Exotic Decay Research Articles

Nanosecond anomaly detection with decision trees and real-time application to exotic Higgs decays

We present an interpretable implementation of the autoencoding algorithm, used as an anomaly detector, built with a forest of deep decision trees on FPGA, field programmable gate arrays. Scenarios at the Large Hadron Collider at CERN are considered, for which the autoencoder is trained using known physical processes of the Standard Model. The design is then deployed in real-time trigger systems for anomaly detection of unknown physical processes, such as the detection of rare exotic decays of the Higgs boson. The inference is made with a latency value of 30 ns at percent-level resource usage using the Xilinx Virtex UltraScale+ VU9P FPGA. Our method offers anomaly detection at low latency values for edge AI users with resource constraints.

ALP-assisted strong first-order electroweak phase transition and baryogenesis

Axion-like particles (ALPs) can be naturally lighter than the electroweak scale. We consider an ALP that couples to the Standard Model Higgs to achieve the strong first-order electroweak phase transition. We discuss the two-field dynamics of the phase transition and the associated computation in detail and identify the viable parameter space. The ALP mass can be from the MeV to GeV scale. Baryon asymmetry can be explained by local baryogenesis without violating the current electron and atom electric dipole moment bound in most of the viable parameter space. The viable parameter space can be probed through Higgs exotic decay, rare kaon decay, the electron and atomic electric dipole moment, and the effective number of neutrinos in the cosmic microwave background in the future. The gravitational-wave signal is too weak to be detected.

Rare and exclusive few-body decays of the Higgs, Z, W bosons, and the top quark

Abstract We perform an extensive survey of rare and exclusive few-body decays ---defined as those with branching fractions $\mathcal{B} \lesssim 10^{-5}$ and two or three final particles--- of the Higgs, Z, W bosons, and the top quark. Such rare decays can probe physics beyond the Standard Model (BSM), constitute a background for exotic decays into new BSM particles, and provide precise information on quantum chromodynamics factorization with small nonperturbative corrections. We tabulate the theoretical $\mathcal{B}$ values for almost 200 rare decay channels of the four heaviest elementary particles, indicating the current experimental limits in their observation. Among those, we have computed for the first time ultrarare Higgs boson decays into photons and/or neutrinos, H and Z radiative decays into leptonium states, radiative H and Z quark-flavour-changing decays, and semiexclusive top-quark decays into a quark plus a meson, while updating predictions for a few other rare H, Z, and top quark partial widths. The feasibility of measuring each of these unobserved decays is estimated for p-p collisions at the high-luminosity Large Hadron Collider (HL-LHC), and for $e^+e^-$ and p-p collisions at the future circular collider (FCC).

Search for an exotic decay of the Higgs boson into a Z boson and a pseudoscalar particle in proton-proton collisions at [formula omitted]

A search for an exotic decay of the Higgs boson to a Z boson and a light pseudoscalar particle (a), decaying to a pair of leptons and a pair of photons, respectively, is presented. The search is based on proton-proton collision data at a center-of-mass energy of s=13TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 138fb−1. The analysis probes pseudoscalar masses ma between 1 and 30 GeV, leading to two pairs of well-isolated leptons and photons. Upper limits at 95% confidence level are set on the Higgs boson production cross section times its branching fraction to two leptons and two photons. The observed (expected) limits are in the range of 1.1–17.8 (1.7–17.9)fb within the probed ma interval. An excess of data above the expected standard model background with a local (global) significance of 2.6 (1.3) standard deviations is observed for a mass hypothesis of ma=3GeV. Limits on models involving axion-like particles, formulated as an effective field theory, are also reported.

Pair production of the singlet vector-like B quark at the CLIC

Vector-like quarks (VLQs) are a common feature of many scenarios of new physics beyond the Standard Model (SM), which generally decay into a SM third-generation quark with a SM gauge boson or a Higgs boson. The presence of a new exotic decay mode of VLQs will reduce the branching ratios of these standard decay modes and thus relax the current mass exclusion limits from LHC experiments. Based on a model-independent framework, we investigate the prospect of discovering the pair production of the weak-singlet VLQ-B at the future 3-TeV Compact Linear Collider (CLIC), by focusing on the final states including one Z boson and four b-jets via two types of modes: Z→ℓ+ℓ-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\rightarrow \\ell ^{+}\\ell ^{-}$$\\end{document} and Z→νν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\rightarrow \ u {\\bar{\ u }}$$\\end{document}. By performing a rapid detector simulation of the signal and background events, and considering the initial state radiation and beamstrahlung effects, the exclusion limit at the 95% confidence level and the 5σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$5\\sigma $$\\end{document} discovery prospects are respectively obtained on the branching ratio of B→bZ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B\\rightarrow bZ$$\\end{document} and the VLQ-B masses at the future 3-TeV CLIC with an integrated luminosity of 5 ab-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}.

Two proton emission and other exotic decays in the 48Ni region with ACTAR TPC

Since the first indirect measurements of the two proton radioactivity in 2002 [1], some theoretical descriptions have been able to reproduce experimental results until the 2-proton radioactivity was established for 67Kr at RIKEN [2], with a lifetime about 20 times lower than expected. New theory inputs have recently been developed [3][4], predicting angular distributions of the emitted protons for some of the two proton emitters, that need to be confirmed experimentally. An experiment at GANIL/LISE3 facility was performed in May 2021 aiming to produce one of the 2 proton emitters (48Ni) and measure the angular distribution of the emitted protons. We used the ACTAR TPC detector to implant the ions and perform the tracking of their proton decays. In addition, other exotic nuclei in the 48Ni region were produced. For several of them we have found a first evidence of exotic decays such as β delayed 3- and 2-proton emission or low energy proton branches for β delayed single proton emission. The analysis of this decays will provide helpful experimental information about the structure and the partial decay schemes of these unstable nuclei.

Search for the exotic decay of the Higgs boson into two light pseudoscalars with four photons in the final state in proton-proton collisions at sqrt{s} = 13 TeV

A search for the exotic decay of the Higgs boson to a pair of light pseudoscalars, each of which subsequently decays into a pair of photons, is presented. The search uses data from proton-proton collisions at sqrt{s} = 13 TeV recorded with the CMS detector at the LHC that corresponds to an integrated luminosity of 132 fb−1. The analysis probes pseudoscalar bosons with masses in the range 15–62 GeV, coming from the Higgs boson decay, which leads to four well-isolated photons in the final state. No significant deviation from the background-only hypothesis is observed. Upper limits are set on the product of the Higgs boson production cross section and branching fraction into four photons. The observed (expected) limits range from 0.80 (1.00) fb for a pseudoscalar boson mass of 15 GeV to 0.26 (0.24) fb for a mass of 62 GeV at 95% confidence level.

Higgs rare and exotic decays at CMS and ATLAS

Higgs rare and exotic decays at CMS and ATLAS

Search for H → aa → 4b exotic decays and VBF HH → 4b with CEPC and ATLAS

Search for H → aa → 4b exotic decays and VBF HH → 4b with CEPC and ATLAS

New Geiger-Nuttall law for cluster radioactivity half-lives* *Supported in part by the National Natural Science Foundation of China (12175100, 11975132), the construct program of the key discipline in hunan province, the Research Foundation of Education Bureau of Hunan Province, China (18A237), the Shandong Province Natural Science Foundation, China (ZR2022JQ04), the Opening Project of Cooperative Innovation Center for Nuclear Fuel Cycle Technology and Equipment, University of South China (2019KFZ10), the Innovation Group of Nuclear and Particle Physics in USC, Hunan Provincial Innovation Foundation for Postgraduate (CX20210942)

In this study, derived from Balasubramaniam's formula [Phys. Rev. C 70, 017301 (2004)] and further considering the effect of the parent nucleus mass, blocking effect, and effect of reduced mass on cluster radioactivity half-lives, we propose a new Geiger-Nuttall law that is model-independent to systematically evaluate the half-lives of this process for 16 even-even nuclei and 10 odd-A nuclei. For comparison, a single universal curve for cluster radioactivity and α decay proposed by Poenaru [Phys. Rev. C 83, 014601 (2011)], a scaling law proposed by Horoi [J. Phys. G: Nucl. Part. Phys. 30, 945 (2004)], an extension of the Viola-Seaborg formula from α decay to cluster radioactivity proposed by Ren et al. [Phys. Rev. C 70, 034304 (2004)], a new semi-empirical formula for exotic cluster decay proposed by Balasubramaniam et al. [Phys. Rev. C 70, 017301 (2004)], and a unified formula for the half-lives of α decay and cluster radioactivity proposed by Ni et al. [Phys. Rev. C 78, 044310 (2008)] are also used. The calculated results of our new Geiger-Nuttall law are in good agreement with the experimental half-lives, with the least rms being 0.606, and are better than the compared values. Moreover, we extend this formula to predict the cluster radioactivity half-lives of 51 nuclei whose decay energies are energetically allowed or observed but not yet quantified in NUBASE2020.

Search for exotic decays of the Higgs boson into long-lived particles with jet pairs in the final state at CLIC

A study of the sensitivity of the CLIC_ILD detector model for massive long-lived particles produced in the decay of the Higgs boson is presented, using a data sample of e+e− collisions at sqrt{textrm{s}} = 350 GeV and sqrt{textrm{s}} = 3 TeV, corresponding to an integrated luminosity of 1 ab−1 and 3 ab−1, respectively. The sensitivity range covers long-lived particle lifetimes from 1 to 300 ps, masses between 25 and 50 GeV/c2, and a parent Higgs mass of 126 GeV/c2. Sensitivities to the production cross-section as a function of the long-lived-particle mass and lifetime are determined.

A novel hermetic detection system of KAPAE for measuring multiphoton decays of positronium

The detection system of the Kyungpook National University Advanced Positronium Annihilation Experiment (KAPAE) has a 4π coverage with fine segmentation for measuring multi- photon decays of positronium to improve the charge (C), charge-parity (CP), and charge-parity-time reversal (CPT) violations in lepton sector as well as for studying rare decays. In addition, various exotic decays of positronium can be studied with the KAPAE detector. In the KAPAE, all aspects of the detector design, fabrication, and data analysis for physics studies related to positronium annihilation are covered. In this paper, we describe the above-mentioned first fully assembled detection system developed for KAPAE, which consists of a trigger and a gamma-ray detector. The newly proposed multi-layered trigger consists of a 22Na positronium source deposited on a plastic scintillator and a silicon photomultiplier (SiPM), and the gamma-ray detector contains an aerogel at the centre in a nitrogen environment. The gamma-ray detector minimizes pile-up events by fine segmentation of 196 Bi4Ge3O12 (BGO) crystal scintillators, whose scintillation lights from both sides are readout by the SiPM. The signals of a 392-channel SiPM are fed to a preamplifier followed by a 65 MHz flash analog-to-digital converter (FADC). In this paper, the KAPAE detector design, fabrication, and performance are presented.

High event rate analysis technique for the dual-axis duo-lateral position-sensitive silicon detectors of FAUST

The dual-axis duo-lateral (DADL) position-sensitive silicon detector was developed to obtain precise position and energy information for detected charged particles. The Forward Array Using Silicon Technology (FAUST) is currently equipped with 68 DADL detectors backed by CsI(Tl) scintillators for the study of charged particle correlations in heavy-ion collisions where precise position and energy information is essential. When conventional signal processing electronics were used for the DADL detectors, a position dependence of the measured energy as well as distortions in the calculated particle positions were observed. In previous work, waveforms from the detector after preamplification were studied to better understand the features that give rise to these distortions; therein, a waveform analysis technique was developed to improve the energy resolution and linearity in position reconstruction. However, the reading and writing of waveforms for an entire detector array limits data collection rates and adds significant burden in data storage and analysis speed. In this work, the integrators of a Struck SIS3316 ADC were utilized to process 228Th source data to develop and optimize a new analysis method that captures the benefits of the waveform analysis technique while circumventing the waveform writing requirement. This integrator method – capable of 59keV (FWHM) energy resolution – was used in the collection of 35 MeV/nucleon 28Si + 12C collision data using FAUST to investigate exotic decays of highly excited highly deformed nuclei. In this data, a position resolution of 0.4mm (FWHM) was obtained for 25MeV α-particles; for α-particles near this energy that originate from 8Be ground state decays, a 8Be ground state width of 30keV (FWHM) was obtained. The impact of the energy-dependent DADL position resolution emergent from electronic noise on the quality of excited state measurement was modeled and compared to the experimental data.

First results for searches of exotic decays with NA62 in beam dump mode

We report the results of a search for dark photon in-flight decays to μ + μ − pairs at NA62. Dark photons could be produced by dumping protons onto a copper-iron absorber, reach the NA62 decay volume more than 80 m downstream of the dump and decay therein. The measurement is based on data collected in 2021 which correspond to 1.4 × 1017 dumped protons.

Probing highly collimated photon-jets with deep learning

Many extensions of the standard model (SM) predict the existence of axion-like particles and/or dark Higgs in the sub-GeV scale. Two new sub-GeV particles, a scalar and a pseudoscalar, produced through the Higgs boson exotic decays, are investigated. The decay signatures of these two new particles with highly collimated photons in the final states are discriminated from the ones of SM backgrounds using the Convolutional Neural Networks and Boosted Decision Trees techniques. The sensitivities of searching for such new physics signatures at the Large Hadron Collider are obtained.

Analysis methods to determine the bound-state beta-decay half-life of Thallium-205

Bound-state β−-decay is an exotic decay mode that produces temperature-dependent stability in nuclei. A striking example is 205Tl, in part because of its impact on the 205Pb/204Pb cosmochronometer—a short-lived ra-dionuclide clock that can provide unique constraints on s process material in the early solar system. The bound-state β−-decay of 205Tl was measured at GSI, where fully stripped 205Tl81+ ions were produced and stored in the Experimental Storage Ring. Decay occurred during storage producing increased 205Pb daughters with increased storage time. This contribution briefly outlines the experiment and describes analytical corrections required to extract the half-life.

A walk along the proton drip-line by β-decay spectroscopy

During the last decade we have carried out a systematic study of the β decay of neutron-deficient nuclei, providing rich spectroscopic information of importance for both nuclear structure and nuclear astrophysics. We present an overview of the most relevant achievements, including the discovery of a new exotic decay mode in the fp-shell, the β-delayed γ-proton decay in 56Zn, the first observation of the 2+ isomer in 52Co and the latest results on the heavier systems 60Ge and 62Ge. We also report on our deduced mass excesses in comparison with systematics and a recent measurement. Finally, we summarise our results on the half-lives of Tz = -1/2, -1 and -2 neutron-deficient nuclides, and analyse their trend.

Proton decay from quark and lepton compositeness

Within a chiral SU(15) gauge theory in which the Standard Model fermions are bound states of massless preons, we show that proton-decay operators are likely induced at the compositeness scale, Λpre. Our estimate of the limit imposed by searches for proton decays is Λpre> 104 TeV1/2 {C}_8^{1/4} {m}_{mathcal{Q}}^{1/2} , where C8 is a rescaled coefficient of an 8-prebaryon operator induced by SU(15) dynamics, and {m}_{mathcal{Q}} is the mass of a composite vectorlike quark. The latter has a lower limit related to the mass of a composite vectorlike lepton, which in turn is required by LHC searches to be above 1 TeV. For C8 in the 10−5 – 1 range, the lower limit on Λpre varies between 3 × 103 TeV and 5 × 104 TeV. We point out that exotic proton decay modes, into a π+ and a heavy right-handed neutrino, could be observed using the Super-Kamiokande or DUNE detectors.

Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar

The current experimental data allow for a sub-TeV colourless weak-singlet scalar or pseudoscalar. If such a singlet field is present together with TeV-range vectorlike top and bottom partners, there is a possibility that the heavy quarks decay dominantly to the singlet state and a third-generation quark, and the singlet state decays to quark and boson pairs. Such a possibility may arise in various models but it has not been explored experimentally, especially in the context of vectorlike-quark searches. We consider some minimal models, covering the possible weak representations of the top and bottom partners, that can be mapped to many well-motivated ultraviolet-complete theories. We chart out the possible interesting and unexplored signatures of the exotic decay of vectorlike quarks and identify benchmark points representing different signal topologies for the high luminosity LHC. We perform a general scan of the parameter space with the relevant direct search bounds and find that large regions, which do not require any fine-tuning, remain open for the unexplored channels. We also perform a simple projection study in the cleanest channel and indicate how other new but experimentally challenging channels can be used to probe more regions of the parameter space.

Cluster decays of 12Be excited states

An experimental study of the helium-cluster decays of the 12Be excited states has been performed using the 9Li + 7Li → α + α + 8He and 9Li + 7Li → α + 6He + 6He reactions at the 9Li beam energy of 74.8 MeV. At excitation energies between 10 and 25 MeV, the 12Be excited states decaying into the 4He + 8He, 6He + 6He, and 6He + 6He*(1.8 MeV, Jπ = 2+) have been observed. Most of the observed states decaying into the 4He + 8He and 6He + 6He correspond to previously reported states. The decay to the 6He + 6He*(1.8 MeV, Jπ = 2+) channel has been observed for the first time. Two of the five states observed in this new decay channel are also observed in the ground state channel 6He + 6He, while two may correspond to the 4He + 8He decaying states. The states around 13.5 and 20.0 MeV decay to the 6He + 6He and 4He + 8He channels, while the state around 22.3 MeV decays into all three decay channels examined. This experiment is complementary to all previous studies of the 12Be cluster states because of the different reaction mechanisms used for the population of the 12Be cluster states. The observation of the states at high excitations with these exotic decay properties strongly supports the molecular structure of the 12Be excited states.