Liquid argon as an active medium Better title What has been learned by ICARUS collaboration from ~20 years of drifting electrons in LAr Carl Bromberg Michigan State University & Fermilab (2004) November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 1
Sources See list of ICARUS talks and papers on FLARE web site /www-off-axis/flare/documents. htm Particularly: • Talk by F. Sergiampietri, at Nu. Fact ‘ 01 (LANNDD) • Talk by A. Para at Fermilab (Wine & Cheese) • Publications – “Design, construction and tests of the ICARUS T 600 detector”, NIM A 527, 329 (2004) – “Study of electron recombination in liquid Argon with the ICARUS TPC” NIM A 523, 275 (2004) – Measurement of the muon decay spectrum with the ICARUS T 600 liquid Argon TPC”, Euro Phys J C 33, 2 (2004) 233 November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 2
Liquid Argon basics Wion (1 Me. V e–) 23. 6 e. V Radiation Length 19. 55 g/cm 2 (14. 0 cm) Density 1. 395 g/cm 3 (1 bar) Boiling Point 87. 2 K (1 bar) 89. 3 K (1. 25 bar) Nucl. Int. Length 117 g/cm 3 Diffusion Coef. 4. 8 cm 2/s Recombination factor 0. 64 (decreases ions/cm) d. E/dx (min) 2. 1 Me. V/cm e– in 3 mm sample November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 3
November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 4
TPC operation • Time Projection – electrons drift toward transparent wire planes (minimum 1), and collection wire plane – planes with wires at various angles for stereo delta ray • Ambiguities – track parallel to wire planes, all hits have same time, i. e. , x. – track “dip” resolved by space points: vertices, delta rays or ionization bumps – distance between space points changes in the two views November 4, 2004 vertex Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 5
Signal characteristics FWHM ~ 4. 5 mm D tracks = 16 mm D • Diffusion not a big factor in signal shape for d ~ 2 m • Fit for x-position, resolution < 1 mm (2. 5 MHz clock), helps with ambiguity resolution. • Even with significant overlap in time, distinguish 1 track from 2, by consistent ionization/pulse width over many wires. • But tracks in drift direction have very distorted pulse shapes November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 6
Energy Resolution November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 7
FLARE is not ICARUS • Typical ICARUS capacitance is 20 p. F/m + 200 p. F cable ~400 p. F (max) induction wire • Induction signals are smaller than collection signals by ~30% • FLARE will have wires 4 times as long, noise will be 1. 6 times larger, yielding S/N ~ 8 • Does increasing wire spacing (to say 5 mm) help by lowering capacitance and increasing the signal? • Cables for horizontal or stereo wires? Long cables mean more capacitance. Restrict to collection wires. • Pixels anyone? K. Mc. Donald. November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 8
For what is needed? • Energy resolution of 2% great for EM shower. For total energy, make corrections based on particle ID via ionization changes, range, p->m->e decays, nuclear fragments & n-stars • Full reconstruction is probably not needed. Automated scanning perhaps possible in 2 D • In scanning simulations, stereo views were not that useful. Helped in large angle particle ID, but not often in electron ID. • Automatic space point finding is a challenge • Cosmic Rays (during 1. 3 ms readout). Should do simulation. Get ICARUS raw data? Interest by others trying to do surface calorimetry and tracking. November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4 -6, 2004 9
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