Yifang Wang
The physics of tau and charm started in early 70's after J/$ψ$ and $τ$ were discovered. Since then several dedicated accelerators and experiments were built with increasing luminosities and studies on light hadron spectroscopy, charmonium, electroweak and QCD were never interupted. New interests and surprises are not rare in this area. With the newly built BEPCII/BESIII, an even brighter future is foreseen.
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Tau Physics Opportunities at the Super Tau-Charm Facility
本文概述了超级陶-粲装置在极高统计量、可控系统误差和低本底条件下，对陶轻子性质进行高精度研究的广泛物理项目。
Tests of discrete symmetry violation have played an important role in understand the structure of weak interactions in the Standard Model of particle physics. Historically these measurements have been extensively performed at experiments with large samples of K and B mesons. A high luminosity tau-charm facility presents physicists with the opportunity to comprehensively explore discrete symmetry violation and test the Standard Model using tau leptons, charm mesons and charmed baryons. This paper discusses several possible measurements for a future tau-charm factory.
Overview of tau lepton physics at a super tau-charm facility
本文介绍了超 tau-charm 厂房在tau轻子物理中的研究重点和未来发展方向
The Beijing Spectrometer (BESIII) collaboration uses $e^+e^-$ collisions in the tau-charm energy region to study a broad spectrum of topics. These include studies of light mesons and light baryons, studies of charmonium, including exotic mesons and baryons containing charmonium, studies of charmed mesons and baryons, studies of QCD and tau physics, as well as searches for new physics. The following is a Snowmass white paper that outlines the BESIII accomplishments and potential in each of these areas.
Main parameters of the linac-ring type charm-tau factory are discussed. Different sets of parameters for an electron linac and a positron ring have been considered. It is shown that L=10^33 cm-2 s-1 and even more can be achieved. The physics goals of this machine in investigation for charmed particles and tau lepton properties are briefly discussed. Advantages of the proposed machine in comparison with standard (ring-ring) type charm-tau factory proposals will be the possibility of the search for rare decays of tau lepton and charm quark and study of D^0-D^-0 oscillations.
The charm physics program accessible to a Tau-Charm Factory is summarized. Semileptonic, leptonic, hadronic, rare and forbidden charm decay modes are discussed, as well as \dmix\ mixing and CP violation in the charm sector. The theoretical expectations in the Standard Model and beyond as well as the experimental capabilities of a Tau-Charm Factory are examined for each of the above processes. {To appear in {\it The Tau-Charm Factory in the Era of B-Factories and CESR}, Stanford, CA, August 15-16, 1994}
The prospects for tau physics at future high-luminosity facilities are briefly discussed. Although important (and often complementary) contributions will be made from other machines, the unique experimental environment near threshold makes the Tau-Charm Factory the best experimental tool for $τ$ physics.
I discuss the special opportunities that a Tau-Charm Factory offers for identifying gluonic excitations, hybrid charmonium and other exotic hadronic states. (Invited talk at TCF Workshop, Marbella, 1-6June)
This talk summarizes the status of the charmonium system, with particular emphasis on outstanding problems in QCD spectroscopy which a tau-charm factory can address.
$D^0-\bar{D}^0$ mixing leads to the mass and width differences in the mass eigenstates of $D^0$ and $\bar{D}^0$ mesons (measured by parameters $x^{~}_D$ and $y^{~}_D$ respectively), but their magnitudes cannot be reliably predicted by the standard model. We show that it is possible to separately determine $x^{~}_D$ and $y^{~}_D$ through {\it time-integrated} measurements of the dilepton events of coherent $D^0\bar{D}^0$ decays on the $ψ(4.14)$ resonance at a $τ$-charm factory.
The Tau-Charm Factory combines the optimum conditions to perform a high-precision investigation of the $τ$ and $ν_τ$ leptons, the $c$ quark, and light-quark, glueball and hybrid spectroscopy. An overview of the broad physics program that this facility will address is presented.
I review the sensitivities achieved by and projected for fixed-target charm experiments in CP violation, flavor-changing neutral-current and lepton-number-violating decays, and mixing, and I describe the Charm2000 experiment intended to run at Fermilab in the Year ~2000. If approved, Charm2000 will in many of these areas exceed the sensitivities projected for a Tau/Charm Factory, but the Tau/Charm Factory retains certain qualitative advantages.
Entanglement measures and Bell-type spin-correlation observables in tau-lepton pairs at the Super Tau-Charm Facility
研究在STCF中通过τ轻子对的强子衰变通道，利用自旋相关系数测量纠缠度量和贝尔型相关组合，探讨其在标准模型下的高显著性解析能力。
In this paper, we present a preliminary study of $CP$ violation effect of $K^{0}-\bar{K}^{0}$ system in $J/ψ$ decay. The $CP$ violation parameters $η_{+-}$ and $η_{00}$ as well as their corresponding phase $ϕ_{+-}$ and $ϕ_{00}$ can be determined by the difference of the time-dependent decay rates between $K^{0}$ and $\bar{K}^{0}$ produced from $J/ψ\rightarrow K^{-}π^{+}K^{0} + c.c.$ processes. We investigate the precisions of the measurements of the CP violation effect at the Super Tau-Charm facility(STCF), a $e^{+}e^{-}$ collider with a peak luminosity of $0.5\times10^{35}\ \rm{cm}^{-2}\rm{s}…
Searching for axion-like particles from tau exotic decays at the Super Tau-Charm Facility and its far detectors
研究在超τ-charm设施及其远探测器中通过τ异常衰变寻找轴子类粒子，探讨其在轻子ophilic和LFU场景下的探测潜力与新区域的测量能力。
We present an evaluation of the atmospheric tau neutrino flux in the energy range between $10^2$ and $10^6$ GeV. The main source of tau neutrinos is from charmed particle production and decay. The $ν_τN\to τX$ event rate for a detector with a water equivalent volume of 1 km$^3$ is on the order of 60-100 events per year for $E_τ>100$ GeV, reducing to 18 events above 1 TeV. Event rates for atmospheric muon neutrino oscillations to tau neutrinos are also evaluated.
The Physics and Prospects of Super-Tau Charm Factories
超tau魅工厂是一种高亮度电子-正电子对撞机，能精确测量魅子性质、CP破坏及非微扰QCD现象，为标准模型检验和新物理探索提供独特机遇。
In a recent paper, eight semileptonic parameters were defined to specify the most general Lorentz-invariant spin correlation functions for tau semileptonic decays. The parameters were physically defined in terms of tau-decay partial-width intensities for polarized final states. This paper studies how these parameters can be simply measured at a tau/charm factory with longitudinally polarized beams without using spin-correlation techniques. Thereby the parameters can also be used to bound the effective-mass scales $ Λ$ for ``new physics" such as arising from lepton compositeness, leptonic CP vi…
CP violation studies at Super Tau-Charm Facility
本文探讨了未来超级陶粲装置在2.0-7.0 GeV能区、峰值亮度0.5×10^35 cm^-2s^-1下，研究粲强子衰变及超子和τ轻子产生衰变中的CP破坏，并改进CPT不变性检验的前景。
We systematically investigate the possibility of finding CP/T violation in the $τ$ sector at Tau-Charm Factory. CP/T violation may occur at $τ$ pair production process, expressed as electric dipole moment, and at $tau$ decay processes. By assuming that electric dipole moment as large as $10^{-19}$e-cm and CP/T violation effect orignating from $τ$ decay as large as $10^{-3}$ are observable at Tau-Charm Factory, we studied all the possible extensions of the SM which are relevent for generating CP/T violation in $τ$ sector. And we pointed there are a few kind of models, which are hopeful for gene…
In tau physics, we are at the frontier between the completion of the LEP program and the start of analyses from b-factories, which are expected to produce results in the coming years. Nice results from CLEO are steadily delivered in the meantime. For charm, impressive progress have been achieved by fixed target experiments in the search for CP violation and D^0 - \bar D^0 oscillations. First results from b-factories demonstrate the power of these facilities in such areas. The novel measurement of the D* width by CLEO happens to be rather different from current expectations. The absence of a ch…
Long-lived sterile neutrinos from axionlike particles at the Super Tau-Charm Facility
研究超 Tau-charm 实验中通过轴子类粒子衰变产生长寿命重中性轻子对的探测前景，探讨其对中微子混合参数的灵敏度提升。
The present data imply that $ϕ(2170)$ may not be an excited state of $ϕ$, but is a four quark state with $ss\bar s \bar s$ constituents. Furthermore, there are no two mesons of $s\bar s$ available to form a molecule which fits the mass spectrum of $ϕ(2170)$, thus we suggest it should be an $ss\bar s \bar s$ tetraquark state. In this scenario, we estimate its decay rates through the fall-apart mechanism. Our theoretical estimates indicate that its main decay modes should be $ϕ(2170)$ into $ϕf_0(980)$, $ h_1η$, $ h_1η'$, $K_1(1270)K$ and $K_1(1400)K$. Under this hypothesis the modes $ϕ(2170)\to …
Can millicharge be probed at future Super Tau Charm Facility via mono-$π^0$ searches?
本研究提出在未来超级陶粲装置上通过单$\pi^0$ 信号搜寻微电荷粒子的新通道，计算了信号与标准模型本底事例，推导了不同能量下的微电荷上限，指出该方法在低质量区有一定提升，可作为不可见粒子研究的补充。
To measure the $R$ value in an energy scan experiment with $\ee$ collisions, precise calculation of initial state radiation is required in event generators. We present an event generator for this consideration, which incorporates initial state radiation effects up to the second order accuracy, and the radiative correction factor is calculated using the totally hadronic Born cross section. The measured exclusive processes are generated according to their cross sections, while the unknown processes are generated using the LUND Area Law model, and its parameters are tuned with data collected at $…
The Heavy Flavor Averaging Group provides this Letter of Interest (LOI) as input to the Snowmass 2021 Particle Physics Community Planning Exercise organized by the Division of Particles and Fields of the American Physical Society. Research in heavy flavor physics is an essential component of particle physics, both within and beyond the Standard Model. To fully realize the potential of this field, we advocate strong support within the U.S. high energy physics program for ongoing and future experimental and theory research in heavy flavor physics.
We re-analyze the results of the searches for Heavy Neutral Leptons (HNLs) by the CHARM experiment. We study HNL decay channel $N\to e^{+}e^{-}ν/μ^{+}μ^{-}ν$ and show that, in addition to the constraints on the HNL's mixings with $ν_e$ or $ν_μ$, the same data also implies limits on the HNLs that mix only with $ν_τ$ and have masses in the range $380 \text{ MeV}<m_{N}\lesssim 1.6\text{ GeV}$ - the region in the parameter space that was considered in the literature as a target for HNLs searches.
A method for measuring the average longitudinal polarization of the electron beam at an electron-positron collider operating near the $J/ψ$ resonance is proposed. The method utilizes the differential cross-section of $J/ψ\to [Λ\to pπ^-][\barΛ\to\bar{p}π^+]$ decay. It can be used to measure the average longitudinal polarization of electrons with the statistical precision better than $10^{-3}$ at a Super Charm-Tau factory operating at the luminosity of $10^{35}~\mathrm{cm}{}^{-2}\mathrm{s}{}^{-1}$. The method is discussed in the context of the weak mixing angle measurement in the same experiment…
Searching for apparent baryon number violation in $Λ_c^+$ decays at the Super Tau-Charm Facility
提出在$Λ_c^+$衰变中搜索表观重子数破坏（BNV）通道$Λ_c^+\to M^+ +$缺失能量（$M=\pi, K$），利用STCF模拟评估灵敏度，并解释为$\nu$LEFT和RPV超对称模型中的新物理。
In contrast with $B^0-\bar B^0$, $B_s-\bar B_s$ mixing where the standard model (SM) contributions overwhelm that of new physics beyond standard model (BSM), a measured relatively large $D^0-\bar D^0$ mixing where the SM contribution is negligible, definitely implies the existence of new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the rare decay $D^0\to μ^+μ^-$ could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of new physics BSM in the leptonic decays …
Prospects for $P$ and $C\!P$ violation in $Λ_{c}^{+}$ decays with polarized beam at Super Tau-Charm Facility
本文研究了在超 Tau-charm 设施中利用极化束流对$Λ_{c}^{+}$衰变中$P$和$C\!P$违反的探测能力，评估了不同极化设置下的灵敏度。
IceCube Neutrino Astronomy is considered. The tau neutrino flavor paucity and the asymmetry for the tracks suggest a dominant atmospheric charm noise. The correlated cascades and tracks asymmetry with relevant statistics enforce the charm noise dominance in the data. The charm signal may explain at once the absence of correlation for the tracks data with the galactic plane and with known brightest gamma sources.
Higgs Yukawa coupling constraints on a benchmark one-loop radiative mass model for the bottom, charm and tau
研究希格斯玻色子与费米子的汤川耦合对辐射质量模型的约束，构建基准模型产生多种费米子质量，当前约束显示其有可行参数空间，未来测量难排除该模型，且模型中的暗物质候选者能重现正确遗迹密度。
We investigate the possibility of searching the lepton-flavor-violating (LFV) $τ\rightarrow μγ$ rare decay at the Super Charm-Tau Factory (CTF). By comparing the kinematic distributions of the LFV signal and the standard model (SM) background, we develop an optimized event selection criteria which can significantly reduce the background events. It is concluded that new $2 σ$ upper limit of about $1.9 \times 10^{-9}$ on $Br(τ\rightarrow μγ)$ can be obtained at the CTF, which is beyond the capability of Super-B factory in searching $τ$ lepton rare decay. Within the framework of the scalar leptoq…
Non-leptonic two-body weak decays of baryons are an important tool to probe the combined charge-conjugation--parity symmetry (CP) violation. We explain why the decays of strange baryons provide complementary information to the decays of kaons. A model-independent parameterization of the non-leptonic decays of the $Λ$- and $Ξ$-baryons is reviewed, and the amplitudes are updated according to the latest experimental input. We demonstrate the potential of performing precision tests in strange baryon decays at the next generation electron-positron $J/ψ$ factories with luminosity of $10^{35}$ cm$^{-…
The recent measurements on $R_K$ and $R_π$ imply that there exists a possible violation of the leptonic flavor universality which is one of the cornerstones of the standard model. It is suggested that a mixing between sterile and active neutrinos might induce such a violation. In this work we consider the scenarios with one or two sterile neutrinos to explicitly realize the data while the constraints from the available experiments have been taken into account. Moreover, as indicated in literature, the deviation of the real PMNS matrix from the symmetric patterns may be due to a $μ-τ$ asymmetry…
We study rare decays of Charm in NSIs. We calculate the NSIs Branching ratios of these decays. There is a strong dependence of these on new physics parameter. They provide, stringent constraints on free parameter in tau.
We discuss production of far-forward $D$ mesons/antimesons and neutrinos/antineutrinos from their semileptonic decays in pp-collisions at the LHC. We include the gluon-gluon fusion $gg \to c\bar{c}$, the intrinsic charm (IC) $gc \to gc$ as well as the recombination $gq \to Dc$ partonic mechanisms. The calculations are performed within the $k_T$-factorization approach and the hybrid model using different unintegrated parton distribution functions (uPDFs) for gluons from the literature, as well as within the collinear approach. We compare our results to the LHCb data for forward $D^{0}$-meson pr…
Charged lepton flavor violation has long been recognized as unambiguous signature of New Physics. Here we describe the physics capabilities and discovery potential of New Physics models with charged lepton flavor violation in the tau sector as its experimental signature. Current experimental status from the B-Factory experiments BaBar, Belle and Belle II, and future prospects at Super Tau Charm Factory, LHC, EIC and FCC-ee experiments to discover New Physics via charged lepton flavor violation in the tau sector are discussed in detail. Submitted to the Proceedings of the US Community Study on …
We report on an estimate of α_s, renormalised in the MSbar scheme at the tau and Z^0 mass scales, by means of lattice QCD. Our major improvement compared to previous lattice calculations is that, for the first time, no perturbative treatment at the charm threshold has been required since we have used statistical samples of gluon fields built by incorporating the vacuum polarisation effects of u/d, s and c sea quarks. Extracting α_s in the Taylor scheme from the lattice measurement of the ghost-ghost-gluon vertex, we obtain α_s^{MSbar}(m^2_Z)=0.1200(14) and α_s^{MSbar}(m^2_tau)=0.339(13).
Motivated by the disagreement between experimental and lattice QCD results on the D_s decay constant we systematically reinvestigate role of leptoquarks in charm meson decays. We consider scalar leptoquarks that transform as a weak interaction triplet, doublet, or singlet in a model independent approach, and also argue that in a particular SU(5) GUT model these leptoquark states, contained in the 45-dimensional Higgs representation, could be safe against proton decay bounds. Using the current experimental measurements in tau, kaon and charm sectors, we find that scalar leptoquarks cannot natur…
Charm physics at the Belle and Belle II experiments
本文综述了Belle和Belle II实验在粲物理方面的最新成果，包括寿命、分支比、不对称参数、稀有衰变搜索及CP破坏参数测量。
Novel Method to Reliably Determine the QCD Coupling from $R_{\rm uds}$ Measurements and its effects to Muon $g-2$ and $α(M_Z^2)$ within the Tau-Charm Energy Region
提出基于最大共形原理与贝叶斯 UHO 估计的 $R_{\rm uds}$ 分析新方法，消除重整化标度歧义并降低理论误差，用于精确提取 QCD 耦合及缪子 $g-2$、$α(M_Z^2)$ 强子贡献。
Precision studies at electron-positron colliders with center-of-mass energies in the charm-tau region and below have strongly contributed to our understanding of light-meson interactions at low energies. We focus on the processes involving two or three light mesons with invariant masses below nucleon-antinucleon threshold. A prominent role is given to the interactions of the nine lightest pseudoscalar mesons (pions, kaons, $η$, and $η'$) and the two narrow neutral isoscalar vector mesons $ω$ and $ϕ$. Experimental methods used to produce the mesons are reviewed as well as theory tools to extrac…
An overview of the most important progresses in charm physics since the last CKM Workshop (2014) is presented. Due emphasis is given to the experimental measurements directly related to the CKM matrix.
We review the physics goals of an ultrahigh-statistics charm experiment and place them in the broader context of the community's efforts to study the Standard Model and to search for physics beyond the Standard Model, and we point out some of the experimental difficulties which must be overcome if these goals are to be met.
Charm physics has attracted increased attention after first evidence for charm mixing was observed in 2007. The level of attention has risen sharply after LHCb reported first evidence for CP violation in the charm sector. Neither mixing nor CP violation have been established by a single unambiguous measurement to date. This review covers the status of mixing and CP violation measurements and comments on the challenges on the road ahead, both on the experimental and theoretical side, and on ways to tackle them.
We discuss the potential of $τ$-charm and B factories for the search of new physics through the study of rare $τ$ decays. We consider decays that involve the violation of lepton flavour conservation. Such decays bear a close relationship to the physics of neutrino mass and the properties of the lepton sector of the electroweak theory.
We closed the CHARM 2007 workshop with a lively panel discussion on the future of the field. This document presents a summary of the key points, and a lightly edited transcript of the discussion itself.
Charm Physics at the Super $τ$-Charm Factory
超级τ-粲工厂（STCF）将通过高亮度和全球最大粲阈值数据，在粲物理的电弱参数测量、D⁰-$\bar{D}^0$混合、CP破缺研究等方面实现高灵敏度，补充LHCb和Belle II的研究，推动新物理探索。
Semileptonic Flavor Changing Neutral Current decays of charmed hadrons uniquely probe the up-sector of the Standard Model. Clean null test observables, such as CP-asymmetries, lepton-universality ratios, missing energy modes, lepton flavor violating modes and angular observables can be studied in a variety of charmed meson and baryon modes. An overview of null test opportunities with rare charm decays is presented and similarities and complementarities of different modes are worked out.
In this review, we discuss some interesting issues in charm physics which is full with puzzles and challenges. So far in the field there exist many problems which have not obtained satisfactory answers yet and more unexpected phenomena have been observed at the present facilities of high energy physics. Charm physics may become an ideal place for searching new resonances and studying non-perturbative QCD effects, moreover probably is an area to explore new physics beyond the Standard Model. More data will be available at BESIII, B-factories, LHC and even future ILC which may open a wide window…
This is part I of a two-part review of charm physics. After briefly recapitulating the history of the charm quantum number we sketch the experimental environments and instruments employed to study the behaviour of charm hadrons and then describe the theoretical tools for treating charm dynamics. After discussing a wide range of inclusive production processes we analyze the spectroscopy of hadrons with hidden and open charm and the weak lifetimes of charm mesons and baryons. In part II we shall address exclusive charm decays, $D^0 - \bar D^0$ oscillations and CP violation. This review is meant …
Abundance of charm data in the current and future low energy flavor experiments makes it possible to study rare decays of D-mesons with ever increased precision. I discuss theoretical implications of derived constraints on New Physics models from these transitions. I argue that those constraints could be competitive with results of direct searches for New Physics particles (including Dark Matter) at the Large Hadron Collider.
Recent developments in charm physics within the standard model and beyond are reviewed. The precision study of leptonic charm meson decays accompanied with the constraints coming from K, B and tau physics enables to determine constraints on models of new physics. The standard model contributions in the D0 - D0bar system are still under investigation including operators of higher dimensions. New physics models such as the Littlest Higgs model or warped extra-dimensional models might modify the amount of CP violation, although CP violating asymmetries are still predicted to be at most of the ord…
We review recent developments in charm physics, focusing on the physics of charmed mesons. We discuss charm spectroscopy, decay constants, as well as searches for new physics with charmed mesons. We discuss D0-anti-D0 mixing and CP-violation in charm decays. We also present the modified Nelson plot of charm mixing predictions.
We report on the charm physics potential at BES-III at BEPC-II which will make significant contribution to quark flavor physics this decade. The charm physics program will include studies of leptonic, semileptonic and hadronic charm decays, and tests for physics beyond the Standard Model. Event samples of the order of 30 million $\DD$ pairs, 2 million $\DspDsm$ pairs at threshold and $10\times 10^9$ $J/ψ$ decays will be produced with one year design luminosity. High precision charm data will enable us to validate forthcoming Lattice QCD calculations at the few percent level. These can then be …
We introduce the contributions to the proceedings of Working Group V. The main topics were: present and future experiments dedicated to charm physics, the interplay between high-precision measurements and better control over theoretical uncertainties, and searches for signals of new physics in the charm sector. The comparison of Lattice QCD calculations with precise measurements of charm semi-leptonic and leptonic decays can have a major impact on the determination of CKM matrix elements from measurements of B meson decays.
We consider the prospect of using the charm system as a laboratory for probing new physics. The theoretical expectations for rare charm meson decays, $D^0-bar D^0$ mixing, and charm quark asymmetries in $Z$ decays are examined in the Standard Model. The effects of new physics from several classes of non-standard dynamical models are summarized for these phenomena. {Presented at {\it Lafex International School on High Energy Physics (LISHEP95)}, Rio de Janeiro, Brazil, February 6-22, 1995}
This Fifth International WEIN Symposium is devoted to physics beyond the standard model. This talk is about tau lepton physics, but I begin with the question: do we know how to find new physics in the world of elementary particles? This question is interwoven with the various tau physics topics. These topics are: searching for unexpected tau decay modes; searching for additional tau decay mechanisms; radiative tau decays; tau decay modes of the W, B, and D; decay of the Z^0 to tau pairs; searching for CP violation in tau decay; the tau neutrino, dreams and odd ideas in tau physics; and tau res…
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