Vladimir Epshteyn

Forward calorimeters, located near the incident beams, complete the nearly 4π coverage for high pT particles resulting from proton-proton collisions in the ATLAS detector at the Large Hadron Collider at CERN. Both the technology and the deployment of the forward calorimeters in ATLAS are novel. The liquid argon rod/tube electrode structure for the forward calorimeters was invented specifically for applications in high rate environments. The placement of the forward calorimeters adjacent to the other calorimeters relatively close to the interaction point provides several advantages including nearly seamless calorimetry and natural shielding for the muon system. The forward calorimeter performance requirements are driven by events with missing ET and tagging jets.

We present measurements of the reduction of light output by plastic scintillators irradiated in the CMS detector during the 8 TeV run of the Large Hadron Collider and show that they indicate a strong dose rate effect. The damage for a given dose is larger for lower dose rate exposures. The results agree with previous measurements of dose rate effects, but are stronger due to the very low dose rates probed. We show that the scaling with dose rate is consistent with that expected from diffusion effects.

One of the two ATLAS Forward Calorimeters (FCal), consisting of three modules, one behind the other, was exposed to particle beams of known energies in order to obtain the energy calibration. The data were taken in the H6 beamline at CERN in the summer of 2003, using electron and hadron beams with energies from 10 to 200 GeV. The beam test setup and collected data samples are described in detail. Using data samples taken with a minimal amount of material upstream of the calorimeter, the FCal response to electrons and pions, as measured by the linearity and resolution as a function of energy, is extracted and compared to ATLAS performance requirements.

A pre-production prototype of the Forward Calorimeter (FCal) for the ATLAS detector presently under construction at the Large Hadron Collider (LHC) at CERN, Geneva, Switzerland, was exposed to electrons in the momentum range from 20 to 200 GeV/c in a test beam experiment at CERN in 1998. The measured performance, including a signal linearity within about ±1% and a high energy limit in the relative energy resolution of about 4%, meets the expectations for this kind of calorimeter, and exceeds the physics requirements for successful application in ATLAS.

The PMTs of the CMS Hadron Forward calorimeter were found to generate a large size signal when their windows were traversed by energetic charged particles. This signal, which is due to Čerenkov light production at the PMT window, could interfere with the calorimeter signal and mislead the measurements. In order to find a viable solution to this problem, the response of four different types of PMTs to muons traversing their windows at different orientations is measured at the H2 beam-line at CERN. Certain kinds of PMTs with thinner windows show significantly lower response to direct muon incidence. For the four anode PMT, a simple and powerful algorithm to identify such events and recover the PMT signal using the signals of the quadrants without window hits is also presented. For the measurement of PMT responses to Čerenkov light, the Hadron Forward calorimeter signal was mimicked by two different setups in electron beams and the PMT performances were compared with each other. Superior performance of particular PMTs was observed.

A readout box prototype for the CMS Hadron Forward calorimeter upgrade was built and tested in the CERN H2 beamline. The prototype was designed to enable simultaneous tests of different readout options for the four anode upgrade PMTs, new front-end electronics design and new cabling. The response of the PMTs with different readout options was uniform and the background response was minimal. Multi-channel readout options further enhanced the background elimination. Passing all the electronic, mechanical and physics tests, the readout box proved to be capable of providing the forward hadron calorimeter operational requirements in the upgrade era.

We study the light output, light collection efficiency and signal timing of a variety of organic scintillators that are being considered for the upgrade of the hadronic calorimeter of the CMS detector. The experimental data are collected at the H2 test-beam area at CERN, using a 150 GeV muon beam. In particular, we investigate the usage of over-doped and green-emitting plastic scintillators, two solutions that have not been extensively considered. We present a study of the energy distribution in plastic-scintillator tiles, the hit efficiency as a function of the hit position, and a study of the signal timing for blue and green scintillators.

One of two ATLAS Forward Calorimeters, consisting of three modules, one behind the other, was exposed to particle beams of known energies in order to study the detector performance with and without the presence of upstream material in the beam, and at the inner edge of the acceptance where shower energy containment is incomplete.Data were taken in the H6 beamline at CERN using electron and hadron beams with energies from 10 to 200 GeV.Results related to the intrinsic detector calibration, based on data taken with a minimal amount of material in front of the detector, have been previously published, but are updated here.This paper focuses on studies of data taken with additional upstream material in place.The effects of this additional material on the linearity and resolution of the response are presented.The response at the inner edge of the acceptance is also investigated.For all analyses, results based on a GEANT4 simulation of the beam-test setup and detector response are also presented.

The Phase I upgrade of the CMS Hadron Endcap Calorimeters consists of new photodetectors (Silicon Photomultipliers in place of Hybrid Photo-Diodes) and front-end electronics. The upgrade will eliminate the noise and the calibration drift of the Hybrid Photo-Diodes and enable the mitigation of the radiation damage of the scintillators and the wavelength shifting fibers with a larger spectral acceptance of the Silicon Photomultipliers. The upgrade also includes increased longitudinal segmentation of the calorimeter readout, which allows pile-up mitigation and recalibration due to depth-dependent radiation damage. As a realistic operational test, the responses of the Hadron Endcap Calorimeter wedges were calibrated with a 60Co radioactive source with upgrade electronics. The test successfully established the procedure for future source calibrations of the Hadron Endcap Calorimeters. Here we describe the instrumentation details and the operational experiences related to the sourcing test.