CERN Accelerating science

A sketch of what the Muon Collider timeline could look like, superimposed with approximate HL-LHC and LBNF/DUNE schedules. Future collider decision tree adopted from Ref.~\cite{Pushpa:EFtalk} is also shown. The decision tree is "optimistic" in the sense that the timeline is driven by physics goals and technology readiness rather than financial considerations. We also assume that globally more than one future collider can be pursued at the same time.

Schematic layout of 10 TeV-class muon collider complex being studied within the International Muon Collider Collaboration. From https://muoncollider.web.cern.ch/

The COM energy for a proton collider $\sqrt{s}_\mathrm{p}$ and a muon collider $\sqrt{s}_\mathrm{\mu}$ such that the $2\rightarrow 2$ cross sections are the same based on different assumptions for the partonic cross sections characterized by $\beta$. Separate curves for gluon and quark annihilation channels are shown, with the bands given by two choices of PDFs, i.e. NNPDF3.0LO and CT18NNLO~\cite{AlAli:2021let}.

Figure reproduced from~\cite{Forslund:2022xjq} showing various Higgs process as a function of COM energy. The dashed curves correspond to s-channel annihilation processes, while the solid curves all are from Vector Boson Fusion.

Figure from Energy Frontier Higgs topical report illustrating the centrality of the Higgs and the connections to numerous fundamental questions.

The one-sigma precision reach on the effective Higgs couplings from a global fit of the Higgs and electroweak measurements in the SMEFT framework. The first set of (red) columns represents the HL-LHC S2 scenario with electroweak measurements at LEP and SLD. The second (blue) and third (yellow) sets of columns represent the 3 TeV muon collider and 10 TeV muon collider projections, respectively. The fourth (green) sets of columns represent the 10 TeV muon collider combined with a 125 GeV muon collider Higgs factory. The measurements are combined with the HL-LHC S2 and LEP/SLD measurements for all the muon collider scenarios. The semi-opaque bars represent the results with the Higgs width being a free parameter, e.g., allowing for exotic decays that are hard to constrain through direct searches. The solid bars are for the results without exotic Higgs decays.

$2\sigma$ exclusion of fermion DM masses with horizontal bars for individual search channels and muon collider energies by the different colors. The vertical bars indicate the thermal mass targets~\cite{Han:2020uak,Han:2022ubw}.

$2\sigma$ exclusion of DM masses with horizontal (thick) bars for combined channels and various muon collider running scenarios for $\sqrt s = 3, 10$ and 14 TeV~\cite{Han:2022ubw}. The thin bars show the reach of the mono-photon plus one disappearing track search. The vertical bars indicate the thermal mass targets.

Figure from~\cite{Aime:2022flm} showing the discovery reach of a top partner and several supersymetric particles for a 10, 14, and 30 TeV muon collider shown as horizontal lines. The lightly shaded and darker bars correspond to the 95\% C.L mass reach of the HL-LHC and FCC-hh as determined for the European Strategy Update briefing book.

Figures from~\cite{AlAli:2021let}, the left hand plot shows the exclusion limits for a massive scalar singlet $\phi$ that mixes with SM Higgs with mixing angle $\gamma$. The various colored curves correspond to different muon collider COM energies, while the expected limits at HL-LHC (solid) and a FCC-hh (dashed) are shown as black lines for comparison. The thin dashed lines indicate two possible scalings of the mixing angle in realistic models with fixed coupling. The left hand plot represents a more generic statement than that of naturalness, and is a more general illustration of the powerful Higgs portal reach of a muon collider. The right hand plot usese the same limits as the LH plot re-interpreted in terms of the reach on the sigma-model scale f in the context of a Twin Higgs model.

The reach for a 10 TeV muon collider (thick red lines) to discover a flavor-violating signal from mixed slepton production compared to the complementary constraints from LFV experiments (purple and green lines) and EDM limits (blue lines). More details can be found in Ref.~\cite{Homiller:2022iax}.

The reach for a 10 TeV muon collider (thick red lines) to discover a flavor-violating signal from mixed slepton production compared to the complementary constraints from LFV experiments (purple and green lines) and EDM limits (blue lines). More details can be found in Ref.~\cite{Homiller:2022iax}.

Required luminosity to yield a 2$\sigma$ exclusion of singlets responsible for $(g-2)_\mu$. A 125 GeV muon collider (left) has superior sensitivity to 1 TeV (right) and to 10 TeV (not shown) through the combination of direct singlet production when kinematically accessible and deviations from muonic Bhabha scattering for heavier singlets, even considering the lower luminosity. Based on the analysis of Ref.~\cite{Capdevilla:2021rwo}.

Required luminosity to yield a 2$\sigma$ exclusion of singlets responsible for $(g-2)_\mu$. A 125 GeV muon collider (left) has superior sensitivity to 1 TeV (right) and to 10 TeV (not shown) through the combination of direct singlet production when kinematically accessible and deviations from muonic Bhabha scattering for heavier singlets, even considering the lower luminosity. Based on the analysis of Ref.~\cite{Capdevilla:2021rwo}.

The projected sensitivities for probing HNL on the $\sqrt{s} = 10$ TeV muon collider. The black curve refers to the electron-flavored HNL, while the red curve is for the muon-flavored case. The results for the tau-flavored HNL will be similar to the electron-flavored case. More details of the analysis can be found in Ref.~\cite{ZhenLiuTeamHNLMuC}.

Top: IR layout of the 6 TeV COM collider with 5$\sigma$ envelopes and quadrupole apertures. In cyan are shown the quadrupoles with up to 5 T dipole component. Bottom: 3 TeV arc cell concept.

MARS15 MDI model with tungsten nozzles on each side of IP, tungsten masks in interconnect regions and tungsten liners inside each magnet.

Intense highly collimated neutrino fluxes around MC~\cite{King:1999rr}

Intense highly collimated neutrino fluxes around MC~\cite{King:1999rr}

Left: Dose in the orbit plane vs radial distance from the ring center of 2, 3 and 4~TeV COM MC. Right: Dose downstream of a 0.5~m drift with $2.6\times10^{16}$~decays/yr of a 1.5~TeV muon beam there vs. distance in soil downstream of the drift. Red line shows annual off-site regulatory limit at Fermilab, that is, $10\text{ mrem/year} = 0.1\text{ mSv/year}$~\cite{Mokhov:2000gt}.

Left: Dose in the orbit plane vs radial distance from the ring center of 2, 3 and 4~TeV COM MC. Right: Dose downstream of a 0.5~m drift with $2.6\times10^{16}$~decays/yr of a 1.5~TeV muon beam there vs. distance in soil downstream of the drift. Red line shows annual off-site regulatory limit at Fermilab, that is, $10\text{ mrem/year} = 0.1\text{ mSv/year}$~\cite{Mokhov:2000gt}.

Neutrino flux and dose reduction around the 4~TeV COM muon collider using beam wobbling induced by wave field of 0, 0.05, 0.1, 0.2 and 0.4~tesla. The red line is the Fermilab offsite annual limit which is reached at 57~km with no wave field and at 14~km with 0.4~T wave field.

A schematic view of the Fermilab site and the layout of a possible complex for the Muon Collider. The protons start at PIP-II and are accelerated, bunched and pulsed onto a high power target. Muon cooling chain is indicated in green. Acceleration happens in stages with the final stage taking place inside the large Accelerator Ring. Muons at the nominal energy are injected into the Collider Ring, where the experiment(s) are located.

Kinematic properties of BIB particles entering the detector region: momentum (left) and arrival time with respect to the bunch crossing (right).

Kinematic properties of BIB particles entering the detector region: momentum (left) and arrival time with respect to the bunch crossing (right).

Comparison of multiplicities of different types of particles produced in each bunch crossing by the BIB at different energies. The uncertainties are about 20\%. The MDI optimized for 750 GeV is used for the 1.5 and 5.0 TeV columns. Vast majority of these particles have very low momenta.

Rendering of the muon collider detector geometry used for the presented simulation studies, including the cone-shaped shielding nozzles (cyan) and the beryllium beampipe (violet). Shown are the cross sections of the full detector geometry (left) and two zoomed-in portions: up to ECAL (top right) and up to Vertex Detector (bottom right). Muon Detector (violet and green) surrounds the solenoid (cyan), which encloses the HCAL (magenta), ECAL (yellow) and the Tracking Detector (green and black).

Average hit density per bunch crossing in the tracker as a function of the detector layer~\cite{https://doi.org/10.48550/arxiv.2203.07224}.

Performance of a BIB-reduction algorithm at the hit level of the vertex detector, after a fiducial timing window selection of [-250, +300] ps. An ideal resolution case is shown in black, while the other colors represent a range of timing and angular resolutions. Different hue ribbons represent different detector capabilities, while the surface of the ribbon represents different choices for cut values~\cite{https://doi.org/10.48550/arxiv.2203.06773}.

Tracking efficiency for single muon in events with beam-induced background versus transverse momentum (top) and resolution versus $\theta$ (bottom) from ~\cite{MuonCollider2022ded}. The loss of efficiency at small angle comes from the effects of the nozzle used to limit the beam-induced background flux into the detector. Work to improve tracking algorithm and to recover the loss of efficiency is ongoing.

Tracking efficiency for single muon in events with beam-induced background versus transverse momentum (top) and resolution versus $\theta$ (bottom) from ~\cite{MuonCollider2022ded}. The loss of efficiency at small angle comes from the effects of the nozzle used to limit the beam-induced background flux into the detector. Work to improve tracking algorithm and to recover the loss of efficiency is ongoing.

Distribution of the secondary vertex proper lifetime for b, c and light tagged jets (top). Distributions are normalized to the unit area. Jet transverse momentum ($p_T$) resolution as a function of the $p_T$ of the jet for $b-$, $c-$, and light jets (bottom). Differences between flavors are mainly due to different angular distributions of jets.

Distribution of the secondary vertex proper lifetime for b, c and light tagged jets (top). Distributions are normalized to the unit area. Jet transverse momentum ($p_T$) resolution as a function of the $p_T$ of the jet for $b-$, $c-$, and light jets (bottom). Differences between flavors are mainly due to different angular distributions of jets.

Result of the dijet invariant mass fit used to extract the $H \rightarrow b \bar{b}$ yield and uncertainty. Pseudo-data are obtained by exploiting the Muon Collider experiment simulation at $\sqrt{s} =$3 TeV, and assuming an integrated luminosity of 1 ab$^{-1}$.

Expected sensitivity using 10~ab$^{-1}$ of 10~TeV $\mu^{+}\mu^{-}$ collision data as a function of the $\tilde \chi^\pm$ mass and lifetime. The contours represent the $5~\sigma$ discovery expectation. The solid lines show the predictions from full simulation, while the dashed lines the predictions from the fast simulation.

The reach of a 1.5 TeV muon beam dump experiment for a dark photon (left) or $L_{\mu} - L_{\tau}$ gauge boson, adapted from Ref.~\cite{Cesarotti:2022ttv}.

The reach of a 1.5 TeV muon beam dump experiment for a dark photon (left) or $L_{\mu} - L_{\tau}$ gauge boson, adapted from Ref.~\cite{Cesarotti:2022ttv}.

Kinematic coverage of $Q^{2}$ and $x$ in deep inelastic lepton-proton scattering for two muon-ion collider design options and for the EIC at BNL, HERA at DESY, and the LHeC and FCC-eh options at CERN, each at their maximum beam energies. The inelasticity ($y$) range is assumed to be $0.01