Development of the muon monitor for the T2K experiment

1. Development of the muon monitor for the T2K experiment H. Kubo, K. Matsuoka, M. Yokoyama, T. Nakaya for T2K collaboration DPF/JPS 2006, Hawaii • contents • introduction to the T2K • muon monitor • 2. beam test results • ionization chambers • diamond detectors • 3. future plans

2. Introduction • off axis beam • provides “narrow band” neutrinos ～0.7GeV • requires a precise control of the beam direction beam axis off axis angle neutrino energy spectrum at various off axis angles

3. Introduction ν decay volume beam dump p π target & horn We determine the beam axis by measuring the profile center of muons. →muon monitor (MUMON) μ(>5GeV) 110m diagram of the T2K neutrino beamline muon monitor

4. Requirement • determine the direction of neutrino beam within 1mrad → 3cmprecision of the muon profile center • high intensity measurement ～10^8 muons/cm2/spill (at maximum) • bunch by bunch monitoring(～700ns interval) • survive in a high radiation environment 700 ns 58 ns 1spill = 8 bunches 3.5 s 6 μs 0.9 - 1.6×10^7 muons/cm2/bunch at full intensity T2K beam structure

5. Basic design • We usetwo independent systems, the arrays of ionization chambers and semiconductor detectors (Si PIN PDs or diamond detectors) • To obtain 3cm precision of the profile center, we require less than 5% systematic errors for each chamber in this 7×7 configuration. 160cm beam 7×7 tubes of ionization chambers 160cm semiconductor detectors

6. Detectors (1) • parallel plate ionization chambers • simple ― robust & maintenance free • A tube contains 7 pairs of plates. • similar to NuMI design • 7.5cm×7.5cm signal electrodes • 10cm×10cm bias electrodes • made by radiation tolerant parts • We use 2 gases to cover a wide dynamic range. • Ar gas (for commissioning beam, from 1% of the T2K beam) • He gas (up to full intensity of the T2K beam) • operated in 1 atm 10cm prototype ceramic spacer

7. Detectors (2) （HAMAMATSU S3590-08） 10mm • Si PIN photodiodes • low cost • well known properties • radiation damage for commissioning beam • CVD (chemical vapor deposition) diamond detectors • developed by CERN RD42 • radiation hard • fast response • unknown properties • expensive for full intensity beam 10mm thickness 300μm 9.5mm 9.5mm thickness 500μm

8. Beam test

9. Motivation & measured items • To fix the IC design gap size, chamber gases, ... • bias voltage scan • linearity (with 2 gap sizes, He and Ar gas) • To check the basic performance of CVD diamonds • bias voltage scan • linearity • warm-up time • stability

10. Beam status of Uji electron LINAC • beam status • 100 MeV • electron • beam radius ～0.8 cm • pulse width ～50 ns (T2K 1bunch-like) • interval ～60 ms 10^6 - 10^9 electrons/pulse covers T2K 1% to 100% 50 ns test beam 60 ms

11. Test of ionization chambers

12. IC prototype 10mm 3mm 3mm 50cm • prototype • A tube contains 3 pairs of plates. • G10 plate (not radiation tolerant) • 7.5cm×7.5cm signal electrodes (same as actual type) • gap 3mm(left, center) and 10mm • gap precision ～100μm • Chamber tube slides horizontally. → tested one by one

13. Setup for ionization chambers Si profile monitor IC CT0 CT1 CT2 3mm 3mm 10mm beam line oscilloscope AMP AMP attenuator ADC 3ch ADC ADC ADC 9ch • Beam intensity is monitored by three CTs. • Beam profile is monitored by the Si PD array. • Electron beam is well contained in a detector area. • beam radius ～0.8cm << signal electrode size = 7.5cm

14. Raw signal 200 mV bias 1000V (1kV/cm) intensity ～9×10^8 e-/pulse (corr. T2K full intensity) He gas 10mm-gap • triangle-shape • pulse size ― same as expected charge (～1nC) • response ≒ electron drift time • Drift velocity is faster than expected, because of existence of impurity gases. • 10 mm-gap may be too slow to separate bunches (700ns). • 3 mm-gap is about 3 times faster than it. 600 ns

15. He gas, bias voltage scan 3mm 10mm • scan 0 → 400 (1200) V, and some points again • Bias fluctuations will not cause problem in high voltages. • 10 mm-gap chamber losses more charge. ← attachment (by O2) • We expect that it will be improved by increasing gas flow. • reproducibility : within 2%→ OK! • Difference between two 3mm-gap chambers is within 3% as expected from gap precision 0.1mm/3mm. → OK! 0.05% / V operation voltage operation voltage

16. He gas, linearity • 3mm-gap chamber responses almost linear up to 9×10^8 particles/pulse/plate ≒ T2K full intensity. about 3% differencefrom the extrapolated line →OK! • 10mm-gap chamber slightly saturates. about 10% difference from the extrapolated line → because of recombination 3mm is OK, but 10mm may needs a correction to use. T2K 10% T2K 10% T2K full T2K full 3mm-gap 10mm-gap beam intensity beam intensity

17. Ar gas, bias voltage scan gap size normalized • T2K commissioning beam intensity (～1%) • scan 0 → 400 (1200) V, and some points again operation voltages • Both 3mm and 10mm has plateau around 300 V/cm. After that, gain decreases (dissociative electron attachment ). • reproducibility : within 1%→ OK! • Difference between two 3mm-gap chambers is within 3% (gap precision) → OK!

18. Ar gas, linearity Enough size of signals are obtained down to T2K 1% intensity. • 3mm-gap chambers response almost linear up to around T2K 5% intensity. T2K 1% T2K 50% T2K 10% 3mm-gap 3mm-gap beam intensity beam intensity

19. IC conclusion We can use ICs for T2K MUMON. • good reproducibility ～ 2% • difference between two 3mm-gaps ～ 3% → within the requirement for 7×7 ch • Response of 3mm-gap chamber is so linear with both gases that we can use it without correction. → We choose 3mm-gap than 10mm-gap. → We can operate ICs with 2 gases

20. Test of diamond detectors

21. Setup for diamond detectors Si profile monitor CT0 CT1 CT2 4 diamonds between 2 Sis • put four diamond detectors between Si PDs (reference) • about 20% of the electron beam hits the diamonds beam line attenuator oscilloscope AMP AMP attenuator ADC 6ch ADC ADC ADC 9ch

22. Raw signal • Diamond responses very quickly. • Si have a long tail in such a high intensity. • need some attenuation bias 400 V 6×10^7 e-/cm^2/pulse (T2K full ×4) signal size ～ 50V 100mV, 1/500 ATT.

23. Diamond, bias voltage scan 30% • scanned up to 600V • no plateau • bias voltage dependence is less than 0.1%/V @ 500V • 30% variation among samples beam dia3 Si1 dia1 Si2 dia4 dia2 intensity ～ 9×10^6e-/cm^2/pulse (corr. T2K full intensity)

24. Diamond, linearity • linear within 2% among T2K intensities → OK ±2% beam intensity from the change of the beam condition

25. Warm-up time & stability • Diamonds need some irradiation before reaching stable gains. • Warm-up times are much different among samples. • after the warm-up time, the gain is stable within 2%

26. CVD diamond conclusion Basic performance is not bad. • acceptable bias dependence～ 0.1%/V@500V • good linearity～ 2% among T2K intensities • stability ～2% →OK But there are unknown properties, we need more study . • large variation among 4 samples ～30% • warm-up time is quite unknown. • reproducibility is not good (maybe from the references or the beam condition)

27. Future plans Now We are producing the next prototype of IC ( 7ch a tube, using ceramic plates, ...) and testing actual readout electronics. 2006.12 next beam test @Uji ～JFY2006 finalize MUMON design JFY2007 start production of MUMON 2008.12 MUMON installation start ! 2009.4 beam on

28. backup slides

29. T2K neutrino beam line ２８０ｍ １１０ｍ Pions are made at the target from the proton beam. Then only π＋s are focused by the sequence of horns. Some of them decay into neutrinos and muons in the 110m-long decay volume. Muons over 5GeV penetrates the beam dump. Neutrinos goes through the near detectors toward the far detector, SK.

30. Error estimate of the beam center • in 7×7 configuration 5% systematic errors make 3cm uncertainty of the beam center

31. Non-linearity (He gas) • about -3% for 3mm-gaps, -10% for 10mm-gap @T2K full intensity • fluctuations is about ±2% around T2K 10% intensity (but it also contains CT fluctuations) • from 10% to 100% of T2K intensity, 3mm-gap is OK ! • 10-mm gap may needs correction T2K full T2K full T2K 10% T2K 10% difference from the extrapolated lines

32. Linearity (Ar gas) T2K 1% T2K 1% 3 mm 100V T2K 1% T2K 1% 10 mm 300V difference from extrapolated lines

33. Linearity (Ar gas) @ higher intensity T2K 10% T2K 50% T2K 10% 3mm-gap 100V T2K 50% 10mm-gap 300V T2K 10% T2K 10% difference from extrapolated lines

34. Recombination correction • we can correct the effect of recombination with this fitting method • but for 3mm chambers, it is found that we don’t have to do this within T2K intensities T2K 10% T2K 10% difference from the fit curve

35. Linearity (diamond) • linear within 2% among T2K intensities • Because of the small active area and the beam radius, yields are much affected by the beam condition. (second points from the left) from the change of beam condition

36. Warm up time • diamonds need some time to warm up • 2 types of the responses • dia1,2 fast response • dia3,4 slow response • HV on/off & beam on/off test • both show similar responses case1 ― keep beam on & HV off, then HV on(500V) it takes about 10sec to supply case2 ― keep HV on(500V) & beam off, then beam on it takes 1sec to open the shutter

37. Warm up time • beam on/off continually • at first dia1,2 ～5sec to warm up dia3,4 ～3min to warm up • after the 5min interval dia1,2　～5sec to warm up dia3,4 ～20sec to warm up • we have to check at 3.5sec interval (actual spill)

38. Stability • stable within 2% after 3minutes no point regions are ADC overflow