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Search results

Measurements of $e^+e^-\rightarrow \eta_{\rm c}\pi^+ \pi^-\pi^0$, $\eta_{\rm c}\pi^+ \pi^-$ and $\eta_{\rm c}\pi^0\gamma$ at $\sqrt{s}$ from 4.18 to 4.60 GeV, and search for a $Z_{\rm c}$ state close to the $D\bar{D}$ threshold at 4.23 GeV decaying to $\eta_{\rm c}\pi$

BESIII Collaboration , Ablikim M., Achasov M. N., Adlarson P., Ahmed S., Albrecht M., Aliberti R., Amoroso A., An M. R., An Q.
27 Oct 2020 hep-ex arxiv.org/abs/2010.14415

We study $\eta_{\rm c}$ production at center-of-mass energies $\sqrt{s}$ from 4.18 to 4.60 GeV in $e^+e^-$ annihilation data collected with the BESIII detector operating at the BEPCII storage ring, corresponding to 7.3 fb$^{-1}$ of integrated luminosity. We measure the cross sections of the three different exclusive reactions $e^+e^-\rightarrow \eta_{\rm c}\pi^+ \pi^-\pi^0$, $e^+e^- \rightarrow \eta_{\rm c}\pi^+ \pi^-$, and $e^+e^- \rightarrow \eta_{\rm c}\pi^0\gamma$. We find significant $\eta_{\rm c}$ production in $e^+e^-\rightarrow \eta_{\rm c}\pi^+ \pi^-\pi^0$ at $\sqrt{s}$ of 4.23 GeV and 4.26 GeV and observe a significant energy-dependent Born cross section that we measure to be consistent with the production via the intermediate $Y(4260)$ resonance. In addition, we perform a search for a charmonium-like $Z_{\rm c}$ state close to the $D\bar{D}$ threshold that decays to $\eta_{\rm c}\pi$, involving ground state charmonium, and observe no signal. Corresponding upper limits on the cross section of $\eta_{\rm c}$ and $Z_{\rm c}$ production are provided, where the yields are not found to be significant.

Search for New Hadronic Decays of $h_c$ and Observation of $h_c\rightarrow K^{+}K^{-}\pi^{+}\pi^{-}\pi^{0}$

BESIII Collaboration , Ablikim M., Achasov M. N., Adlarson P., Ahmed S., Albrecht M., Aliberti R., Amoroso A., An M. R., An Q.
22 Oct 2020 hep-ex arxiv.org/abs/2010.12092

Ten hadronic final states of the $h_c$ decays are investigated via the process $\psi(3686)\rightarrow \pi^0 h_c$, using a data sample of $(448.1 \pm 2.9) \times 10^6$ $\psi(3686)$ events collected with the BESIII detector. The decay channel $h_c\rightarrow K^{+}K^{-}\pi^{+}\pi^{-}\pi^{0}$ is observed for the first time with a significance of $6.0 \sigma$. The corresponding branching fraction is determined to be $\mathcal{B}(h_c\rightarrow K^{+}K^{-}\pi^{+}\pi^{-}\pi^{0}) =(3.3 \pm 0.6 \pm 0.6)\times 10^{-3}$ (the first uncertainty is statistical and the second systematical). Evidence for the decays $h_c\rightarrow \pi^{+} \pi^{-} \pi^{0} \eta$ and $h_c\rightarrow K^{0}{S}K^{\pm}\pi^{\mp}\pi^{+}\pi^{-}$ is found with a significance of $3.6 \sigma$ and $3.8 \sigma$, respectively. The corresponding branching fractions (and upper limits) are obtained to be $\mathcal{B}(h_c\rightarrow \pi^{+} \pi^{-} \pi^{0} \eta ) =(7.2 \pm 1.8 \pm 1.3)\times 10^{-3}$ $(< 1.8 \times 10^{-2})$ and $\mathcal{B}(h_c\rightarrow K^{0}{S}K^{\pm}\pi^{\mp}\pi^{+}\pi^{-}) =(2.8 \pm 0.9 \pm 0.5)\times 10^{-3}$ $(<4.7\times 10^{-3})$. Upper limits on the branching fractions for the final states $h_c \rightarrow K^{+}K^{-}\pi^{0}$, $K^{+}K^{-}\eta$, $K^{+}K^{-}\pi^{+}\pi^{-}\eta$, $2(K^{+}K^{-})\pi^{0}$, $K^{+}K^{-}\pi^{0}\eta$, $K^{0}_{S}K^{\pm}\pi^{\mp}$, and $p\bar{p}\pi^{0}\pi^{0}$ are determined at a confidence level of 90\%.

Measurement of cross-section for $e^+e^-\to\Xi^-\bar{\Xi}^+$ near threshold at BESIII

BESIII Collaboration , Ablikim M., Achasov M. N., Adlarson P., Ahmed S., Albrecht M., Aliberti R., Amoroso A., An M. R., An Q.
16 Oct 2020 hep-ex arxiv.org/abs/2010.08320

The Born cross-sections and effective form factors for process $e^+e^-\to\Xi^-\bar{\Xi}^+$ are measured at eight center-of-mass energies between 2.644 and 3.080 GeV, using a total integrated luminosity of 363.9 pb$^{-1}$ $e^+e^-$ collision data collected with the BESIII detector at BEPCII. After performing a fit to the Born cross-section of $e^+e^-\to\Xi^-\bar{\Xi}^+$, no significant threshold effect is observed.

Bayesian Fixed-domain Asymptotics: Bernstein-von Mises Theorem for Covariance Parameters in a Gaussian Process Model

Li Cheng
05 Oct 2020 math.ST stat.TH arxiv.org/abs/2010.02126

Gaussian process models typically contain finite dimensional parameters in the covariance functions that need to be estimated from the data. We study the Bayesian fixed-domain asymptotic properties of the covariance parameters in a Gaussian process with an isotropic Matern covariance function. Under fixed-domain asymptotics, it is well known that when the dimension of data is less than or equal to three, the microergodic parameter can be consistently estimated with asymptotic normality while the variance parameter and the range (or length-scale) parameter cannot. Motivated by the frequentist theory, we prove a Bernstein-von Mises theorem for the covariance parameters in isotropic Matern covariance functions. We show that under fixed-domain asymptotics, the joint posterior distribution of the microergodic parameter and the range parameter can be factored independently into the product of their marginal posteriors as the sample size goes to infinity. The posterior of the microergodic parameter converges in total variation norm to a normal distribution with shrinking variance, while the posterior of the range parameter does not necessarily converge to any degenerate distribution in general. Our theory allows unbounded prior support for the range parameter. Furthermore, we propose a new property called the posterior asymptotic efficiency in linear prediction, and show that the Bayesian kriging predictor at a new spatial location with covariance parameters randomly drawn from their posterior has the same prediction mean squared error as if the true parameters were known. In the special case of one-dimensional Ornstein-Uhlenbeck process, we derive an explicit form for the limiting posterior distribution of the range parameter and an explicit posterior convergence rate for the posterior asymptotic efficiency. We verify these asymptotic results in numerical examples.

Mapping the Nanoscopic Filament Growth Kinetics in Lithium Solid Electrolytes

Lu Ziheng, Yang Ziwei, Li Cheng, Wang Kai, Han Jinlong, Yang Chunlei, Li Wenjie
04 Oct 2020 physics.app-ph physics.chem-ph arxiv.org/abs/2010.01624

Ceramic lithium conductors such as Li7La3Zr2O12 (LLZO) are promising solid electrolytes for solid-state batteries. However, the lithium filaments can penetrate the electrolytes at high current densities, leading to cell failure. Due to the limited spatial resolution of macroscopic electrochemical measurement techniques, the nanoscopic growth kinetics of lithium filaments and its physical origin remain unrevealed. Here, we report in-situ nanoscale electrochemical characterizations of the filament growth kinetics in LLZO using conductive-atomic force microscope (c-AFM). Significant local inhomogeneity is observed with a hundredfold decrease in the filament triggering bias at the grain boundaries compared with the grain interiors. The origin of the local weakening is assigned to the nanoscopic variation of elastic modulus and surface potential. Further reverse cycles lead to the discovery of the memristive behavior of lithium filament in LLZO based on which a model memristor is designed and demonstrated. A high on/off ratio of ~1E5 is achieved consistently for over 200 cycles. This work provides insights into the nanoscale electrochemical deposition stability in solid-state batteries and opens up opportunities for novel designs of memristive devices.

ALMaQUEST -- IV. The ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) Survey

Lin Lihwai, Ellison Sara L., Pan Hsi-An, Thorp Mallory D., Su Yung-Chau, , Belfiore Francesco, Bothwell M. S., Bundy Kevin, Chen Yan-Mei
04 Oct 2020 astro-ph.GA arxiv.org/abs/2010.01751

The ALMaQUEST (ALMA-MaNGA QUEnching and STar formation) survey is a program with spatially-resolved $^{12}$CO(1-0) measurements obtained with the Atacama Large Millimeter Array (ALMA) for 46 galaxies selected from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) DR15 optical integral-field spectroscopic survey. The aim of the ALMaQUEST survey is to investigate the dependence of star formation activity on the cold molecular gas content at kpc scales in nearby galaxies. The sample consists of galaxies spanning a wide range in specific star formation rate (sSFR), including starburst (SB), main-sequence (MS), and green valley (GV) galaxies. In this paper, we present the sample selection and characteristics of the ALMA observations, and showcase some of the key results enabled by the combination of spatially-matched stellar populations and gas measurements. Considering the global (aperture-matched) stellar mass, molecular gas mass, and star formation rate of the sample, we find that the sSFR depends on both the star formation efficiency (SFE) and the molecular gas fraction ($f_{\rm H_{2}}$), although the correlation with the latter is slightly weaker. Furthermore, the dependence of sSFR on the molecular gas content (SFE or $f_{\rm H_{2}}$) is stronger than that on either the atomic gas fraction or the molecular-to-atomic gas fraction, albeit with the small HI sample size. On kpc scales, the variations in both SFE and $f_{\rm H_{2}}$ within individual galaxies can be as large as 1-2 dex thereby demonstrating that the availability of spatially-resolved observations is essential to understand the details of both star formation and quenching processes.

Leveraging Semantic and Lexical Matching to Improve the Recall of Document Retrieval Systems: A Hybrid Approach

Kuzi Saar, Zhang Mingyang, Li Cheng, Bendersky Michael, Najork Marc
02 Oct 2020 cs.IR arxiv.org/abs/2010.01195

Search engines often follow a two-phase paradigm where in the first stage (the retrieval stage) an initial set of documents is retrieved and in the second stage (the re-ranking stage) the documents are re-ranked to obtain the final result list. While deep neural networks were shown to improve the performance of the re-ranking stage in previous works, there is little literature about using deep neural networks to improve the retrieval stage. In this paper, we study the merits of combining deep neural network models and lexical models for the retrieval stage. A hybrid approach, which leverages both semantic (deep neural network-based) and lexical (keyword matching-based) retrieval models, is proposed. We perform an empirical study, using a publicly available TREC collection, which demonstrates the effectiveness of our approach and sheds light on the different characteristics of the semantic approach, the lexical approach, and their combination.

Qualification tests of 997 8-inch photomultiplier tubes for the water Cherenkov detector array of the LHAASO experiment

Jiang Kun, Tang Zebo, Li Xin, Cao Zehua, Li Cheng, Li Yang, Li Ziwei, Li Ziyang, Liang Zheng, Lu Pengzhong
27 Sep 2020 physics.ins-det hep-ex arxiv.org/abs/2009.12742

The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi Mountain, Sichuan province of China at an altitude of 4410 meters. One of its main goals is to survey the northern sky for very-high-energy gamma ray sources via its ground-based water Cherenkov detector array (WCDA). 900 8-inch photomultiplier tubes (PMTs) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP) are installed in the WCDA, collecting Cherenkov photons produced by air shower particles crossing water. The design of the PMT base with a high dynamic range for CR365-02-1, the PMT batch test system, and the test results of 997 PMTs are presented in this paper.

Study of the water Cherenkov detector with high dynamic range for LHAASO

Jiang Kun, Tang Zebo, Li Xin, Li Cheng
26 Sep 2020 physics.ins-det hep-ex arxiv.org/abs/2009.12737

The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi mountain, Sichuan, China at an altitude of 4410 m. One of its main goals is to survey the northern sky for very-high-energy (above 100 GeV) gamma ray sources via its ground-based Water Cherenkov Detector Array (WCDA). WCDA is 78000 $m^2$ in dimension and consists of 3120 water detector cells divided into 3 water ponds. A hemispherical 8-inch photomultiplier tube (PMT) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP) is installed at the bottom-center of each cell of the first water pond to collect Cherenkov light produced by air shower particles crossing water. This proceeding includes the technical design of WCDA, the design of a high dynamic range base for CR365-02-1, the PMT test system and test results of 997 PMTs.

How to empirically model star formation in dark matter halos: I. Inferences about central galaxies from numerical simulations

Chen Yangyao, Mo H. J., Li Cheng, Wang Kai
25 Sep 2020 astro-ph.GA arxiv.org/abs/2009.12467

We use TNG and EAGLE hydrodynamic simulations to investigate the central galaxy - dark matter halo relations that are needed for a halo-based empirical model of star formation in galaxies. Using a linear dimension reduction algorithm and a model ensemble method, we find that for both star-forming and quenched galaxies, the star formation history (SFH) is tightly related to the halo mass assembly history (MAH). The quenching of a low-mass galaxy is mainly due to the infall-ejection process related to a nearby massive halo, while the quenching of a high-mass galaxy is closely related to the formation of a massive progenitor in its host halo. The classification of star-forming and quenched populations based solely on halo properties contains contamination produced by sample imbalance and overlapping distributions of the two populations. Guided by the results from hydrodynamic simulations, we build an empirical model to predict the SFH of central galaxies based on the MAH of their host halos, and we model the star-forming and quenched populations separately. Our model is based on the idea of adopting star formation templates from hydrodynamic simulations to reduce model complexity. We use various tests to demonstrate that the model can recover star formation histories of individual galaxies, and can statistically reproduce the galaxy bimodal distribution, stellar mass - halo mass and star formation rate - halo mass relations from low to high redshift, and assembly bias. Our study provides a framework of using hydrodynamic simulations to discover, and to motivate the use of, key ingredients to model galaxy formation using halo properties.