Development of muon polarization preserved scintillators

We measured the residual μ⁺ polarizations in various liquid scintillators to search for an ideal material for an active muon stopper in which the muon spin polarization can be preserved and at the same time their energy loss and tracks can be measured by scintillation lights from the stopper material. We found the residual polarizations of mineral‐oil base liquid scintillators were \sim 4 times larger than that of a plastic scintillator. Further increase of the residual polarization was observed with a mixture of CCl₄. This revised version was published online in August 2006 with corrections to the Cover Date.     

Exact calculation of the muon polarization function

The spin dynamics of a polarized muon at an interstitial lattice site interacting with four or six nearest neighbouring nuclear spins withJ=1/2 has been investigated. The difference from the results of the Kubo-Toyabe theory is pointed out. The interaction of a muon with four nuclei with spinJ=1 including both dipolar and quadrupolar effects is considered, and some numerical results are shown.     

An experimental study of the relative response of plastic scintillators to photons and beta particles

A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6 keV to 1.332 MeV and a Ni-63 beta source with a maximum energy of 66 keV. Scintillator thicknesses ranged from 10 μm to 2500 μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. These experimental findings were used to empirically determine the optimum thickness of scintillator material with which to build a low energy beta detector which discriminates against high energy gamma photons in a mixed radiation field environment.     

Electron polarization in polarized muon decay: Radiative corrections

We calculate the first-order radiative corrections to the decay spectrum of polarized muons, for the case where the electron polarization is also observed. The significance of the results for further studies on muon decay is discussed.     

Electron scavenger effects on diamagnetic muon polarization in cyclohexane

The effect of electron scavengers on diamagnetic polarization P_D in cyclohexane were examined and compared with the experimental yield of Ps formation (inhibition and anti-inhibition effects) for the same solutions. The effect of C₆F₆ on P_D has been shown to sharply contrast, as we call non anti-inhibition, to the anti-inhibition effect in Ps formation. These results suggest that Muonium formation is different from Ps formation, and does not agree with the simple spur reaction model.     

A precise measurement of 180 GeV muon energy losses in iron

The energy loss spectrum of 180 GeV muons has been measured with the 5.6 m long finely segmented Module 0 of the ATLAS hadron Tile Calorimeter at the CERN SPS. The differential probability per radiation length of a fractional energy loss has been measured in the range ; it is compared with theoretical predictions for energy losses due to bremsstrahlung, production of electron–positron pairs, and energetic knock-on electrons. The iron elastic form factor correction to muon bremsstrahlung in the region of no screening of the nucleus by atomic electrons has been measured for the first time, and is compared with different theoretical predictions. Received: 28 December 2000 / Revised version: 14 February 2001 / Published online: 28 May 2001     

Longitudinal polarization of the emitted neutron in direct muon capture

The neutron longitudinal polarization has been calculated for ⁴⁰Ca using different wave functions for the bound proton and the emitted neutron. It is shown to be more sensitive to the final state interaction than to the details of the nuclear density.     

Calculation of the muon polarization function for longitudinal fields

Fields for a muon interacting with a single nucleus is presented. The results demonstrate quantitatively the phenomenon of the level-crossing resonance between the muon Zeeman splitting and the induced quadrupolar coupling of neighboring nuclei. Approximate numerical solutions are given for the cases of a muon interacting with four (tetrahedral site) or six (octahedral site) Cu nuclei.     

Study of the quarkonium polarization in the muon channel at ALICE

The study of quarkonium polarization at hadron colliders represents an important test of the production models. Recent results, obtained at CDF, are in striking disagreement with NRQCD predictions, although such a model correctly reproduces the production cross sections. Furthermore, in nucleus-nucleus collisions, the observed degree of polarization may be related to the characteristics of deconfined matter. Because of these interesting features, quarkonium polarization will surely represent an interesting observable at LHC energies. In ALICE, the polarization of the Ω and Γ states can be measured in the dilepton channel, both in the central barrel and in the forward (2.5<y<4) muon arm. We present the results of a feasibility study, relative to the muon channel, concerning p-p and Pb-Pb collisions, showing the expected performance for the measurement of J/Ω and Γ polarization, both as a function of transverse momentum and centrality.     

Minimal energy losses in light polarization and brightness considerations

We studied the possibility to obtain linear-polarized light from a partially polarized beam, subject to the requirement of minimal energy losses. In the case when the two components of the beam carry equal amounts of energy and are fully time-correlated, an ideal polarizer will cause energy losses of at least 41%. In any other situation the losses of such a polarizer will range from this value down to zero. This results from brightness conservation considerations. The analysis was carried out for quasi zero entropy light sources.     

Field dependence of the longitudinal muon polarization for anomalous muonium

The constant muon polarization for anomalous muonium exhibits a peculiar field dependence which represents an easily measurable signature of anomalous muonium centers even in polycrystalline materials. Furthermore it can be used to extract information on the dynamical destruction of the state upon temperature variations and it might also be useful to investigate muonium in amorphous materials.This work has been partially supported by the Swiss National Science Foundation.     

Low frequency double electron muon resonance (Demur) in fused quartz

Double electron muon resonance was studied with comparable amplitudes of the static and rf magnetic fields. The experiments were carried out in fused quartz and employed a resonant linearly-polarized rf field and a small static field. For small amplitudes of the rf field a three-line frequency spectrum was obtained consisting of a central line at the rf frequency and two weaker lines of equal amplitude symmetrically positioned about the central line. A symmetrical three line spectrum is predicted for muonium using the rotating wave approximation (RWA). For large rf fields the amplitudes of the three lines were not symmetric and depended on whether positrons were observed parallel or perpendicular to the beam. For very large rf fields the total amplitude of all the lines was less than for lower rf fields. These results do not agree with the theory using the RWA and no satisfactory theory currently exists.     

Quantum polarization and dielectric losses at low temperatures

We propose a mechanism for the quantum polarization of solid dielectrics, and use it to create and study the kinetic equation taking into account the tunneling of relaxation oscillators. The frequency dependences of both and tan are determined theoretically and compared with experiment. The density of thermally stimulated currents in the dielectrics are calculated. We find that one must take into account tunneling transitions of relaxation oscillators in order to explain the low-temperature features in the dielectric spectra.Translated from Izvestiya Vysshikh Uchebnykh Zavenenii, Fizika, No. 2, pp. 6–9, February, 1984.     

Light yield of plastic scintillators in relation to the energy of external electrons

It is shown that the specific light yield of plastic scintillators irradiated with external electrons is not a constant quantity, owing to the probability of quenching at the surface of the scintillator. The degree of proportionality of plastic scintillators can be influenced by the choice of primary additive and its concentration.