Up-down Asymmetry Research Articles

Feasibility study of measuring brightarrow sgamma photon polarisation in D^0rightarrow K_1(1270)^- e^+nu _e at STCF

We report a sensitive study of measuring brightarrow sgamma photon polarisation in D^{0}rightarrow K_1(1270)^-e^+nu _e with an integrated luminosity of mathscr {L} = 1 ab^{-1} at a center-of-mass energy of 3.773 GeV at a future Super Tau Charm Facility. More than 61,000 signals of D^{0}rightarrow K_1(1270)^-e^+nu _e are expected. Based on a fast simulation software package, the statistical sensitivity for the ratio of up-down asymmetry is estimated to be 1.5times 10^{-2} by performing a two-dimensional angular analysis in D^{0}rightarrow K_1(1270)^-e^+nu _e. Combining with measurements of up-down asymmetry in Brightarrow K_1gamma , the photon polarisation in brightarrow sgamma can be determined model-independently.

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

The algorithm for bolometer tomography at Wendelstein 7-X (W7-X) has been recently improved using a novel regularization functional, based on relative gradient smoothing of the sought radiation profile. It has been validated using radiation patterns provided by 3D modeling under real plasma conditions as phantoms and then applied to bolometer measurements performed during the first divertor operation phase of W7-X. The following results are presented: (1) edge-localized 2D radiation patterns with clearly resolved magnetic island radiation structures, (2) an up-down asymmetry in the impurity radiation that is not captured by the 3D edge plasma transport modeling, (3) reversal of the asymmetry with reversed magnetic field direction. Further analysis reveals a poloidal variation of the emissivity in the outer confined plasma region with a field-direction dependent asymmetry, also supported by the soft x-ray measurements. This asymmetry is considered to be related to asymmetric impurity distributions, driven by the pronounced ion-impurity friction force at the plasma edge where the collisionality of the W7-X plasma is sufficiently high to develop impurity asymmetry as predicted by neoclassical theory of parallel impurity transport.

Up-down asymmetries and angular distributions in D→K1(→Kππ)ℓ+νℓ

Using the helicity amplitude technique, we derive differential decay widths and angular distributions for the decay cascade $D\to K_{1}(1270,1400)\ell^+\nu_{\ell}\to (K\pi\pi)\ell^+\nu_{\ell} (\ell=e,\mu)$, in which the electron and muon mass is explicitly included. Using a set of phenomenological results for $D\to K_1$ form factors, we calculate partial decay widths and branching fractions for $D^0\to K_1^-\ell^+\nu_{\ell}$ and $D^+\to K_1^0\ell^+\nu_{\ell}$, but find that results for ${\cal B}(D\to K_1(1270)e^+\nu_{e})$ are larger than recent BESIII measurements by about a factor 1.5. We further demonstrate that the measurement of up-down asymmetry in $D\to K_{1}e^+\nu_e\to (K\pi\pi)e^+\nu_{e}$ and angular distributions in $D\to K_{1}\ell^+\nu_\ell\to (K\pi\pi)\ell^+\nu_{\ell}$ can help to determine the hadronic amplitude requested in $B\to K_1(\to K\pi\pi)\gamma$. Based on the Monte-Carlo simulation with the LHCb geometrical acceptance, we find that the angular distributions of MC events can be well described.

Influence of up-down asymmetry in plasma shape on RMP response

Shaping effect on the plasma response to the externally applied resonant magnetic perturbation field is investigated for both DIII-D and MAST experiments, utilizing toroidal modeling. The plasma boundary shape is systematically varied ranging from single-null (SN) to double-null (DN) configurations, while other equilibrium quantities are kept largely unchanged. The relative amplitude of the computed plasma surface displacement, between the top/bottom of the torus and the outboard mid-plane, is identified as the most reliable indicator that distinguishes the plasma response between the SN and DN configurations. The underlying physics is the weakening of the edge-peeling component in the plasma response with increasing up-down symmetry of the plasma boundary shape.

Natural interpretation on the data of Λc→Σπ

Even though the Standard Model (SM) has achieved great success, its application to the field of low energies still lacks solid foundation due to our limited knowledge on non-perturbative QCD. Practically, all theoretical calculations of the hadronic transition matrix elements are based various phenomenological models. There indeed exist some anomalies in the field which are waiting for interpretations. The goal of this work is trying to solve one of the anomalies: the discrepancy between the theoretical prediction on the sign of the up-down asymmetry parameter of $\Lambda_c\to\Sigma\pi$ and the experimental measurement. In the literatures several authors calculated the rate and determined the asymmetry parameter within various schemes, but there exist obvious loopholes in those adopted scenarios. To solve the discrepancy between theory and data, we suggest that not only the direct transition process contributes to the observed $\Lambda_c\to\Sigma\pi$, but also other portals such as $\Lambda_c\to \Lambda\rho$ also play a substantial role via an isospin-conserving re-scattering $\Lambda\rho\to\Sigma\pi$. Taking into account of the effects induced by the final state interaction, we re-evaluate the relevant quantities. Our numerical results indicate that the new theoretical prediction based on this scenario involving an interference between the direct transition of $\Lambda_c\to\Sigma\pi$ and the portal $\Lambda_c\to\Lambda\rho\to\Sigma\pi$ can make both the decay rate and sign of the asymmetry parameter to be consistent with data.

Novel Method to Reliably Determine the Photon Helicity in B→K_{1}γ.

A sizable right-handed photon polarization in b→sγ is a clear signal for new physics. In this Letter, we point out that the photon helicity in b→sγ can be unambiguously extracted by combining the measurements in B→K_{1}γ and the Cabibbo-favored D→K_{1}e^{+}ν decay. We propose a ratio of up-down asymmetries in D→K_{1}e^{+}ν to quantify the hadronic effects. A method for measuring, in experiment, the involved partial decay widths in the ratio is discussed, and experimental facilities like BESIII, Belle-II and LHCb are likely to measure this ratio. We also give the angular distribution that is useful for extracting the photon polarization in the presence of different kaon resonances.

Global ITG eigenmodes: From ballooning angle and radial shift to Reynolds stress and nonlinear saturation

We present global linear and nonlinear simulations of ion temperature gradient instabilities based on a fluid formulation, with an adapted version of the JOREK code. These simulations are performed in realistic global tokamak equilibria based on the solution of the Grad–Shafranov equation. Benchmarking of linear growth rates was successfully completed with respect to previously published data. We find two distinct types of eigenstructures, depending on the magnetic shear. For high shear, when the coupling of poloidal harmonics is strong, ballooning-type eigenmodes are formed, which are up-down asymmetric with a finite ballooning angle, θ0. The poloidal harmonics which form the global eigenmode are found to demonstrate a radial shift, being centered well outside of their corresponding rational surface. Stronger diamagnetic effects increase both θ0 and proportionately shift the m harmonics to larger radii (by as much as two rational surfaces). In the low shear regime, the unstable eigenmodes become narrowly localized between neighboring pairs of rational surfaces, and exhibit no up-down asymmetry. Our simulations also show the generation of finite Reynolds stress due to nonlocal/global profile effects. This stress possesses both poloidally symmetric (n=m=0) and asymmetric (finite-m) components. Turbulent saturation in nonlinear simulations is demonstrated for both shear regimes.

Recent results from OKA setup at U-70 synchrotron

Several radiative decays are under study by OKA setup at U-70 synchrotron. First, the radiative decay K + → µ + νγ(K µ2γ ) is studied on statistics of about 95K events for 25 MeV < < 150 MeV. A clear destructive interference between bremsstrahlung and structure dependent SD − term is observed. As a result, the vector and axial-vector form factors difference is measured: F V − F A = 0.134 ± 0.021(stat.) ± 0.027(syst.) which is 2.3 σ away from χP T O(p 4). Moreover, the decay K + → π + π − π + γ is studied on statistics of about 450 events for 30 Mev < < 70 Mev. The total and differential branching fractions of the decay are measured. Br(K + → π + π − π + γ) = (7.1±0.4(stat.)±0.3(syst.))·10−6 to be compared with χP T O(p 4) (6.65 ± 0.05) · 10−6. In addition, a search for an up-down photon asymmetry with respect to the hadronic system decay plane is performed.

Two-body hadronic weak decays of antitriplet charmed baryons

We study Cabibbo-favored (CF) and singly Cabibbo-suppressed (SCS) two-body hadronic weak decays of the antitriplet charmed baryons ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$, ${\mathrm{\ensuremath{\Xi}}}_{c}^{0}$, and ${\mathrm{\ensuremath{\Xi}}}_{c}^{+}$ with more focus on the last two. Both factorizable and nonfactorizable contributions are considered in the topologic diagram approach. The estimation of nonfactorizable contributions from $W$-exchange and inner $W$-emission diagrams relies on the pole model and current algebra. The nonperturbative parameters in both factorizable and nonfactorizable parts are calculated in the MIT bag model. Branching fractions and up-down decay asymmetries for all the CF and SCS decays of antitriplet charmed baryons are presented. The prediction of $\mathcal{B}({\mathrm{\ensuremath{\Xi}}}_{c}^{+}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}^{0}{\ensuremath{\pi}}^{+})$ agrees well with the measurements inferred from Belle and CLEO, while the calculated $\mathcal{B}({\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+})$ is too large compared to the recent Belle measurement. We conclude that these two ${\mathrm{\ensuremath{\Xi}}}_{c}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Xi}}{\ensuremath{\pi}}^{+}$ modes cannot be simultaneously explained within the current-algebra framework for $S$-wave amplitudes. This issue needs to be resolved in future study. The long-standing puzzle with the branching fraction and decay asymmetry of ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}^{0}{K}^{+}$ is resolved by noting that only the type-II $W$-exchange diagram contributes to this mode. We find that not only does the calculated rate agree with experiment but also the predicted decay asymmetry is consistent with the SU(3)-flavor symmetry approach in sign and magnitude. Likewise, the CF mode ${\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Sigma}}}^{+}{K}^{\ensuremath{-}}$ and the SCS decays ${\mathrm{\ensuremath{\Xi}}}_{c}^{0}\ensuremath{\rightarrow}p{K}^{\ensuremath{-}}$, ${\mathrm{\ensuremath{\Sigma}}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ proceed only through type-II $W$ exchange. They are predicted to have large and positive decay asymmetries. These features can be tested in the near future.

Influences of orientation on the Ponzo, contrast, and Craik-O\u2019Brien-Cornsweet illusions

Explanations of the Ponzo size illusion, the simultaneous contrast illusion, and the Craik-O’Brien-Cornsweet brightness illusions involve either stimulus-driven processes (assimilation, enhanced contrast, and anchoring) or prior experiences. Real-world up-down asymmetries for typical direction of illumination and ground planes in our physical environment should influence these illusions if they are experience based, but not if they are stimulus driven. Results presented here demonstrate differences in illusion strengths between upright and inverted versions of all three illusions. A left-right asymmetry of the Cornsweet illusion was produced by manipulating the direction of illumination, providing further support for the involvement of an experience-based explanation. When the inducers were incompatible with the targets being located at the different distances, the Ponzo illusion persisted and so did the influence from orientation, providing evidence for involvement of processes other than size constancy. As defined here, upright for the brightness illusions is consistent with an interpretation of a shaded bulging surface and a 3D object resulting from a light-from-above assumption triggering compensation for varying illumination. Upright for the Ponzo illusion is consistent with the inducers in the form of converging lines being interpreted as railway tracks receding on the ground triggering size constancy effects. The implications of these results, and other results providing evidence against experience-based accounts of the illusions, are discussed.

Up-down asymmetries of charmed baryon three-body decays

We study the up-down asymmetries in the three-body anti-triplet charmed baryon decays of mathbf{B}_{mathbf{c}}rightarrow mathbf{B}_{mathbf{n}}MM' with the SU(3)_f flavor symmetry, where mathbf{B}_{mathbf{c}} presents the anti-triplet charmed baryon of (Xi _c^0,-Xi _c^+,Lambda _c^+), while mathbf{B}_{mathbf{n}} and M^{(')} denote octet baryon and meson states, respectively. By assuming the s-wave meson-pairs to be the dominant constituents in final state configurations, we can write the spin-dependent decay amplitude into parity-conserving and parity-violating parts, parametrized by 6 real parameters under SU(3)_f, respectively. Fitting these parameters by 16 experimental data points with the minimum chi ^2 method, we obtain that chi ^2/d.o.f=2.4. With the fitted parameters, we evaluate the up-down asymmetries along with the decay branching ratios of mathbf{B}_{mathbf{c}}rightarrow mathbf{B}_{mathbf{n}}MM' . Some of these up-down asymmetries are accessible to the experiments at BESIII, BELLE-II and LHCb.

Drift effects on W7-X divertor heat and particle fluxes

Classical particle drifts are known to have substantial impacts on fluxes of particles and heat through the edge plasmas in both tokamaks and stellarators. Here we present results from the first dedicated investigation of drift effects in the W7-X stellarator. By comparing similar plasma discharges conducted with a forward- and reverse-directed magnetic field, the impacts of drifts could be isolated through the observation of up-down asymmetries in flux profiles on the divertor targets. In low-density plasmas, the radial locations of the strike lines (i.e. peaks in the target heat flux profiles) exhibited discrepancies of up to 3 cm that reversed upon magnetic field reversal. In addition, asymmetric heat loads were observed in regions of the target that are shadowed by other targets from parallel flux from the core plasma. A comparison of these asymmetric features with the footprints of key topological regions of the edge magnetic field on the divertor suggests that the main driver of the asymmetries at low density is poloidal E × B drift due to radial electric fields in the scrape-off layer and private flux region. In higher-density plasmas, upper and lower targets collected non-ambipolar currents with opposite signs that also inverted upon field reversal. Overall, in these experiments, almost all up-down asymmetry could be attributed to the field reversal and, therefore, field-dependent drifts.

First results of the 2D gas electron multiplier in the dominant electron heating scenario on EAST

The 2D gas electron multiplier (GEM) is used to measure the chord-integrated soft x-ray radiation in the direction tangential to the magnetic field. With the Tikhonov tomography algorithm, the soft x-ray emissivity is derived considering the soft x-ray air transmission factor. The cooling factors are also determined according to the continuum and impurity line radiations. The impurity concentration is then obtained from the measured emissivity. In the dominant electron heating scenario, iron is the main impurity of which the high ionization states contribute to the total counting rate of GEM. The up-down asymmetry of concentrated impurity is observed before the plasma confinement conversion from edge localized mode (ELM)-free high confinement mode (H-mode) to ELMy H-mode. A large scale perturbation is observed which is radially elongated on the tomography plots as the electron temperature profile shows in–out asymmetry. The perturbation drives outward impurities and energy transport, reducing the impurity concentration and the electron temperature gradient in the core. The underlying instability is also discussed which shows the relevance of the macroscopic mode with the iron impurity density and electron temperature profiles.

Charmed baryon weak decays with decuplet baryon and SU(3) flavor symmetry

We study the branching ratios and up-down asymmetries in the charmed baryon weak decays of ${\bf B}_c\to {\bf B}_DM$ with ${\bf B}_{c(D)}$ anti-triplet charmed (decuplet) baryon and $M$ pseudo-scalar meson states based on the flavor symmetry of $SU(3)_F$. We propose equal and physical-mass schemes for the hadronic states to deal with the large variations of the decuplet baryon momenta in the decays in order to fit with the current experimental data. We find that our fitting results of ${\cal B}({\bf B}_c\to {\bf B}_DM) $ are consistent with the current experimental data in both schemes, while the up-down asymmetries in all decays are found to be sizable, consistent with the current experimental data, but different from zero predicted in the literature. We also examine the processes of $\Xi_c^0 \to \Sigma^{\prime 0}K_S/K_L$ and derive the asymmetry between the $K_L/K_S$ modes being a constant.

Asymmetries of anti-triplet charmed baryon decays

We analyze the decay processes of Bc→BnM with the SU(3)F flavor symmetry and spin-dependent amplitudes, where Bc(Bn) and M are the anti-triplet charmed (octet) baryon and nonet meson states, respectively. In the SU(3)F approach, it is the first time that the decay rates and up-down asymmetries are fully and systematically studied without neglecting the O(15‾) contributions of the color anti-symmetric parts in the effective Hamiltonian. Our results of the up-down asymmetries based on SU(3)F are quite different from the previous theoretical values in the literature. In particular, we find that the up-down symmetry of α(Λc+→Ξ0K+)SU(3)=0.94−0.11+0.06, which is consistent with the recent experimental data of 0.77±0.78 by the BESIII Collaboration, but predicted to be zero in the literature. We also examine the KS0−KL0 asymmetries between the decays of Bc→BnKS0 and Bc→BnKL0 with both Cabibbo-allowed and doubly Cabibbo-suppressed transitions.

Testing the standard model with D(s)→K1(→Kππ)γ decays

The photon polarization in $D_{(s)} \to K_1 (\to K\pi\pi) \gamma$ decays can be extracted from an up-down asymmetry in the $K \pi \pi$ system, along the lines of the method known to $B \to K_1 (\to K\pi\pi) \gamma$ decays. Charm physics is advantageous as partner decays exist: $D^+ \to K_1^+ (\to K\pi\pi) \gamma$, which is standard model-like, and $D_s \to K_1^+ (\to K\pi\pi) \gamma$, which is sensitive to physics beyond the standard model in $|\Delta c| =|\Delta u|=1$ transitions. The standard model predicts their photon polarizations to be equal up to U-spin breaking corrections, while new physics in the dipole operators can split them apart at order one level. We estimate the proportionality factor in the asymmetry multiplying the polarization parameter from axial vectors $K_1(1270)$ and $K_1(1400)$ to be sizable, up to the few ${\cal{O}}(10)\%$ range. The actual value of the hadronic factor matters for the experimental sensitivity, but is not needed as an input to perform the null test.

Study of the decay K^{+}rightarrow pi ^{+}pi ^{-}pi ^{+}gamma in the OKA experiment

A high statistics data sample of the decays of K^+ mesons to three charged particles was accumulated by the OKA experiment in 2012 and 2013. This allowed to select a clean sample of about 450 events with K^{+}rightarrow pi ^{+}pi ^{-}pi ^{+}gamma decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the K^{+}rightarrow pi ^{+}pi ^{-}pi ^{+}gamma , with E_{gamma }^{*} > 30 hbox {MeV} is equal to (0.71 pm 0.05) times 10^{-5}. The measured differential branching fraction over photon energy is compared with the prediction of the chiral perturbation theory to {mathcal {O}}(p^{4}). A search for an up-down asymmetry of the photon with respect to the hadronic system decay plane is also performed.

Color-allowed bottom baryon to charmed baryon nonleptonic decays

We study color allowed $\Lambda_b\to \Lambda^{(*,**)}_c M^-$, $\Xi_b\to\Xi_c^{(**)} M^-$ and $\Omega_b\to\Omega^{(*)}_c M^-$ decays with $M=\pi, K,\rho, K^*, D, D_s, D^*, D^*_s, a_1$, $\Lambda^{(*,**)}_c=\Lambda_c$, $\Lambda_c(2595)$, $\Lambda_c(2765)$, $\Lambda_c(2940)$, $\Xi_c^{(**)}=\Xi_c, \Xi_c(2790)$ and $\Omega^{(*)}_c=\Omega_c, \Omega_c(3090)$, in this work. There are three types of transitions, namely ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^+)$, ${\cal B}_b({\bf 6_f},1/2^+)$ to ${\cal B}_c({\bf 6_f},1/2^+)$ and ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^-)$ transitions. The bottom baryon to charmed baryon form factors are calculated using the light-front quark model. Decay rates and up-down asymmetries are predicted using na\"{i}ve factorization and can be checked experimentally. We find that in ${\cal B}_b\to {\cal B}_cP$ decays, rates in type~(ii) transition are smaller than those in type (i) transition, but similar to those in type (iii) transition, while in ${\cal B}_b\to{\cal B}_c V, {\cal B}_c A$ decays, rates in type~(ii) transition are much smaller than those in type (i) transition and are also smaller than those in type (iii) transition. For the up-down asymmetries, the signs are mostly negative, except for those in the type (ii) transition. All of these asymmetries are large in sizes. The study on these decay modes may shed light on the quantum numbers of some of the charmed baryons as the decays depend on the bottom baryon to charmed baryon form factors, which are sensitive to the configurations of the final state charmed baryons.

Hyperbolic umbilic caustics from oblate water drops with tilted illumination: Observations

Various groups have reported observations of hyperbolic umbilic diffraction catastrophe patterns in the far-field scattering by oblate acoustically levitated drops with symmetric illumination. In observations of that type the drop's symmetry axis is vertical and the illuminating light beam (typically an expanded laser beam) travels horizontally. In the research summarized here, scattering patterns in the primary rainbow region and drop measurements were recorded with vertically tilted laser beam illumination having a grazing angle as large as 4 degrees. The findings from these observations may be summarized as follows: (a) It remains possible to adjust the drop aspect ratio (diameter/height) = D/H so as to produce a V-shaped hyperbolic umbilic focal section (HUFS) in the far-field scattering. (b) The shift in the required D/H was typically an increase of less than 1% and was quadratic in the tilt. (c) The apex of the V-shaped HUFS was shifted vertically by an amount proportional to the tilt with a coefficient close to unity. The levitated drops had negligible up-down asymmetry. Our method of investigation should be useful for other generalized rainbows with tilted illumination.

Effect of impurity source locations on up-down asymmetry in impurity distributions in the ergodic layer of large helical device

A space-resolved spectroscopy using a 3m normal incidence vacuum ultraviolet (VUV) spectrometer was developed to measure the VUV emission profiles in wavelength range of 300–3200Å from impurities in the edge plasmas in Large Helical Device (LHD). The edge plasma of the LHD is characterized by stochastic magnetic fields with three-dimensional structure intrinsically formed by helical coils called the “ergodic layer”. The VUV spectroscopy has revealed that intensity profiles of the impurity emission from the ergodic layer have strong up-down asymmetries, namely, the emission intensities are quite different between top and bottom plasma edges. Observations of the up-down asymmetries are summarized on the following impurity line emissions: (1) CII 1335.71Å (2s-2p), CIII 977.02Å (2s-2p), and CIV 1548.20Å (2s-2p) from intrinsic carbon impurity ions sputtered from the carbon divertor plates, (2) NeVII 465.22Å (2s-2p), NeVIII 770.41Å (2s-2p), ArVII 585.75Å (3s-3p), and ArVIII 700.24Å (3s-3p) from Ne or Ar ions introduced in plasmas by gas puffing, and (3) WVI 639.68Å (5d-6p) from W ions introduced in plasmas by pellet injection.