Physics Interplay of the LHC and the ILC

TL;DR

The paper surveys the physics potential and synergy between the LHC and a future linear collider (LC) across a broad landscape of theories beyond the Standard Model. It foregrounds how concurrent operation and cross-fertilization—via combined data interpretations and joint analyses—can sharpen measurements of Higgs properties, SUSY spectra, gauge sectors, extra dimensions, and Dark Matter, thereby illuminating the mechanism of electroweak symmetry breaking and the structure of new physics at the TeV scale and beyond. The report covers a spectrum of scenarios (SM-like Higgs, MSSM/NMSSM Higgs sectors, Little Higgs, strong EW breaking, extra dimensions) and details concrete methods (threshold scans, decay-channel measurements, mass determinations, and CP-violation studies) that demonstrate substantial gains when LHC and LC inputs are integrated. It emphasizes precision measurements (e.g., top Yukawa coupling, tanβ, MA, neutralino masses) and indirect probes (GigaZ, EW precision tests) as complementary to direct discoveries, showing how LC capabilities—especially in a clean environment and polarized beams—can resolve ambiguities left by the LHC and vice versa. The work also outlines future directions and benchmark scenarios (e.g., SPS 1a) to guide ongoing simulations and collider planning, illustrating that a combined LHC/LC program is crucial for a robust, model-discriminating understanding of TeV-scale physics and its cosmological implications (e.g., Dark Matter relic density). Overall, the paper argues that maximizing physics return requires coordinated, overlapping machine operation and thorough cross-calibration of measurements across collider platforms.

Abstract

Physics at the Large Hadron Collider (LHC) and the International e+e- Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC / LC Study Group so far is summarised in this report. Possible topics for future studies are outlined.

Figures (62)

• Figure 1: Production cross-sections for several representative processes at hadron colliders (left) and $e^+e^-$ colliders (right), as a function of the machine center-of-mass energy.
• Figure 2: Achievable precision on the top Yukawa coupling from 30 $\mathrm{fb}^{-1}$ at the LHC and 500 $\mathrm{fb}^{-1}$ at the LC (left), and from 300 $\mathrm{fb}^{-1}$ at the LHC and 500 $\mathrm{fb}^{-1}$ at the LC (right). The red curve shows the precision obtainable from the ${H}^{0}$$\to$${b}\bar{b}$ final state, the green from the ${H}^{0}$$\to$${W}^+{W}^-$ final state and the blue curve from the combination of the two. The dashed lines show the expected precision taking into account only statistical errors.
• Figure 18: $\sigma \times$ BR for $\phi_2 \rightarrow VV$ with $V = W/Z$, relative to the SM expectation for the same for a mass of 250 GeV, as a function of $\tan \beta$ and $\Phi_{HA}$ for LHC, LC and PLC.
• Figure 19: 1-$\sigma$ bands for the determination of $\tan \beta$ and $\Phi_{HA}$ from measurements at LHC, LC and PLC, for the case $\tan \beta = 0.7$ and $\Phi_{HA} = -0.2$. The assumed parameter values are indicated by a star ($\star$).
• Figure 20: The experimental accuracies for the branching ratios BR($h \to b \bar{b}$) and BR($h \to WW^*$) at the LC of about 2.5% and 5%, indicated by a vertical and horizontal band, respectively, are compared with the theoretical prediction in the MSSM. The light shaded (yellow) region indicates the full allowed parameter space. The medium shaded (light blue) region indicates the range of predictions in the MSSM being compatible with the assumed experimental information from LHC and LC, $\Delta M_A = 10\%$, $\tan\beta > 15$, $\Delta m_{\tilde{t}}, \Delta m_{\tilde{b}} = 5\%$, $\Delta m_t = 0.1$ GeV. The dark shaded (dark blue) region arises if furthermore a measurement of the light CP-even Higgs mass, including a theory uncertainty of $\Delta m_h = 0.5$ GeV, is assumed.