arXiv subjects

L. Chen

Publications and source records attributed to L. Chen.

At least 19 recordsLinked to original sources

arXiv2026

First measurement of the masses of the $Υ_1(1D)$ and $Υ_3(1D)$ states and the energy dependence of the cross sections for $e^+e^-\toΥ_J(1D)η$ and $e^+e^-\toΥ_J(1D)π^+π^-$

We study the processes $e^+e^-\toΥ_J(1D)η$ and $e^+e^-\toΥ_J(1D)π^+π^-$ at center-of-mass energies $\sqrt{s}$=(10.73 -- 11.02) GeV using a $142.5\,\mathrm{fb}^{-1}$ data sample, including 122~fb$^{-1}$ near the $Υ$(10860) peak ($\sqrt{s}$ = 10.866 GeV), collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. From the peak sample, the products of Born cross section times branching fraction are obtained for $σ_{\rm Born}(e^+e^-\toΥ_J(1D)η)$ or $σ_{\rm Born}(e^+e^-\toΥ_J(1D)π^+π^-)$ and ${\cal B}(Υ_J(1D)\toχ_{b1}γ)$ or ${\cal B}(Υ_J(1D)\toχ_{b2}γ)$ for each $Υ_J(1D)$ state. The corresponding branching fractions for $Υ(10860)$ decays are also obtained. The significances of the $Υ_1(1D)$, $Υ_2(1D)$, and $Υ_3(1D)$ signals are 4.8$σ$, ${>}10σ$, and 3.0$σ$, respectively, including systematic uncertainties. The mass for $Υ_2(1D)$ is measured to be $(10167.0\pm 1.0\pm 0.2)$ MeV/$c^2$, where the first and second uncertainties are statistical and systematic. The mass splittings $Δm_{12}=m(Υ_2(1D))-m(Υ_1(1D))$ and $Δm_{23}=m(Υ_3(1D))-m(Υ_2(1D))$ are $(11.8\pm1.5\pm0.4)$ MeV/$c^2$ and $(7.6\pm2.4\pm0.6)$ MeV/$c^2$, respectively.~We determine the energy dependence of the cross sections for $e^+e^-\toΥ_J(1D)η$ and $e^+e^-\toΥ_J(1D)π^+π^-$ for the $Υ_1(1D)$, $Υ_2(1D)$, and $Υ_3(1D)$ states, combined.

hep-ex↗

arXiv2026

Electrochemical functionalization of graphene rationalized by Hammett and Swain-Lupton parameters

Graphene's sp^{2}-bonded carbon lattice makes it exceptionally resistant to covalent functionalization, with existing approaches relying on chemically specific and often harsh methods, fragmenting our understanding of its reactivity. Here we show that electric fields of approximately 1 V nm^{-1} in non-aqueous electrolytes enable the electrochemical functionalization of monolayer graphene with a broad range of substituents, leading to two-order-of-magnitude conductance modulation stable over 5,000 cycles and semi-reversible electronic conductor-insulator transitions. Analysis of the oxidation potentials across substituents reveals trends governed by classical descriptors. Species forming localised σ bonds display increasing oxidation potentials with the meta-Hammett constant (σ_m), whereas substituents interacting via delocalised π orbitals follow an inverse dependence on the modified Swain-Lupton resonance parameter (R). These relationships indicate that graphene's oxidation potential increases with the electron-withdrawing strength of the substituent. Our results provide new insights into the electrochemical activity of inert materials under strong electric fields.

physics.chem-ph↗

arXiv2026

Inclusive jet cross section in $pp$ collisions at $\sqrt{s} = 200$ and $510$ GeV

Jets are collimated clusters of particles formed by the hadronization of partons following a hard interaction. In proton-proton ($pp$) collisions at the Relativistic Heavy Ion Collider (RHIC), jet production is dominated by $gg$ and $qg$ partonic processes, allowing us to directly probe the gluon parton distribution function (PDF) in the proton in a way complementary to deep inelastic scattering. In this paper, we report the double-differential inclusive-jet cross sections as a function of jet transverse momentum, $p_{\rm T}$, and pseudorapidity, $η$, at center-of-mass energies $\sqrt{s} = 200$ and $510$~GeV, from $pp$ collisions studied with the STAR detector. The jet $p_{\rm T}$ is corrected for underlying event contributions by applying an off-axis cone method. At mid-pseudorapidity, $|η| < 0.9$, the kinematic coverage of our data extends to $0.07 < x_{\rm T} \text{ (}= 2p_{\rm T}{} / \sqrt{s} \text{)} < 0.5$ and $0.03 < x_{\rm T} < 0.31$ at $\sqrt{s} = 200$~and 510 GeV, respectively, where the gluon PDF is poorly constrained by the TeV-scale $pp$~($p\bar{p}$) colliders. The inclusive jet cross sections are compared to the next-to-next-to-leading order perturbative quantum chromodynamics calculations using several recent PDF sets as inputs. These results will further constrain the gluon PDF, help tune Monte Carlo generators, and provide critical reference data needed to study the quark-gluon plasma.

hep-ex↗

arXiv2026

EmbodiedWorld-200K: Toward Embodied World Agents via Embodied-Planning Dataset and Interactive World Models

Building embodied agents that can perceive, reason, and act across diverse 3D worlds is a central research direction toward artificial general intelligence. Yet most existing work remains confined to specific tasks in a single scene and transfers poorly to new environments, leaving general embodied agents for open-world settings under-explored. We refer to such agents as Embodied World Agents (EWAs), whose defining property is the ability to understand diverse visual environments and execute general actions in open-world conditions. To advance EWA research, we study open-world embodied navigation-planning and release EmbodiedWorld-200K, a large-scale dataset of over 200K samples spanning diverse scenes. Each example is equipped with multi-level annotations, ranging from low-level camera-motion trajectories to high-level semantic instructions. The dataset also provides unified evaluation splits and task-specific metrics, supporting offline pretraining and fair evaluation of EWAs. Beyond offline supervision, a defining characteristic of an EWA is its interaction with the environment; training solely on offline data is therefore insufficient, especially for generalizing to scenes not covered in the training distribution. Building dedicated real interactive environments, however, is often prohibitively expensive. To address this, we propose a novel training scheme that employs a video world model as a low-cost environment proxy and performs interactive reinforcement-learning (RL) post-training of the EWA within it. Empirically, pretraining on EmbodiedWorld-200K substantially improves the open-world embodied planning ability of the EWA, and further RL post-training inside a world model yields clear gains on out-of-distribution scenes. The dataset, baseline checkpoints, and training and evaluation code are available at https://xiaokunfeng.github.io/EmbodiedWorld-200K/.

cs.AI↗

arXiv2026

Measurements of the branching fractions of $Λ_c^+\toΛK^+ π^0$ and $Λ_c^+\toΛK^+ η$ decays at Belle and Belle II

We present a study of the three-body, singly Cabibbo-suppressed decays $Λ_c^+ \to ΛK^+ π^0$ and $Λ_c^+ \to ΛK^+ η$ using data recorded with the Belle and Belle II detectors at the KEKB and SuperKEKB $e^+ e^-$ colliders. The data samples correspond to integrated luminosities of 980$\,\mathrm{fb}^{-1}$ and 570$\,\mathrm{fb}^{-1}$, respectively. We measure their branching-fraction ratios relative to the Cabibbo-favored decay $Λ_c^+ \to Λπ^+ π^0$ as $\mathcal{B}(Λ_c^+ \to ΛK^+ π^0)/\mathcal{B}(Λ_c^+ \to Λπ^+ π^0)=(1.82 \pm 0.07 \pm 0.07)\%$, with significantly improved precision compared to the previous measurement, and $\mathcal{B}(Λ_c^+ \to ΛK^+ η)/\mathcal{B}(Λ_c^+ \to Λπ^+ π^0)=(8.73 \pm 0.35 \pm 0.43)\times10^{-3}$, corresponding to the first observation of the $Λ_c^+ \to ΛK^+ η$ decay with a statistical significance exceeding 10 standard deviations. The first and second uncertainties are statistical and systematic, respectively. Using the world-average value of the branching fraction for $Λ_c^+ \to Λπ^+ π^0$, we obtain the branching fractions $\mathcal{B}(Λ_c^+ \to ΛK^+ π^0)=(1.29\pm 0.05\pm 0.05\pm 0.06)\times10^{-3}$ and $\mathcal{B}(Λ_c^+ \to ΛK^+ η)=(6.20\pm 0.25\pm 0.31\pm 0.30)\times10^{-4}$, where the third uncertainty arises from the uncertainty in the world-average value of $\mathcal{B}(Λ_c^+ \to Λπ^+ π^0)$. The measured $\mathcal{B}(Λ_c^+\toΛK^+η)$ is significantly larger than predictions based on $SU(3)$ flavor symmetry.

hep-ex↗

arXiv2026

Search for the $\boldsymbol{B^0 \to K^0_{\rm S} τ^+ τ^-}$ decay

We present the first search for $B^0 \to K^0_{\rm S} τ^+τ^-$ decays. We look for signal decays in $B^0\bar B^0$ events produced in asymmetric-energy electron-positron collisions. This work uses samples from the Belle and Belle~II detectors, comprising 1.16 billion $Υ(4S)$ events. In $Υ(4S)\to B^0\bar{B}^0$ decays, the non-signal $\bar{B}^0$ meson is fully reconstructed in a hadronic channel. For the signal $B^0$ meson, $τ$-lepton decays into final states with a single charged particle are selected. We observe no evidence for the signal and set an upper limit on the branching fraction $\mathcal{B}(B^0\to K^0_{\rm S} τ^+τ^-) < 8.3 \times 10^{-4}$ at the 90\% confidence level. Combining this with the recent measurement of the isospin-partner decay $B^+\to K^+τ^+τ^-$, we determine an upper limit $\mathcal{B}(B\to Kτ^+τ^-) < 5.4\times10^{-4}$ at the 90\% confidence level.

hep-ex↗

arXiv2026

Measurements of jet quenching with semi-inclusive hadron-jet correlations in Ru+Ru and Zr+Zr collisions at $\sqrt{s_\mathrm{NN}}=200$ GeV

The STAR experiment at RHIC reports measurements of the semi-inclusive yield of charged-particle jets recoiling from high transverse momentum charged-hadron triggers in centrality-selected Ru+Ru and Zr+Zr collisions at the nucleon-nucleon center-of-mass energy of 200 GeV. The effects of jet quenching, arising from the interaction of jets with the quark-gluon plasma, are quantified by comparing trigger-normalized recoil yields in central and peripheral collisions. Suppression of the recoil yield in central collisions is observed, indicating medium-induced partonic energy loss due to quenching. The ratio of recoil jet yields for small and large resolution parameter is found to be suppressed in central relative to peripheral collisions, characteristic of medium-induced intra-jet broadening. The results are compared to similar measurements in smaller and larger collision systems, providing unique insight into the system-size dependence of jet quenching.

nucl-ex↗

arXiv2026

Observation of the decays $B^{+} \to Σ_{c}(2455)^{++} \barΞ_{c}^{\prime-}$ and $B^{0} \to Σ_{c}(2455)^{0} \barΞ_{c}^{\prime0}$

We report the first observation of the decays $B^{+} \to Σ_{c}(2455)^{++} \barΞ_{c}^{\prime-}$ and $B^{0} \to Σ_{c}(2455)^{0} \barΞ_{c}^{\prime0}$, with significances of $6.4\,σ$ and $5.3\, σ$, respectively, including systematic uncertainties. This analysis is based on data samples containing $771.6 \times 10^{6}$ $Υ(4S)$ decays collected with the Belle detector at the KEKB collider and $520.6 \times 10^{6}$ $Υ(4S)$ decays collected with the Belle~II detector at the SuperKEKB collider. The branching fractions are measured to be $\mathcal{B}(B^+ \to Σ_c(2455)^{++} \barΞ_c^{\prime -}) = (1.69 \pm 0.31 \pm 0.12^{+1.39}_{-0.56}) \times 10^{-3}$ and $\mathcal{B}(B^0 \to Σ_c(2455)^{0} \barΞ_c^{\prime 0}) = (1.28 \pm 0.32 \pm 0.10^{+0.26}_{-0.22}) \times 10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third arises from the uncertainties in the absolute branching fractions of $\barΞ_{c}^{-}$ and $\barΞ_{c}^{0}$ decays. This result represents the first observation of $B$-meson decays into a pair of charmed baryon-antibaryon states belonging to the same $SU(3)$ flavor sextet.

hep-ex↗

arXiv2026

Measurement of time-dependent $CP$ violation parameters in $B^{0} \to K_{S}^{0} π^{0} γ$ decays at Belle and Belle II

We perform a measurement of time-dependent $CP$ violation parameters in $B^{0} \to K_{S}^{0} π^{0} γ$ decays using a dataset of approximately $772 \times 10^6$ and $521 \times 10^6$ $Υ(4S)$ decays collected by the Belle and Belle II experiments, respectively. The measured parameters for the combined dataset in the $K^{*0}(892)$ dominated region ($M_{K_{S}^{0} π^{0}} \in [0.8,1.0] \mathrm{GeV}/c^2$) are $S = 0.09 \pm 0.16 \pm 0.02$ and $C = -0.09 \pm 0.08 \pm 0.04$. For the non-$K^{*0}(892)$ region ($M_{K_{S}^{0} π^{0}} \in [1.0,1.8] \mathrm{GeV}/c^2$), the corresponding values are $S = -0.32 \pm 0.33 \pm 0.09$ and $C = -0.07 \pm 0.17 \pm 0.08$. The first quoted uncertainties are statistical, while the second ones are systematic. These results are consistent with Standard Model predictions and more precise than previous measurements.

hep-ex↗

arXiv2026

Search for the decay $B^+ \rightarrow K^+τ^+τ^-$ using data from the Belle and Belle II experiments

We report a search for the rare decay $B^{+} \rightarrow K^{+} τ^{+} τ^{-}$ using $1.2 \times 10^9$ $Υ(4S)$ mesons produced near threshold in electron-positron collisions and collected by the Belle and Belle~II experiments. We fully reconstruct the hadronic decay of one $B$ meson produced in the $Υ(4S)\rightarrow B^{+} B^{-}$ decay, and search for $B^{\pm}\rightarrow K^{\pm} τ^{+}τ^{-}$ candidates among the remaining collision products, reconstructing a charged kaon and leptonic decays of the $τ$ leptons. We optimize the selection for best sensitivity and look for an excess over background at low values of the residual energy detected in the calorimeter after full event reconstruction. We observe no significant excess and set the limit $\mathcal{B}(B^{+}\rightarrow K^{+}τ^{+}τ^{-})< 0.56\times 10^{-3}$ at the 90% confidence level, improving on the only previous result by a factor of four.

hep-ex↗

arXiv2026

Test of lepton flavor universality with $\bar{B} \rightarrow D^{()} τ^{-} \barν_τ$ and $\bar{B} \rightarrow D^{()} \ell^{-} \barν_{\ell}$ decays at Belle II

We test lepton flavor universality with a measurement of the branching-fraction ratios $R(D^{(*)}) \equiv \mathcal{B}(\bar{B} \rightarrow D^{(*)} τ^{-} \barν_τ)/\mathcal{B}(\bar{B} \rightarrow D^{(*)} \ell^{-} \barν_{\ell})$, where $\ell$ denotes an electron or muon. The analysis uses $387\times 10^6$ $Υ(\mathrm{4S})$ decays collected with the Belle II detector in energy-asymmetric $e^+e^-$ collisions. One $B$ meson is fully reconstructed in a hadronic decay mode, while the other is reconstructed either in $\bar{B}\rightarrow D^{(*)}τ^{-}\barν_τ$, with $τ^- \rightarrow \ell^- \barν_{\ell}ν_τ$, or in $\bar{B}\rightarrow D^{(*)}\ell^{-}\barν_{\ell}$. We extract the signal from the distributions of the residual calorimeter energy and the squared mass of the undetected particles, obtaining $R(D^{*}) = 0.242 \pm0.019(\mathrm{stat}) \pm0.016(\mathrm{syst})$ and $R(D) = 0.439 \pm 0.055(\mathrm{stat}) \pm 0.046(\mathrm{syst})$. These results are consistent with both the standard model predictions and previous measurements, and constitute the most precise determination of $R(D^{(*)})$ with hadronic tagging.

hep-ex↗

arXiv2026

Study of $e^+e^- \to π^+π^-Υ(1D)$ at Belle II

The bottomonium spectrum, consisting of bound states of a $ b $ quark and an anti-$ b $ quark, provides an excellent laboratory for probing quantum chromodynamics in the non-perturbative regime. While S and P-wave bottomonium states are well studied experimentally, information on D-wave states remains scarce. We search for the D-wave bottomonium states $ Υ_2(1D) $ and $ Υ_3(1D) $ via the decay of a vector bottomonium-like state $Υ(10753)$ in the reaction $e^+e^- \to π^+π^- Υ(1D)$, using $19.6~\mathrm{fb}^{-1}$ of data collected with the Belle II detector at center-of-mass energies $\sqrt{s} = 10.653$, 10.701, 10.745, and 10.805~GeV, in the vicinity of the $ Υ(10753) $ resonance. No significant signals are observed. We set upper limits at the 90\% credibility level on the products of the cross sections and branching fractions, $σ[e^+e^- \to π^+π^- Υ_2(1D)] \times \mathcal{B}[Υ_2(1D) \to γχ_{b1}]$ and $σ[e^+e^- \to π^+π^- Υ_3(1D)] \times \mathcal{B}[Υ_3(1D) \to γχ_{b2}]$, at each center-of-mass energy.

hep-ex↗

arXiv2026

Energy Correlators Within Jets in Transversely Polarized Proton-Proton Collisions at $\sqrt{s} = 200$ GeV

We report the first measurement of one- and two-point energy correlators within jets in transversely polarized proton-proton collisions at $\sqrt{s}=200$ GeV, using the STAR detector at RHIC. These observables quantify the energy-weighted angular distribution of single hadrons and hadron pairs within jets, respectively. Sizable spin-dependent asymmetries are observed for $π^+$, $π^-$, and $π^+π^-$ pairs, revealing the onset of nonperturbative dynamics at specific angular scales. By projecting the fragmentation dynamics onto Mellin moments, these measurements provide sensitivity to the nucleon's transversity while minimizing uncertainties from nonperturbative fragmentation functions. These results establish energy correlators as a novel and precise probe of nucleon structure and open a promising avenue for three-dimensional nucleon tomography at the future Electron-Ion Collider.

hep-ex↗

arXiv2026

Electrostatic control of Li+ density and transport rate in double-gated van der Waals devices

Ion transport in crystalline hosts is controlled by an applied potential that simultaneously sets ionic distribution and transport rate, restricting operation to a one-dimensional control space. Here we show that the transport rate of Li+ ions in double-gated van der Waals devices can be modulated while the system occupies fixed ionic-density states. We measure the ionic current along the van der Waals interfaces between hexagonal boron nitride and graphene or MoS2 while simultaneously monitoring the in-plane electronic response. The ionic current exhibits pronounced hysteresis, with plateaus marking discrete ionic-density states balanced by electronic charge, while an independently tuneable electrochemical-potential drop controls the ionic transport rate. The devices sustain over 1,000 switching cycles and function as hybrid ionic-electronic transistors capable of logic operations and memory retention, with ON/OFF ratios exceeding two orders of magnitude. This work demonstrates a two-dimensional control space for ions intercalated in layered materials.

cond-mat.mes-hall↗

arXiv2026

Search for the lepton-flavor-violating decay $ τ^{\pm} \to μ^{\pm} γ$ at Belle II

We present a search for the lepton-flavor-violating decay $τ^{\pm}\toμ^{\pm}γ$ using a data sample that corresponds to an integrated luminosity of 428 fb$^{-1}$ recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^{+}e^{-}$ collider. We employ a multivariate classifier to suppress the backgrounds from the Standard Model processes, and the signal extraction is performed using an extended maximum-likelihood fit. Since no significant excess over the expected background is observed, we set an upper limit on the branching fraction $\mathcal{B}(τ^{\pm}\toμ^{\pm}γ) < 9.5$ $ (12.2)\times10^{-8}$ at the 90\% (95\%) confidence level, using the CL${_s}$ technique.

hep-ex↗

arXiv2026

Probing dark matter interactions with a RES-NOVA prototype cryogenic detector

We report on the operation of a 13 g PbWO$_4$ crystal, grown from archaeological Pb and operated as a cryogenic calorimeter in an underground environment. Read out with a Ge thermistor, the detector achieves a low energy threshold and, for the first time, enables the derivation of a dark matter exclusion limit using PbWO$_4$ as target material, for both spin-dependent interactions on neutrons and spin-independent interactions. Although limited in mass and not representative of the final RES-NOVA detector design, this prototype demonstrates effective control of mechanical vibrations and low-energy noise in a cryogenic system, which is a key requirement for rare-event searches. The experiment therefore provides a proof of principle for the RES-NOVA detection concept, validating the use of archaeological Pb-based PbWO$_4$ crystals, low-background operation, and robust data-analysis procedures. These results establish a solid technological and methodological foundation for future RES-NOVA detectors employing larger target masses and advanced thermal readout technologies.

physics.ins-det↗

arXiv2026

Probing large mass-splitting inelastic Dark Matter with RES-NOVA

Probing inelastic dark matter at large mass splittings requires heavy target nuclei, an extended recoil-energy range, and the high-velocity tail of the dark-matter distribution. We exploit these features with the RES-NOVA prototype detector, featuring a PbWO4 cryogenic calorimeter, produced from archaeological Pb and operated at the deep-underground laboratory of Gran Sasso of INFN (Italy), analyzing a 32.4 g day exposure over 2.5 keV - 1 MeV under both the Standard Halo Model (SHM) and a Large Magellanic Cloud (LMC)-motivated velocity distribution. We extend direct-detection constraints beyond the 330 keV reach of established technologies (e.g. Xe-based TPCs), probing splittings up to 510 (780) keV in the SHM (LMC) benchmark, while future exposures will probe new regions of the parameter space.

astro-ph.CO↗

arXiv2026

Solar axion searches with RES-NOVA: projected sensitivity and first prototype limit

RES-NOVA is a cryogenic experiment based on PbWO4 scintillating bolometers produced from archaeological lead, originally designed to detect coherent elastic neutrino-nucleus scattering (CEvNS) from galactic core-collapse supernovae. We show that the same high-density, high-Z absorbers and sub-keV energy resolution make RES-NOVA an appealing probe of solar axions. We compute the expected signal from the Primakoff, ABC (atomic recombination and de-excitation, Bremsstrahlung, Compton), longitudinal-plasmon (LP), and 57Fe nuclear-line components of the solar axion flux, folded through the inverse-Primakoff and axioelectric detection channels in PbWO4, which probe the axion couplings to photons (g_a-gamma), electrons (g_ae), and nucleons (g_aN), respectively. We derive projected sensitivities for a 1 ton*y exposure of the RES-NOVA demonstrator in the (g_ae,g_a-gamma), (g_ae,g_aN), and (g_a-gamma,g_aN) planes. The projected reach in g_ae approaches that of XENONnT to within a factor of ~2, despite a background roughly four orders of magnitude higher, thanks to the large target mass, the high-Z enhancement of the axioelectric and inverse-Primakoff cross sections, and the sub-keV energy resolution. Because the inverse-Primakoff constraint on g_a-gamma relies on absorption rather than coherent conversion, it is independent of the axion mass, unlike bounds from magnetic helioscopes. We complement these projections with the first solar-axion exclusion limit obtained on real data with a 13 g PbWO4 prototype grown from archaeological lead, using a background-model-independent optimum-interval analysis. These results establish RES-NOVA as a promising multi-coupling probe of solar axions, with simultaneous sensitivity to g_ae, g_a-gamma and g_aN that is complementary to existing helioscope and direct-detection searches.

hep-ex↗