Missing mass analysis of the A−2 at 6.0 GeV/c

The missing mass spectrum in the region of the A^?₂ has been measured in the reaction π^?p→X^?p at 6.0 GeV/c in the interval 0.27 <|t|<0.42 (GeV/c)², with an optical spark chamber system which simultaneously observed the decay X^?→ηπ^?. A signal of 230 events above background per five MeV interval is observed at the A₂ peak, with a signal-to-background ratio of greater than 1:1. A single D-wave Breit-Wigner distribution with a quadratic background gives a good fit to the data, yielding the parameters M₀=(1.324±0.003) GeV/c² and Γ₀=(0.104±0.009) GeV/c². The spectrum is incompatible with a dipole shape.     

Measurement of photons via conversion pairs in $\sqrt{s_{NN}}$ =200 GeV Au+Au collisions with the PHENIX experiment at RHIC

Thermal photons can provide information on the temperature of the new state of matter created at RHIC. In the p_T region of 1–3 GeV/c thermal photons are expected to be the dominant direct photon source. Therefore, a possible excess compared to a pure decay photon signal due to a thermal photon contribution should be seen in the double ratio (γ/γ(π⁰))_Measured/(γ/γ(π⁰))_Simulated, if sufficient accuracy can be reached. We present a method to reconstruct direct photons by measuring e⁺e^--pairs from external photon conversions.     

Experimental evaluation of effective atomic number of composite materials using back-scattering of gamma photons

A method has been presented for calculation of effective atomic number (Z_eff) of composite materials, by using back-scattering of 662?keV gamma photons obtained from a ¹³⁷Cs mono-energetic radioactive source. The present technique is a non-destructive approach, and is employed to evaluate Z_eff of different composite materials, by interacting gamma photons with semi-infinite material in a back-scattering geometry, using a 3^″?×?3^″ NaI(Tl) scintillation detector. The present work is undertaken to study the effect of target thickness on intensity distribution of gamma photons which are multiply back-scattered from targets (pure elements) and composites (mixtures of different elements). The intensity of multiply back-scattered events increases with increasing target thickness and finally saturates. The saturation thickness for multiply back-scattered events is used to assign a number (Z_eff) for multi-element materials. Response function of the 3^″?×?3^″ NaI(Tl) scintillation detector is applied on observed pulse-height distribution to include the contribution of partially absorbed photons. The reduced value of signal-to-noise ratio interprets the increase in multiply back-scattered data of a response corrected spectrum. Data obtained from Monte Carlo simulations and literature also support the present experimental results.     

Atmospheric ultraviolet and red-infrared flashes from Universitetsky-Tatiana-2 satellite data

Millisecond ultraviolet (240–400 nm) and red-infrared (610–800 nm) flashes were detected in the nighttime atmosphere with the scientific payload installed onboard the Universitetsky-Tatiana-2 micro-satellite. Flashes with various numbers of photons, from 10²⁰ to 10²⁶, were detected within the atmospheric area 300 km in diameter observed by the detector. The flashes differ in duration and temporal profile: from single short flashes ～1 ms in duration to flashes with a complex profile more than 100 ms in duration. Different global geographic distributions are observed for flashes with different numbers of photons. Flashes with fewer than 10²² photons are distributed uniformly over the Earth’s map. Flashes with more than 10²² photons are concentrated near the equator and above the continents. Series of flashes were observed in one turn of the satellite when flying not only over thunderstorm regions but also over cloudless ones. The flash number distribution has been derived from the ratio of the numbers of red-infrared and ultraviolet photons. As applied to discharges in the upper atmosphere, whose glow is dominated by the emission in the first and second positive systems of molecular nitrogen bands (1PN₂ and 2PN₂), this distribution is equivalent to the flash altitude distribution in the atmosphere. The observed ratio of the numbers of photons in red-infrared and ultraviolet flashes agrees with the calculated one for electric discharges at altitudes higher than 50 km. In-orbit measurements of the charged particle flux (with a threshold energy for electrons of 1 MeV) provide no evidence for a synchronous occurrence of an ultraviolet flash and a burst in the particle flux in the orbit.     

Limitations of an optically pumped rubidium laser imposed by atom recycle rate

A rubidium laser pumped on the 5²S_1/2–5²P_3/2 D₂ transition by a pulsed dye laser at pump intensities exceeding 3.5 MW/cm² (>1000 times threshold) has been demonstrated. Output energies as high as 12 μJ/pulse are limited by the rate for collision relaxation of the pumped ²P_3/2 state to the upper laser ²P_1/2 state. More than 250 photons are available for every rubidium atom in the pumped volume during each pulse. For modest alkali atom and ethane spin–orbit relaxer concentrations, the gain medium can only process about 50 photons/atom during the 2–8 ns pump pulse. At 110°C and 550 Torr of ethane, the system is bottlenecked in the ²P_3/2 state and all of the incident photons cannot be absorbed. The output energy is linearly dependent on pump pulse duration for a given pump energy. The highly saturated pump limit of the recently developed three-level model for diode pumped alkali lasers (DPALs) is developed. The system efficiency based on absorbed photons approaches 36% even for these extreme pump conditions.     

Mesures de durees de vie dans le cas de faibles intensites lumineuses

A simple method concerning the possibility of lifetime's measurement in the case of low light level, 20 photons/s, is described. Application to some n¹S₀ and ¹D₂ excited states of the Hg atom is given.     

Red and near infrared down-conversion in Er3+/Yb3+ co-doped YF3 performed by quantum cutting

Er³⁺/Yb³⁺ co-doped YF₃ powder is prepared by combining a nitrate decomposition method with a NH₄HF₂ fluorization process, from which efficient energy transfer induced down-conversion is achieved. An absorbed 365 nm near ultraviolet photon is split into two photons of 650 nm red and 1000 nm near infrared radiations, both falling in the responding region of Si-based solar cells. The quantum cutting mechanism has been proposed and discussed and the energy transfer efficiency for the quantum cutting is evaluated by developing an emission intensity ratio contrast method. The investigation might offer a new possible approach to achieve Si-based solar cells of high efficiency by down-converting the near ultraviolet part of the solar spectrum.     

Electron/pion identification in the CBM TRD applying a ω<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript><Emphasis Type="Italic">k</Emphasis></Superscript></Stack> goodness-of-fit criterion

The problem of electron/pion identification in the CBM experiment based on the measurements of energy losses and transition radiation in the TRD detector is discussed. Earlier we analyzed a possibility to solve such a problem using an artificial neural network (ANN) [1]. Here we consider an approach based on a nonparametric ω _n ^k goodness-of-fit criterion, and comparison with the ANN method is also performed. We show that both methods provide a comparable level of pion suppression and electron identification, the ω _n ^k test is more simple for practical applications, the ANN method provides the needed level of pions suppression only if “clever” variables are used. We demonstrate that application of the ω _n ^k -criterion to the J/Ψ reconstruction provides a high level of pion background suppression and significantly improves a signal-to-background ratio. The text was submitted by the authors in English.     

Limits on the production of large transverse momentum direct photons deduced from the measurement of low-mass electron pairs

The hadronic production of electron pairs with masses between 200 and 500 MeV and large transverse momentum has been measured at the CERN Intersecting Storage Rings (ISR). The expected relation between low-mass electron pairs and real photons is used to determine the direct hadronic production of photons. Contrary to indications from some previous experiments, the observed spectrum is consistent with expectations from the decay of known mesons, and leads to a value for the ratio of direct photons to π⁰ of γ/π⁰ = (0.55 ± 0.92)% for 2 < p_T < 3 GeV and 〈√s〉 = 55 GeV.     

Comparison of focusing optics for femtosecond X-ray diffraction

We characterize and compare four different types of focusing optics for hard X-rays, suitable for femtosecond X-ray diffraction experiments, usinga tabletop femtosecond laser-based plasma source. We demonstrate a 23 μmfocus with a toroidally bent Ge single crystal. A maximum flux of 7× 10⁸ photons/(s mm²) is generated in a 32 μm focus using a multi-layer mirror. An elliptical glass capillary yields the highest number of photons per Bragg angle [2× 10⁵ photons/(s mrad)]. The largest number of photons[3× 10⁶ photons/s] per second is obtained in the 105 μm focus of a poly-capillary optical lens system. All numbers are given for characteristic Cu K _α photons.This revised version was published online in May 2005. The Article Category was removed.This revised version was published online in August 2005 with a corrected cover date.     

Plasma — Processed obliquely deposited Bi-Ge-Se and Ag/Bi-Ge-Se films as resist materials

Lithographic properties of photoexposed Bi₁₀Ge₂₀Se₇₀ and Ag/Bi₁₀Ge₂₀Se₇₀ films and hydrogen plasma exposed Ag/Bi₁₀Ge₂₀Se₇₀ films have been investigated. The asdeposited films show a positive resist behavior on exposure to photons and the silver overlayered films show a negative resisti behavior on exposure to both photons and hydrogen plasme. The contrast values are 1.25 and 2.3 for photoexposed positive and negative resists, respectively, and 5.0 for plasma-exposed negative resist. The sensitivity is 10²⁰ photons/cm² for the photoexposed positive and negative resists and 10¹⁸ ions/cm² (0.11 C/cm²) for the plasma-exposed negative resist.     

Two-photon fluorescence spectrum in an atom + dielectric microsphere system

A strong resonant interaction of a two-level atom with a dielectric microsphere is studied on the basis of quantum electrodynamics. The initial condition considered is one in which the atom is initially excited and the resonant mode of the microsphere has been excited by a single photon. The spectrum of two emitted photons depends strongly on the method used to excite the microsphere, i.e., on the spatial distribution of the photon energy. The most characteristic feature of the two-photon fluorescence spectrum is a strong energy correlation of the emitted photons. This correlation is expressed in the fact that the energies of the emitted photons are related by the equation of an ellipse (ω+ω ₂−2ω _vA )²+3(ω ₁−ω ₂)²= 4Ω _Rabi ² . The relation between the results obtained and the predictions of the theory of dressed states is discussed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 192–197 (10 August 1999)     

Laser frequency stabilization using an Fe-Ar hollow cathode discharge cell

Polarization spectroscopy of an Fe-Ar hollow cathode discharge cell was used to lock a frequency-doubled Ti:sapphire laser to the 372-nm⁵D₄⁵F₅ transition of ⁵⁶Fe. The discharge cell produced a density of 10¹⁸ m^-3 ground-state ⁵⁶Fe atoms at a temperature of 650 K, this density being comparable to a conventional oven at 1500 K. Saturated absorption spectroscopy and two schemes of polarization spectroscopy were compared with respect to signal-to-background ratio and the effect of velocity-changing collisions. The laser was locked within 0.2 MHz for hours by feedback of the dispersive polarization spectroscopy signal. PACS 33.55.Ad; 42.62.Fi; 52.25.Ya     

Neutron production in picosecond laser-generated plasma on a be target

Experimental data on neutron production in a plasma generated on a Be target by a picosecond laser of intensity 2 × 10¹⁸ W/cm² are presented. In contrast to previous measurements, a Ta converter is not used in this study to generate γ rays. The neutron yield is equal to 2 × 10³ over a solid angle of 4π steradians per laser pulse. A simultaneous measurement of the maximum energy of hard x rays gave E _γmax ～ 6 MeV, the number of these photons being 5 × 10⁸ over an angle of 4π steradians per laser pulse. The energy distributions of fast electrons and photons are estimated theoretically.     

Measurement of K absorption edge energies of silver and tin targets using a weak beta source

K absorption edge energies of Ag and Sn elements have been determined by using a weak beta source. In this method, the beta particles from a ⁹⁰Sr? ⁹⁰Y beta source interact with an iron foil to produce the external bremsstrahlung (EB) photons. The spectrum of EB photons is passed through the elemental target and the spectrum of transmitted photons is recorded with a high resolution HPGe detector spectrometer coupled to 16K multichannel analyzer. The recorded transmitted EB spectrum shows a sharp decrease in intensity at the K shell binding energy of elemental target. Such a sharp decrease region, which is corrected for Kβ′₂ contribution, has been used to determine the K absorption edge energies of Ag and Sn elemental targets. The measured values have been compared with theoretical and experimental values. Copyright © 2010 John Wiley & Sons, Ltd.     

Length of formation of processes in a constant external field at high energies

The complex time method is used to show that length l _C of formation of processes involving emission of photons and production of pairs in a constant external field can be determined correctly and that the resultant values of l _C have not only qualitative, but also quantitative meaning. Analysis based on the complex time method makes it possible to express the amplitudes of processes in the form of rapidly converging integrals. It is found that the radiation formation length for low-energy (soft) photons decreases upon an increase in the radiation frequency in accordance with the familiar law l _C ∼ ω^−1/3, while for higher frequencies, this dependence changes to l _C ∼ ω^−1/2. The formulas derived for l _C make it possible to indicate the accuracy with which this quantity can be treated as the radiation formation length.     

40.81 eV photoelectron spectroscopy of the thallous halides

Photoelectron spectra (using 40.81 eV photons) of TlF, TlCl, TlBr and TlI are presented. Absolute binding energies of the outermost halogen np levels with respect to the vacuum level and the energy separations between the thallium 5d_5/2 level and the halogen np level are compared with the corresponding energies predicted using the Born model for ionic solids. The thallium ion ²D_5/2 and ²D_3/2 final states display a non-statistical branching ratio and this is explained in terms of the relative photoionization cross-sections of d_5/2 and d_3/2 electrons. Structure in the spectrum of TIF is interpreted in terms of molecular orbital-like states.     

On the mechanism of rhodamine 6G fluorescence quenching

The fluorescence of the widely used TPF dye rhodamine 6G is quenched by photons of the ruby as well as the Nd-glass laser. Taking into consideration the polarisation of the ground- and excited-state absorptions of rhodamine 6G a simple model of quenching results. The main process is an S₁ absorption with subsequent leave of the ordinary rhodamine 6G singlet system. For Nd-laser photons the cross section of the concerned transition following from our quenching experiments is σS₁→S₂ = 1.2×10^-16 cm².     

Method for background reduction in an experiment devoted to WIMP searches with a liquid-xenon (liquid-argon) ionization chamber

A method for detecting ultraviolet photons from Xe ₂ ^* deexitation with an efficiency of nearly 100% is proposed. This method allows a reliable discrimination between Xe (Ar) recoil nuclei and background electrons. As a result, the β and γ background is almost completely suppressed. The neutron background can be reduced by water shielding and by selection of events involving only one recoil nucleus. The developed grid screen will remove the photon feedback. The small prototype TPC with a preliminary multiplication of ionization electrons in a proportional gap and a subsequent detection of the multiplied charges in the induction gap is constructed. The shape of an electron component of the proportional signal is obtained in this chamber for Penning mixtures. A chamber 636 mm long is now being prepared for WIMP searches. A background of about 10^?5 event/(keV kg d) can be obtained in this experiment.     

Silicon isotope separation utilizing infrared multiphoton dissociation of Si<Subscript>2</Subscript>F<Subscript>6</Subscript> irradiated with two-frequency CO<Subscript>2</Subscript> laser lights

Silicon isotope separation has been performed utilizing the infrared multiphoton dissociation (IRMPD) of Si₂F₆ irradiated with two-frequency CO₂ laser lights. The two-frequency excitation method improved the separation efficiency by keeping the high enrichment factors. For example, Si₂F₆ with the ²⁸Si fraction of 99.4% was obtained at 40.0% dissociation of Si₂F₆ after the simultaneous irradiation of 100 pulses with 966.23 cm^-1 photons (0.089 J/cm²) and 954.55 cm^-1 photons (0.92 J/cm²), while 1000 pulses were needed to obtain 99.0% of ²⁸Si at 27.2% dissociation in the case of single frequency irradiation at 954.55 cm^-1 (0.92 J/cm²). The single-step enrichment factors of ²⁹Si and ³⁰Si increased with increasing Si₂F₆ pressure. The reason for this enhancement has been discussed in terms of the rotational and vibrational relaxations by collisions with ambient gases. PACS 42.62.Cf; 82.30.Lp; 82.50.Bc