A Totally Active Liquid Xenon or Krypton Electromagnetic Calorimeter for High Luminosity Hadron Colliders

Abstract

A totally active liquid Xenon or Krypton electromagnetic calorimeter is proposed for a dedicated Higgs search experiment at LHC, SSC or ELOISATRON. Detection of fast scintillation permits excellent energy resolution (σE ≤ 1%√E) while detection of ionization (by drift) gives precise determination of the direction (≈1 mr) and vertex origin (≈1 mm) of high energy (E ≥ 25 GeV) photons or electrons.

Slow (≈750 ns) drift at high luminosity (2·10³⁴/cm²s) leads to a pileup background of transverse energy (per tower) E_t ≤ 1 GeV at polar angles θ ≥ 20°.

The liquid Xenon scintillation is found to be fast (τ ≤ 20 ns) and intense (3·10⁴ photons/MeV) and the liquid is transparent to its own radiation. Large surface area in-situ photodiodes have been developed which efficiently detect the fast scintillation signal.

To transport 99% of the ionization electrons 15 mm or scintillation photons 1250 mm requires an impurity level of about 13 ppb. In pure Xenon a large electric field (≈100 kV/cm) is needed to collect 99% of the ionization charge however, doping with 3% methane increases the electron drift velocity from 3 to 20 mm/μs and so reduces the field required to 15 kV/cm.

The energy needed to produce a free electron is measured to be W=42 eV with (15 to 67 keV) electron excitation whereas, the canonical value W=15.6 eV obtains for higher energy (1 MeV) electron excitation.

A dedicated Higgs experiment will require 60 tons of Xenon or 110 tons of Krypton. The availability and cost of this materiel is addressed.

Presented by J. Seguinot and T. Ypsilantis at the 12th Workshop “New Technologies for Supercolliders” Erice, Sicily: 15–20 September 1990.