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

16 Nov 2020, 12:00 → 20 Nov 2020, 19:00 Europe/Zurich

Virtually, worldwide

Albert De Roeck (CERN), Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH)), Giovanna Cottin (Universidad Adolfo Ibañez), James Beacham (Duke University (US)), Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US)), Katherine Pachal (Duke University (US)), Matthew Daniel Citron (Univ. of California Santa Barbara (US)), Nishita Desai (Tata Institute of Fundamental Research), Rebeca Gonzalez Suarez (Uppsala University (SE))

https://cern.ch/longlivedparticles

NEW: Registration is open and the agenda is live!

The eighth LLP Community workshop will occur from 16 to 19 November 2020.  It was originally planned to take place at the Tokyo Institute of Technology, but due to the ongoing COVID-19 pandemic, it will be fully virtual again.  We look forward to having a workshop in person in Japan as soon as possible.

LLP8 will be more focused on virtual working groups than the May workshop, this time featuring vital results and open questions in dark showers, reinterpretations, HNLs, and LLPs at future colliders.  We're also featuring the latest results from ATLAS, CMS, and LHCb, as well as NA62, as usual, and nearly all of Thursday is dedicated to a new-ideas lightning round.

Discussions in Working Groups will be over the Mattermost LLP Channel

Make sure you're registered to receive remote connection information.

 

 

Monday 16 November

13:00 → 15:20 Plenary: 1

Conveners: Albert De Roeck (CERN), Nishita Desai (LUPM, Montpellier)

13:00 Introduction and welcome

Speaker: James Beacham (Duke University (US))

Beacham_LHC_LLP_Eighth_Virtual_Intro_v1_2020Nov16.pdf

13:05 Dark showers overview and WG kickoff

Speaker: Felix Kahlhoefer (RWTH Aachen)

LLP8.pdf

13:25 Reinterpretations of LLP searches overview and WG kickoff

Speakers: Prof. Andre Lessa (CCNH - Univ. Federal do ABC), Andre Lessa (IFGW - UNICAMP)

llpworkshop2020.pdf

13:45 New LLP results: ATLAS

Speaker: Elodie Deborah Resseguie (Lawrence Berkeley National Lab. (US))

ATLAS_results_LLP_workshop_111620_er.pdf

14:05 New LLP results: CMS

Speaker: Joseph Reichert (Cornell University (US))

2020-11-16 LLP8 CMS Results Final.pdf

14:25 New LLP results: LHCb

Speaker: Mr Igor Kostiuk (Nikhef National institute for subatomic physics (NL))

IK_LLP8_2020_11_16_v3p1.pdf

14:45 Latest result from the NA62 experiment at CERN

The NA62 experiment at the CERN SPS is designed to measure the branching ratio of the K+→π+vv ̅ decay, one of the best candidates to reveal indirect effects of new physics beyond the Standard Model (SM) at the highest mass scales in the flavour sector. The large data sample collected by NA62 in 2016-2018 provides sensitivities to rare kaon decays with branching ratios as low as 10-11. The high-intensity setup and the detector performance make NA62 particularly suited for searching new physics effects from different scenarios involving feebly interacting particles in the MeV—GeV mass range: heavy-neutral leptons, axion-like particles, and others.
The preliminary new result of the 𝐵𝑟(𝐾+→𝜋+𝜈𝜈¯) measurement, the most precise achieved so far, will be presented.
New results from an analysis of the flavour-changing neutral current decay K+→π+mu+mu-, well suited to explore the SM structure and, possibly, its extensions, and new results of searches for lepton flavour and lepton number violating decays of the charged kaon are also available.
Searches for heavy neutral lepton production in K+ → e+N and K+ → mu+N decays, which established upper limits on the elements of the extended neutrino mixing matrix |Ue4|2 and |Umu4|2 at the levels of 10-9 and 10-8, respectively, improving on the earlier searches in the kinematically accessible mass range, are reviewed.
Future prospects and plans for data taking from 2021 will be outlined.

Speaker: Roberta Volpe (Comenius University)

NA62VolpeLLP8.pdf

15:05 Philippe Mermod remembrance

Speakers: James Beacham (Duke University (US)), James Pinfold (University of Alberta (CA)), Tobias Golling (Universite de Geneve (CH))

Mermod-in memoriam.pdf

Philippe Mermod (1978 – 2020)

15:20 → 15:40 Coffee

15:40 → 17:15 Plenary: 2

Conveners: Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))

15:40 Overview of LLP detectors and ideas at the LHC

Speaker: Jonathan Lee Feng (University of California Irvine (US))

2011llplhc.pdf

15:50 Forward Physics Facility

Speakers: Felix Kling (SLAC), Felix Kling (University of California, Irvine)

FPF_at_LLP.pdf

16:10 CMS forward detector

Speaker: Michael Albrow (Fermi National Accelerator Lab. (US))

albrow-FMS-LLP-20201116.pdf

albrow-FMS-LLP-20201116.pptx

16:25 FASER

Speakers: Susanne Kuehn (CERN), susanne kuehn

FASER_LLP-SK.pdf

16:40 Codex-b and Codex-ß

Speaker: Xabier Cid Vidal (Instituto Galego de Física de Altas Enerxías)

CODEXb_LLP_workshop.pdf

16:55 MilliQan

Speaker: Francesco Setti (Univ. of California Santa Barbara (US))

milliQan_LLP.pdf

17:15 → 17:20 WORKSHOP PHOTO

17:20 → 17:35 Coffee

17:35 → 18:55 Plenary: 3

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

17:35 MoEDAL-MAPP

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

LLP workshop Nov. 2020.pdf

17:50 MATHUSLA

Speakers: Miriam Deborah Joy Diamond (University of Toronto (CA)), Miriam Diamond (SLAC National Laboratory)

MATHUSLA_LLP2020 v2.pdf

18:05 ANUBIS

Speaker: Giulio Aielli (INFN e Universita Roma Tor Vergata (IT))

LLP2020_-Aielli.pdf

LLP2020_-Aielli.pptx

18:20 SND@LHC

Speakers: Antonia Di Crescenzo (Universita e sezione INFN di Napoli (IT)), Antonia Di Crescenzo

8th_LLP_DiCrescenzo_SND.pdf

18:35 FORMOSA

Speakers: Yu-Dai Tsai (Lawrence Berkeley National Lab. (US)), Dr Yu-Dai Tsai (Fermilab)

FORMOSA_Forward-DUNE_Tsai.pdf

Tuesday 17 November

14:30 → 15:15 Dark showers WG: 1: Astrophysical and cosmological constraints on dark shower models

Conveners: James Beacham (Duke University (US)), Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))

Discussion Google Doc

14:30 Indirect Signatures of a Dark Glueball Spectrum

I report on an ongoing investigation of how a hidden ‘dark’ confining gauge sector, common in Hidden Valley models such as Mirror Twin Higgs and Folded Supersymmetry, could lead to novel signatures in indirect detection searches for dark matter. Dark matter annihilation can then lead to dark showers of multiple and various hadrons, distinct from particle pair production. If there are no light fermions charged under this force, the lightest hadrons are glueballs, a spectrum of a dozen metastable states that is reasonably well understood from lattice calculations. The lightest of these states, the 0++ glueball, can mix with the Higgs and decay through this portal into the Standard Model (SM). The decay of 0++ glueballs has been studied within the context of collider searches, as it is the shortest lived state, decaying on scales that can be observed as displaced vertices. However, since indirect detection methods probe astrophysical length and time scales, they are also sensitive to the decays of longer living glueball states that can decay into 0++ and SM particles; this leads to an increased multiplicity of particles such as positrons and antiprotons, but also possibly probes the properties of the entire glueball spectrum. Since the decays depend on the allowed operators, this may allow information on the UV completion of the sector to be determined. Understanding the possible indirect signatures from a pure glue gauge theory is especially relevant as the next generation of cosmic ray telescopes, such as GAPS, begin their searches.

Speaker: Caleb Gemmell (University of Toronto)

IndirectGlueballs.pdf

14:45 Discussion and live-document idea-tossing

Speakers: Caterina Doglioni (Lund University (SE)), David Curtin (University of Toronto), Simon Knapen (CERN)

15:15 → 15:20 Dark showers group activity for Snowmass 2021

Speaker: Suchita Kulkarni (University of Graz)

Kulkarni_Snowmass_darkshowers_LOI.pdf

15:20 → 15:30 Coffee

15:30 → 16:50 Dark showers WG: 2: Dark shower collider phenomenology: Dark jet structure, event isotropy, SUEP-to-jets, tools, and techniques

Conveners: James Beacham (Duke University (US)), Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))

Discussion Google Doc

15:30 Dark Shower Simulation

Speaker: Dr Marat Freytsis (Rutgers University)

LLPWorkshop1120.pdf

15:55 Tools and Observables

Speakers: Cari Cesarotti (Harvard University), Simon Knapen (CERN)

toolsLLP_Nov17.pdf

toolsLLP_Nov17.pdf

16:20 Experimental capabilities and prospects

Speakers: Andrii Usachov (Nikhef National institute for subatomic physics (NL)), Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), Kevin Pedro (Fermi National Accelerator Lab. (US)), Sascha Mehlhase (Ludwig Maximilians Universitat (DE)), Simone Pagan Griso (Lawrence Berkeley National Lab. (US))

cms dark showers LLP2020.pdf

LHCb_DarkShowers.pdf

spagan_darkshower_exp.pdf

16:50 → 17:05 Coffee

17:05 → 18:55 Heavy neutral leptons (HNLs) session

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

17:05 HNL Introduction

Speaker: Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH))

17:20 News from FIPs workshop and discussions on HNLs

Speaker: Marco Drewes (Universite Catholique de Louvain (UCL) (BE))

Drewes_LLP_HNL_Nov2020.pdf

17:40 MeV-scale Seesaw and Leptogenesis

Speaker: Michele Lucente (RWTH Aachen)

MeV seesaw leptogenesis.pdf

18:00 A quantitative study on helicity inversion in Majorana neutrino decays at the LHC

Speaker: Richard Ruiz (Universite Catholique de Louvain)

rruiz_LLP8_LNVHelicity.pdf

18:20 Discussion round on MCs for HNLs

Speakers: Jan Hajer (Université catholique de Louvain), Jean-Loup Tastet (University of Copenhagen (DK)), Lesya Shchutska (EPFL - Ecole Polytechnique Federale Lausanne (CH)), Sonia Amina Bouchiba (EPFL - Ecole Polytechnique Federale Lausanne (CH)), Various contributers

11-17-LLP-HNL-MC.pdf

HNLs in Pythia

JeanLoup_LLP_20201117.pdf

LLP8_EPFL_HNL_status.pdf

Wednesday 18 November

13:00 → 15:00 Re-interpretations WG session

Conveners: Katherine Pachal (Duke University (US)), Nishita Desai (LUPM, Montpellier)

LLP8 Reinterpretations Google Doc

13:00 Introduction

Speaker: Nishita Desai (Tata Institute of Fundamental Research)

LLP-reinterpretations.pdf

15:00 → 15:30 Coffee

15:30 → 16:30 Long-lived particles at future colliders

Conveners: Matthew Daniel Citron (Univ. of California Santa Barbara (US)), Rebeca Gonzalez Suarez (Uppsala University (SE))

15:30 Overview theory perspective

Speaker: Matthew Philip Mccullough (CERN)

LLPFuture.pdf

15:45 Overview experimental perspective

Speaker: Ryu Sawada (University of Tokyo (JP))

ryu_sawada_futureLLP_experiment.pdf

16:00 New ideas: HADES

Speaker: Jan Hajer (Université catholique de Louvain)

HADES: A long lived particle detector concept for the FCC-ee or CEPC

16:15 Discussion

Speakers: Katherine Pachal (Duke University (US)), Rebeca Gonzalez Suarez (Uppsala University (SE))

Discussion LLPs at future colliders.pdf

16:30 → 16:45 Coffee

16:45 → 18:15 Joint session: HEP Software Foundation / LLP Community on triggering and reconstruction software for dedicated LLP detectors

Joint HSF / LLP Community meeting

Thursday 19 November

13:00 → 14:00 WG reports

13:00 Dark showers WG report

LLP_dark_shower_summary.pdf

13:30 Re-interpretations WG report

Speaker: Nishita Desai (Tata Institute of Fundamental Research)

LLP-reinterpretations-summary.pdf

14:00 → 15:00 New ideas: 1

Conveners: Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), James Beacham (Duke University (US))

14:00 Exotic Higgs decays into displaced jets at the LHeC (12'+3')

Abstract: Profiling the Higgs boson requires the study of its non-standard decay modes. In this work we discuss the prospects of the Large Hadron electron Collider (LHeC) to detect scalar particles with masses >= 10 GeV produced from decays of the Standard Model (SM) Higgs boson. These scalar particles decay mainly to bottom pairs, and in a vast portion of the allowed parameter space they acquire a macroscopic lifetime, hence giving rise to displaced hadronic vertices. The LHeC provides a very clean environment that allows for easy identification of these final states, in contrast to hadronic colliders where the overwhelming backgrounds and high pile-up render such searches incredibly challenging. We find that the LHeC provides a unique window of opportunity to detect scalar particles with masses between 10 GeV and half the SM Higgs mass. In the Higgs Portal scenarios we can test the mixing angle squared, sin^2(α), as low as 10^{−5} − 10^{−7} , with the exact value depending on the vacuum expectation value of the new scalar. Our results are also presented in a model-independent fashion in the lifetime-branching ratio and mass-branching ratio planes. We have found that exotic branching ratios of the Higgs boson at the sub-percent level can be probed, for the scalar decay length in the range 10^{−4} m <= cτ <= 10^{−1} m. The expected coverage of the parameter space largely exceeds the published sensitivity of the indirect reach at the high-luminosity Large Hadron Collider via the invisible Higgs branching ratio.

Speaker: Zeren Simon Wang (National Tsing Hua University)

slides.pdf

14:15 Probing Dark Matter with Disappearing Tracks at the LHC (12'+3')

Models where dark matter is a part of an electroweak multiplet feature charged particles with macroscopic lifetimes due to the charged-neutral mass split of the order of pion mass. At the Large Hadron Collider, the ATLAS and CMS experiments will identify these charged particles as disappearing tracks, since they decay into a massive invisible dark matter candidate and a very soft charged Standard-Model particle which fails to pass the reconstruction
requirements. We have performed here the reinterpretation of the latest ATLAS disappearing track search for a suite of dark matter multiplets with different spins and electroweak quantum numbers. We consider the cases of the inert Two Higgs Doublet, Minimal Fermion Dark Matter and Vector Triplet Dark Matter models. Our procedure is validated by using the same wino and higgsino benchmark models employed by the ATLAS collaboration. We have found that with the disappearing track signature one can probe a vast portion of the parameter space, well beyond the reach of prompt missing energy searches (notably mono-jets). We providethe upper limits on the cross-section and efficiencies
in the lifetime - dark matter mass plane for all the models under consideration
which can be used for an easy recast for similar classes of models. Moreover we provide the recasting code employed here, as part of the public LLP Recasting Repository.

Speaker: Prof. Alexander Belyaev (University of Southampton & Rutherford Appleton Laboratory)

Belyaev-LLP8_workshop-19-11-2020.pdf

14:30 Enhancing Sensitivities to Long-lived Particles with High Granularity Calorimeters at the LHC (12'+3')

The search for long-lived particles (LLP) is an exciting physics opportunity in the upcoming runs of the Large Hadron Collider. In this paper, we focus on a new search strategy of using the High Granularity Calorimeter (HGCAL), part of the upgrade of the CMS detector, in such searches. In particular, we demonstrate that the high granularity of the calorimeter allows us to see ``shower tracks" in the calorimeter, and can play a crucial role in identifying the signal and suppressing the background. We study the potential reach of the HGCAL using a signal model in which the Standard Model Higgs boson decays into a pair of LLPs, $h \to XX$. After carefully estimating the Standard Model QCD and the misreconstructed fake-track backgrounds, we give the projected reach for both an existing vector boson fusion trigger and a novel displaced-track-based trigger. In comparison with these previous searches, our new search shows enhanced sensitivity in complementary regions of the LLP parameter space. We also comment on many improvements can be implemented to further improve our proposed search.

Speaker: Jia Liu (Peking University)

2020-11-19-LLP-8th-v2.pdf

14:45 New directions in BSM searches at FASER and beyond (12'+3')

A new far-forward physics program has recently been approved at the LHC to probe displaced decays of light and long-lived particles, as well as to study interactions of high-energy neutrinos in the FASER experiment. This also opens up a new direction in the LHC searches that could be continued in the longer time-scale during the HL-LHC phase. In this talk, we will focus on further BSM prospects of such future far-forward experimental programs. Among other ideas, we will discuss possible dark matter direct detection searches and the potential to study new physics particles emerging from high-energy neutrino interactions.

Speaker: Sebastian Trojanowski

forwardnewdirections_STrojanowski.pdf

15:00 → 15:20 Coffee

15:20 → 17:20 New ideas: 2

Conveners: Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), James Beacham (Duke University (US))

15:20 Extending the reach of FASER, MATHUSLA, and SHiP towards smaller lifetimes using secondary particle production (12'+3')

Many existing or proposed intensity-frontier search experiments look for decay signatures of light long-lived particles (LLPs), highly displaced from the interaction point. This approach is, however, limited to new particles with decay lengths similar to or larger than the baseline of those experiments. We will discuss how this basic constraint can be overcome in BSM models that go beyond the simplest scenarios due to additional secondary production of LLPs right in front of the detector. This way a new lifetime regime can be probed. We illustrate the prospects of such searches in the future experiments FASER, MATHUSLA, and SHiP. We also analyze additional advantages from employing dedicated neutrino detectors placed in front of the main decay volume.
The talk is based on https://arxiv.org/pdf/1911.11346.pdf

Speaker: Krzysztof Jodlowski (National Centre for Nuclear Research)

LHC_LLP_Community_Jodlowski.pdf

15:35 R-parity Violation and Light Neutralinos at ANUBIS and MAPP (12'+3')

n R-parity-violating supersymmetry the lightest neutralino can be very light, even massless. For masses in the range 500 MeV to 4.5 GeV the neutralino can be produced in hadron collisions from rare meson decays via an R-parity violating coupling, and subsequently decay to a lighter meson and a charged lepton. Due to the small neutralino mass and for small R-parity violating coupling the lightest neutralino is long-lived, leading to displaced vertices at fixed-target and collider experiments. In this work, we study such signatures at the proposed experiments ANUBIS and MAPP at the LHC. We also compare their sensitivity reach in these scenarios with that of other present and proposed experiments at the LHC such as ATLAS, CODEX-b, and MATHUSLA. We find that ANUBIS and MAPP can show complementary or superior sensitivity.

Speaker: Julian Günther

Nov2020_LLP_LHC_Workshop_Guenther.pdf

15:50 Probing the long lived heavy neutrinos at the colliders (12'+3')

The neutrino oscillation experiment has clearly pointed out that the Standard Model neutrinos have tiny masses and their flavors are mixed. There are a plenty of models which explain the mechanism of the generation of the neutrino mass. In this talk we will discuss about the simple neutrino mass generation process at the TeV scale which is often called the seesaw mechanism and its phenomenological aspects at the high energy colliders from the long-lived scenarios.

Speaker: Arindam Das (Osaka University)

Das_LLP8.pdf

16:05 Long-lived Sterile Neutrinos at the LHC in Effective Field Theory (12'+3')

We study the prospects of a displaced-vertex search of sterile neutrinos at the Large Hadron Collider (LHC) in the framework of the neutrino-extended Standard Model Effective Field Theory. The production and decay of sterile neutrinos can proceed via the standard active-sterile neutrino mixing in the weak current, as well as through higher-dimensional operators arising from decoupled new physics. If sterile neutrinos are long-lived, their decay can lead to displaced vertices which can be reconstructed. We investigate the search sensitivities for the ATLAS/CMS detector, the future far-detector experiments: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA, and MoEDAL-MAPP, and at the proposed fixed-target experiment SHiP. We study scenarios where sterile neutrinos are predominantly produced via rare charm and bottom mesons decays through minimal mixing and/or dimension-six operators in the νSMEFT Lagrangian. We perform simulations to determine the potential reach of high-luminosity LHC experiments in probing the EFT operators, finding that these experiments are very competitive with other searches.

Speaker: Mr Guanghui Zhou (University of Massachusetts Amherst)

EFT and sterile neutrino.pdf

16:20 Fast convolutional neural networks for identifying long-lived particles in a high-granularity calorimeter (12'+3')

We present a first proof of concept to directly use neural network based pattern recognition to trigger on distinct calorimeter signatures from displaced particles, such as those that arise from the decays of exotic long-lived particles. The study is performed for a high granularity forward calorimeter similar to the planned high granularity calorimeter for the high luminosity upgrade of the CMS detector at the CERN Large Hadron Collider. Without assuming a particular model that predicts long-lived particles, we show that a simple convolutional neural network, that could in principle be deployed on dedicated fast hardware, can efficiently identify showers from displaced particles down to low energies while providing a low trigger rate.
https://arxiv.org/abs/2004.10744

Speaker: Juliette Alimena (CERN)

L1CNNDispHGCal_LLP8_19Nov2020.pdf

16:35 Dark Pion Searches at Colliders and High Intensities (12'+3')

We plan to study the phenomenology and experimental searches of the dark pions, which are the lightest hadrons in a hidden sector confining gauge theory. Such a scenario arises in many extensions of the Standard Model (SM). We consider that the leading interactions between the light hidden sector quarks and the SM particles come from the mixing of the light hidden quarks with heavy electroweak doublet states through Higgs Yukawa couplings, so that the leading portals are the $Z$ and Higgs bosons. The plan is to study their productions and decays, and the search reaches at current and future experimental facilities, including high energy colliders and low energy, high intensity fixed target experiments.

Speaker: LINGFENG LI (HKUST)

Dark_Pion.pdf

16:50 A new trigger for hadronic showers in the CMS muon system sensitive to particles with large lifetimes (12'+3')

Long-lived particles are predicted in many extensions beyond the standard model. They often have unique signatures in the detector. A particularly interesting model considers long-lived particles decaying hadronically just in front of or inside the CMS muon system. These particles are capable of producing large shower of hits in the muon chambers. Due to bandwidth limitations the current muon trigger is not equipped to detect such showers. We will present expected efficiency and trigger rates for the proposed baseline scenario and outline potential future improvements

Speaker: Sven Dildick (Rice University (US))

HadronicShowerTrigger_SD_20201119_LLP8.pdf

17:05 Uniting low-scale leptogeneses (12'+3')

In this talk we will demonstrate that what was previously considered as different mechanisms of baryon asymmetry generation involving two right-handed Majorana neutrinos with masses far below the GUT scale -- leptogenesis via neutrino oscillations and resonant leptogenesis -- are actually united. We show that the observed baryon asymmetry can be generated for all experimentally allowed values of the right-handed neutrino masses above M ​≳100 MeV. Leptogenesis is effective in a broad range of the parameters, including mass splitting between two right-handed neutrinos as big as ΔMN​/MN​∼0.1, as well as mixing angles between the heavy and light neutrinos large enough to be accessible to planned intensity experiments or future colliders.

Speaker: Juraj Klaric (EPFL - Ecole Polytechnique Federale Lausanne (CH))

UnitingLeptogeneses.pdf

17:20 → 17:40 Coffee

17:40 → 20:00 New ideas: 3

Conveners: Katherine Pachal (Duke University (US)), Rebeca Gonzalez Suarez (Uppsala University (SE))

17:40 Identifying the Origin of Long-Lived Particles with MATHUSLA and CMS (12'+3')

MATHUSLA is a proposed large-volume displaced vertex (DV) detector, situated on the surface above CMS and designed to search for long-lived particles (LLPs) produced at the HL-LHC. We show that a discovery of LLPs at MATHUSLA would not only prove the existence of BSM physics, it would also uncover the theoretical origin of the LLPs, despite the fact that MATHUSLA gathers no energy or momentum information on the LLP decay products. Our analysis is simple and robust, making it easily generalizable to include more complex LLP scenarios, and our methods are applicable to LLP decays discovered in ATLAS, CMS, LHCb, or other external detectors. In the event of an LLP detection, MATHUSLA can act as a Level-1 trigger for the main detector, guaranteeing that the LLP production event is read out at CMS. We perform an LLP simplified model analysis to show that combining information from the MATHUSLA and CMS detectors would allow the LLP production mode topology to be determined with as few as ∼100 observed LLP decays. Underlying theory parameters, like the LLP and parent particle masses, can also be measured with ≲10% precision. Together with information on the LLP decay mode from the geometric properties of the observed DV, it is clear that MATHUSLA and CMS together will be able to characterize any newly discovered physics in great detail.

Speaker: Jared Barron (University of Toronto)

17:55 Probing the High-Quality QCD Axion (12'+3')

Motivated by the Strong CP and the Axion Quality problem, I will consider heavier variants of the QCD axion which has a large and uncharted parameter space where it is long-lived. By focusing on the defining axionic coupling to gluons, I will evaluate the prospect of discovery of GeV-scale axions at the HL-LHC relying on the CMS track trigger upgrade. I will also comment on vetoing possible backgrounds, including those from fake-tracks.

Speaker: Soubhik Kumar (University of Maryland)

axion-quality-llp8.pdf

18:10 LLP and multi-lepton signatures from neutrino mass models (12'+3')

We will discuss multi-lepton signals of LNV that can arise with experimentally interesting rates in certain loop models of neutrino mass generation. Interestingly, in such models the observed smallness of the active neutrino masses, together with the high-multiplicity of the final states, leads in large parts of the viable parameter space to the prediction of long-lived charged particles. We focus on one particular 1-loop neutrino mass model in this class and discuss its LHC phenomenology.

Speaker: Dr juan carlos Helo (Universidad de La Serena)

LLP Multi-lepton (2).pdf

18:25 Searching for Bino-Stop Coannihilation Region in Open Data with Displaced Tracks (12'+3')

Light top quark superpartners are the key ingredients for supersymmetric models to solve the electroweak hierarchy problem. The compressed region of the parameter space that $m_{\tilde t_1} \approx m_{\chi^0_1}$ is notoriously difficult to search. In this region, if the LSP neutralino is pure bino, $\tilde t_1$ can be long-lived, which produces displaced vertices in detectors. We propose to use the monojet trigger plus the analysis of displaced vertices to cover this region. We apply this method to the 8 TeV CMS Open Data with a luminosity of 11.6~fb$^{-1}$, and find that using this method the $2\sigma$ limit of $m_{\tilde t}$ in the region $m_{\tilde t} - m_{\chi^0} \approx 15-30$ GeV is about $m_{\tilde t} > 350$ GeV.

Speaker: Haipeng An (Tsinghua University)

LLP_workshop_HaipengAN.pdf

18:40 Charming ALPs (12'+3')

We explore the phenomenology of a pseudo-Nambu-Goldstone bosons of a spontaneous broken global U(1) symmetry, axion-like particles (ALPs), with flavour violating couplings to up-quarks and vanishing couplings to down-quarks and leptons. Such a scenario is motivated by a confining ‘dark QCD’ UV completion. For light ALPs the phenomenology is governed by the couplings to charm- and up-quarks. We consider constraints from flavour physics and cosmology and find that in part of the remaining parameter space the ‘charming ALPs’ have large lifetimes. At fixed target experiments and hadron colliders the ALPs are produced in D meson decays. The discovery prospects for FASER, FASER2, MATHUSLA, NA62 and SHiP are explored. We found that already FASER can probe the allowed part of the parameter space, where the ALPs are long-lived.

Speaker: Christiane Scherb (Universität Mainz)

LLP_charming_ALPs.pdf

18:55 Detecting signatures of heavy displaced with input hit-level features (12'+3')

Long-lived massive particles, predicted in numerous Standard Model extensions, are a particularly difficult target for online event reconstruction. This work presents a study of detecting signatures of heavy displaced vertices in a collider experiment based on input hit-level features. Preliminary results from the classification of events of a benchmark supersymmetric signal will be presented for different pile-up environments.

Speaker: Kim Albertsson

nnvx-llp8.pdf

Friday 20 November

15:00 → 16:00 Plenary: LHC LLP WG 2nd meeting

Conveners: Federico Leo Redi (EPFL - Ecole Polytechnique Federale Lausanne (CH)), Sascha Mehlhase (Ludwig Maximilians Universitat (DE))

15:00 General WG report: current status and future plans

Speaker: Carlos Vazquez Sierra (CERN)

LHC LLP WG report.pdf

15:15 Status of the Run 3 trigger white paper

link to google slides:

https://docs.google.com/presentation/d/1TGaV29r9Ed_4u2fz8XgpjQEV4XcpEp_ow0VvpgBRzAY/edit?usp=sharing

you can leave comments in the slides, so please go ahead and leave feedback and ideas, or email Yuri/David/LLP WG conveners.

Speakers: David Curtin (University of Toronto), Yuri Gershtein (Rutgers State Univ. of New Jersey (US))

Status of the Run 3 trigger white paper.pdf

15:30 Questions and comments

Please add comments and ideas to the document below to be discussed and followed-up.

Collaborative google docs