9 modules were assembled at INR,

1
LONGITUDINALLY SEGMENTED LEAD/SCINTILLATOR HADRON
CALORIMETER WITH MICROPIXEL APD READOUT
M.Golubeva, F.Guber, A.Ivashkin,
A.Kurepin, V.Marin, A.Maevskaya,
Yu.Musienko,
A.Sadovsky, K.Shileev
Institute for Nuclear Research, Moscow, Russia
pr. 60-letiya Oktyabrya 7a, Moscow, Russia
New generation of heavy ion experiments (CBM at
GSI 1 and NA61 at CERN 2) is focused on the
search for the critical point of strongly
interacting matter and analysis of the properties
of deconfinement. A crucial goal of this
experimental program is the study of
event-by-event fluctuations of as a function
collision energy, size of colliding nuclei and
the collision centrality. The experimental
extraction of the critical fluctuations requires
a very precise control over the fluctuations
caused by the variation of the number of
interacting nucleons due to event-by-event
changes in the collision geometry. The number of
non-interacting nucleons is measured by very
forward hadron calorimeter or by Projectile
Spectator Detector (PSD). Main requirements to
PSD are excellent energy resolution (about
50/sqrt(E(GeV)), good transverse uniformity of
this resolution and fine granularity. Full
compensating modular lead/scintillator hadron
calorimeter meets the above requirements.
Calorimeter includes 12x9 array of the individual
modules placed at the distance of about 15 m
downstream from the target. The single module
with the dimensions 10x10x120 cm3 consists of 60
lead/scintillator layers with 16 mm and 4 mm
thick, respectively.

Light readout is provided by the WLS-fibers
embedded in the round grooves in scintillator
plates. WLS-fibers from each 6 consecutive
scintillator tiles are collected together and
viewed by a single photodiode at the end of the
module. The longitudinal segmentation in 10
sections ensures the uniformity of the light
collection along the module and the rejection of
secondary particles from interaction in the
target.
Assembling of PSD module.
Schematic front view of module.
Micropixel avalanche photodiodes, MAPDs are an
optimum choice due to their remarkable properties
as high internal gain, compactness, low cost and
immunity to the nuclear counter effect. 10 MAPDs
per module are placed at the rear side of the
module together with the front-end-electronics.
MAPDs with active area 3x3 mm2 and pixel density
104/mm2 were selected. These MAPDs with
individual micro-wells are produced by
Dubna-Mikron collaboration 3. Improved versions
MAPD3, produced by Zecotek Imaging Systems Pte
Ltd (Singapore) will be used further for full
calorimeter.
MAPD has linear response up to 104 photoelectrons.
Photon detection efficiency is about 20 for
green light.
9 modules were assembled at INR, Moscow and
first beam test of the PSD supermodule (3x3
array) was performed at hadron beam at SPS,
CERN in 2007. The calibration of each readout
channel was done with the muon beam. To obtain
full set of the calibration coefficients the
muon beam scan was performed for all 9 modules.
After that the central module of the calorimeter
was irradiated by pion beam with 5 energies 20,
30, 40, 80 and 158 GeV.
Spectra of 70 GeV muon energy deposition in each
section of single module used for calibration.
Energy resolution of calorimeter
Stochastic term 54, constant term 1.9
Energy spectrum in first section of module for
mixed 30 GeV beam of pions, positrons and muons.

• References
• http//www.gsi.de/fair/experiments/CBM.
• http//na61.web.cern.ch/na61.
• Z.Sadygov et al., NIM A567 (2006) 70-73.

Comparison of hadron energy deposition in
experiment and GEANT3 simulation.
We thank NA61 and CBM collaborations for support
of this project.