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