Negative Ion TPC as the LC Main Tracker G. Bonvicini, Jan. 2003

1. Negative Ion TPCas the LC Main TrackerG. Bonvicini, Jan. 2003 • Overview • Early Simulations (by A. Schreiner) • Also in the collaboration J. Martoff and R. Ayad (Temple), D. Snowden-Ifft (Occidental)

2. What is a NITPC? • It is a TPC where the primary ionization and the avalanche are made of electrons, but the drift is done by negative ions • Uses any electronegative gas, with thermal electron capture and ion stripping (at high E) cross section of order 10^7 Barn, and appreciable gain • Three such gases are known: CS2, biacetyl and methylchloride • NI gas tubes first studied and operated in 1953

3. NITPC in modern times (post 1995) • Developed by J. Martoff and collaborators • DRIFT collaboration (1998-): 1m3 NITPC to study dark matter (seeks annual, daily, and directional signature of dark matter) (Boulby, UK) – a very robust detector • DRIFT-II proposed: 9m3 He/CS2 80/20 detector

4. Properties of the NITPC • Thermal diffusion at all E-fields: • Good gain (10^4 at 7700V) • Drift velocity approx. 20m/sec (at 1 kV/cm) drift • Negligible Lorentz angle allows radial, azimuthal drift • Properties conspire to allow “single electron detection” • Extreme photon and electron quenching

5. Motivation of the NITPC • Improve event information by detecting single electrons (F. Villa, NIM 217, 273,1983, J. Huth and D. Nygren, NIM 241, 375, 1985, G. Bonvicini, Hellaz Note 93-01) – momentum resolution, two-track separation, and tracking efficiency • Decrease material and cost through the use of novel detector planes • Keep alive the TPC option for the far future (E=1 TeV)

6. Simulations • In progress • One event is 1+GByte • GEANT4 crashes on events this big • We are writing an algorithm to reject background hits before tracking • Main tracker for TESLA discussed below • Temporarily, we have abandoned the axial and radial TPC and concentrated on the azimuthal TPC

8. NITPC for TESLA (Here are only 2% of background at Tesla) 5-section axial TPC 12-section azimuthal TPC read out planes do not produce background at all

9. regular TPC

10. TPC detector plane (azimuthal TPC) • A modified version of a Micromegas detector plane (Gorodetzky-Giomataris) • Blue pads are ganged NW-SE, white pads are ganged NE-SW (angle to wire is 60 degrees) • Hits are recorded as a triplet

11. TPC backgrounds (TESLA) • Incoherent noise backgrounds • Approximately 2X10^9 “wire pixels” due to long drift • Pulse height matching: 1) strip-strip; 2) wire-(s1+s2) (not done yet)

12. Backgrounds comparison vs regular TPC (TESLA) • A regular TPC will see 19 times less backgrounds at TESLA • Factor of 2 less hits in NITPC due to gas density • Factor 1.6 from linac veto • The rest (at least a factor 6) will have to come from higher B-field

13. Simulated wire occupancies (backgrounds = 6XNLC) Using Maruyama’s ntuples, FADC bucket = 100 nsec, no cuts)

14. background signal in background average strip occupancy is 11% radius [cm]

15. Momentum resolution comparison with reg. TPC (both large TPC, using Bruce Schumm’ s program, red=NITPC, blue=reg. TPC)

17. Space charge • An issue if a wire/strip detector plane is used • For gain = 10^4, n=3X10^7, V=100 kV, Delta(V)=17V • Some drift velocity saturation also helps

18. Conclusions • The NITPC niche: small, low cost, low material, very competitive momentum resolution and pattern recognition • Working point is relatively well defined • Early studies point to manageable backgrounds