Search

Axion-like particles (ALPs), which are pseudo-scalar particles, appear in various new physics models with the spontaneous global symmetry breaking. The difference between ALPs and axion models is that for the former both masses and couplings of ALPs are free parameters. It appears that the ALPs with masses above 1 GeV are beyond the reach of low-energy accelerators, existing cosmological and astrophysical constraints, while high-energy colliders provide unique possibilities to explore such particles. With the establishment of the International Muon Collider Collaboration, muon colliders have been widely concerned. In general, ALPs are mainly produced at muon colliders through the μ + μ − annihilation and electroweak vector-boson-fusion (VBF) processes. In this paper, we study the prospect of the production of heavy ALPs with mass greater than 10 GeV via the massless γ γ -fusion process at the multi-TeV muon collider. Focusing on the couplings of ALPs to the Standard Model gauge bosons, we obtain the excluding and discovering capabilities for ALPs at the 3 TeV and 10 TeV muon colliders. Our numerical results suggest that the multi-TeV muon collider may be more sensitive to ALPs with the mass of 35–400 GeV than LHC, and can provide the possibility to search for ALPs with masses greater than 3 TeV. In addition, we also discuss the effect of narrow width approximation on the ALP search sensitivity. [ABSTRACT FROM AUTHOR]

High-temperature superconducting REBa{2} Cu{3}O{7-x} (rebco) conductors have the potential to generate a high magnetic field over a broad temperature range. The corresponding accelerator magnet technology, still in its infancy, can be attractive for future energy-frontier particle colliders such as a multi-TeV muon collider. To help develop the technology, we explore the requirements and potential characteristics of a rebco magnet, operating at 4.2 or 20 K, with a dipole field of 8-10 T in a clear aperture of 150 mm. We use the canted \cos \theta magnet configuration to reduce the electromagnetic stresses on the conductors. We present the resulting dipole fields, field gradients for combined-function cases, conductor stresses, magnet dimensions and conductor lengths. We also discuss the conductor performance that is required to achieve the target dipole field at 4.2 and 20 K. The information can provide useful input to the development of rebco magnet and conductor technology for collider-ring magnets in a muon collider.

Heavy neutral gauge boson Z′ is proposed in many new physics models. It has rich phenomena at the future muon collider. We study the properties of Z′ boson with the process of and μ+μ− → W+W−. The discrepancy of Z′ coupling to different types of particles can be shown in the cross section distributions around the resonance peak of various decay modes. Angular distributions of the final quark or lepton in process are sensitive to the parameters such as mass of Z′ and the Z − Z′ mixing angle. The interaction of new gauge boson coupling to the standard model gauge particles and Higgs boson are also studied through and . The cross section and the final particles' angular distributions with the contribution of Z′ boson differ from those processes with only standard model particles. A forward-backward asymmetry defined by the angular distribution is provided to show the potential of searching for new physics at the muon collider. Especially, the beam polarization with certain value can effectively enlarge the forward-backward asymmetry. [ABSTRACT FROM AUTHOR]

The pursuit of discovery in particle physics has always required study at the highest possible energies. Multi-TeV muon colliders, which have important advantages, offer unprecedented potential for investigating new physics beyond the Standard Model. We extensively assume a range of center-of-mass energies from 3 to 30 TeV and a range of integrated luminosities from 1 to 90 ab−1 for future multi-TeV muon colliders. We perform a phenomenological study of the anomalous WWγ couplings via the process μ + μ − → μ + γ * μ − → μ + ℓ − ν ℓ ν ¯ ℓ using a model-independent analysis in the effective field theory framework at multi-TeV muon colliders. The sensitivity estimates obtained for the anomalous WWγ couplings at systematic uncertainties of δsys = 0%, 3%, 5% are compared with the experimental results. Our best sensitivity limits at 95% confidence level for cWWW/Λ2, c W ~ WW / Λ 2 , cB/Λ2, cW/Λ2, and c W ̃ / Λ 2 couplings are [−0.030; 0.025], [−0.014; 0.014], [−0.185; 0.187], [−0.187; 0.189], and [−1.177; 1.097] TeV−2 at the multi-TeV muon collider with center-of-mass energy of 30 TeV and integrated luminosity of 90 ab−1, respectively. [ABSTRACT FROM AUTHOR]

Neutrinos are the most elusive particles known. Heavier sterile neutrinos mixing with the standard neutrinos might solve the mystery of the baryon asymmetry of the universe. In this letter, we show that among all future energy frontier accelerators, muon colliders will provide the farthest search reach for such neutrinos for mass ranges above the Z pole into the multi-TeV regime, becoming the optimal machine for this kind of studies. We compare the performance of muon with electron colliders of the same machine energy and briefly discuss the complementarity in flavor space between the two types of accelerators.

We review key challenges for future next and next-next (-next) generation particle colliders and possible technological paths to address them.

One of the challenges of future muon colliders involves the production of muon beams carrying high phase space densities. In particular, the muon beam normalised transverse emittance is a relevant figure of merit used to meet luminosity requests. A typical issue impacting the achieved transverse emittance in muon collider schemes, thus far considered, is the phase space dilution caused by the Coulomb interaction of primary particles propagating into the target where muons were generated. In this study, we present a new scheme(named electrons and X-rays to muon pairs) for muon beam generation occurring in a vacuum via interactions of electron and photon beams. Setting the center of mass energy at about twice the threshold (i.e., around 350 MeV), the normalised emittance of the muon beam generated via muon pair production reaction ( e − + γ → e − + μ + + μ − ) is largely independent on the emittance of the colliding electron beam and is set basically by the excess of transverse momentum in the muon pair creation. In absence of any other mechanism for emittance dilution, the resulting muon beam, with energy in the range of a few tens of GeV, is characterised by an ultra-low normalised transverse RMS emittance of a few nm rad, corresponding to a geometrical emittance below 10 π pm rad. This opens up the way to a new muon collider paradigm based on muon sources conceived with primary colliding beams delivered by 100 GeV-class energy recovery LINACs interacting with hard-X ray free electron lasers. The challenge is to achieve the requested luminosity of the muon collider adopting a strategy of low muon fluxes/currents combined to ultra-low emittances, to largely reduce the levels of muon beam-induced backgrounds. [ABSTRACT FROM AUTHOR]

A future multi-TeV muon collider requires new ideas to tackle the problems of muon production, accumulation and acceleration. In the Low EMittance Muon Accelerator concept a 45 GeV positron beam, stored in an accumulation ring with high energy acceptance and low angular divergence, is extracted and driven to a target system in order to produce muon pairs near the kinematic threshold. However, this scheme requires an intensity of the impinging positron beam so high that the energy dissipation and the target maintenance are crucial aspects to be investigated. Both peak temperature rises and thermomechanical shocks are related to the beam spot size at the target for a given material: these aspects are setting a lower bound on the beam spot size itself. The purpose of this paper is to provide a fully theoretical approach to predict the temperature increase, the thermal gradients, and the induced thermomechanical stress on targets, generated by a sequence of 45 GeV positron bunches. A case study is here presented for Beryllium and Graphite targets. We first discuss the Monte Carlo simulations to evaluate the heat deposited on the targets after a single bunch of 3 × 1011 positrons for different beam sizes. Then a theoretical model is developed to simulate the temperature increase of the targets subjected to very fast sequences of positron pulses, over different timescales, from ps regime to hundreds of seconds. Finally a simple approach is provided to estimate the induced thermomechanical stresses in the target, together with simple criteria to be fulfilled (i.e., Christensen safety factor) to prevent the crack formation mechanism. [ABSTRACT FROM AUTHOR]

One of the challenges of future muon colliders involves the production of muon beams carrying high phase space densities. In particular, the muon beam normalised transverse emittance is a relevant figure of merit used to meet luminosity requests. A typical issue impacting the achieved transverse emittance in muon collider schemes, thus far considered, is the phase space dilution caused by the Coulomb interaction of primary particles propagating into the target where muons were generated. In this study, we present a new scheme(named electrons and X-rays to muon pairs) for muon beam generation occurring in a vacuum via interactions of electron and photon beams. Setting the center of mass energy at about twice the threshold (i.e., around 350 MeV), the normalised emittance of the muon beam generated via muon pair production reaction (e−+γ→e−+μ++μ−) is largely independent on the emittance of the colliding electron beam and is set basically by the excess of transverse momentum in the muon pair creation. In absence of any other mechanism for emittance dilution, the resulting muon beam, with energy in the range of a few tens of GeV, is characterised by an ultra-low normalised transverse RMS emittance of a few nm rad, corresponding to a geometrical emittance below 10 π pm rad. This opens up the way to a new muon collider paradigm based on muon sources conceived with primary colliding beams delivered by 100 GeV-class energy recovery LINACs interacting with hard-X ray free electron lasers. The challenge is to achieve the requested luminosity of the muon collider adopting a strategy of low muon fluxes/currents combined to ultra-low emittances, to largely reduce the levels of muon beam-induced backgrounds.

Significant progress has been made in recent years in R&D towards a neutrino factory and muon collider. The U.S. Muon Accelerator Program (MAP) has been formed recently to expedite the R&D efforts. This paper will review the U.S. MAP R&D programs for a neutrino factory and muon collider. Muon ionization cooling research is the key element of the program. The first muon ionization cooling demonstration experiment, MICE (Muon Ionization Cooling Experiment), is under construction now at RAL (Rutherford Appleton Laboratory) in the UK. The current status of MICE will be described.

We describe the scientific motivation for a new type of accelerator, the muon collider. This accelerator would permit an energy-frontier scientific program and yet would fit on the site of an existing laboratory. Such a device is quite challenging, and requires a substantial R&D program. After describing the ingredients of the facility, the ongoing R&D activities of the Muon Accelerator Program are discussed. A possible U.S. scenario that could lead to a muon collider at Fermilab is briefly mentioned.

This document contains a description of a multi-year national R&D program aimed at completing a Design Feasibility Study (DFS) for a Muon Collider and, with international participation, a Reference Design Report (RDR) for a muon-based Neutrino Factory. It also includes the supporting component development and experimental efforts that will inform the design studies and permit an initial down-selection of candidate technologies for the ionization cooling and acceleration systems. We intend to carry out this plan with participants from the host national laboratory (Fermilab), those from collaborating U.S. national laboratories (ANL, BNL, Jlab, LBNL, and SNAL), and those from a number of other U.S. laboratories, universities, and SBIR companies. The R&D program that we propose will provide the HEP community with detailed information on future facilities based on intense beams of muons--the Muon Collider and the Neutrino Factory. We believe that these facilities offer the promise of extraordinary physics capabilities. The Muon Collider presents a powerful option to explore the energy frontier and the Neutrino Factory gives the opportunity to perform the most sensitive neutrino oscillation experiments possible, while also opening expanded avenues for the study of new physics in the neutrino sector. The synergy between the two facilities presents the opportunity for an extremely broad physics program and a unique pathway in accelerator facilities. Our work will give clear answers to the questions of expected capabilities and performance of these muon-based facilities, and will provide defensible ranges for their cost. This information, together with the physics insights gained from the next-generation neutrino and LHC experiments, will allow the HEP community to make well-informed decisions regarding the optimal choice of new facilities. We believe that this work is a critical part of any broad strategic program in accelerator R&D and, as the P5 panel has recently indicated, is essential for the long-term health of high-energy physics.

We describe the scientific motivation for a new type of accelerator, the muon collider. This accelerator would permit an energy-frontier scientific program and yet would fit on the site of an existing laboratory. Such a device is quite challenging, and requires a substantial R&D program. After describing the ingredients of the facility, the ongoing R&D activities of the Muon Accelerator Program are discussed. A possible U.S. scenario that could lead to a muon collider at Fermilab is briefly mentioned.

Both a Neutrino Factory and a Muon Collider place stringent demands on the proton beam used to generate the desired beam of muons. Here we discuss the advantages and challenges of muon accelerators and the rationale behind the requirements on proton beam energy, intensity, bunch length, and repetition rate. Example proton driver configurations that have been considered in recent years are also briefly indicated.

Ideas of use the particle channeling in bent crystals for steer the beams have been checked up and advanced in many experiments. However, until now, this method of beam formation has limitations in application, since the channeling process involves beam particles with low angular divergence, limited by the angle of Lindhard. Here we describe the focusing crystals, which expand the boundaries of application of bent crystals at accelerators. [ABSTRACT FROM AUTHOR]

The measurements of the top quark flavor changing neutral current interactions are one of the most important goals of the top quark physics program in the present and the future collider experiments. These measurements provide direct information on nonstandard interactions of the top quark. Within the framework of new physics beyond the Standard Model, these interactions can be defined by an effective Lagrangian. In this study, we have investigated the potential of the future μ p colliders on the top quark flavor changing neutral current interactions through the subprocesses γ q → t → W b , where q = u , c. These subprocesses have been produced through the main reaction μ p → μ γ p → μ W b X at the LHC- μ p , the FCC- μ p and the SPPC- μ p. For the main reaction, the total cross-sections have been calculated as a function of the anomalous t q γ couplings. In addition, sensitivities on BR (t → q γ) at 95% Confidence Level have been calculated. We obtain that the best constraints on BR (t → q γ) are at the order of 1 0 − 7 which is four orders of magnitude better than the LHC's experimental results. [ABSTRACT FROM AUTHOR]

Cooling is a critical aspect for a high-performance Neutrino Factory or a Muon Collider. For this reason, considerable effort is being put toward the experimental verification of this technique. The international Muon Ionization Cooling Experiment, MICE, was approved to operate at Rutherford Appleton Laboratory (RAL) in the UK and beam line commissioning commenced in March, 2008. The MICE collaboration comprises about 130 scientists and engineers from Asia, Europe, and the U.S. In this paper we present the motivation and goals for this experiment and describe its present status. MICE is scheduled for completion in 2011. We will also indicate the prospects for a future 6D muon cooling experiment and discuss its possible time schedule.

We describe recent work on the physics of the Higgs boson and breaking of the electroweak symmetry at future muon colliders. Starting from the low-energy muon collider at the Higgs boson pole we extend our discussion to the multi-TeV muon collider and outline the physics case for such machines about the properties of the Higgs boson and physics beyond the Standard Model that can be possibly discovered.

Abstract Discoveries at high-energy particle colliders have established the standard model of particle physics. Technological innovation has helped to increase the collider energy at a much faster pace than the corresponding costs. New concepts will allow reaching ever higher luminosities and energies throughout the coming century. Cost-effective strategies for the collider implementation include staging. For example, a future circular collider could first provide electron–positron collisions, then hadron collisions (proton–proton and heavy-ion), and finally the collision of muons. Cooling-free muon colliders, realizable in a number of ways, promise an attractive and energy-efficient path towards lepton collisions at tens of TeV. While plasma accelerators and dielectric accelerators offer unprecedented gradients, the construction of a high-energy collider based on these new technologies still calls for significant improvements in cost and performance. Pushing the accelerating gradients or bending fields ever further, the breakdown of the QED vacuum may set an ultimate limit to electromagnetic acceleration. Finally, some ideas are sketched for reaching, or exceeding, the Planck energy. Highlights • Particle accelerators, especially colliders, are outstanding engines of discovery. • Technology advances enabled higher energy and performance at lower cost. • One cost-effective strategy for future collider implementation is staging. • Cooling-free muon colliders offer an attractive path towards tens of TeV. • QED vacuum breakdown and Planck energy may, or may not, be ultimate limits. [ABSTRACT FROM AUTHOR]

The idea of a muon collider has been developed since the 70s. In these projects, muons are produced at targets at low or intermediate energies. Then, after reducing the emittance, they should accelerate very quickly, since the lifetime is very short ( τ μ = 2 μ s in the rest frame). Here, we want to propose the option of the collider, where the muons can be obtained on the hadron collider at high energy using a focusing bent crystals. [ABSTRACT FROM AUTHOR]

Neutrinos are the most elusive particles known. Heavier sterile neutrinos mixing with the standard neutrinos might solve the mystery of the baryon asymmetry of the universe. In this letter, we show that among all future energy frontier accelerators, muon colliders will provide the farthest search reach for such neutrinos for mass ranges above the Z pole into the multi-TeV regime, becoming the optimal machine for this kind of studies. We compare the performance of muon with electron colliders of the same machine energy and briefly discuss the complementarity in flavor space between the two types of accelerators. [ABSTRACT FROM AUTHOR]

Present availability of high brilliance photon beams in combination with intense TeV hadron beams makes it possible to conceive the generation of low emittance TeV-class energy pion/muon beams via photoproduction in a highly relativistic Lorentz boosted frame. We analyze the secondary beams brightness achievable by the coupling of advanced high efficiency high repetition rate FEL pulses and Large Hadron Collider or Future Circular Collider hadron beams. The phase space distributions of the pion and muon beams are obtained by means of an event generator code and the characteristics, such as emittance and energy spread, are benchmarked against analytical expressions. [ABSTRACT FROM AUTHOR]

Detectors for new energy frontier experiments require excellent spatial, time, and energy resolutions to resolve the structure of collimated high-energy jets. In a future Muon Collider, the beam-induced backgrounds represent the main challenge for detector design and event reconstruction. Our proposal – Crilin – consists in a semi-homogeneous Cherenkov electromagnetic calorimeter based on PbF 2 crystals with surface-mount UV-extended Silicon Photomultipliers readout. [ABSTRACT FROM AUTHOR]

The project of a Multi-TeV Muon Collider represents a unique opportunity to explore the high energy physics frontier and to measure with high precision the Higgs coupling with the other particles of the Standard Model as well as the trilinear and quadrilinear Higgs self-coupling, leading to a precise determination of the Higgs potential, in order to confirm the theoretical predictions of the SM and possibly to find evidences for new physics. One of the major challenges for the design and optimization of the technologies suitable for a Muon Collider experiment is represented by the high background induced by the decay of the muons coming from the beam. This contribution present the design of an innovative MPGD-based hadronic calorimeter (HCAL). The detector consists of a sampling calorimeter exploiting the Micro Pattern Gas Detectors (MPGDs) as active layers: MPGDs offer a fast and robust technology for high radiation environments and a high granularity for precise spatial measurements. Moreover, the detector is designed to optimize the jet reconstruction and for background suppression. The calorimeter is simulated using the Geant4 toolkit to support the detector R&D. The detector design and layout optimization supported by the simulation is described. [ABSTRACT FROM AUTHOR]

A Muon Collider represents a promising possibility to combine the high energy and luminosity of hadron machines with very precise measurements of lepton colliders. The main challenges, that impact both the machine and detector design, arise from the short muon lifetime and the harsh Beam-induced Background (BIB). Therefore, a full simulation is crucial to understand the feasibility of the experiment implementation. Focusing in particular on the muon system, a preliminary simulation of sensitivity and hit rate reveals that the technology inherited from CLIC, i.e. glass Resistive Plate Chambers, is already at the limit of its rate capability. Thus, alternative MicroPattern Gaseous Detector solutions are under investigation to try to match the required performance. In parallel, studies of muon reconstruction are ongoing. Results of the muon reconstruction efficiency and BIB sensitivity are presented for multimuon final state processes at a centre-of-mass energy of 1.5 TeV. Besides, PICOSEC technology, based on a Micromegas detector coupled to a Cherenkov radiator and equipped with a photocathode, is discussed. [ABSTRACT FROM AUTHOR]

The design of a feasible multi-TeV muon collider facility is the mandate of the International Muon Collider Collaboration based at CERN and is considered with great interest along the presently on-going US Snowmass 2021 process. The physics potential of such a novel future collider is overwhelming, ranging from precision measurements to direct searches for new Physics. Despite the machine-design challenges, it gives access to the uncharted territory of leptonic collisions at a center-of-mass energy of 10 TeV or higher with an instantaneous luminosity up to a few 1 0 35 cm−2 s−1. The experiment design, the detector technology choices, and the event reconstruction tools are strongly affected by the presence of the beam-induced background, generated by the interactions of the muon decay products with the machine elements. Full simulation studies at s = 1. 5 TeV and 3 TeV, adopting the CLIC experiment technologies, represent the starting point to optimize the detector design and propose future dedicated R&D. [ABSTRACT FROM AUTHOR]