1. Model independent extraction of neutron structure functions from deuterium data. Svyatoslav Tkachenko University of South Carolina

2. Structure functions and parton distribution functions

3. Structure Functions and Moments Precise PDFs at large x needed as input for LHC –Large x, medium Q 2 evolves to medium x, large Q 2 Moments can be directly compared with OPE (twist expansion), Lattice QCD and Sum Rules –All higher moments are weighted towards large x PDF uncertainties (CTEQ-JLab) From Accardi et al, arXiv.org:1102.3686v1

4. Structure Functions and Resonances Precise structure functions in Resonance Region constrain nucleon models [Separate resonant from non- resonant background; isospin decomposition] Needed as input for spin structure function data, radiative corrections,… Compare with DIS structure functions to test duality

5. To extract d/u ratio, we need neutron data. Extracting structure function ratio is model dependent and the results from the same data set might differ a lot depending on the model applied for analysis.

6. Large x - Large Nuclear Effects Even simple “Fermi Smearing” leads to significant dependence on D wave function Different models for off-shell and “EMC” effects lead to large additional variations Contributions from MEC,  (1232) and “exotic” degrees of freedom unknown FSI? Deuteron wave function model dependence R – ratio of deuteron and nucleon F 2 structure functions From Accardi et al, arXiv.org:1102.3686v1

7. Bound neutron… Free neutron…  How can we study free neutron structure without free neutrons available?  Emulate them with nuclear targets: –In 3 He, due to fortuitous cancellation of proton spins, we can study neutron spin structure. –If we can find observables that are mostly sensitive to the low-momentum part of the deuteron wave function, we can treat the nucleons as quasi-free and thus study neutrons.

8. Spectator tagging ( aka pinpointing the low-momentum part of the deuteron wave function )

9. Spectator Tagging * E = 4.223 GeV e p n = 1.19 (GeV/c) 2

10. “Rules” for the spectator. Final state interactions. The momentum and angular dependence of the ratio of spectral functions with and without FSI effects. Blue boxes mark preferred kinematics – regions where FSI have smaller effect. Ciofi degli Atti and Kopeliovich, Eur. Phys. J. A17(2003)133

11. “Rules” for the spectator. “ Off-shellness” depends on the spectator momentum magnitude. Ratio of the bound to free F 2 neutron structure functions vs spectator momentum. Model by W.Melnitchouk. Preferred kinematics denoted by blue box.

12. Rules for the spectator. Summary. Low momentum spectators P S < 100 MeV/c Minimize uncertainty due to the deuteron wave function and on-shell extrapolation. O (1%) correction. Backward kinematics θ qp > 110 o Minimize effects from FSI and target fragmentation. O (5%) correction.

13. Validation of the spectator tagging method (BoNuS experiment) Check angular dependence of effective (bound) structure functions in comparison with PWIA spectator model Check spectator momentum dependence of effective (bound) structure functions in comparison with PWIA spectator model

14. Low Spectator Momenta - Nearly Free Neutrons ? * BoNuS = Bound Nucleon Scattering ** RTPC = Radial Time Projection Chamber Radial TPC (view from downstream) e-e- backwards p TheExperiment BoNuS Region VIPs 0.07 0.2 GeV/c CLAS 20%

15. Bonus Radial Time Projection Chamber. (Detector system for slow protons)‏ Thin-walled gas target (7 atm., room temperature)‏ Radial Time Projection Chamber (RTPC) with Gaseous Electron Multipliers (GEMs)‏ 4 - 5 Tesla longitudinal magnetic field (to suppress Möller electrons and to measure momentum)‏ 3-dimensional readout of position and energy loss (“pads”)‏

16. Spectator momentum dependence (preliminary) Ratio to simulationEffective F 2 n Simulation uses PWIA spectator model, radiative effects, full model of RTPC and CLAS. P. Bosted and M.E. Christy F 2 n model is used. 78 MeV/c93 MeV/c 110 MeV/c135 MeV/c 78 MeV/c93 MeV/c 110 MeV/c135 MeV/c Backwards angles (cos θ pq < -0.2) data are shown

17. Angular dependence (preliminary) 78 MeV/c93 MeV/c 110 MeV/c135 MeV/c Q 2 = 1.66 (GeV/c) 2 W* = 1.73 GeV No significant deviations from PWIA (p s <100 MeV/c), first 2 panels Possible θ dependence at higher momenta

18. Extracted F 2 n (analyses comparison) (preliminary) ▼ - Analysis 1 ■ - Analysis 2 Simulation in PWIA spectator picture CTEQ-JLab band Systematic errors shown for analysis 1

19. Extracted F 2 n /F 2 p (N. Baillie)

20. Plans for 12 GeV BoNuS E12-06-113 Data taking of 35 days on D 2 and 5 days on H 2 with L = 2 · 10 34 cm -2 sec -1 Planned BoNuS detector DAQ and trigger upgrade DIS region with – Q 2 > 1 GeV 2 /c 2 – W *> 2 GeV – p s < 100 MeV/c –  pq > 110° Largest value for x* = 0.80 (bin centered x* = 0.76) Relaxed cut of W *> 1.8 GeV gives max. x* = 0.83 CLAS12 Central Detector

21. Conclusions Preliminary analysis does not contradict spectator model Technically different analyses of BoNuS data converge Analysis note review underway BoNuS12 proposal approved