Search

Molecular beam epitaxy and optical investigation of ${\mathrm{Zn}}_{1-x}{\mathrm{Mn}}_x\mathrm{Se}$ epilayers over a large composition range $(x=0\mathrm{}–0.78),$ grown on GaAs (001) substrates, are reported. The far-infrared (FIR) reflectance and Raman scattering were performed to characterize the film quality and study their optical and electrical properties. FIR and Raman data provide experimental evidence on the intermediate-mode phonon behavior for ${\mathrm{Zn}}_{1-x}{\mathrm{Mn}}_x\mathrm{Se}$ with x up to 0.78. Theoretical modeling fits of FIR spectra lead to the determination of optical parameters such as mode frequency, strength, damping constant, and electrical properties of dielectric constant, carrier concentration, mobility, conductivity, and effect mass, and their dependence on the Mn composition. Values of force constants of $F_{\mathrm{MnSe}}=17.1\mathrm{}\times {10}^4{\mathrm{dyn}\mathrm{}\mathrm{cm}}^1$ and $F_{\mathrm{ZnSe}}=14.7\mathrm{}\times {10}^4{\mathrm{dyn}\mathrm{}\mathrm{cm}}^{\mathrm{-}1},$ and the high-frequency limit dielectric constant of MnSe, ${\epsilon }_{\infty }=5.4,$ are obtained.

The ($\alpha , d$) reactions on targets of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ were studied using $\alpha$-particle beams of 40.1, 46.0, 45.4, and 44.5 MeV, respectively. Angular distributions were obtained. States where the captured protonneutron pair is in the ${{\left(1\mathrm{}{d}_{\frac{5}{2}}\right)}_{5+,0}}^2$ configuration coupled to an unperturbed target core are located and possible spin assignments are suggested. These states are ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, 13.03 MeV ($\frac{11}{2}-$), 11.95 MeV ($\frac{9}{2}-$); ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$, 5.75 MeV (5+); ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$, 7.74 MeV ($\frac{11}{2}-$), 9.14 MeV ($\frac{9}{2}-$); ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$, 1.528 MeV (5+). Separated isotopes ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{54,56}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{58,60,62}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{64,66,68}{}_{}{}^{}\mathrm{Zn}$ were used as targets to study the ($\alpha , d$) reaction with a 50-MeV $\alpha$-particle beam. States with a probable configuration of ${{\left(1\mathrm{}{g}_{\frac{9}{2}}\right)}_{9+,0}}^2$ were located. These states are ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$, 9.47 MeV; ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$, 8.92 MeV; ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$, 6.79 MeV; ${}_{}{}^{60}{}_{}{}^{}\mathrm{Cu}$, 5.99 MeV; ${}_{}{}^{62}{}_{}{}^{}\mathrm{Cu}$, 4.75 MeV; ${}_{}{}^{64}{}_{}{}^{}\mathrm{Cu}$, 4.57 MeV; ${}_{}{}^{66}{}_{}{}^{}\mathrm{Ga}$, 2.99 MeV; ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ga}$, 2.88 MeV; ${}_{}{}^{70}{}_{}{}^{}\mathrm{Ga}$, 2.88 MeV. The residual-interaction energies between the proton and neutron in the configurations ${{\left(1\mathrm{}{d}_{\frac{5}{2}}\right)}_{5+,0}}^2$, ${{\left(1\mathrm{}{f}_{\frac{7}{2}}\right)}_{7+,0}}^2$, and ${{\left(1\mathrm{}{g}_{\frac{9}{2}}\right)}_{9+,0}}^2$ were derived from the excitation energies determined in the present work and previous work on ${{\left(1\mathrm{}{d}_{\frac{5}{2}}\right)}_{5+,0}}^2$ and ${{\left(1\mathrm{}{f}_{\frac{7}{2}}\right)}_{7+,0}}^2$ states. For $T_z\ne 0$ nuclides, an "interactionmodel" method was proposed to extract the residual-interaction energy. The mean values of the residualinteraction energies are about -3.9, -3.0, and -2.2 MeV, respectively, for the three mentioned configurations. There is a slight decrease of residual-interaction energy with increasing $A$. These results are reproduced satisfactorily by conventional shell-model calculations. Both the interaction-model method and Talmi's shell-model calculation method were used to calculate the excitation energies of states with the ${{\left(1\mathrm{}{d}_{\frac{5}{2}}\right)}_{5+,0}}^2$ configuration. In general, the former method gives better agreement with the experimental results.

Dwarf spheroidal galaxies of the Local Group are close satellites of the Milky Way characterized by a large mass-to-light ratio and are not expected to be the site of nonthermal high-energy gamma-ray emission or intense star formation. Therefore they are among the most promising candidates for indirect dark matter searches. During the last years the High Energy Stereoscopic System (H.E.S.S.) of imaging atmospheric Cherenkov telescopes observed five of these dwarf galaxies for more than 140 hours in total, searching for TeV gamma-ray emission from annihilation of dark matter particles. The new results of the deep exposure of the Sagittarius dwarf spheroidal galaxy, the first observations of the Coma Berenices and Fornax dwarves and the reanalysis of two more dwarf spheroidal galaxies already published by the H.E.S.S. Collaboration, Carina and Sculptor, are presented. In the absence of a significant signal new constraints on the annihilation cross section applicable to weakly interacting massive particles (WIMPs) are derived by combining the observations of the five dwarf galaxies. The combined exclusion limit depends on the WIMP mass and the best constraint is reached at 1–2 TeV masses with a cross-section upper bound of $\sim 3.9\times {10}^{-24}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at a 95% confidence level.

Gamma-ray line signatures can be expected in the very-high-energy ($E_{\gamma }>100\mathrm{GeV}$) domain due to self-annihilation or decay of dark matter (DM) particles in space. Such a signal would be readily distinguishable from astrophysical $\gamma$-ray sources that in most cases produce continuous spectra that span over several orders of magnitude in energy. Using data collected with the H.E.S.S. $\gamma$-ray instrument, upper limits on linelike emission are obtained in the energy range between $\sim 500\mathrm{GeV}$ and $\sim 25\mathrm{TeV}$ for the central part of the Milky Way halo and for extragalactic observations, complementing recent limits obtained with the Fermi-LAT instrument at lower energies. No statistically significant signal could be found. For monochromatic $\gamma$-ray line emission, flux limits of $(2\times {10}^{-7}–2\times {10}^{-5}){\mathrm{m}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ and $(1\times {10}^{-8}–2\times {10}^{-6}){\mathrm{m}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ are obtained for the central part of the Milky Way halo and extragalactic observations, respectively. For a DM particle mass of 1 TeV, limits on the velocity-averaged DM annihilation cross section $⟨\sigma v{⟩}_{\chi \chi \to \gamma \gamma }$ reach $\sim {10}^{-27}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$, based on the Einasto parametrization of the Galactic DM halo density profile.

An annihilation signal of dark matter is searched for from the central region of the Milky Way. Data acquired in dedicated on-off observations of the Galactic center region with H.E.S.S. are analyzed for this purpose. No significant signal is found in a total of $\sim 9\mathrm{h}$ of on-off observations. Upper limits on the velocity averaged cross section, $⟨\sigma v⟩$, for the annihilation of dark matter particles with masses in the range of $\sim 300\mathrm{GeV}$ to $\sim 10\mathrm{TeV}$ are derived. In contrast to previous constraints derived from observations of the Galactic center region, the constraints that are derived here apply also under the assumption of a central core of constant dark matter density around the center of the Galaxy. Values of $⟨\sigma v⟩$ that are larger than $3\times {10}^{-24}{\mathrm{cm}}^3/\mathrm{s}$ are excluded for dark matter particles with masses between $\sim 1$ and $\sim 4\mathrm{TeV}$ at 95% C.L. if the radius of the central dark matter density core does not exceed 500 pc. This is the strongest constraint that is derived on $⟨\sigma v⟩$ for annihilating TeV mass dark matter without the assumption of a centrally cusped dark matter density distribution in the search region.

A search for a very-high-energy (VHE; $\ge 100\mathrm{GeV}$) $\gamma$-ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance $r\sim 45–150\mathrm{pc}$ from the Galactic center. The background-subtracted $\gamma$-ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) $\gamma$-ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual $\gamma$-ray flux. Assuming conventional Navarro-Frenk-White and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section $⟨\sigma v⟩$ as a function of the DM particle mass. These are among the best reported so far for this energy range and in particular differ only little between the chosen density profile parametrizations. In particular, for the DM particle mass of $\sim 1\mathrm{TeV}$, values for $⟨\sigma v⟩$ above $3\times {10}^{-25}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ are excluded for the Einasto density profile.

Diffuse $\gamma$-ray emission is the most prominent observable signature of celestial cosmic-ray interactions at high energies. While already being investigated at GeV energies over several decades, assessments of diffuse $\gamma$-ray emission at TeV energies remain sparse. After completion of the systematic survey of the inner Galaxy, the H.E.S.S. experiment is in a prime position to observe large-scale diffuse emission at TeV energies. Data of the H.E.S.S. Galactic Plane Survey are investigated in regions off known $\gamma$-ray sources. Corresponding $\gamma$-ray flux measurements were made over an extensive grid of celestial locations. Longitudinal and latitudinal profiles of the observed $\gamma$-ray fluxes show characteristic excess emission not attributable to known $\gamma$-ray sources. For the first time large-scale $\gamma$-ray emission along the Galactic plane using imaging atmospheric Cherenkov telescopes has been observed. While the background subtraction technique limits the ability to recover modest variation on the scale of the H.E.S.S. field of view or larger, which is characteristic of the inverse Compton scatter-induced Galactic diffuse emission, contributions of neutral pion decay as well as emission from unresolved $\gamma$-ray sources can be recovered in the observed signal to a large fraction. Calculations show that the minimum $\gamma$-ray emission from ${\pi }^0$ decay represents a significant contribution to the total signal. This detection is interpreted as a mix of diffuse Galactic $\gamma$-ray emission and unresolved sources.

The ${\tau }^{-}\to \eta {\pi }^{-}{\pi }^{+}{\pi }^{-}{\nu }_{\tau }$ decay with the $\eta \to \gamma \gamma$ mode is studied using $384{\mathrm{fb}}^{-1}$ of data collected by the BABAR detector. The branching fraction is measured to be $(1.60\pm 0.05\pm 0.11)\times {10}^{-4}$. It is found that ${\tau }^{-}\to f_1(1285){\pi }^{-}{\nu }_{\tau }\to \eta {\pi }^{-}{\pi }^{+}{\pi }^{-}{\nu }_{\tau }$ is the dominant decay mode with a branching fraction of $(1.11\pm 0.06\pm 0.05)\times {10}^{-4}$. The first error on the branching fractions is statistical and the second systematic. Note that no particle identification algorithm is applied to the charged tracks to distinguish pions from kaons. In addition, a 90% confidence level upper limit on the branching fraction of the ${\tau }^{-}\to {\eta }^{\prime }(958){\pi }^{-}{\nu }_{\tau }$ decay is measured to be $7.2\times {10}^{-6}$. This last decay proceeds through a second-class current and is expected to be forbidden in the limit of isospin symmetry.

We report a measurement of the production ratio of charged and neutral B mesons from ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ decays based on the ratio of efficiency-corrected yields for the charmonium modes $J/\psi K^{+}$ and $J/\psi K_s^0$ with 81.9 ${\mathrm{fb}}^{\mathrm{-}1}$ of data collected with the BABAR detector on the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance at 10.580 GeV. We find a value of $1.006\pm 0.036\left(\mathrm{stat}\right)\pm 0.031\left(\mathrm{syst}\right)$ for the ratio $R^{+/0\mathrm{}}=\Gamma \left({\rm Y}\mathrm{}\right(4S)\mathrm{}\to B^{+}{B}^{-})/\Gamma \left({\rm Y}\mathrm{}\right(4S)\mathrm{}\to B^0{B}^0).$

We present measurements of branching fractions of $B^0$ decays to multibody final states containing protons, based on $232\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy $B$ factory. We measure the branching fractions $\mathcal{B}(B^0\to {\overline{D}}^{0}p\overline{p})=(1.13\pm 0.06\pm 0.08)\times {10}^{-4}$, $\mathcal{B}(B^0\to {\overline{D}}^{*0}p\overline{p})=(1.01\pm 0.10\pm 0.09)\times {10}^{-4}$, $\mathcal{B}(B^0\to D^{-}p\overline{p}{\pi }^{+})=(3.38\pm 0.14\pm 0.29)\times {10}^{-4}$, and $\mathcal{B}(B^0\to D^{*-}p\overline{p}{\pi }^{+})=(4.81\pm 0.22\pm 0.44)\times {10}^{-4}$ where the first error is statistical and the second systematic. We present a search for the charmed pentaquark state, ${\Theta }_c(3100)$ observed by H1 and put limits on the branching fraction $\mathcal{B}(B^0\to {\Theta }_c\overline{p}{\pi }^{+})\times \mathcal{B}({\Theta }_c\to D^{*-}p)<14\times {10}^{-6}$ and $\mathcal{B}(B^0\to {\Theta }_c\overline{p}{\pi }^{+})\times \mathcal{B}({\Theta }_c\to D^{-}p)<9\times {10}^{-6}$. Upon investigation of the decay structure of the above four $B^0$ decay modes, we see an enhancement at low $p\overline{p}$ mass and deviations from phase-space in the $\overline{D}\overline{p}$ and $\overline{D}p$ invariant mass spectra.

We present measurements of the branching fractions, longitudinal polarization, and direct $CP$-violation asymmetries for the decays $B^{+}\to {\rho }^0{K}^{*+}$ and $B^{+}\to f_0(980)K^{*+}$ with a sample of $(467\pm 5)\times {10}^{6}B\overline{B}$ pairs collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at the SLAC National Accelerator Laboratory. We observe $B^{+}\to {\rho }^0{K}^{*+}$ with a significance of $5.3\sigma$ and measure the branching fraction $\mathcal{B}(B^{+}\to {\rho }^0{K}^{*+})=(4.6\pm 1.0\pm 0.4)\times {10}^{-6}$, the longitudinal polarization $f_L=0.78\pm 0.12\pm 0.03$, and the $CP$-violation asymmetry ${\mathcal{A}}_{CP}=0.31\pm 0.13\pm 0.03$. We observe $B^{+}\to f_0(980)K^{*+}$ and measure the branching fraction $\mathcal{B}(B^{+}\to f_0(980)K^{*+})\times \mathcal{B}(f_0(980)\to {\pi }^{+}{\pi }^{-})=(4.2\pm 0.6\pm 0.3)\times {10}^{-6}$ and the $CP$-violation asymmetry ${\mathcal{A}}_{CP}=-0.15\pm 0.12\pm 0.03$. The first uncertainty quoted is statistical and the second is systematic.

We measure the rate of $D^0\mathrm{\text{−}}{\overline{D}}^0$ mixing with the observable $y_{CP}=({\tau }_{K\pi }/{\tau }_{KK})-1$, where ${\tau }_{KK}$ and ${\tau }_{K\pi }$ are, respectively, the mean lifetimes of $CP$-even $D^0\to K^{+}{K}^{-}$ and $CP$-mixed $D^0\to K^{-}{\pi }^{+}$ decays, using a data sample of $384{\mathrm{fb}}^{-1}$ collected by the BABAR detector at the SLAC PEP-II asymmetric-energy $B$ Factory. From a sample of $D^0$ and ${\overline{D}}^0$ decays where the initial flavor of the decaying meson is not determined, we obtain $y_{CP}=[1.12\pm 0.26(\mathrm{stat})\pm 0.22(\mathrm{syst})]\%$, which excludes the no-mixing hypothesis at $3.3\sigma$, including both statistical and systematic uncertainties. This result is in good agreement with a previous BABAR measurement of $y_{CP}$ obtained from a sample of $D^{*+}\to D^0{\pi }^{+}$ events, where the $D^0$ decays to $K^{-}{\pi }^{+}$, $K^{+}{K}^{-}$, and ${\pi }^{+}{\pi }^{-}$, which is disjoint with the untagged $D^0$ events used here. Combining the two results taking into account statistical and systematic uncertainties, where the systematic uncertainties are assumed to be 100% correlated, we find $y_{CP}=[1.16\pm 0.22(\mathrm{stat})\pm 0.18(\mathrm{syst})]\%$, which excludes the no-mixing hypothesis at $4.1\sigma$.

Using a sample of $232\times {10}^6{\rm Y}(4S)\to B\overline{B}$ events collected with the BABAR detector at the PEP-II $B$ factory we study the decay $B^{-}\to [K^{+}{\pi }^{-}{]}_D{K}^{*-}$ where the $K^{+}{\pi }^{-}$ is either from a Cabibbo-favored ${\overline{D}}^0$ decay or doubly-suppressed $D^0$ decay. We measure two observables that are sensitive to the Cabibbo-Kobayashi-Maskawa angle $\gamma$; the ratio $R$ of the charge-averaged branching fractions for the suppressed and favored decays; and the charge asymmetry $A$ of the suppressed decays: $R=0.046\pm 0.031(\mathrm{stat})\pm 0.008(\mathrm{syst})$, $A=-0.22\pm 0.61(\mathrm{stat})\pm 0.17(\mathrm{syst})$.

A search for the decay of the $\tau$ lepton to five charged and two neutral pions is performed using data collected by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider. The analysis uses $232{\mathrm{fb}}^{-1}$ of data at center-of-mass energies on or near the ${\rm Y}(4S)$ resonance. We observe 10 events with an expected background of ${6.5}_{-1.4}^{+2.0}$ events. In the absence of a signal, we set the limit on the branching ratio $\mathcal{B}({\tau }^{-}\to 3{\pi }^{-}2{\pi }^{+}2{\pi }^0{\nu }_{\tau })<3.4\times {10}^{-6}$ at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode ${\tau }^{-}\to 2\omega {\pi }^{-}{\nu }_{\tau }$. We observe 1 event with an expected background of $0.4\genfrac{}{}{0ex}{}{+1.0}{-0.4}$ events and calculate the upper limit $\mathcal{B}({\tau }^{-}\to 2\omega {\pi }^{-}{\nu }_{\tau })<5.4\times {10}^{-7}$ at the 90% confidence level. This is the first upper limit for this mode.

We present an updated measurement of the $CP$-odd fraction and the time-dependent $CP$ asymmetries in the decay $B^0\to D^{*+}{D}^{*-}$ using $(383\pm 4)\times {10}^{6}B\overline{B}$ pairs collected with the BABAR detector. We determine the $CP$-odd fraction to be $0.143\pm 0.034(\mathrm{stat})\pm 0.008(\mathrm{syst})$. The time-dependent $CP$ asymmetry parameters are determined to be $C_{+}=-0.05\pm 0.14(\mathrm{stat})\pm 0.02(\mathrm{syst})$ and $S_{+}=-0.72\pm 0.19(\mathrm{stat})\pm 0.05(\mathrm{syst})$. The nonzero value of the measured $S_{+}$ indicates the evidence of $CP$ violation at the $3.7\sigma$ confidence level.

We present measurements of branching fractions and $CP$-violating asymmetries in decays of $B$ mesons to two-body final states containing a $K^0$. The results are based on a data sample of approximately $88\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We measure $\mathcal{B}(B^{+}\to K^0{\pi }^{+})=(22.3\pm 1.7\pm 1.1)\times {10}^{-6}$, $\mathcal{B}(B^0\to K^0{\pi }^0)=(11.4\pm 1.7\pm 0.8)\times {10}^{-6}$, $\mathcal{B}(B^{+}\to {\overline{K}}^0{K}^{+})<2.5\times {10}^{-6}$, and $\mathcal{B}(B^0\to K^0{\overline{K}}^0)<1.8\times {10}^{-6}$, where the first uncertainty is statistical and the second is systematic, and the upper limits are at the $90\%$ confidence level. In addition, the following $CP$-violating asymmetries have been measured: ${\mathcal{A}}_{CP}(B^{+}\to K^0{\pi }^{+})=-0.05\pm 0.08\pm 0.01$ and ${\mathcal{A}}_{CP}(B^0\to K^0{\pi }^0)=0.03\pm 0.36\pm 0.11$.

We present a study of the decay $B^0\to {\pi }^0{\pi }^0$ based on a sample of $124\times {10}^6$ $B\overline{B}$ pairs recorded by the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We observe $46\pm 13\pm 3$ events, where the first error is statistical and the second is systematic, corresponding to a significance of $4.2$ standard deviations including systematic uncertainties. We measure the branching fraction $\mathcal{B}(B^0\to {\pi }^0{\pi }^0)=(2.1\pm 0.6\pm 0.3)\times {10}^{-6}$, averaged over $B^0$ and ${\overline{B}}^0$ decays.

We present a measurement of $CP$-violating asymmetries in fully reconstructed $B^0\to D^{(*)\pm }{\pi }^{\mp }$ decays in approximately $88\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ factory at SLAC. From a time-dependent maximum-likelihood fit we obtain the following for the $CP$-violating parameters: $a=-0.022\pm 0.038(\mathrm{stat})\pm 0.020(\mathrm{syst})$, $a^{*}=-0.068\pm 0.038(\mathrm{stat})\pm 0.020(\mathrm{syst})$, $c_{\mathrm{lep}}=+0.025\pm 0.068(\mathrm{stat})\pm 0.033(\mathrm{syst})$, and $c_{\mathrm{lep}}^{*}=+0.031\pm 0.070(\mathrm{stat})\pm 0.033(\mathrm{syst})$. Using other measurements and theoretical assumptions we interpret the results in terms of the angles of the Cabibbo-Kobayashi-Maskawa unitarity triangle, and find $|\sin (2\beta +\gamma )|>0.69$ at $68\%$ confidence level. We exclude the hypothesis of no $CP$ violation $[\sin (2\beta +\gamma )=0]$ at $83\%$ confidence level.