Searching for long-lived particles at the LHC and beyond: Ninth workshop of the LLP Community

25 May 2021, 13:00 → 28 May 2021, 20:00 Europe/Zurich

Virtually, worldwide

James Beacham (Duke University (US)), Nishita Desai (Tata Institute of Fundamental Research), Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US)), Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH)), José Francisco Zurita, Sascha Mehlhase (Ludwig Maximilians Universitat (DE)), Juliette Alimena (CERN), Albert De Roeck (CERN), Louie Dartmoor Corpe (CERN), Katherine Pachal (Duke University (US)), Matthew Daniel Citron (Univ. of California Santa Barbara (US))

https://cern.ch/longlivedparticles

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LLP9: The ninth LLP Community workshop will occur from 25 to 28 May, 2021, fully virtually again. We will feature new results from the central detectors of the LHC (in both summary and more detailed form, directly from the analyzers), plenty of lightning round / new ideas talks, discussions of LLPs at future detectors, brainstorming about re-interpreting LLP results that use BDTs, and more.

We're also pleased to be co-hosting a special session about dark showers simulation tools in collaboration with Suchita Kulkarni and Marie-Hélène Genest, organizers of the dark showers Snowmass project group [ https://indico.cern.ch/category/12893/ ].

The agenda is now live!

Tuesday, 25 May

14:00 → 14:15 Welcome and introduction: Five years of the LLP Community

Speaker: James Beacham (Duke University (US))

Beacham_LLP9_Intro_2021May25.pdf

14:15 → 15:15 Status of long-lived particle searches at the central detectors of the LHC

Conveners: Albert De Roeck (CERN), Louie Dartmoor Corpe (CERN)

14:15 Long-lived particles at LHCb

Speaker: Andrii Usachov (Nikhef National institute for subatomic physics (NL))

ausachov_LLPs_LHCb.pdf

14:35 Long-lived particles at CMS

Speaker: Cristián Peña (Fermi National Accelerator Lab. (US))

CP-LLP9-CMS_V3.pdf

14:55 Long-lived particles at ATLAS

Speaker: Christian Ohm (KTH Royal Institute of Technology (SE))

Ohm_ATLAS_overview_LLP9.pdf

15:15 → 15:20 Workshop photo

15:20 → 15:30 Coffee

15:30 → 16:00 FIPs 2020 and the FIPs Physics Centre

Speaker: Maxim Pospelov

LLP2021CERN_pospelov.pdf

16:00 → 16:35 Dedicated LLP detectors and projects at the LHC: Session 1

Conveners: Carlos Vazquez Sierra (CERN), James Beacham (Duke University (US)), José Francisco Zurita, Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))

16:00 Results and future plans of the MoEDAL experiment

The unprecedented collision energy of the LHC has opened up a new discovery frontier. Unfortunately, signs of new physics have yet to be seen. The LHC's first dedicated search experiment, MoEDAL, started data taking for LHC's Run-2. MoEDAL is designed to search highly ionising particle avatars of new physics using p-p and heavy-ion collisions at the LHC. The planned upgrade for MoEDAL at Run-3 - the MAPP detector ( MoEDAL Apparatus for Penetrating Particles) - will extend MoEDAL's physics reach to include feebly interacting and long lived messengers of physics beyond the Standard Model. This will allow us to explore a number of models of new physics, including dark sector models, in a complementary way to that of conventional LHC collider detectors. The presentation focuses on recent results and plans for the LHC Run 3.

Speaker: James Pinfold (University of Alberta (CA))

LLP-Workshop 2021.pdf

16:20 CODEX-b

Speaker: Biplab Dey (Eotvos U.)

CODEX-b_LLP9_Biplab.pdf

16:35 → 16:45 Coffee

16:45 → 17:40 Dedicated LLP detectors and projects at the LHC: Session 2

Conveners: Carlos Vazquez Sierra (CERN), James Beacham (Duke University (US)), José Francisco Zurita, Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))

16:45 SND@LHC

Speaker: Lesya Shchutska (EPFL - Ecole Polytechnique Federale Lausanne (CH))

05-25-LLP9-SND@LHC.pdf

17:05 FASER

Speaker: Eric Torrence (University of Oregon (US))

FASER_LLP9.pdf

17:25 MATHUSLA & Cosmic Rays

Speaker: Juan Carlos Arteaga-Velazquez (Universidad Michoacana)

CRMathusla_LLP_25May2021_JC.pdf

17:40 → 17:50 Coffee

17:50 → 18:50 Dedicated LLP detectors and projects at the LHC: Session 3

Conveners: Carlos Vazquez Sierra (CERN), James Beacham (Duke University (US)), José Francisco Zurita, Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))

17:50 FACET

Speaker: Bora Isildak (Ozyegin University (TR))

FACET_LLP9.pdf

18:10 MilliQan

Speakers: Ryan Schmitz (Univ. of California Santa Barbara (US)), Ryan Schmitz (UCSB)

milliQan_ A search for millicharged particles -- LHC Run 3 Plans (3).pdf

18:30 Forward Physics Facility

Speaker: Maria Vittoria Garzelli

semllp.pdf

Wednesday, 26 May

14:00 → 15:00 Heavy neutral leptons (HNLs) session

Conveners: Albert De Roeck (CERN), Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH))

14:00 Introduction

Speakers: Albert De Roeck (CERN), Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH))

HNL@LHC introduction.pdf

14:05 HNLs in MadGraph

Speakers: Richard Ruiz (Institute of Nuclear Physics (IFJ) PAN), Richard Ruiz (Fermi National Accelerator Lab. (US))

rruiz_LLP9_HeavyN.pdf

14:25 HNL production from mesons

Speaker: Philip Ilten (University of Cincinnati (US))

ilten.pdf

14:45 Discussion

15:00 → 15:10 Coffee

15:10 → 16:22 Reinterpretation

Conveners: Dr Louie Dartmoor Corpe (CERN), Nishita Desai (LUPM, Montpellier)

15:10 Reinterpretation of LLP searches with SModelS 2.0

Speaker: Jan Heisig (Université catholique de Louvain (UCL))

Heisig_SModelS_LLP_May2021.pdf

15:22 Brainstorming: what would it take to be able to re-interpret analyses which use machine learning ?

This session will be a discussion on issues related to re-interpretation of LLP searches which use machine learning: something which is very non-trivial but will become urgent to resolve as increasing numbers of analyses adopt these techniques.

Please feel free to add ideas to the live doc:

https://docs.google.com/document/d/1c0GwC1mzwePqWzfD9PgNTRV078m560vCpviw_t7NALU/edit

audio_only.m4a

Live Doc

16:22 → 16:35 Coffee

16:35 → 17:35 Non-standard backgrounds for the HL-LHC

Conveners: Matthew Daniel Citron (Univ. of California Santa Barbara (US)), Sascha Mehlhase (Ludwig Maximilians Universitat (DE))

NonStandardBkgDiscussion.pdf

16:35 Beam induced backgrounds at the HL-LHC (CMS perspective)

Speakers: Anne Dabrowski (CERN), Bhawna Gomber (University of Hyderabad, India)

LLP_Workshop_25thMay_BG.pdf

16:50 Rejecting BIB at the HL-LHC (CMS perspective)

Speaker: Laurent Thomas (Universite Libre de Bruxelles (BE))

beamhalo_LLP.pdf

17:05 Open discussion

17:35 → 17:45 Coffee

17:45 → 18:57 Lightning round / new ideas: New results from ATLAS and CMS, in detail

Conveners: Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH)), Matthew Daniel Citron (Univ. of California Santa Barbara (US))

17:45 Stopped particles with ATLAS

A search for long-lived particles, which have come to rest within the ATLAS detector, is presented. The subsequent decays of these long-lived particles can produce high-momentum jets, resulting in large out-of-time energy deposits in the ATLAS calorimeters. These decays are detected using data collected during periods in the LHC bunch structure when collisions are absent. The analysed dataset is composed of events from proton--proton collisions produced by the LHC at a centre-of-mass energy of $\sqrt{s}=13$~TeV and recorded by the ATLAS experiment during 2017 and 2018. The results of this search are used to derive lower limits on the mass of gluino $R$-hadrons, assuming a branching fraction $\mathcal{B}(\tilde{g}\rightarrow q \bar{q} \tilde{\chi}_1^0)=100$\%, with masses of up to $1.4$~TeV excluded for gluino lifetimes of $10^{-5}$ to $10^3$~s.

Speaker: Stefanie Morgenstern (University of Warwick (UK))

StoppedParticles_LHCLLP9.pdf

17:57 Neutral Long-lived Particles Decaying in the CSCs with CMS

A search for long-lived particles (LLPs) produced in decays of standard model (SM) Higgs bosons in $137~\mathrm{fb}^{-1}$ of proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ recorded by the CMS experiment during $2016$$-$$2018$ is presented. The search employs a novel technique to reconstruct hadronic decays of LLPs in the endcap muon system. The search is sensitive to a broad range of LLP decay modes including $\tau^{-}\tau^{+}$, LLP masses as low as a few GeV, and is largely model-independent. No excess of events above the SM background is observed and stringent limits on the Higgs boson ($\mathrm{h}^0$) branching fraction to LLPs ($\mathrm{S}$) are obtained, particularly for proper decay lengths greater than a few meters. This search result represents the most stringent limits on the branching fraction $\mathcal{B}(\mathrm{h}^0 \rightarrow\mathrm{S}\mathrm{S})$ for proper decay lengths greater than $6$$-$$40$ m for S masses between $7$$-$$40$ GeV.

Speaker: Christina Wenlu Wang (California Institute of Technology (US))

CW_LLP9_20210526.pdf

18:09 Disappearing tracks with ATLAS

This talk is based on the result of ATLAS-CONF-2021-015. The search for long-lived charginos based on a disappearing track signature with the full Run-2 ATLAS dataset is performed. Improvements from the previous analysis are increasing statistics and implementing calorimeter veto for the background reduction. We only use 4-layer tracklets in this analysis. We observed 3 events and 1 event with the high-pT signal region in the electroweak channel and strong channel respectively. These are consistent with the background, so we updated the limits. Chargino masses up to 660 (210) GeV are excluded in the pure wino (higgsino) LSP scenario in the electroweak channel, and the maximum reach for the chargino mass with 0.2 ns lifetime is 1.4 TeV in the strong channel.

Speaker: Toshiaki Kaji (Waseda University (JP))

LLPWS_2021May26_0.pdf

18:21 Higgs boson decays to long-lived scalar particles in associated Higgs boson production with CMS

This talk presents a search for long-lived particles (LLPs) produced in association with a $\mathrm{Z}$ boson. The search is performed with data from $13\,\mathrm{TeV}$ proton-proton collisions recorded by the CMS experiment during 2016--2018, corresponding to an integrated luminosity of $117\,\mathrm{fb}^{-1}$. The LLPs are assumed to decay into a pair of standard model fermions inside the tracker volume, which results in displaced jets. A trigger and selections based on Z boson decays to electron or muon pairs provide sensitivity to light ($15\,\mathrm{GeV}$ or less) LLPs, which have up to now been difficult to access. Decays of LLPs are selected by requiring the presence of displaced jets which are identified using information from the CMS tracking system. The results are interpreted in the context of exotic decays of the Higgs boson to LLPs ($\mathrm{H} \to \mathrm{S}\mathrm{S}$). The search is sensitive to branching fractions $\mathcal{B}(\mathrm{H} \to \mathrm{S}\mathrm{S})$ of $4$--$5\%$ (less than $20\%$) for LLP masses of 40 (15)$\,\mathrm{GeV}$ and mean proper decay lengths of 10--$100\,\mathrm{mm}$ (10--$50\,\mathrm{mm}$).

Speaker: Daniel Diaz (Univ. of California San Diego (US))

LLP9_CMS_AssociatedZH_v3.pdf

18:33 Search for exotic decays of the Higgs boson to long-lived particles using displaced vertices in the ATLAS inner detector

A novel search for exotic decays of the Higgs boson to pairs of long-lived neutral particles, each decaying to a bottom quark pair, is performed using 139 fb$^{-1}$ of $\sqrt{s} = 13$ TeV proton-proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a $Z$ boson are analyzed, with the leptonic decay of the $Z$ mitigating the trigger challenges associated with displaced objects. Long-lived particle (LLP) decays are reconstructed from inner detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively suppressing Standard Model backgrounds. The residual background contribution is estimated using a fully data driven technique. No excess over the Standard Model prediction is observed, and upper limits are set on the branching ratio of the Higgs boson to pairs of LLPs. Branching ratios of $10\%$ are excluded at the $95\%$ confidence level for LLP mean proper lifetimes $c\tau$ as small as 4 mm and as large as 110 mm. For LLP masses below 40 GeV, these results represent the most stringent constraints to date for this range of proper lifetimes.

Speaker: Jackson Carl Burzynski (University of Massachusetts (US))

LHCLLP2021.pdf

18:45 Scouting for displaced di-muon resonances with CMS

A search for displaced dimuon resonances is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2017−2018, corresponding to an integrated luminosity of 101 fb−1 . The data sets used in this search were collected using a dedicated dimuon trigger stream with low transverse momentum thresholds, recorded at high rate by retaining a reduced amount of trigger-level information, in order to explore otherwise inaccessible phase space at low dimuon mass and non-zero displacement from the interaction point. We find no significant excess, and use the data to set stringent constraints on a wide range of mass and lifetime hypotheses for models of physics beyond the standard model where a Higgs boson decays to a pair of long-lived dark photons, or where a long-lived scalar resonance arises from the decay of a B hadron

Speaker: Hardik Routray (Rutgers State Univ. of New Jersey (US))

LHCLLP9_EXO-20-014.pdf

Thursday, 27 May

14:00 → 14:48 Lightning round / new ideas

Conveners: Juliette Alimena (CERN), Nishita Desai (Tata Institute of Fundamental Research)

14:00 Dark photon from scalar boson decays at FASER

FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this talk, we focus on dark photon associating with an additional U(1) gauge symmetry, and also a scalar boson breaking this U(1) symmetry. The sensitivity to the dark photon originated from U(1) breaking scalar decays is studied. We show that a sizable number of dark photon signatures can be expected in wider parameter space than previous studies.

Speaker: Takashi Shimomura (University of Miyazaki)

LLP2021-Shimomura.pdf

14:12 Long-lived light neutralinos at Belle II

We consider light neutralinos of mass about 1 GeV, produced from $\tau$ lepton rare decays at Belle II, in the context of R-parity-violating (RPV) supersymmetry. With large and clean samples of $\tau$ leptons produced at the Belle II experiment, excellent sensitivity to such light neutralinos with the exotic signatures of displaced vertices is expected. We focus on two benchmark scenarios of single RPV operators, $\lambda'_{311} L_3 Q_1 \bar{D}_1$ and $\lambda'_{312} L_3 Q_1 \bar{D}_2$, which induce both the production and decay of the lightest neutralino. For the reconstruction of a displaced vertex, we require at least two charged pions in the final states. We perform Monte-Carlo simulations for both signal and background events, and find that Belle II can explore regions in the parameter space competitive with other probes. In particular, for the $\lambda'_{311}$ scenario, it can put limits up to two orders of magnitude stronger than the current bounds.

Speaker: Zeren Simon Wang (National Tsing Hua University)

lightneutralino_belleII_Wang.pdf

14:24 Triggering on Emerging Jets

Confining dark sectors at the GeV scale can lead to novel collider signatures including those termed emerging jets with large numbers of displaced vertices. The triggers at the LHC experiments were not designed with this type of new physics in mind, and triggering can be challenging, especially if the mediator is relatively light and/or has quantum numbers such that additional jets are not automatically produced in each event. We show that the efficiency and the total event rate at current triggers can be significantly improved by considering initial state radiation of the events, with the largest increase in rate coming from simulation of two additional jets. We also explore possible new triggers that employ hit counts in different tracker layers as input into a machine learning algorithm. We show that these new triggers can have reasonably low background rates, and that they are sensitive to a wide range of new physics parameters even when trained on a single model.

Speaker: Dylan Linthorne (Carleton University)

EmergingJetsLLP9.pdf

14:36 Searching for a sterile neutrino that mixes predominantly with ντ at B factories

The phenomenon of neutrino flavor oscillations motivates searches for sterile neutrinos in a broad range of masses and mixing-parameter values. A sterile neutrino $N$ that mixes predominantly with the $\tau$ neutrino is particularly challenging experimentally. To address this challenge, we propose a new method to search for a $\nu_\tau$-mixing with $N$ lighter than the $\tau$ lepton. The method uses the large $e^+e^-\to\tau^+\tau^-$ samples collected at $B$-factory experiments to produce the $N$ in $\tau$-lepton decays. We exploit the long lifetime of a sterile neutrino in this mass range to suppress background and apply kinematic and vertexing constraints that enable measuring the sterile neutrino mass. Estimates for the sensitivities of the BABAR, Belle, and Belle II experiments are calculated and presented.

Speaker: Nicolas Neill (Universidad de Tarapacá (CL))

LLP2021_heavyNBelleII_2021may27_NNeill.pdf

14:48 → 15:00 Coffee

15:00 → 17:00 Dark showers simulation tools session: Tutorial

Conveners: Marie-Helene Genest (LPSC-Grenoble, CNRS/UGA (FR)), Nishita Desai (Tata Institute of Fundamental Research), Suchita Kulkarni (University of Graz)

DarkShowers_Setup_Instructions_LLP9_2021May27.txt

GMT20210527-132944_Recording_3360x1440.mp4

GMT20210527-132944_Recording.m4a

Google doc with summary of session & action points

Recording

15:00 Simulating semi-visible jets via pythia HV module

Speakers: Daniel Stolarski (Carleton University (CA)), Simon Knapen (CERN), Suchita Kulkarni (University of Graz)

DS_clean.zip

Kulkarni_DS_tutorial.pdf

16:00 Simulating SUEP signatures

Speaker: Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))

2020.05.26.kdp.SUEPTutorial.pdf

dropbox:suepHepMC

github:suep_generator

github:suepTutorial

17:00 → 17:15 Coffee

17:15 → 18:00 Dark showers simulation tools session: Discussion

Conveners: Marie-Helene Genest (LPSC-Grenoble, CNRS/UGA (FR)), Nishita Desai (Tata Institute of Fundamental Research), Suchita Kulkarni (University of Graz)

DarkShowers_Setup_Instructions_LLP9_2021May27.txt

GMT20210527-132944_Recording_3360x1440.mp4

GMT20210527-132944_Recording.m4a

Google doc with summary of session & action points

Recording

17:15 Discussion on limitations of Pythia HV module

Participants: Marat Freytsis, Torbjörn Sjöstrand, Simon Knapen, Karri Folan DiPetrillo, Matt Strassler

Speakers: Marat Freytsis (Rutgers University), Marat Freytsis (Harvard University)

LLPWorkshop0521.pdf

18:00 → 18:15 Coffee

18:15 → 19:15 Lightning round / new ideas

Conveners: Carlos Vazquez Sierra (CERN), Katherine Pachal (Duke University (US))

18:15 Perturbative benchmark models for a dark shower search program

Speaker: Dr Jessie Shelton

210527-LHCLLP.pdf

18:27 A Displaced Fat Jet Signature at LHeC

Extending the Standard Model with right-handed neutrinos (RHNs) is well motivated by the observation of neutrino oscillations. In the type-I seesaw model, the RHNs interact with the SM particles via tiny mixings with the active neutrinos, which makes their discovery in the laboratory, and in particular at collider experiments in general challenging. In this work we instead consider an extension of the type-I seesaw model with the addition of a leptoquark (LQ), and employ a non-minimal production mechanism of the RHN via LQ decay, which is unsuppressed by neutrino mixing. We focus on relatively light RHN with mass $\mathcal{O}(10)$ GeV and LQ with mass 1.0 TeV, and explore the discovery prospect of the RHN at the proposed Large Hadron electron Collider. In the considered mass range and with the given interaction strength, the RHN is long lived and, due to it stemming from the LQ decay, it is also heavily boosted, resulting in collimated decay products. The unique signature under investigation is thus a displaced fat jet. We use kinematic variables to separate signal from background, and demonstrate that the ratio variables with respect to energy/number of displaced and prompt tracks are useful handles in the identification of displaced decays of the RHN. We also show that employing a positron beam provides order of magnitude enhancement in the detection prospect of this signature.

Speaker: ROJALIN PADHAN (Institute of Physics, Bhubaneswar)

LHC-LPP-Rojalin.pdf

18:39 Quasistable charginos in ultraperipheral proton-proton collisions at the LHC

We propose a model-independent approach for the search of charged long-lived particles produced in ultraperipheral collisions at the LHC. The main idea is to improve event reconstruction at ATLAS and CMS with the help of their forward detectors. Detection of both scattered protons in forward detectors allows complete recovery of event kinematics. Though this requirement reduces the number of events, it greatly suppresses the background, including the large background from the pile-up.

Speaker: Evgenii Zhemchugov (National Research Nuclear University MEPhI (RU))

llp-upc-lhc.pdf

18:51 Modeling exotic Higgs decays to vector bosons with displaced dimuons in the final states

Models for long-lived dark Z bosons are considered where the dark sector interacts with the standard model either via hypercharge or Higgs portals. In this context, the production mechanism of the dark Z is determined based on two simultaneous mixings where the standard-model Z boson can mix kinetically with the dark Z and the standard-model Higgs can mix with a dark Higgs. An exotic decay mode is induced if one of the two mixings is dominant over the other. However, we also address the case if nature prefers equal strength of the two mixings regardless of the decay mode. We study exotic decays of the standard-model Higgs that produce a dark Z that then decays directly to a final state of displaced dimuons with decay lengths in the range of 1-1000 mm. The production and total cross sections of the processes of interest as well as decay widths and decay lengths are calculated with Monte Carlo simulations using the framework of MadGraph5_aMC@NLO v2.7.0. The sensitivity for such searches in Runs 2 and 3 of the Large Hadron Collider is discussed. The kinematics of the displaced dimuons is also investigated.

Speaker: Tamer Elkafrawy (Florida Institute of Technology (US))

LL_DM_T.Elkafrawy_LLP9_2021_v2.pdf

Friday, 28 May

14:00 → 14:48 Lightning round / new ideas

Conveners: Dr José Francisco Zurita (IFIC - Univ. of Valencia and CSIC (ES)), Katherine Pachal (Duke University (US))

14:00 Probing naturally light singlets with a displaced vertex trigger

Speaker: Dr Diego Redigolo (CERN-INFN Florence)

talk_displaced.pdf

14:12 Probing the early universe with displaced new physics at colliders

Displaced vertices at colliders, arising from the production and decay of long-lived particles, probe dark matter candidates produced via freeze-in. If one assumes a standard cosmological history, these decays happen inside the detector only if the dark matter is very light because of the relic density constraint. Here, we argue how displaced events could very well point to freeze-in within a non-standard early universe history. Focusing on the cosmology of inflationary reheating, we explore the interplay between the reheating temperature and collider signatures for minimal freeze-in scenarios. Observing displaced events at the LHC would allow to set an upper bound on the reheating temperature and, in general, to gather indirect information on the early history of the universe.

Speaker: Sam Junius (ULB & VUB)

LLP_workshop_2021_SJ.pdf

14:24 Displaced Vertex signatures of a pseudo-Goldstone sterile neutrino

Low-scale models of neutrino mass generation often feature sterile neutrinos with masses in the GeV-TeV range, which can be produced at colliders through their mixing with the Standard Model neutrinos. We consider an alternative scenario in which the sterile neutrino is produced in the decay of a heavier particle, such that its production cross section does not depend on the active-sterile neutrino mixing angles. The mixing angles can be accessed through the decays of the sterile neutrino, provided that they lead to observable displaced vertices. We present an explicit realization of this scenario in which the sterile neutrino is the supersymmetric partner of a pseudo-Nambu-Goldstone boson, and is produced in the decays of higgsino-like neutralinos and charginos. The model predicts the active-sterile neutrino mixing angles in terms of a small number of parameters. We show that a sterile neutrino with a mass between a few 10 GeV and 200 GeV can lead to observable displaced vertices at the LHC.

Speaker: Dr Anibal Medina (Instituto de Fisica La Plata)

LLP9talkMedina.pdf

14:36 Portal Effective Theories: A framework for the model independent description of light hidden sector interactions

We present a framework for the construction of portal effective theories(PETs) that couple effective field theories of the Standard Model (SM) to light hidden messenger fields. Using this framework we construct electroweak and strong scale PETs that couple the SM to messengers carrying spin zero, onehalf, or one. The electroweak scale PETs encompass all portal operators up to dimension five, while the strong scale PETs additionally contain all portal operators of dimension six and seven that contribute at leading order to quark-flavour violating transitions. Using the strong scale PETs, we define a set of portal currents that couple hidden sectors to QCD, and construct portal chiral perturbation theories (χPTs) that relate these currents to the light pseudoscalar mesons. We estimate the coefficients of the portal χPTLagrangian that are not fixed by SM observations using non-perturbative matching techniques and give a complete list of the resulting one- and two-meson portal interactions. From those, we compute transition amplitudes for three golden channels that are used in hidden sector searches at fixed target experiments: i) charged kaon decay into a charged pion and a spin zero messenger, ii) charged kaon decay into a charged lepton and a spin one half messenger, and iii) neutral pion decay into a photon and a spin one messenger. Finally, we compare these amplitudes to specific expressions for models featuring light scalar particles, axion-like particles, heavy neutral leptons,and dark photons.

Speakers: Philipp Klose, Philipp Mauritz Klose (Universität Bern)

klose_LLP9.pdf

klose_LLP9.pdf

14:48 → 15:00 Coffee

15:00 → 16:00 LHC LLP Working Group meeting

Conveners: Albert De Roeck (CERN), Carlos Vazquez Sierra (CERN), Dave Casper (University of California Irvine (US)), Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH)), James Beacham (Duke University (US)), James Pinfold (University of Alberta (CA)), Dr José Francisco Zurita (IFIC - Univ. of Valencia and CSIC (ES)), Juliette Alimena (CERN), Nishita Desai (Tata Institute of Fundamental Research), Sascha Mehlhase (Ludwig Maximilians Universitat (DE))

15:00 Status of the WG

Speaker: Juliette Alimena (CERN)

LHCLLPWGreport_LLP9_28May2021.pdf

15:15 Discussion

16:00 → 16:10 Coffee

16:10 → 17:10 LLPs at future colliders -- and future ideas: (muon colliders)

Conveners: Albert De Roeck (CERN), Carlos Vazquez Sierra (CERN), Sergo Jindariani (Fermi National Accelerator Lab. (US))

GMT20210528-141211_Recording.m4a

Live doc

Recording

16:10 LLPs at a muon collider: Theory

Speaker: Zhen Liu (University of Minnesota)

MuC_LLP9_May2021_ZhenLiu.pdf

16:25 Introduction to the muon collider

Speaker: Simone Pagan Griso (Lawrence Berkeley National Lab. (US))

spagan-muoncollider-intro-exp.pdf

16:40 LLPs at a muon collider: Experiment

Speaker: Federico Meloni (Deutsches Elektronen-Synchrotron (DE))

MuonCollider_LLP9.pdf

17:10 → 17:20 Coffee

17:20 → 18:05 LLPs at future colliders -- and future ideas: (Future detector at FCChh)

Conveners: Andrew Haas (New York University), David Curtin (University of Toronto), James Beacham (Duke University (US)), Matthew Daniel Citron (Univ. of California Santa Barbara (US)), Matthew Low (Fermilab)

GMT20210528-141211_Recording.m4a

Live doc

Recording

18:05 → 19:05 Lightning round / new ideas

Conveners: Juliette Alimena (CERN), Sascha Mehlhase (Ludwig Maximilians Universitat (DE))

18:05 GAZELLE - a new long-lived particle detector for Belle II?

A future far detector at Belle II - GAZELLE - could enhance the search potential for long-lived particles at electron-positron experiments. An initiative of theorists and experimentalists has explored this potential for three common LLP scenarios with different production mechanisms. In this talk, we compare the projections of finding these LLPs at Belle II or GAZELLE. Due to Belle II's excellent sensitivity to LLPs, we find little extra gain in building a far detector like GAZELLE.

Speaker: Ruth Schäfer (Universität Heidelberg)

GAZELLE_Schaefer_LLP9.pdf

Physics reach of a long-lived particle detector at Belle II

18:17 Model-independent probes of hidden sectors

Hidden sectors are well motivated theoretically, and there is increasingly focused experimental activity to probe them. In this talk, I will present the theoretical framework to probe such sectors in a model-independent manner. I will focus on sectors that communicate with the standard model through irrelevant portal operators. Such portals can be shown to arise naturally, on very general principles. I will focus on sectors with approximate scale invariance dynamics, and elucidate how this allows model-independent bounds to be derived. I will present constraints from various classes of experiments and explain the procedures and assumptions involved. The general picture that emerges is that these sectors are poorly constrained at the moment and points to the kind of future experimental facilities that will improve the reach.
(based on 2012.08537)

Speaker: Rashmish Mishra (Harvard University)

LLP9_DS.pdf

18:29 Detecting long-lived multi-charged particles in neutrino mass models with MoEDAL

Monopole and Exotics Detector at the LHC (MoEDAL) is a mostly passive detector located in the LHCb cavern, just outside LHCb detector. MoEDAL was designed to search for magnetic monopoles, but it also sensitive to long-lived charged particles.

A certain class of neutrino mass models predicts long-lived particles whose electric charge
is four or three times larger than that of protons. Such particles, if they are light enough,
may be produced at the LHC and detected. We investigate the possibility of observing those
long-lived multi-charged particles with the MoEDAL detector.

To demonstrate the performance of MoEDAL on multi-charged long-lived particles, two concrete neutrino mass models are studied. In the first model, the new physics sector is non-coloured and contains long-lived particles with electric charges 2, 3 and 4. The second model has a coloured new physics sector, which possesses long-lived particles with electric charges 4/3, 7/3 and 10/3. We explore the parameter space of these models and identify the regions that can be probed with MoEDAL at the end of Run-3 and the High-Luminosity LHC.

Speaker: Rafal Maselek (University of Warsaw)

LLPworkshop_RM.pdf

18:41 Long-lived bi$\nu$o at the LHC

A pseudo-Dirac bino could be responsible for generating nuetrino masses in R-symmetric MSSM. We show that this bino, which we rename bi$\nu$o can be long lived in certain parameter regions and could be searched for in proposed experiments like MATHUSLA and CODEX-b. These experiments can probe biνo masses of 10 GeV-2 TeV and SUSY messenger scales $10^{2−11}$ TeV for a range of squark masses.

Speaker: Seyda Ipek

ipek_LLPworkshop.pdf

18:53 Leptogenesis across the electroweak scale

Speaker: Yannis Georis (Catholic University of Louvain)

Slides_LLP_presentation.pdf