1. BoNuS: Radial-Drift TPC using Curved GEMs A Time Projection Chamber having Radial Drift Direction, based on GEMs which have been Curved to form cylinders. Howard Fenker a *, Jefferson Lab N. Baillie b, P. Bradshaw c, S. Bueltmann c, V. Burkhert a, M. Christy d, G. Dodge c, D. Dutta e, R. Ent a, J. Evans b, R. Fersch b, K. Giovanetti f, K. Griffioen b, M. Ispiryan g, C. Jayalath d, N. Kalantarians g, C. Keppel d, S. Kuhn c, G. Niculescu f, I. Niculescu f, S. Tkachenko c, V. Tvaskis d, J. Zhang c Graduate Student Undergraduate a Thomas Jefferson National Accelerator Facility (Jlab) b College of William and Mary c Old Dominion University d Hampton University e Tri-Universities Nuclear Lab (TUNL) f James Madison University g University of Houston * This work was partially supported by DOE Contract No. DE- AC05-84ER40150 under which the Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility (Jefferson Lab). Hall-C Collaborators indicated by bold type

3. Motivation PR-97-107 “LENT”

4. Motivation Purpose –Provide almost-free neutron target to improve our understanding of neutron structure.

5. Purpose –Neutron Structure-function measurements unencumbered by Final- State Interaction Effects BoNuS Experiment - Structure Functions Ratio F 2 n /F 2 p vs.x. The small data points indicate the expected results of the BONUS experiment for several different bins in Q 2 with statistical error bars. Estimated systematic errors due to experimental and theoretical uncertainties are indicated by the band at the bottom (total systematic error / point-to-point error after normalization at low x). Arrows indicate the different possible approaches to the limit x->1. The shaded area indicates the range of uncertainty from existing data due to different treatment of nuclear effects.

6. Method Measure slow protons –Identify spectator protons to tag e - d events in which the neutron was struck. n

7. Spectator Proton Characteristics –Angular distribution is isotropic. Backwards proton almost certain to be a spectator. –Momentum distribution favors low values. –Tracks are 20x - 50x minimum ionizing.

8. dE/dx is HIGH for slow protons Tells us two things: 1. Protons easy to identify 2. Detector must be thin

9. Tracking a low energy, heavily-ionizing particle requires a low-mass detector Time Projection Chamber (TPC) –Just a box of gas –Readout elements only on the surfaces. –Windows can be made thin. –Information density is high, but each channel of readout may need to record an entire waveform for several  s -- like having an oscilloscope per channel! CathodeAnodeReadout

10. BoNuS is just a curled-up TPC. For convenience, the gas-gain elements are GEMs.

11. GEM Readout http://gdd.web.cern.ch/GDD

12. Studies w/flat prototype Uses standard 10cm x 10cm GEMs. Drift region similar to planned final detector. Uses 3x 3M GEMs to allow tracking cosmics (min-I). At present, tests are performed using 80/20 Ar/CO 2.

13. Cosmic tracks easily recognized. Position resolution would be better with charge sharing over ≥3 pads. Gain ~ 30 3 Cosmic Studies w/flat prototype

15. Heavily Ionizing Protons from TUNL’s Tandem Proton Studies w/flat prototype

16. Curved GEM for Prototype

17. Curved prototype RTPC

18. Cosmic event from Curved GEM TPC

19. BoNuS RTPC: Exploded View

20. Inserting Pre-amp cards

21. BoNuS Readout Crate

22. What it really looks like

23. A Way to Mount Everything

24. Tracks are Pretty Obvious

25. Remember: we are working in 3D. That helps!

26. Results are Making Sense Vertex position agreement between CLAS and BoNuS: Angle measurements agree, too.

27. Measured dE/dx vs. P proton / deuteron / 3He / 4HeCurves: Bethe-Bloch Formula:

28. Particle ID via dE/dx After determining track momentum p, histogram the ratio: under the assumption that the particle was a proton.

29. NIM article to be submitted soon:

30. BoNuS Physics Analysis E beam = 4.223 GeV N. Baillie Recoil mass with and w/o using measured p s momentum.

31. Status of BoNuS Analysis model for σ n /σ D by P. Bosted

32. BoNuS: Next 6 GeV/c Experiment

33. BoNuS: 12 GeV/c Experiment

34. Conclusion Specialized spectator proton detector developed First use of GEMs at JLab First application of Curved GEMs Experiment Run More to come