arXiv subjects

H. Gao

Publications and source records attributed to H. Gao.

At least 163 records · Page 9Linked to original sources

arXiv2024

Long-term radio monitoring of the fast X-ray transient EP240315a: evidence for a relativistic jet

The recent launch of Einstein Probe (EP) in early 2024 opened up a new window onto the transient X-ray sky, allowing for real-time discovery and follow-up of fast X-ray transients (FXRTs). Multi-wavelength observations of FXRTs and their counterparts are key to characterize the properties of their outflows and, ultimately, identify their progenitors. Here, we report our long-term radio monitoring of EP240315A, a long-lasting ($\sim 1000$ s) high redshift ($z=4.9$) FXRT associated to GRB~240315C. Our campaign, carried out with the Australian Telescope Compact Array (ATCA), followed the transient's evolution at two different frequencies (5.5 GHz and 9~GHz) for three months. In the radio lightcurves we identify an unusual steep rise at 9 GHz, possibly due to a refreshed reverse shock, and a late-time rapid decay of the radio flux, which we interpret as a jet break due to the outflow collimation. We find that the multi-wavelength counterpart of EP240315A is well described by a model of relativistic jet seen close to its axis, with jet half-opening angle $θ_j \approx 3 ^{\circ}$ and beaming-corrected total energy $E \simeq 4\times 10^{51}$~erg, typical of GRBs. These results show that a substantial fraction of FXRTs may be associated to standard GRBs and that sensitive X-ray monitors, such as Einstein Probe and the proposed HiZ-GUNDAM and Theseus missions, can successfully pinpoint their relativistic outflows up to high-redshifts.

astro-ph.HE↗

arXiv2024

Anomaly Detection and Approximate Similarity Searches of Transients in Real-time Data Streams

We present LAISS (Lightcurve Anomaly Identification and Similarity Search), an automated pipeline to detect anomalous astrophysical transients in real-time data streams. We deploy our anomaly detection model on the nightly ZTF Alert Stream via the ANTARES broker, identifying a manageable $\sim$1-5 candidates per night for expert vetting and coordinating follow-up observations. Our method leverages statistical light-curve and contextual host-galaxy features within a random forest classifier, tagging transients of rare classes (spectroscopic anomalies), of uncommon host-galaxy environments (contextual anomalies), and of peculiar or interaction-powered phenomena (behavioral anomalies). Moreover, we demonstrate the power of a low-latency ($\sim$ms) approximate similarity search method to find transient analogs with similar light-curve evolution and host-galaxy environments. We use analogs for data-driven discovery, characterization, (re-)classification, and imputation in retrospective and real-time searches. To date we have identified $\sim$50 previously known and previously missed rare transients from real-time and retrospective searches, including but not limited to: SLSNe, TDEs, SNe IIn, SNe IIb, SNe Ia-CSM, SNe Ia-91bg-like, SNe Ib, SNe Ic, SNe Ic-BL, and M31 novae. Lastly, we report the discovery of 325 total transients, all observed between 2018-2021 and absent from public catalogs ($\sim$1% of all ZTF Astronomical Transient reports to the Transient Name Server through 2021). These methods enable a systematic approach to finding the "needle in the haystack" in large-volume data streams. Because of its integration with the ANTARES broker, LAISS is built to detect exciting transients in Rubin data.

astro-ph.HE↗

arXiv2024

Search for $η_{c}(2S)\to K^+ K^- η^{\prime}$ decay

Using $(2.712\pm0.014)\times10^{9}$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII, we find an evidence of the $η_{c}(2S)\to K^+ K^- η^{\prime}$ decay with a statistical significance of 3.1$σ$. Its decay branching fraction is measured to be $(12.24\pm4.60(\mathrm{stat.})\pm2.37(\mathrm{syst.})\pm4.68(\mathrm{extr.}))\times 10^{-4}$, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is from the branching fraction of the $ψ(3686)\toγη_{c}(2S)$ decay. The upper limit on the product branching fraction $B[ψ(3686)\toγη_{c}(2S)] \times$ $B[η_{c}(2S)\to K^+ K^- η^{\prime}]$ is set to be $1.14 \times 10^{-6}$ at $90\%$ confidence level. In addition, the branching fractions of $χ_{c1}\to K^+ K^- η^{\prime}$ and $χ_{c2}\to K^+ K^- η^{\prime}$ are updated to be $(8.47\pm0.09(\mathrm{stat.})\pm0.47(\mathrm{syst.}))\times 10^{-4}$ and $(1.53\pm0.04(\mathrm{stat.})\pm0.08(\mathrm{syst.}))\times 10^{-4}$, respectively. The precision is improved by twofold.

hep-ex↗

arXiv2024

Strong and weak $CP$ tests in sequential decays of polarized $Σ^0$ hyperons

The $J/ψ, ψ(3686) \to Σ^0 \barΣ^{0}$ processes and subsequent decays are studied using the world's largest $J/ψ$ and $ψ(3686)$ data samples collected with the BESIII detector. The strong-$CP$ symmetry is tested in the decays of the $Σ^0$ hyperons for the first time by measuring the decay parameters, $α_{Σ^0} = -0.0017 \pm 0.0021 \pm 0.0018$ and $\barα_{Σ^0} = 0.0021 \pm 0.0020 \pm 0.0022$. The weak-$CP$ test is performed in the subsequent decays of their daughter particles $Λ$ and $\barΛ$. Also for the first time, the transverse polarizations of the $Σ^0$ hyperons in $J/ψ$ and $ψ(3686)$ decays are observed with opposite directions, and the ratios between the S-wave and D-wave contributions of the $J/ψ, ψ(3686) \to Σ^0 \barΣ^{0}$ decays are obtained. These results are crucial to understand the decay dynamics of the charmonium states and the production mechanism of the $Σ^0-\barΣ^0$ pairs.

hep-ex↗

arXiv2024

Measurements of Normalized Differential Cross Sections of Inclusive $η$ Production in $e^{+}e^{-}$ Annihilation at Energy from 2.0000 to 3.6710 GeV

Using data samples collected with the BESIII detector operating at the BEPCII storage ring, the cross section of the inclusive process $e^{+}e^{-} \to η+ X$, normalized by the total cross section of $e^{+}e^{-} \to \text{hadrons}$, is measured at eight center-of-mass energy points from 2.0000 GeV to 3.6710 GeV. These are the first measurements with momentum dependence in this energy region. Our measurement shows a significant discrepancy from calculations with the existing fragmentation functions. To address this discrepancy, a new QCD analysis is performed at the next-to-next-to-leading order with hadron mass corrections and higher twist effects, which can explain both the established high-energy data and our measurements reasonably well.

hep-ex↗

arXiv2024

Study of $e^+e^-\toωX(3872)$ and $γX(3872)$ from 4.66 to 4.95 GeV

Using data samples with an integrated luminosity of $4.5~\text{fb}^{-1}$ collected by the BESIII detector at center-of-mass energies ranging from 4.66 to 4.95 GeV, we study the processes of $e^+e^-\toωX(3872)$ and $e^+e^-\toγX(3872)$. With the $e^+e^-\toωX(3872)$ process, the branching fraction ratio $R\equiv\frac{\mathcal{B}(X(3872)\toγJ/ψ)}{\mathcal{B}(X(3872)\toπ^+π^- J/ψ)}$ is measured to be $0.38\pm0.20_\text{stat.}\pm0.01_\text{syst.}$ ($R< 0.83$ at 90\% confidence level). In addition, we measure the ratio of the average cross section of $e^+e^-\toωX(3872)$ to $e^+e^-\toωχ_{c1}(ωχ_{c2})$ to be $σ_{ωX(3872)}/σ_{ωχ_{c1}}~(σ_{ωX(3872)}/σ_{ωχ_{c2}})=5.2\pm1.0_\text{stat.}\pm1.9_\text{syst.}~ (5.5\pm1.1_\text{stat.}\pm2.4_\text{syst.})$. Finally, we search for the process of $e^+e^-\toγX(3872)$, and no obvious signal is observed. The upper limit on the ratio of the average cross section of $e^+e^-\toγX(3872)$ to $e^+e^-\toωX(3872)$ is set as $σ_{γX(3872)}/σ_{ωX(3872)}<0.23$ at 90\% confidence level.

hep-ex↗

arXiv2024

Study of the decay and production properties of $D_{s1}(2536)$ and $D_{s2}^*(2573)$

The $e^+e^-\rightarrow D_s^+D_{s1}(2536)^-$ and $e^+e^-\rightarrow D_s^+D^*_{s2}(2573)^-$ processes are studied using data samples collected with the BESIII detector at center-of-mass energies from 4.530 to 4.946~GeV. The absolute branching fractions of $D_{s1}(2536)^- \rightarrow \bar{D}^{*0}K^-$ and $D_{s2}^*(2573)^- \rightarrow \bar{D}^0K^-$ are measured for the first time to be $(35.9\pm 4.8\pm 3.5)\%$ and $(37.4\pm 3.1\pm 4.6)\%$, respectively. The measurements are in tension with predictions based on the assumption that the $D_{s1}(2536)$ and $D_{s2}^*(2573)$ are dominated by a bare $c\bar{s}$ component. The $e^+e^-\rightarrow D_s^+D_{s1}(2536)^-$ and $e^+e^-\rightarrow D_s^+D^*_{s2}(2573)^-$ cross sections are measured, and a resonant structure at around 4.6~GeV with a width of 50~MeV is observed for the first time with a statistical significance of $15σ$ in the $e^+e^-\rightarrow D_s^+D^*_{s2}(2573)^-$ process. It could be the $Y(4626)$ found by the Belle collaboration in the $D_s^+D_{s1}(2536)^{-}$ final state, since they have similar masses and widths. There is also evidence for a structure at around 4.75~GeV in both processes.

hep-ex↗

arXiv2024

Measurement of the J/$ψ$ photoproduction cross section over the full near-threshold kinematic region

We report the total and differential cross sections for $J/ψ$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/ψ$ photoproduction and its relation to the $J/ψ-$proton interaction. These measurements of $J/ψ$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.

nucl-ex↗

arXiv2024

Measurement of Spin-Density Matrix Elements in $ρ(770)$ Production with a Linearly Polarized Photon Beam at $E_γ= 8.2\,-\,8.8\,\text{GeV}$

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $ρ$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $ρ(770)$ differ by two units are negligible for $-t<0.5\,\text{GeV}^{2}/c^{2}$.

nucl-ex↗

arXiv2024

Improved measurement of the semileptonic decay $D^+_{s}\to K^0 e^+ν_e$

Analyzing $e^+e^-$ collision data corresponding to an integrated luminosity of $7.33~\mathrm{fb}^{-1}$ collected at center-of-mass energies between 4.128 and 4.226~GeV with the BESIII detector, we measure the branching fraction of the semileptonic decay $D^+_{s}\to K^0 e^+ν_e$ to be $(2.98\pm0.23\pm0.12)\times10^{-3}$. The $D_s^+\to K^0$ hadronic form factor is determined from the differential decay rate of $D^+_s\to K^0 e^+ν_e$ to be $f^{K^0}_+(0)=0.636\pm0.049\pm0.013$. For both measurements, the first uncertainty is statistical and the second systematic. The branching fraction and form factor measurements are factors of 1.6 and 1.7 more precise than the previous world averages, respectively.

hep-ex↗

arXiv2024

Discovery of the optical and radio counterpart to the fast X-ray transient EP240315a

Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified >10 years ago. Since then, nearly 40 events have been discovered, although almost all of these have been recovered from archival Chandra and XMM-Newton data. To date, optical sky surveys and follow-up searches have not revealed any multi-wavelength counterparts. The Einstein Probe, launched in January 2024, has started surveying the sky in the soft X-ray regime (0.5-4 keV) and will rapidly increase the sample of FXTs discovered in real time. Here, we report the first discovery of both an optical and radio counterpart to a distant FXT, the fourth source publicly released by the Einstein Probe. We discovered a fast-fading optical transient within the 3 arcmin localisation radius of EP240315a with the all-sky optical survey ATLAS, and our follow-up Gemini spectrum provides a redshift, z=4.859+/-0.002. Furthermore, we uncovered a radio counterpart in the S-band (3.0 GHz) with the MeerKAT radio interferometer. The optical (rest-frame UV) and radio luminosities indicate the FXT most likely originates from either a long gamma-ray burst or a relativistic tidal disruption event. This may be a fortuitous early mission detection by the Einstein Probe or may signpost a mode of discovery for high-redshift, high-energy transients through soft X-ray surveys, combined with locating multi-wavelength counterparts.

astro-ph.HE↗

arXiv2024

Search for $X(1870)$ via the decay $J/ψ\to ωK^+ K^-η$

Using a sample of $(10087\pm 44)\times10^{6}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider, we search for the decay $X(1870)\to K^+ K^-η$ via the $J/ψ\to ωK^+ K^- η$ process for the first time. No significant $X(1870)$ signal is observed. The upper limit on the branching fraction of the decay $ J/ψ\to ωX(1870) \toωK^+ K^- η$ is determined to be $9.55\times 10^{-7}$ at the $90\%$ confidence level. In addition, the branching faction $B(J/ψ\toωK^+ K^- η)$ is measured to be $(3.33\pm0.02(\rm{stat.})\pm 0.12(\rm{syst.}))\times 10^{-4}$.

hep-ex↗

arXiv2024

Observation of $η_{c}$(1S, 2S) and $χ_{cJ}$ decays to 2$(π^{+}π^{-})η$ via $ψ$(3686) radiative transitions

Based on $2.7 \times 10^9~ψ(3686)$ decays collected with the BESIII detector, the radiative decay $ψ(3686)\to\gamma2(π^{+}π^{-})η$ is investigated to measure properties of S- and P-wave charmonium states. The branching fraction of the decay $η_{c}(1S) \to 2(π^{+}π^{-})η$, which is found to have a strong dependence on the interference pattern between $η_c(1S)$ and non-$η_c(1S)$ processes, is measured in both destructive and constructive interference scenarios for the first time. The mass and width of the $η_{c}(1S)$ are measured to be $M=(2984.14 \pm 0.13 \pm 0.38)$ MeV/$c^{2}$ and $Γ=(28.82 \pm 0.11 \pm 0.82)$ MeV, respectively. Clear signals for the decays of the $χ_{cJ}(J=0,1,2)$ and the $η_{c}(2S)$ to $2(π^{+}π^{-})η$ are also observed for the first time, and the corresponding branching fractions are measured. The ratio of the branching fractions between the $η_{c}(2S)$ and $η_{c}(1S)$ decays is significantly lower than the theoretical prediction, which might suggest different dynamics in their decays.

hep-ex↗

arXiv2024

Measurements of the branching fractions of the $P$-wave charmonium spin-singlet state $h_c(^1P_1) \to h^+ h^-π^0/η$

Based on $(2712.4\pm 14.3)\times10^{6}$ $ψ(3686)$ events, we investigate four hadronic decay modes of the $P$-wave charmonium spin-singlet state $h_c(^1P_1) \to h^+ h^- π^0/η$ ($h=π$ or $K$) via the process $ψ(3686) \to π^{0}h_c$ at BESIII. The $h_c \to π^+ π^- π^0$ decay is observed with a significance of 9.6$σ$ after taking into account systematic uncertainties. Evidences for $h_c \to K^+ K^- π^0$ and $h_c \to K^+ K^- η$ are found with significances of $3.5σ$ and $3.3σ$, respectively, after considering the systematic uncertainties. The branching fractions of these decays are measured to be $\mathcal{B}(h_c \to π^+ π^- π^0)=(1.36\pm0.16\pm0.14)\times10^{-3}$, $\mathcal{B}(h_c \to K^+ K^- π^0)=(3.26\pm0.84\pm0.36)\times10^{-4}$, and $\mathcal{B}(h_c \to K^+ K^- η)=(3.13\pm1.08\pm0.38)\times10^{-4}$, where the first uncertainties are statistical and the second are systematic. No significant signal of $h_c\toπ^+π^-η$ is found, and the upper limit of its decay branching fraction is determined to be $\mathcal{B}(h_c\toπ^+π^-η) < 4.0 \times 10^{-4}$ at 90% confidence level.

hep-ex↗

arXiv2024

Evidence of the Singly Cabibbo Suppressed decay $Λ_c^+\to pπ^0$

Evidence for the singly Cabibbo suppressed decay $Λ_c^+\to pπ^0$ is reported for the first time with a statistical significance of $3.7σ$ based on 6.0 $\mathrm{fb}^{-1}$ of $e^+e^-$ collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of $Λ_c^+\to pπ^0$ is measured to be $(1.56^{+0.72}_{-0.58}\pm0.20)\times 10^{-4}$. Combining with the branching fraction of $Λ_c^+\to nπ^+$, $(6.6\pm1.3)\times10^{-4}$, the ratio of the branching fractions of $Λ_c^+\to nπ^+$ and $Λ_c^+\to pπ^0$ is calculated to be $3.2^{+2.2}_{-1.2}$. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of $Λ_c^+\to pη$ is measured to be $(1.63\pm0.31_{\rm stat}\pm0.11_{\rm syst}) \times10^{-3}$.

hep-ex↗

arXiv2024

Study of the decays $χ_{cJ} \rightarrow Λ\barΛϕ$

Based on $(2712.4 \pm 14.3) \times 10^{6}$ $ e^{+}e^{-}\toψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, we report the first evidence of $χ_{c0}\to Λ\bar Λϕ$ decays and the first observation of $χ_{c1,2}\to Λ\bar Λϕ$ decays, with significances of $4.5σ$, $11.3σ$ and $13.0σ$, respectively. The decay branching fractions of $χ_{c0,1,2}\to Λ\bar Λϕ$ are measured to be $( 2.99\pm1.24\pm0.19) \times 10^{-5}$, $(6.01\pm0.90\pm0.40 )\times 10^{-5}$, and $(7.13\pm0.81\pm0.36) \times 10^{-5}$, where the first uncertainties are statistical and the second systematic. No obvious enhancement near the $Λ\barΛ$ production threshold or excited $Λ$ state is found in the $Λϕ$ (or $\barΛϕ$) system.

hep-ex↗

arXiv2024

Measurement of absolute branching fractions of $D_s^+$ hadronic decays

Using $e^+ e^-$ collision data collected at the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV, corresponding to an integrated luminosity of $7.33~{\rm fb}^{-1}$, we determine the absolute branching fractions of fifteen hadronic $D_s^{+}$ decays with a double-tag technique. In particular, we make precise measurements of the branching fractions $\mathcal{B}(D_s^+ \to K^+ K^- π^+)=(5.49 \pm 0.04 \pm 0.07)\%$, $\mathcal{B}(D_s^+ \to K_S^0 K^+)=(1.50 \pm 0.01 \pm 0.01)\%$ and $\mathcal{B}(D_s^+ \to K^+ K^- π^+ π^0)=(5.50 \pm 0.05 \pm 0.11)\%$, where the first uncertainties are statistical and the second ones are systematic. The \emph{CP} asymmetries in these decays are also measured and all are found to be compatible with zero.

hep-ex↗

arXiv2024

Determination of the number of $ψ(3686)$ events taken at BESIII

The number of $ψ(3686)$ events collected by the BESIII detector during the 2021 run period is determined to be $(2259.3\pm 11.1)\times 10^6$ by counting inclusive $ψ(3686)$ hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of $ψ(3686)$ events collected during the 2009 and 2012 run periods are updated to be $(107.7\pm0.6)\times 10^6$ and $(345.4\pm 2.6)\times 10^6$, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of $ψ(3686)$ events in the three data samples is $(2712.4\pm14.3)\times10^6$.

hep-ex↗