A Janus Logic Gate with Sensing Function

A layered metastructure (LM) formed by a quasi-periodic arrangement of graphene and isotropic dielectric mediums, which can realize the functions of the tunable logic gate and refractive index (RI) sensing based on spin Hall effect (SHE), is theoretically studied. The asymmetric arrangement of the mediums and the increased angle of the incident electromagnetic waves (EWs) equip the LM with Janus feature. Through the modulation of the graphene chemical potential, the sharp absorption peak (AP) in the terahertz (THz) range can be obtained, and then the AP can be used to implement NOT logic and OR logic respectively corresponding to the forward and backward scales. By locating the incident angle of light corresponding to the SHE displacement peak, the linear measurement relationship between RI and SHE angle can be realized, and the widest RI measurement range is 1–1.4 with the angles changing from 21.88° to 61.84°. Additionally, a good linear range can be achieved, owning the optimum sensitivity (S) up to 153.5° RIU⁻¹. The RI sensing still strictly follows the logic functions of the forward NOT and backward OR via adjusting the chemical potential of graphene and discriminating the peak value of SHE displacement.     

A search for πNN bound systems

The d(π⁺, π⁻)T⁺⁺⁺ and the d(π⁻, π⁺) T⁻ reactions were studied at an incident pion energy of 260 MeV. Outgoing negative pions were detected at 35° and 55° in the first reaction, and the positive pions at 45° in the second. Indications for structures corresponding to a (π⁺pp) system with a mass of 2003.0±1.0 MeV and a (π⁻nn) system with a mass of 200.1±1.5 MeV were observed with marginal statistical significance. Upper limits for the cross sections are obtained.     

Observation of charmless B meson decays

Using the ARGUS detector at the e⁺e⁻ storage ring DORIS II, we have observed charmless decays of B mesons into the final states pp̄π^± and pp̄π⁺π⁻. The significance of the signal corresponds to more than five standard deviations. The branching ratios are (5.2±1.4±1.9)×10⁻⁴ for the three-body and (6.0±2.0±2.2)×10⁻⁴ for the four-body final state. These decays cannot proceed via the dominant b→c transitions, and we show that they are not the result of penguin-type processes. Thus, the observed decays must represent b→u quark transitions. Consequently, the Kobayashi-Maskawa matrix element V_ub is non-zero.     

Inclusiveπ +/π - ratio in meson-proton reactions and the quark recombination model

The inclusiveπ ⁺/π ^- inπ ^± p andK ^± p reactions at different incident energies has been compared to that ofpp reactions. Up to ? 100 GeV/c a significant dependence on the beam quantum numbers has been observed for this ratio in the target fragmentation region. Since the naive quark recombination model cannot account for this effect, we discuss qualitatively valence quark annihilation with subsequent recombination as an additional mechanism.     

An improved upper limit on the ντ-mass from the decay π−→π−π−π−π+π+ντ

Using the ARGUS detector at the e⁺e⁻ storage ring DORIS II, we have observed the decay τ⁻→π⁻π⁻π⁻π⁺π⁺ν_τ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m(ν_τ)<35 MeV/c² at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.     

Fission and particle evaporation following stopped-negative-pion absorption in 209Bi

Fission and particle evaporation following stopped- π⁻ absorption were measured for ²⁰⁹Bi. The fission probability per captured π⁻ was obtained as W_f = (3.01 ± 0.34) × 10⁻³ from the number of fission tracks observed in the mica track detector and that of π⁻ stopped in the Bi target. The latter was derived from the observed absolute intensities of pionic Bi X-rays. The isotopic yield distributions for the (π⁻, xn) and (π⁻, pxn) reactions were also determined by in-beam and activation γ-ray measurements. From the analysis of the fission probability and the product-yield distribution, it was concluded that the thermally equilibrated nuclear states have a wide energy distribution and rather low excitation energies (∼50 MeV) compared to the initially involved energy of 140 MeV. A model was proposed for the formation and decay of ²⁰⁹Bi nuclei excited by the capture of the stopped π⁻. The model well reproduces the experimental results.     

Search for rare φ decays in π+π−γ final state

A search for φ radiative decays has been performed using a data sample of about 2.0 million φ decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From the selected e⁺e⁻→π⁺π⁻γ events the following results were obtained:B(φ→f₀(980)γ)<1×10⁻⁴ for destructive andB(φ→f₀(980)γ)<7×10⁻⁴ for constructive interference with the Bremsstrahlung process respectively,B(φ→γ→π⁺π⁻γ)<3×10⁻⁵ for E_γ>20 MeV,B(φ→ργ)<7×10⁻⁴. From the selected e⁺e⁻→μ⁺μ⁻γ eventsB(φ→μ⁺μ⁻γ)=(2.3±1.0)×10⁻⁵ has been obtained for E_γ>20 MeV. The upper limit on the P,CP-violating decay η→π⁺π⁻ has also been placed:B(η→π⁺π⁻)<9×10⁻⁴. All upper limits are at 90% C.L.     

Measurement of the reaction π+ p→π+π+ n near threshold

The reaction π⁺ p→π⁺π⁺ n was studied in the vicinity of the reaction threshold at ten incident pion beam momenta from 297 MeV/c to 480 MeV/c. From data angular distributions, invariant mass spectra and integrated cross-sections were deduced. The chiral symmetry breaking parameter as determined by this reaction equals to ξ=1.56±0.26±0.39, where the first error is experimental, while the latter reflects the uncertainty in the ansatz used in the extrapolation to the reaction threshold. A comparison with the other reaction channels of the reaction πp→ππN indicates that a single parameter (ξ) is not sufficient to describe low energy ππ interactions.     

High-precision measurement of π−p elastic scattering in a wide angular range at incident momenta between 2.06 and 3.48 GeV/c

We have measured the differential cross section for π^?p elastic scattering at eight incident momenta, 2.06, 2.26, 2.45, 2.65, 2.86, 3.05, 3.26 and 3.48 GeV/c, in a wide range of c.m. scattering angle between 15° and 160°. A pronounced dip-bump structure has been found at large angles. Details of the structure are quantitatively described as functions of the incident momentum.     

A three-body calculation of the πd → πnp reaction in the Δ-resonance region

The reaction d(π^±, pπ^±)n at incident pion momentum 340 MeV/c is analyzed based on a relativistic three-body formalism. The contributions of the various reaction mechanisms such as impulse processes, pion multiple scattering and nucleon-nucleon final-state interactions are investigated for several cases of typical kinematics. The impulse term is dominant when the recoil neutron momentum is small. On the other hand, the NN final-state interaction is found to be relatively important when the recoil neutron momentum is large. The effects of dibaryon resonances which have been suggested in πd elastic scattering are estimated using a phenomenological model. Comparisons with other work are also made.     

Study of a possible exotic 1.5 GeV meson decaying into ϕπ0

New data have been obtained on a resonance in the ϕπ⁰ system, the C meson, which is formed in the π⁻p→ϕπ⁰n charge-exchange reaction. The experiment has been performed at the Serpukhov 70 GeV accelerator. The mass and the width of the resonance are measured to be M=1480±40 MeV, Γ=130±60 MeV. The production cross section is determined at a π⁻ momentum of 32.5 GeV/c:σ(π⁻p→Cn)·BR(C→ϕπ⁰)=40±15nb. The C(1480) meson has an isospin I=1 and spin-parity J^PC=1^{− −}. It is strongly coupled to the ϕπ⁰ channel and is considered as a possible exotic meson.     

Inclusive measurements of pionic double charge exchange on 3He at low energies

Using the CHAOS spectrometer at TRIUMF pion momentum spectra and angular distributions were measured for the ³He(π⁻,π⁺) reaction at incident energies from 65 to 120 MeV and total cross sections were deduced. The data are compared to Monte Carlo simulations for the conventional reaction process as well as to predictions for the production of the hypothetical πNN resonance d′ with and without collision damping.     

Cross section determination for the reaction K+p → K+pπ+π−π0 and K+π+π+π−n at 8.2 and 16 GeV/c

The cross sections for the reactions: (a) K⁺p → K⁺pπ⁺π^?π⁺ and (b) K⁺p → K⁺π⁺π⁺π^?n have been determined at 8.2 and 16 GeV/c with the following results:at 8.2 GeV/c: (a) 0.99 ± 0.07 mb, (b) 0.41 ± 0.04 mb;at 16 GeV/c: (a) 0.72 ± 0.05 mb, (b) 0.28 ± 0.05 mb.Using the available data at other energies, the cross-section dependence of these reactions on the incident momentum is discussed.     

Coherent two pion photoproduction on 12C

We develop the formalism for coherent two pion photoproduction in nuclei and perform actual calculations of cross sections for π⁻π⁺ and π⁰π⁰ photoproduction on ¹²C. We find that due to the isospin symmetry the cross section for π⁰π⁰ production is very small and has a maximum when the pions propagate together. However, the kinematical region where the energies and polar angles of the two π⁰ mesons are equal and their relative azimuthal angle Ø = 180° is forbidden. Conversely in the π⁻π⁺ production the pions prefer to have a relative azimuthal angle 180° and the production of the pions propagating together is suppressed. The dominant one-body mechanism in both channels is related to the excitation of the Δ isobar. Hence the reaction can serve as a source of information about Δ's properties in nucleus. We have found that the reaction is sensitive to effects of the pion and Δ renormalization in the nuclear medium, similar to those found in the coherent (γ, π⁰) reaction, but magnified because of the presence of the two pions.     

Two-body pion production d(p, π+)t AT 470 and 590 MeV

The differential cross section for the reaction d(p, π⁺)t has been measured for c.m. angles between 37° and 160°, at incident proton energies of 470 and 590 MeV. The results are in qualitative agreement with the predictions of a two-nucleon model of the reaction when the D-state contribution is included, except for the existence of a backward peak at 470 MeV. Other models of the reaction are discussed; none of them gives a rationale for the backward peak at 470 MeV. A similar peak is present in older data at 325 MeV.     

A two-component model definition of two-body nucleon diffraction dissociation in πp → π(Nπ)reactions at 3.9 GeV/c and comparison with other experiments

Four low-mass “diffractive like” reactions π^±p → π^±(pπ⁰) and π^±p → π^±(nπ⁺) have been studied at 3.9 GeV/c incident pion momentum. These channels have been studied in the framework of a two-component model and we have proposed a definition of the diffraction dissociation amplitude. The following three features of the data are discussed: (1) an apparent violation of the predictions of isospin invariance for the cross section ratios, (2) the marked anisotropy of the s-channel helicity distributions and (3) the absence of the cross-over effect in the differential cross sections. The predictions of a two-component model previously used to explain the low mass $\text{I =}\text{1}\text{2}\text{(}\text{N}\text{π)}$ enhancement [1] and s- and t-channel helicity non-conservation [2] are seen to be in agreement with these observations. Predictions are also made for higher energy incident pions and incident K, p, and $\text{p}$ projectiles. These predictions are compared with available data including recent results at Fermilab and ISR energies.     

Conformational stability from Raman spectra,r0 structural parameters,and vibrational assignment of methylcyclohexane

The Raman spectra (3500–50 cm⁻¹) of the liquid and solid methylcyclohexane and the infrared spectra of the gas and solid methylcyclohexane have been recorded. The Raman band at 754 cm⁻¹ in the liquid has been confidently assigned to the less stable axial conformer and its intensity was recorded as a function of temperature from 25 to −95 °C. By the utilization of 15 different temperatures, the enthalpy difference between the more stable chair‐equatorial conformer and the chair‐axial form was determined to be 712 ± 71 cm⁻¹ (8.50 ± 0.84 kJ/mol). The ab initio predicted value of 710 cm⁻¹ (8.50 kJ/mol) from the MP2(full)/6‐311G(2d,2p) calculations with and without diffuse functions is in excellent agreement. The harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational wavenumbers have been obtained for both conformers from MP2(full)/6‐31G(d) ab initio calculations. With two scaling factors of 0.88 for the C‐H stretches and 0.9 for the remaining ones, the fundamental wavenumbers have been predicted and along with the depolarization values and infrared band contours (B‐type for A″ modes) a complete vibrational assignment has been made for the chair‐equatorial conformer. Predicted r₀ structural parameters have been provided from adjusted parameters from ab initio MP2(full)/6‐311+G(d,p) calculations. The results are discussed and compared with the corresponding properties of some similar molecules. Copyright © 2009 John Wiley & Sons, Ltd.     

Measurement of radiative Σ±→nπ±γ decay

The radiativeΣ ⁺ → nπ⁺ γ decay mode was analysed in the 81 cm SACLAY hydrogen bubble chamber exposed to a stoppingK ^? beam at the CERN PS. The pion spectrum was measured up to momenta of 150 MeV/c in theΣ rest frame. We obtain the following branching ratios based on 180 Σ⁺→nπ⁺γ and 292Σ ^?→ nπ^?γ events:Γ(Σ⁺ → nπ⁺ γ)/Γ(Σ⁺→nπ⁺)=(0.93±0.10)×10^?3 Γ(Σ^?→nπ^? γ)/Γ(Σ^?→nπ^?)=(0.46±0.06)×10^?3. An unambiguous assignment ofS-wave to the Σ^?→nπ^? andP-wave toΣ ⁺→nπ⁺ was obtained. The absolute and differential decay rates as well as the parity assignments are in good agreement with theoretical predictions.     

Measurement of the pion axial form factor from radiative decay

The decay π⁺→e⁺νγ has been measured by detecting the positron with a magnetic spectrometer and the photon with an array of NaI scintillators. Using CVC to compute the vector form factor from the π⁰ lifetime we use our data to determine the ratio γ of the axial-vector form factor to the vector form factor. With the best present value for the π⁰ lifetime (0.897±0.022±0.017)×10⁻¹⁶ s and F_V=(2.55 ±0.05)×10⁻² we obtain two solutions: γ=0.52 ±0.06, favored by a likelihood ratio greater than 8.5 against γ=−2.48±0.06.     

The strong interaction shift and width of the ground state of pionic hydrogen

The 3p-1s transition in pionic hydrogen was investigated with a high-resolution crystal spectrometer system. From the precisely measured transition energy, together with the (calculated) electromagnetic energy, the strong interaction shift of the 1s state was obtained as ϵ_1s = −7.127 ± 0.028(stat.)± 0.036(syst.) eV (attractive). From the natural line width, measured for the first time, we determine the decaywidth of the 1s state: Γ_1s^(decay) = 0.97 ± 0.10(stat.)± 0.05(syst.) eV. With the recently calculated electromagnetic corrections the s-wave scattering lengths of an isospin symmetric strong interaction are deduced. The scattering length for elastic scattering of a negative pion on a proton is a_{π⁻p→π⁻p}^h = 0.0885±0.00003(stat.)±0.0006(syst.)m_π⁻¹. The scattering lengthe for single charge exchange is found to be a_{π⁻p→π⁰n}^h = −0.136 ± 0.007(stat.) ± 0.003(syst.)m_π⁻¹.The experiment was performed at the Paul Scherrer Institute (PSI) in Switzerland. A focussing crystal spectrometer with an array of bent crystals, the cyclotron trap (a magnetic system designed to increase the particle stop density) and a CCD (charge-coupled device) detector system were employed. The results from the pionic hydrogen experiment — together with those from the pionic deuterium experiment — were used to test the isospin symmetry of the strong interaction. The present data are still consistent with isospin sysmmetry.