The $τ$ polarization in semileptonic $B$ decays provides probes of new physics complementary to decay rate distributions of the three-body final state. Prior calculations for inclusive decays used a definition for the polarization axis that is different from the choice used in calculations (and the only measurement) for exclusive channels. To compare inclusive and exclusive predictions, we calculate the $τ$ polarization in inclusive $B\to Xτ\barν$ using the same choice as in the exclusive decays, and construct a sum rule relating the inclusive $τ$ polarization to a weighted sum of exclusive decay polarizations. We use this relation, experimental data, and theoretical predictions for the decays to the lightest charm or up-type hadrons to make predictions for excited channels.
Stimulated by the new discovery of $P_{c}(4312)^{+}$ by LHCb Collaboration, we endeavor to perform the study of $P_{c}(4312)^{+}$ as a $Σ_{c}\bar{D}$ state in the framework of QCD sum rules. Taking into account the results from two sum rules, a conservative mass range $4.07\sim4.97~\mbox{GeV}$ is presented for the $Σ_{c}\bar{D}$ hadronic system, which agrees with the experimental data of $P_{c}(4312)^{+}$ and could support its interpretation as a $Σ_{c}\bar{D}$ state.
Though not considered in general, purely baryonic decays could shed light on the puzzle of the baryon number asymmetry in the universe by means of a better understanding of the baryonic nature of our matter world. As such, they constitute a yet unexplored class of decay processes worth investigating. We propose to search for purely baryonic decay processes at the LHCb experiment. No such type of decay has ever been observed. In particular, we concentrate on the decay $Λ_b^0\to p\bar pn$, which is the simplest purely baryonic decay mode, with solely spin-1/2 baryons involved. We predict its dec…
The newly observed $X, Y, Z$ exotic states are definitely not in the standard $Q\bar Q'$ structures, thus their existence composes a challenge to our understanding on the fundamental principles of hadron physics. Therefore the studies on their decay patterns which are determined by the non-perturbative QCD will definitely shed light on the concerned physics. Generally the four-quark states might be in a molecular state or tetraquark or their mixture. In this work, we adopt the suggestion that $Y(4630)$ is a charmonium-like tetraquark made of a diquark and an anti-diquark. If it is true, its fa…
The observation of anomalies in the charged current $b\rightarrow c\bar{\ell}ν_{\ell}$ transitions hints the possibility of the existence of new physics beyond the standard model. Inspired by the work done in the beauty quark sector, we explore new physics in the charm quark sector with $c \rightarrow (s,d)\bar{\ell}ν_{\ell}$ charged current transitions. We analyze the decay modes $D_{(s)}^+ \to η^{(')} \bar{\ell} ν_{\ell}$ within an effective Lagrangian framework which includes both standard model and new physics contributions. We use the available experimental measurements of the semileptoni…
Exploring CP violation with $B_s^0 \to \bar{D^0} ϕ$ decays
我们注意到，从衰变$B_s^0(t) (\bar B_s^0 (t)) \to \bar D^0 ϕwithout any hadronic uncertainties. These decays are described by the color suppressed tree diagrams and hence are free from the penguin pollutions. We further demonstrate that γcan also be extracted with no hadronic uncertainties from an angular analysis of corresponding vector vector modes, $ B_s^0（t）（\bar B_s^0（t））\to \bar D^{* 0} $. Although the branching ratios for these decay modes are quite small $ { \cal O}（10^{-5}-10 ^{-6}）$的随时间变化的测量中确定弱相γ是可能的，这里提出的策略似乎对强子B工厂的“第二代”实验特别有意义。
In the present work, we assign the newly observed $P_c(4312)$ as a $I(J^P)= \frac{1}{2} (\frac{1}{2})^-$ molecular state composed of $Σ_c \bar{D}$, while $P_c(4440)$ and $P_c(4457)$ as $Σ_c \bar{D}^\ast$ molecular states with $I(J^P)= \frac{1}{2} (\frac{1}{2})^-$ and $\frac{1}{2} (\frac{3}{2})^-$, respectively. In this molecular scenario, we investigate the $P_c\to J/ψp$ process of these three states and further predict the ratios of the $\mathcal B(P_c\to J/ψp)$ and those of $\mathcal B(Λ_b\to P_c K)$ between these three states, which could serve as a crucial test of the present molecular sce…
Exploring the $t\bar{t}$ threshold at an electron-positron collider
School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University（北京大学物理学院和核物理与技术国家重点实验室）；Center for High Energy Physics, Peking University（北京大学高能物理中心）；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）
We examine scenarios in the Next-to-Minimal Supersymmetric Standard Model (NMSSM), where pair-produced squarks and gluinos decay via two cascades, each ending in a stable neutralino as Lightest Supersymmetric Particle (LSP) and a Standard Model (SM)-like Higgs boson, with mass spectra such that the missing transverse energy, $E_{T}^{\text{miss}}$, is very small. Performing two-dimensional parameter scans and focusing on the hadronic $H\rightarrow b\bar{b}$ decay giving a $b\bar{b}b\bar{b} + E_{T}^{\text{miss}}$ final state we explore the sensitivity of a current LHC general-purpose jets+$E_{T}…
In the light of the 125 GeV Higgs ($h$) discovery at the Large Hadron Collider (LHC), one of the primary goals of the LHC and possible future colliders is to understand its interactions more precisely. Here we have studied the $h$-$b$-$\bar b$-$γ$ effective interaction terms arising out of gauge invariant dimension six operators in a model independent setting, as a potential source of new physics. Their role in some detectable final states have been compared with those coming from anomalous $h$-$b$-$\bar b$ interactions. We have considered the bounds coming from the existing collider and other…
We investigate the possibility that scalar leptoquarks generate consequential effects on the flavor-changing neutral-current decays of charmed hadrons into final states with missing energy ($\not\!\!E$) carried away by either standard model or sterile neutrinos. We focus on scenarios involving the $R_2$, $\tilde R_2$, and $\bar S_1$ leptoquarks and take into account various pertinent constraints, learning that meson-mixing ones and those inferred from collider searches can be of significance. We find in particular that the branching fractions of charmed meson decays $D\to M\!\not\!\!E$, $M=π,ρ…
The recent measurements on $R_D$, $R_{D^*}$ and $R_{J/ψ}$ by three pioneering experiments, BaBar, Belle and LHCb, indicate that the notion of lepton flavour universality is violated in the weak charged-current processes, mediated through $b \to c \ell \bar ν_\ell$ transitions. These intriguing results, which delineate a tension with their standard model predictions at the level of $(2-3)σ$ have triggered many new physics propositions in recent times, and are generally attributed to the possible implication of new physics in $ b \to c τ\bar ν$ transition. This, in turn, opens up another avenue,…
In this work, the lepton-number-violating processes in $|ΔL|=2$ decays of $Λ_b^0$ baryon, $Λ_b^0 \to p π^+μ^- μ^-$ and $Λ_b^0 \to Λ_c^+ π^+μ^- μ^-$, are investigated for the first time, via an intermediate on-shell Majorana neutrino $N$ with a mass in the GeV scale. We explore the experimental sensitivity of these dimuon channels at the LHCb and CMS experiments, in which heavy neutrino lifetimes in the accessible ranges of $τ_N = [1, 100, 1000]$ ps are considered. For a integrated luminosity collected of 10 and 50 fb${}^{-1}$ at the LHCb and 30, 300 and 3000 fb${}^{-1}$ at the CMS, we found si…
Exploring interference between $P_{c \bar c}$ resonances and background in the pion-induced reaction
Hunan Normal University（湖南师范大学）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；The George Washington University（乔治华盛顿大学）；Lanzhou University of Technology（兰州理工大学）
In this study, we explore the detectability of heavy Higgs bosons in the $pp \to b\bar{b}H/A \to b\bar{b}t\bar{t}$ channel at a 100 TeV hadron collider within the semi-constrained Next-to-Minimal Supersymmetric Standard Model (NMSSM). We calculate their production cross sections and decay branching ratios, comparing these with simulation results from existing reference. We focus on the heavy, doublet-dominated CP-even Higgs $H$ and CP-odd Higgs $A$, with mass limits set below 10 TeV to ensure detectability. We find that at a collider with 3 ab$^{-1}$ of integrated luminosity, the potential for…
Exploring Higgs EFT in $t\bar{t}hh$ at High Luminosity LHC
Instituto de Física Teórica, Universidade Estadual Paulista (UNESP)（圣保罗州立大学理论物理研究所）；Departamento de Física Matemática, Instituto de Física, Universidade de São Paulo（圣保罗大学数学物理系物理研究所）；IRFU - CEA, University Paris-Saclay（巴黎萨克雷大学CEA IRFU）；The Hubert Curien Pluridisciplinary Institute, IPHC, CNRS/IN2P3（CNRS/IN2P3伊夫·居里多学科研究所）
Investigation of the resonances $X(4140)$ and $X(4274)$, which were recently confirmed by the LHCb Collaboration [1], is carried out by treating them as the color triplet and sextet $[cs][\bar{c}\bar {s}]$ diquark-antidiquark states with the spin-parity $J^{P}=1^{+}$, respectively. We calculate the masses and meson-current couplings of these tetraquarks in the context of QCD two-point sum rule method by taking into account the quark, gluon and mixed vacuum condensates up to eight dimensions. We also study the vertices $X(4140)J/ψϕ$ and $X(4274)J/ψϕ$, and evaluate corresponding strong couplings…
Exploring the flavour structure of the MSSM with rare K decays
在标准模型的最小超对称扩展中，我们对稀有K衰变，特别是两种中微子模式K+->pi+ nu nu bar和KL-> pi 0 nu bar进行了广泛的分析.我们分析了这些模式的分支比的期望，无论是在限制性的框架内的最小的味道违反假设，并在一个更一般的框架内与新的来源的味道对称性破坏。在这两种情况下，可以从两个中微子模式的精确测量中提取的信息在限制模型的参数空间方面是非常有用的，即使在考虑了高能对撞机产生的质谱的可能信息和B物理实验的约束之后。在存在新的味道对称性破缺源的情况下，对模型的附加的显著约束也可以从两个KL-> P10 1 + 1-模式导出。
We investigate Majorana dark matter in a new variant of $U(1)_{L_μ-L_τ}$ gauge extension of Standard Model, where the scalar sector is enriched with an inert doublet and a $(\bar{3},1,1/3)$ scalar leptoquark. We compute the WIMP-nucleon cross section in leptoquark portal and the relic density mediated by inert doublet components, leptoquark and the new $Z^{\prime}$ boson. We constrain the parameter space consistent with Planck limit on relic density, PICO-60 and LUX bounds on spin-dependent direct detection cross section. Furthermore, we constrain the new couplings from the present experimenta…
We perform an updated analysis on the searches for the anomalous FCNC Yukawa interactions between the top quark, the Higgs boson, and either an up or charm quark ($\rm tqh,\ q=u,\ c$). We probe the observability of the FCNC top-Higgs couplings through the processes $\rm e^- p\rightarrow ν_e \bar{t} \rightarrow ν_e h \bar{q}$ (signal.I) and $\rm \ e^- p \to ν_e h b$ (singal.II) at the proposed electron proton (ep) colliders, where the Higgs boson decays to a $\rm b\bar{b}$ pair. We find that at the high luminosity (1 $\rm ab^{-1}$) ep colliders where the electrons have a polarisation of $\rm 80…
The primordial heavy or superheavy dark matter that could be created during the reheating or preheating stage of the Universe can undergo QCD cascade decay process to produce leptons or $γ$ as end products. Although these could be rare decays, the energy involved in such decay process can influence 21-cm signal of hyperfine transition of neutral hydrogen during the reionization era. We explore in this work, possible multimessenger signals of such heavy dark matter decays. One of which could be the source of ultra high energy neutrino (of $\sim$ PeV energy regime) signals at IceCube detector wh…
