Search

Methods for measuring the absolute center-of-mass energy using dileptons from e$^{+}$e$^{-}$ collision events are further developed with an emphasis on accelerator, detector, and physics limitations. We discuss two main estimators, the lepton momentum-based center-of-mass energy estimator, $\sqrt{s}_{p}$, discussed previously, and new estimators for the electron and positron colliding beam energies, denoted $E^{\text{C}}_{-}$ and $E^{\text{C}}_{+}$. In this work we focus on the underlying limitations from beam energy spread, detector resolution, and the modeling of higher-order QED radiative corrections associated with photon emissions originating from initial-state-radiation (ISR), final-state-radiation (FSR), and their interference. We study the consequent implications for the potential of these methods at center-of-mass energies ranging from 90 GeV to 1 TeV relevant to a number of potential accelerator realizations in the context of measurements of masses of the Z, W, H, top quark, and new particles. The statistical importance of the Bhabha channel for Higgs factories is noted. Additional extensive work on improving the modeling of the luminosity spectrum including the use of copulas is also reported., Comment: 22 pages, 10 figures, LCWS 2023 Proceedings

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., Comment: 55 pages; Report of the EF04 topical group for Snowmass 2021; v2: few typos corrected and references added

Methods for measuring the absolute center-of-mass energy, $\sqrt{s}$, and its distribution, are investigated for future $e^+e^-$ Higgs-factory colliders using in situ $e^+e^-$ collisions. We emphasize the potential of an estimator based on the measurement of muon momenta that we denote $\sqrt{s}_p$. It can be determined with high precision in $e^+e^-$ to $\mu^+\mu^-$($\gamma$) events while being sensitive to effects from beam energy spread, beamstrahlung, initial-state radiation (ISR), final-state radiation (FSR), crossing angle, and detector resolution. The measurement precision is enabled by a high-precision low-mass tracker; the reported performance estimates are based on full simulation of the tracker response of the ILD detector concept for the ILC operating at $\sqrt{s} = 250$ GeV. The underlying statistical precision is 1.9 ppm for a 2.0 ab$^{-1}$ dataset at ILC. The ultimate utility will depend largely on how well one can calibrate and maintain the tracker momentum scale., Comment: 30 pages; Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021). v3 correct scaling formula in footnote 1 and add corresponding reference

A program to build a lepton-collider Higgs factory, to precisely measure the couplings of the Higgs boson to other particles, followed by a higher energy run to establish the Higgs self-coupling and expand the new physics reach, is widely recognized as a primary focus of modern particle physics. We propose a strategy that focuses on a new technology and preliminary estimates suggest that can lead to a compact, affordable machine. New technology investigations will provide much needed enthusiasm for our field, resulting in trained workforce. This cost-effective, compact design, with technologies useful for a broad range of other accelerator applications, could be realized as a project in the US. Its technology innovations, both in the accelerator and the detector, will offer unique and exciting opportunities to young scientists. Moreover, cost effective compact designs, broadly applicable to other fields of research, are more likely to obtain financial support from our funding agencies., Comment: 11 pages, 2 figures, contribution to Snowmass 2021

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., Comment: 356 pages, Large pdf file (40 MB) submitted to Snowmass 2021; v2 references to Snowmass contributions added, additional authors; v3 references added, some updates, additional authors

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., Comment: 49 pages, 1 figure, 1 table; v2: correction of some web links; v3: new Section 3 with a description of the ILC simulation framework put in place for Snowmass

We present an overview of the capabilities that the International Linear Collider (ILC) offers for precision measurements that probe the Standard Model. First, we discuss the improvements that the ILC will make in precision electroweak observables, both from W boson production and radiative return to the Z at 250 GeV in the center of mass and from a dedicated GigaZ stage of running at the Z pole. We then present new results on precision measurements of fermion pair production, including the production of b and t quarks. We update the ILC projections for the determination of Higgs boson couplings through a Standard Model Effective Field Theory fit taking into account the new information on precision electroweak constraints. Finally, we review the capabilities of the ILC to measure the Higgs boson self-coupling., Comment: 58 pages, 8 figures, 13 tables; v2: minor corrections to Table 11; v3: typo corrections; v4: additions to the W boson section

The International Linear Collider (ILC) is now under consideration as the next global project in particle physics. In this report, we review of all aspects of the ILC program: the physics motivation, the accelerator design, the run plan, the proposed detectors, the experimental measurements on the Higgs boson, the top quark, the couplings of the W and Z bosons, and searches for new particles. We review the important role that polarized beams play in the ILC program. The first stage of the ILC is planned to be a Higgs factory at 250 GeV in the centre of mass. Energy upgrades can naturally be implemented based on the concept of a linear collider. We discuss in detail the ILC program of Higgs boson measurements and the expected precision in the determination of Higgs couplings. We compare the ILC capabilities to those of the HL-LHC and to those of other proposed e+e- Higgs factories. We emphasize throughout that the readiness of the accelerator and the estimates of ILC performance are based on detailed simulations backed by extensive RandD and, for the accelerator technology, operational experience., Comment: 104 pages, 88 figures; v2: minor typo corrections; v3: many minor changes, including small corrections to the Tables and Figures in Section 11

A large, world-wide community of physicists is working to realise an exceptional physics program of energy-frontier, electron-positron collisions with the International Linear Collider (ILC). This program will begin with a central focus on high-precision and model-independent measurements of the Higgs boson couplings. This method of searching for new physics beyond the Standard Model is orthogonal to and complements the LHC physics program. The ILC at 250 GeV will also search for direct new physics in exotic Higgs decays and in pair-production of weakly interacting particles. Polarised electron and positron beams add unique opportunities to the physics reach. The ILC can be upgraded to higher energy, enabling precision studies of the top quark and measurement of the top Yukawa coupling and the Higgs self-coupling. The key accelerator technology, superconducting radio-frequency cavities, has matured. Optimised collider and detector designs, and associated physics analyses, were presented in the ILC Technical Design Report, signed by 2400 scientists. There is a strong interest in Japan to host this international effort. A detailed review of the many aspects of the project is nearing a conclusion in Japan. Now the Japanese government is preparing for a decision on the next phase of international negotiations, that could lead to a project start within a few years. The potential timeline of the ILC project includes an initial phase of about 4 years to obtain international agreements, complete engineering design and prepare construction, and form the requisite international collaboration, followed by a construction phase of 9 years.

The International Linear Collider is now proposed with a staged machine design, with the first stage at $\sqrt{s}=$~250 GeV and an integrated luminosity goal of 2~ab$^{-1}$. One of the questions for the machine design is the importance of positron polarization. In this report, we review the impact of positron polarization on the physics goals of the $250$ GeV stage of the ILC and demonstrate that positron polarization has distinct advantages., Comment: 19

This paper addresses the question of whether the International Linear Collider has the capability of discovering new particles that have not already been discovered at the CERN Large Hadron Collider. We summarize the various paths to discovery offered by the ILC, and discuss them in the context of three different scenarios: 1. LHC does not discover any new particles, 2. LHC discovers some new low mass states and 3. LHC discovers new heavy particles. We will show that in each case, ILC plays a critical role in discovery of new phenomena and in pushing forward the frontiers of high-energy physics as well as our understanding of the universe in a manner which is highly complementary to that of LHC. For the busy reader, a two-page executive summary is provided at the beginning of the document., Comment: 52 pages, 18 figures

An updated study of measuring the W mass from a polarized threshold scan at ILC is presented with an emphasis on evaluating scan strategies that control experimental systematics. Highly longitudinally polarized beams of electrons and positrons such as are feasible at ILC offer significant advantages in terms of statistical power and in-situ control of background. Eventual experimental precision of around 2 MeV can be envisaged from this technique. Further work on both the accelerator design and theoretical uncertainties will likely be needed to take full advantage of this opportunity., Comment: Talk presented at The International Workshop on Future Linear Colliders (LCWS15), Whistler, Canada, 2-6 November 2015. Revised version v2 fixes typo in Table 4 (3.62 fb uncertainty on 4q background cross-section - instead of 3.62 ab))

We investigate improving the hadronic jet energy resolution using mass-constrained fits of pi0 decays using high granularity electromagnetic calorimeters. Single pi0 studies have indicated a large potential for improvement in the energy resolution of pi0's, typically reducing the average energy resolution by a factor of two for 4 GeV pi0's. We apply this method to fully simulated multi-hadronic events with multiple pi0's with widely varying energies using the ILD00 detector model. Several methods for identifying the correct pairings of photons with parent pi0's were explored. The combinatorics become challenging as the number of pi0's increases and we employ the Blossom V implementation of Edmonds' matching algorithm for handling this. For events where both photons of the pi0 are detected, the resulting solutions lead to an improvement in the pi0 component of the event energy resolution for 91.2 GeV Z0 events from 18.0%/sqrt(E) to 13.9%/sqrt(E) using the ILD00 detector and its reconstruction algorithms. This can be compared to a maximum potential improvement to 12.2%/sqrt(E) if all photon pairs are matched correctly using the current photon reconstruction., Comment: LCWS11 Conference Proceedings, 15 pages, 8 figures

We analyze the collider signatures of models with a vector-like top-prime quark and a massive color-octet boson. The top-prime quark mixes with the top quark in the Standard Model, leading to richer final states than ones that are investigated by experimental collaborations. We discuss the multi-lepton final states, and show that they can provide increased sensitivity to models with a top-prime quark and gluon-prime. Searches for new physics in high multiplicity events are an important component of the LHC program and complementary to analyses that have been performed., Comment: 7 pages, 4 figures, 2 tables