1. NA48/2 KABES detector: a short overview Massimiliano Fiorini (Università degli Studi di Ferrara) On behalf of: M. Boyer, C. Cheshkov, J.B. Cheze, X. Coppolani, A. Delbart, J. Derré, S. Herlant, P. Le-Bourlout, P. Legou, O. Maillard, I. Mandjavidze, C. Mazur, E. Mazzucato, F. Nizery, F. Orsini, B. Peyaud, M. Riallot, B. Vallage. CEA DSM/Dapnia Saclay S. Basilev, Y. Potrebenikov, I. Slepnev, V. Slepnev. JINR/Dubna The NA48 Collaboration CERN, Cambridge, Chicago, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Northwestern, Perugia, Pisa, Saclay, Siegen, Torino, Vienna K RARE DECAY WORKSHOP - Frascati - 27 May 2005

2. 2 T drift1 T drift2 Operated @ E drift = 0.83 kV/cm v DRIFT = 8 cm/μs T drift1 + T drift2 = 750 ns 48 strips with 0.8 mm pitch Very low discharge probability Micromegas Gap 50 μm Micromegas Gap 50 μm NA48 KABES principle: TPC + micromegas TOTAL X/X 0 ~1.3x10 -3

3. 3 TOT =T trailing -T leading = 35 ns Low occupancy @20 MHz = 1.5 T leading T trailing Threshold Gas mixture Ne(79%)+C 2 H 6 (11%)+CF 4 (10%) Time window (extraction) 0.5 s Number of TDC channels6x48=288 Central strips rate~ 2 MHz Limits of TDC readout Maximum particle flux 40 Mp/s Maximum hit rate /strip 8 Mhit/s KABES main features Reference : B. Peyaud et al. NIM A 535 (2004) 247-252 K2 K1 K3K4 K5K6

4. 4 Performance in NA48/2 blank (T 0 ) KABES - (T 0 ) DCH Spectrometer (ns) Time resolution : ~0.6 ns Using TOT to correct time slewing Efficiency ~ 100% Momentum resolution ~ 0.9% Wrong K ± tagging ~ 4% Space resolution [from drift time measurement] ~70 μm

5. 5 time units (2×1.04 ns) TEST of 25 μm mesh detector + FADC readout 8 bit FADC 960 MHz (2 interleaved 480 MHz) only 18 channels at 480 MHz sampling frequency new mesh gap reduced to ~ 20 ns beam momentum 75 GeV/c (only K + ) beam intensity scan up to ~16x nominal intensity better double pulse resolution with FADC extract time information from fit reconstruction of tracks even in high rate beam

6. 6 Conclusions high rate and high-resolution TPC operating with 50 μm micromegas amplification gap @20 MHz further improvement of occupancy with 25 μm amplification gap is expected all mesh currents are linear at high beam rate (up to 16xI 0 ) KABES does NOT saturate LATEST RESULT: use of a faster preamplifier reduces the pulse width of a factor of 2 Further Investigations: different gas mixture, use of double amplification gap