Leveraging recent advancements in machine learning-based flavor tagging, we develop an optimal analysis for measuring the hadronic cross-section ratios $R_b$, $R_c$, and $R_s$ at the FCC-ee during its $WW$, $Zh$, and $t\bar{t}$ runs. Our results indicate up to a two-order-of-magnitude improvement in precision, providing an unprecedented test of the SM. Using these observables, along with $R_\ell$ and $R_t$, we project sensitivity to flavor non-universal four-fermion (4F) interactions within the SMEFT, contributing both at the tree level and through the renormalization group (RG). We highlight a subtle complementarity with RG-induced effects at the FCC-ee's $Z$-pole. Our analysis demonstrates significant improvements over the current LEP-II and LHC bounds in probing flavor-conserving 4F operators involving heavy quark flavors and all lepton flavors. As an application, we explore simplified models addressing current $B$-meson anomalies, demonstrating that FCC-ee can effectively probe the relevant parameter space. Finally, we design optimized search strategies for quark flavor-violating 4F interactions.
We propose a method to probe the coupling of the Higgs to strange quarks by tagging strange jets at future lepton colliders. For this purpose we describe a jet-flavor observable, $J_F$, that is correlated with the flavor of the quark associated with the hard part of the jet. Using this variable, we set up a strangeness tagger aimed at studying the decay $h\to s\bar{s}$. We determine the sensitivity of our method to the strange Yukawa coupling, and find it to be of the order of the standard-model expectation.
Exploring $Z/γ$-mediated heavy FCNCs at the FCC-ee
Indian Institute of Technology Guwahati（印度理工学院古瓦哈提分校）；Shanghai Institute for Advanced Studies（上海高等研究院）；University of Science and Technology of China（中国科学技术大学）
Flavor-resolved four-fermion probes at the FCC-ee $Z$ pole
Institute for Advanced Research, Nagoya University（名古屋大学高等研究院）；Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University（名古屋大学小林-益川粒子宇宙起源研究所）
We present a new scheme for tagging high-$p_{T}$ bottom and charm jets using energetic muons. Contemporary track-based $b$ tags lose their ability to reject light jet background as jet $p_{T}\rightarrow\mathcal{O}(\mathrm{TeV})$, where the massive boost exposes fundamental limits in tracking resolution. For our "$μ_{x}$" tag, the signal efficiency and light jet rejection is robust versus $p_{T}$. In the tested regime (jet $p_{T}\in[\mathrm{0.5,2.1}]$ TeV), $μ_{x}$ tags $\sim14\%$ of $b$ jets, $\sim6.5\%$ of $c$ jets and $\sim0.65\%$ of light jets. Since $μ_{x}$ tagging should be immediately us…
At present, two outstanding discrepancies between experiment and the standard model are the measurements of the hadronic branching fractions $R_b$ and $R_c$. We note that an independent measurement of these branching fractions may be obtained from the width of hadronic $Z$ decays with a prompt photon, $Γ_{qqγ}$, along with the total hadronic decay rate, $Γ_{had}$, and an additional theoretical assumption. Such an analysis requires no flavor tagging. We consider several plausible theoretical assumptions and find that the current value of $Γ_{qqγ}$ favors larger $R_b$ and smaller $R_c$ relative …
A method is proposed for tagging the flavor of neutral $B$ mesons in the study of CP-violating decay asymmetries. The method makes use of a possible difference in interactions in $B π$ or $B^* π$ systems with isospins 1/2 and 3/2, and would be particularly clean if the $I = 1/2$ systems can be detected as ``$B^{**}$'' resonances.
We describe a general approach to quark flavor tagging in polarized hadronic processes, with particular emphasis on semi-inclusive deep inelastic scattering. A formalism is introduced that allows one to relate chosen quark flavor polarizations to an arbitrary combination of final-state hadron spin asymmetries. Within the context of the presented formalism, we quantify the sensitivity of various semi-inclusive hadron asymmetries to the light quark flavors. We show that unpolarized Lambda's may allow one to measure strange quark and antiquark polarizations independently. We also highlight severa…
We discuss some highlights of the FCC-ee flavor physics program. It will help to explore various aspects of flavor physics: to test precision calculations, to probe nonperturbative QCD methods, and to increase the sensitivity to physics beyond the standard model. In some areas, FCC-ee will do much better than current and near-future experiments. We briefly discuss several probes that can be relevant for maximizing the gain from the FCC-ee flavor program.
A neutrino mass dominance quantity is introduced for tagging the neutrino flavor in the phenomenological two-parameter four neutrino mixing matrix with two neutrino mass doublets and thorough maximal neutrino doublet mixing. While there is no hierarchy of the neutrino masses in the neutrino flavor eigenstates of this model, it may rather be a special hierarchy of the mass dominance ratios in these eigenstates. A neutrino flavor hierarchy condition is suggested: a direct link between the neutrino flavor and the flavor of the charged leptons which interconnects the two mixing angles, theta and p…
Jet flavor tagging with Particle Transformer for Higgs factories
International Center for Elementary Particle Physics, The University of Tokyo（东京大学基础粒子物理国际中心）；Department of Physics, Graduate School of Science, The University of Tokyo（东京大学理学研究科物理学系）；MI-6 Ltd.（MI-6有限公司）
We study the effect of flavor changing charged current(FCCC) of lepton sector in the hadronic tau decays, tau \to nu_X K^- pi^0 (X=e,mu). In general two Higgs doublet model, the lepton flavor changing neutral current (FCNC) arises in the charged lepton sector and contributes to the process such as tau \to mu mu^+ mu^- and tau \to mu(e) P^0 where P^0=pi^0,eta, eta'. We derive a relation between the FCCC in charged Higgs boson and the FCNC due to the neutral Higgs boson. Then by using the recent experimental upper bound on FCNC of tau \to l_X eta (pi^0) (l_X=e,mu) processes, we study how large t…
We revisit the exclusive signature $e^\pm (μ^\pm) + b\bar b$ in the associated production of the intermediate mass Higgs boson with a $W$ boson. We show that it is feasible to use this signature to identify the Higgs boson in the lower intermediate mass region ($90$ to $130$ GeV) at the LHC with reasonable acceptance cuts by assuming effective bottom-jet identification. We further demonstrate that the background can be reduced with judicious cuts down to the level of the signal.
Despite no new physics so far at the LHC, a $Z'$ boson with $m_{Z'} \sim 100$ GeV could still emerge via Drell-Yan (DY) production, $q \bar q \to Z' \to μ^+ μ^-$, in the next few years. To unravel the nature of the $Z'$ coupling, we utilize the $c$- and $b$-tagging algorithms developed by ATLAS and CMS to investigate $cg \to c Z'$ at 14 TeV LHC. While light-jet contamination can be eliminated, mistagged $b$-jets cannot be rejected in any of the tagging schemes we adopt. On the other hand, for nonzero $bbZ'$ coupling, far superior $b$-tagging could discover the $bg \to b Z'$ process, where agai…
I present a new scheme for tagging boosted heavy flavor jets called "$μ_x$ tagging" and its application to TeV-scale physics beyond the Standard Model. Using muons from B hadron decay to define a particular combination "x" of angular information, and jet substructure variables, we identify a clean ($ε_{\mathrm{fake}}/ε_b\sim 1/100$) good efficiency ($ε_b = 14\%$) tag. I demonstrate the usefulness of this new scheme by showing the reach for discovery of leptophobic $Z^\prime\to b\bar b$ and $tH^\pm\to t t b$.
We propose to study the flavor properties of the top quark at the future Circular Electron Positron Collider (CEPC) in China. We systematically consider the full set of 56 real parameters that characterize the flavor-changing neutral interactions of the top quark, which can be tested at CEPC in the single top production channel. Compared with the current bounds from the LEP2 data and the projected limits at the high-luminosity LHC, we find that CEPC could improve the limits of the four-fermion flavor-changing coefficients by one to two orders of magnitude, and would also provide similar sensit…
We investigate the possible presence of Flavor Changing Neutral Current (FCNC) couplings of the top quark with gluon and photon through $e^-p\to e^-tj$ process at the Future Circular Collider in the proton-electron mode (FCC-he). Focusing on disentangling the effects of different couplings that could be present, we exploit the presence of the scattered electron, the angular distribution of which is sensitive to the type of coupling involved. Top quark polarisation accessed through the angular distribution of the decay lepton provides additional handle in identifying the nature of the couplings…
Circular colliders have the advantage of delivering collisions to multiple interaction points, which allow different detector designs to be studied and optimized - up to four for FCC-ee. On the one hand, the detectors must satisfy the constraints imposed by the invasive interaction region layout. On the other hand, the performance of heavy-flavour tagging, of particle identification, of tracking and particle-flow reconstruction, and of lepton, jet, missing energy and angular resolution, need to match the physics programme and the exquisite statistical precision offered by FCC-ee. During the FC…
The identification of b jets is a crucial issue to study and characterize various channels like top quark events and many new physics scenarios. Different b-tagging techniques are defined in CMS which benefit from the long life time, high mass and large momentum fraction of the b-hadron produced in b-quark jet. Effcient algorithms have been developed based on the measure of b-hadron secondary vertex or on tracks with a large impact parameter. Data collected in pp collisions at 7TeV in 2011 are used to estimate both the b-tagging effciency and the mistag rate from light flavor jets.
This thesis demonstrate the efficacy of designing and developing machine learning (ML) algorithms to selected use cases that encompass many of the outstanding challenges in the field of experimental high energy physics. Although simple implementations of neural networks and boosted decision trees have been used in high energy physics for a long time, the field of ML has quickly evolved by devising more complex, fast and stable implementations of learning algorithms. The complexity and power of state-of-the-art deep learning far exceeds those of the learning algorithms implemented in the CERN-d…
Deep-learning jet flavor tagging for precision hadronic Higgs measurements at future $e^+e^-$ Higgs factories
Shanghai Jiao Tong University（上海交通大学）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大李政道研究所）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）
Distinguishing the flavor of $B$ and $\overline B$ hadrons is critical in studies of CP-violation, $B^0 -\overline{B^0}$ mixing, and the underlying $b$-decay mechanisms. Methods of $b$ ``flavor tagging" are broadly divided into ``opposite $b$" tagging and self-tagging of the signal $b$ hadron. The former, while understood, has the perceived drawback of low efficiency. The latter, while having the potential for an order of magnitude higher efficiency, has yet to be demonstrated for neutral $B$ hadrons. In this article we review opposite $b$ tagging in light of methods whose efficacy has only re…
We study the effective field theory sensitivity of an LHC analysis for the $τν$ final state with an associated b-jet. To illustrate the improvement due to the b-tagging, we first recast the recent CMS analysis in the $τν$ channel, using an integrated luminosity of 35.9 fb$^{-1}$ at $\sqrt{s}=13$ TeV, and provide limits on all the dimension-six effective operators which contribute to the process. The expected limits from the b-tagged analysis are then derived and compared. We find an improvement of approximately $\sim 30\%$ in the bounds for operators with a b quark. We also discuss in detail p…
We propose a new variable, the charm fraction, for collider searches for new physics. We analyze this variable in the context of searches for simplified supersymmetry models with squarks, the gluino, and the bino, assuming that only the lightest mass-degenerate squarks can be produced at the high-luminosity LHC. The charm fraction complements event counting and kinematic information, increasing the sensitivity of the searches for models with heavy gluinos, for which squark production is flavor-blind. If squarks are discovered at the LHC, this variable can help discriminate between different un…
Deep learning is a standard tool in the field of high-energy physics, facilitating considerable sensitivity enhancements for numerous analysis strategies. In particular, in identification of physics objects, such as jet flavor tagging, complex neural network architectures play a major role. However, these methods are reliant on accurate simulations. Mismodeling can lead to non-negligible differences in performance in data that need to be measured and calibrated against. We investigate the classifier response to input data with injected mismodelings and probe the vulnerability of flavor tagging…
Top-quark pair production sensitivity to heavy new physics at the FCC-ee
Istituto Nazionale di Fisica Nucleare - Sezione di Padova（意大利国家核物理研究所帕多瓦分部）；Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova（帕多瓦大学伽利略·伽利雷物理与天文学系）；Center for Cosmology, Particle Physics and Phenomenology (CP3), University of Louvain (UCLouvain)（鲁汶宇宙学、粒子物理与现象学中心（CP3）/鲁汶大学）；Departamento de Física and ICTEA, Universidad de Oviedo（奥维耶多大学物理系及ICTEA）；European Organisation for Nuclear Research (CERN)（欧洲核子研究组织（CERN））
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 …
A Novel Approach to Short Baseline Oscillation Searches Using Neutrino Tagging with nuSCOPE
Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), CNRS/IN2P3, Sorbonne Université, Université Paris Cité（核物理与高能物理实验室（LPNHE），CNRS/IN2P3，索邦大学，巴黎西岱大学）；European Organization for Nuclear Research (CERN)（欧洲核子研究组织（CERN））
In this article we investigate the prospects of searching for sterile neutrinos in lowscale seesaw scenarios via the lepton flavour violating (but lepton number conserving) dilepton dijet signature. In our study, we focus on the final state $e^\pm μ^\mp jj$ at the HL-LHC and the FCC-hh (or the SppC). We perform a multivariate analysis at the detector level including the dominant SM backgrounds from di-top, di-boson, and tri-boson. Under the assumption of the active-sterile neutrino mixings $|V_{ l N}|^2=|θ_e|^2=|θ_μ|^2$ and $|V_{ τN}|^2 = |θ_τ|^2=0$, the sensitivities on the signal production …
The neutron's deep-inelastic structure functions provide essential information for the flavor separation of the nucleon parton densities, the nucleon spin decomposition, and precision studies of QCD phenomena in the flavor-singlet and nonsinglet sectors. Traditional inclusive measurements on nuclear targets are limited by dilution from scattering on protons, Fermi motion and binding effects, final-state interactions, and nuclear shadowing at x << 0.1. An Electron-Ion Collider (EIC) would enable next-generation measurements of neutron structure with polarized deuteron beams and detection of for…
We investigate the top quark anomalous Flavor Changing Neutral Current (FCNC) $tqg$ interactions to probe limits on the couplings $ζ_c$ and $ζ_u$ through the $qg \to lνb$ signal suprocess at FCC-hh collider with center of mass energy of 100 TeV. To separate signal from relevant Standard Model background processes, selection criteria based on Boosted Decision Trees (BDT) is used with a set of useful kinematic variables. The sensitivities on the anomalous top FCNC couplings $ζ_u$ and $ζ_c$ are found to be $1.239\times10^{-4}$ and $1.149\times10^{-4}$ for FCC-hh with $L_{int}$=10 ab$^{-1}$ at 95 …
Quantum Graph Neural Networks for Jet Tagging on Quantum Hardware
University of California, Los Angeles（加州大学洛杉矶分校）；University of Maryland, College Park（马里兰大学帕克分校）；National Quantum Lab, University of Maryland（马里兰大学国家量子实验室）；Mani L. Bhaumik Institute for Theoretical Physics, University of California, Los Angeles（加州大学洛杉矶分校马尼·L·巴乌米克理论物理研究所）；Center for Quantum Science and Engineering, University of California, Los Angeles（加州大学洛杉矶分校量子科学与工程中心）
We propose two new analysis strategies for studying charm and beauty quarks at colliders. The first strategy is aimed at testing the kinematics of heavy-flavor quarks within an identified jet. Here, we use the SoftDrop jet-declustering algorithm to identify two subjets within a large-radius jet, using subjet flavor tagging to test the heavy-quark splitting functions of QCD. For subjets containing a $J / ψ$ or $Υ$, this declustering technique can also help probe the mechanism for quarkonium production. The second strategy is aimed at isolating heavy-flavor production from gluon splitting. Here,…
We propose a way to differentiate between various extra $U(1)$ models using flavor tagging in the decay modes $Z^{\prime}\rightarrow q{\bar{q}}$ once the extra $Z^{\prime}$ is observed at future colliders in the lepton channel. A generalization of the R parameter, namely, one for charge $\frac{1}{3}$ and one for charge $\frac{2}{3}$ quark gives a two parameter test for the various models. Flavor tagging eliminates the uncertainty because of extra fermions and can reduce the QCD background at SSC/LHC dramatically. For $E_{6}$ and $SO(10)$ based models the former is always 3. This seems to be a …
The observation of lepton flavor violation indicates new physics beyond the Standard Model. Lepton colliders are ideal facilities to probe charged lepton flavor violation (CLFV) signals induced by new physics at high energy. In this work we perform a comprehensive study of the sensitivity of future lepton colliders to charged lepton flavor violation. We consider the most general renormalizable Lagrangian coupling two leptons to new bosonic particles, involving both $ΔL=0$ and $ΔL=2$ interactions. The CLFV processes are introduced by the exchange of off-shell new particles at tree-level. We fin…
We summarize measurements of b and c jet production at the LHC, which are an important signature and background for decays of massive particles such as H-to-b-bbar. These include measurements of the inclusive and dijet production of heavy quark jets, b and c jets produced in association with vector bosons Z and W, and decays of boosted Z bosons into pairs of b-bbar. The current status of b tagging and b jet energy scale is also reviewed. These measurements test perturbative QCD in the four and five-flavor number schemes, and provide insight into the relative importance of heavy flavor producti…
Beyond the Standard Model Higgs physics: Hunting $h \rightarrow bs$ with Higgs-strahlung at CEPC and FCC-ee
Benemérita Universidad Autónoma de Puebla（普埃布拉自治大学）；Centro Interdisciplinario de Investigación y Enseñanza de la Ciencia (CIIEC)（科学交叉研究与教育中心）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）
