We have developed a novel technique for the measurement of the avalanche fluctuation of gaseous detectors using a UV laser. The technique is simple and requires a short data-taking time of about ten minutes. Furthermore, it is applicable for relatively low gas gains. Our experimental setup as well as the measurement principle, and the results obtained with a stack of Gas Electron Multipliers (GEMs) operated in several gas mixtures are presented.

Cargo containers passing through ports are scanned by non-intrusive inspection systems to search for concealed illicit materials. By using two photon beams with different energy spectra, dual energy inspection systems are sensitive to both the area density and the atomic number of cargo contents. Most literature on the subject assumes a simple exponential attenuation model for photon intensity in which only free streaming photons are detected. However, this approximation neglects second order effects such as scattering, leading to a biased model and thus incorrect material predictions. This work studies the accuracy of the free streaming model by comparing it to simulation outputs, finding that the model shows poor atomic number reconstruction accuracy at high-Z and suffers significantly if the source energy spectra and detector response function are not known exactly. To address these challenges, this work introduces a semiempirical transparency model which modifies the free streaming model by rescaling different components of the mass attenuation coefficient, allowing the model to capture secondary effects ignored by the free streaming model. The semiempirical model displays improvement agreement with simulated results at high-Z and shows excellent extrapolation to materials and thicknesses which were not included during the calibration step. Furthermore, this work demonstrates that the semiempirical model yields accurate atomic number predictions even when the source spectra and detector response are not known exactly. Using the semiempirical model, manufacturers can perform a simple calibration to enable more precise Z reconstruction capabilities, which has the potential to significantly improve the performance of existing dual energy radiographic systems.

Cargo containers passing through ports are scanned by non-intrusive inspection systems to search for concealed illicit materials. By using two photon beams with different energy spectra, dual energy inspection systems are sensitive to both the area density and the atomic number of cargo contents. Most literature on the subject assumes a simple exponential attenuation model for photon intensity in which only free streaming photons are detected. However, this approximation neglects second order effects such as scattering, leading to a biased model and thus incorrect material predictions. This work studies the accuracy of the free streaming model by comparing it to simulation outputs, finding that the model shows poor atomic number reconstruction accuracy at high-Z and suffers significantly if the source energy spectra and detector response function are not known exactly. To address these challenges, this work introduces a semiempirical transparency model which modifies the free streaming model by rescaling different components of the mass attenuation coefficient, allowing the model to capture secondary effects ignored by the free streaming model. The semiempirical model displays improvement agreement with simulated results at high-Z and shows excellent extrapolation to materials and thicknesses which were not included during the calibration step. Furthermore, this work demonstrates that the semiempirical model yields accurate atomic number predictions even when the source spectra and detector response are not known exactly. Using the semiempirical model, manufacturers can perform a simple calibration to enable more precise Z reconstruction capabilities, which has the potential to significantly improve the performance of existing dual energy radiographic systems.

For the precision study at the ILC 250, measurement of A_LR is important as it can constrain SMEFT parameters. The current best measured A_LR value is A_LR = 0.1514 ± 0.0019 (stat) ± 0.0011 (syst) which was measured at the SLC, and a more precise value is required for the global fit for the new physics search in TeV-scale. At the ILC, we can use the e^+ e^- →γ Z process to evaluate the A_LR. We performed a full simulation study of the e^+ e^- →γ Z process at the center-of-mass energy of 250 GeV and evaluated how much we can improve the precision of this observable. The statistical error on A_LR at the ILC 250 turned out to be 1.8 × 10^-4. Major source of the systematic error was error from the beam polarization. As other sources of the systematic error, the uncorrelated parts of error on the product of luminosity and selection efficiency for each polarization combination contribute. Including those systematic errors, total absolute error on A_LR was estimated to be 0.00025, 8.8 times better precision than that from the SLC (0.00219).

We studied the e + e − → hγ process at the full simulation level, using a realistic detector model to study the feasibility to constrain the SM effective field theory (SMEFT) hγZ coefficient, ζ AZ , at the ILC. Assuming International Large Detector (ILD) oper-ating at 250 GeV ILC, it is shown that the e + e − → hγ process is much more difficult to observe than naively expected if there is no BSM contribution. We thus put upper limits on the cross section of this process. The expected combined 95% C.L. upper limits for full polarisations ( P e − , P e + ) = ( − 100% , +100%) and (+100% , − 100%) are σ Lhγ σ LSM < 5 . 0 and σ Rhγ σ RSM < 61 . 9, respectively. The resultant 95% C.L. limit on ζ AZ is − 0 . 020 < ζ AZ < 0 . 003. 1

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.

The precise measurement of physics observables and the test of their consistency within the standard model (SM) are an invaluable approach, complemented by direct searches for new particles, to determine the existence of physics beyond the standard model (BSM). Studies of massive electroweak gauge bosons (W and Z bosons) are a promising target for indirect BSM searches, since the interactions of photons and gluons are strongly constrained by the unbroken gauge symmetries. They can be divided into two categories: (a) Fermion scattering processes mediated by s- or t-channel W/Z bosons, also known as electroweak precision measurements; and (b) multi-boson processes, which include production of two or more vector bosons in fermion-antifermion annihilation, as well as vector boson scattering (VBS) processes. The latter categories can test modifications of gauge-boson self-interactions, and the sensitivity is typically improved with increased collision energy. This report evaluates the achievable precision of a range of future experiments, which depend on the statistics of the collected data sample, the experimental and theoretical systematic uncertainties, and their correlations. In addition it presents a combined interpretation of these results, together with similar studies in the Higgs and top sector, in the Standard Model effective field theory (SMEFT) framework. This framework provides a model-independent prescription to put generic constraints on new physics and to study and combine large sets of experimental observables, assuming that the new physics scales are significantly higher than the EW scale.

A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx.

The International Linear Collider (ILC) is on the table now as a new global energy-frontier accelerator laboratory taking data in the 2030s. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community.

We consider a gauged B$-$L (Baryon number minus Lepton number) extension of the Standard Model (SM), which is anomaly free in the presence of three SM singlet Right Handed Neutrinos (RHNs). Associated with the $U(1)_{\rm B-L}$ gauge symmetry breaking, the RHNs acquire Majorana masses and then with the electroweak symmetry breaking, tiny Majorana masses for the SM(-like) neutrinos are naturally generated by the seesaw mechanism. As a result of the seesaw mechanism, the heavy mass eigenstates which are mainly composed of the SM-singlet RHNs obtain suppressed electroweak interactions through small mixings with the SM neutrinos. To investigate the seesaw mechanism, we study the pair production of heavy Majorana neutrinos through the $U(1)_{\rm B-L}$ gauge boson $Z^\prime$ at the 250 GeV and 500 GeV International Linear Collider (ILC). Considering the current and prospective future bounds on the B$-$L model parameters from the search for a resonant $Z^\prime$ boson production at the Large Hadron Collider (LHC), we focus on a"smoking-gun"signature of the Majorana nature of the heavy neutrinos: a final state with a pair of same-sign, same-flavor leptons, small missing momentum, and four hadronic jets. We estimate the projected significance of the signature at the ILC.

We have developed a novel technique for the measurement of the size of avalanche fluctuation using a gating device (gating foil) developed for the TPC in the future linear collider experiment. In addition to the gating function, the gating foil is capable of controlling the average fraction of drift electrons to be detected after gas amplification. The signal charge width and shape for laser irradiation as a function of the transmission rate of the gating foil can be used to determine the relative variance of gas gain. We present the measurement principle and the preliminary results obtained with a stack of Gas Electron Multipliers (GEMs).

To aid contributions to the Snowmass 2021 US Community Study on physics at the International Linear Collider and other proposed $e^+e^-$ colliders, we present a list of study questions that could be the basis of useful Snowmass projects. We accompany this with links to references and resources on $e^+e^-$ physics, and a description of a new software framework that we are preparing for $e^+e^-$ studies at Snowmass.

We studied the e^+e^- → h γ process at the International Linear Collider (ILC) at √(s)=250 GeV, based on the full detector simulation of the International Large Detector (ILD). This process is loop-induced in the Standard Model (SM) and is sensitive to new physics which alters h γγ or h γ Z coupling. We performed the analysis by employing the leading signal channels with h → b b̅ and h → WW^* and including full SM background processes. The results are obtained for two scenarios of beam polarisations each with an integrated luminosity of 900 fb^-1. We found the expected significance of the SM signal is 0.40σ for P(e^-,e^+)=(-0.8,+0.3) (the left-handed polarisation), and 0.06σ for P(e^-,e^+)=(+0.8,-0.3) (the right-handed polarisation). The bounds on new physics effects are reported as the 95 of e^+e^- → h γ: σ_hγ^L < 1.8 fb and σ_hγ^R < 0.5 fb respectively for left- and right-handed polarisations. The constraints on effective hγ Z couplings are to be further studied.

Received 28 April 2021DOI:https://doi.org/10.1103/PhysRevD.103.099903© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Physical SystemsHiggs bosonsPropertiesMassTechniquesLepton collidersPrecision measurementsParticles & Fields

The primary target of ILC 250 is to precisely measure the coupling constants between the Higgs boson and other Standard Model particles. For this, we need to precisely calibrate the energy scales for various particles. In this paper, the necessary calibration methods using the e+e− → γZ process will be discussed. We will focus on the photon energy reconstruction methods and report the calibration precision.

We study the h γ Z coupling, which is a loop induced coupling in the Standard Model (SM), to probe new physics. In a global fit based on the SM Effective Field Theory, measurement of the SM h γ Z coupling can provide a very useful constraint, in particular for the precise determination of hZZ and hWW couplings. At the International Linear Collider (ILC), there are two direct ways to study the h γ Z coupling: one is to measure the branching ratio of the h →γ Z decay and the other to measure the cross section for the e^+e^- → h γ process. We have performed a full simulation study of the e^+e^- → h γ process at the 250 GeV ILC, assuming 2 ab^-1 data collected by the International Large Detector (ILD). The expected 1σ bound on the effective hγ Z coupling (ζ_AZ) combining measurements of the cross section for e^+e^- → h γ followed by h → b b̅ and the h →γ Z branching ratio is -0.0015<ζ_AZ<0.0015. The expected significance for the signal cross section in the fully hadronic h → WW^* channel is 0.09 σ for beam polarizations of P(e^-,e^+)=(-80%,+30%).

The requirement of electroweak naturalness in simple supersymmetric models implies the existence of a cluster of four light Higgsinos with a mass $\ensuremath{\sim}100--300\text{ }\text{ }\mathrm{GeV}$, the lighter the better. While such light compressed spectra may be challenging to observe at the LHC, the International Linear ${e}^{+}{e}^{\ensuremath{-}}$ Collider (ILC) with $\sqrt{s}g2{m}_{\text{Higgsino}}$ would serve as both a SUSY discovery machine and a precision microscope. We study Higgsino pair production signatures at the ILC based on a full, geant4-based simulation of the ILD detector concept. We examine several benchmark scenarios that may be challenging for discovery at the HL-LHC due to mass differences between the Higgsino states between 20 and 4 GeV. Assuming $\sqrt{s}=500\text{ }\text{ }\mathrm{GeV}$ and $1000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity, the individual Higgsino masses can be measured to 1%--2% precision in the case of the larger mass differences, and at the level of 5% for the smallest mass difference case. The Higgsino mass splittings are sensitive to the electroweak gaugino masses and allow extraction of gaugino masses to $\ensuremath{\sim}3%--20%$ (depending on the model). Extrapolation of gaugino masses via renormalization group running can test the hypothesis of gaugino mass unification. We also examine a case with natural generalized mirage mediation, where the unification of gaugino masses at an intermediate scale apparently gives rise to a natural SUSY spectrum somewhat beyond the reach of HL-LHC.