Counting rate is a key parameter of superconducting nanowire single photon detectors (SNSPD) and is determined by the current recovery time of an SNSPD after a detection event. We propose a new method to study the transient detection efficiency (DE)
and pulse amplitude during the current recovery process by statistically analyzing the single photon response of an SNSPD under photon illumination with a high repetition rate. The transient DE results match well with the DEs deduced from the static current dependence of DE combined with the waveform of a single-photon detection event. This proves that the static measurement results can be used to analyze the transient current recovery process after a detection event. The results are relevant for understanding the current recovery process of SNSPDs after a detection event and for determining the counting rate of SNSPDs.
The $e^+e^- to pi^+ pi^- pi^0 chi_{bJ}$ ($J=0,~1,~2$) processes are studied using a 118~fb$^{-1}$ data sample collected at a center-of-mass energy of 10.867 GeV, in the $Upsilon(10860)$ energy range, with the Belle detector. The $pi^+ pi^- pi^0 chi_{
b1}$, $pi^+pi^-pi^0chi_{b2}$, $omegachi_{b1}$ signals and the evidence of $omegachi_{b2}$ are observed for the first time and the cross sections are measured. No significant $pi^+pi^-pi^0chi_{b0}$ or $omegachi_{b0}$ signal is observed and 90% confidence level upper limits on the cross sections for these two processes are obtained. In the $pi^+pi^-pi^0$ invariant mass spectrum, significant non-$omega$ signals are also observed. We search for the $X(3872)$-like state with a hidden $bbar{b}$ component (named $X_b$) decaying into $omega Upsilon(1S)$; no significant signal is observed with a mass between $10.55$ and $10.65$ GeV/$c^2$.
A CO,2-1 line survey is performed toward a sample of 58 high Galactic latitude post-AGB (pAGB) stars. To complement the observations, a compilation of literature CO,2-1 line data of known pAGB stars is done. After combining the datasets, CO,2-1 line
data are available for 133 pAGB stars (about 34 per cent of known pAGB stars) among which 44 are detections. The CO line strengths are compared with infrared dust emission for these pAGB stars by defining a ratio between the integrated CO,2-1 line flux and {it IRAS} 25,mu flux density (CO-IR ratio). The relationship between the CO-IR ratio and the {it IRAS} color C23 (defined with the 25 and 60,mu flux densities) is called here the CO-IR diagram. The pAGB objects are found to be located between AGB stars and planetary nebulae (PNe), and segregate into three distinctive groups (I, II and III) on the CO-IR diagram. By analyzing their various properties such as chemical types, spectral types, binarity, circumstellar envelope expansion velocities, and pAGB sub-types on the CO-IR diagram, it is argued that the group-I objects are mainly intermediate mass C-rich pAGB stars in early pAGB stage (almost all of the considered carbon rich `21,mu stars belong to this group); the group-II objects are massive or intermediate mass pAGB stars which already follow the profound trend of PNe; and the group-III objects are mainly low mass binary pAGB stars with very weak CO,2-1 line emission (almost all of the considered RV,Tau variables belong to this group). The CO-IR diagram is proven to be a powerful tool to investigate the co-evolution of circumstellar gas and dust during the short pAGB stage of stellar evolution.
We report the results of a search for the $X(1835)$ state in the process $e^+e^-to J/psi+X(1835)$ using a data sample of 672 fb$^{-1}$ collected with the Belle detector at and near the $Upsilon(4S)$ resonance at the KEKB asymmetric-energy $e^+e^-$ co
llider. No significant evidence is found for this process, and an upper limit is set on its cross section times the branching fraction: $sigma_{rm Born}(e^+e^- to J/psi X(1835)) cdot$ {${cal B}(X(1835)to ge 3$ charged tracks)} $< 1.3 {rm fb}$ at 90% confidence level.
A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials such as the cuprate high temperature superconductors. Because of its unique momentum-space discrimination, angle-resolve
d photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping-and-temperature dependence ARPES study of spectral gaps in Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ (Bi-2212), covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p$=$0.19 for the pseudogap phase and p$=$0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T$_c$ and exists p$>$0.19 at higher temperatures. Our data imply a revised phase diagram which reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.
The interplay between superconductivity and the pseudogap is an important aspect of cuprate physics. However, the nature of the pseudogap remains controversial, in part because different experiments have suggested different gap functions. Here we pre
sent a photon-energy-dependence angle-resolved photoemission spectroscopy (ARPES) study on Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+delta}$. We find that antinodal ARPES spectra at low photon energies are dominated by background signals which can lead to a misevaluation of the spectral gap size. Once background is properly accounted for, independent of photon energy, the antinodal spectra robustly show two coexisting features at different energies dominantly attributed to the pseudogap and superconductivity, as well as an overall spectral gap which deviates from a simple d-wave form. These results support the idea that the spectral gap is distorted due to the competition between the pseudogap and superconductivity.
A northern subsample of 89 Spitzer GLIMPSE extended green objects (EGOs), the candidate massive young stellar objects, are surveyed for molecular lines in two 1-GHz ranges: 251.5- 252.5 and 260.188-261.188 GHz. A comprehensive catalog of observed mol
ecular line data and spectral plots are presented. Eight molecular species are undoubtedly detected: H13CO+, SiO, SO, CH3OH, CH3OCH3, CH3CH2CN, HCOOCH3, and HN13C. H13CO+ 3-2 line is detected in 70 EGOs among which 37 ones also show SiO 6-5 line, demonstrating their association to dense gas and supporting the outflow interpretation of the extended 4.5 um excess emission. Our major dense gas and outflow tracers (H13CO+, SiO, SO and CH3OH) are combined with our previous survey of 13CO, 12CO and C18O 1-0 toward the same sample of EGOs for a multi-line multi- cloud analysis of line width and luminosity correlations. Good log-linear correlations are found among all considered line luminosities, which requires a universal similarity of density and thermal structures and probably of shock properties among all EGO clouds to explain. It also requires that the shocks should be produced within the natal clouds of the EGOs. Diverse degrees of correlation are found among the line widths. However, both the line width and luminosity correlations tend to progressively worsen across larger cloud subcomponent size-scales, depicting the increase of randomness across cloud subcomponent sizes. Moreover, the line width correlations among the three isotopic CO 1-0 lines show data scatter as linear functions of the line width itself, indicating that the velocity randomness also increases with whole-cloud sizes and has some regularity behind.
We present angle-resolved photoemission spectroscopy (ARPES) studies of the cuprate high-temperature superconductors which elucidate the relation between superconductivity and the pseudogap and highlight low-energy quasiparticle dynamics in the super
conducting state. Our experiments suggest that the pseudogap and superconducting gap represent distinct states, which coexist below T$_c$. Studies on Bi-2212 demonstrate that the near-nodal and near-antinodal regions behave differently as a function of temperature and doping, implying that different orders dominate in different momentum-space regions. However, the ubiquity of sharp quasiparticles all around the Fermi surface in Bi-2212 indicates that superconductivity extends into the momentum-space region dominated by the pseudogap, revealing subtlety in this dichotomy. In Bi-2201, the temperature dependence of antinodal spectra reveals particle-hole asymmetry and anomalous spectral broadening, which may constrain the explanation for the pseudogap. Recognizing that electron-boson coupling is an important aspect of cuprate physics, we close with a discussion of the multiple kinks in the nodal dispersion. Understanding these may be important to establishing which excitations are important to superconductivity.
In conventional superconductors, a gap exists in the energy absorption spectrum only below the transition temperature (Tc), corresponding to the energy price to pay for breaking a Cooper pair of electrons. In high-Tc cuprate superconductors above Tc,
an energy gap called the pseudogap exists, and is controversially attributed either to pre-formed superconducting pairs, which would exhibit particle-hole symmetry, or to competing phases which would typically break it. Scanning tunnelling microscopy (STM) studies suggest that the pseudogap stems from lattice translational symmetry breaking and is associated with a different characteristic spectrum for adding or removing electrons (particle-hole asymmetry). However, no signature of either spatial or energy symmetry breaking of the pseudogap has previously been observed by angle-resolved photoemission spectroscopy (ARPES). Here we report ARPES data from Bi2201 which reveals both particle-hole symmetry breaking and dramatic spectral broadening indicative of spatial symmetry breaking without long range order, upon crossing through T* into the pseudogap state. This symmetry breaking is found in the dominant region of the momentum space for the pseudogap, around the so-called anti-node near the Brillouin zone boundary. Our finding supports the STM conclusion that the pseudogap state is a broken-symmetry state that is distinct from homogeneous superconductivity.
[Context] Water fountain stars are very young post-AGB stars with high velocity water maser jets. They are the best objects to study the onset of bipolar jets from evolved stars due to their young dynamical ages. [Methods] We use the Arizona Radio Ob
servatory 10m telescope to observe the CO J=2-1 line and compare the line parameters with that of masers. [Results] We report the detection of 12CO and 13COJ=2-1 lines from IRAS 16342-3814. The inferred 12CO mass loss rate is an order of magnitude lower than the infrared and OH mass loss rates, indicating a very cold and thick O-rich circumstellar envelope around the star. We also find a 12CO expansion velocity of Vexp = 46 +- 1 km/s that is too high for an AGB wind and confirm the systemic velocity of 44 +- 1 km/s. In addition we measure a very low 12CO/13CO line ratio of 1.7. [Conclusions] The first detection of CO lines has provided a new way to investigate the water fountain stars. Given the high expansion velocity of the CO gas and its relation to maser velocities, we infer that the CO emission region is co-located with the OH mainline masers in the warm base of the optical bipolar lobes, while the high velocity OH1612MHz and H2O masers are located in the side walls and at the farthest ends of the bipolar lobes, respectively. Further observations are highly desired to understand the very low 12CO/13CO line ratio.
