Trilepton production by neutrinos and antineutrinos

We calculate the electromagnetic and hadronic contributions to neutrino production of μ^?e⁺e^? events and antineutrino production of μ⁺e⁺e^? events. Due to an increase in cross section and acceptance, these rates are much larger in bubble-chamber experiments than the corresponding rates for trimuon events in counter experiments. Verification of these rates would confirm our understanding of the physics behind trilepton events. We stress the importance of measuring also a rate for μ^?e^? events to determine the cross section for the associated production of charmed particles.     

On two-body decays of a scalar glueball

We study two-body decays of a scalar glueball. We show that in QCD a spin-0 pure glueball (a state with only gluons) cannot decay into a pair of light quarks if chiral symmetry holds exactly, i.e., the decay amplitude is chirally suppressed. However, this chiral suppression does not materialize itself at the hadron level such as in decays into π⁺π^- and K⁺K^-. We show this explicitly in the two cases with the glueball much lighter and much heavier than the QCD scale using low-energy theorems and perturbative QCD. For a heavy glueball, using QCD factorization based on an effective Lagrangian, we find that the hadronization into ππ and KK leads to a large difference between Br(π⁺π^-) and Br(K⁺K^-); even the decay amplitude is not chirally suppressed. Our results can provide some understanding of the partonic contents if Br(ππ) or Br(KK̄) is measured reliably.     

大功率低功耗快速软恢复SiGeC功率开关二极管

为满足电力电子电路对功率开关二极管高频化的发展要求，提出了一种大功率低功耗快速软恢复p⁺(SiGeC)-n^--n⁺异质结二极管.与常规的Si p-i-n二极管相比，在正向电流密度不超过1000 A/cm²情况下，p⁺(SiGeC)-n^--n⁺二极管的正向压降减少了约1/5，有效降低了器件的通态功耗；反向恢复时间缩短了一半多，反向峰值电流降低了约25%，软 关键词： 快速软恢复 大功率低功耗 SiGeC/Si异质结功率二极管     

SUSY effects in Higgs production at high energy e+e- colliders

Considering the constraints from collider experiments and dark matter detection, we investigate the SUSY effects in the Higgs production channels e⁺e^-→Zh at an e⁺e^- collider with a center-of-mass energy above 240 GeV and γγ→h→bb at a photon collider with a center-of-mass energy above 125 GeV. In the parameter space allowed by current experiments, we find that the SUSY corrections to e⁺e^-→Zh can reach a few percent and the production rate of γγ→h→bb can be enhanced by a factor of 1.2 over the SM prediction. We also calculate the exotic Higgs production e⁺e^-→Zh₁ in the next-to-minimal supersymmetric model (NMSSM) (h is the SM-like Higgs, h₁ is the CP-even Higgs bosons which can be much lighter than h). We find that at a 250 GeV e⁺e^- collider the production rates of e⁺e^-→Zh₁ can reach 60 fb.     

Tuneable laser operation of F+2 and (F+2)A centers in OH- and SH- doped alkali halides

Stabilization and tuneable laser operation of F⁺₂ and (F⁺₂)_A centers using OH^- and SH^- doped alkali halide crystals are reported. The new stabilization technique improves previously described laser systems and produced a new F⁺₂(KBr) laser (1.72–2 μm), covering an important gap around 2 μm. All crystals can easily be reactivated for laser operation after extended periods of storage at room temperature.     

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species Si_Ga ⁺ and as shallow acceptor species Si_As ^-. The solubility of Si_As ^- is much lower than that of Si_Ga ⁺ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is Si_Ga ⁺ which will convert into Si_As ^- in accordance with their solubilities and that the point defect species governing the diffusion of Si_Ga ⁺ are triply-negatively-charged Ga vacancies V_Ga ^3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n⁺-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently. Received: 19 April 1999 / Accepted: 3 May 1999 / Published online: 4 August 1999     

Experimental resolution of the 145Gd ϵ/β-decay branching ratio anomalies

Previously reported large anomalies in ¹⁴⁵Gd ?/β⁺ decay branching ratios can be completely explained by improved experimental data. New, high-statistics decay-scheme data show conclusively that the anomalies resulted from numerous, formerly unobserved, weak transitions from levels in ¹⁴⁵Eu fed primarily by ?-decay. In addition, the ¹⁴⁵Gd β⁺ endpoint is measured by β-γ coincidence techniques to be 240 keV lower than originally reported.     

Charged ρ photoproduction in the energy range 2.8–4.8 GeV

Measurements of the photoproduction processes γρ→ρ⁺ n and γρ→ρ^-Δ⁺⁺ (1236) are reported in the energy range 2.8 to 4.8 GeV. The data show shrinkage of the differential cross section in this energy region for the process γρ→ρ^-Δ⁺⁺ (1236); no shrinkage is observed for the ρ⁺ n process. The energy dependences of the ρ⁺ n and ρ^-Δ⁺⁺ (1236) total cross sections are much steeper than current model prediction. The ρ spin density matrices for each process are also presented.     

Relation between anomaly in type-I superstring and anomaly in its effective theory

We explicitly calculate the hexagon and heptagon (covariant) gauge anomaly including the precise numerical coefficients in type-I open superstring. The calculation is performed by using the Pauli-Villars regularization on the basis of the stringy Ward identity, which is an assumption weaker than the cancelled propagator argument. We show that the anomalies in the effective theory are realized as the zero slope limit (α^′→0) of the string anomalies in a very non-trivial way in the present calculational scheme. This non-trivial realization in higher point (n≧8) anomalies is also discussed.     

Static sims studies of adsorbate structure: II. CO adsorption on Pd(111); adsorbate-adsorbate interactions on Ru(001), Ni(111) and Pd(111)

In a study of CO adsorption on Pd(111) it is shown that the secondary ion mass spectrum contains information on both adsorbate site geometry and adsorbate coverage. The fractional yields of PdCO⁺, Pd₂CO⁺ and Pd₃CO⁺, as a function of CO coverage are correlated with the changing site geometries suggested by reflection IR data. A relationship between secondary ion emission and the adsorbate-adsorbate interactions revealed by IR and EELS is also demonstrated for CO adsorption on Ru(001), Ni(111) and Pd(111).     

小变形原子核中的相干效应

本文考察了在转动的小变形核力场中运动的核子-核子对、核子-空穴对中的相干效应。计算了O¹⁸最低的偶宇称态0⁺,2⁺,4⁺和O¹⁶最低的奇宇称态0^-,1^-,2^-,3^-波函数;和壳模型经典方法计算出的结果作了比较,二者相当一致。得出的初步结论如下:核力主要是P₂力再加上一定成分具有相干性质的力。前者与转动的变形场等效。不但对于0⁺,2⁺,4⁺,3^-态,而且对于1^-,2^-态,附加的相干成分都很重要;它们的内部态混合组态是比较多的,粒子-粒子之间、或粒子-空穴之间的关联都比较显著。只有0^-态的内部态是纯组态。     

Lepton number violation in D meson decay

The lepton number violation(LNV) process can be induced by introducing a fourth generation heavy Majorana neutrino,which is coupled to the charged leptons of the Standard Model(SM). There have been many previous studies on the leptonic number violating decay processes with this mechanism. We follow the trend to study the process: D→Kllπ with the same-sign dilepton final states. We restrict ourselves to certain neutrino mass regions,in which the heavy neutrino could be on-shell and the dominant contribution to the branching fraction comes from the resonance enhanced effect. Applying the narrow width approximation(NWA),we found that the upper limit for the branching fractions for D0→ K-l+l+π-are generally at the order of 10-12 to 10-9,if we take the most stringent upper limit bound currently available in the literature for the mixing matrix elements. We also provide the constraints,which is competitive compared to the LNV B decays,on the mixing matrix element |VeN|2 based on the upper limit of D0→ K-e+e+π-estimated from the Monte-Carlo(MC) study at BESⅢ. Although the constraints are worse than the ones from(0νββ) decay in the literature,the future experiment at the charm factory may yield more stringent constraints.     

Diffusion of positive muons in zone-refined iron below room temperature

The relaxation rate λ of μ⁺ spin in α-iron polycrystals and single crystal of 99.995% purity has been measured from 299 down to 50 K. At room temperature it is 0.14 μsec^-1, much smaller than ever observed. Above 120 K its temperature dependence obeys an Arrhenius law (activation energy 44 ± 3 meV) for the μ⁺ diffusion. Previous values in less pure samples are discussed in terms of internal field inhomogeneity and of μ⁺ trapping by chemical or non-chemical defects. The deduced diffusion rate is proportional to T² in the whole temperature region studied.     

Water-like anomalies in the core-softened systems: Dependence on the trajectory in density-temperature plane

We show that the existence of the water-like anomalies in kinetic coefficients in the core-softened systems depends on the trajectory in ρ-T plane along which the kinetic coefficients are calculated. In particular, it is shown that the diffusion anomaly does exist along the isotherms, but disappears along the isochors. We analyze the applicability of the Rosenfeld entropy scaling relations to the systems with the core-softened potentials demonstrating the water-like anomalies. It is shown that the validity of the Rosenfeld scaling relation for the diffusion coefficient also depends on the trajectory in the ρ-T plane along which the kinetic coefficients and the excess entropy are calculated. In particular, it is valid along isochors, but it breaks down along isotherms.     

To search for four-quark states in γγ-collisions

It is shown that the reactions γγ into hadrons is a rather effective means of searching for fourquark states. We predict the suppression ofS ^*(980,0⁺) and δ(980,0⁺) in γγ→ππ and γγ→π⁰ η respectively, if they are four-quark states from (9.0⁺). The well-known anomaly in γγ→ρ ⁰ ρ ⁰ is interpreted as the production of the tensor four-quark resonances with the isospin 0 and 2. We predict the absence of similar enhancement in γγ→ρ ⁺ ρ ^?. The bright anomalies are predicted near thresholds of γγ→ρ ⁰ ω and γγ→ρ ⁰ ?     

Comparison of electron and muon charged current neutrino and antineutrino interactions in a neonH2 mixture

From an exposure of the Fermilab 15 ft Neon(64 atomic %)H₂ filled bubble chamber to a single-horn-focussed $\text{ν}$ beam, we have found 60 e^?X and 35 e⁺X events, which we compare with 227 μ^?X and 202 μ⁺X events. No statistically significant departures from μ-e universality are seen in the shapes of various differential cross sections.     

Flavor changing neutral currents and multileptons in e+e- and vμN,vμN

New quarks and new flavor-changing neutral currents give multiple lepton plus hadron final states in e⁺e^-, $\text{v}{}_{\mathrm{\mu }}\text{N,}\text{v}{}_{\mathrm{\mu }}\text{N}$. We observe that (i) e⁺e^- is a favored place to search for their effects through inclusive ratios σ(e⁺e^-+x:σ (μ⁺μ^- +x): σ(e±μ±+x) and same sign leptons e±e±+x, μ±μ±+x,e±μ±+x. Above a new flavor threshold four charged lrpton final states may become important. (ii) Trilepton final states in $\text{v}{}_{\mathrm{\mu }}\text{N,}\text{v}{}_{\mathrm{\mu }}\text{N}$ are not sensitive to the presence of flavor-changing neutral currents. Much more sensitive are the processes $\text{v}{}_{\mathrm{\mu }}\text{N}$ are ⁺e^-+βand (for charm changing neutral currents) $\text{v}{}_{\mathrm{\mu }}\text{N→e}{}^{\mathrm{+}}\text{β}$.     

Associated production of sfermions and gauginos at high-energy ee colliders: The case of selectrons and electronic sneutrinos

We analyze the associated production at future high-energy e ⁺ e ^- colliders, of first generation sleptons with neutralinos and charginos in the modes e ⁺ e ^- and , in the framework of the minimal supersymmetric extension of the standard model. We show that the production rates, in particular for associated production of right-handed selectrons and the lightest neutralino which in general is the first accessible kinematically, can be much larger than the corresponding ones for second and third generation scalar leptons and for scalar quarks. With the high luminosities expected at these colliders, the detection of first generation sleptons with masses significantly above the kinematical two-body threshold, , is thus possible in favorable regions of the parameter space. Received: 27 June 2002 / Published online: 20 September 2002     

Electron and positron work functions of Cr(100)

We report measurements of the electron and positron work functions of submonolayer contaminated single crystal surfaces of Cr(100) in ultra high vacuum. The positron work function ø₊ is obtained by measuring the spectrum of slow positrons reemitted by the Cr(100) surface when it is bombarded with keV energy positrons. The electron work function ø_- is measured relative to Al(100) by comparing the target biases at which the slowest emitted positrons are recollected by the target. We obtain ø₊ = ?1.76(10) eV and ø_- = 4.46(6) eV for our Cr(100) surface using the value ø_- = 4.41(3) eV for Al(100) reported by Grepstad, Gartland and Slagsvold. The ø₊ value is in agreement with the ?2.2 eV calculated by Nieminen and Hodges. The positronium work function for Cr implied by these results is ?4.10(10) eV; the positronium negative ion (Ps^-) work function for this surface is calculated to be + 0.37(7) eV. A search for Ps^- showed that at a 90% confidence level less than one in 10³ thermalized positrons reaching the Cr surface are emitted as Ps^-. The slow positron emission spectrum was observed not to change over the 70–300 K range in contrast to recent theoretical predictions.     

Ti-Pd系合金的比热测量

本文给出了Ti-Pd系合金样品的低温比热的测量结果,得出样品Ti_0.92Pd_0.08及Ti_0.8Pd_0.2的电子比热系数r分别为5.89mJ/mol·K²和4.78mJ/mol·K²,显然比纯Ti的r值3.32mJ/mol·K²高得多。因此,它们的费密面的电子态密度也比纯Ti的高,这正是Ti-Pd系合金的超导转变温度T_c比纯Ti的有较大幅度提高的原因。 关键词：