We propose a novel possibility to detect a very distinctive signal with more than four muons originating from pair-produced vector-like leptons decaying to a muon-philic $Z^\prime$ boson. These new particles are good candidates to explain the anomalies in the muon anomalous magnetic moment and the $b\to s\ell\ell$ processes. The doublet (singlet) vector-like leptons lighter than 1.3 (1.0) TeV are excluded by the latest data at the LHC if $\mathrm{BR}(E\to Z^\prime μ) = 1$. We also show that the excess in the signal region with more than five leptons can be explained by this scenario if the vector-like lepton is a weak singlet, with mass about 400 GeV and $\mathrm{BR}(E\to Z^\prime μ) = 0.25$. The future prospects at the HL-LHC are discussed.
The present anomaly in muon anaomalous magnetic moment can be explained by the presence of a muon-philic $X$ boson which could be a scalar particle or a vector particle with mass less than twice the mass of muon. The muon-philic $X$ boson could interestingly not be a parity eigenstate as well. If there exists such a boson, irrespective of its parity, it can be directly observed in the decay $J/ψ\to μ^- μ^+ X$ where $X$ remains invisible. We show that by using the angular distribution or the distribution of events in the square Dalitz plot, along with two well defined dimensionless ratios, one …
Motivated by the long-lasting $3.5σ$ discrepancy in the anomalous magnetic moment of muon, we consider a new muon-specific force mediated by a light gauge boson, $X$, with mass $m_X < 2m_μ$ and the coupling constant $g_X \sim (10^{-4}, 10^{-3})$. We show that the Belle~II experiment has a robust chance to probe such a light boson in $e^+ e^- \to μ^+ μ^- + X$ channel and cover the most interesting parameter space explaining the discrepancy with the planned target luminosity, $\int dt \ {\cal L}=50~{\rm ab^{-1}}$. The clean signal of muon-pair plus missing energy at Belle II can be a smoking gun…
DREAMuS: Dark matter REsearch with Advanced Muon Source
Shanghai Jiao Tong University（上海交通大学）；Advanced Energy Science and Technology Guangdong Laboratory（广东省实验室）；Institute of Modern Physics, CAS（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）
We propose a two-Higgs-doublet model in which one Higgs doublet has the same interactions with fermions as the SM, and another Higgs doublet only has the $μ$-$τ$ LFV interactions. Assuming that the Yukawa matrices are real and symmetric, we impose various relevant theoretical and experimental constraints, and find that the excesses of muon $g-2$ and lepton flavour universality in the $τ$ decays can be simultaneously explained in the region of small mass splittings between the heavy CP-even Higgs and the CP-odd Higgs ($m_A > m_H$). The multi-lepton event searches at the LHC can sizably reduce t…
We examine the possibilities of accommodating the muon $g-2$ anomaly reported by Fermilab in the 2HDM with a discrete $Z_4$ symmetry in which an inert Higgs doublet field ($H,~A,~H^\pm$) has the lepton flavor violation $μ$-$τ$ interactions. We study the case of light $H$ (5 GeV $<m_H<$ 115 GeV) and assume the Yukawa matrices to be real and symmetrical. Considering relevant theoretical and experimental constraints, especially for the multi-lepton searches at the LHC, we find the muon $g-2$ anomaly can be explained within $2σ$ range in the region of 5 GeV $<m_H<20$ GeV, 130 GeV $< m_A~(m_{H^\pm}…
Discrepancy between the measured value and the Standard Model prediction of the muon anomalous magnetic moment is a possible hint for new physics. A $Z^\prime$ particle with $μτ$ flavor violating couplings can give a large contribution to the muon anomalous magnetic moment due to the $τ$ mass enhancement at the one-loop level, and is known to explain the above discrepancy. In this paper, we study the potential of the Large Hadron Collider (LHC) for detecting such a $Z^\prime$ boson via the $p p \toμ^-μ^-τ^+τ^+ $ process. Earlier studies in the literature only considered the production channel …
We propose a minimal model which accommodates the long-standing anomaly of muon magnetic moment based on abelian discrete flavor symmetries. The standard model is extended by scalar doublets charged under a $Z_n$ lepton flavor symmetry. In these models, a large contribution to the muon magnetic moment can be obtained by the chirality enhancement from new scalar mediated diagrams without conflicting with the flavor symmetry. Thanks to the lepton flavor symmetry, these models automatically forbid lepton flavor violation. The minimal model is based on $Z_4$ symmetry with only one extra scalar dou…
The extension of Standard Model made by inclusion of additional $U(1)$ gauge $L_μ-L_τ$ symmetry can explain the difference between the measured and the predicted value of the muon magnetic moment and solve the tension in $B$ meson decays. This model predicts the existence of a new, light $Z^\prime$ vector boson, predominantly coupled to second and third generation leptons, whose interaction with electrons is due to a loop mechanism involving muons and taus. In this work, we present a rigorous evaluation of the upper limits in the $Z^\prime$ parameter space, obtained from the analysis of the da…
We analyze the decays to muons of a light dilaton produced via vector boson fusion at the LHC. We investigate models in which the electroweak symmetry breaking is triggered by a spontaneously broken, approximately conformal sector. Taking into account the possibility of shifts in the dilaton Yukawa couplings to muons, we find a rather promising scenario for the conformal model search in the channel, with the possibility for a dilaton discovery at a delivered luminosity of 100 fb-1 at the LHC or, alternatively, for an extension of the exclusion zone in the model parameter space, until now fixed…
Current LHC searches for non-supersymmetric singly-charged scalars, based on Two-Higgs-Doublet models, in general focus the analysis on third-generation fermions in the final state. However, singly-charged scalars in alternative extensions of the scalar sector involve Yukawa couplings not proportional to the mass of the fermions. Assuming the scalar decays into electrons and muons, it can manifest cleaner experimental signatures. In this paper we suggest that a singly-charged scalar singlet, with electroweak production, can start to be probed in the near future with dedicated search strategies…
Investigation of Higgs Boson Decaying to Di-muon, Dark Matter Produced in Association with a Higgs Boson Decaying to $b$-quarks and Unbinned Profiled Unfolding
We investigate the bounds on tau-mu lepton flavor violation (LFV). Our main focus is on the collider constrains on tau-mu LFV. We use the Type-III Two-Higgs-Doublet-Model (2HDM) as a set up for our study. While the LFV branching fraction of the 125 GeV is well constrained by current LHC searches, the heavier neutral states could have a large branching fraction to tau and muon. We estimate the LHC reach for the 13 TeV center of mass energy with 300 $\text{fb}^{-1}$ luminosity for a neutral boson decaying into a tau and a muon. We identify parts of the LFV parameter space where the searches for …
We analyse the muon longitudinal polarization asymmetry Δ_long in the decay K^+ --> π^+ μ^+ mu^-. It is stressed that, since the muon helicities are not Lorentz-invariant quantities, the magnitude of Δ_long depends in general on the reference frame. We consider the muon helicities in the LAB system, and study the sensitivity of the longitudinal polarization asymmetry to the flavour-mixing parameters in the Standard Model for stopped and in-flight decaying K^+. A similar analysis is carried out for the decay K_L --> μ^+ μ^-. We find that in both cases the asymmetry is diluted when increasing th…
In this paper the charged Higgs signal through the decay to a pair of muon and neutrino (H -> mu nu) is analyzed. The analysis attempts to estimate the amount of muonic signal of the charged Higgs at LHC at a center of mass energy of 14 TeV. The signal process is the top quark pair production with one of the top quarks decaying to a charged Higgs (non SM anomalous top quark decay) and the other decaying to a W boson which is assumed to decay hadronically to two light jets. Due to the small branching ratio of charged Higgs decay to muon, results are quoted for data corresponding to an integrate…
The MiniBooNE experiment has observed a significant excess of electron neutrinos in a muon neutrino beam at source-detector distances too short to be compatible with standard neutrino oscillations. The most straightforward explanation for this signal in terms of oscillations between Standard Model neutrinos and a new, sterile, neutrino, is disfavored by null results from experiments looking for muon neutrino disappearance. Here, we discuss the possibility that MiniBooNE data are instead explained by a sterile neutrino that decays quickly back into active neutrinos plus a light boson. The flavo…
In the internal shock model of gamma ray bursts ultrahigh energy muons, pions, neutrons and kaons are likely to be produced in the interactions of shock accelerated relativistic protons with low energy photons (KeV-MeV). These particles subsequently decay to high energy neutrinos/antineutrinos and other secondaries. In the high internal magnetic fields of gamma ray bursts, the ultrahigh energy charged particles ($μ^+$, $π^+$, $K^+$) lose energy significantly due to synchrotron radiations before decaying into secondary high energy neutrinos and antineutrinos. The relativistic neutrons decay to …
Various theories beyond the Standard Model predict the existence of heavy resonances decaying to Higgs (H) boson pairs. In order to maximize the sensitivity of searches for such resonances, it is important that experimental analyses cover a variety of decay modes. The decay of H boson pairs to four $τ$ leptons (HH$ \to ττττ$) has not been discussed in the literature so far. This decay mode provides a small branching fraction, but also comparatively low backgrounds. We present an algorithm for the reconstruction of the mass of the H boson pair in events in which the H boson pair decays via HH$ …
The muon $g-2$ anomaly was strengthened by recent experimental results at Fermilab, which may be signatures of new physics. A scenario of leptophilic scalar $ϕ_L$ accounting for the muon $g-2$ anomaly is investigated in this paper. Though a light $ϕ_L$ mainly decaying into standard model (SM) particles has been excluded by experiments, a dark leptophilic scalar $ϕ_L$ predominantly decaying into invisible fermionic dark matter (DM) $χ\barχ$ is still allowed. Considering the decay mode $ϕ_L \to χ\barχ$ opened (here $m_{ϕ_L} = 3 m_χ$), the coupling preferred by the muon $g-2$ and the $ϕ_L-χ$ coup…
We study a model with $U(1)_{L_μ- L_τ}$ gauge symmetry and discuss collider searches for a scalar boson, which breaks $U(1)_{L_μ- L_τ}$ symmetry spontaneously, decaying into light $Z'$ gauge boson. In this model, the new gauge boson, $Z'$, with a mass lighter than $\mathcal{O}(100)$ MeV, plays a role in explaining the anomalous magnetic moment of muon via one-loop contribution. For the gauge boson to have such a low mass, the scalar boson, $ϕ$ with $\mathcal{O}(100)$ GeV mass appears associated with the symmetry breaking. We investigate experimental constraints on $U(1)_{L_μ- L_τ}$ gauge coupl…
We study the search for an extra scalar $S$ boson produced in association with the $Z$ boson at the International Linear Collider (ILC). The study is performed at center-of-mass energies of 250 GeV and 500 GeV based on the full simulation of the International Large Detector (ILD). In order to be as model-independent as possible, the analysis uses the recoil technique, in particular with the $Z$ boson decaying into a pair of muons. As a result, exclusion cross-section limits are given in terms of a scale factor $k$ with respect to the Standard Model Higgs-strahlung process cross section. These …
This analysis shows a search for dark fermion particles produced in association with a heavy neutral gauge boson (Z$^{\prime}$). The studied events topology are dimuon and a large missing transverse momentum. %We considered the muonic decay of Z$^{\prime}$. The analyzed data were the Open Data collected by the CMS detector in proton-proton collisions at the LHC in 2012 and correspond to an integrated luminosity of 11.6 fb$^{-1}$ at $\sqrt{s} = $ 8 TeV. One benchmark scenario the light vector was used for interpreting the data, based on a simplified model so called the mono-Z$^{\prime}$ model. …
Connecting Vector-like Muons, pNGB Dark Matter and Electroweak Phase Transition through Collider and Gravitational Wave
Indian Institute of Technology Guwahati（印度理工学院古瓦哈提分校）；Gokhale Memorial Girls’ College（戈卡尔纪念女子学院）；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）
The spectrum of electrons from muons decaying in an atomic bound state is significantly modified by their interaction with the nucleus. Somewhat unexpectedly, its first measurement, at the Canadian laboratory TRIUMF, differed from basic theory. We show, using a combination of techniques developed in atomic, nuclear, and high-energy physics, that radiative corrections eliminate the discrepancy. In addition to solving that outstanding problem, our more precise predictions are potentially useful for interpreting future high-statistics muon experiments that aim to search for exotic interactions at…
We propose an explanation of the LSND evidence for electron antineutrino appearance based on neutrino decay. We introduce a heavy neutrino, which is produced in pion and muon decays because of a small mixing with muon neutrinos, and then decays into a scalar particle and a light neutrino, predominantly of the electron type. We require values of $g m_4\sim$ few eV, $g$ being the neutrino--scalar coupling and $m_4$ the heavy neutrino mass, e.g. $m_4$ in the range from 1 keV to 1 MeV and $g \sim 10^{-6} - 10^{-3}$. Performing a fit to the LSND data as well as all relevant null-result experiments,…
We explore the potential of the Large Hadron Collider to observe the h1 -> a1 a1 -> 4 muons signal from the lightest scalar Higgs boson (h1) decaying into the two lightest pseudoscalar Higgs bosons (a1), followed by their decays into four muons in the Next-to-Minimal Supersymmetric Standard Model (NMSSM). The signature under study applies to the region of the NMSSM parameter space in which m_a1 < 2 m_tau, which has not been studied previously. In such a scenario, the suggested strategy of searching for a four-muon signal with the appropriate background suppression would provide a powerful meth…
Many models of electroweak symmetry breaking have an additional light pseudoscalar. If the Higgs boson can decay to a new pseudoscalar, LEP searches for the Higgs can be significantly altered and the Higgs can be as light as 86 GeV. Discovering the Higgs boson in these models is challenging when the pseudoscalar is lighter than 10 GeV because it decays dominantly into tau leptons. In this paper, we discuss discovering the Higgs in a subdominant decay mode where one of the pseudoscalars decays to a pair of muons. This search allows for potential discovery of a cascade-decaying Higgs boson with …
Tel-Aviv University（特拉维夫大学）；Weizmann Institute of Science（魏茨曼科学研究所）；Max-Planck-Institut für Physik (Werner-Heisenberg-Institut)（马克斯·普朗克物理研究所（维尔纳·海森堡研究所））；University of California, Los Angeles（加州大学洛杉矶分校）
Sub-GeV light dark matter often requires new light mediators, such as a dark $Z$ boson in the $L_μ- L_τ$ gauge theory. We study the search potential for such a $Z^\prime$ boson via the process $μe^- \to μe^- X$, with $X$ decaying invisibly, in a muon on-target experiment using a high-intensity 1-10 GeV muon beam from facilities such as HIAF-HIRIBL. Events are identified by the scattered muon and electron from the target using silicon strip detectors in a single-station telescope system. Backgrounds are suppressed through a trained boosted decision tree (BDT) classifier, and activity in downstr…
A recent paper by the CDF collaboration suggests (but does not claim) an anomalous event sample containing muons produced with large impact parameter, often with high multiplicity and at small angles from one another. This curious hint of a signal is potentially consistent with the hidden valley scenario, as well as with some other classes of models. Despite its tenuous nature, this hint highlights the experimental difficulties raised by such signals, and merits some consideration. Some of the simplest interpretations of the data, such as a light neutral particle decaying to muon and/or tau pa…
Recent PAMELA data show that positron fraction has an excess above several GeV while anti-proton one is not. Moreover ATIC data indicates that electron/positron flux have a bump from 300 GeV to 800 GeV. Both annihilating dark matter (DM) with large boost factor and decaying DM with the life around $ 10^{26} s$ can account for the PAMELA and ATIC observations if their main final products are charged leptons ($e$, $μ$ and $τ$). In this work, we calculated the neutrino flux arising from $μ$ and $τ$ which originate from annihilating/decaying DM, and estimated the final muon rate in the neutrino te…
