincidence experiments  excite system with a known (q,) and observe its evolution • Three Simultaneous Beams with Independently Variable Energy and Intensity • complementary, long experiments • Polarization (85% beam (!) and reaction products) • spin degrees of freedomweak neutral currents (extremely small helicity-correlated changes)  > 106 X SLAC at the time of the original DIS experiments

  5. Hall A: Two High Resolution (10-4) Spectrometers Maximum luminosity 1038 cm-2s-1

  6. Hall B: The CEBAF Large Acceptance Spectrometer (CLAS) Maximum luminosity 1034 cm-2s-1

  7. Hall C: A High Momentum and a Broad Range Spectrometer Set-up Space for Unique Experiments

  8. Upgrade magnets and power supplies CHL-2 Enhance equipment in existing halls Add new hall 12 11 6 GeV CEBAF

  9. 12 GeV Upgrade: Schedule • (based on funding guidance provided by DOE-NP in July 2007) • 2004-2005 Conceptual Design (CDR) - finished • 2004-2008 Research and Development (R&D) - ongoing • 2006 Advanced Conceptual Design (ACD) - finished • 2006-2008 Project Engineering & Design (PED) - ongoing • 2009-2014 Construction – starts in 13 months! • Accelerator shutdown starts mid 2012 • (end of 6 GeV research) • Accelerator commissioning mid 2013 • 2013-2015 Pre-Ops (beam commissioning) • Hall commissioning (and first experiments) starts late 2013

  10. Many High Impact (Unpublished) Results from JLab • The Structure of the Nuclear Building Blocks • Elastic Scattering (nucleon form factors) G0 completed and GEn analysis progressing well • Parton Distribution Functions BoNuS will provide our first clean measurements of neutron PDFs • Deeply Virtual Compton Scattering Major progress in analysis and understanding of the first dedicated experiments • Medium Modification / Medium Effects New data on proton GE/GM in medium Color transparency seen in rho production • N* Physics polarized photon data set taken, FROST target ready for next experiments • The Structure of Nuclei • N-N Correlations Quantified N-N and 3N correlations via (e,e’pN) triple coincidence expts. • Symmetry Tests in Nuclear Physics • PRIMEx Result released for two photon decay width for neutral pion Grabmayr Lhuillier Guidal Rosner

  11. The Structure of the Neutron D H Studying the structure of the neutron has been complicated by the lack of a free Neutron target Inclusive electron scattering off hydrogen and deuterium Q2=1.5 GeV2 Neutron structure inferred from the (d-p) difference (with corrections for Fermi motion, binding, etc….)

  12. BoNuS access to Nearly Free Neutrons in Deuterons e- + n + (ps) →e- + ps+X Detected in CLAS Detected in BoNuS Technique: Measure spectator proton down to 70 MeV/c in RTPC, and reconstruct initial neutron momentum dE/dx from charge along track (particle ID) Difference of vertices

  13. CLAS/BoNuS Inclusive mass spectrum before and after corrections for the initial neutron momentum, inferred from the proton spectator kinematics. The “elastic” en → en peak and the 1st and 2nd resonance regions show up clearly only after inclusion of the corrected neutron kinematics. Spectrum corrected for neutron initial momentum & 4He contamination Tagged electron spectrum before corrections

  14. Polarization Transfer in Inner uncertainties are statistical only; full analysis of E03-104 will have reduced systematic uncertainties • Previous data effectively described by proton medium modified form factors • Alternative explanation given by adding spin-dependent charge-exchangeFSI that suppresses “super-ratio” R by about 6% • New data will set tight constraints, and possibly hint at an unexpected trend

  15. Induced Polarization in • Pyis a measure of final-state interactions • Observed final-state interactions are small • RDWIA results consistent with data • Spin-dependent charge-exchange terms not constrained by N-N scattering and possibly overestimated • E03-104 took specific data that will set tight constraints on FSI Inner uncertainties are statistical only; full analysis of E03-104 will have reduced systematic uncertainties

  16. Color Transparency CT refers to the vanishing of the hadron-nucleon interaction for a hadron produced in exclusive processes at high Q2 • At high Q2, the hadron involved fluctuates to a small transverse size – called the point-like configuration (PLC) • The PLC experiences a reduced interaction with the nucleus – it is color screened • The PLC remains small as it propagates out of the nucleus • So far, no hint of CT in (e,e’p) reactions

  17. Color Transparency Identified in production propagating quark gluons quarks in nuclei L nucleus CLAS: eg2 No change w/ Lcoh @ fixed Q2 TFe Lcoh (fm) T changes w/ Q2 @ fixed Lcoh Coherence length Lcoh~ formation time of a gluon radiated by a group of scattering centers

  18. PrimEx : Preliminary Result • PrimEx Preliminary Result: (0) = 7.93 eV2.1%(stat) 2.0%(sys) • andlifetime:(8.20±0.24)x10-17s • PDG average: • (8.4±0.6)x10-17 s (0) = 7.93eV2.1%2.0%

  19. Hypernuclear Spectra Emerging from Halls A and C Hall C HKS Hall A HRS & Septum p3/2 s1/2 Preliminary s(Core Ex.) Preliminary Published Resolution now ~460 keV (reached experiment goal) Preliminary Preliminary Nearly Final

  20. 2-N and 3-N SRC in Inclusive Electron Scattering 2N-SRC   4o 1.f 1.7f o = 0.17 GeV/fermi3 Nucleons Nuclear momentum distributions Can the correlations be seen directly in (e,e’pN)? SRC dominance At any moment, the number of 2-nucleon SRC are 0.3, 1.2 and 6.7 in 4He, 12C and 56Fe, respectively Analysis shows that 3-N SRC are 10 times smaller than 2-N SRC

  21. Ratio of (pp) to (pn) pairs in 12C Scattered Electron Incident Electron E01-015 Triple coincident hadron knock-out (e,e’pn) and (e,e’pp) from 12C Scattered Proton Correlated Partner Proton or Neutron First Experiment To Use BigBite Spectrometer and Neutron Detector In Hall A

  22. Summary of SRC findings in 12C Preliminary E07-006 (e,e’pp) Result PRL 99, 072501 (2007) (e,e’pn) Result Being Prepared For Publication

  23. High Q2 GEn • Since 1984, when Blankleider&Woloshin suggested , several experiments of this type have been performed at NIKHEF and Mainz for Q2 up to 0.7 GeV2, with large success in part duenew accurate3-body calculations at low Q2 (Gloeckle et al.) • At Q2above 1-2 GeV2 Glauber method becomes sufficiently accurate (Sarksian) • Electron-polarized neutron luminosity and high polarization of 3He target made measurement about 10 times more effective than with ND3. In combination with a large acceptance electron spectrometer the total enhancement is more than 100, which allows to reach 3.5 GeV2 • Polarized target • Electron spectrometer • Neutron detector

  24. Exclusive QE scattering: 3He(e,e′n) 7 Iron/scintillator sandwich planes Q2 = 1.3, 1.7, 2.5, 3.5 GeV2 n Target polarization ~50% Beam polarization 84% 2 veto planes e e′

  25. Polarized target 3He = p + p + n S + S’ + P waves Pn = 0.86 PHe Laser light Pumping chamber PHe of 50% with 8 A beam Beam Scattered electron Rb + K mixture has shortened spin-up time to 5-8 hours. Hybrid method used for the first time in actual target. Target chamber Recoiled neutron

  26. Electron Spectrometer BigBite Useful Q2/Q2~ 0.1 and max  leads to a large aspect ratio, limited just of 30o for the polar. target. BigBite was designed at NIKHEF for aspect ratio  = 1/5. Spectrometer hassolid angle up to 95 msr. At luminosity of polarized target, 1037cm-2/s, the open geometry - a dipole spectrometer -works well with all MWDCs located behind the magnet.

  27. Neutron Detector • Match BigBite solidangleto QE kinematics • Flight distance ~ 10 m • Operation at 3.1037 cm2/s • 1.6 x 5 m2 active area • 0.38 ns time resolution • Active layers: • 2 thin “veto” planes (200 bars) • 7 planes of scintillator (~250 bars) • Shielding/Conversion material: • 2” Pb + 1” Fe before veto planes • 1” before each detector plane • Shielding necessary to reduce background • rate on the veto planes, but causes the • complication of p↔n conversion....

  28. Data analysis: BigHand and BigBite Kin #4: Q2=1.7 GeV2 • σBH~ <400 ps timing resolution achieved • σp/p ~ 0.8% for BigBite protons Neutral hits Charged hits pions

  29. Data analysis Asymmetry then corrected for p-n identification A|| contribution FSI for e,e’n process Target, beam polarizations Selection of QE (e,e’n) events

  30. Proton↔Neutron conversion... • Observed number of protons and neutrons is a product of detection efficiencies, conversion probabilities, and initial fluxes. Study through simulation (Geant4) and data analysis. • Use nuclear targets with different initial ratios of neutrons and protons (H, 3He, N2 and 12C). • Ratio of neutrons to protons is complicated by the electronic dead time, that introduces a rate dependence to the ratio.

  31. Contributions to GEn at 1.7 GeV2 Expect final systematic uncertainty < 15%

  32. First physics result from Hall A GEn • Result is well above Galster • Nuclear corrections include neutron polarization and estimate (5%) of Glauber • Present error (∼20%) dominated by preliminary “neutron dilution factor”, and is expected to be ∼7% stat. and 8% syst. with further analysis • 3.4 GeV2 result to be released in October DNP meeting at Newport News

  33. GEP-15: GEp/GMp up to 15 GeV2 Perdrisat, Pentchev, Cisbani, Punjabi, BW Beam: 75 A, 85% polarization Target is 40 cm liquid H2 Electron arm at 37o, covers Q2 = 12.5 to 16 GeV2 Proton arm at 14o,  ~ 35 msr 58 days of production time resulting accuracy: approved by PAC32 for 12 GeV program

  34. GEP-15: Projected accuracy Plan for GEP-15

  35. Perspective: GEn up to 7 GeV2 The plan for GEN-7 is: • Beam at 8.8 GeV • Resolution p/p for electron - BNL magnet, GEM • He-3 cell in vacuum, lower background in neutron arm • Hybrid He-3 cell with narrow pumping laser line Electron 3He Neutron Proton GEn at 7 GeV2 with uncertainty 15% of Miller’s value in 30-day run

  36. Deeply Virtual Compton Scattering(DVCS) hard vertices Simplest reaction to study GPDs x – quark momentum fraction  – longitudinal momentum transfer √–t – Fourier conjugate to transverse impact parameter “handbag” mechanism Flavor separation through Deeply Virtual Meson Production

  37. Experimental observables linked to GPDs Experimentally, DVCS is indistinguishable from Bethe-Heitler However, since we know the EMFF at low t, theBH process is exactly calculable Using a polarized beam on an unpolarized target, 2 observables can be measured: At JLab energies, |TDVCS|2 is supposed to be small, but…. Kroll, Guichon, Diehl, Pire, …

  38. hadronic plane   e-’ * e- p leptonic plane The harmonic structure of DVCS |TBH|2 twist-2 Interference term BH propagators dependence Belitsky, Mueller, Kirchner

  39. DVCS in Hall A (E00-110 and E03-106) • 75% polarized 2.5 µA electron beam • 15 cm LH2 target -> L = 1037 cm-2s-1 • Left Hall A HRS with electron package • 11x12 blocks PbF2 electromagnetic calorimeter • 5x20 blocks plastic scintillator array • Digital sampling of PMT signals at 1 GHz • Clear DVCS identification from HRS+calo Clermont-Ferrand, Saclay, Grenoble, ODU, Rutgers

  40. Difference of cross sections PRL97, 262002 (2006) Im(CII)∝ s1I Twist-2 Im(CII)∝ s2ITwist-3 Extracted twist-3 contribution small ! Corrected for real+virtual RadCor Corrected for efficiency Corrected for acceptance Corrected for resolution effects Checked elastic cross section @ ~1% New work by P. Guichon

  41. Total cross section PRL97, 262002 (2006) Again, extracted twist-3 contribution small ! Corrected for real+virtual RC Corrected for efficiency Corrected for acceptance Corrected for resolution effects BH*DVCS + DVCS2 is large, comparable to BH2

  42. Q2 dependence and test of scaling Twist-2 Twist-3 No Q2 dependence: strong indication for scaling behavior and handbag dominance Cross-section coefficients much larger than VGG

  43. VGG Code GPD model : LO/Regge/D-term=0 Goeke et al., Prog. Part. Nucl. Phys 47 (2001), 401. DVCS on the neutron in JLab/Hall A: E03-106 MODEL-DEPENDENT Ju-Jd extraction LD2 target 24000 fb-1 xB=0.36, Q2=1.9 GeV2 Follow-up experiment in Hall A (to be proposed to PAC-33) will reduce experimental error significantly (larger xB-range)

  44. Next Hall A DVCS experiment : E07-007 Measure the total DVCS cross section at fixed xB = 0.36 for three Q2-values - 2.3, 1.9 and 1.5 GeV2- at two beam energies with improved πo subtraction in order to separate the DVCS2 term test scaling of the unpolarized cross section separate the five response functions of deep πo production

  45. DVCS@CLAS – a dedicated experiment Superconducting solenoid Saclay Beam energy: ~5.8 GeV Beam Polarization: 75-85% Integ. Luminosity: 45 fb-1 ITEP Orsay Saclay Inner calorimeter (PbWO4) 424 crystals, 16 mm long, pointing geometry, ~ 1 degree/crystal, APD readout

  46. <-t> = 0.18 GeV2 <-t> = 0.30 GeV2 <-t> = 0.49 GeV2 <-t> = 0.76 GeV2 Asymmetry as a function of xB and Q2 Accurate data in a large kinematical domain Integrated over t

  47. Asymmetry as a function of |t| First constraints for a global fit of GPDs over a wide kinematic domain Slope dα/dt decreases with xB/Q2 As yet, no direct comparison with Hall A data possible VGG model does not describe data well

  48. Summary Presented overview of recent results from JLab, not covered in other talks More details given for GEn to higher Q2 and DVCS at high luminosity First preliminary datum for GEn indicates that GEn indeed drops off slower than ancient Galster parametrization, possibly in agreement with similar scaling as GEp Results of the first dedicated DVCS experiment in Hall A have indicated that factorization (handbag dominance) is applicable at Q2 ≈ 2 GeV2 the DVCS2 term is much larger than previously assumed and provided a model-dependent estimate of the quark angular momenta

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