This note describes the validation of a new form of re-interpretation material provided by an ATLAS search for hadronically-decaying neutral long-lived particles in association with jets or leptons, using the full Run-2 dataset. This reference ATLAS analysis provided a set of machine-learning-based “surrogate models” which return the probability of an event being selected in a given channel of the analysis, using as input truth-level kinematic information (decay position, transverse momentum and decay products of the long-lived particles). In this document, we describe the surrogate model framework in detail, and how it responds to issues identified in other re-interpretation procedures. We describe independent validations of the surrogate models’ performance in reproducing the original analysis results – first using a stand-alone framework and then employing the HackAnalysis framework.

France

Louie Corpe

Abdelhamid Haddad

Mark Goodsell

Recasting the ATLAS search for displaced hadronic jets in the ATLAS calorimeter with additional jets or leptons using surrogate models

We present new recasts of the CMS Run 2 soft-leptons + missing energy analysis and the ATLAS Run 2 multijet + missing energy analysis. These analyses are relevant for probing the parameter space of electroweak-charged particles with compressed spectra. We review these analyses and detail their implementation and validation in (for CMS) and (ATLAS). We then use these new recasts to combine four LHC analyses to identify a region of parameter space of the “wino-bino” simplified model, which corresponds to a limit of the Minimal Supersymmetric Standard Model in which higgsinos are decoupled, that is preferred over the Standard Model by excesses in the data. We find that the favoured region is compatible with the observed dark matter relic density, assuming freeze out within a standard cosmology, and we comment on the importance of this result and on how the simplified model should be mapped onto a complete supersymmetric model.

Diyar Agin

Benjamin Fuks

United States

Taylor Murphy

A joint explanation for the soft lepton and monojet LHC excesses in the wino-bino model

Belgium

Chiara Arina

Italy

Luca Panizzi

Michael Baker

South Africa

Alan Cornell

Germany

Jan Heisig

United Kingdom

Benedikt Maier

Portugal

Rute Pedro

Dominique Trischuk

Alexandre Arbey

Giorgio Arcadi

Emanuele Bagnaschi

Kehang Bai

Brazil

Disha Bhatia

Mathias Becker

Alexander Belyaev

Ferdinand Benoit

Monika Blanke

Canada

Jackson Burzynski

Jonathan Butterworth

Antimo Cagnotta

China

Lorenzo Calibbi

Linda Carpenter

Spain

Xabier Cid Vidal

Emanuele Copello

Francesco D’Eramo

Aldo Deandrea

Australia

Aman Desai

Caterina Doglioni

South Korea

Sunil Dogra

Mathias Garny

Norway

Sohaib Hassan

Philip Harris

Julia Harz

Alejandro Ibarra

Alberto Iorio

Felix Kahlhoefer

Deepak Kar

Egypt

Shaaban Khalil

Valery Khoze

Pyungwon Ko

Sabine Kraml

Greg Landsberg

Andre Lessa

Laura Lopez-Honorez

Alberto Mariotti

Vasiliki Mitsou

Kirtimaan Mohan

Chang-Seong Moon

Colombia

Alexander Moreno Briceno

Maria Moreno Llacer

Leandre Munoz-Aillaud

Anele Ncube

Wandile Nzuza

Clarisse Prat

Lena Rathmann

Thobani Sangweni

Dipan Sengupta

William Shepherd

Sukanya Sinha

Tim Tait

Andrea Thamm

Michel Tytgat

Zirui Wang

David Yu

Shin-Shan Yu

Publisher Erratum: $\textit{t}$-channel dark matter models – a whitepaper

This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $\textit{t}$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring $\textit{t}$-channel dark matter models at colliders and in cosmology.

$\textit{t}$-channel dark matter models – a whitepaper

We demonstrate that neural networks can be used to improve search strategies, over existing strategies, in LHC searches for light electroweak-charged scalars that decay to a muon and a heavy invisible fermion. We propose a new search involving a neural network discriminator as a final cut and show that different signal regions can be defined using networks trained on different subsets of signal samples (distinguishing low-mass and high-mass regions). We also present a workflow using publicly-available analysis tools, that can lead, from background and signal simulation, to network training, through to finding projections for limits using an analysis and libraries to interface network and recasting tools. We provide an estimate of the sensitivity of our search from Run 2 LHC data, and projections for higher luminosities, showing a clear advantage over previous methods.

Improving smuon searches with neural networks

The most recent searches by the ATLAS and CMS Collaborations in final states with soft leptons and missing transverse energy show mild excesses predominantly associated with dilepton invariant masses of about  $$10{-}20$$  <math> <mrow> <mn>10</mn> <mo>-</mo> <mn>20</mn> </mrow> </math>   GeV, which can result from decays of electroweakinos that are heavier than the lightest neutralino by  $$\mathcal {O}(10)$$  <math> <mrow> <mi>O</mi> <mo>(</mo> <mn>10</mn> <mo>)</mo> </mrow> </math>   GeV. On the other hand, these analyses are insensitive to electroweakino mass splittings smaller than about 5 GeV. In previous work, we demonstrated that while recent searches in the monojet channel can exclude some of the smallest  $$\mathcal {O}(1)$$  <math> <mrow> <mi>O</mi> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </math>   GeV mass splitting configurations for electroweakinos, they also exhibit excesses that can overlap with the soft-lepton excesses in certain models, including a simplified scenario with pure higgsinos. In this work we dive deeper into these excesses, studying the analyses in detail and exploring an array of models that go beyond the simplified scenarios considered by the experimental collaborations. We show that, in the Minimal Supersymmetric Standard Model, the overlapping excesses are not unique to the pure-higgsino limit, instead persisting in realistic parameter space featuring a bino-like lightest supersymmetric particle with some wino admixture. On the other hand, for the Next-to-Minimal Supersymmetric Standard Model with a singlino-like lightest supersymmetric particle and higgsino-like next-to-lightest supersymmetric particle(s), the excess in the two-lepton channel fits rather well with the parameter space predicting the correct relic abundance through freeze out, but the monojet fit is much poorer. Interestingly, the excesses either do not overlap or do not exist at all for two non-supersymmetric models seemingly capable of producing the correct final states.

Seeking a coherent explanation of LHC excesses for compressed spectra

We introduce a phenomenological model for a string-derived  $$Z^\prime $$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   scenario, and study its predictions for the mass of the W boson. In the process, we compare it to collider constraints for both pair-produced particles, Higgs boson properties, and  $$Z^\prime $$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   searches. We also describe the implementation of new tools in the scanning code BSMArt.

Alon Faraggi

$$M_W$$  <math> <msub> <mi>M</mi> <mi>W</mi> </msub> </math>   in string derived Z $$^\prime $$  <math> <msup> <mrow></mrow> <mo>′</mo> </msup> </math>   models

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

Gudrun Heinrich

Switzerland

Valentin Hirschi

Stefan Höche

Marius Höfer

Joshua Isaacson

Olivier Mattelaer

Thorsten Ohl

Davide Pagani

Jürgen Reuter

Peter Richardson

Steffen Schumann

Hua-Sheng Shao

Frank Siegert

Marco Zaro

UFO 2.0: the ‘Universal Feynman Output’ format

Active learning (AL) has interesting features for parameter scans of new models. We show on a variety of models that AL scans bring large efficiency gains to the traditionally tedious work of finding boundaries for BSM models. In the MSSM, this approach produces more accurate bounds. In light of our prior publication, we further refine the exploration of the parameter space of the SMSQQ model, and update the maximum mass of a dark matter singlet to 48.4 TeV. Finally we show that this technique is especially useful in more complex models like the MDGSSM.

Ari Joury

Active learning BSM parameter spaces

We investigate the conditions for alignment in Dirac Gaugino models with minimal matter content. This leads to several scenarios, including an aligned Dirac Gaugino NMSSM that allows a light singlet scalar. We then investigate the compatibility of minimal Dirac Gaugino models with an enhanced W boson mass, using a new precise computation of the quantum corrections included in the code SARAH 4.15.0.

Karim Benakli

Wenqi Ke

Pietro Slavich

W boson mass in minimal Dirac gaugino scenarios