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BoNuS: Radial-Drift TPC using Curved GEMs

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. Hall-C Collaborators indicated by bold type.

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BoNuS: Radial-Drift TPC using Curved GEMs

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  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 Fenkera*, Jefferson Lab Hall-C Collaborators indicated by bold type N. Baillieb, P. Bradshawc, S. Bueltmannc, V. Burkherta, M. Christyd, G. Dodgec, D. Duttae, R. Enta, J. Evansb, R. Ferschb, K. Giovanettif, K. Griffioenb, M. Ispiryang, C. Jayalathd, N. Kalantariansg, C. Keppeld, S. Kuhnc, G. Niculescuf, I. Niculescuf, S. Tkachenkoc, V. Tvaskisd, J. Zhangc 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 Graduate Student Undergraduate * 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).

  2. Motivation PR-97-107 “LENT”

  3. Motivation • Purpose • Provide almost-free neutron target to improve our understanding of neutron structure.

  4. BoNuS Experiment - Structure Functions • Purpose • Neutron Structure-function measurements unencumbered by Final-State Interaction Effects Ratio F2n/F2p vs.x. The small data points indicate the expected results of the BONUS experiment for several different bins in Q2 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.

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

  6. 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.

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

  8. 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. Cathode Anode Readout • 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!

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

  10. GEM Readout • http://gdd.web.cern.ch/GDD

  11. 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/CO2.

  12. Cosmic Studies w/flat prototype • Cosmic tracks easily recognized. • Position resolution would be better with charge sharing over ≥3 pads. • Gain ~ 303

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

  14. Curved GEM for Prototype

  15. Curved prototype RTPC

  16. Cosmic event from Curved GEM TPC

  17. BoNuS RTPC: Exploded View

  18. Inserting Pre-amp cards

  19. BoNuS Readout Crate

  20. What it really looks like

  21. A Way to Mount Everything

  22. Tracks are Pretty Obvious

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

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

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

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

  27. NIM article to be submitted soon:

  28. BoNuS Physics Analysis Recoil mass with and w/o using measured ps momentum. Ebeam = 4.223 GeV N. Baillie

  29. Status of BoNuS Analysis model for σn/σD by P. Bosted

  30. BoNuS: Next 6 GeV/c Experiment

  31. BoNuS: 12 GeV/c Experiment

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

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