Andrey Uzunian

The electromagnetic calorimeter of PANDA at the FAIR facility will rely on the operation of lead tungstate (PbWO4, PWO) scintillating crystals at temperatures near -25∘C to provide sufficient resolution for photons in the energy range from 8 GeV down to 10 MeV. The radiation hardness of PWO crystals was studied at the IHEP (Protvino) irradiation facility in the temperature range from +20∘C (room temperature) down to -23∘C. These studies have indicated significantly different behavior in the time evolution of the damaging processes well below room temperature. Different signal loss levels at the same dose rate but at different temperatures were observed. The effect of a deep suppression of the crystal recovery process at temperatures below 0∘C has been seen.

For the first time, full size lead tungstate crystals of different suppliers, quality and dopant concentration have been irradiated with gamma-rays at low temperatures down to -25degC at IHEP Protvino. In contrast to the behavior at room temperature, increased damage and extremely slow recovery processes have been observed. These first results are discussed in the light of several very different interpretations. Further more sensitive measurements are under preparation. The outcome will have a strong impact on the presently assembled ALICE-PHOS detector and the design of the EM calorimeter of PANDA at the future FAIR facility.

The energy dependence of the energy and position resolutions of the electromagnetic calorimeter prototype made of lead tungstate crystals produced in Bogoroditsk (Russia) and Shanghai (China) is presented. These measurements were carried out at the Protvino accelerator using a 1–45GeV electron beam. The crystals were coupled to photomultiplier tubes. The dependence of energy and position resolutions on different factors as well as the measured electromagnetic shower lateral profile are presented.

We report on the effects of radiation on the light output of lead tungstate crystals. The crystals were irradiated by pure, intense high energy electron and hadron beams as well as by a mixture of hadrons, neutrons and gammas. The crystals were manufactured in Bogoroditsk, Apatity (both Russia), and Shanghai (China). These studies were carried out at the 70-GeV proton accelerator in Protvino.

Influence of irradiation on the light yield of PWO (lead tungstate, PbWO 4 ) scintillation crystals was studied in the temperature range from −25 °C to +60 °C. Light output and optical transmittance were simultaneously measured as a function of time under irradiation in PWO single crystals grown in first and second recrystallization cycle of raw material, doped with different lanthanides and annealed in different conditions. Increased sensitivity to irradiation and slower recovery of the initial light yield were observed at decreased temperatures. The model of tungsten oxide clusters in a regular PWO lattice is used to interpret the experimental results, and dynamics of the light yield under irradiation at different temperatures are qualitatively explained using rate equations describing composition changes in the clusters.

A beam line for electrons with energies in the range of 1–45GeV, low contamination of hadrons and muons and high intensity up to 106 per accelerator spill at 27GeV was setup at U70 accelerator in Protvino, Russia. A beam tagging system based on drift chambers with 160μm resolution was able to measure relative electron beam momentum precisely. The resolution σp/p was 0.13% at 45GeV where multiple scattering is negligible. This test beam setup provided a possibility to study properties of lead tungstate crystals (PbWO4) for the BTeV experiment at Fermilab.

The prevailing role of defect clusters, WO3−x, of variable composition in the coloration of scintillation crystals PbWO4 (PWO) and mechanisms underlying this process are revealed. Comparative studies of the influence of irradiation and reductive annealing on the optical properties of the material show that both treatments cause variation of tungsten valency in the WO3−x clusters that results in a variation of the optical absorption spectrum and, consequently, in the color of the entire PWO crystal. Irradiation causes reversible redistribution of electrons inside the cluster, while the reductive annealing initiates migration of oxygen atoms out of the crystal which makes the coloration unrecoverable. The negative influence of intentionally introduced variable-valency element (niobium) on the radiation hardness as well as possibilities for improvement of the radiation hardness by growth optimization based on the model proposed are demonstrated.

PANDA is a challenging experimental setup to be implemented at the high-energy storage ring (HESR) at the international facility FAIR, GSI (Germany). PANDA physics program relies heavily on the capability to measure photons with excellent energy, position and timing resolution. For this purpose PANDA proposed to employ electromagnetic calorimeters using two different technologies: compact crystal calorimeter cooled to -25∘C around target and lead–scintillator sandwich calorimeter with optical fibers light collection (so-called shashlyk calorimeter) in the forward region. Institute for High Energy Physics (IHEP) PANDA group reports on two types of measurements performed at IHEP, Protvino: radiation hardness of the PWO crystals at -25∘C and testbeam studies of the energy and position resolution of the shashlyk calorimeter prototype in the energy range up to 19 GeV.

A new experiment SPASCHARM devoted to a systematic study of polarization phenomena in hadron-hadron interactions in the energy range 10-70 GeV is under preparation at IHEP (Protvino). The physical observables will be single-spin asymmetries, hyperon polarizations and spin-density matrix elements. A universal setup will detect and identify various neutral and charge particles in the full azimuthal angle and a wide polar angle range. A polarized target is used to measure the SSA. The SPASCHARM sub-detectors are being designed and constructed now. The possibility of obtaining a polarized proton beam for the SPASCHARM experiment from Lambda decays is under study.

Studies of the radiation hardness of lead tungstate crystals produced by the Bogoroditsk Techno-Chemical Plant in Russia and the Shanghai Institute of Ceramics in China have been carried out at IHEP, Protvino. The crystals were irradiated by a 40GeV pion beam. After full recovery, the same crystals were irradiated using a 137Csγ-ray source. The dose rate profiles along the crystal length were observed to be quite similar. We compare the effects of the two types of radiation on the crystal's light output.

We report on the performance of a monitoring system for a prototype calorimeter for the BTeV experiment that uses Lead Tungstate crystals coupled with photomultiplier tubes. The tests were carried out at the 70 GeV accelerator complex at Protvino, Russia.

A highly stable monitoring system based on blue and red light emitting diodes coupled to a distribution network comprised of optical fibers has been developed for an electromagnetic calorimeter that uses lead tungstate crystals readout with photomultiplier tubes. We report of the system prototype design and on the results of laboratory tests. Stability better than 0.1% (r.m.s.) has been achieved during one week of prototype operation.

Radiation damage in lead tungstate crystals reduces their transparency. The calibration that relates the amount of light detected in such crystals to incident energy of photons or electrons is of paramount importance to maintaining the energy resolution the detection system. We report on tests of lead tungstate crystals, read out by photomultiplier tubes, exposed to irradiation by monoenergetic electron or pion beams. The beam electrons themselves were used to measure the scintillation light output, and a blue light emitting diode (LED) was used to track variations of crystals transparency. We report on the correlation of the LED measurement with radiation damage by the beams and also show that it can accurately monitor the crystal recovery from such damage.

The PANDA detector will be one of the major experimental installations at the future acceleration facility FAIR at GSI (Darmstadt) for hadron physics studies using a cooled antiproton beam. A new type of the lead tungstate crystals (PWO-II) was developed as the scintillation material for the electromagnetic calorimeter of the target spectrometer of PANDA, which has to provide photon detection in the energy range from 10MeV up to 10GeV with excellent energy resolution operating at high interaction rates. The new PWO-II crystals of improved quality are characterized by light yield of 17–22 photoelectron per MeV of deposited energy and radiation induced absorption coefficient at 420 nm (luminescence maximum) below 1m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> (integral dose 3krad), both determined at room temperature. The crystals were optimized with respect to light yield and radiation hardness for operation at low temperatures down to T=−25°C. The paper presents studies of the quality parameters of two pre-production lots of 120 and 600 PWO-II full size crystals comprising samples of 11 different shapes for the barrel part of the calorimeter.

This paper investigates the role of the muon production mechanism and that of fluctuations of the energy losses and angular deviations in matter due to 101 − 105 GeV muon interactions. The method of statistical simulation, as it is realized in the MUTRAN programme, is developed. When considering physical processes the corresponding simulation algorithms are described. Some regularities of muonic field production in big accelerators are presented.

We employed two independent methods to study possible damage to the scintillation mechanism in lead tungstate crystals due to irradiation by a 34 GeV pion beam. First, 10 crystals were irradiated simultaneously over 30 hours by a narrow beam, so that only a small region of each crystal was affected. We studied the effect of the irradiation on the light output non-uniformity. If a localized degradation was observed, it would indicate damage to the scintillation mechanism. Secondly, we detected light output using two phototubes attached to sides of a crystal. Since these phototubes detect scintillation light only from a small localized region, the effect of transmission loss should be minimal. We did not see any statistically significant evidence for scintillation mechanism damage with either method. The effect is consistent with zero, and the upper limit is 0.5% at 95% C.L.

BTeV is a new dedicated B-physics project at Fermilab. It requires excellent photon detection which is crucial to study CP violations in B decays and rare decays of B's to explore physics beyond the standard model. Electromagnetic calorimeter (EMCAL) built of lead tungstate (PbWO4) scintillating crystals can provide excellent energy and position resolution, compact shower size, fast signal, and reasonable radiation hardness. We have carried out beam studies of a prototype of the BTeV electromagnetic calorimeter. The test took place at the Institute for High Energy Physics, Protvino, Russia. The prototype was built of 25 PbWO4 crystals, from russian and chinese manufacturers. The results of the first set of measurements have confirmed the expected good energy and position resolution of the prototype, though revealed the fact that PbWO4 was not as radiation hard as expected when irradiated with intense high energy hadron and electron beams. The next step included additional studies of radiation hardness, methods of monitoring changes of crystal signal due to radiation using LEDs with different wavelength, and possible procedures for testing PbWO4 radiation hardness without high energy beams.

The transport of muons and hadrons, arising from beam losses, in the magnetic structure of a proton accelerator is investigated. A method of statistical simulation of this transport has been developed and incorporated into the RING program. Muonic fields in the UNK and Tevatron soil shield are calculated for some model cases. The essential role of magnet elements and of prompt muons in the production of the muon field is emphasized. The radiation shield outside large accelerator rings is shown to be defined completely by muons.

Abstract The electromagnetic calorimeter for a new Fermilab collider program named BTeV is based on lead tungstate scintillating crystals (PbWO4). Various properties of crystals manufactured by Russian and Chinese companies were measured at the U70 accelerator in Protvino. A dedicated beam momentum tagging system was used to measure the energy and spatial resolution.

The first stage of the proposed polarization program SPASCHARM includes the measurements of the single-spin asymmetry (SSA) in exclusive and inclusive reactions with production of stable hadrons and the light meson and baryon resonances.In this study we foresee of using the variety of the unpolarized beams (pions, kaons, protons and antiprotons) in the energy range of 30-60 GeV. The polarized proton and deuteron targets will be used for revealing the flavor and isotopic spin dependencies of the polarization phenomena. The neutral and charged particles in the final state will be detected.

A precise measurement of the angle α in the CKM triangle is very important for a complete test of the Standard Model. A theoretically clean method to extract α is provided by B 0 → ρπ decays. Monte Carlo simulations to obtain the BTeV reconstruction efficiency and to estimate the signal-to-background ratio for these decays were performed. Finally the time-dependent Dalitz plot analysis, using the isospin amplitude formalism for tree and penguin contributions, was carried out. It was shown that, in one year of data taking, BTeV could achieve an accuracy on α better than 5°.

The new polarization program SPASCHARM is being prepared in Protvino. The program has two stages. The first stage is dedicated to single-spin asymmetries in the production of miscellaneous light resonances with the use of 34 GeV $π^-$-beam. Inclusive and exclusive reactions will be studied simultaneously. The second stage is dedicated to single-spin and double-spin asymmetries in charmonium production with the use of 70 GeV polarized proton beam which will allow us to understand charmonium hadronic production mechanism and make gluon polarization $Δg(x)$ extraction at large $x$.

Abstract The design of a magnetized muon filter was elaborated for τ neutrino research in beam dump experiments. The parameters of the muon filter were optimized for 3000 GeV initial proton beam and 2 m detector radius installed at distance 300 m from the target. The main sources determining muon background on the detector were analyzed. It is shown that the filter provides a muon flux on the detector less than 10−11 muon·proton−1.