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Register a new userProbing the $R_{K^{(*)}}$ Anomaly at a Muon Collider
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The LHCb measurements of the $mu / e$ ratio in $B to K ell ell$ decays $(R_{K^{}})$ indicate a deficit with respect to the Standard Model prediction, supporting earlier hints of lepton universality violation observed in the $R_{K^{(*)}}$ ratio. Possible explanations of these $B$-physics anomalies include heavy $Z$ bosons or leptoquarks mediating $b to s mu^+ mu^- $. We note that a muon collider can directly measure this process via $mu^+ mu^- to b bar s$ and can shed light on the lepton non-universality scenario. Investigating currently discussed center-of-mass energies $sqrt{s} = 3$, 6 and 10 TeV, we show that the parameter space of $Z$ and $S_3$ leptoquark solutions to the $R_{K^{(*)}}$ anomalies can be mostly covered. Effective operators explaining the anomalies can be probed with the muon collider setup $sqrt{s} = 6~{rm TeV}$ and integrated luminosity $L = 4~{rm ab^{-1}}$.
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We identify a single six-dimensional effective operator $O_{ellell}$ that can account for the Cabibbo angle anomaly naturally, without any tension with the electroweak precision observables. The renormalization group running of $O_{ell ell}$ yields the required new couplings of $W$ and $Z$ bosons in exactly the right proportion. When generated as a result of a $Z$ model, the non-universal leptonic coupling needed for this operator can also contribute to the lepton flavor universality violating $R_{K^{(*)}}$ anomaly, generating the preferred relation $C_9=-C_{10}$ between the Wilson coefficients. We find the region in parameter space of $Z$ mass and couplings that offer a simultaneous solution to both these anomalies, and argue that $O_{ell ell}$ is a unique single operator that can offer such a resolution. Our arguments may also be extended to multi-operator scenarios like $U_1$ vector leptoquark, which is known to address multiple anomalies that violate the lepton flavor universality.
We explore the ability of current and future dark matter and collider experiments in probing anomalous magnetic moment of the muon, $(g-2)_mu$, within the Minimal Supersymmetric Standard Model (MSSM). We find that the latest PandaX-II/LUX-2016 data gives a strong constraint on parameter space that accommodates the $(g-2)_{mu}$ within $2sigma$ range, which will be further excluded by the upcoming XENON-1T (2017) experiment. We also find that a 100 TeV $pp$ collider can cover most of our surviving samples that satisfy DM relic density within $3sigma$ range through $Z$ or $h$ resonant effect by searching for trilepton events from $tilde{chi}^0_2tilde{chi}^+_1$ associated production. While the samples that are beyond future sensitivity of trilepton search at a 100 TeV $pp$ collider and the DM direct detections are either higgsino/wino-like LSPs or bino-like LSPs co-annihilating with sleptons. Such compressed regions may be covered by the monojet(-like) searches at a 100 TeV $pp$ collider.
We explore the sensitivity of directly testing the muon-Higgs coupling at a high-energy muon collider. This is strongly motivated if there exists new physics that is not aligned with the Standard Model Yukawa interactions which are responsible for the fermion mass generation. We illustrate a few such examples for physics beyond the Standard Model. With the accidentally small value of the muon Yukawa coupling and its subtle role in the high-energy production of multiple (vector and Higgs) bosons, we show that it is possible to measure the muon-Higgs coupling to an accuracy of ten percent for a 10 TeV muon collider and a few percent for a 30 TeV machine by utilizing the three boson production, potentially sensitive to a new physics scale about $Lambda sim 30-100$ TeV.
We further investigate the case where new physics in the form of a massive $Z^prime$ particle explains apparent measurements of lepton flavour non-universality in $B rightarrow K^{(ast)} l^+ l^-$ decays. Hadron collider sensitivities for direct production of such $Z^prime$s have been previously studied in the narrow width limit for a $mu^+ mu^-$ final state. Here, we extend the analysis to sizeable decay widths and improve the sensitivity estimate for the narrow width case. We estimate the sensitivities of the high luminosity 14 TeV Large Hadron Collider (HL-LHC), a high energy 27 TeV LHC (HE-LHC), as well as a potential 100 TeV future circular collider (FCC). The HL-LHC has sensitivity to narrow $Z^prime$ resonances consistent with the anomalies. In one of our simplified models the FCC could probe 23 TeV $Z^prime$ particles with widths of up to 0.35 of their mass at 95% confidence level (CL). In another model, the HL-LHC and HE-LHC cover sizeable portions of parameter space, but the whole of perturbative parameter space can be covered by the FCC.
Measuring longitudinally polarized vector boson scattering in, e.g., the ZZ channel is a promising way to investigate the unitarization scheme from the Higgs and possible new physics beyond the Standard Model. However, at the LHC, it demands the end of the HL-LHC lifetime luminosity, 3000/fb, and advanced data analysis technique to reach the discovery threshold due to its small production rates. Instead, there could be great potential for future colliders. In this paper, we perform a Monte Carlo study and examine the projected sensitivity of longitudinally polarized ZZ scattering at a TeV scale muon collider. We conduct studies at 14 TeV and 6 TeV muon colliders respectively and find that a 5 standard deviation discovery can be achieved at a 14 TeV muon collider, with 3000/fb of data collected. While a 6 TeV muon collider can already surpass HL-LHC, reaching 2 standard deviations with around 4000/fb of data. The effect from lepton isolation and detector granularity is also discussed, which may be more obvious at higher energy muon colliders, as the leptons from longitudinally polarized Z decays tend to be closer.
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