November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 1

Liquid argon as an active medium

Carl Bromberg Michigan State University

& Fermilab (2004)

Better titleWhat has been learned by

ICARUS collaboration from ~20 years of drifting electrons in LAr

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 2

Sources

• Talk by F. Sergiampietri, at NuFact ‘01 (LANNDD)• Talk by A. Para at Fermilab (Wine & Cheese)• Publications

– “Design, construction and tests of the ICARUS T600 detector”, NIM A527, 329 (2004)

– “Study of electron recombination in liquid Argon with the ICARUS TPC” NIM A523, 275 (2004)

– Measurement of the muon decay spectrum with the ICARUS T600 liquid Argon TPC”, Euro Phys J C33,2 (2004) 233

See list of ICARUS talks and papers onFLARE web site

/www-off-axis/flare/documents.htm

Particularly:

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 3

Liquid Argon basicsWion (1 MeV e–) 23.6 eVRadiation Length 19.55 g/cm2 (14.0 cm)Density 1.395 g/cm3 (1 bar)Boiling Point 87.2 K (1 bar)

89.3 K (1.25 bar)Nucl. Int. Length 117 g/cm3

Diffusion Coef. 4.8 cm2/s Recombination factor

0.64 (decreases ions/cm)

dE/dx (min) 2.1 MeV/cme– in 3mm sample : 16,000e−t/t , t : 5 −10m s

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 4

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 5

TPC operation• Time Projection

– electrons drift toward transparent wire planes (minimum 1), and collection wire plane

– planes with wires at various angles for stereo

• 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

ZX (Time)Y60°

delta ray

vertex

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 6

Signal characteristics

• 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

FWHM ~ 4.5 mm tracks = 16 mm

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 7

Energy ResolutionElectron energy

E resolution

s =11% E(MeV) ⊕ 2%

Stopping m± → e±ν ν

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 8

FLARE is not ICARUS• Typical ICARUS capacitance is 20 pF/m + 200

pF cable ~400 pF (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. McDonald.

November 4, 2004 Carl Bromberg, FNAL LAr Exp. Workshop Nov. 4-6, 2004 9

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, ->m->e decays, nuclear fragments & n-stars

• Full reconstruction is probably not needed. Automated scanning perhaps possible in 2D

• 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.

νm → νe