Sensitivity to dark matter production at future e$^+$e$^-$ colliders

This report describes the physics potential and experiments at a future multi- TeV e+e collider based on the Compact Linear Collider (CLIC) technology. The physics scenarios considered include precision measurements of known quantities as well as the discovery potential of physics beyond the Standard Model. The report describes the detector performance required at CLIC, taking into account the interaction point environment and especially beaminduced backgrounds. Two detector concepts, designed around highly granular calorimeters and based on concepts studied for the International Linear Collider (ILC), are described and used to study the physics reach and potential of such a collider. Detector subsystems and the principal engineering challenges are illustrated. The overall performance of these CLIC detector concepts is demonstrated by studies of the performance of individual subdetector systems as well as complete simulation studies of six benchmark physics processes. These full detector simulation and reconstruction studies include beaminduced backgrounds and physics background processes. After optimisation of the detector concepts and adopting the reconstruction algorithms the results show very efficient background rejection and clearly demonstrate the physics potential at CLIC in terms of precision mass and cross section measurements. Finally, an overview of future plans of the CLIC detector and physics study is given and a list of key detector R&D topics needed for detectors at CLIC is presented.

A bstract We study the electromagnetic form factors of electrically neutral dark-sector particles in this paper. Concretely speaking, we focus on the operators that can lead to interactions of fermionic dark states with the Standard-Model (SM) photon, including both dimension-5 (the magnetic and electric dipole moments) and dimension-6 (the anapole moment and charge radius) operators. Correspondingly, instead of the SM-photon form factors, we employ hypercharge gauge-field form factors that can induce additional couplings to the SM Z -boson. Utilizing the mono-photon production channel at future linear electron-positron colliders, the International Linear Collider (ILC) and the Compact Linear Collider (CLIC), we demonstrate that tuning beam polarization allows for simultaneous enhancement of signal-event rates and suppression of dominant SM background events, i.e. neutrino-induced processes, and hence improvement of sensitivity reach. Our analysis reveals that ILC and CLIC can probe electromagnetic form factors of dark-sector particles up to about two orders of magnitude beyond existing experimental limits. We also estimate, at the order-of-magnitude level, the validity range of the effective-field-theory (EFT) approach we adopt, finding that for the dimension-5 operators the EFT remains valid in most of the parameter regions to which the ILC and CLIC can be sensitive, while it breaks down in the entire sensitivity region for the dimension-6 operators.

The International Linear Collider (ILC) and the Compact Linear Collider (CLIC) are the two options for a future high-energy, high-luminosity linear electron-positron collider. Both are expected to be built in stages, optimised for their physics potential. The main goals are the precision measurements of Higgs-boson and top-quark properties as well as direct and indirect searches for new physics Beyond Standard Model. In my talk I will review some of the latest results from both ILC and CLIC demonstrating their physics potential, pointing to similarities and complementarity of both projects.

We discuss the production of the doubly charged leptons in future linear electron positron colliders, such as the International Linear Collider and Compact Linear Collider. Such states are introduced in extended weak-isospin multiplets by composite models. We discuss the production cross section of and carry out analyses for hadronic, semi-leptonic and pure leptonic channels based on the full simulation performance of the silicon detector. The 3- and 5-sigma statistical significance exclusion curves are provided in the model parameter space. It is found that the hadronic channel could offer the most possible detectable signature.

Most of our universe is dark. It is dark literally—visible matter makes up only 5% of the energy density—and conceptually, as many outstanding questions remain unsolved. The discovery of particle dark matter would shed light on our dark universe and throw open a window on the highest energy scales. This research made progress toward dark matter and new particle searches in three ways. Extreme compact objects, such as black holes, neutron stars, and stellar cores, can parametrically increase the production rates of feebly interacting particles and yield observable signatures. Specifically, a process known as superradiance leads to exponential growth of the number of ultralight particles gravitationally bound to rotating black holes, and turns astrophysical black holes into particle detectors. This research broadened the scope of applicability of superradiance studies to particles with a wide range of interactions and masses, predicting multi messenger signals. When ultralight particles are produced as dark matter in the early universe, they can be detected directly in laboratory experiments. However, these feebly interacting particles lead to small signals that are inevitably difficult to tease out from backgrounds; their detection requires the theoretical development of unique signatures that can be searched for in low-noise experiments. Some dark matter particles could be detectable with thin film metamaterials combined with low noise single-photon detectors. This research develop the theoretical framework and supported experimental efforts for ambitious searches for a wider class of ultralight particles. Overall, the outcome of this theoretical particle physics program developed novel signatures of new dark matter particles, and thereby expanded the particle parameter space which can be explored with astrophysical observations and precision experiments.

Future large-scale particle accelerators, for example, the Future Circular Collider (FCC), the Compact Linear Collider (CLIC) and the International Linear Collider (ILC), will require significant RF drive power on the order of 100 MW. Thus, an RF source with high efficiency is preferable to minimise the overall power required. Klystrons represent an attractive RF source, with the current state of the art operating at efficiencies of up to 70%. Such devices feature monotonic bunching, where at the output cavity, a number of electrons will not be in the main bunch, and instead will be present in the anti-bunch, and therefore not contributing to the output power. Therefore, novel bunching methods, such as the Core Oscillation Method (COM), are worthy of investigation. By allowing the core of the electron beam to bunch and de-bunch between successive cavities, the number of electrons contained in the final bunch can increase, and therefore improve the efficiency of the device. Numerical simulation of klystrons featuring COM will be presented, with efficiencies of up to 85% being predicted thus far.

Energy consumption is a major concern for future large-scale high-energy accelerator projects such as the compact linear collider (CLIC), future circular collider (FCC), and international linear collider (ILC). Thus, efficient generation of microwave power recently gained new attention by the accelerator community. In response, we propose an innovative two-stage multibeam klystron (TS-MBK) concept. It combines a very high RF power generation efficiency (84%) with a compact and cost effective electro-mechanical configuration. This article presents the concept and design study of a 1.0-GHz, 24-MW klystron. The technological novelties and mitigation of issues specific to this concept are described. TS-MBK performance has been validated using particle-in-cell computer simulations.

The quest for the nature of dark matter has reached a historical point in time, with several different and complementary experiments on the verge of conclusively exploring large portions of the parameter space of the most theoretically compelling particle dark matter models. This focus issue on dark matter and particle physics brings together a broad selection of invited articles from the leading experimental and theoretical groups in the field. The leitmotif of the collection is the need for a multi-faceted search strategy that includes complementary experimental and theoretical techniques with the common goal of a sound understanding of the fundamental particle physical nature of dark matter. These include theoretical modelling, high-energy colliders and direct and indirect searches. We are confident that the works collected here present the state of the art of this rapidly changing field and will be of interest to both experts in the topic of dark matter as well as to those new to this exciting field.Focus on Dark Matter and Particle Physics ContentsDARK MATTER AND ASTROPHYSICSScintillator-based detectors for dark matter searches I S K Kim, H J Kim and Y D KimCosmology: small-scale issues Joel R PrimackBig Bang nucleosynthesis and particle dark matter Karsten Jedamzik and Maxim PospelovParticle models and the small-scale structure of dark matter Torsten BringmannDARK MATTER AND COLLIDERSDark matter in the MSSM R C Cotta, J S Gainer, J L Hewett and T G RizzoThe role of an e+e- linear collider in the study of cosmic dark matter M BattagliaCollider, direct and indirect detection of supersymmetric dark matter Howard Baer, Eun-Kyung Park and Xerxes TataINDIRECT PARTICLE DARK MATTER SEARCHES:EXPERIMENTSPAMELA and indirect dark matter searches M Boezio et alAn indirect search for dark matter using antideuterons: the GAPS experiment C J HaileyPerspectives for indirect dark matter search with AMS-2 using cosmic-ray electrons and positrons B Beischer, P von Doetinchem, H Gast, T Kirn and S SchaelAxion searches with helioscopes and astrophysical signatures for axion(-like) particles K Zioutas, M Tsagri, Y Semertzidis, T Papaevangelou, T Dafni and V AnastassopoulosThe indirect search for dark matter with IceCube Francis Halzen and Dan HooperDIRECT DARK MATTER SEARCHES:EXPERIMENTSGaseous dark matter detectors G Sciolla and C J MartoffSearch for dark matter with CRESST Rafael F Lang and Wolfgang SeidelDIRECT AND INDIRECT PARTICLE DARK MATTER SEARCHES:THEORYDark matter annihilation around intermediate mass black holes: an update Gianfranco Bertone, Mattia Fornasa, Marco Taoso and Andrew R ZentnerUpdate on the direct detection of dark matter in MSSM models with non-universal Higgs masses John Ellis, Keith A Olive and Pearl SandickDark stars: a new study of the first stars in the Universe Katherine Freese, Peter Bodenheimer, Paolo Gondolo and Douglas SpolyarDetermining the mass of dark matter particles with direct detection experiments Chung-Lin ShanThe detection of subsolar mass dark matter halos Savvas M KoushiappasNeutrino coherent scattering rates at direct dark matter detectors Louis E StrigariGamma rays from dark matter annihilation in the central region of the Galaxy Pasquale Dario Serpico and Dan HooperDARK MATTER MODELSThe dark matter interpretation of the 511 keV line Céline BoehmAxions as dark matter particles Leanne D Duffy and Karl van BibberSterile neutrinos Alexander KusenkoDark matter candidates Lars BergströmMinimal dark matter: model and results Marco Cirelli and Alessandro StrumiaShedding light on the dark sector with direct WIMP production Partha Konar, Kyoungchul Kong, Konstantin T Matchev and Maxim PerelsteinAxinos as dark matter particles Laura Covi and Jihn E Kim

The presence of a non-baryonic Dark Matter (DM) component in the Universe is motivated from the observation of its gravitational interaction. Production of DM particles at LHC via weak interactions is a promising target. The ATLAS Collaboration has developed a broad search programme for DM candidates in final states with large missing transverse momentum produced in association with other SM particles (light and heavy quarks, photons, $Z$ and $H$ bosons, as well as additional heavy scalar particles) and searches where the Higgs boson provides a portal to Dark Matter, leading to invisible Higgs boson decays. The results of recent searches on 13 TeV $pp$ data from the LHC, their interplay and interpretation are presented.

New vectorlike quarks have been predicted in many scenarios of new physics beyond the Standard Model, which may be potentially discovered at the current and future high-energy colliders. Based on a model-independent framework, we study the single production process of the doublet vectorlike B-quark (VLQ-B) at the future Compact Linear Collider (CLIC) and explore the possible signals through the decay channel B→bh with subsequent decay mode of the Higgs boson: h→WW⁎→ℓνjj. By performing a rapid detector simulation of the signal and background events as well as considering the initial state radiation and beamstrahlung effects, the exclusion limit at the 95% confidence level and the 5σ discovery reach in the parameter spaces (the coupling strength κB and the VLQ-B mass) are obtained at the future 3 TeV CLIC with an integrated luminosity of 5 ab−1.

The GAPS experiment is designed to carry out a sensitive dark matter search by measuring low-energy cosmic ray antideuterons and antiprotons. GAPS will provide a new avenue to access a wide range of dark matter models and masses that is complementary to direct detection techniques, collider experiments and other indirect detection techniques. Well-motivated theories beyond the Standard Model contain viable dark matter candidates which could lead to a detectable signal of antideuterons resulting from the annihilation or decay of dark matter particles. The dark matter contribution to the antideuteron flux is believed to be especially large at low energies (E < 1 GeV), where the predicted flux from conventional astrophysical sources (i.e. from secondary interactions of cosmic rays) is very low. The GAPS low-energy antiproton search will provide stringent constraints on less than 10 GeV dark matter, will provide the best limits on primordial black hole evaporation on Galactic length scales, and will explore new discovery space in cosmic ray physics. Unlike other antimatter search experiments such as BESS and AMS that use magnetic spectrometers, GAPS detects antideuterons and antiprotons using an exotic atom technique. This technique, and its unique event topology, will give GAPS a nearly background-free detection capability that is critical in a rare-event search. GAPS is designed to carry out its science program using long-duration balloon flights in Antarctica. A prototype instrument was successfully flown from Taiki, Japan in 2012. GAPS has now been approved by NASA to proceed towards the full science instrument, with the possibility of a first long-duration balloon flight in late 2020. This presentation will motivate low-energy cosmic ray antimatter searches and it will discuss the current status of the GAPS experiment and the design of the payload.

If the mass of dark matter is generated from a cosmological phase transition involving the nucleation of bubbles, the corresponding bubble walls can filter out dark matter particles during the phase transition. Only particles with sufficient momentum to overcome their mass inside the bubbles can pass through the walls. As a result, the dark matter number density after the phase transition has a suppression factor $\exp(-M_\chi/2\tilde \gamma T)$, where $M_\chi$ is the dark matter mass, and $\tilde \gamma$ and $T$ are the Lorentz factor and temperature of the incoming fluid in the bubble wall rest frame, respectively. Under certain assumptions, we show that the filtering-out process can naturally provide a large suppression consistent with the observed dark matter density for a wide range of dark matter masses up to the Planck scale. Since the first-order phase transition is the decisive ingredient in our mechanism, a new connection is made between heavy dark matter scenarios and gravitational wave observations.

Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W^{±}W^{∓} or ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb^{-1} of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13TeV. The s→V(qq[over ¯])V(qq[over ¯]) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with m_{s}>160 GeV are excluded.

We study the effect of dark matter (DM) particles in the Sun, focusing in particular on the possible reduction of the solar neutrinos flux due to the energy carrie d away by DM particles from the innermost regions of the Sun, and to the consequent reduction of the temperature of the solar core. We find that in the very low-mass range between 4 and 10 Ge V, recently advocated to explain the findings of the DAMA and CoGent experiments, the e ffects on neutrino fluxes are detectable only for DM models with very small, or vanishing, self-annihilation cross section, such as the so-called asymmetric DM models, and we study the combination of DM masses and Spin Dependent cross sections which can be excluded with current solar neutrino data. Finally, we revisit the recent claim that DM models with large self-interacting cross sections can lead to a modification of the position of the convective zone, allevi ating or solving the solar composition problem. We show that when the ‘geometric’ upper limit on the capture rate is correctly taken into account, the effects of DM are reduced by orders of magnitude, and the position of the convective zone remains unchanged.

The Inert Doublet Model (IDM) is a simple extension of the Standard Model, introducing an additional Higgs doublet that brings in four new scalar particles. The lightest of the IDM scalars is stable and is a good candidate for a dark matter particle. The potential of discovering the IDM scalars in the experiment at the Compact Linear Collider (CLIC), an e^{+}e^{-} collider proposed as the next generation infrastructure at CERN, has been tested for two high-energy running stages, at 1.5 TeV and 3 TeV centre-of-mass energy. The CLIC sensitivity to pair-production of the charged IDM scalars was studied using the full detector simulation with Geant4 for selected high-mass IDM benchmark scenarios and the semi-leptonic final state. To extrapolate full simulation results to a wider range of IDM benchmark scenarios, the CLIC detector model defined in the Delphes fast simulation framework was modified to take into account the gamma gamma rightarrow had. beam-induced background. Results of the study indicate that heavy charged IDM scalars can be discovered at CLIC for most of the considered benchmark scenarios, up to masses of the order of 1 TeV.