arXiv subjects

X. Han

Publications and source records attributed to X. Han.

At least 37 records · Page 2Linked to original sources

arXiv2023

First measurement of the Q^2 distribution of X(3915) single-tag two-photon production

We report the first measurement of the $Q^2$ distribution of $X(3915)$ produced by single-tag two-photon interactions. The decay mode used is $X(3915) \rightarrow J/ψω$. The covered $Q^2$ region is from 1.5 (GeV/$c$)$^2$ to 10.0 (GeV/$c$)$^2$. We observe $7.9\pm 3.1({\rm stat.})\pm 1.5({\rm syst.})$ events, where we expect $4.1\pm 0.7$ events based on the $Q^2=0$ result from the no-tag two-photon process, extrapolated to higher $Q^2$ region using the $c\bar{c}$ model of Schuler, Berends, and van Gulik. The shape of the distribution is also consistent with this model; we note that statistical uncertainties are large.

hep-ex↗

arXiv2023

Search for lepton-flavor-violating $τ$ decays into a lepton and a vector meson using the full Belle data sample

Charged-lepton-flavor-violation is predicted in several new physics scenarios. We update the analysis of $τ$ lepton decays into a light charged lepton ($\ell$ = $e^{\pm}$ or $μ^{\pm}$) and a vector meson ($V^0$ = $ρ^0$, $ϕ$, $ω$, $K^{\ast0}$, or $\overline{K}{}^{\ast0}$) using 980 fb$^{-1}$ of data collected with the Belle detector at the KEKB collider. No significant excess of such signal events is observed, and thus 90% credibility level upper limits are set on the $τ\rightarrow \ell V^0$ branching fractions in the range of (1.7--$4.3) \times 10^{-8}$. These limits are improved by 30% on average from the previous results.

hep-ex↗

arXiv2023

Measurement of the mass and width of the $Λ_c(2625)^+$ and the branching ratios of $Λ_c(2625)^+ \to Σ_c^{0}π^{+}$ and $Λ_c(2625)^+ \to Σ_c^{++}π^{-}$

Using the entire data sample of $980\,\textrm{fb}^{-1}$ collected with the Belle detector operating at the KEKB asymmetric-energy collider, we report the measurement of the mass, width, and the relative branching ratios of the $Λ_c(2625)^+$ charmed baryon. The mass difference between $Λ_c(2625)^+$ and $Λ_c^+$ is measured to be $M(Λ_c(2625)^{+}) - M(Λ_c^{+}) = 341.518 \pm 0.006 \pm 0.049\ \mathrm{MeV}/\mathit{c}^2$. The upper limit on the width is measured to be $Γ(Λ_c(2625)^+) < 0.52\,\mathrm{MeV}/\textit{c}^2$ at 90\% credibility level. Based on a full Dalitz plot fit, branching ratios with respect to the mode $Λ_c(2625)^+ \to Λ_c^+ π^+ π^-$ are measured to be $\frac{\mathcal{B}(Λ_c(2625)^+ \to Σ_c^{0} π^{+})} {\mathcal{B}(Λ_c(2625)^+ \to Λ_c^+ π^{+} π^{-})} = (5.19 \pm 0.23 \pm 0.40) \%$ and $\frac{\mathcal{B}(Λ_c(2625)^+ \to Σ_c^{++} π^{-})} {\mathcal{B}(Λ_c(2625)^+ \to Λ_c^+ π^{+} π^{-})} = (5.13 \pm 0.26 \pm 0.32) \%$. These measurements can be used to further constrain the parameters of the underlying theoretical models.

hep-ex↗

arXiv2022

Study of $B^+ \rightarrow p \overline{n} π^0$

We search for the tree-diagram dominated process $B^+ \rightarrow p \overline{n} π^0$, using a data sample of $772 \times 10^6~B\overline B$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. This is the first search with the Belle detector for a decay mode including an anti-neutron. No significant signal is observed and an $90\%$ credible upper limit on the branching fraction is set at $6.1\times10^{-6}$.

hep-ex↗

arXiv2022

Evidence for the singly Cabibbo-suppressed decay $Ω^0_c\toΞ^-π^+$ and search for $Ω^0_c\toΞ^-K^+$ and $Ω^-K^+$ decays at Belle

Using a data sample of 980 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, we study for the first time the singly Cabibbo-suppressed decays $Ω^0_c\toΞ^{-}π^{+}$ and $Ω^-K^+$ and the doubly Cabibbo-suppressed decay $Ω^0_c\to Ξ^- K^{+}$. Evidence for an $Ω^0_c$ signal in the $Ω^0_c\toΞ^-π^+$ mode is reported with a significance of $4.5σ$ including systematic uncertainties. The ratio of branching fractions to the normalization mode $Ω_c^0\to Ω^-π^+$ is measured to be $${\cal B}(Ω_{c}^{0} \to Ξ^{-} π^{+} )/{\cal B}(Ω_c^0\to Ω^-π^+)=0.253\pm 0.053({\rm stat.})\pm 0.030({\rm syst.}).$$ No significant signals of $Ω^0_c\toΞ^-K^+$ and $Ω^-K^+$ modes are found. The upper limits at $90\%$ confidence level on ratios of branching fractions are determined to be $${\cal B}(Ω_{c}^{0} \to Ξ^{-} K ^{+})/{\cal B}(Ω_c^0\to Ω^-π^+) < 0.070$$ and $${\cal B}(Ω_{c}^{0} \to Ω^{-}K^{+})/{\cal B}(Ω_c^0\to Ω^-π^+) < 0.29.$$

hep-ex↗

arXiv2022

Measurement of branching fractions of $Λ_c^+\to{}pK_S^0K_S^0$ and $Λ_c^+\to{}pK_S^0η$ at Belle

We present a study of a singly Cabibbo-suppressed decay $Λ_c^+\to{}pK_S^0K_S^0$ and a Cabibbo-favored decay $Λ_c^+\to{}pK_S^0η$ based on 980 $\rm fb^{-1}$ of data collected by the Belle detector, operating at the KEKB energy-asymmetric $e^+e^-$ collider. We measure their branching fractions relative to $Λ_c^+\to{}pK_S^0$: $\mathcal{B}(Λ_c^+\to{}pK_S^0K_S^0)/\mathcal{B}(Λ_c^+\to{}pK_S^0)={(1.48 \pm 0.08 \pm 0.04)\times 10^{-2}}$ and $\mathcal{B}(Λ_c^+\to{}pK_S^0η)/\mathcal{B}(Λ_c^+\to{}pK_S^0)={(2.73\pm 0.06\pm 0.13)\times 10^{-1}}$. Combining with the world average $\mathcal{B}(Λ_c^+\to{}pK_S^0)$, we have the absolute branching fractions: $\mathcal{B}(Λ_c^+\to{}pK_S^0K_S^0) = {(2.35\pm 0.12\pm 0.07 \pm 0.12 )\times 10^{-4}}$ and $\mathcal{B}(Λ_c^+\to{}pK_S^0η) = {(4.35\pm 0.10\pm 0.20 \pm 0.22 )\times 10^{-3}}$. The first and second uncertainties are statistical and systematic, respectively, while the third ones arise from the uncertainty on $\mathcal{B}(Λ_c^+\to{}pK_S^0)$. The mode $Λ_c^+\to{}pK_S^0K_S^0$ is observed for the first time and has a statistical significance of $>\!10σ$. The branching fraction of $Λ_c^+\to{}pK_S^0η$ has been measured with a threefold improvement in precision over previous results and is found to be consistent with the world average.

hep-ex↗

arXiv2022

Search for the lepton flavour violating decays $B^{+} \to K^{+} τ^\pm \ell^\mp$ ($\ell = e, μ$) at Belle

We present a search for the lepton-flavour-violating decays $B^+ \to K^+ τ^\pm \ell^\mp$, with $\ell = (e, μ)$, using the full data sample of $772 \times 10^6$ $B\overline{B}$ pairs recorded by the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We use events in which one $B$ meson is fully reconstructed in a hadronic decay mode. We find no evidence for $B^\pm \to K^\pm τ\ell$ decays and set upper limits on their branching fractions at the 90% confidence level in the $(1$-$3) \times 10^{-5}$ range. The obtained limits are the world's best results.

hep-ex↗

arXiv2021

Long-range Rydberg-atom-ion molecules of Rb and Cs

We propose a novel type of Rydberg dimer, consisting of a Rydberg-state atom bound to a distant positive ion. The molecule is formed through long-range electric-multipole interaction between the Rydberg atom and the point-like ion. We present potential energy curves (PECs) that are asymptotically connected with Rydberg $nP$- or $nD$-states of rubidium or cesium. The PECs exhibit deep, long-range wells which support many vibrational states of Rydberg-atom-ion molecules (RAIMs). We consider photo-association of RAIMs in both the weak and the strong optical-coupling regimes between initial and Rydberg states of the neutral atom. Experimental considerations for the realization of RAIMs are discussed.

physics.atom-ph↗

arXiv2021

Flame interactions in a stratified swirl burner: flame stabilization, combustion instabilities and beating oscillations

The present article investigates the interactions between the pilot and main flames in a novel stratified swirl burner using both experimental and numerical methods. Experiments are conducted in a test rig operating at atmospheric conditions. The system is equipped with the BASIS (Beihang Axial Swirler Independently-Stratified) burner fuelled with premixed methane-air mixtures. To illustrate the interactions between the pilot and main flames, three operating modes are studied, where the burner works with: (i) only the pilot flame, (ii) only the main flame, and (iii) the stratified flame (with both the pilot and main flames). We found that: (1) In the pilot flame mode, the flame changes from V-shape to M-shape when the main stage is switched from closed to supplying a pure air stream. Strong oscillations in the M-shape flame are found due to the dilution of the main air to the pilot methane flame. (2) In the main flame mode, the main flame is lifted off from the burner if the pilot stage is supplied with air. The temperature of the primary recirculation zone drops substantially and the unsteady heat release is intensified. (3) In the stratified flame mode, unique beating oscillations exhibiting dual closely-spaced frequencies in the pressure spectrum. is found. This is observed within over narrow window of equivalence ratio combinations between the pilot and main stages. Detailed analysis of the experimental data shows that flame dynamics and thermoacoustic couplings at these two frequencies are similar to those of the unstable pilot flame and the attached main flame cases, respectively. Large Eddy Simulations (LESs) are carried out with OpenFOAM to understand the mechanisms of the time averaged flame shapes in different operating modes. Finally, a simple acoustic analysis is proposed to understand the acoustic mode nature of the beating oscillations.

physics.flu-dyn↗

arXiv2021

Inlet temperature driven supercritical bifurcation of combustion instabilities in a lean premixed prevaporized combustor

The present article reports experimental observation and analyses of a supercritical bifurcation of combustion instabilities triggered by the air inlet temperature (Ta). The studies are performed with a pressurised kerosene fuelled Lean Premixed Prevaporized (LPP) combustor operated under elevated temperature. Unlike some previous studies, starting from an unstable condition of the system, the amplitude of combustion instabilities suddenly decrease when Ta exceeds a critical value of Ta =570 K. When the temperature is lowered back the system returns to being unstable without featuring any hysteresis behaviour, as expected in case of a supercritical bifurcation. The unstable flames feature a periodic axial motion of lift-off and re-ignition, characterized as Helmholtz mode. The phase difference between chemiluminescence and pressure signals is found to increase with Ta, exceeding 90 degrees (out of phase) for temperatures higher than 570 K. A low order network framework is conducted, illustrating that when Ta is increased a stability shift of this mode is predicted at Ta near 570 K, in good agreement with the experimental observations. The impact of Ta on the spray characteristics is also examined, finding that higher Ta promotes fuel evaporation and reduces equivalence ratio fluctuation at the exit of the swirler.

physics.flu-dyn↗

arXiv2021

Giant topological longitudinal circular photo-galvanic effect in the chiral multifold semimetal CoSi

The absence of mirror symmetry, or chirality, is behind striking natural phenomena found in systems as diverse as DNA and crystalline solids. A remarkable example occurs when chiral semimetals with topologically protected band degeneracies are illuminated with circularly polarized light. Under the right conditions, the part of the generated photocurrent that switches sign upon reversal of the light's polarization, known as the circular photogalvanic effect, is predicted to depend only on fundamental constants. The conditions to observe quantization are non-universal, and depend on material parameters and the incident frequency. In this work, we perform terahertz emission spectroscopy with tunable photon energy from 0.2 eV - 1.1 eV in the chiral topological semimetal CoSi. We identify a large longitudinal photocurrent peaked at 0.4 eV reaching $\sim$ 550 $μA/V^{2}$, which is much larger than the photocurrent in any chiral crystal reported in the literature. Using first-principles calculations we establish that the peak originates from topological band crossings, reaching 3.3$\pm$0.3 in units of the quantization constant. Our calculations indicate that the quantized CPGE is within reach in CoSi upon doping and increase of the hot-carrier lifetime. The large photo-conductivity suggests that topological semimetals could potentially be used as novel mid-infrared detectors.

cond-mat.mtrl-sci↗

arXiv2020

Tunable coupler for realizing a controlled-phase gate with dynamically decoupled regime in a superconducting circuit

Controllable interaction between superconducting qubits is desirable for large-scale quantum computation and simulation. Here, based on a theoretical proposal by Yan et al. [Phys. Rev. Appl. 10, 054061 (2018)] we experimentally demonstrate a simply-designed and flux-controlled tunable coupler with a continuous tunability by adjusting the coupler frequency, which can completely turn off adjacent superconducting qubit coupling. Utilizing the tunable interaction between two qubits via the coupler, we implement a different type of controlled-phase (CZ) gate with 'dynamically decoupled regime', which allows the qubit-qubit coupling to be only 'on' at the usual operating point while dynamically 'off' during the tuning process of one qubit frequency into and out of the operating point. This scheme not only efficiently suppresses the leakage out of the computational subspace, but also allows for the acquired two-qubit phase being geometric at the operating point. We achieve an average CZ gate fidelity of 98.3(0.6), which is dominantly limited by qubit decoherence. The demonstrated tunable coupler provides a desirable tool to suppress adjacent qubit coupling and is suitable for large scale quantum computation and simulation.

quant-ph↗

arXiv2019

The first six months of the Advanced LIGO's and Advanced Virgo's third observing run with GRANDMA

We present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA). The network consists of 21 telescopes with both photometric and spectroscopic facilities. They are connected together thanks to a dedicated infrastructure. The network aims at coordinating the observations of large sky position estimates of transient events to enhance their follow-up and reduce the delay between the initial detection and the optical confirmation. The GRANDMA program mainly focuses on follow-up of gravitational-wave alerts to find and characterise the electromagnetic counterpart during the third observational campaign of the Advanced LIGO and Advanced Virgo detectors. But it allows for any follow-up of transient alerts involving neutrinos or gamma-ray bursts, even with poor spatial localisation. We present the different facilities, tools, and methods we developed for this network, and show its efficiency using observations of LIGO/Virgo S190425z, a binary neutron star merger candidate. We furthermore report on all GRANDMA follow-up observations performed during the first six months of the LIGO-Virgo observational campaign, and we derive constraints on the kilonova properties assuming that the events' locations were imaged by our telescopes.

astro-ph.HE↗

arXiv2018

Deep learning framework DNN with conditional WGAN for protein solubility prediction

Protein solubility plays a critical role in improving production yield of recombinant proteins in biocatalyst and pharmaceutical field. To some extent, protein solubility can represent the function and activity of biocatalysts which are mainly composed of recombinant proteins. Highly soluble proteins are more effective in biocatalytic processes and can reduce the cost of biocatalysts. Screening proteins by experiments in vivo is time-consuming and expensive. In literature, large amounts of machine learning models have been investigated, whereas parameters of those models are underdetermined with insufficient data of protein solubility. A data augmentation algorithm that can enlarge the dataset of protein solubility and improve the performance of prediction model is highly desired, which can alleviate the common issue of insufficient data in biotechnology applications for developing machine learning models. We first implemented a novel approach that a data augmentation algorithm, conditional WGAN was used to improve prediction performance of DNN for protein solubility from protein sequence by generating artificial data. After adding mimic data produced from conditional WGAN, the prediction performance represented by $R^{2}$ was improved compared with the $R^{2}$ without data augmentation. After tuning the hyperparameters of two algorithms and organizing the dataset, we achieved a $R^{2}$ value of $45.04\%$, which enhanced $R^{2}$ about $10\%$ compared with the previous study using the same dataset. Data augmentation opens the door to applications of machine learning models on biological data, as machine learning models always fail to be well trained by small datasets.

q-bio.QM↗

arXiv2018

Develop machine learning based predictive models for engineering protein solubility

Protein activity is a significant characteristic for recombinant proteins which can be used as biocatalysts. High activity of proteins reduces the cost of biocatalysts. A model that can predict protein activity from amino acid sequence is highly desired, as it aids experimental improvement of proteins. However, only limited data for protein activity are currently available, which prevents the development of such models. Since protein activity and solubility are correlated for some proteins, the publicly available solubility dataset may be adopted to develop models that can predict protein solubility from sequence. The models could serve as a tool to indirectly predict protein activity from sequence. In literature, predicting protein solubility from sequence has been intensively explored, but the predicted solubility represented in binary values from all the developed models was not suitable for guiding experimental designs to improve protein solubility. Here we propose new machine learning models for improving protein solubility in vivo. We first implemented a novel approach that predicted protein solubility in continuous numerical values instead of binary ones. After combing it with various machine learning algorithms, we achieved a prediction accuracy of 76.28 percent when Support Vector Machine algorithm was used. Continuous values of solubility are more meaningful in protein engineering, as they enable researchers to choose proteins with higher predicted solubility for experimental validation, while binary values fail to distinguish proteins with the same value. There are only two possible values so many proteins have the same one.

q-bio.QM↗

arXiv2018

A mathematical solve on the three-interfering-resonances' parameters

The multiple-solution problem in determining the three-interfering-resonances' parameters from a fit to an experimentally measured distribution is considered in a mathematical viewpoint. In this paper it is shown that there are four numerical solutions for the fit with three coherent Breit-Wigner functions. Although the explicit analytical formulae can not be derived in this case, we provide some constraint equations between the four solutions. For the cases of nonrelativistic and relativistic Breit-Wigner forms of amplitude functions, numerical method is provided to derive the other solutions from the already obtained one based on the obtained constraint equations. In real experimental measurements with more complicated amplitude forms similar to Breit-Wigner functions, the same method can be deduced and performed to get numerical solutions. The well agreement between the solved solutions using this mathematical method and those from the fit directly verifies the correctness of the supplied constraint equations and mathematical methodology.

hep-ph↗

arXiv2016

The Deep and Transient Universe in the SVOM Era: New Challenges and Opportunities - Scientific prospects of the SVOM mission

To take advantage of the astrophysical potential of Gamma-Ray Bursts (GRBs), Chinese and French astrophysicists have engaged the SVOM mission (Space-based multi-band astronomical Variable Objects Monitor). Major advances in GRB studies resulting from the synergy between space and ground observations, the SVOM mission implements space and ground instrumentation. The scientific objectives of the mission put a special emphasis on two categories of GRBs: very distant GRBs at z$>$5 which constitute exceptional cosmological probes, and faint/soft nearby GRBs which allow probing the nature of the progenitors and the physics at work in the explosion. These goals have a major impact on the design of the mission: the on-board hard X-ray imager is sensitive down to 4 keV and computes on line image and rate triggers, and the follow-up telescopes on the ground are sensitive in the NIR. At the beginning of the next decade, SVOM will be the main provider of GRB positions and spectral parameters on very short time scale. The SVOM instruments will operate simultaneously with a wide range of powerful astronomical devices. This rare instrumental conjunction, combined with the relevance of the scientific topics connected with GRB studies, warrants a remarkable scientific return for SVOM. In addition, the SVOM instrumentation, primarily designed for GRB studies, composes a unique multi-wavelength observatory with rapid slew capability that will find multiple applications for the whole astronomy community beyond the specific objectives linked to GRBs. This report lists the scientific themes that will benefit from observations made with SVOM, whether they are specific GRB topics, or more generally all the issues that can take advantage of the multi-wavelength capabilities of SVOM.

astro-ph.IM↗

arXiv2016

Tellurene-a monolayer of tellurium from first-principles prediction

A two dimensional (2D) Group-VI Te monolayer, tellurene, is predicted by using the first-principles calculations, which consists of planner four-membered and chair-like six-membered rings arranged alternately in a 2D lattice. The phonon spectra calculations, combined with ab initio molecular dynamics (MD) simulations, demonstrate that tellurene is kinetically very stable. The tellurene shows a desirable direct band gap of 1.04 eV and its band structure can be effectively tuned by strain. The effective mass calculations imply that tellurene should also exhibit a relatively high carrier mobility, e.g. compared with MoS2. The significant direct band gap and the high carrier mobility imply that tellurene is a very promising candidate for a new generation of nanoelectronic devices.

cond-mat.mes-hall↗