arXiv subjects
Publications and source records attributed to Timothy L. Barklow.
This document expands on the Comprehensive Summary submitted to the EPPSU 2026. It contains details on aspects of the HALHF project that could not be fitted into the Summary. Some sections contain work that is still preliminary and/or status reports on current progress.
HALHF is a hybrid linear collider that uses electron-driven plasma-wakefield acceleration to accelerate electrons to high energy while using radio-frequency cavity technology to accelerate positrons. The most cost-effective solution collides low-energy positrons with high-energy electrons, producing a boost to the final state in the electron direction with $\gamma= 1.67$. The current HALHF baseline design produces a luminosity comparable to that of the baseline ILC but with a greatly reduced construction and carbon footprint and hence much lower cost than the mature linear-collider designs ILC and CLIC. Costs for HALHF are evaluated, together with that for the approximate 15-year R\&D programme necessary to realise HALHF. Time scales and cost for the R\&D are estimated. Upgrade paths for HALHF technology from a 250~GeV Higgs factory, through 380 and 550~GeV, up to 10~TeV are sketched.
The HALHF collaboration has discussed a new baseline for the project, taking into account comments from the accelerator community on various aspects of the original design. In particular, these concerned the practicality of the dual-purpose linac to accelerate both colliding positron bunches and the drive beams required for the plasma linac. In addition, many other aspects of the project were also considered; the discussion and conclusions are documented in this paper. Finally, a new baseline is outlined that has been optimised and addresses several weaknesses in the original design, has higher luminosity, reduced centre-of-mass energy boost and additional features such as positron polarization as well as electron polarization. Although HALHF has become longer and more expensive, it remains significantly smaller and cheaper than other mature Higgs factory designs currently under discussion.
We have explored a concept for an advanced Normal-Conducting Radio-Frequency (NCRF) C-band linear accelerator (linac) structure to achieve a high gradient, high power e$^+$e$^-$ linear collider in the TeV class. This design study represents the first comprehensive investigation for an emerging class of distributed coupling accelerator topology exploring nominal cavity geometries, frequency and temperature of operation. The structure features internal manifolds for distributing RF power separately to each cell, permitting the full structure geometry to be designed for high shunt impedance and low breakdown. Optimized within operational constraints, we find that it is advantageous for the structure to be cooled directly by liquid nitrogen (LN), further increasing the shunt impedance. A crucial part of this design process has been cost optimization, which is largely driven by the cost of peak RF power. The first operation of a distributed coupling structure at cryogenic temperatures and the nominal operating gradient 120 MeV/m is also presented, demonstrating the feasibility of achieving high-gradient performance with a cryogenically-cooled normal-conducting accelerating structure.
We present a study performed for the CLIC CDR on the measurement of chargino and neutralino production at sqrt(s) = 3 TeV. Fully hadronic final states with four jets and missing transverse energy were considered. Results obtained using full detector simulation for the masses and for the production cross sections of the changino and the lightest and next-to-lightest neutralinos are discussed.
Recent progress in Higgs boson studies for the International e+e- Linear Collider (ILC) is reported. These studies include extended simulations of the measurement of the Higgs mass, measurements of the Higgs boson branching ratios at higher center-of-mass energies, and methods for extracting the Higgs boson self-coupling. Also, the interplay between the LHC and the ILC in the measurement of the top Yukawa coupling and in the extraction of the supersymmetric Higgs sector parameters is discussed.
Methods for extracting Higgs boson signals at a 1 TeV center-of-mass energy e+e- linear collider are described. In addition, estimates are given for the accuracy with which branching fractions can be measured for Higgs boson decays to bb, WW, gluon-gluon, and gamma-gamma.
We discuss the possible signatures in the electroweak symmetry breaking sector by new strong dynamics at future hadron colliders such as the Tevatron upgrade, the LHC and VLHC, and $e^+e^-$ linear colliders. Examples include a heavy Higgs-like scalar resonance, a heavy Technicolor-like vector resonance and pseudo-Goldstone states, non-resonance signatures via enhanced gauge-boson scattering and fermion compositeness.
The physics at an e+e- linear collider with a center of mass energy of 3-5 TeV is reviewed. The following topics are covered: experimental environment, Higgs physics, supersymmetry, fermion pair-production, WW scattering, extra dimensions, non-commutative theories, and black hole production.
The study of strong symmetry breaking at an e+e linear collider with sqrt(s)=0.5-1.5 TeV is reviewed. It is shown that processes such as e+e- --> nu nubar W+ W-, e+e- --> nu nubar t tbar, and and e+e- --> W+ W- can be used to measure chiral Lagrangian and strong resonance parameters. The linear collider results are compared with those expected from the LHC.
Measurements of triple gauge boson couplings and strong electroweak symmetry breaking effects at future e+e- linear colliders are reviewed. The results expected from a future e+e- linear collider are compared with LHC expectations.
Drees and Godbole have proposed that, at the interaction point of an e+e- linear collider, one expects a high rate of hadron production by gamma-gamma collisions, providing an additional background to studies in e+e- annihilation. Using a simplified model of the gamma-gamma cross section with soft and jet-like components, we estimate the expected rate of these hadronic events for a variety of realistic machine designs. The final background rates are quite small, and they become smaller still when viewed with a realistic detector simulation.