The decay $K_L \to invisible$ has never been experimentally tested. In the Standard Model (SM) its branching ratio for the decay into two neutrinos is helicity suppressed and predicted to be $Br(K_L \to ν\barν) \lesssim 10^{-10}$. We consider several natural extensions of the SM, such as two-Higgs-doublet (2HDM), 2HDM and light scalar, and mirror dark matter models, those main feature is that they allow to avoid the helicity suppression factor and lead to an enhanced $Br(K_L \to invisible)$. For the decay $K_L \to ν\barν$ the smallness of the neutrino mass in the considered 2HDM model is explained by the smallness of the second Higgs doublet vacuum expectation value. The small nonzero value of the second Higgs isodoublet can arise as a consequence of nonzero quark condensate. We show that taking into account the most stringent constraints from the $K \to π+invisible$ decay, this process could be in the region of $Br(K_L \to invisible) \simeq 10^{-8}-10^{-6}$, which is experimentally accessible. In some scenarios the $K_L \to invisible$ decay could still be allowed while the $K \to π+invisible$ decay is forbidden. The results obtained show that the $K_L \to invisible$ decay is a clean probe of new physics scales well above 100 TeV, that is complementary to rare $K \to π+invisible$ decay, and provide a strong motivation for its sensitive search in a near future experiment.
A class of extra dimensional models with a warped metric predict tunneling of a massive particle localized on our brane and escaping into additional dimensions. The experimental signature of this effect is the disappearance of the particle from our world, i.e. the particle $\to invisible$ decay. We point out that measurements of $Z\prime \to invisible$ decay width of a new heavy gauge boson $Z\prime$ at the CERN LHC can be effectively used to probe the existence of large extra dimensions. This result enhances motivations for a more sensitive search and study for this decay mode and suggests ad…
We examine in a model-independent manner the measurements that can be performed at B-factories with sensitivity to dark matter. If a singlet scalar, pseudo-scalar, or vector is present and mediates the Standard Model - dark matter interaction, it can mediate invisible decays of quarkonium states such as the $Υ$, $J/Ψ$, and $η$. Such scenarios have arisen in the context of supersymmetry, extended Higgs sectors, solutions the supersymmetric $μ$ problem, and extra U(1) gauge groups from grand unified theories and string theory. Existing B-factories running at the $Υ(4S)$ can produce lower $Υ$ res…
In the standard model the rate of the $π^0, η, η', K_S, K_L\to ν\overlineν$ decays is predicted to be extremely small. Therefore, observation of any of these mesons ($M^0$) decaying into an invisible final state would signal the presence of new physics. The Bell-Steinberger relation connects CP and CPT violation in the mass matrix to CP and CPT violation in all decay channels of neutral kaons. It is a powerful tool for testing CPT invariance in the $K^0-\overline{K}^0$ system, assuming that there are no significant undiscovered decay modes of either $K_S$ or $K_L$ which could contribute to the…
We explore the possibility that $Z'$ couplings can be probed using decay modes which involve neutrinos once Standard Model backgrounds are directly determined by the data itself. For some models, sufficient statistics are available at either the SSC or LHC to render these modes useful for coupling determinations, provided the mass of the $Z'$ is not much larger than 1 TeV, if we assume other new physics background sources are absent.
Quantum probes of invisible particles in top-quark pair production at the LHC
Barcelona Supercomputing Center（巴塞罗那超级计算中心）；Universitat de Barcelona（巴塞罗那大学）；Institut de Física d’Altes Energies（高能物理研究所）；The Barcelona Institute of Science and Technology（巴塞罗那科学技术研究所）；Institució Catalana de Recerca i Estudis Avançats（加泰罗尼亚研究与高等教育机构）
We investigate the potential of multivariate techniques to improve the LHC search for invisible Higgs decays in weak boson fusion. We find that in the coming runs the LHC will be able to probe an invisible Higgs width of 28% within a year and 3.5% during a high luminosity run. A significant improvement over these estimates requires an analysis of QCD radiation patterns down to 10 GeV. Such an analysis can improve the reach at the high luminosity run to 2%. Throughout our analysis we employ a conservative, data driven background determination.
In the Standard Model (SM) the branching ratio for the decay $K_L \to ν\barν$ into two neutrinos is helicity suppressed and predicted to be very small $ \leq O(10^{-17})$. We consider two natural extensions of the SM, such as two-Higgs-doublet model (2HDM) and the $ν$MSM with additional singlet scalar, those main features is that they can lead to an enhanced $Br(K_L \to invisible)$. In the 2HDM the smallness of the neutrino mass is explained due to the smallness of the second Higgs doublet vacuum expectation value. Moreover, the $ν$MSM extension with additional singlet field can explain the $(…
While the Higgs characterisation programme is well underway, direct signs for new physics beyond the Standard Model remain elusive. Performing a fit of fully differential Higgs production cross sections at the LHC to a subset of Higgs-relevant effective operators, we discuss the extent to which theoretical uncertainties can limit the sensitivity in such a new physics search programme. Extending the dimension-6 Higgs Effective Field Theory framework by introducing new light degrees of freedom that can contribute to an invisible (or undetectable) Higgs decay width $h \to ϕϕ$, we show how differe…
Observation of Higgs pair production is an important long term objective of the LHC physics program as it will shed light on the scalar potential of the Higgs field and the nature of electroweak symmetry breaking. While numerous studies have examined the impact of new physics on di-Higgs production, little attention has been given to the well-motivated possibility of exotic Higgs decays in this channel. Here we investigate the consequences of exotic invisible Higgs decays in di-Higgs production. We outline a search sensitive to such invisible decays in the $b\bar b+{\not \!\! E}_T$ channel. We…
Motivated by the experimental study of $J/ψ\toγ~+$ invisible decay by the CLEO Collaboration, we analyze the process $J/ψ\to γν\barν$, as the standard model background for this invisible decay, at the lowest order. Our investigation shows that Br($J/ψ\to γν\barν$) is far below the present experimental upper limit on the branching ratio of $J/ψ\toγ~+$ invisible, which indicates that some interesting room for new physics in this channel might be expected. We also present a similar analysis of the $η_c\to γν\barν$ decay.
In the Standard Model there are several canonical examples of pure leptonic processes involving the muon, the electron and the corresponding neutrinos which are connected by the crossing symmetry: i) the decay of muon, ii) the inverse muon decay, and iii) the annihilation of a muon and an electron into two neutrinos. Although the first two reactions have been observed and measured since long ago, the third process, resulting in the invisible final state, has never been experimentally tested. It may go either directly, or, at low energies, via the annihilation of a muon and an electron from an …
The LHC is well on track toward the discovery or exclusion of a light Standard Model (SM)-like Higgs boson. Such a Higgs has a very small SM width and can easily have large branching fractions to physics beyond the SM, making Higgs decays an excellent opportunity to observe new physics. Decays into collider-invisible particles are particularly interesting as they are theoretically well motivated and relatively clean experimentally. In this work we estimate the potential of the 7 and 8 TeV LHC to observe an invisible Higgs branching fraction. We analyze three channels that can be used to direct…
The first limit on the branching ratio of the electric charge-nonconserving invisible muon decay $Br(μ^+ \to invisible) < 5.2 \times 10^{-3}$ is obtained from the recently reported results on new determination of the Fermi constant from muon decays. The results of a feasibility study of a new proposed experiment for a sensitive search for this decay mode at the level of a few parts in 10^{11} are presented. Constrains on the $τ\to invisible$ decay rate are discussed. These leptonic charge-nonconserving processes may hold in four-dimensional world in models with infinite extra dimensions, thus …
Invisible particles frequently appear in final state in studying physics at colliders. Experimental precision is also low in measuring missing energy. In this paper, we propose a general approach for studying process involving invisible particles. We provided two kinematical observables which are sensitive to production kinematics in different regions, and hence are complementary. Usage of our approach is illustrated by three examples. It is shown that our observables are still useful in case of that the significance S/B is relatively low.
Vector boson fusion proposed initially as an alternative channel for finding heavy Higgs has now established itself as a crucial search scheme to probe different properties of the Higgs boson or for new physics. We explore the merit of deep-learning entirely from the low-level calorimeter data in the search for invisibly decaying Higgs. Such an effort supersedes decades-old faith in the remarkable event kinematics and radiation pattern as a signature to the absence of any color exchange between incoming partons in the vector boson fusion mechanism. We investigate among different neural network…
The invisible signals of right-handed sneutrino decays originating from a Z' are analysed at the Large Hadron Collider. The possibility of accessing these events helps disentangling the B-L extension of Minimal Supersymmetric Standard Model from more popular scenarios of Supersymmetry. We assess the scope of the CERN machine in establishing the aforementioned signatures when accompanied by mono-jet, single-photon or Z-radiation probes through sophisticated signal-to-background simulations carried out in presence of parton shower, hadronisation as well as detector effects. We find substantial s…
The dark photon ($A'$) production through the mixing with the bremsstrahlung photon from the electron scattering off nuclei can be accompanied by the dominant invisible $A'$ decay into dark-sector particles. In this work we discuss the missing energy signature of this process in the experiment NA64 aiming at the search for $A'\to invisible$ decays with a high-energy electron beam at the CERN SPS. We show the distinctive distributions of variables that can be used to distinguish the $A'\to invisible$ signal from background. The results of the detailed simulation of the detector response for the…
Braking protons at the EIC: from invisible meson decay to new physics searches
University of California Santa Cruz（加州大学圣克鲁兹分校）；Santa Cruz Institute for Particle Physics（圣克鲁兹粒子物理研究所）；Technion - Israel Institute of Technology（以色列理工学院）；Brookhaven National Laboratory（布鲁克海文国家实验室）；CERN（欧洲核子研究中心）；Massachusetts Institute of Technology（麻省理工学院）；Universität Zürich（苏黎世大学）
The Higgs invisible decay width may soon become a powerful tool to probe extensions of the Standard Model with dark matter candidates at the Large Hadron Collider. In this work, we calculate the next-to-leading order (NLO) electroweak corrections to the 125 GeV Higgs decay width into two dark matter particles. The model is the next-to-minimal 2-Higgs-doublet model (N2HDM) in the dark doublet phase, that is, only one doublet and the singlet acquire vacuum expectation values. We show that the present measurement of the Higgs invisible branching ratio, BR$(H \to$ invisible $< 0.11$), does not lea…
In this work we study the current bounds from the CEνNS process and meson invisible decays on generic neutrino interactions with sterile neutrinos in effective field theories. The interactions between quarks and left-handed SM neutrinos and/or right-handed neutrinos are first described by the low-energy effective field theory (LNEFT) between the electroweak scale and the chiral symmetry breaking scale. We complete the independent operator basis for the LNEFT up to dimension-6 by including both the lepton-number-conserving (LNC) and lepton-number-violating (LNV) operators involving right-handed…
Assuming flat universal extra dimensions, we demonstrate that for a light Higgs boson the process $pp\to W^*W^* +X \to Higgs,graviscalars +X \to invisible+X$ will be observable at the $5 σ$ level at the LHC for the portion of the Higgs-graviscalar mixing ($ξ$) and effective Planck mass ($M_D$) parameter space where channels relying on visible Higgs decays fail to achieve a $5 σ$ signal. Further, we show that even for very modest values of $ξ$ the invisible decay signal probes to higher $M_D$ than does the ($ξ$-independent) jets/$\gam$ + missing energy signal from graviton radiation. We also di…
We consider the process in which a Higgs particle is produced in association with jets and show that monojet searches at the LHC already provide interesting constraints on the invisible decays of a 125 GeV Higgs boson. Using the existing monojet searches performed by CMS and ATLAS, we show the 95% confidence level limit on the invisible Higgs decay rate is of the order of the total Higgs production rate in the Standard Model. This limit could be significantly improved when more data at higher center of mass energies are collected, provided systematic errors on the Standard Model contribution t…
We consider the mass measurement at hadron colliders for a decay chain of two steps, which ends with a missing particle. Such a topology appears as a subprocess of signal events of many new physics models which contain a dark matter candidate. From the two visible particles coming from the decay chain, only one invariant mass combination can be formed and hence it is naïvely expected that the masses of the three invisible particles in the decay chain cannot be determined from a single end point of the invariant mass distribution. We show that the event distribution in the $\log(E_{1T}/E_{2T})$…
Mass variable \sqrt{\hat{S}_{min}} and its variants were constructed by minimising the parton level center of mass energy that is consistent with all inclusive measurements. They were proposed to have the ability to measure mass scale of new physics in a fully model independent way. In this work we relax the criteria by assuming the availability of partial informations of new physics events and thus constraining this mass variable even further. Starting with two different classes of production topology, i.e. antler and non-antler, we demonstrate the usefulness of these variables to constrain t…
The traditional realm of astronomy is the observation and study of the largest objects in the Universe, while the traditional domain of high-energy physics is the study of the smallest things in nature. But these two sciences concerned with opposite ends of the size spectrum are, in Muir's words, bound fast by a thousand invisible cords that cannot be broken. In this essay I propose that collaborations of astronomers and high-energy physicists on common problems are beneficial for both fields, and that both astronomy and high-energy physics can advance by this close and still growing relations…
We analyze the extent to which the LHC and Tevatron results as of the end of 2012 constrain invisible (or undetected) decays of the Higgs boson-like state at ~ 125 GeV. To this end we perform global fits for several cases: 1) a Higgs boson with Standard Model (SM) couplings but additional invisible decay modes; 2) SM couplings to fermions and vector bosons, but allowing for additional new particles modifying the effective Higgs couplings to gluons and photons; 3) no new particles in the loops but tree-level Higgs couplings to the up-quarks, down-quarks and vector bosons, relative to the SM, tr…
New physics coupled to the Higgs boson may hide it in the standard decay channels to be investigated at LHC. We consider the models where new invisible dominant decay modes of the Higgs boson are responsible for this hiding. We propose to study at LHC the weak boson production associated with heavy quarks: our analysis revealed that boson pair invariant mass distribution is sensitive to both mass and width of the invisible Higgs boson, if it is not too far from the weak boson pair threshold. We present tree-level results for the most relevant cases of top quarks and of bottom quarks in Standar…
Using the Higgs boson mass $m_h=125$ GeV, the radiative Higgs decays $h\rightarrowγν_l\barν_l$ with $ν_l = ν_e,\,ν_μ$ and $ν_τ$ are analyzed in the standard model. Our calculation shows that the inclusive width of these processes, i.e., the sum of $Γ(h\toγν_l\barν_l)$ for ${ν_l=ν_e,ν_μ,ν_τ}$, is $1.41$ keV, which is about $15\%$ of $Γ(h\toγγ)$. Therefore, the observation of these channels in the future precise experiments may provide us some useful information on the Higgs physics both in the standard model and in its possible extensions.
We consider the strangeness-changing decays of hyperons into another baryon and missing energy which is carried away by a pair of invisible spinless bosons. Pursuing a model-independent approach and taking into account constraints from the kaon sector, we find that these hyperon modes can have large rates, especially if the bosons have parity-odd effective couplings to light quarks. In that case the rates could attain values which are well within the expected reach of the currently running BESIII experiment. Since the branching fractions of hyperon decays with missing energy are tiny in the st…
The measurement of the invisible Z-boson decay width at e+e- colliders can be done "indirectly", by subtracting the Z-boson visible partial widths from the Z-boson total width, or "directly", from the process e+e- -> γν\barν. Both procedures are sensitive to different types of new physics and provide information about the couplings of the neutrinos to the Z-boson. At present, measurements at LEP and CHARM II are capable of constraining the left-handed Zνν-coupling, 0.45 <~ g_L <~ 0.5, while the right-handed one is only mildly bounded, |g_R| <= 0.2. We show that measurements at a future e+e- li…
We propose to search the monophoton events at the BESIII detector and future Super Tau Charm Factory to probe the sub-GeV dark photon decay into lighter dark matter. We compute the cross section due to the dark photon associated a standard model photon production, and study the corresponding standard model irreducible/reducible backgrounds. By using the data about 17 fb$^{-1}$ collected at the BESIII detector since 2011, we derive new leading limits of the mixing strength $\varepsilon$, $\varepsilon\lesssim(1.1-1.6)\times 10^{-4}$, in the mass range of 0.04 GeV $\lesssim m_{A^\prime} \lesssim$…
We study the implication of $J/ψ$ decay into invisible particles for light sterile neutrino and sub-GeV dark matter (DM). The low-energy effective field theories (EFTs) are used for the description of general neutrino interactions and the Dirac fermion DM coupled to charm quark. For $J/ψ\to γ+{\rm invisible}$, we perform the likelihood fits for the individual neutrino and DM operators with distinct Lorentz structures and photon spectra. The limits on the decay branching fractions are obtained for different neutrino or DM scenarios and then converted to the lower bounds on the new energy scales…
Many extensions of the Standard Model (SM) predict new neutral vector bosons at energies accessible by the Large Hadron Collider (LHC). We study an extension of the SM with new chiral fermions subject to non-trivial anomaly cancellations. If the new fermions have SM charges, but are too heavy to be created at LHC, and the SM fermions are not charged under the extra gauge field, one would expect that this new sector remains completely invisible at LHC. We show, however, that a non-trivial anomaly cancellation between the new heavy fermions may give rise to observable effects in the gauge boson …
In this work, we sift a simple supersymmetric framework of late invisible decays to/of the gravitino. We investigate two cases where the gravitino is the lightest supersymmetric particle or the next-to-lightest supersymmetric particle. The next-to-lightest supersymmetric particle decays into two dark matter candidates and has a long lifetime due to gravitationally suppressed interactions. However, because of the absence of any hadronic or electromagnetic products, it satisfies the tight bounds set by big bang nucleosynthesis and cosmic microwaved background. One or both of the dark matter cand…
We performed a search for a new generic $X$ boson, which could be a scalar ($S$), pseudoscalar ($P$), vector ($V$) or an axial vector ($A$) particle produced in the 100 GeV electron scattering off nuclei, $e^- Z \to e^- Z X$, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such process was found in the full NA64 data set of $2.84\times 10^{11}$ electrons on target. We place new bounds on the $S, P, V, A$ coupling strengths to electrons, and set constraints on their contributions to the electron anomalous magnetic moment $a_e$, $|Δa_{X}| \lesssim 10^{-15} - 10^{-…
Vector boson fusion established itself as a highly reliable channel to probe the Higgs boson and an avenue to uncover new physics at the Large Hadron Collider. This channel provides the most stringent bound on Higgs' invisible decay branching ratio, where the current upper limits are significantly higher than the one expected in the Standard Model. It is remarkable that merely low-level calorimeter data from this characteristically simple process can improve this limit substantially by employing sophisticated deep-learning techniques. The construction of such neural networks seems to comprehen…
Invisible neutrino decay modes are difficult to target at laboratory experiments, and current bounds on such decays from solar neutrino and neutrino oscillation experiments are somewhat weak. It has been known for some time that Cosmology can serve as a powerful probe of invisible neutrino decays. In this work, we show that in order for Big Bang Nucleosynthesis to be successful, the invisible neutrino decay lifetime is bounded to be $τ_ν> 10^{-3}\,\text{s}$ at 95\% CL. We revisit Cosmic Microwave Background constraints on invisible neutrino decays, and by using Planck2018 observations we find …
The Higgs sector of the Standard Model offers a unique probe of the hidden sector. In this work, we explore the possibility of renormalizable Higgs couplings to the hidden sector vector fields which can constitute dark matter (DM). Abelian gauge sectors with minimal field content, necessary to render the gauge fields massive, have a natural Z_2 parity. This symmetry ensures stability of the vector fields making them viable dark matter candidates, while evading the usual electroweak constraints. We illustrate this idea with the Stueckelberg and Higgs mechanisms. Vector DM is consistent with the…
Several theories of particle physics beyond the Standard Model consider that neutrinos can decay. In this work we assume that the standard mechanism of neutrino oscillations is altered by the decay of the heaviest neutrino mass state into a sterile neutrino and, depending on the model, a scalar or a Majoron. We study the sensitivity of the forthcoming KM3NeT-ORCA experiment to this scenario and find that it could improve the current bounds coming from oscillation experiments, where three-neutrino oscillations have been considered, by roughly two orders of magnitude. We also study how the prese…
In models of Randall-Sundrum type orthopositronium (o-Ps) can disappear due to tunnelling into additional dimension(s). The experimental signature of this effect is the invisible decay of orthopositronium. We point out that this process may occur at a rate within two or three orders of magnitude of the present experimental upper limit. We discuss this in details and stress that the existence of invisible decay of orthopositronium in vacuum could explain the o-Ps decay rate puzzle. Thus, our result enhances the existing motivation and justifies efforts for a more sensitive search for o-Ps->invi…
A light Higgs boson with substantial branching ratio into invisible channels can occur in a variety of models with: light neutralinos, spontaneously broken lepton number, radiatively generated neutrino masses, additional singlet scalar(s) and/or right handed neutrinos in the extra dimensions of TeV scale gravity. We study the observability of the WH and ZH modes at LHC with H decaying invisibly, by carrying out a detailed simulation with two event generators HERWIG and PYTHIA and realistic detector simulations (GETJET and CMSJET). We find that the signal with `single lepton plus missing $E_T$'…
If the Higgs boson were the only particle within the LHC accessible range, precision measurement of the Higgs's properties would play a unique role in studying electroweak symmetry breaking as well as possible new physics. We try to use low energy experiments such as rare B decay to constrain a challenging decay mode of Higgs, in which a Higgs decays to a pair of light (\approx 1 \sim 2 GeV) SM singlet S and becomes invisible. By using the current experimental bound of rare decay B\to Kν\barν and computing the contribution of B\to K SS to (the) B\to K+\cancel{E}, we obtain an upper bound on th…
We recompute the invisible Higgs decay width arising from Higgs-graviscalar mixing in the ADD model, comparing the original derivation in the non-diagonal mass basis to that in a diagonal mass basis. The results obtained are identical (and differ by a factor of 2 from the original calculation) but the diagonal-basis derivation is pedagogically useful for clarifying the physics of the invisible width from mixing. We emphasize that both derivations make it clear that a direct scan in energy for a process such as $WW\to WW$ mediated by Higgs plus graviscalar intermediate resonances would follow a…
