arXiv subjects

Z. Chen

Publications and source records attributed to Z. Chen.

At least 91 records · Page 5Linked to original sources

arXiv2025

Neutral hydrogen in and around galaxies during the Epoch of Reionization

JWST spectra revealing Lyman-$α$ (Ly$α$) absorption in $z\sim 5-14$ galaxies offer a unique probe of reionization's earliest stages. However, disentangling absorption by the increasingly neutral intergalactic medium (IGM) from that in galaxies' interstellar and circumgalactic medium (ISM, CGM) remains challenging due to the poorly constrained nature of neutral hydrogen (HI) in and around galaxies at these redshifts. We use the SERRA high-resolution cosmological zoom-in simulations to characterize the HI distribution and its evolution along sightlines to star-forming regions during reionization, to interpret the contribution of local HI (ISM+CGM) to Ly$α$ absorption in $z>5$ spectra. We analyze $\sim 100$ $z=6-9.5$ galaxies, generating mock sightlines from each galaxy's star formation peak. We study the sightline distribution of HI column densities ($N_{\rm HI}$) and its variation with radius, halo mass and redshift. We find broad sightline variation in $N_{\rm HI}$ (0.5-1.5dex) due to complex ISM morphology driven by bursty star formation, with median $\log(N_{\rm HI}/{\rm cm}^{-2}) \simeq 21-22$. Dense ISM gas is the dominant origin of damped Ly$α$ absorption (DLA) systems along sightlines towards star-forming regions, outweighing gas in the CGM, filaments and proximate absorbers. Median $N_{\rm HI}$ increases with halo mass, scaling roughly with the virial radius, as expected due to larger potentials and more extended CGM, but shows negligible redshift evolution at fixed halo mass. This suggests post-reionization $N_{\rm HI}$ distributions may provide useful priors to interpret IGM damping wings at higher redshifts. To interpret strong $z>5$ DLA candidates found by JWST, we investigate $N_{\rm HI}>10^{22}{\rm cm}^{-2}$ sightlines. These trace dense, metal-enriched ISM within <1 kpc of massive halos, a scenario testable with higher-resolution spectroscopy.

astro-ph.GA↗

arXiv2025

Limiting the Parameter Space for Unstable eV-scale Neutrinos Using IceCube Data

This Letter extends a recent IceCube sterile neutrino search to include unstable sterile neutrinos within the context of a model termed 3+1+Decay, which expands upon the 3+1 model by introducing sterile neutrino decay to invisible particles with coupling constant $g^2$. The model is attractive since it reduces tension between oscillation experiments within the global fits and with constraints that come from cosmological observables. The analysis uses 10.7 years of up-going muon neutrino data with energy 500 GeV to 100 TeV and with improved reconstruction and modeling of systematics. The best-fit point is found to be $g^2 = 0$, $\sin^2(2θ_{24}) = 0.16$, and $Δm^{2}_{41} = 3.5$ eV$^2$, in agreement with the recent 3+1 sterile neutrino search. Values of $g^2 \geq π$ are excluded at 95\% confidence level. This result substantially limits decay parameter space indicated by recent global fits, disfavoring the decay scenario.

hep-ex↗

arXiv2025

Observation of Transverse Polarization and Determination of Psionic Form Factors of the $Λ$ Hyperon at $\sqrt{s}= 3.773$ GeV

Using a data sample of $e^{+}e^{-}$ collision data corresponding to an integrated luminosity of 20.3 fb$^{-1}$ collected by the BESIII detector at the BEPCII collider, we present an observation of transverse polarization and a complete determination of the psionic form factors of the $Λ$ hyperon in $e^{+}e^{-}\toΛ\barΛ$ decay with the entangled $Λ-\barΛ$ pair at $\sqrt{s}=3.773$ GeV. The relative phase between the psionic form factors is determined to be $ΔΦ=(1.53\pm0.36\pm0.03)$~rad with a significance of 5.5 $σ$ taking into account systematic uncertainty. This result indicates a non-zero phase between the transition amplitudes of the $Λ\barΛ$ helicity states. Additionally, we measure the angular distribution parameter and the modulus of the ratio between the psionic form factors to be $η=0.86\pm0.05\pm0.03$ and $R(s)=|G_{E}(s)/G_{M}(s)|=0.47\pm0.08\pm0.05$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2025

Measurement of the space-like $π^0$ transition form factor

Based on $2.93\,\text{fb}^{-1}$ of $e^+e^-$ collision data taken with the BESIII detector at a center-of-mass energy of $3.773\,\text{GeV}$, the two-photon fusion process $e^+e^-\to e^+e^-π^0$ is investigated using a single-tag approach. The differential Born cross section $\text{d}σ/\text{d}Q^2$ and the space-like transition form factor $|F(Q^2)|$ of the $π^0$ are measured as functions of the squared momentum transfer $Q^2$ of the tagged, scattered lepton. The measurement covers the range $0.2 < Q^2 < 3.5\,\text{GeV}^2$. The results are consistent with previous measurements, and provide a significant improvement for $Q^2<2\,\text{GeV}^2$.

hep-ex↗

arXiv2025

Search for a bound state of $Λ_{c}\barΣ_{c}$ near threshold

We search for a possible $Λ_{c} \bar{Σ}_{c}$ bound state, denoted as $H_{c}^{\pm}$, via the $ e^{+}e^{-} \to π^{+} π^{-} Λ_{c}^{+}\barΛ_{c}^{-}$ process for the first time. This analysis utilizes 207.8 and 159.3 pb$^{-1}$ of $e^{+}e^{-}$ annihilation data at the center-of-mass energies of 4918.02 and 4950.93 MeV, respectively, collected with the BESIII detector at the BEPCII collider. No statistically significant signal is observed. The upper limits of the product of Born cross section and branching fraction $σ(e^{+}e^{-} \to π^{+} H_c^{-} + c.c.) \times \mathcal{B}(H_c^{-} \rightarrow π^{-}Λ_{c}^{+}\barΛ_{c}^{-})$ at a 90\% confidence level are reported at each energy point and for various $H_{c}$ mass hypotheses (4715, 4720, 4725, 4730, and 4735 MeV/$c^{2}$) and widths (5, 10, or 20 MeV), with the upper limits ranging from 1.1 pb to 6.4 pb.

hep-ex↗

arXiv2025

Measurement of the branching fraction of $\psip \to ωηη$

Using a sample of (2.712 $\pm$ 0.014)$\times 10^{9}$ $\psip$ events collected with the BESIII detector at the BEPCII collider in 2009, 2012, and 2021, the decay $\psip \to ωηη$ is observed for the first time. The branching fraction of the $ψ(3686)\toωηη$ decay is measured to be (1.65 $\pm$ 0.02 $\pm$ 0.21)$\times 10^{-5}$, where the first uncertainty is statistical and the second systematic. Clear structures associated with the well-established $ω(1420)$ and $f_{0}(1710)$ resonances are observed in the $ωη$ and $ηη$ invariant-mass spectra, respectively.

hep-ex↗

arXiv2025

Onset of Constituent Quark Number Scaling in Heavy-Ion Collisions at RHIC

Partonic collectivity is one of the necessary signatures for the formation of quark-gluon plasma in high-energy nuclear collisions. Number of constituent quarks (NCQ) scaling has been observed for hadron elliptic flow $v_2$ in top energy nuclear collisions at the Relativistic Heavy Ion Collider and the LHC, and this has been theoretically suggested as strong evidence for partonic collectivity. In this Letter, a systematic analysis of $v_2$ of $π^{\pm}$, $K^{\pm}$, $K^{0}_{S}$, $p$, and $Λ$ in Au+Au collisions at ${\sqrt{s_{_{\rm{NN}}}}}$ = 3.2, 3.5, 3.9, and 4.5 GeV, with the STAR experiment at the Relativistic Heavy Ion Collider, is presented. NCQ scaling is markedly violated at 3.2 GeV, consistent with a hadronic-interaction dominated equation of state. However, as the collision energy increases, a gradual evolution to NCQ scaling is observed. This beam-energy dependence of $v_2$ for all hadrons studied provides evidence for the onset of dominant partonic interactions by ${\sqrt{s_{_{\rm{NN}}}}}$ = 4.5 GeV.

nucl-ex↗

arXiv2025

The LED calibration systems for the mDOM and D-Egg sensor modules of the IceCube Upgrade

The IceCube Neutrino Observatory, instrumenting about 1 km$^3$ of deep, glacial ice at the geographic South Pole, is due to be enhanced with the IceCube Upgrade. The IceCube Upgrade, to be deployed during the 2025/26 Antarctic summer season, will consist of seven new strings of photosensors, densely embedded near the bottom center of the existing array. Aside from a world-leading sensitivity to neutrino oscillations, a primary goal is the improvement of the calibration of the optical properties of the instrumented ice. These will be applied to the entire archive of IceCube data, improving the angular and energy resolution of the detected neutrino events. For this purpose, the Upgrade strings include a host of new calibration devices. Aside from dedicated calibration modules, several thousand LED flashers have been incorporated into the photosensor modules. We describe the design, production, and testing of these LED flashers before their integration into the sensor modules as well as the use of the LED flashers during lab testing of assembled sensor modules.

astro-ph.IM↗

arXiv2025

Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with 12 yr of Data Collected by the IceCube Neutrino Observatory

We analyzed the 7.92$\times 10^{11}$ cosmic-ray-induced muon events collected by the IceCube Neutrino Observatory from May 13, 2011, when the fully constructed experiment started to take data, to May 12, 2023. This dataset provides an up-to-date cosmic-ray arrival direction distribution in the Southern Hemisphere with unprecedented statistical accuracy covering more than a full period length of a solar cycle. Improvements in Monte Carlo event simulation and better handling of year-to-year differences in data processing significantly reduce systematic uncertainties below the level of statistical fluctuations compared to the previously published results. We confirm the observation of a change in the angular structure of the cosmic-ray anisotropy between 10 TeV and 1 PeV, more specifically in the 100-300 TeV energy range.

astro-ph.HE↗

arXiv2025

The IceCube Collaboration -- Contributions to the 39th International Cosmic Ray Conference (ICRC2025)

The IceCube Observatory at the South Pole has been operating in its full configuration since May 2011 with a duty cycle of about 99%. Its main component consists of a cubic-kilometer array of optical sensors deployed deep in the Glacial ice designed for the detection of high-energy astrophysical neutrinos. A surface array for cosmic ray air shower detection, IceTop, and a denser inner subdetector, DeepCore, significantly enhance the capabilities of the observatory, making it a multipurpose facility. This list of contributions to the 39th International Cosmic Ray Conference in Geneva, Switzerland (July 15-24, 2025) summarizes the latest results from IceCube covering a broad set of key questions in physics and astrophysics. The papers in this index are grouped topically to highlight IceCube contributions related to high-energy neutrino and multi-messenger astrophysics, atmospheric fluxes, cosmic-ray physics, low-energy neutrino transients, physics beyond the Standard Model, detector calibration and event reconstruction, and the status and performance of the IceCube Upgrade, a dense sensor infill complemented by calibration devices to be deployed by the end of 2025. Contributions related to IceCube-Gen2, the planned future extension of IceCube, are available in a separate collection.

astro-ph.HE↗

arXiv2025

The IceCube-Gen2 Collaboration -- Contributions to the 39th International Cosmic Ray Conference (ICRC2025)

IceCube-Gen2 is a planned next-generation neutrino observatory at the South Pole that builds upon the successful design of IceCube. Integrating two complementary detection technologies for neutrinos, optical and radio Cherenkov emission, in combination with a surface array for cosmic-ray air shower detection, IceCube-Gen2 will cover a broad neutrino energy range from MeV to EeV. This index of contributions to the 39th International Cosmic Ray Conference in Geneva, Switzerland (July 15-24, 2025) describes research and development efforts for IceCube-Gen2. Included are summaries of the design, status, and sensitivity of the IceCube-Gen2 optical, surface, and radio components; performance studies of next-generation surface detectors and in-ice optical sensors; advanced reconstruction techniques of cosmic-ray air showers and neutrino events; sustainability and environmental impact; and sensitivity studies of astrophysical neutrino fluxes and cosmic-ray physics. Contributions related to IceCube and the scheduled IceCube Upgrade are available in a separate collection.

astro-ph.HE↗

arXiv2025

Observation of the electromagnetic radiative decays of the \boldmath{$Λ(1520)$} and \boldmath{$Λ(1670)$} to \boldmath{$γΣ^0$}

Using $(10087\pm 44)\times10^6$ $J/ψ$ events collected with the BESIII detector, we report the first observation of the electromagnetic radiative decays of the $Λ(1520)$ and $Λ(1670)$ to $γΣ^0$, with a statistical significance of $16.6σ$ and $23.5σ$, respectively. The ratio of the branching fractions $\frac{\mathcal{B}(Λ(1520)\toγΛ)}{\mathcal{B}(Λ(1520)\toγΣ^0)}$ is determined to be $2.88\pm0.27(\text{stat.})\pm0.21(\text{syst.})$, which is in good agreement with flavor SU(3) symmetry. The branching fraction of $Λ(1520)\toγΣ^0$ is measured to be $\mathcal{B}(Λ(1520)\toγΣ^0)=(2.95\pm0.28(\text{stat.})\pm0.56(\text{syst.}))\times 10^{-3}$, corresponding to a partial width of $Γ(Λ(1520)\toγΣ^0)=(47.2\pm4.5(\text{stat.})\pm9.0(\text{syst.}))$ keV, which is inconsistent with predictions from the relativized constituent quark model and the Algebraic model. Additionally, we observe a clear resonant structure in the $γΣ^0$ mass spectrum around 1.67 GeV/$c^2$, attributed to the $Λ(1670)$. The product branching fraction $\mathcal{B}(J/ψ\to\barΛΛ(1670)+c.c.)\times\mathcal{B}(Λ(1670)\toγΣ^0)$ is measured for the first time as $(5.39\pm0.29(\text{stat.})\pm 0.44(\text{syst.}))\times 10^{-6}$. However, no corresponding structure is seen in the $γΛ$ mass spectrum, so an upper limit on the product branching fraction $\mathcal{B}(J/ψ\to\barΛΛ(1670)+c.c.)\times\mathcal{B}(Λ(1670)\toγΛ)$ is determined to be $5.97\times10^{-7}$ at the 90\% confidence level.

hep-ex↗

arXiv2025

The calibration house in JUNO

As an auxiliary system within the calibration system of the Jiangmen Underground Neutrino Observatory, a calibration house is designed to provide interfaces for connecting the central detector and accommodating various calibration sub-systems. Onsite installation has demonstrated that the calibration house interfaces are capable of effectively connecting to the central detector and supporting the installation of complex and sophisticated calibration sub-systems. Additionally, controlling the levels of radon and oxygen within the calibration house is critical. Radon can increase the experimental background, while oxygen can degrade the quality of the liquid scintillator. The oxygen concentration can be maintained at levels below 10 parts per million, and the radon concentration can be kept below 15 mBq/m$^{3}$. This paper will provide detailed information on the calibration house and its methods for radon and oxygen concentration control.

physics.ins-det↗

arXiv2025

Search for High-Energy Neutrinos From the Sun Using Ten Years of IceCube Data

In this Letter, we present the results of a search for high-energy neutrinos produced by the annihilation of dark matter particles trapped in the Sun. Using 9.3 and 10.4 years of data from the DeepCore and IceCube neutrino detectors, we establish world-best limits for spin-dependent interactions between dark matter and Standard Model particles for dark matter masses from tens of GeV to tens of TeV. We additionally place constraints on the neutrino background produced by interactions of cosmic rays with the solar atmosphere.

hep-ex↗

arXiv2025

Search for the lepton number violating process $J/ψ\to K^+K^+e^-e^- +c.c.$

Based on $(10087\pm 44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, we search for the lepton number violating decay $J/ψ\to K^+K^+e^-e^- + c.c.$ for the first time. The upper limit on the branching fraction of this decay is set to be $2.1 \times 10^{-9}$ at the 90$\%$ confidence level with a frequentist method. This is the first search for $J/ψ$ decays with the lepton number change by two, offering valuable insights into the underlying physical processes.

hep-ex↗

arXiv2025

Search for Extremely-High-Energy Neutrinos and First Constraints on the Ultrahigh-Energy Cosmic-Ray Proton Fraction with IceCube

We present a search for the diffuse extremely-high-energy neutrino flux using $12.6$ years of IceCube data. The nonobservation of neutrinos with energies well above $10 \, \mathrm{PeV}$ constrains the all-flavor neutrino flux at $10^{18} \, \mathrm{eV}$ to a level of $E^2 Φ_{ν_e + ν_μ+ ν_τ} \simeq 10^{-8} \, \mathrm{GeV} \, \mathrm{cm}^{-2} \, \mathrm{s}^{-1} \, \mathrm{sr}^{-1}$, the most stringent limit to date. Using these data, we constrain the proton fraction of ultra-high-energy cosmic rays (UHECRs) above $\simeq 30 \, \mathrm{EeV}$ to be $\lesssim 70\,$% (at $90\,$% CL) if the cosmological evolution of the sources is comparable to or stronger than the star formation rate. This is the first result to disfavor the ``proton-only" hypothesis for UHECRs in this evolution regime using neutrino data. This result complements direct air-shower measurements by being insensitive to uncertainties associated with hadronic interaction models. We also evaluate the tension between IceCube's nonobservation and the $\sim 200 \, \mathrm{PeV}$ KM3NeT neutrino candidate (KM3-230213A), finding it to be $\sim 2.9 σ$ based on a joint-livetime fit between neutrino datasets.

astro-ph.HE↗

arXiv2025

A Search for Millimeter-Bright Blazars as Astrophysical Neutrino Sources

The powerful jets of blazars have been historically considered as likely sites of high-energy cosmic-ray acceleration. However, particulars of the launched jet and the locations of leptonic and hadronic jet loading remain unclear. In the case when leptonic and hadronic particle injection occur jointly, a temporal correlation between synchrotron radiation and neutrino production is expected. We use a first catalog of millimeter (mm) wavelength blazar light curves from the Atacama Cosmology Telescope for a time-dependent correlation with twelve years of muon neutrino events from the IceCube South Pole Neutrino Observatory. Such mm emission is known to trace activity of the bright jet base, which is often self-absorbed at lower frequencies and potentially gamma-ray opaque. We perform an analysis of the population, as well as analyses of individual, selected sources. We do not observe a significant signal from the stacked population. TXS 0506+056 is found as the most significant, individual source, though this detection is not globally significant in our analysis of selected AGN. Our results suggest that the majority of mm-bright blazars are neutrino dim. In general, it is possible that many blazars have lighter, leptonic jets, or that only selected blazars provide exceptional conditions for neutrino production.

astro-ph.HE↗

arXiv2025

Measurement of the inelasticity distribution of neutrino-nucleon interactions for $\mathbf{80~GeV<E_ν<560~GeV}$ with IceCube DeepCore

We report a study of the inelasticity distribution in the scattering of neutrinos of energy $80-560$ GeV off nucleons. Using atmospheric muon neutrinos detected in IceCube's sub-array DeepCore during 2012-2021, we fit the observed inelasticity in the data to a parameterized expectation and extract the values that describe it best. Finally, we compare the results to predictions from various combinations of perturbative QCD calculations and atmospheric neutrino flux models.

hep-ex↗