Muonium quantum diffusion in cryocrystals

In this paper we review our recent study on muonium (Mu) diffusion in simplest solids — Van der Waals cryocrystals. We give experimental evidence for the quantum nature of Mu diffusion in these matters. The results are compared with the current theory of quantum diffusion in insulators. The first direct observation of theT ⁷ power-law for the Mu hop rate (in solid nitrogen) is taken as confirmation of two-phonon scattering mechanism. In solid xenon the one-phonon interaction is shown to be dominant. Muonium diffusion in solid neon is discussed in terms of band-like motion. Finally, we report a dramatic effect of impurities on Mu quantum diffusion.     

Muonium quantum diffusion and localization in cryocrystals

We review our recent study of atomic muonium ( ⁺e^– or Mu, a light isotope of the hydrogen atom) diffusion in the simplest solids-van der Waals cryocrystals. We give experimental evidence of the quantum-mechanical nature of the Mu diffusion in these solids. The results are compared with the current theories of quantum diffusion in insulators. In solid nitrogen bothT ⁷ andT ^–7 temperature dependences of the Mu hop rate are observed directly for the first time, which is taken as a confirmation of a two-phonon scattering mechanism. In solid xenon and krypton, by contrast, the one-phonon interaction is dominant in the whole temperature range under investigation due to extremely low values of the Debye temperatures. Particular attention is dedicated to processes of inhomogeneous quantum diffusion and Mu localization. It is shown that at low temperatures static crystal disorder results in an inhomogeneity of the Mu quantum diffusion which turns out to be inconsistent with diffusion models using a single correlation time _c . Conventional trapping mechanisms are shown to be ineffective at low temperatures in insulators. The localization effects in Mu quantum diffusion are studied in detail in solid Kr. In all the cryocrystals studied muonium atom turns out to be localized at low temperatures.     

Lattice rearrangement induced by excitons in cryocrystals

Experiments on permanent lattice-defect formation induced by electronic excitation of rare-gas solids are presented. The creation of triplet excitons Γ(3/2) is found to be the primary process, followed by the exciton self-trapping. Probable models of defect formation are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 903–906 (May 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Photo-Production of Muons

The total cross-section for the photo-production of muons in the reaction γ + e^? → μ^? + v_e + v_μ is calculated. The dependence of the total cross-section on the incident photon energy is explicitly shown.     

Quadrupole moment of muonium and hyperfine structure of muonium levels in silicon

It is shown that experimental data on Mu¹ in silicon are most satisfactorily described by the uniaxial symmetric spin hamiltonian which means muonium displacement from the octa-cell center.     

Muons and neutrinos in the cosmic radiation

Summary This report covers 86 papers presented in HE4 and HE5 sessions of the XXIV ICRC. The topics of the papers are atmospheric muons and neutrinos, muon bundles, horizontal air showers, ?muon astronomy?, neutrino oscillations, high-energy neutrinos and neutrinos from collapsing stars. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Hydrogen and muonium in silicon

First principles calculations of the properties of hydrogen and muonium in silicon are presented. H⁺ and H⁻ are shown to have definite preferences for bond-centred and tetrahedral interstitial sites respectively whereas H⁰ (or a muon) is shown to be stable at two sites with almost equal energies, the bond-centred and antibonding sites. The structures of normal and isotropic muonium are discussed. In contrast to common belief the tetrahedral site is shown to be unstable with the muon moving spontaneously towards one of the neighbouring silicon atoms. The barrier to motion between equivalent antibonding sites is low suggesting that the normal muonium signal is isotropic because of motional averaging, not due to the symmetry of a well defined equilibrium site.     

Muons from high-energy cosmic photino

Summary The muon production at photino-nucleon interaction for high-energy photino (E⊂)10⁴GeV) is studied. The production of muons is the result of the creation and the subsequent decay of charmed hadrons. The quark subprocess considered is . In the calculation the chains of reactions and c→D→μ are taken into account. The main contribution to a muon flux is given by the production of -quark. Muon fluxes from high-energy cosmic photino absorbed in water (ground) and atmosphere are calculated. For muon energy above −2.10³GeV the ration of equilibrium underground muon flux to photino flux decreases with a rise of energyE because of nuclear interactions of D-mesons at decay length, and at energy −2·10⁵GeV the vertical muon flux created in the atmosphere becomes comparable with underground equilibrium flux. The production of muons by photino is less effective than by neutrino: the ratio is higher than for all energies. On the other hand, the cross-section at superhigh energies is by a factor of −10² larger than the cross-section. This fact gives some signature of photino flux from source in case of combined observations by sea-level EAS arrays and underground detectors: large EAS flux and relatively small flux of underground high-energy muons.

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Riassunto Si studia la produzione di muoni nell'interazione fra il fotino e il nucleone per il fotino ad alta energia (E>-10⁴GeV). La produzione dei muoni è il risultato della creazione e del conseguente decadimento di adroni con charm. Il subprocesso dei quark considerato è . Nel calcolo sono considerate le catene di reazioni e c→D→μ. Il contributo principale al flusso dei muoni è dato dalla produzione del quark . Si calcolano i flussi dei muoni dal fotino cosmico ad alta energia assorbito nell'acqua (terra) e nell'atmosfera. Per un'energia dei muoni sopra ≈2·10³GeV il rapporto tra il flusso dei muoni sotterranei in equilibrio e il flusso dei fotini diminuisce al crescere dell'energiaE a causa delle interazioni dei mesoni D a lunghezza di decadimento, e ad un'energia ∼2·10⁵GeV il flusso dei muoni verticale creato nell'atmosfera diventa paragonabile al flusso in equilibrio sotterraneo. La produzione di muoni da parte del fotino è meno efficace di quella causata dal neutrino: il rapporto è maggiore di per tutte le energie. D'altra parte, la sezione d'urto ad energie super alte è maggiore della sezione d'urto di un fattore di ∼10². Essa dà un qualche segno del flusso dei fotini dalla sorgente in caso di osservazioni combinate da schiere EAS a livello del mare e rilevatori sotterranei: un alto flusso EAS e uno relativamente ridotto di muoni sotterranei ad alta energia.

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Реэуме Исспедется роздение муонов ири взаямцеиствиях фотино с нуклонами ири энергиях фотино (E>=10⁴ ГэВ). Роздение муонов ирецтавляет реэултат обраэования и поцледыюшего раццада ачарованных адронов. Рааццматqrиваетця кварковыи цубпроцецц . При вычициениях учитываутця кварковыи реакций и c→D→μ. Оцновной вклац в мюнный поток опредчтця рождением -кварка. Вычицяютця потокоцмичецнмх фотино, поглощенные в воде (эемле) и в атмосфере. Для мюонов с энергиями выще ∼ 2·10³ ГэВ отнощение равновесного потока мюонов поц эемлей к пооку фотино уменящается с ростом энерпии Э иэ-эа ядерных бэаимодействий Д-меэонов на длине распада, и при энергии ∼2·10⁵ ГэВ вертикальный поток мюнов, образованных в атмосфере, становится сравнимым с равновесным потоком под землей. Рождение мюонов фотино оказывается менее эффективным, чем рождение мюонов нейтрино: отношение выше, чем для всех энергиях. С другой стороны, поперечное сечение при супервысоких энергиях оказывается примерно в 10² раз больше, чем сечение. В работе приводятся некоторые сигнатуры для потока фотино от источника в случае комбинированных наблюдений с помощью антенн широких атмосферных ливней на уровне моря и с помщью подземных детекторов: большой поток широких атмосферных ливней и относительно малый поток подземных мюонов высоких энергий.

     

Preliminary calculations confirming that anomalous muonium in diamond and silicon is bond-centered interstitial muonium

The model of anomalous muonium as bond-centered interstitial muonium has been examined by approximate ab-initio Hartree-Fock calculations in diamond and silicon and found to be in excellent agreement with experiment.     

Local phase transition near impurity center in neon cryocrystals

The effect of impurity centers (Ar, Kr or Xe) on the character of neon lattice rearrangement around these centers is studied by the VUV luminescence method. The temperature and time dependences of spectral intensity distribution are measured in a wide range of impurity concentrations. The observed stepwise changes in spectral characteristics are treated as a f.c.c.-h.c.p. phase transition in a local region. It is found that the region size may include 10³ atoms.     

Hyperfine splitting in positronium and muonium

We calculate corrections to the ground state hyperfine structure of relative order α² ln α^?1 in positronium and relative order $\text{(}\text{m}{}_{\mathrm{<mtext>e</mtext>}}\text{m}{}_{\mathrm{\mu }}\text{)α}{}^2\text{lnα}{}^{\mathrm{?1}}$ in muonium due to the exchange of virtual photons. Our results are in agreement with those of Lepage. Contributions arising from the Coulomb potential and from the exchange of one transverse photon along with any number of ladder Coulomb photons are discussed in detail. In treating the single transverse photon-multiple Coulomb photon exchanges, we sum the contributions involving different numbers of Coulomb photons and reexpand the resulting expression in terms of a quantity that is inherently smaller than the Coulomb potential in the non-relativistic region. The procedure enables us to take into account from the beginning important cancellations that occur between the various terms in an expansion in powers of the Coulomb potential. The techniques developed here may be useful in calculating higher order corrections.     

Defect formation stimulated by localization of excitation in atomic cryocrystals

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 5, pp. 757–762, November, 1991.     

Low-temperature muonium depolarization in Si and Ge

Measurements of the normal muonium depolarization rate in high purity silicon and germanium have been performed between 1.5 and 4.2 K. Two different Si samples and one Ge sample were investigated in a transverse field of 5 G, and in all cases, a temperature-independent depolarization rate was observed. The silicon results disagree with earlier work which showed a depolarization rate which decreased with increasing temperature in this temperature range. These results are compared with measurements of the direct muonium hyperfine transition.The authors wish to acknowledge the support of the N.S.F. grant DMR-79-09223.     

Muons of very and ultra-high energy cosmic rays

In many cosmic rays experiments at very and ultra-high energies, an excess of muons (including those of very high energy, >100 TeV) is observed that cannot be explained within existing models of hadron interactions. This excess is usually explained in terms of the heavier mass composition of primary cosmic rays. However, the excess over the predicted values even for extremely heavy compositions, and especially the observed excesses of muons with energies of >100 TeV, requires that we consider other possibilities with respect to the generation of muons, including changes in models of hadron interaction.     

Current trends in muonium chemistry

As “rapporteur” for the papers submitted to this conference in the general area of muonium chemistry, I briefly review the major developments since μSR86, and attempt to show how the papers presented at μSR90 relate to each other and work published in the intervening years. Some topics are discussed in more detail than others, reflecting my own interests and views on what is of current importance. Nevertheless, I try to cover all current research in muonium chemistry. The major areas are: early events following muon thermalization, including subsequent loss of muon polarization (the “missing fraction”); molecular structure and dynamics, primarily of muonium-substituted free radicals: and reaction kinetics.