1. BONuS experiment. Svyatoslav Tkachenko University of Virginia for the CLAS collaboration

2. Structure functions and parton distribution functions

3. Structure Functions and Moments q up (x, Q 2 )‏ q down (x, Q 2 )‏ 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

4. 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. - Bjorken x

5. Bound neutron… Free neutron… How can we study free neutron structure without free neutrons available? Emulate them with nuclear targets: 3 He: due to fortuitous cancellation of proton spins, we can study neutron spin structure. D 2 : 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 neutron

6. Spectator tagging (aka pinpointing those observables)

7. Spectator tagging in a nutshell

8. “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

9. “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.

10. Deviations from free structure function: Off-shell Effects [should depend on  (p s ), x, Q 2 ] Modification of the off-shell scattering amplitude (Thomas, Melnitchouk et al.) Color delocalization Close et al. Suppression of “point-like configurations” Frankfurt, Strikman et al. p T = 0 939 MeV 905 MeV 823 MeV 694 MeV “Off-shell” mass of the nucleon M * P s = 0 0.09 0.17 0.25 0.32 0.39 GeV/c … plus 6-quark bags, , MEC… And of course FSI!

11. 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 ≥ 102 o Minimize effects from FSI and target fragmentation. O (5%) correction.

12. Checking if spectator tagging works (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. 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”)‏

15. e - reconstructed in CLAS & RTPC RTPC Performance   z  =8mm  =4º  =1.4º Out-of-time track suppression Gain constants for every channel (RTPC-Right on top) – red (blue) indicates “hotter” (“colder”) than average pads Particle ID (after gain calibration of each channel)

16. Tracks from the RTPC

17. Some results

18. Monte-Carlo (MC) and ratio methods. MC method:  Tagged and inclusive events simulated  Cross-normalized with data  Get experiment to model ratio Extract F 2 n,eff by multiplying the ratio of experiment to model by the model input Ratio method:  Form the ratio: tagged over inclusive (experimental)  Get F 2 n /F 2 d  Extract F 2 n,eff by multiplying the ratio by fit to F 2 d  Extract F 2 n /F 2 p by multiplying the ratio by fit to F 2 d /F 2 p

19. Spectator momentum dependence (MC method) 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. Backwards angles (cosθ pq < -0.2) data are shown 70-85 MeV/c85-100 MeV/c 100-120 MeV/c120-150 MeV/c

20. Angular dependence (MC method) Q 2 = 1.66 (GeV/c) 2 W* = 1.48 GeV Lowest momentum bin: flat distribution except for increase at forward angles Increased θ dependence at higher momenta 70-85 MeV/c 85-100 MeV/c 100-120 MeV/c 120-150 MeV/c

21. Extracted F 2 n /F 2 p (ratio method)

22. Extracted F 2 n (ratio method)

23. Extracted F 2 n (both methods) ▼ - MC method ◙ - ratio method ___ CJ band

24. BONuS6 paper output Howard C. Fenker et al. Nucl.Instrum.Meth.A592:273-286,2008. N.Baillie et al., PRL 108, 199902, 2012. S. Tkachenko et al., PRC 89, 045206, 2014. *More papers on: duality, deuteron EMC effect, pion production underway

25. Quark-Hadron duality Low-energy cross-section, when averaged over appropriate energy intervals, is found to exhibit the scaling behavior expected from perturbative QCD Truncated moments:

26. Quark-Hadron duality ` First: 1.3-1.9 GeV 2 Second: 1.9-2.5 GeV 2 Third: 2.5-3.1 GeV 2 Fourth: 1.3-4.0 GeV 2

27. Quark-Hadron duality First: 1.3-1.9 GeV 2 Second: 1.9-2.5 GeV 2 Third: 2.5-3.1 GeV 2 Fourth: 1.3-4.0 GeV 2

28. 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

29. Current state and outlook Tagging technique was tested Technically different analyses of BONuS data converged More physics output from BONuS6 coming R&D of different detector possibilities for BONuS12 underway Will be ready to run in about 2 years