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Scientific Report 2007-2009
Particle physics
P21. Scintillator calorimeters for the detection of low energy photons,
electrons and hadrons.
The KLOE experiment has taken data at the e + e − accelerator
DAFNE from 1999 to 2006. The results of this
experiment are discussed elsewhere in this report. A program
of detector and accelerator upgrade is in progress
aiming to restart data taking in spring 2010 with improved
luminosity and extended detection capability. We
describe here the contributions to this program of the
Sapienza University group.
An important part of the detector upgrade is the construction
of the “electron taggers” at small angle. The
aim of these detectors is the identification of the so called
γγ annihilations, that is the process: e + e − → e + e − X
where X is a generic hadronic state. In such events the
two electrons in the final state are typically emitted at
small angles with respect to the direction of the beams.
Two pairs of detectors have been built: the HET (High
Energy Tagger) designed to detect the electrons emitted
at very small angle and with an energy very close
to the beam energy (510 MeV), and the LET (see Fig.1)
for electrons at intermediate angles and with energies approximately
between 150 and 250 MeV. The Rome group
has built the 2 LET detectors. Each LET is an array of
20 1.5 × 1.5 × 12 cm 3 LYSO crystals with the long dimension
almost parallel to the electron arrival direction.
Each crystal is read-out by a SiPM photo-detector placed
on the bottom face. The LYSO + SiPM technology allows
to have a compact detector with a good energy resolution
and a sufficiently fast response. A prototype of
the LET detector has been assembled and tested with
electron beams in the energy range between 100 and 500
MeV.
lead-scintillating fibers calorimeter with a lead-fiber-glue
ratio of 48-42-10 in volume. We have exposed a prototype
of it to the neutron beam of the TSL Laboratory
of the Uppsala University (Sweden). We have measured
the calorimeter efficiency for neutrons of kinetic energies
between 20 and 180 MeV. The results are shown
in Fig.2. By comparing the efficiency of the KLOE
calorimeter with the one of a bulk scintillator with the
same scintillator equivalent thickness, we observe in
average an efficiency enhancement of a factor 2.5. This
somehow unexpected result opens the possibility to
develop high efficiency and compact neutron detectors
for this energy range with the lead-scintillating fibers
technology.
ε CALO (%)
60
50
40
30
20
10
0
E n = 180 MeV - R = 1.5 kHz/cm 2
E n = 180 MeV - R = 3.0 kHz/cm 2
E n = 180 MeV - R = 6.0 kHz/cm 2
0 5 10 15 20 25 30 35 40
Thr(MeV eq.el.en.)
Figure 2: Neutron detection efficiency for 180 MeV neutrons
as a function of the threshold, expressed in equivalent electron
energy. The efficiency refers to a 16.5 cm thick calorimeter
with about 8 cm equivalent scintillator thickness.
References
1. M. Anelli et al., Nucl.Instr. and Meth. A581 368 (2007).
2. F. Ambrosino et al., Nucl.Instr. and Meth. A598 239
(2009).
3. M. Anelli et al., Nucl.Instr. and Meth. A598 243 (2009).
4. D. Babusci et al., arXiv:0906.0875.
Figure 1: Schematic view of the KLOE interaction region
including the beam pipe, the magnets and one of the LET
detectors (the purple box in the left).
A second important study carried on by the Sapienza
University group is the measurement of the response to
neutrons of the KLOE calorimeter. In fact, part of the
extended KLOE physics program requires the detection
of neutrons with kinetic energies between few MeV
and few hundreds MeV. The KLOE calorimeter is a
Authors
C. Bini, V. Bocci 1 , A. De Santis, G. De Zorzi, A. Di
Domenico, S. Fiore, P. Gauzzi
http://www.roma1.infn.it/exp/kloe
Sapienza Università di Roma 128 Dipartimento di Fisica