Light-cone distribution amplitudes (LCDAs) of heavy meson within heavy quark effective theory (HQET) are crucial for predicting physical observables in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math> decays, but unfortunately there is no first-principle result due to severe challenges. After analyzing these challenges, we propose a realistic method to determine heavy meson LCDA. We utilize equal-time correlations and incorporate a dynamic quark field for a fast moving heavy quark. To verify this method, we make use of lattice QCD simulation on a lattice ensemble with spacing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>a</mi><mo>=</mo><mn>0.05187</mn><mtext> </mtext><mtext> </mtext><mi>fm</mi></math>. The preliminary findings for HQET LCDAs qualitatively align with phenomenological models, and the fitted result for the first inverse moment <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>λ</mi><mi>B</mi><mrow><mo>−</mo><mn>1</mn></mrow></msubsup></math> is consistent with the experimentally constrained region from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo stretchy="false">→</mo><mi>γ</mi><mo>ℓ</mo><msub><mi>ν</mi><mo>ℓ</mo></msub></math>. We explore how our findings can reduce model uncertainties in predictions of heavy-to-light form factors at large recoil. These results demonstrate the promise of our method in providing first-principle predictions for heavy meson LCDAs.

China

Xue-Ying Han

Jun Hua

United States

Xiangdong Ji

Cai-Dian Lü

Wei Wang

Ji Xu

Qi-An Zhang

Shuai Zhao

Realistic method to access heavy meson light-cone distribution amplitudes from first-principle

Detailed studies of two-neutrino double electron capture (2$\textit{ν}$DEC) is a crucial step towards searching for the neutrinoless mode to explore the Majorana nature of neutrinos. We have measured precisely the half-life of the 2$\textit{ν}$DEC process in Xe, utilizing a total exposure of 1.73 tonne year from the commissioning run and the first science run of the PandaX-4T experiment. A time-dependent background model in the $$ \mathcal{O} $$ (10 keV) energy is constructed for the first time in PandaX-4T data. With an unbinned maximum likelihood fit, we determine the half-life of the 2$\textit{ν}$DEC process to be (1.03 ± 0.15 ± 0.08 ) × 10 yr. Furthermore, we have evaluated the capture fraction for both electrons captured from the $\textit{K}$ shell ($\textit{KK}$) to be (65 ± 5)%, which aligns with the Xe nuclear model calculations within 1.8 $\textit{σ}$.

Zihao Bo

Wei Chen

Xun Chen

Yunhua Chen

Zhaokan Cheng

Xiangyi Cui

Yingjie Fan

Deqing Fang

Zhixing Gao

Lisheng Geng

Karl Giboni

Xunan Guo

Xuyuan Guo

Zichao Guo

Chencheng Han

Ke Han

Changda He

Jinrong He

Di Huang

Houqi Huang

Junting Huang

Ruquan Hou

Yu Hou

Xiangpan Ji

Yonglin Ju

Chenxiang Li

Jiafu Li

Mingchuan Li

Shuaijie Li

Tao Li

Zhiyuan Li

Qing Lin

Jianglai Liu

Congcong Lu

Xiaoying Lu

Lingyin Luo

Yunyang Luo

Wenbo Ma

Yugang Ma

Yajun Mao

Yue Meng

Xuyang Ning

Binyu Pang

Ningchun Qi

Zhicheng Qian

Xiangxiang Ren

Dong Shan

Xiaofeng Shang

Xiyuan Shao

Guofang Shen

Manbin Shen

Wenliang Sun

Yi Tao

Anqing Wang

Guanbo Wang

Hao Wang

Jiamin Wang

Lei Wang

Meng Wang

Qiuhong Wang

Shaobo Wang

Siguang Wang

Xiuli Wang

Xu Wang

Zhou Wang

Yuehuan Wei

Weihao Wu

Yuan Wu

Mengjiao Xiao

Xiang Xiao

Kaizhi Xiong

Yifan Xu

Shunyu Yao

Binbin Yan

Xiyu Yan

Yong Yang

Peihua Ye

Chunxu Yu

Ying Yuan

Zhe Yuan

Youhui Yun

Xinning Zeng

Minzhen Zhang

Peng Zhang

Shibo Zhang

Shu Zhang

Tao Zhang

Wei Zhang

Yang Zhang

Yingxin Zhang

Yuanyuan Zhang

Li Zhao

Jifang Zhou

Jiaxu Zhou

Jiayi Zhou

Ning Zhou

Xiaopeng Zhou

Yubo Zhou

Measurement of two-neutrino double electron capture half-life of

We perform a search of double beta decay of Xe to the excited state, $$ {0}_1^{+} $$ , of Ba (2$\textit{νββ}$- $$ {0}_1^{+} $$ ), using the dual-phase xenon detector of PandaX-4T with the first 94.9-day commissioning data. The multi-site events are reconstructed up to the MeV energy scale, which helps to improve the background model significantly. The background contribution from the stainless steel platform outside PandaX-4T cryostat is evaluated for the first time. No significant evidence for 2$\textit{νββ}$- $$ {0}_1^{+} $$ is observed, resulting in a lower limit on half-life of 7$\textit{.}$5 × 10 yr at the 90% confidence level. This is the first experimental limit on such a rare decay in a natural xenon-based detector.

Zhizhen Zhou

Search for double beta decay of

We present a novel constraint on light dark matter utilizing 1.54 metric ton/year of data acquired from the PandaX-4T dual-phase xenon time projection chamber. This constraint is derived through detecting electronic recoil signals resulting from the interaction with solar-enhanced dark matter flux. Low-mass dark matter particles, lighter than a few <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>MeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math>, can scatter with the thermal electrons in the Sun. Consequently, with higher kinetic energy, the boosted dark matter component becomes detectable via contact scattering with xenon electrons, resulting in a few keV energy deposition that exceeds the threshold of PandaX-4T. We calculate the expected recoil energy in PandaX-4T considering the Sun’s acceleration with heavy mediators and the detection capabilities of the xenon detector. The first experimental search results using the xenon detector yield the most stringent upper limits cross section of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>3.51</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>39</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>0.08</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> for a solar boosted dark matter mass ranging from 0.02 to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></mrow></math>, achieving a 23-fold improvement compared with earlier experimental studies.

Search for Solar Boosted Dark Matter Particles at the PandaX-4T Experiment

We report a search for a lepton-portal dark matter model, where dark matter couples to a charged lepton in the standard model. This simplified model naturally leads to photon-mediated dark matter interactions with nuclei, making it suitable for direct dark matter detection experiments. Matching to the framework of non-relativistic effective field theory for dark matter, we report the first sensitive search for this model using data from the PandaX-4T commissioning run. Our results yield strong constraints on Dirac fermion dark matter but relatively weaker constraints on Majorana dark matter due to the suppression of effective photon interactions. These constraints complement those obtained from the collider and indirect detection experiments.

Search for lepton portal dark matter in the PandaX-4T experiment

Parton distribution functions (PDFs) at large are challenging to extract from experimental data, yet they are essential for understanding hadron structure and searching for new physics beyond the Standard Model. Within the framework of the large momentum expansion of lattice quasi-PDFs, we investigate large PDFs, where the matching coefficient is factorized into the hard kernel, related to the active quark momentum , and the threshold soft function, associated with the spectator momentum (1 − ) . The renormalization group equation of the soft function enables the resummation of the threshold double logarithms ln (1 − ), which is crucial for a reliable and controllable calculation of large PDFs. Our analysis with pion valence PDFs indicates that perturbative matching breaks down when the spectator momentum (1 − ) approaches Λ , but remains valid when both and (1 − ) are much larger than Λ . Additionally, we incorporate leading renormalon resummation within the threshold framework, demonstrating good perturbative convergence in the region where both spectator and active quark momenta are perturbative scales.

Poland

Yizhuang Liu

Yushan Su

Rui Zhang

Effects of threshold resummation for large-

Axionlike particles (ALPs) and dark photons (DPs) are viable dark matter particle candidates. We have searched for possible ALP/DP signals in the PandaX-4T liquid xenon detector using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>440</mn><mtext> </mtext><mtext> </mtext><mi>kg</mi><mo>·</mo><mi>yr</mi></mrow></math> of data. A binned likelihood fit is constructed to search for possible mono-energetic peaks induced by the absorption processes between ALPs/DPs and atomic electrons of xenon. A detailed temporal model of decays associated with xenon isotopes is introduced to constrain the number of background events. No signal excess over background expectations is observed, and we have established the most stringent exclusion limits for most ALP/DP masses across the range of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>150</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math>. The improvement is particularly significant within the mass range of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>150</mn><mi>–</mi><mn>400</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>, with the average factor of 3.5 compared to previous results.

Search for MeV-Scale Axionlike Particles and Dark Photons with PandaX-4T

We calculate the leading-twist light cone distribution amplitudes of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi><mo stretchy="false">(</mo><mi>u</mi><mi>d</mi><mi>s</mi><mo stretchy="false">)</mo></math> baryon using lattice QCD methods within the framework of large-momentum effective theory. Our numerical computations are carried out with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>N</mi><mi>f</mi></msub><mo>=</mo><mn>2</mn><mo>+</mo><mn>1</mn></math> stout smeared clover fermions and a Symanzik gauge action on a lattice with spacing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>a</mi><mo>=</mo><mn>0.077</mn><mtext> </mtext><mtext> </mtext><mi>fm</mi></math> and a pion mass of 303 MeV. To approach the large-momentum region, we simulate the equal-time correlations with the hadron momentum <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>P</mi></mrow><mrow><mi>z</mi></mrow></msup><mo>=</mo><mo stretchy="false">{</mo><mn>2.52</mn><mo>,</mo><mn>3.02</mn><mo>,</mo><mn>3.52</mn><mo stretchy="false">}</mo><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>. We investigate the analytic properties of the baryon quasidistribution amplitude in coordinate space and validate them through our lattice calculations. After renormalization and extrapolation, we present results for the three-dimensional distribution in momentum fractions of the two light quarks. Based on these findings, we briefly discuss the phenomenological impact on weak decays of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="normal">Λ</mi><mi>b</mi></msub></math> and outline potential systematic uncertainties that can be improved in the future. This work lays the theoretical foundation for accessing baryon light cone distribution amplitudes from lattice QCD.

Min-Huan Chu

Haoyang Bai

Jian Liang

Germany

Andreas Schäfer

Xiaonu Xiong

Yi-Bo Yang

Jun Zeng

Jian-Hui Zhang

Light cone distribution amplitude for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi></math> baryon from lattice QCD

We develop an approach for calculating heavy quark effective theory (HQET) light-cone distribution amplitudes (LCDAs) by employing a sequential effective theory methodology. The theoretical foundation of the framework is established, elucidating how the quasidistribution amplitudes (quasi-DAs) with three scales can be utilized to compute HQET LCDAs. We provide theoretical support for this approach by demonstrating the rationale behind devising a hierarchical ordering for the three involved scales, discussing the factorization at each step, clarifying the underlying reason for obtaining HQET LCDAs in the final phase, and addressing potential theoretical challenges. The lattice QCD simulation aspect is explored in detail, and the computations of quasi-DAs are presented. We employ three fitting strategies to handle contributions from excited states and extract the bare matrix elements. For renormalization purposes, we apply hybrid renormalization schemes at short and long distance separations. To mitigate long-distance perturbations, we perform an extrapolation in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>λ</mi><mo>=</mo><mi>z</mi><mo>·</mo><msup><mi>P</mi><mi>z</mi></msup></math> and assess the stability against various parameters. After two-step matching, our results for HQET LCDAs are found in agreement with existing model parametrizations. The potential phenomenological implications of the results are discussed, shedding light on how these findings could impact our understanding of the strong interaction dynamics and physics beyond the standard model. It should be noted, however, that systematic uncertainties have not been accounted for yet.

Yibo Yang

Calculation of heavy meson light-cone distribution amplitudes from lattice QCD

New particles beyond the standard model of particle physics, such as axions, can be effectively searched through their interactions with electrons. We use the large liquid xenon detector PandaX-4T to search for novel electronic recoil signals induced by solar axions, neutrinos with anomalous magnetic moment, axionlike particles, dark photons, and light fermionic dark matter. A detailed background model is established using the latest datasets with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1.54</mn><mtext> </mtext><mtext> </mtext><mi>ton</mi><mtext> </mtext><mi>yr</mi></mrow></math> exposure. No significant excess above the background has been observed, and we have obtained competitive constraints for axion couplings, neutrino magnetic moment, and fermionic dark matter interactions.

Exploring New Physics with PandaX-4T Low Energy Electronic Recoil Data