We study the capabilities of a muon collider, at 3 and 10 TeV center-of-mass energy, of probing the interactions of the Higgs boson with the muon. We consider all the possible processes involving the direct production of EW bosons (W, Z and H) with up to five particles in the final state. We study these processes both in the HEFT and SMEFT frameworks, assuming that the dominant BSM effects originate from the muon Yukawa sector. Our study shows that a Muon Collider has sensitivity beyond the high-luminosity LHC, especially as it does not rely on the Higgs-decay branching fraction to muons. A 10 TeV muon collider provides a unique sensitivity on muon and (multi-) Higgs interactions, significantly better than the 3 TeV option. Particularly, we find searches based purely on multi-Higgs production to be particularly effective in probing these couplings.

Italy

United Kingdom

Eugenia Celada

United States

Tao Han

Germany

Wolfgang Kilian

Nils Kreher

Yang Ma

Belgium

Fabio Maltoni

Davide Pagani

Jürgen Reuter

Tobias Striegl

Keping Xie

Probing Higgs-muon interactions at a multi-TeV muon collider

We study the discrimination power of future multi-TeV muon colliders for a large set of models with extended gauge symmetries and additional neutral gauge bosons (“ $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>  -models”). Our study is carried out using a  $$\chi ^2$$  <math> <msup> <mi>χ</mi> <mn>2</mn> </msup> </math>  -analysis of leptonic observables of s-channel scattering in effective  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>  -models. We make use of angular and chiral asymmetries induced in such models to find the discovery reach of a given muon collider setup in terms of the  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   mass and to discriminate between the different scenarios. In this context, we discuss how polarized beams – should they become available at muon colliders – or polarization measurements can help in the discrimination. Our results show that typical muon collider setups which are currently under consideration can give a significantly higher reach compared to existing bounds and projections for high-luminosity LHC.

Ukraine

Kateryna Korshynska

Maximilian Löschner

Netherlands

Mariia Marinichenko

Poland

Krzysztof Mękała

Z’ boson mass reach and model discrimination at muon colliders

In this paper we investigate how well the nature of heavy neutral leptons can be determined at a future lepton collider, after its potential discovery. Considered in a simplified model are prompt decays of the neutrino in the mass range from 100 GeV to 10 TeV. We study event selection and application of multivariate analyses to determine whether such a newly discovered particle is of the Dirac or Majorana nature. Combining lepton charge and kinematic event variables, we find that the nature of a heavy neutrino, whether it is a Dirac or a Majorana particle, can be determined at 95% C.L. almost in the whole discovery range. We will briefly speculate about other than the studied channels and the robustness of this statement in more general models of heavy neutral leptons, particularly on the complementarity of high-energy electron-positron vs. muon colliders on resolving the flavor structure of heavy neutrinos.

Aleksander Żarnecki

Discriminating Majorana and Dirac heavy neutrinos at lepton colliders

CERN

Carlotta Accettura

Dean Adams

Rohit Agarwal

Claudia Ahdida

Chiara Aimè

Nicola Amapane

David Amorim

Paolo Andreetto

Fabio Anulli

Robert Appleby

Artur Apresyan

Aram Apyan

France

Sergey Arsenyev

Pouya Asadi

Egypt

Mohammed Mahmoud

Aleksandr Azatov

John Back

Lorenzo Balconi

Laura Bandiera

Roger Barlow

Nazar Bartosik

Emanuela Barzi

Fabian Batsch

Matteo Bauce

J. Berg

Andrea Bersani

Alessandro Bertarelli

Alessandro Bertolin

Kevin Black

Fulvio Boattini

Alex Bogacz

Maurizio Bonesini

Bernardo Bordini

Salvatore Bottaro

Luca Bottura

Alessandro Braghieri

Marco Breschi

Natalie Bruhwiler

Xavier Buffat

Laura Buonincontri

Philip Burrows

Graeme Burt

Dario Buttazzo

Barbara Caiffi

Marco Calviani

Simone Calzaferri

Daniele Calzolari

Rodolfo Capdevilla

Christian Carli

Fausto Casaburo

Massimo Casarsa

Luca Castelli

Maria Catanesi

Lorenzo Cavallucci

Gianluca Cavoto

Spain

Francesco Celiberto

Luigi Celona

Alessandro Cerri

Gianmario Cesarini

Cari Cesarotti

Portugal

Grigorios Chachamis

Antoine Chance

Switzerland

Siyu Chen

Yang-Ting Chien

Mauro Chiesa

Anna Colaleo

Francesco Collamati

Gianmaria Collazuol

Marco Costa

Nathaniel Craig

Camilla Curatolo

Canada

David Curtin

Giacomo Molin

Magnus Dam

Heiko Damerau

Sridhara Dasu

Jorge Blas

Stefania Curtis

Ernesto Matteis

Stefania Rosa

Jean-Pierre Delahaye

Dmitri Denisov

Türkiye

Haluk Denizli

Christopher Densham

Radovan Dermisek

Luca Luzio

Elisa Meco

Biagio Micco

Keith Dienes

Eleonora Diociaiuti

Tommaso Dorigo

Alexey Dudarev

Robert Edgecock

Filippo Errico

Marco Fabbrichesi

Stefania Farinon

Anna Ferrari

Jose Somoza

Frank Filthaut

Davide Fiorina

Erratum: Towards a muon collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.

Towards a muon collider

We present an update of the Universal FeynRules Output model format, commonly known as the UFO format, that is used by several automated matrix-element generators and high-energy physics software. We detail different features that have been proposed as extensions of the initial format during the last ten years, and collect them in the current second version of the model format that we coin the Universal Feynman Output format. Following the initial philosophy of the UFO, they consist of flexible and modular additions to address particle decays, custom propagators, form factors, the renormalisation group running of parameters and masses, and higher-order quantum corrections.

Luc Darmé

Céline Degrande

Claude Duhr

Benjamin Fuks

Mark Goodsell

Gudrun Heinrich

Valentin Hirschi

Stefan Höche

Marius Höfer

Joshua Isaacson

Olivier Mattelaer

Thorsten Ohl

Peter Richardson

Steffen Schumann

Hua-Sheng Shao

Frank Siegert

Marco Zaro

UFO 2.0: the ‘Universal Feynman Output’ format

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.

Aleksander Filip Żarnecki

Optimal search reach for heavy neutral leptons at a muon collider

We present results on NLO electroweak (EW) corrections to multiple massive boson production processes at a future muon collider. Inclusive cross sections with   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (α) corrections for processes for up to four bosons in the final state as well as differential distributions for HZ production are computed for   <math> <msqrt> <mi>s</mi> </msqrt> </math>  $$ \sqrt{s} $$  = 3, 10 and 14 TeV by using FKS subtraction in the NLO EW automated Monte-Carlo framework WHIZARD+RECOLA. Large logarithmic effects due to collinear ISR and EW virtual correction factors as well as the impacts of an energy cut on hard photons are discussed with an emphasis on the properties of Higgsstrahlung. The potential of a proposed muon collider for studying physics of the EW sector is underlined by the EW corrections significantly affecting observables for processes at high energies and boson multiplicities.

Pia Bredt

Pascal Stienemeier

NLO electroweak corrections to multi-boson processes at a muon collider

Neutrinos are among the most mysterious particles in nature. Their mass hierarchy and oscillations, as well as their antiparticle properties, are being intensively studied in experiments around the world. Moreover, in many models of physics beyond the Standard Model, the baryon asymmetry or the dark matter density in the Universe are explained by introducing new species of neutrinos. Among others, heavy neutrinos of Dirac or Majorana nature were proposed to solve open questions in High Energy Physics. Such neutrinos with masses above the electroweak (EW) scale could be produced at future linear e+e −  colliders, like the Compact LInear Collider (CLIC) or the International Linear Collider (ILC).

Heavy neutrinos at future linear e+e −  colliders

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 Λ ∼ 30 − 100 TeV.

Precision test of the muon-Higgs coupling at a high-energy muon collider