Double spin asymmetry in exclusive ρ0 muoproduction at COMPASS

The longitudinal double spin asymmetry A₁ ^ρ for exclusive leptoproduction of ρ⁰ mesons, μ+N→μ+N+ρ, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive ρ⁰ production on polarised deuterons. The Q² and x dependence of A₁ ^ρ is presented in a wide kinematical range, 3×10^-3<Q²< 7 (GeV/c)² and 5×10^-5<x<0.05. The results presented are the first measurements of A₁ ^ρ at small Q² (Q²< 0.1 (GeV/c)²) and small x (x<3×10^-3). The asymmetry is in general compatible with zero in the whole kinematical range. PACS 13.60.Le; 13.88.+e     

A Study of Compton Form Factors in Scalar QED

Deeply virtual Compton scattering has been proposed as a tool to study the structure of hadrons in an exclusive process. The Compton-scattering amplitude can be expressed in terms of scalar quantities, the Compton form factors. Their number depends on the spin of the target as well as the virtuality of the incoming and outgoing photons. For high values of the virtuality Q ² of the incoming photon, these form factors are expected to scale with inverse powers of Q ². In this paper these features are studied for a scalar target hadron.     

Kaon electro-production on protons at JLab in Hall A

The elementary reaction of kaon exclusive electro-production on protons has been studied in a broad kinematical range at Jefferson Lab in Hall A. Data have been taken at different values of the invariant center-of-mass energy W in the range W=1.8-2.2 GeV, for two values of the transferred 4-momentum Q² =1.9 and 2.4 (GeV/c)². Each kinematics was measured at different electron beam energies so as to separate the longitudinal (L) and transverse (T) contributions to the cross-section. The LT interference term has also been measured for a limited number of kinematics. The preliminary data are compared to results of different models developed in the framework of hadronic field and Regge theories.     

The radiative leptonic decays D^0 \to e^+ e^-\gamma,\mu^+\mu^-\gamma in the standard model and beyond

We present a calculation of the rare decay modes and in the framework of the standard model. For the short distance part we have derived QCD corrections to the Wilson coefficients involved, including C₉. The latter is found to be strongly suppressed by the corrections, leading to diminished values for the branching ratios in the 10^-10 range. Within SM the exclusive decays are dominated by long distance effects. Non-resonant contributions are estimated using heavy quark and chiral symmetries to be at the level of , compared to the contributions arising from , with . The total SM branching ratio is predicted to be in the range (1-. We also consider contributions coming from MSSM with and without R parity conservation. The effects from MSSM are significant only for the R parity violating case. Such contributions enhance the branching ratio to , based on appropriately allowed values for C₉ and C₁₀. This selects as a possible probe of new physics. Received: 25 October 2002 / Published online: 24 January 2003     

Spin wave stiffness parameters in lithium-zinc ferrites

The spin wave exchange stiffness has been calculated for a series of zinc substituted lithium ferrites and compared with measured values obtained by Brillouin light scattering. The theory yields values of 2.9×10⁻⁹ to 0.9×10⁻⁹ Oe-cm², relative to the observed values of 11.6×10⁻⁹ to 0 Oe-cm², for 0 to 0.4 Zn at./ formula unit, respectively.     

Role of hadronic dynamics in proton decay

Aspects of hadronic dynamics which play a crucial role in proton decay (exclusive and inclusive) are examined in the context of a comprehensive Bethe-Salpeter (BS) formalism forq \(\bar q\) andqqq systems, under harmonic confinement. The BS model which is characterized by two basic parameters—the universal spring constant \(\tilde \omega \) GeV and the quark massm _q =0.28 GeV, has already provided an impressive set of agreements in respect of a large number and variety of hadronic observables (mass spectra, and an extensive list of e.m. and pionic couplings of both mesons and baryons). TheSU(5) GUT parameters, on the other hand, are kept fixed at the ‘standard’ values, (see e.g. Langacker's review). The absolute normalization of the baryon, which is rather crucial in this case, is fixed with reference to the (topologically equivalent) process of its ‘dissociation’ into three quarks by a hard photon, which makes use of the structure function sum rule \(\int\limits_0^1 {dxF_2^p (x)/x = \sum {Q_i^2 } } \) , instead of the usual BS normalization (which amounts to the conservation of charge). Thee ⁺ inclusive rate, which is about three times that of thee ⁺π⁰ mode, works out at0.54×10 ^?33 yr ^?1 which is smaller than most contemporary calculations by two orders of magnitude. Other exclusive modes are also consistent with the above estimate. The theoretical implications of these results vis a vis contemporary calculations as well as current experimental searches are discussed.     

Semiconducting properties of refractory oxides systems

Abstract

The electrical conductivity and thermoelectric power of pure and doped oxides system La₂O₃-Cr₂O₃-Al₂O₃ were investigated. Only single phase was observed in the compositions studied (20 atom fraction of aluminium).

The conductivity increases with increasing chromium content in the range of compositions studied, the values ranging from 10^?4 (ω-cm)^?1 to 1. 2 × 10^?1(ω-cm)^?1. In the case of samples doped with calcium (0. 01) the corresponding values range from 2 × 10^?1 (ω-cm)^?1 to 1. 67(ω-cm)^?1. The significance of the results has been discussed.     

The role of the pion cloud in the interpretation of the valence light-cone wavefunction of the nucleon

The pion cloud renormalises the light-cone wavefunction of the nucleon which is measured in hard, exclusive photon-nucleon reactions. We discuss the leading twist contributions to high-energy exclusive reactions taking into account both the pion cloud and perturbative QCD physics. The nucleon’s electromagnetic form-factor at high Q² is proportional to the bare nucleon probability Z and the cross-sections for hard (real at large angle or deeply virtual) Compton scattering are proportional to Z². Our present knowledge of the pion-nucleon system is consistent with Z = 0.7 ± 0.2. If we apply just perturbative QCD to extract a light-cone wavefunction directly from these hard exclusive cross-sections, then the light-cone wavefunction that we extract measures the three valence quarks partially screened by the pion cloud of the nucleon. We discuss how this pion cloud renormalisation effect might be understood at the quark level in terms of the (in-)stability of the perturbative Dirac vacuum in low energy QCD.     

Twenty-parameter eigenfunctions and energy values of the 23 S States of He and He-like Ions

Twenty-parameter calculations of the energies and wave functions of the first excited states 2³ S of He, Li⁺, Be⁺⁺, B⁺⁺⁺, O⁶⁺, Ne⁸⁺, Mg¹⁰⁺, have been carried out using Hylleraas' method. The energy values have been corrected for mass polarization. The coefficients of the best wave functions are listed. Similar calculations for the 2³ S state of the H^? ion yield an energy value which cannot be distinguished from the energy of a free H atom. For He and Li⁺, in addition, forty-parameter calculations have been carried out. The results compare well with the recent calculations of Pekeris using a somewhat different method. Even after the inclusion of the relativistic correction, the theoretical energy values deviate slightly from the observed. The differences, ?0·10±0·05 cm^?1 for He and ?1·07±0·10 cm^?1 for Li⁺, represent observed values of the Lamb shifts in the 2³ S states. These values agree within their uncertainties with the values predicted from quantum electrodynamics.     

Total FTIR Spectra Translation for Improving Quantification of Protids

Abstract

In infrared spectroscopy, uncertain variations of the baseline are observed and these add an arbitrary constant to every absorbance. We have recently proposed an automatic baseline correction method by total translation of the infrared spectrum with regard to a reference spectrum (Cadet and Offmann, 1996a). This method improved the precision of the values obtained during quantitative determination of parotids in raw sugar cane juices: the mean and standard deviation values before correction were 1.3 × 10^?2 and 8.58 × 10^?2 and after correction they were 1.4 × 10^?2 and 7.05 × 10^?2respectively.     

On the applicability of perturbative QCD to exclusive processes at currently available momentum transfer

We re-examine the problems connected with the end-point dominance in the calculation of exclusive processes in perturbative QCD. In a re-analysis we construct nucleon quark distribution amplitudes from the respective moments obtained from a QCD sum rule approach. These functions lead to acceptable values for the e.m. Dirac form factorsF ₁ ^p,n of the nucleon if effective gluon masses of ca. 300–600 MeV are included into the hard-scattering amplitude. In addition we also find a reasonable Q₂ — dependence of the proton form factor. The results point at the importance of the end-point k-dependence of distribution amplitude and hard-scattering amplitude in the calculation of exclusive processes.Work is supported by Deutsche Forschungsgemeinschaft (Ga 153-13-1) and partially by NATO (0581/87)     

Inclusive and exclusive measurements in the projectile breakup of 7Li

The inclusive and exclusive measurements were carried out for ⁷Li projectile breakup on ²⁷Al target at 48 MeV. In the inclusive data we have observed a broad peak around the beam velocity for alphas and tritons. The exclusive data for alpha-triton coincidences show good agreement with the post-form DWBA theory of breakup reactions.     

Study of dimuon rare beauty decays with ATLAS and CMS

The LHC experiments will perform sensitive tests of physics beyond the standard model (BSM). The investigation of decays of beauty hadrons represents an alternative approach in addition to direct BSM searches. The ATLAS and CMS efforts concentrate on those B-decays that can be efficiently selected already at the first and second level trigger. The most favorable trigger signature will be for B-hadron decays with muons in the final state. Using this trigger, ATLAS and CMS will be able to accommodate very high statistics in the rare decay sector. These are purely dimuon decays, and families of semimuonic exclusive channels. Already with data corresponding to an integrated luminosity of 1 fb^-1, the sensitivity in the dimuon channels will be comparable to present measurements (world average). The strategy is to carry on the dimuon channel program up to nominal LHC luminosity. In particular the B_s→μμ signal with ∼5 sigma significance can be measured combining low luminosity 10³³ cm^-2 s^-1 samples with those of one year of LHC operation at a luminosity of 10³⁴ cm^-2 s^-1. PACS 13.30.Ce; 13.20.He     

A note on the elastic constants of sodium bromate from 350 K to 77 K

The elastic constantsC ₁₁,C ₁₂ andC ₄₄ of sodium bromate single crystals have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC ₁₁=5.57₈,C ₁₂=1.07₅,C ₄₄=1.51₀ (×10¹⁰ N/m²) at 290 K and 6.35, 1.98 and 1.65 (×10¹⁰ N/m²) at 77 K. The present room temperature values agree closely with the recent values of Gluyaset al. but the other earlier measurements show some scatter. A comparison between the elastic constants of sodium bromate and sodium chlorate is also made.     

Double vector-charmonium production in electron-positron annihilation into two photons at $$\sqrt s = 10.6$$ GeV

In experimentally studying the exclusive production of two \(c\bar c\) mesons in electron-positron annihilation, the BELLE Collaboration obtained results that differ substantially from theoretical predictions. Recently, it was assumed that a significant part of this discrepancy can be explained by the process e⁺e^? → 2γ* → 2J/ψ, and its cross section was published. It is shown here that these results are incorrect (the cross sections are overestimated). The correct values of the cross sections for the double production of various vector charmonia are given.     

Elastic constants of sodium chlorate from 77 K to 350 K

The elastic constantsC ₁₁,C ₁₂ andC ₄₄ of sodium chlorate single crystal have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC ₁₁=4.90,C ₁₂=1.39,C ₄₄=1.17 (× 10¹⁰ N/m ²) at 298 K and 6.15, 2.16, 1.32 (×10¹⁰ N/m ²) at 77 K. The data agree well with the values measured earlier up to 223 K. Brief mention is also made of the low temperature bonding problems in these soft crystals.     

Mössbauer Characterization of Iron-Based Nanogranular Films

The electric field gradients (EFG) of the Hf₂Fe intermetallic compound were calculated using the full-potential linearized augmented plain-wave (FP-LAPW) method as embodied in the WIEN 97 code. The obtained values are compared with other ab-initio calculations and on a qualitative basis with the previously reported experimental data obtained from TDPAC. The calculated results, −23.1·10²¹ V/m² and 2.7·10²¹ V/m² for Hf 48f and Fe 32e position, respectively, are in excellent agreement with experimental data (23.4·10²¹ V/m² and 2.7·10²¹ V/m²), better than those reported in earlier calculations. The calculated EFG for Hf 16c position (4.2·10²¹ V/m²) is stronger than the experimental one (1.1·10²¹ V/m²).     

Modeling and simulation of long-wave infrared InAs/GaSb strained layer superlattice photodiodes with different passivants

Current–voltage characteristics of long-wave infrared (LWIR) InAs/GaSb strained layer superlattice photodiodes (cut-off wavelength ∼10 μm), passivated with different surface passivants, have been modeled and simulated using ATLAS software from SILVACO. The simulated results are fitted to previous experimental results obtained on unpassivated devices and those passivated by silicon-dioxide (SiO₂), silicon nitride (Si_xN_y) and zinc sulfide (ZnS). Surface parameters in terms of surface recombination velocity, shunt resistance and interface trap density are extracted for different passivants. The performance of silicon-dioxide passivated diode is solely dominated by a shunt leakage path with a shunt resistance value of 0.56 Ω-cm². Extracted electron and hole surface recombination velocities have values of 10⁵ cm/s and 10⁷ cm/s for unpassivated, 10³ cm/s and 10⁵ cm/s for Si_xN_y passivated and 10² cm/s and 10³ cm/s for ZnS passivated devices. Interface trap density follows a similar trend with values of 10¹⁵ cm⁻², 8.5 × 10¹⁴ cm⁻² and 10¹⁰ cm⁻² for unpassivated, Si_xN_y passivated and ZnS passivated devices respectively. The suitability and limitations of the simulation tool are discussed.