Linear Collider Research Articles

Commissioning, characterisation and temperature stabilisation of a 22000 channel SiPM-on-tile hadron calorimeter system

With the successful construction and operation of a highly granular hadron calorimeter system, featuring ∼22000 individually read out SiPM-on-tile channels, the CALICE collaboration has set the next milestone in proving the scalability of the concept for a future high energy linear collider experiment. For this large sample of photosensors a new approach of quality control was required to sufficiently characterise and monitor device parameters for both, test bench and in-situ beam test data. In the presence of temperature fluctuations during operation, it was possible to stabilise the SiPM responses with a fully automated adjustment of the bias voltage based on frequent temperature measurements, thanks to the excellent parameter uniformity of the devices. This contribution presents the results of SiPM parameter studies during the construction and commissioning phase and reports about the system performance and the experience of automated temperature compensation at system level during operation.

The carbon footprint of proposed {mathrm{e}}^+{mathrm{e}}^- Higgs factories

The energy consumption of any of the {mathrm{e}}^+{mathrm{e}}^- Higgs factory projects that can credibly operate immediately after the end of LHC, namely three linear colliders (CLIC, operating at sqrt{s},=,380 GeV; and ILC and {mathrm{C}}^3, operating at sqrt{s},=,250 GeV) and two circular colliders (CEPC and FCC-ee, operating at sqrt{s},=,240 GeV), will be everything but negligible. Future Higgs boson studies may therefore have a significant environmental impact. This note proposes to include the carbon footprint for a given physics performance as a top-level gauge for the design optimisation and, eventually, the choice of the future facility. The projected footprints per Higgs boson produced, evaluated using the 2021 carbon emission of available electricity, are found to vary by a factor 100 depending on the considered Higgs factory project.

Explainable machine learning for breakdown prediction in high gradient rf cavities

The occurrence of vacuum arcs or radio frequency (rf) breakdowns is one of the most prevalent factors limiting the high-gradient performance of normal conducting rf cavities in particle accelerators. In this paper, we search for the existence of previously unrecognized features related to the incidence of rf breakdowns by applying a machine learning strategy to high-gradient cavity data from CERN's test stand for the Compact Linear Collider (CLIC). By interpreting the parameters of the learned models with explainable artificial intelligence (AI), we reverse-engineer physical properties for deriving fast, reliable, and simple rule-based models. Based on 6 months of historical data and dedicated experiments, our models show fractions of data with a high influence on the occurrence of breakdowns. Specifically, it is shown that the field emitted current following an initial breakdown is closely related to the probability of another breakdown occurring shortly thereafter. Results also indicate that the cavity pressure should be monitored with increased temporal resolution in future experiments, to further explore the vacuum activity associated with breakdowns.

Phenomenology of a 96 GeV Higgs boson in the 2HDM with an additional singlet

We discuss a $\ensuremath{\sim}3\ensuremath{\sigma}$ signal (local) in the light Higgs-boson search in the diphoton decay mode at $\ensuremath{\sim}96\text{ }\text{ }\mathrm{GeV}$ as reported by CMS, together with a $\ensuremath{\sim}2\ensuremath{\sigma}$ excess (local) in the $b\overline{b}$ final state at the Large Electron Positron Collider (LEP) in the same mass range. We interpret this possible signal as a Higgs boson in the 2 Higgs doublet model type II with an additional Higgs singlet, which can be either complex (2HDMS) or real (N2HDM), where the 2HDMS so far has never been analyzed as an explanation of these excesses. An emphasis of our work is the differences between and the possible distinction of the two models in this context. We find that the lightest $\mathcal{C}\mathcal{P}$-even Higgs boson of the two models can equally yield a perfect fit to both excesses simultaneously, while the second lightest state is in full agreement with the Higgs-boson measurements at 125 GeV, and the full Higgs-boson sector is in agreement with all Higgs exclusion bounds from LEP, the Tevatron and the LHC as well as other theoretical and experimental constraints. We derive bounds on the 2HDMS and N2HDM Higgs sectors from a fit to both excesses and describe how this signal can be further analyzed at future ${e}^{+}{e}^{\ensuremath{-}}$ colliders, such as the International Linear Collider (ILC). We analyze in detail the anticipated precision of the coupling measurements of the 96 GeV Higgs boson at the ILC. We find that these Higgs-boson measurements at the LHC and the ILC cannot distinguish between the two Higgs-sector realizations.

Optimized design method study for cavity BPM system

Beam-based alignment and feedback systems are essential for the operation of the Free Electron Lasers (FELs) and Linear colliders. They require a certain number of beam position monitors (BPMs) at selected locations and that their resolution can reach hundreds of nanometers or even the order of nanometers. Cavity BPMs adopting a resonant cavity structure having the advantage of high position resolution are widely used in the field of accelerators. A typical system includes a cavity BPM pickup, a radio frequency signal conditioning front-end and a digital signal processing electronic. How to systematically analyze the impact of the key parameters of each subsystem on the performance of the whole system, and combine the requirements of the system, operation mode of the facilities, the current level of equipment processing and the development of the electronics, so as to achieve the optimal and balanced allocation of the key technical indicators of each subsystem, is the primary issue to be considered when designing a CBPM system. In this paper, based on theoretical analysis, the relationship between the relative amplitude extraction uncertainty of the CBPM system and the key parameters of each subsystem is proposed, which could provide clear guidance for the design and optimization of a CBPM system. In addition, considering the engineering requirements of the Shanghai High repetition rate X-ray Free Electron Laser and Extreme Light facility (SHINE) for beam position monitor, the allocation of the key technical indicators of the CBPM system using the optimized design method is also introduced. Accordingly, the development of each subsystem was completed, and the beam test bench was also built at the Shanghai Soft X-ray FEL facility (SXFEL), based on the evaluation method of divided power, the beam experiment results show that the position measurement uncertainty of the CBPM system can reach 40 nm at the bunch charge of 100 pC, which is consistent with the theoretical analysis results and better than the requirements of the SHINE.

Self-stabilizing positron acceleration in a plasma column

Plasma accelerators sustain extreme field gradients, and potentially enable future compact linear colliders. Although tremendous progress has been achieved in accelerating electron beams in a plasma accelerator, positron acceleration with collider-relevant parameters is challenging. A recently proposed positron acceleration scheme relying on the wake generated by an electron drive beam in a plasma column has been shown to be able to accelerate positron witness beams with low emittance and low energy spread. However, since this scheme relies on cylindrical symmetry, it is possibly prone to transverse instabilities that could lead, ultimately, to beam break-up. In this article, we show that the witness beam itself is subject to various damping mechanisms and, therefore, this positron acceleration scheme is inherently stable towards misalignment of the drive and witness beams. This enables stable, high-quality plasma-based positron acceleration.

Search for noncommutative interactions in gamma gamma rightarrow gamma gamma process at the LHC

The noncommutative QED (NCQED) has a non-Abelian nature due to the presence of 3- and 4-photon vertices in the lagrangian. Thus, NCQED predicts a new physics contribution to the gamma gamma rightarrow gamma gamma scattering already at the tree level. We have examined NCQED by studying the light-by-light process at the 14 TeV LHC with intact protons. Our results show that the NC scale up to Lambda _{mathrm {NC}} = 1.64(1.35) TeV can be probed in the pprightarrow p(gamma gamma )p rightarrow p'(gamma gamma )p' collision for the time-space (space-space) NC parameters. These bounds are stronger than the limits that can be obtained in the light-by-light scattering at high energy linear colliders.

Searching for the QCD axion with the proposed International Linear Collider beam facility

One of the most promising methods to search for axions is a light-shining-through-walls (LSW) experiment. In this work, we discuss the possibility of performing a LSW experiment at the International Linear Collider facility, where photon beams are generated for positron production. The photon beam is energetic and intense; the energy is of order MeV and the number of photons is about ${10}^{24}$ per year. Because of the high energy and intensity, this LSW experiment can probe a parameter region of the axion unexplored by previous ground-based experiments.

Inclusive J/ψ photoproduction at the ILC within the framework of non-relativistic QCD

Based on the non-relativistic quantum chromodynamics factorization framework, we study the inclusive J/ψ photoproduction at the future high energy e+e− collider, International Linear Collider(ILC), where the initial photons come from the back-scattering of laser and electron (positron). The intermediate states, coverline{c} (3 {S}_1^{left[mathbf{1}right]} ,1 {S}_0^{left[mathbf{8}right]} ,3 {S}_1^{left[mathbf{8}right]} , 3 {P}_{0,1,2}^{left[mathbf{8}right]} ), and resolved photoproduction processes are considered. Numerical results show that the cross section of J/ψ photoproduction at the ILC could be very large, and the single resolved pro- cess via coverline{c} (3 {S}_0^{left[mathbf{8}right]} ) intermediate state dominates primarily the production. We also present various kinematic distributions for J/ψ photoproduction. Combining the high luminosity of the collision, J/ψ photoproduction at the ILC shall provide a good platform to test the NRQCD factorization.

Search for the singlet vector-like lepton through the pair production in the Wν τ channel at the ILC

We study the pair production of the vector-like lepton singlet decaying into at the International Linear Collider (ILC) with the center-of-mass in a simplified model. Considering the polarized degrees of electron and photon beams , , we implement a detailed detector simulation of the signal and backgrounds. For comparison, we investigate the search at leptonic channel and hadronic channel of the W boson, respectively. We find that the ILC can exclude (discover) the region [180 GeV, 240 GeV] with an integrated luminosity of ([0.305, 1.102] ) in the hadronic channel, and can exclude (discover) the region [180 GeV, 240 GeV] with an integrated luminosity of [1.83, 19.4] ([11.7, 117.8] ) in the leptonic channel. If these two results are combined, we find that the ILC can exclude (discover) the region [180 GeV, 240 GeV] with lower integrated luminosity.

Study on Conduction Cooling of Superconducting Magnets for the ILC Main Linac

In the main linac of the International Linear Collider (ILC), superconducting magnets for beam focusing and steering will be located periodically in superconducting RF (SRF) cavity string for beam acceleration in common cryomodules. A concept of conduction cooling of the combined-functioned, splittable superconducting magnets has been proposed and investigated to adapt much different features and to meet different requirements for the superconducting magnet and SRF cavity in fabrication, assembly, and operation. It is required to integrate the superconducting magnet after the SRF cavity string assembly which completed under an ultra-clean environment. The magnet must be conductively cooled down through thermal links to a liquid helium supply pipe. According to this concept, a model magnet development was carried out in cooperation with Fermilab and KEK, and has been demonstrated in KEK superconducting RF test facility (STF). In addition, an important issue has been recently identified. High gradient SRF cavities naturally emit field emission electron flux from the inner surface, so-called dark current. It may pass through the subsequent SRF cavity string and penetrate into the superconducting magnets placed downstream. It may heat up the superconducting coils, and may cause a quench. Therefore, further study on reliable conduction cooling and to secure the superconducting magnet operation with a keeping sufficient safety margin is quite essential. In this paper, we report the installation, the improvement achieved in STF, and the R&D progress in the study on the conduction cooling of the superconducting magnet for the ILC main linac.

Pair-production of the charged IDM scalars at high energy CLIC

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.

Dark Z at the International Linear Collider

A dark Z is a massive Abelian gauge boson which is coupled to the Standard Model through both kinetic and mass mixing with the electroweak sector. We study the phenomenology of the dark Z at an energy-frontier electron-positron collider, such as the proposed International Linear Collider (ILC). We show that precision electroweak constraints and the current bounds from the hadron colliders allow a dark Z that is kinematically accessible at the ILC with 250 GeV or 500 GeV center-of-mass energy. Further, the reach of the ILC searches for a dark Z significantly exceeds the expected reach of the high luminosity LHC. If a signal consistent with a dark Z is discovered, it would motivate a dedicated run of the ILC at the center-of-mass energy matching the dark Z mass. We demonstrate that a short one month run at design luminosity could measure the dark Z chiral couplings to fermions with percent precision. This measurement can be used to discriminate between competing theoretical models of the resonance: for example, the dark Z can be distinguished from a dark photon with purely kinetic mixing.

Searching for a vector-like B quark through a tW decay channel at future electron–positron colliders

Vector-like quarks are predicted by several theoretical scenarios of new physics which could solve the hierarchy problem in particular and might be produced through electroweak interactions. In this work, we investigate the prospects for discovering the SU(2) singlet vector-like bottom quark (VLQ-B) in e^{+}e^{-} collisions at the future proposed 3 TeV Compact Linear Collider (CLIC). The analysis is performed within the framework of a simplified model featuring only two free parameters: the VLQ-B mass m_B and the coupling constant g^{*}. We study its single production process e^{+}e^{-}rightarrow B{bar{b}} and perform a detailed analysis in the decay channel Brightarrow tW^{-} at the 3 TeV CLIC. The 2sigma exclusion limit and 5sigma discovery prospects are obtained for the model parameters, respectively. Our results show that the future CLIC will be an ideal hunting ground for such vector-like quarks which have electroweak interactions.

Bhabha scattering in the gauge-Higgs unification

We examine effects of $Z'$ bosons in gauge-Higgs unification (GHU) models at $\mathrm{e}^{+}\mathrm{e}^{-}\to \mathrm{e}^{+}\mathrm{e}^{-}$ Bhabha scatterings. We evaluate differential cross sections in Bhabha scatterings including $Z'$ bosons in two types of $\mathrm{SO}(5) \times \mathrm{U}(1) \times \mathrm{SU}(3)$ GHU models. We find that deviations of differential cross sections in the GHU models from those in the SM can be seen at $\sqrt{s} = 250\,\mathrm{GeV}$. With $80\%$-longitudinally polarized electron and $30\%$-longitudinally polarized positron beams, the left-right asymmetries in the GHU A- and B-models are resolved at more than $3\,\sigma$ at $L_{\rm int} =250\,\mathrm{fb}^{-1}$. We also show that Bhabha scattering with scattering angle less than 100 mrad can be safely used as luminosity measurements in $\mathrm{e}^{+}\mathrm{e}^{-}$ colliders since the effects of $Z'$ bosons are well suppressed for small scattering angle. We propose a new observable which can be measured at future TeV-scale $\mathrm{e}^{+} \mathrm{e}^{-}$ linear colliders.

Dark matter searches with mono-photon signature at future e$^+$e$^-$ colliders

As any e^++e^-− scattering process can be accompanied by a hard photon emission from the initial state radiation, the analysis of the energy spectrum and angular distributions of those photons can be used to search for hard processes with an invisible final state. Thus high energy e^++e^-− colliders offer a unique possibility for the most general search of Dark matter based on the mono-photon signature. We consider production of DM particles via a mediator exchange at the International Linear Collider (ILC) and Compact Linear Collider (CLIC) experiments taking into account detector effects within the Delphes fast simulation framework. Limits on the light DM production in a generic model are set for a wide range of mediator masses and widths. For mediator masses up to the centre-of-mass energy of the collider, results from the mono-photon analysis are more stringent than the limits expected from direct resonance searches in Standard Model decay channels.

Searches for invisible scalar decays at CLIC

The Compact Linear Collider (CLIC) is a proposed TeV-scale high-luminosity electron-positron collider at CERN. The first CLIC running stage, at 380 GeV, will focus on precision Higgs boson and top quark studies while the main aim of the subsequent high-energy stages, at 1.5 TeV and 3 TeV, is to extend the sensitivity of CLIC to different Beyond the Standard Model (BSM) scenarios. We studied the prospects for measuring invisible Higgs boson and additional heavy scalar decays using CLIC data at 380 GeV and 1.5 TeV. The analysis is based on the Whizard event generator, with fast simulation of the CLIC detector response parametrised by the Delphes package. We present the expected limits for the invisible decays of the 125 GeV Higgs boson, the cross section limits for production of an additional neutral Higgs scalar, assuming its invisible decays, and limits on the mixing angle between the SM-like Higgs boson and the new scalar of the "dark sector" in the framework of the vector-fermion dark matter model.

Pair production of charged IDM scalars at high energy CLIC

The Compact Linear Collider (CLIC) was proposed as the next energy-frontier infrastructure at CERN, to study e^++e^-− collisions at three centre-of-mass energy stages: 380,GeV, 1.5,TeV and 3,TeV. The main goal of its high-energy stages is to search for the new physics beyond the Standard Model (SM). The Inert Doublet Model (IDM) is one of the simplest SM extensions and introduces four new scalar particles: H^\pm±, A and H; the lightest, H, is stable and hence a natural dark matter (DM) candidate. A set of benchmark points is considered, which are consistent with current theoretical and experimental constraints and promise detectable signals at future colliders.Prospects for observing pair-production of the IDM scalars at CLIC were previously studied using signatures with two leptons in the final state. In the current study, discovery reach for the IDM charged scalar pair-production is considered for the semi-leptonic final state at the two high-energy CLIC stages. Full simulation analysis, based on the current CLIC detector model, is presented for five selected IDM scenarios. Results are then extended to the larger set of benchmarks using the Delphes fast simulation framework. The CLIC detector model for Delphes has been modified to take pile-up contribution from the beam-induced \gamma\gammaγγ interactions into account, which is crucial for the presented analysis. Results of the study indicate that heavy, charged IDM scalars can be discovered at CLIC for most of the proposed benchmark scenarios, with very high statistical significance.

Jet charge: A new tool to probe the anomalous [formula omitted] couplings at the EIC

We propose to probe the Zbb¯ interactions at the Electron-Ion Collider (EIC) by utilizing the average jet charge weighted single-spin asymmetry AebQ, which is induced by different cross sections of a left-handed and right-handed electron beam scattering off an unpolarized proton beam in the neutral current deeply-inelastic scattering processes with one observed b-tagged jet. This novel observable at the EIC is sensitive to the axial-vector component of the Zbb¯ coupling, providing similar information as the gg→Zh cross section measurement at the high-luminosity Large Hadron Collider, and is complementary to the single-spin asymmetry measurement at the EIC which is sensitive to the vector component of the Zbb¯ coupling. We show that the apparent degeneracy of the allowed Zbb¯ coupling in its vector and axial-vector components, implied by the Large Electron-Positron Collider (LEP) and the Stanford Linear Collider (SLC) precision electroweak data, can be broken by the AebQ measurement at the EIC. With a large enough integrated luminosity collected at the EIC, the measurement of AebQ could also resolve the long-standing discrepancy between bottom quark forward-backward asymmetry AFBb at the LEP and the Standard Model prediction, with a strong dependence on the b-tagging efficiency.

Full electroweak 𝒪(α) corrections to Higgs-boson production processes with beam polarization at the International Linear Collider

Abstract We present the full ${{\cal O}}(\alpha )$ electroweak radiative corrections to the production of nine Higgs bosons with beam polarization at the International Linear Collider (ILC). The computation is performed with the help of GRACE-Loop. We compare the full ${{\cal O}}(\alpha )$ electroweak radiative corrections with the factorized initial-state radiation (ISR) effects to estimate the pure weak corrections. This reveals that the pure weak corrections are not negligible and should be taken into account for precision measurements of the Higgs-boson property at the ILC experiments.