—
The time and energy resolutions were measured for four prototypes of the PHOS electromagnetic calorimeter for the ALICE experiment at the Large Hadron Collider at CERN. Each prototype was made up ...of nine identical detection elements assembled as a 3 × 3 array. The detection element was based on a lead tungstate (PbWO
4
) scintillating crystal with a length of 180 mm and a cross section of 22 × 22 mm
2
, which was viewed from its end face by a photodetector. Avalanche photodiodes and silicon photomultipliers with different active areas (Hamamatsu, Japan) were used as photodetectors. The measurements were made with the electron component of secondary particle beams of the PS proton synchrotron at CERN in the momentum range of 1−10 GeV/
c
at a temperature of 17.5°C.
It is shown that an increase in the area of photodetectors allows the PHOS electromagnetic calorimeter of the ALICE experiment to operate at room temperature with better spectrometric ...characteristics. The linearity of the calorimeter response has been investigated in the 1–110 GeV energy range using both Hamamatsu S8664-1010 avalanche photodiodes with a large area (10 × 10 mm
2
) and arrays of MPPC Hamamatsu S12572-015C silicon photomultipliers with a sensitive area of 6 × 6 mm
2
. The calorimeter based on avalanche photodiodes is linear in the energy range under investigation compared to a calorimeter composed of silicon-photomultiplier arrays.
The use of S12572 MPPC silicon photomultipliers (Hamamatsu) for improving the timing characteristics of the PHOS electromagnetic calorimeter in the ALICE experiment at CERN is described. It is shown ...that by introducing an additional photodetector, that is, a silicon photomultiplier, it is possible, without worsening the energy resolution, to significantly improve the time resolution of the PHOS spectrometer from the current values of 3–4 ns to 150–200 ps.
The Time of Flight (TOF) resolution of one of the LHC ALICE detectors, a prototype of the electromagnetic calorimeter PHOS (PHOton Spectrometer), was measured in beam tests carried out at CERN PS. ...The prototype of the calorimeter consists of 256
(
22
×
22
×
180
mm
3
)
cells of light-detecting
PbWO
4
(PWO) monocrystals read out with
5
×
5
mm
2
Avalanche Photo Diodes (APDs). Three dedicated front end cards with 24 channels of electronics were designed and produced for using in the tests, each channel consisting of one fast and two slow shapers, a time to amplitude converter and three identical 12-bit peak sensitive Analog to Digital Converters (ADCs). The high voltage bias regulator for APD is located on the same card. The measured TOF resolution is described as
σ
t
=
0.24
/
E
GeV
2
+
0.4
ns
.
The light response of a BGO crystal has been measured for particles
Z=1–8,
A=1–16 in the energy range ∼2–
60
A
MeV
. The reaction products are identified by a Δ
E(Si)−
E(Sci/PD) telescope. The ...position of the jump in the value of the signal from the PD at the punch-through points is used to calibrate both the Δ
E(Si) and
E(Sci/PD) scales in MeV. The dependence of the light output on the energy
E, ion atomic number
Z and mass
A is parameterized by the power law relation,
L(
Z,
A,
E)=
a
1(
Z,
A)
E
a
2(
Z,
A)
. The parameters
a
1 and
a
2 have a smooth dependence on
Z for all three crystals. The mass dependence of
a
1,
a
2 is deduced as a simple analytical expression. The systematics of these parameters is presented for BGO, CsI(Tl) and GSO(Ce) scintillators as a function of
Z,
A. Calculations of the response function, based on the Murray–Mayer model provide an excellent description of the shape of
L(
Z,
A,
E) versus
E dependence, but show some deviations in the individual ion normalization constant for the BGO and GSO(Ce) scintillators.
The light radiation from various internal targets at the nuclotron can be utilized for the operative control and time optimization of the interaction intensity of the beam. The examples presented in ...the paper illustrate information about the space characteristics of the circulating beam during one cycle of the accelerator run at the stages of injection, acceleration and during the physical experiments, respectively.
On-beam calibration of the Δ E(Si)–Sci/PD charged particle telescope Avdeichikov, V.; Jakobsson, B.; Nikitin, V.A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2001, Volume:
466, Issue:
3
Journal Article
Peer reviewed
The reaction products emitted in the
14
N(45
A
MeV
)+(
CH
2/
CD
2)
interactions are identified by a Δ
E(Si)–
E(Scintillator/Photodiode) telescope by the conventional Δ
E–
E method. The position of ...“jumps” in the amplitude of the photodiode signal for ions passing through the scintillator (Sci) is used to calibrate on-beam both the Δ
E and the Sci/PD scales in MeV. The accuracy of an absolute energy calibration is better than 2.3% and 1.8% for CsI(Tl) and GSO(Ce) detectors, respectively. It is defined mostly by the correctness of the range-energy relations of ions in the Si and Sci crystals. The light response function,
L(
E,
Z,
A), of isotopes up to
Z(
A)=8(16) in the range of energy
∼(2.5–60)
A
MeV
is extracted. The effects of doping concentration and pulse shaping on the light response are analyzed. The validity of the existing empirical light-energy relations is checked in a wide interval of ion energies and a new power law relation is proposed. Calculations of the response function based on the Murray–Mayer model are found to be in excellent agreement with experimental data for the CsI(Tl) crystal.
Results on transverse mass spectra of neutral pious measured at central rapidity are presented for impact parameter selected 158-A GeV Pb + Pb-1 and Pb + Nb collisions. The distributions cover the ...range 0.5 GeV/c(2) less than or equal to MT - Mo less than or equal to 4 GeV/c(2). The change of the spectral shape and the multiplicity with centrality is studied in detail. In going from p+p to semi-peripheral Pb+Pb collisions there is a nuclear enhancement increasing with transverse mass similar to the well known Cronin effect, while for very central collisions this enhancement appears to be weaker than expected.
Measurements of direct photon production in p+Pb and p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$ are presented. Upper limits on the direct photon yield as a function of $p_\mathrm{T}$ ...are derived and compared to the results for Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 17.3$ GeV. The production of the $\eta$ meson, which is an important input to the direct photon signal extraction, has been determined in the $\eta \rightarrow 2\gamma$ channel for p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$.
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