1. Low energy underground experimentation with a TPC G
Low energy underground experimentation with a TPC G. Bonvicini, Wayne State University
The entire low energy underground scientific program can be covered optimally with gaseous TPCs.
Dark matter
Solar neutrinos
Double beta decay

2. Needs for each type of experiment (all need large mass)
Dark matter (20 keV): maximal point resolution, directionality
Solar neutrino ( keV): directionality, 0.1% systematic errors.
Double beta decay (2.5 MeV): energy resolution through single electron detection.

3. Dark matter
NITPC (invented by J. Martoff, D. Snowden-Ifft) provides ultimate (thermal) diffusion
DRIFT a successful low pressure first prototype
Needs to be coupled to microdetectors to fully exploit the low diffusion
Atm. Pressure desirable. Surprisingly, gain increases when adding helium

4. GEM and NITPC at atmospheric pressure (NIM A526,409, 2004 – see also physics/0406114)

5. KK axion Typical event (ma=2keV)
2l (k=500 eV, He/CS2 9/1)=0.42cm
2l (k=3000 eV, He/CS2 9/1)=5.5cm

6. Momentum resolution at the ILC with an azimuthal NITPC

7. The TPC as a solar neutrino detector
measures electron angle to degrees
Measures, subtracts all backgrounds
Measures neutrino energy to ~20% ( En > 200 keV)
Sensitivity to neutrino flavor through Te distribution, luminosity constraint, and (pp)/(pep) ratio
18000 events per year (LMA) for 61 Tons detector

8. LMA solution is bad for business

9. Very large Solar Neutrino TPC

10. How to build this TPC (NIM A491,402, 2002)
In fact much more similar to MUNU than to the original HELLAZ concept
The gas must be He/CH4 (radon, 14C - see hep-ex/ ).
He/CH4 has surprisingly high gain (LPC-96-31), exceeding 104
Single electron detection buys nothing
Can work at low depths (NIM 493, 90, 2002), 2500 mwe preferred
Polyethylene as structural material found to have several advantages (low el. resistance, transparency to helium, high thermal expansion, radiopure in bulk, no gaseous microsources)
Very low rates + polyethylene allow the usage of semi-resistive TPC

11. Solar neutrino TPC Physics Reach

12. 0.1% systematics in a solar neutrino TPC
Like an e+e- expt, the TPC has its own Bhabha events and K0 evts
107 evts/yr from cosmic rays with a d>100 keV. Te=2me cotg2q +O(M/E)
evts/yr from double-Compton. 5 d.o.f. in the event, with 8 variables measured. T1/pcosq1+T2/pcosq2=2 (exact)

13. Many uses of gold-plated background events
Calibration of TPC drift velocity, diffusion, gain
Calibration of triggering efficiency using 100keV/m dE/dx
Calibration of relative tracking efficiency from d Te distribution (ds/dTe=pa2/2meTe2)
Fn,d=Rn,d/Ntsn,d. One can then substitute to obtain
Fn= (Rn/ Rd) (sd/sn) Fm

14. Poor Weld Between Two Copper Plates

15. Double beta decay A TPC this large can fit a lot of Xenon
Energy resolution is crucial, and for Xenon (Fe)g=0.005(Fe)l (see E. Conti et al., hep-ex )
This is where single electron detection really matters
Low drift velocity, high diffusion, high gain, low noise all possible with Xenon
Simulations of 10/40/50 CH4/He/Xe in progress (with B. Koupparis). That corresponds to 104 Tons of Xenon

16. A Q=2512keV double electron event has a track length of 4 meters
For a 400ns sampling, the occupancy is <0.03.

17. “Traditional” backgrounds (M. K. Moe, M. A. Nelson, M. A. Vient, Progr
“Traditional” backgrounds (M.K. Moe, M. A. Nelson, M. A. Vient, Progr. Part. Nucl. Phys., 32, 247, 1994)
Gamma pairs (requires a magnetic field). Vastly improved due to low gas density
Moller scattering. Vastly improved due to low gas density
Delta ray at head. Vastly improved due to low gas density

18. Some preliminary results

19. Conclusions
All of the low energy underground program could be optimally covered with gaseous TPC
NITPC (dark matter) has good affinity with microdetectors and several potential applications
Very large TPC can be an optimal solar neutrino AND double beta detector.
For solar neutrinos the challenge is in the control of systematic errors,
for double beta decays it is in single electron detection.