The Endcap Hadron Calorimeters (HE)
In collaboration with NC PPHE
(Minsk), KPTI and the Institute of Monocrystals (Kharkiv), NIKIET
(Moscow), and IHEP (Protvino), JINR bears a full responsible for
design and construction of the endcap hadron calorimeters (HE).
JINR is coordinating this activity and is responsible for construction
of the calorimeter absorbers.
Solving the problems of both standard and new physics depends on
the energy and spatial jet resolution, and on the energy resolution
of the transverse energy missed in the hadron calorimeter. It requires
good hermiticity, good transverse segmentation (important for separation
of the two-jet events), decent energy resolution, sufficient depth of the
absorber, and, lastly, minimization of the dead zones (required for the
measurement of the missing energy). The effects of the clustering algorithms,
influence of the magnetic field, pileup and noncompensation of the
calorimeter structure (originating from the difference in the structures
of ECAL and HCAL) deteriorate the two-jet resolution. Therefore, the
energy resolution is not critical. The calorimeter based on the light
collection through a wavelength-shifting fiber imbedded into the
scintillating tiles SCSN81 that are sandwiched with a brass absorber
satisfies all the above conditions [3].
Fig. 3 shows a layout of the endcap calorimeter. HE covers the
pseudorapidities range from 1.3 to 3.0. It has a projective transverse
segmentation matched with the segmentation of EE. The total thickness
of the calorimeter with EE included amounts to almost 10 absorption
lengths. A layer of the calorimeter is composed of 79 mm brass
- 5,52 X0, 2.0 mm aluminium - 0,02 X0,
and 3.7 mm - 0,01 X0 scintillator layers.
The experimental energy resolution of the calorimeter is
 E/E = (108,6+/-3,42)%/sqrt(E)
 (2,93+/-0,38)%.The spatial resolution varies
from 14 mm at 20 GeV to 5 mm at 100-300 GeV. Fig. 4 illustrates uniformity
of the calorimeter and its hermiticity in the 530
crack between the endcap and the
barrel calorimeters.
The absorbed dose of radiation at  =3
is estimated
to exceed of 10 Mrad for 10 years of operation at
the collider. The studies have shown that the radiation damage
decreases by 50% the light yield at the above level of the radiation.
Despite this, the energy resolution does not deteriorate if the
longitudinal variation of the light yield in the limits of a
segment of the projective tower is bounded by 20%, and the
light yield caused by a minimally ionising particle is not
less than one photoelectron after the exposure to the radiation.
Furthermore, scintillating tiles for the first five layers
at ~3 made of radiation hard scintillators developed in Kharkiv.
Calibration with a radioactive source will take place to monitor
the light yield. It has been experimentally demonstrated that the
light yield increases ~4% for pions and saturates in axial magnetic
field. For a radioactive source, the behaviour of the light yield
is similar. Since the light yield of an ultraviolet laser is
independent of the field, the effect of the magnetic field can be
compensated by the ratio between these two calibrating signals.
The studies performed on numerous prototypes have confirmed that
the parameters of the endcap calorimeters (HE) meet the CMS physics
requirements.
Industry is extensively involved in the production of the endcap
detectors. For example, the design of the interface system for the
endcap detectors had required a deep study from the engineers
affiliated with all the institutions involved. This design had been
approved by the CMS integration group and other CERN units
[4]. The
study resulted in an elegant solution (see Fig. 3) for the compensation
of the considerable magnetic forces. Dedicated efforts had been undertaken
at NIKIET to develop and deliver materials with improved strength properties.
For example, the brass of the absorber comes from recuperated artillery
shells. Ultimately, Krasny Vyborzhets plant at St.- Petersburg is delivered
the plates of the absorber and the elements of the fastening that are made
from a dedicated brass. Production of the absorber sectors and of the
interface system, and the preliminary assembly is performed at Minsk October
Revolution plant in Belarus. For the HE mechanics, the material delivery,
production supervision, and the quality control at all the stages is
provided by NIKIET. Presently, the brass has been delivered for two
absorbers, and the production of the first absorber is completed.
The production of the scintillator tiles is completed at the Monocrystals
Institute (Kharkiv). In the production, the raw materials provided by the
collaboration are used. The production and assembly of the optical elements
(megatiles) is the responsibility of IHEP. Presently, the mass-production
of the optical elements for the second calorimeter is nearly completed.
As scheduled in the CMS detector construction schedule, and in the RDMS
schedule, the assembly and installation of the first endcap calorimeter
is starting in 2002.
Fig. 4:
Energy resolution of the endcap hadron calorimeter (a)
and energy leakage (b) dependence on the pseudorapidity for the pions with
different energies.
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