We revisit the expected sensitivity of large-scale xenon detectors to Weakly Interacting Massive Particles (WIMPs). Assuming current primary noise sources can be mitigated, we find that with the present discrimination power between nuclear and electron recoils, the experimental sensitivity is limited not only by atmospheric neutrinos’ nuclear recoils (“nuclear recoil neutrino fog”) but also by solar neutrinos’ electron-recoil events (“electron recoil neutrino fog”). While this is known by experimentalists, it is often missed or misunderstood by theorists, and we therefore emphasize this effect. We set up a realistic detector simulation to quantify the contamination of the WIMP signal from both these neutrino backgrounds. We observe that the electron-recoil background remains significant even for signal rates exceeding those of atmospheric neutrinos, as predicted by most electroweak WIMP candidates. We update the projections for the required exposure to exclude/discover a given electroweak WIMP, streamlining the computation of their signal rates and uncertainties. We show that all of the real WIMPs with zero hypercharge can be excluded (discovered) with a 50 tonne year (300 tonne year) exposure. A similar exposure will allow to probe a large portion of the viable parameter space for complex WIMP with non-zero hypercharge.

United States

Itay Bloch

Israel

Salvatore Bottaro

Italy

Diego Redigolo

France

Ludovico Vittorio

Looking for WIMPs through the neutrino fogs

We propose a search at $\textit{Mu3e}$ for lepton flavor violating axion(-like) particles in $\textit{μ}$ → 3$\textit{e}$ + $\textit{a}$ decays. By requiring an additional $\textit{e}$ $\textit{e}$ pair from internal conversion, one can circumvent the calibration challenges which plague the $\textit{μ}$ → $\textit{e}$ + $\textit{a}$ channel for axions lighter than 20 MeV. Crucially, the corresponding reduction in signal rate is to a large extent compensated for by $\textit{Mu3e}$’s ability to resolve highly collimated tracks. For phase I of $\textit{Mu3e}$, we project a sensitivity to decay constants as high as 6 × 10 GeV which probes uncharted parameter space in scenarios of axion dark matter. The sensitivity to axions which couple primarily to right-handed leptons can be further improved by leveraging the polarisation of the muon beam.

Simon Knapen

Kevin Langhoff

Toby Opferkuch

A robust search for lepton flavour violating axions at Mu3e

We present strategies for the $\textit{Mu3e}$ experiment to search for light, weakly coupled particles produced in rare muon decays, focusing on displaced $\textit{e}$ $\textit{e}$ decays within the hollow target. In most scenarios the backgrounds can be fully suppressed with a suitable set of cuts. We furthermore quantify the interplay between displaced and prompt searches at $\textit{Mu3e}$ and existing constraints, showing how $\textit{Mu3e}$ has a unique opportunity to probe unexplored parameter space.

Michele Tammaro

Displaced searches for Axion-Like Particles and Heavy Neutral Leptons at Mu3e

We identify new room for CP violation in lepton flavor violating observables not bound by the electric dipole moment of leptons. By focusing on new physics in the muon-electron sector, we show that CP violation can make its first appearance in lepton flavor violating muon decays rather than in the electric dipole moment of the electron, further motivating the experimental program of Mu3e. We tackle this issue by performing the full one-loop running and matching from the low energy observables at the muon scale, including the T-odd asymmetry in $$\mu \rightarrow 3e$$ decays, to the Standard Model effective field theory above the electroweak scale. We then sketch a simple UV model that can give rise to these patterns.

Andrea Tesi

Large CP violation in flavor violating muon decays

We propose a new search for a diphoton resonance in the e + e  −  + γγ final state at Belle II where the full final state is reconstructed in the detector. This new channel improves the expected reach compared to the γ + γγ channel in most of the available mass range. For simplicity we show our results in the simple parameter space of an ALP coupled solely to Standard Model photons. In addition, we show how an extension of the forward coverage of Belle II, or another similar experiment at the high intensity frontier, could improve the reach in our channel. We show that such a forward extension can be advantageous even with a loss of a factor 100 in luminosity compared to Belle II.

Germany

Francesca Acanfora

Roberto Franceschini

Alessio Mastroddi

Fusing photons into diphoton resonances at Belle II and beyond

We consider an axion-like particle coupled to the Standard Model photons and decaying invisibly at Belle II. We propose a new search in the $\textit{e}$ $\textit{e}$ + invisible channel that we compare against the standard $\textit{γ}$ + invisible channel. We find that the $\textit{e}$ $\textit{e}$ + invisible channel has the potential to ameliorate the reach for the whole ALP mass range. This search leverages dedicated kinematic variables which significantly suppress the Standard Model background. We explore the implications of our expected reach for Dark Matter freeze-out through ALP-mediated annihilations.

Fusing photons into nothing, a new search for invisible ALPs and Dark Matter at Belle II

We reexamine the consequences of perturbative unitarity on dark matter freeze-out when both Sommerfeld enhancement and bound state formation affect dark matter annihilations. At leading order the annihilation cross section is infrared dominated and the connection between the unitarity bound and the upper bound on the dark matter mass depends only on how the different partial waves are populated. We compute how this picture is modified at next-to-leading order with the goal of assigning a reliable theory uncertainty to the freeze-out predictions. We explicitly compute next-to-leading order corrections in a simple model with Abelian gauge interactions and provide an estimate of the theoretical uncertainty for the thermal masses of heavy electroweak <math><mi>n</mi></math>-plets. Along the way, we clarify the regularization and matching procedure necessary to deal with singular potentials in quantum mechanics with a calculable, relativistic UV completion.

Sommerfeld enhancement at NLO and the dark matter unitarity bound

We examine the capability of Mu3e to probe light new physics scenarios that produce a prompt electron-positron resonance and demonstrate how angular observables are instrumental in enhancing the experimental sensitivity. We systematically investigate the effect of Mu3e’s expected sensitivity on the parameter space of the dark photon, as well as on axion-like particles and light scalars with couplings to muons and electrons.

Angling for insights: illuminating light new physics at Mu3e through angular correlations

21-cm cosmology provides an exciting opportunity to probe new physics dynamics in the early universe. In particular, a tiny sub-component of dark matter that interacts strongly with the visible sector may cool the gas in the intergalactic medium and significantly alter the expected absorption signal at Cosmic Dawn. However, the information about new physics in this observable is obscured by astrophysical systematic uncertainties. In the absence of a microscopic framework describing the astrophysical sources, these uncertainties can be encoded in a bottom up effective theory for the 21-cm observables in terms of unconstrained astrophysical fluxes. In this paper, we take a first step towards a careful assessment of the degeneracies between new physics effects and the uncertainties in these fluxes. We show that the latter can be constrained by combining measurements of the UV luminosity function, the Planck measurement of the CMB optical depth to reionization, and an upper bound on the unresolved X-ray flux. Leveraging those constraints, we demonstrate how new physics signatures can be disentangled from astrophysical effects. Focusing on the case of millicharged dark matter, we find sharp predictions, with small uncertainties within the viable parameter space.$^{1}$

Omer Zvi Katz

Nadav Outmezguine

Tomer Volansky

Probing new physics at cosmic dawn with 21-cm cosmology

CERN

Carlotta Accettura

United Kingdom

Dean Adams

Rohit Agarwal

Claudia Ahdida

Chiara Aimè

Nicola Amapane

David Amorim

Paolo Andreetto

Fabio Anulli

Robert Appleby

Artur Apresyan

Aram Apyan

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

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

Netherlands

Frank Filthaut

Davide Fiorina

Erratum: Towards a muon collider