Long-lived Exotic Particles Research Articles

Search for long-lived particles decaying to final states with a pair of muons in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13.6 TeV

An inclusive search for long-lived exotic particles (LLPs) decaying to final states with a pair of muons is presented. The search uses data corresponding to an integrated luminosity of 36.6 fb−1 collected by the CMS experiment from the proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13.6 TeV in 2022, the first year of Run 3 of the CERN LHC. The experimental signature is a pair of oppositely charged muons originating from a secondary vertex spatially separated from the proton-proton interaction point by distances ranging from several hundred μm to several meters. The sensitivity of the search benefits from new triggers for displaced dimuons developed for Run 3. The results are interpreted in the framework of the hidden Abelian Higgs model, in which the Higgs boson decays to a pair of long-lived dark photons, and of an R-parity violating supersymmetry model, in which long-lived neutralinos decay to a pair of muons and a neutrino. The limits set on these models are the most stringent to date in wide regions of lifetimes for LLPs with masses larger than 10 GeV.

Decays of a bino-like particle in the low-mass regime

We study the phenomenology associated with a light bino-like neutralino with mass \lsim m_{\tau}≲mτ in the context of the R-parity violating Minimal Supersymmetric Standard Model. This is a well-motivated example of scenarios producing potentially light and long-lived exotic particles, which might be testable in far-detector experiments, such as the FASER experiment at the Large Hadron Collider. A quantitative assessment of the discovery potential or the extraction of limits run through a detailed understanding of the interactions of the light exotic fermion with Standard Model matter, in particular, the hadronic sector. Here, we propose a systematic analysis of the decays of such a particle and proceed to a model-independent derivation of the low-energy effects, so that this formalism may be transposed to other UV-completions or even stand as an independent effective field theory. We then stress the diversity of the possible phenomenology and more specifically discuss the features associated with the R-parity violating supersymmetric framework, for example neutron-antineutron oscillations.

Search for long-lived particles decaying to a pair of muons in proton-proton collisions at sqrt{s} = 13 TeV

An inclusive search for long-lived exotic particles decaying to a pair of muons is presented. The search uses data collected by the CMS experiment at the CERN LHC in proton-proton collisions at sqrt{s} = 13 TeV in 2016 and 2018 and corresponding to an integrated luminosity of 97.6 fb−1. The experimental signature is a pair of oppositely charged muons originating from a common secondary vertex spatially separated from the pp interaction point by distances ranging from several hundred μm to several meters. The results are interpreted in the frameworks of the hidden Abelian Higgs model, in which the Higgs boson decays to a pair of long-lived dark photons ZD, and of a simplified model, in which long-lived particles are produced in decays of an exotic heavy neutral scalar boson. For the hidden Abelian Higgs model with m(ZD) greater than 20 GeV and less than half the mass of the Higgs boson, they provide the best limits to date on the branching fraction of the Higgs boson to dark photons for cτ(ZD) (varying with m(ZD)) between 0.03 and ≈0.5 mm, and above ≈0.5 m. Our results also yield the best constraints on long-lived particles with masses larger than 10 GeV produced in decays of an exotic scalar boson heavier than the Higgs boson and decaying to a pair of muons.

Neutrino physics and dark matter search with SHiP at CERN

SHiP (Search for Hidden Particles) is a new general purpose fixed target facility, proposed at the CERN SPS accelerator. In its initial phase the 400 GeV protons beam will be dumped on a heavy target with the aim of integrating [Formula: see text] pot in five years. A dedicated detector downstream the target will allow to probe a variety of models with the light long-lived exotic particles and masses below O(10) GeV/c2. The beam dump is also a copious source of neutrinos and in particular it is an ideal source of tau neutrinos, the less known particle in the Standard Model. We report the physics potential of such an experiment. We also describe an ancillary measurement of the charm cross-section carried out in July 2018.

The Use of the BIM Approach from the Conceptual Planning to the Construction Phase: The Case Study of the SHiP Experiment

The Search for Hidden Particles (SHiP) experiment is a new purpose fixed target facility proposed for the CERN Super Proton Synchrotron accelerator to search for long-lived exotic particles associated with Hidden Sectors and Dark Matter. This paper reports on the development of BIM integrated design for the SHiP experiment, applied initially to the Decay Volume, a >2000 m3 conical steel vessel under a vacuum hosting several large particle physics detector systems. A BIM methodology is used to address all the design phases of the Decay Volume of the SHiP experiment from the conceptual planning to the constructive drawings production. This proposed workflow is a basic plan to be repeated for each sub-component of the SHiP experiment in order to have a full and overall integration of the experiment. In particular, the Decay Volume’s geometrical and structural design and the simulation of its assembly process, both in factory and on site, are proposed. Moreover, the use of collaborative platforms to speed up the ideas exchange, as the basis of a highly multidisciplinary and complex project, is discussed. The complexity, multidisciplinary nature, and size of the SHiP project severely challenge design information management. The final plan to solve this issue is to have a BIM integrated design of each experiment sub-component, such as that demonstrated in this work for the Decay Volume, in order to have a full and multidisciplinary integration of the overall project.

The structural design of the decay volume for the Search for Hidden Particles (SHIP) project

The Search for Hidden Particles (SHiP) experiment is a new general-purpose fixed target facility proposed at the CERN Super Proton Synchrotron (SPS) accelerator to search for long-lived exotic particles associated with Hidden Sectors and Dark Matter. This paper reports on the structural design of SHiP’s decay volume, a > 2000 m3 conical vessel under vacuum that should host several large particle physics detector systems. In the field of structural and seismic engineering, the design study in a very multidisciplinary international collaboration has represented a stimulating research challenge. The goal of the design of the decay is to produce a structure as light and as slim as possible to stay within the geometrical envelop determined in the physics simulations. A complete study has been performed with all the steps from the conceptual design, including the interaction with other components and the plant systems, to the assembly procedures for the decay volume realization. The complexity of the case study has been driven by the need of finding the appropriate compromise between the physics performance, the structural aspects, the executive, constructive and operational issues, and the economical constraints. The assembly strategy, the welding techniques, and the expected construction time are discussed in view of the extremely complex installation phase. Building Integrated Model (BIM) methodology is also proposed as an essential tool to coordinate the entire process of designing and managing not only the decay volume but the entire project.

Fast convolutional neural networks for identifying long-lived particles in a high-granularity calorimeter

We present a first proof of concept to directly use neural network based pattern recognition to trigger on distinct calorimeter signatures from displaced particles, such as those that arise from the decays of exotic long-lived particles. The study is performed for a high granularity forward calorimeter similar to the planned high granularity calorimeter for the high luminosity upgrade of the CMS detector at the CERN Large Hadron Collider. Without assuming a particular model that predicts long-lived particles, we show that a simple convolutional neural network, that could in principle be deployed on dedicated fast hardware, can efficiently identify showers from displaced particles down to low energies while providing a low trigger rate.

Prospects of searches for long-lived charged particles with MoEDAL

We study the prospects of searches for exotic long-lived particles with the MoEDAL detector at the LHC, assuming the integrated luminosity of 30 fb^{-1} that is expected at the end of Run 3. MoEDAL incorporates nuclear track detectors deployed a few metres away from the interaction point, which are sensitive to any highly-ionizing particles. Hence MoEDAL is able to detect singly- or doubly-charged particles with low velocities beta < 0.15 or < 0.3, respectively, and lifetimes larger than {{mathcal {O}}}(1) ,mathrm{m}/c. We examine the MoEDAL sensitivity to various singly-charged supersymmetric particles with long lifetimes and to several types of doubly-charged long-lived particles with different spins and SU(2) charges. We compare the prospective MoEDAL mass reaches to current limits from ATLAS and CMS, which involve auxiliary analysis assumptions. MoEDAL searches for doubly-charged fermions are particularly competitive.

Status and Physics of the SHiP experiment at CERN

SHiP is a new general purpose fixed target facility, whose Technical Proposal has been recently reviewed by the CERN SPS Committee and by the CERN Research Board. The two boards recommended that the experiment proceeds further to a Comprehensive Design phase in the context of the new CERN Working group ”Physics Beyond Colliders”, aiming at presenting a CERN strategy for the European Strategy meeting of 2019. In its initial phase, the 400 GeV proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrating 2 × 1020 pot in 5 years. A dedicated detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow probing a variety of models with light long-lived exotic particles and masses below O(10) GeV/c2. The main focus will be the physics of the so-called Hidden Portals, i.e. search for Dark Photons, Light scalars and pseudo-scalars, and Heavy Neutrinos. The sensitivity to Heavy Neutrinos will allow for the first time to probe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could also be explained. Another dedicated detector will allow the study of neutrino cross-sections and angular distributions. ντ deep inelastic scattering cross sections will be measured with a statistics 1000 times larger than currently available, with the extraction of the F4 and F5 structure functions, never measured so far and allow for new tests of lepton non-universality with sensitivity to BSM physics.

Identification of new long-lived particles using deep neural networks

We present the development of a deep neural network for identifying generic displaced jets arising from the decays of exotic long-lived particles in data recorded by the CMS detector at the CERN LHC. Various jet features including detailed information about each clustered particle candidate as well as reconstructed secondary vertices are refined through the use of 1-dimensional convolution layers before being combined with high-level engineered features and passed through a series of fully-connected layers. The proper lifetime of the long-lived particle,cτ0, is treated as a parameter of the neural network model, which allows for hypothesis testing over several orders of magnitude ranging fromcτ0=1 µm to 10 m. Domain adaptation by backward propagation is performed to construct domain-independent features at an intermediate layer of the network to mitiage difference between simulation and data. The training is performed by streaming ROOT trees containingO(100M) jets directly into the TensorFlow queue system, which allows for a flexible selection of input features and asynchronous preprocessing. The application of the tagger is showcased in a search for long-lived gluinos as predicted by split supersymmetric models demonstrating significant gains in sensitivity over a reference analysis.

Mapping the material in the LHCb vertex locator using secondary hadronic interactions

Precise knowledge of the location of the material in the LHCb vertex locator (VELO) is essential to reducing background in searches for long-lived exotic particles, and in identifying jets that originate from beauty and charm quarks. Secondary interactions of hadrons produced in beam-gas collisions are used to map the location of material in the VELO. Using this material map, along with properties of a reconstructed secondary vertex and its constituent tracks, a p-value can be assigned to the hypothesis that the secondary vertex originates from a material interaction. A validation of this procedure is presented using photon conversions to dimuons.

Search for decays of stopped exotic long-lived particles produced in proton-proton collisions at sqrt{s}=13 TeV

A search is presented for the decays of heavy exotic long-lived particles (LLPs) that are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC and come to rest in the CMS detector. Their decays would be visible during periods of time well separated from proton-proton collisions. Two decay scenarios of stopped LLPs are explored: a hadronic decay detected in the calorimeter and a decay into muons detected in the muon system. The calorimeter (muon) search covers a period of sensitivity totaling 721 (744) hours in 38.6 (39.0) fb−1 of data collected by the CMS detector in 2015 and 2016. The results are interpreted in several scenarios that predict LLPs. Production cross section limits are set as a function of the mean proper lifetime and the mass of the LLPs, for lifetimes between 100 ns and 10 days. These are the most stringent limits to date on the mass of hadronically decaying stopped LLPs, and this is the first search at the LHC for stopped LLPs that decay to muons.

SHiP project as a new facility at intensity frontier

SHiP (Search for Hidden Particles) is a new general purpose fixed target facility suggested for SPS accelerator at CERN. The experiment is currently in Comprehensive Design Report preparation phase, aiming to become a part of European Strategy for Particle Physics update in 2019. In the initial phase of SHiP, the 400 GeV proton beam extracted from the SPS will be dumped on a heavy target producing 2 × 1020 protons on target in 5 years. A dedicated detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow probing a variety of models with light long-lived exotic particles and masses below O(10) GeV/c2. The main focus will be the physics of the so-called Hidden Portals, i.e. search for Dark Photons, Light scalars and Heavy Neutrinos. The sensitivity to Heavy Neutrinos will allow for the first time to probe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could be explained simultaneously. Another dedicated detector will allow the study of tau-neutrino physics.

SHiP: a new facility with a dedicated detector for studying tau-neutrino properties and nucleon structure functions

SHiP is a new general purpose fixed target facility, whose Technical Proposal has been recently reviewed by the CERN SPS Committee, who recommended that the experiment proceeds further to a Comprehensive Design phase. In its initial phase, the 400 GeV proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrating 2 × 1020 pot in 5 years. A dedicated detector downstream of the target will allow to probe a variety of models with light long-lived exotic particles and masses below a few GeV/c2. Another dedicated detector will allow the study of neutrino cross-sections and angular distributions, which was the focus of the poster. ντ deep inelastic scattering cross sections will be measured with a statistics 1000 times larger than currently available, with the extraction of the F4 and F5 structure functions, never measured so far and allow for new tests of lepton non-universality with sensitivity to BSM physics. Moreover, ντ’s will be distinguished from ’s, thus providing the first observation of the . With νµ scattering it will be possible to reduce by about 50% the current uncertainty on the strange content of the nucleon in the range of the x variable between 0.05 and 0.3, complementary to LHC measurements. The detector will be based on several techniques developed for the OPERA experiment at LNGS.

SHiP: a new facility with a dedicated detector to search for new neutral particles and studying tau neutrino properties

SHiP (Search for Hidden Particles) is a new general purpose fixed target facility, whose Technical Proposal has been recently reviewed by the CERN SPS Committee and by the CERN Research Board. The two boards recommended that the experiment proceeds further to a Comprehensive Design phase in the context of the new CERNWorking group Physics Beyond Colliders, aiming at presenting a CERN strategy for the European Strategy meeting of 2019. In the initial phase of SHiP, the 400 GeV proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrating 2×1020 pot in 5 years. A dedicated detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow probing a variety of models with light long-lived exotic particles and masses below O (10) GeV/c2 . The main focus will be the physics of the so-called Hidden Portals, i.e. search for Dark Photons, Light scalars and pseudo-scalars, and Heavy Neutrinos. The sensitivity to Heavy Neutrinos will allow for the first time to probe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could also be explained. Another dedicated detector will allow the study of neutrino cross-sections and angular distributions.

Search for Higgs-like bosons decaying into long-lived exotic particles.

A search is presented for massive long-lived particles, in the 20–60 {mathrm {Ge V!/}c^2} mass range with lifetimes between 5 and 100 mathrm{ps}. The dataset used corresponds to 0.62 text{ fb }^{-1} of proton-proton collision data collected by the LHCb detector at sqrt{s} =7mathrm {,Te V} . The particles are assumed to be pair-produced by the decay of a Higgs-like boson with mass between 80 and 140 {mathrm {Ge V!/}c^2}. No excess above the background expectation is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime and of the Higgs-like boson mass.

SHiP: a new facility to search for heavy neutrinos and study ντ properties

SHiP (Search for Hidden Particles) is a newly designed fixed target facility, proposed at the CERN SPS accelerator, with the aim of complementing searches for New Physics at LHC by searching for light long-lived exotic particles with masses below a few GeV/c2. The sensitivity to Heavy Neutrinos will allow for the first time probing a region of the parameter space where Baryogenesis and active neutrino masses and oscillation could also be explained. A dedicated detector, based on OPERA-like bricks, will provide the first observation of the tau anti-neutrino. Moreover, ντ and ν̄τ cross-sections will be measured with a statistics 1000 times larger than currently available data and will allow extracting the F4 and F5 structure functions, never measured so far. Charm physics studies will be performed with significantly improved accuracy with respect to past experiments.

SHiP: a new multipurpose beam-dump experiment at the SPS

SHiP is an experiment to look for very weakly interacting particles at a new to be constructed beam-dump facility at the CERN SPS. The SHiP Technical Proposal has been submitted to the CERN SPS Committee in April 2015. The 400 GeV/c proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrat- ing 2× 10 20 proton on target in five years. A detector located downstream of the targe t, based on a long vacuum tank followed by a spectrometer and particle identifi cation de- tectors, will allow probing a variety of models with light long-lived exotic partic les and masses below a few GeV/c 2 . The main focus will be the physics of the so-called Hid- den Portals, i.e. search for Dark Photons, Light scalars and pseudo-scalars, and Heavy Neutral Leptons (HNL). The sensitivity to HNL will allow for the first time to pr obe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could also be explained. Integrated in SHiP is an Emulsion Cloud Chamber, already used in the OPERA experiment, which will allow to study active neutrino cross-sections and angular distributions. In par ticular SHiP can distinguish betweeno? and ¯ o?, and their deep inelastic scattering cross sections will be measured with statistics three orders of magnitude larger than currently available.

General limit on the relation between abundances of D andLi7in big bang nucleosynthesis with nucleon injections

The injections of energetic hadrons could have occurred in the early universe by decays of hypothetical long-lived exotic particles. The injections induce the showers of nonthermal hadrons via nuclear scattering. Neutrons generated at these events can react with $^7$Be nuclei and reduce $^7$Be abundance solving a problem of the primordial $^7$Li abundance. We suggest that thermal neutron injection is a way to derive a model independent conservative limit on the relation between abundances of D and $^7$Li in a hadronic energy injection model. We emphasize that an uncertainty in cross sections of inelastic $n+p$ scattering affects the total number of induced neutrons, which determines final abundances of D and $^7$Li. In addition, the annihilations of antinucleons with $^4$He result in higher D abundance and trigger nonthermal $^6$Li production. It is concluded that a reduction of $^7$Li abundance from a value in the standard big bang nucleosynthesis (BBN) model down to an observational two $\sigma$ upper limit is necessarily accompanied by an undesirable increase of D abundance up to at least an observational 12 $\sigma$ upper limit from observations of quasi-stellar object absorption line systems. The effects of antinucleons and secondary particles produced in the hadronic showers always lead to a severer constraint. The BBN models involving any injections of extra neutrons are thus unlikely to reproduce a small $^7$Li abundance consistent with observations.

Particle physics explanations for ultra-high energy cosmic ray events

The origin of cosmic ray events withE ≳ 1011 GeV remains mysterious. In this talk I briefly summarize several proposed particle physics explanations: a breakdown of Lorentz invariance, the ‘Z-burst’ scenario, new hadrons with masses of several GeV as primaries, and magnetic monopoles with mass below 1010 GeV as primaries. I then describe in a little more detail the idea that these events are due to the decays of very massive, long-lived exotic particles.