CERN

Carlotta Accettura

United Kingdom

Dean Adams

United States

Rohit Agarwal

Claudia Ahdida

Italy

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

Germany

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

Netherlands

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

In this letter we revisit the Standard Model predictions for  $${\mathcal {B}}(B\rightarrow K^{(*)}\nu {\bar{\nu }})$$  <math> <mrow> <mi>B</mi> <mo>(</mo> <mi>B</mi> <mo>→</mo> <msup> <mi>K</mi> <mrow> <mo>(</mo> <mrow></mrow> <mo>∗</mo> <mo>)</mo> </mrow> </msup> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> <mo>)</mo> </mrow> </math>   and discuss the opportunities that open up when combining its partial decay rate with that of  $$B\rightarrow K^{(*)}\ell \ell $$  <math> <mrow> <mi>B</mi> <mo>→</mo> <msup> <mi>K</mi> <mrow> <mo>(</mo> <mrow></mrow> <mo>∗</mo> <mo>)</mo> </mrow> </msup> <mi>ℓ</mi> <mi>ℓ</mi> </mrow> </math>  . In the Standard Model a suitable ratio of these two modes can be used to extract  $$C_9^\textrm{eff}$$  <math> <msubsup> <mi>C</mi> <mn>9</mn> <mtext>eff</mtext> </msubsup> </math>  , which is essential for a reliable phenomenological analysis of the  $$B\rightarrow K^{(*)}\ell \ell $$  <math> <mrow> <mi>B</mi> <mo>→</mo> <msup> <mi>K</mi> <mrow> <mo>(</mo> <mrow></mrow> <mo>∗</mo> <mo>)</mo> </mrow> </msup> <mi>ℓ</mi> <mi>ℓ</mi> </mrow> </math>   angular observables. The same ratio also proves to be more sensitive to the presence of New Physics in many plausible extensions of the Standard Model. We also suggest that the separate measurement of  $${\mathcal {B}}(B\rightarrow K\nu {\bar{\nu }})$$  <math> <mrow> <mi>B</mi> <mo>(</mo> <mi>B</mi> <mo>→</mo> <mi>K</mi> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> <mo>)</mo> </mrow> </math>   for high and for low  $$q^2$$  <math> <msup> <mi>q</mi> <mn>2</mn> </msup> </math>  ’s can be helpful for testing the assumed shape of the vector form factor, because the lattice QCD data are obtained at high  $$q^2$$  <math> <msup> <mi>q</mi> <mn>2</mn> </msup> </math>  ’s, whereas the low  $$q^2$$  <math> <msup> <mi>q</mi> <mn>2</mn> </msup> </math>   region is obtained through an extrapolation.

Damir Bečirević

Gioacchino Piazza

Olcyr Sumensari

Revisiting  $$B\rightarrow K^{(*)} \nu {\bar{\nu }}$$  <math> <mrow> <mi>B</mi> <mo>→</mo> <msup> <mi>K</mi> <mrow> <mo>(</mo> <mrow></mrow> <mo>∗</mo> <mo>)</mo> </mrow> </msup> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   decays in the Standard Model and beyond

Decays based on the b → sγ transition are expected to yield left-handed photons in the Standard Model, but could be particularly sensitive to New Physics contributions modifying the short-distance Wilson coefficients   <math> <mi>C</mi> </math>  $$ \mathcal{C} $$  7 and   <math> <mi>C</mi> </math>  $$ \mathcal{C} $$  7′ defined in the low-energy Effective Field Theory. These coefficients can be determined by combining observables of several modes, among which B  s  → ϕee at low q 2, in a kinematic range where the photon-pole is dominant. We investigate the impact of B  s  −   <math> <mover> <mi>B</mi> <mo>¯</mo> </mover> </math>  $$ \overline{B} $$   s  mixing on the angular observables available for this mode, which induces a time-dependent modulation governed by interference terms between mixing and decay that are sensitive to the moduli and phases of   <math> <mi>C</mi> </math>  $$ \mathcal{C} $$  7 and   <math> <mi>C</mi> </math>  $$ \mathcal{C} $$  7′. These interference terms can be extracted through a time-dependent analysis but they also affect time-integrated observables. In particular, we show that the asymmetries   <math> <msubsup> <mi>A</mi> <mi>T</mi> <mfenced> <mn>2</mn> </mfenced> </msubsup> </math>  $$ {A}_T^{(2)} $$  and   <math> <msubsup> <mi>A</mi> <mi>T</mi> <mrow> <mfenced> <mo>Im</mo> </mfenced> <mo>;</mo> <mi>CP</mi> </mrow> </msubsup> </math>  $$ {A}_T^{\left(\operatorname{Im}\right); CP} $$  receive terms of potentially similar size from mixing-independent and mixing-induced terms, and we discuss how the constraints coming from the angular analysis of B  s  → ϕee at low q 2 should be interpreted in the presence of mixing.

Sébastien Descotes-Genon

Ioannis Plakias

On the impact of meson mixing on B  s  → ϕee angular observables at low q 2

The long-standing muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> anomaly can be explained by heavy new physics particles through chirally enhanced contributions. It has been recently proposed that a muon collider running at center-of-mass energies of several TeV could test these new physics scenarios in a model-independent way, through the study of high-energy processes such as <math><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup><mo>→</mo><mi>h</mi><mi>γ</mi></math>. In this work, we validate these findings, based on effective field theories, by considering selected renormalizable simplified models and by computing this one-loop process in full generality. Furthermore, we explore the interplay of direct and indirect high-energy searches to pin down the details of the underlying new physics model accommodating the muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> anomaly.

Paride Paradisi

Alessandro Valenti

High-energy frontier of the muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> at a muon collider

We discuss a model that can accommodate the <math><mi>B</mi></math>-physics anomalies, based on combining two scalar leptoquarks, <math><mrow><msub><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math> and <math><msub><mi>S</mi><mn>3</mn></msub></math>, of mass <math><mrow><mi>O</mi><mo>(</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi><mo>)</mo></mrow></math>, and that we proposed in our previous paper. We update the analysis of its parameter space and show that a model remains viable and consistent with a number of low energy and high energy flavor physics constraints. Since the model predicts a nonzero new physics phase, we discuss the possibility to test its contribution to the neutron electric dipole moment and to the angular distributions of the exclusive <math><mi>b</mi><mo>→</mo><mi>c</mi><mi>τ</mi><mover><mi>ν</mi><mo>¯</mo></mover></math> decays. We find that the model can provide a significant enhancement to <math><mrow><mi>B</mi><mo>(</mo><mi>B</mi><mo>→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mi>ν</mi><mi>ν</mi><mo>)</mo></mrow></math> and provides both the upper and lower bounds to <math><mrow><mi>B</mi><mo>(</mo><mi>B</mi><mo>→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mi>μ</mi><mi>τ</mi><mo>)</mo></mrow></math>.

Croatia

Ilja Doršner

Slovenia

Svjetlana Fajfer

Darius A. Faroughy

Florentin Jaffredo

Nejc Košnik

Model with two scalar leptoquarks: <math><mrow><msub><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math> and <math><mrow><msub><mrow><mi>S</mi></mrow><mrow><mn>3</mn></mrow></msub></mrow></math>

We study the impact of triple-leptoquark interactions on matter stability for two specific proton decay topologies that arise at the tree- and one-loop level if and when they coexist. We demonstrate that the one-loop level topology is much more relevant than the tree-level one when it comes to the proton decay signatures despite the usual loop-suppression factor. We subsequently present detailed analysis of the triple-leptoquark interaction effects on the proton stability within one representative scenario to support our claim, where the scenario in question simultaneously features a tree-level topology that yields three-body proton decay p → e + e + e  −  and a one-loop level topology that induces two-body proton decays p → π 0 e + and p → π +   <math> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ \overline{\nu} $$ . We also provide a comprehensive list of the leading-order proton decay channels for all non-trivial cubic and quartic contractions involving three scalar leptoquark multiplets that generate triple-leptoquark interactions of our interest, where in the latter case one of the scalar multiplets is the Standard Model Higgs doublet.

Triple-leptoquark interactions for tree- and loop-level proton decays

This paper presents the prospects for a precise measurement of the branching fraction of the leptonic   <math> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> </math>  $$ {B}_c^{+} $$  → τ + ν  τ  decay at the Future Circular Collider (FCC-ee) running at the Z -pole. A detailed description of the simulation and analysis framework is provided. To select signal candidates, two Boosted Decision Tree algorithms are employed and optimised. The first stage suppresses inclusive   <math> <mi>b</mi> <mover> <mi>b</mi> <mo>¯</mo> </mover> </math>  $$ b\overline{b} $$ ,   <math> <mi>c</mi> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ c\overline{c} $$ , and   <math> <mi>q</mi> <mover> <mi>q</mi> <mo>¯</mo> </mover> </math>  $$ q\overline{q} $$  backgrounds using event-based topological information. A second stage utilises the properties of the hadronic τ + → π + π + π  −    <math> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ \overline{\nu} $$   τ  decay to further suppress these backgrounds, and is also found to achieve high rejection for the B + → τ + ν  τ  background. The number of   <math> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> </math>  $$ {B}_c^{+} $$  → τ + ν  τ  candidates is estimated for various Tera-Z scenarios, and the potential precision of signal yield and branching fraction measurements evaluated. The phenomenological impact of such measurements on various New Physics scenarios is also explored.

Yasmine Amhis

Marie Hartmann

Clément Helsens

Donal Hill

Prospects for   <math> <msubsup> <mi>B</mi> <mi>c</mi> <mo>+</mo> </msubsup> </math>  $$ {B}_c^{+} $$  → τ + ν  τ  at FCC-ee

We revisit the possibilities of accommodating the experimental indications of the lepton flavor universality violation in <math><mi>b</mi></math>-hadron decays in the minimal scenarios in which the Standard Model is extended by the presence of a single <math><mrow><mi>O</mi><mo>(</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi><mo>)</mo></mrow></math> leptoquark state. To do so we combine the most recent low energy flavor physics constraints, including <math><mrow><msubsup><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup></mrow><mrow><mi>exp</mi></mrow></msubsup></mrow></math> and <math><mrow><msubsup><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup></mrow><mrow><mi>exp</mi></mrow></msubsup></mrow></math>, and combine them with the bounds on the leptoquark masses and their couplings to quarks and leptons as inferred from the direct searches at the LHC and the studies of the large <math><msub><mi>p</mi><mi>T</mi></msub></math> tails of the <math><mi>p</mi><mi>p</mi><mo>→</mo><mo>ℓ</mo><mo>ℓ</mo></math> differential cross section. We find that none of the scalar leptoquarks of <math><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>LQ</mi></mrow></msub><mo>≃</mo><mn>1</mn><mo>÷</mo><mn>2</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math> can accommodate the <math><mi>B</mi></math>-anomalies alone. Only the vector leptoquark, known as <math><msub><mi>U</mi><mn>1</mn></msub></math>, can provide a viable solution which, in the minimal setup, provides an interesting prediction, i.e., a lower bound to the lepton flavor violating <math><mrow><mi>b</mi><mo>→</mo><mi>s</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>±</mo></mrow></msup><msup><mrow><mi>τ</mi></mrow><mrow><mo>∓</mo></mrow></msup></mrow></math> decay modes, such as <math><mrow><mi>B</mi><mo>(</mo><mi>B</mi><mo>→</mo><mi>K</mi><mi>μ</mi><mi>τ</mi><mo>)</mo><mo>≳</mo><mn>0.7</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>7</mn></mrow></msup></mrow></math>.

Andrei Angelescu

Single leptoquark solutions to the <math><mi>B</mi></math>-physics anomalies

We investigate scenarios with <math><mi>O</mi><mo>(</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi><mo>)</mo></math> scalar leptoquarks that act as portals between the Standard Model and dark matter. We assume that dark matter is a scalar singlet <math><mi>S</mi></math> which couples to a scalar leptoquark <math><mi>Δ</mi></math> and the Higgs boson via the terms in the scalar potential. In addition, the leptoquark is endowed with Yukawa couplings to quarks and leptons that may address the anomalies in <math><mi>B</mi></math> meson decays. We consider the <math><mi>S</mi><mi>S</mi></math> annihilation cross sections to estimate the dark matter relic abundance and explore the interplay between astrophysical, collider, and flavor physics bounds on such models. In the heavy dark matter window, <math><msub><mi>m</mi><mi>S</mi></msub><mo>&gt;</mo><msub><mi>m</mi><mi>Δ</mi></msub></math>, the leptoquark portal becomes the dominant mechanism to explain the dark matter abundance. We find that the leptoquark Yukawa couplings, relevant for quark and lepton flavor physics, are decoupled from the dark matter phenomenology. By focussing on a scenario with a single leptoquark state, we find that relic density can only be explained when both <math><mi>Δ</mi></math> and <math><mi>S</mi></math> masses are lighter than <math><mi>O</mi><mo>(</mo><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi><mo>)</mo></math>.

Francesco D’Eramo

Federico Pobbe

Aleks Smolkovič

Leptoquarks and real singlets: A richer scalar sector behind the origin of dark matter