1. MDT second coordinate readout: status and perspectives
Yuri Davydov
JINR, Dubna
XXXI PANDA Collaboration meeting
GSI, December 2009

2. Two types of MDTs “Closed geometry” Al profile: 0.6 mm thick
Cover: 0.15mm thick S.S.
Wire: 50 μm W(Au)
Envelop: Noryl
“Open geometry”
Al profile: 0.6 mm thick
Wire: 50 μm W(Au)
Envelop: Noryl
Strips: 1 cm wide, 10cm long
The same tube was used for the test measurements for closed geometry and open geometry (S.S. cover was removed).
Tube length is about 60 cm. Gas mixture: 70%Ar+30%CO2

3. Anode and strip induced signals
Signal induced on the single strip is about 10% of that on the wire
Two preamps AMPL-8.3 were used to detect a strip signal
Trace 1: Anode signal,
K≈60 mV/μA
Trace 2: Strip signal,
inverted, K≈480 mV/μA

4. Counting rate and efficiency
Cosmics, threshold 2 μA
Difference between closed and open geometry is ~80 V

5. Counting rates of an open geometry MDT
with a 60Co source
Thresholds: 1.0 μA, 1.5 μA, 2.0 μA
Counting rate with 60Co at threshold 2.0 μA is close to that for cosmics at the same threshold: similar initial ionizations in the chamber gas.
Could be used for tests during MDT construction, assembly and, possibly, operation

6. Amplitude and time spectra
Open geometry U=2300 V
The time spectra are similar for closed geometry at 2200 V and open geometry at 2300 V

7. Spectra from 55Fe x-rays Closed geometry Open geometry 2200 V 2300 V
Full photo absorption peaks correspond to energy 5.9 keV and allow to estimate a gas gain in the MDTs

8. Gas gain
One needs to apply about 100 V more to the open geometry MDT in order to get the same gas gain

9. The block diagram of the test setup for spatial accuracy study
Sc 1, Sc 2: 100•20•100 мм3
4 strips 1 cm wide 10 cm long on each MDT
AMPL-8.3 preamplifier
LeCroy 2249A ADC
gate 1000 ns

10. Typical individual strip spectra from MDT
Scintillator counters selected particles mostly crossing two central strips

11. Anode and induced signals on four MDTs
Wires
Strips (sum of 4 strips)
MDT 1
MDT 2
MDT 1
MDT 2
MDT 3
MDT 4
MDT 3
MDT 4

12. Wire-strip signals correlation
Sum of 4 strips
Strip signal, μA
QS /QA = 21.6±1.1 %
Anode signal, μA

13. Track reconstruction with strip signals
Signal is defined on each strip
For each MDT a charge distribution is fitted by Gaussian in order to calculate center of gravity
Track is reconstructed by linear fit using 4 points
Residuals are calculated

14. MDT spatial accuracy of the strip readout
1 cm wide, 10 cm long strips
4 MDT layers
near vertical tracks
Achieved a spatial accuracy:
σ~0.4 мм
Much better than PANDA requirements – there is a real room for optimization of a number of channels!

15. The test results are published as JINR preprints and submitted to a referred journal:
V.M. Abazov, G.D. Alexeev, Yu.I. Davydov, V.L. Malyshev,
A.A. Piskun, V.V. Tokmenin
1. A performance comparison of mini-drift tubes with a different design
JINR preprint P (in Russian)
Submitted to: “Pribory i Technika Experimenta” (in Russian) / “Instruments and Scientific Techniques” (English version)
2. The spatial accuracy of mini-drift tubes by detecting the induced signals
JINR preprint P (in Russian)
Submitted to: “Pribory i Technika Experimenta” (in Russian) / “Instruments and Scientific Techniques” (English version)

16. Conclusion Plans for the future
MDT with an open cathode geometry reliably allows to detect signals induced on the outer strips.
Double Ampl-8.3 preams seems to operate stable at least with short strips.
The spatial resolution σ≈ 0.4 mm achieved with 1 cm wide and 10 cm long strips
Plans for the future
Test of a strip readout with long (up to 4 m) strips
Test of a strip readout with strips of a different width
Optimization of the strip widths for all MDTs over the whole PANDA spectrometer (i.e. minimization of a number of channels)