Searching for long-lived particles at the LHC and beyond: Twelfth workshop of the LLP Community
CERN
https://cern.ch/longlivedparticles
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The twelfth LLP Community workshop will occur from 31 October to 4 November, 2022! It will be the last fully virtual LLP community workshop. (For the first day, Monday, only, if you're at CERN and you'd like to join a few of us in the Main Auditorium, feel free.)
The workshop will take place in the afternoons, Switzerland time, from 14h to about 18h or 18:30.
(N.B.: This is the week when Europe has switched away from summer time but North America has not.)
Please join us for the hottest-and-latest in LLPs around the globe.
Previous workshops can be found here.
We'd also like to understand your preferences for future community workshops! Would you prefer to have workshops 1x or 2x per year? Would you prefer they are held at CERN or outside locations? Let us know what you think in this google poll!
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Introduction and welcomeSpeaker: James Beacham (Duke University (US))
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What's new for LHC Run 3?Conveners: Carlos Vazquez Sierra (CERN), James Beacham (Duke University (US))
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First impressions of LHC Run 3: OperationsSpeaker: Silvia Franchino (Ruprecht Karls Universitaet Heidelberg (DE))
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What's new for Run 3 for LLPs at CMS?Speaker: Ka Hei Martin Kwok (Fermi National Accelerator Lab. (US))
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What's new for Run 3 for LLPs at ATLAS?Speaker: Jackson Burzynski (Simon Fraser University (CA))
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Session recording
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15:20
Workshop photo
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15:25
Coffee
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What's new for LHC Run 3?Conveners: Cristián Peña (Fermi National Accelerator Lab. (US)), Matthew Daniel Citron (Univ. of California Santa Barbara (US))
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What's new for Run 3 for LLPs at LHCb?Speaker: Elena Dall'Occo (Technische Universitaet Dortmund (DE))
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New result from CMS: Trackless and delayed jets
A search for long-lived particles decaying in the outer regions of the CMS silicon tracker or in the calorimeters is presented. A novel technique, using trackless and delayed jet information combined in a deep neural network discriminator, is employed to identify decays of long-lived particles. The results are interpreted in a simplified model of chargino-neutralino production, where the neutralino is the next-to-lightest supersymmetric particle, is long-lived, and decays to a gravitino and either a Higgs or Z boson. This search is most sensitive to neutralino proper decay lengths of ~1 m, for which neutralino masses from up to 1180 GeV are excluded at 95% confidence level.
Speaker: Lisa Benato (Hamburg University (DE)) -
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Session recording
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Dedicated LLP projectsConveners: Cristián Peña (Fermi National Accelerator Lab. (US)), Matthew Daniel Citron (Univ. of California Santa Barbara (US))
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Why so many dedicated LLP detectors? ReduxSpeaker: Matthew Citron (Univ. of California Santa Barbara (US))
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FASER's status and first collision data
FASER is designed to discover dark photons, axion-like particles, and other light and very weakly-interacting particles that are produced in the far-forward region, outside the acceptance of the larger LHC detectors. The experiment has been successfully constructed and installed and started taking data with the beginning of Run 3 of the LHC. This talk will present FASER’s physics prospects, detector design, current status, and first collision data.
Speaker: Charlotte Cavanagh (University of Liverpool (GB)) -
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Session recording
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17:05
Coffee
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Dedicated LLP projectsConveners: James Beacham (Duke University (US)), Sai Neha Santpur
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FASERnu: current status and first data from LHC Run 3
FASERnu is a 1-tonne emulsion/tungsten detector that is designed to detect and study collider neutrinos for the first time. The detector is located at the LHC in the far-forward region, 480 m from the ATLAS interaction point, and is detecting neutrinos at the highest human-made energies ever, with implications for neutrino properties, QCD, and BSM searches. The detector started taking data at the beginning of LHC’s Run 3, and the emulsion has been successfully replaced twice. This talk will present FASERnu’s physics prospects, current status, and first collision data.
Speaker: Hiroaki Kawahara (Kyushu University (JP)) -
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A new Scattering and Neutrino Detector at the LHC (SND@LHC)
SND@LHC is a compact and stand-alone experiment to perform measurements with neutrinos and long lived particles produced at the LHC in a hitherto unexplored pseudo-rapidity region of 7.2 < 𝜂 < 8.6, complementary to all the other experiments at the LHC. The experiment is located 480 m downstream of IP1 in the unused TI18 tunnel. The detector is composed of a hybrid system based on an 800 kg target mass of tungsten plates, interleaved with emulsion and electronic trackers, followed downstream by a calorimeter and a muon system. The configuration allows to efficiently distinguish between all three neutrino flavours, opening a unique opportunity to probe physics of heavy flavour production at the LHC in the region that is not accessible to ATLAS, CMS and LHCb. This region is of particular interest also for future circular colliders and for predictions of very high-energy atmospheric neutrinos. The detector concept is also well suited to searching for Feebly Interacting Particles via signatures of scattering in the detector target. The first phase aims at operating the detector throughout LHC Run 3 to collect a total of 290 fb−1. The experiment was recently installed in the TI18 tunnel at CERN and has seen its first data. An intense commissioning phase is ongoing.
Speaker: Martina Ferrillo (University of Zurich (CH))
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LLPs at far-future projectsConveners: Dr José Francisco Zurita (IFIC - Univ. of Valencia and CSIC (ES)), Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))
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Benchmarking the long-lived particle searches at future Higgs factories
Because of their clean environment and triggerless operation, the future Higgs factories seem to be a very good place to search for long-lived particles. Such studies will still be experimentally very challenging, especially in the context of detector and software requirements. Hence, we believe that these searches could constitute a good benchmark for comparisons between different proposals for the experiments at the future Higgs factories.
The experimental sensitivity to various BSM scenarios is usually presented as a function of the parameters describing a particular model. However, if different models are considered by different experiments, this makes comparisons of their results very difficult. To compare the experimental sensitivity, a more experiment-focused approach is needed, where limits are presented as a function of the physical properties of BSM particles, such as their mass, lifetime, or production cross section.
Also, the experiments at e$^+$e$^-$ colliders should allow for full event reconstruction. Higher sensitivity could be expected compared to a hadron collider, where one has to rely only on a given signature. However, one has to define the event topology of interest. For this reason, we propose a classification of the LLP signatures based on the production and decay channels. We show that many of the possible scenarios can be referred to existing theoretical models, allowing the “experimental” benchmarks to be translated into points in a model parameter space.
Speaker: Jan Franciszek Klamka (University of Warsaw (PL)) -
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Analytic formulae for the sensitivity region of DV searches for HNLs at lepton colliders
We find accurate analytic formulae that can accurately describe the shape of the sensitivity region corresponding to any number of events in a cylindrical detector during the FCC-ee or CEPC Z-pole run. This permits to study analytically how the sensitivity region depends on the various parameters (dimension of the detector, number of Z-bosons and IPs etc), without the need for simulations. The approach can be used when backgrounds are negligible, and when the dependence of the efficiency on position and direction can be neglected.
Speaker: Marco Drewes (Universite Catholique de Louvain (UCL) (BE)) -
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Heavy neutral leptons at beam dump experiments of future lepton collidersSpeaker: Douglas Tuckler
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Searching for IDM scalars at future Higgs factoriesSpeaker: Jan Franciszek Klamka (University of Warsaw (PL))
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Session recording
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15:30
Coffee
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Heavy neutral leptonsConveners: Albert De Roeck (CERN), Lisa Benato (Hamburg University (DE))
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New constraints on heavy neutral leptons from the BEBC beam dump experiment
We revisit the search for heavy neutral leptons using BEBC in the 1982 proton beam dump experiment at CERN, focussing on those heavier than the kaon and mixing only with the tau neutrino, as these are far less constrained than their counterparts with smaller mass or other mixings. Carrying out a full reanalysis of the previous data in terms of this model and including additional production and decay channels yields the strongest laboratory bounds to date up to the tau mass.
Speaker: Giacomo Marocco -
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Low-scale leptogenesis with flavour and CP symmetries
We consider a type-I seesaw framework with a flavour symmetry from the series of non-abelian groups $\Delta (3n^2)$ and $\Delta (6 n^2)$ and a CP symmetry and study the impact of these symmetries on the predictions for neutrino oscillation data, for low-scale leptogenesis and the testability prospects of the model. Based on 2203.08538 and some upcoming work.
Speaker: Yannis Georis -
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Long-lived HNLs from meson decays in EFT
In the framework of the low-energy effective field theory of the Standard Model extended with heavy neutral leptons (HNLs), we calculate the production rates of HNLs from meson decays triggered by dimension-six operators. We consider both lepton-number-conserving and lepton-number-violating four-fermion operators involving a pair of HNLs. Assuming that HNLs are long-lived, we perform simulations and investigate the reach of the proposed far detectors at the high-luminosity LHC to (i) active-heavy neutrino mixing and (ii) the Wilson coefficients associated with the effective operators, for HNL masses below the mass of the B-meson. We further convert the latter to the associated new-physics (NP) scales. Our results show that NP scales in excess of hundreds of TeV and the active-heavy mixing as small as $10^{-15}$ can be probed by these experiments.
Speaker: Rebeca Beltran (IFIC (CSIC-UV)) -
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New Benchmark Models for Heavy Neutral Lepton Searches
The sensitivity of direct searches for heavy neutral leptons (HNLs) in accelerator-based experiments depends strongly on the particles properties. Commonly used benchmark scenarios are important to ensure comparability and consistency between experimental searches, re-interpretations, and sensitivity studies at different facilities. In models where the HNLs are primarily produced and decay through the weak interaction, benchmarks are in particular defined by fixing relative strengths of their mixing with SM neutrinos of different flavours, and the interpretation of experimental data is known to strongly depend on those ratios. The commonly used benchmarks in which a single HNL flavour exclusively interacts with one Standard Model generation do not reflect what is found in realistic neutrino mass models. We identify two additional benchmarks for accelerator-based direct HNL searches, which we primarily select based on the requirement to provide a better approximation for the phenomenology of realistic neutrino mass models in view of present and future neutrino oscillation data.
Speaker: Juraj Klaric (Universite Catholique de Louvain (UCL) (BE)) -
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Session recording
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17:05
Coffee
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Heavy neutral leptonsConveners: Albert De Roeck (CERN), Audrey Katherine Kvam (University of Massachusetts (US))
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Simulation of LNV via heavy neutrino-antineutrino oscillations
Collider testable seesaw models predict pseudo-Dirac heavy neutral leptons. These almost mass degenerate pairs of heavy Majorana neutrinos can oscillate between neutrino and anti-neutrino eigenstates. Exploiting long-lived decay signatures, such oscillations can be observed in a modulation between lepton number conserving and violating processes. I present a minimal model capturing the phenomenology of lepton number violation in type I seesaw models and its FeynRules implementation. Additionally, I show how to extend MadGraph to be able to simulate such oscillations and present chosen example results.
Speaker: Jan Hajer (Universidade de Lisboa) -
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Probing neutrino dipole portal at future experiments
The neutrino dipole portal adds a Heavy Neutral Lepton (HNL) coupled to active neutrinos via dipole-like interactions with Standard model electroweak gauge fields. Motivated by the unsolved MiniBooNE, ANITA, and muon g-2 anomalies, the dipole portal provides an alternative way to test the existence of HNLs compared to the minimal model, where HNLs mix with active neutrinos. In this talk, we demonstrate how different future experiments may complementarily explore the parameter space of the dipole portal: neutrino factories (such as DUNE, FASER2) are mainly sensitive to light (< O(5 GeV)) HNLs with relatively large couplings, while collider experiments (LHC and FCC-ee) may probe higher mass HNLs with smaller couplings.
Speaker: Maksym Ovchynnikov (Leiden University (NL)) -
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Probing right-handed neutrinos dipole operators
We consider the minimal see-saw extension of the Standard Model with two right-handed singlet fermions $N_{1,2}$ with mass at the GeV scale, augmented by an effective dipole operator between the sterile states. We firstly review current bounds on this effective interaction from fixed-target and collider experiments as well as from astrophysical and cosmological observations. We then highlight the prospects for testing the decay $N_2 \to N_1 \gamma$ induced by the dipole at future facilities targeting long lived particles such as ANUBIS, CODEX-b, FACET, FASER 2, MAPP and SHiP.
Speaker: Claudio Toni (Sapienza Università di Roma) -
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Assessment of the dimension-5 seesaw portal and impact of exotic Higgs decays on non-pointing photon searches
The Dimension-5 Seesaw Portal is a Type-I Seesaw model extended by $d = 5$ operators involving the sterile neutrino states, leading to new interactions between all neutrinos and the Standard Model neutral bosons. In this work we focus primarily on the implications of these new operators at the GeV-scale. In particular, we recalculate the heavy neutrino full decay width, up to three-body decays. We also review bounds on the dipole operator, and revisit LEP constraints on its coefficient. Finally, we turn to heavy neutrino pair production from Higgs decays, where the former are long-lived and disintegrate into a photon and a light neutrino. We probe this process by recasting two ATLAS searches for non-pointing photons, showing the expected event distribution in terms of arrival time $t_\gamma$ and pointing variable $|\Delta z_\gamma|$.
Speaker: Joel Jones-Perez -
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Session recording
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New results and LLPs around the globeConveners: Lisa Benato (Hamburg University (DE)), Matthew Daniel Citron (Univ. of California Santa Barbara (US))
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New result from MicroBooNE: HNLs and Higgs portal scalarsSpeaker: Luciano Arellano (The University of Manchester)
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LUXE at DESYSpeaker: Torben Ferber (KIT - Karlsruhe Institute of Technology (DE))
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Status of SUB-Millicharge ExperimenT (SUBMET)
SUB-Millicharge ExperimenT (SUBMET) sensitive to low-mass millicharged particles produced at the 30 GeV proton fixed-target collisions at J-PARC has been proposed. The detector is composed of long scintillators that allow the particles with a small electric charge to produce photons by ionization energy loss. With the number of protons on target of $5\times10^{21}$, the experiment is sensitive to particles with electric charge $6 \times 10^{−5} e$ for mass less than 0.2 $\rm{GeV}/\rm{c}^2$ and $1.0 \times 10^{−3} e$ for mass less than $1.6 \textrm{ GeV}/\rm{c}^2$. The status of this experiment will be discussed in this talk.
Speaker: Seokju Chung (Korea University) -
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Session recording
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15:15
Coffee
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New results and LLPs around the globeConveners: Audrey Katherine Kvam (University of Massachusetts (US)), Sai Neha Santpur
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SHiP experiment at the SPS ECN3 beam facility
The SHiP Collaboration has proposed a general-purpose intensity-frontier experimental facility operating in beam dump mode at the CERN SPS accelerator to search for feebly interacting GeV-scale particles and to perform measurements in neutrino physics. SHiP complements the worldwide program of New Physics searches by exploring a large region of parameter space, which cannot be addressed by other experiments, and which reaches several orders of magnitude below existing bounds. The SHiP detector is sensitive to decay and scattering signatures of models with heavy neutral leptons, dark photons, dark scalars, light dark matter, and other super-weakly interacting particles. In neutrino physics, SHiP can perform unprecedented measurements with tau neutrinos and neutrino-induced charm production. Following the Technical Proposal submitted in 2015, the subsequent three-year Comprehensive Design Study, and the recent study of BDF/SHiP in existing beam facilities around the SPS, we restate the motivation and report on the implementation and physics performance of BDF/SHiP in the SPS ECN3 beam facility.
Speaker: Massimiliano Ferro-Luzzi (CERN) -
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Searches for hidden sector physics with the NA62 experiment
NA62 is a multipurpose fixed-target experiment performing precision measurements of charged kaon decays with an unprecedented accuracy and measuring the ultra-rare $K^+ \to \pi^+ \nu\bar{\nu}$, allowing to probe indirectly New Physics scales up to $\mathcal{O}(100)\;\mathrm{TeV}$. NA62 experiment also searches directly for weakly interacting particles of up to $\mathcal{O}(100)\;\mathrm{MeV}$ masses in kaon decays in the standard data-taking mode and up to $\mathcal{O}(1)\;\mathrm{GeV}$ masses when running in the beam-dump mode. After a successful 2016-18 Run 1, NA62 continues to collect data since 2021 in both modes of operation. Current results and future prospects on hidden sector searches at NA62 are presented in this talk.
Speaker: Jan Jerhot (Universite Catholique de Louvain (UCL) (BE)) -
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SHADOWS at the SPS
SHADOWS is a new experiment proposed at the CERN North Area to search for a large variety of FIPs produced in the interactions of a proton beam with a dump. It will use the 400 GeV primary proton beam extracted from the CERN SPS currently serving the NA62 experiment and will run concurrently to HIKE when the line is operated in beam-dump mode.
SHADOWS can expand the exploration for a large variety of Feebly-Interacting Particles (FIPs) well beyond the state of the art in a region of the parameter space that is allowed by cosmological and astrophysical observations.
The relatively small size, the relative low cost, and the excellent physics reach makes SHADOWS one of the most compelling opportunities to search for FIPs at CERN in the next decade.
Speaker: Gaia Lanfranchi (INFN e Laboratori Nazionali di Frascati (IT)) -
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Session recording
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16:45
Coffee
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New ideas for LLP searches at the LHCConveners: Lisa Benato (Hamburg University (DE)), Mason Proffitt (University of Washington (US))
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Searching for light neutralinos with a displaced vertex at the LHC
We study a bino-like light neutralino ($\tilde \chi_1^0$) produced at the LHC from the decay of a scalar lepton ($\tilde e_L$) through the process $pp\to \tilde e_{L} \to e\tilde \chi_1^0$ in the context of R-parity-violating (RPV) supersymmetry where $\tilde \chi_1^0$ is the lightest supersymmetric particle. For small masses and RPV couplings, the neutralino is naturally long-lived and its decay products can be identified as displaced tracks. Following existing searches, we propose a displaced-vertex search strategy for such a light neutralino with a single RPV coupling switched on, $\lambda'_{111}$, in the mass range 10 GeV ~< $m_{\tilde \chi_1^0}$ ~< 230 GeV. We perform Monte Carlo simulations and conclude that at the high-luminosity LHC, the proposed search can probe values of $\lambda'_{111}$ down to two orders of magnitude smaller than current bounds and up to 40 times smaller than projected limits from monolepton searches.
Speaker: Fabián Hernández-Pinto (Universidad de La Serena (CL)) -
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Reinterpretation of CMS search for LLPs using endcap muon detectors
We present the recast and sensitivity projection in a large number of benchmark models, significantly extending the physics scope of the recent search for LLPs using the CMS endcap muons detector (https://arxiv.org/abs/2107.04838). The search uses the endcap muon detectors as sampling calorimeter to identify displaced showers produced by decays of long-lived particles (LLPs). The exceptional shielding provided by the steel return-yoke interleaved between the CMS muon detector stations drastically reduces the SM background that limits other existing searches. We present a new dedicated Delphes module for fast detector response simulation of the muon detector showers. The Delphes module can be used to recast this analysis to any BSM model that predicts the existence of LLPs. I will show the recast and projected sensitivity of this search, using the Delphes module, in a few benchmark models. We show that this new search approach is sensitive to LLPs as light as a few GeV, and can be complementary to proposed and existing dedicated LLP experiments.
Speaker: Christina Wenlu Wang (California Institute of Technology (US)) -
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Session recording
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Dedicated LLP projectsConveners: Audrey Katherine Kvam (University of Massachusetts (US)), Cristián Peña (Fermi National Accelerator Lab. (US))
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A Progress Report from the MoEDAL-MAPP Experiment at the LHC
The MoEDAL experiment was approved by CERN’s Research Board (CRB) for reinstallation for LHC’s Run-3 in 2021 to continue its search for highly ionizing particle (HIP) avatars of new physics at LHC’s Run-3. Likewise, the MoEDAL Apparatus for Penetrating Particles (MAPP) was approved by the CRB for installation in the UA83 tunnel to begin data taking during Run-3. MoEDAL and MAPP-1 are currently being installed at IP8 and in UA83, respectively. The MAPP-1 detector will extend MoEDAL-MAPP’s physics reach to include Feebly Interacting Particles (FIPs) such as milli-charged particles and provide sensitivity to charged and neutral LLPs. We shall report on the: recent progress on the installation of MoEDAL-MAPP; analysis of Run-2 data; and, physics performance studies for MoEDAL-MAPP for Run-3. Last, but not least, we will briefly discuss Phase-2 of the MoEDAL-MAPP project in which the MAPP-2 detector will be deployed in the UGC1 gallery for data taking at the HL-LHC, to greatly enhance MoEDAL-MAPP’s ability to detect neutral LLPs in a cost-effective way.
Speaker: Prof. James Pinfold (University of Alberta (CA)) -
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CODEX-b Status and Plans
The High Luminosity LHC will be a tremendous opportunity to search for long-lived particles (LLPs) from an extended hidden/dark sector, feebly connected to the known SM sector. Such LLP searches will require special detectors, placed far away from the proton-proton collision point and shielded against SM backgrounds. The CODEX-b detector, to be placed behind a thick shielding wall inside the LHCb cavern, around 25m from the LHCb interaction point, provides a novel solution. On the journey to the construction of the full detector, a demonstrator (CODEX-𝛽) is foreseen for installation and operation during LHC Run 3. This talk will present the latest developments for CODEX-b and CODEX-𝛽.
Speaker: Paul Swallow (University of Birmingham (GB)) -
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Sensitivity of the proposed ANUBIS Experiment to beyond the Standard Model Long-Lived Particles at the LHC
Previous searches for BSM LLPs produced at the LHC have been hindered by a lack of tracking detectors existing at a significant distance from the interaction point. The ATLAS Experiment’s detectors only cover up to about 10 m from the LHC’s beam line, which causes the Experiment’s sensitivity to LLPs to drop-off significantly for particles with proper lifetimes in excess of O(10 ns). The ANUBIS project proposes addressing this issue by installing a new set of tracking detectors along the ceiling of the ATLAS Experiment’s cavern and/or within its service shaft. Studies show that these new detectors combined with ATLAS’ existing detectors would be sensitive to the decays of neutral BSM LLPs with ctau reaching up to 10^6 m; a significant improvement which could be realized at a relatively modest cost. This talk will discuss the proposed layouts of the ANUBIS project, their sensitivities to a representative model of BSM LLPs, and the ongoing work of constructing a prototype detector to measure the background rates in this new and exciting region of the ATLAS Experiment.
Speaker: Toby Satterthwaite (SLAC National Accelerator Laboratory (US)) -
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Session recording
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15:15
Coffee
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Dedicated LLP projectsConveners: Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US)), Sai Neha Santpur
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Status of millIQan Run 3 Detector
We will present the status of the of milliQan Run 3 Detector that has been installed in PX56 at CERN LHC P5.
Speaker: Katherine Larina (Univ. of California Santa Barbara (US)) -
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MATHUSLA
The MATHUSLA experiment is a 100m x 100m x 25m long-lived particle detector that will be located above CMS, aiming to discover long-lived particles produced in pp collisions at IP5. The latest status of the MATHUSLA detector will be presented, including detector layout, prototyping, and sensitivity studies.
Speaker: Heather Russell (University of Victoria) -
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Status of FACET - a Forward-Aperture CMS ExTension for LLP Searches
In this talk, we will present the status of the proposed FACET upgrade of the CMS detector for HL-LHC, including its physics reach for various types of LLPs and our progress in understanding the backgrounds and finalizing the detector design.
Speaker: Keith Ulmer (University of Colorado, Boulder (US))
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16:45
Coffee
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Dedicated LLP projectsConveners: James Beacham (Duke University (US)), Karri Folan Di Petrillo (Fermi National Accelerator Lab. (US))
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The Forward Liquid Argon Experiment (FLArE) at FPF
The existing LHC detectors mostly cover proton-proton interactions at high transverse momentum. As a result, they are blind to physics opportunities provided by the enormous flux of particles produced in the far forward direction. The Forward Physics Facility (FPF) will realize this physics potential. The FPF promises to provide the highest energy artificially-produced neutrino beam to date, including, for the first time, a high flux of tau neutrinos. The Forward Liquid Argon Experiment (FLArE) is being designed to take advantage of this opportunity, and will provide unique windows into both Standard Model and BSM physics.
Speaker: Steven Linden -
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Session recording
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New ideas: Searches, pheno, theoryConveners: Dr José Francisco Zurita (IFIC - Univ. of Valencia and CSIC (ES)), Mason Proffitt (University of Washington (US))
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Atmospheric axion-like particles at Super-Kamiokande
We consider a muonphilic axion-like-particle (ALP), denoted as $a$, lighter than twice the muon mass. ALPs of this mass range dominantly decay into a pair of photons, induced by a triangular muon loop. Such light muonphilic ALPs are naturally long-lived. At the atmosphere, the ALPs are copiously produced from charged-meson decays in air showers, such as $\pi^\pm \to \mu^\pm \nu a$, via the ALP-muon coupling $g_{a\mu\mu}$. After propagating tens of kilometers, the ALPs decay with $a\to \gamma \gamma$ inside large-volume Cherenkov detectors near the Earth's surface, such as Super-Kamiokande (SK). We find the present SK observation constrains on muonphilic ALPs of mass range [1 MeV, 30 MeV] and ALP-muon coupling $[10^{-3}$, $10^{2}]$, assuming the proper decay length $c\tau_a$ in [$10^{-3}$ km, $10^6$ km] either dependent on or independent of $g_{a\mu\mu}$. We conclude that atmospheric searches of such exotic states can be complementary to collider and beam-dump experiments as well as astrophysical probes.
Speaker: Zeren Simon Wang (National Tsing Hua University) -
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Shedding light on the electroweak phase transition from exotic Higgs boson decays at the lifetime frontiers
We study the scenarios where a strongly first-order electroweak phase transition (EWPT) is triggered by a light singlet scalar, which has feeble interactions to the Higgs. Since the singlet scalar is light and has weak couplings, it can decay at a macroscopic distance away from the collision point. Therefore, it can be regarded as a long-lived particle (LLP) in such scenarios. We perform the searches of the LLPs from the exotic Higgs decays, at the FASER, MAPP and CMS-timing detectors of the 14 TeV HL-LHC, to probe the strongly first-order EWPT. In certain scenarios, we show that the LLP searches can help to reach the parameter space of the strongly first-order EWPT remarkably, where the searches for promptly exotic Higgs decays are not valid.
Speaker: Wei Liu (Nanjing University of Science and Technology) -
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Analysing some long-lived NSLP signatures in the NMSSM
The Next to Minimal Supersymmetric Standard Model (NMSSM) with singlino-like neutralino as the lightest supersymmetric particle (LSP) can open up possibilities for long-lived electroweakinos. We identify such regions in the NMSSM parameter space where the next to lightest supersymmetric particle (NLSP) is a long-lived bino-like electroweakino, consistent with dark matter direct detection and collider constraints. These long-lived NLSPs can appear as displaced vertex signatures in the cascade decay of directly produced chargino-neutralino pairs at the high luminosity LHC (HL-LHC). We study the prospects of observing such scenarios at the HL-LHC through track-based analysis. We show that the discovery reach of the HL-LHC on the eletroweakino parameter space can be improved through focused long-lived particle searches.
Speaker: Amandip De
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15:00
Coffee
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New ideas: Searches, pheno, theoryConveners: Dr José Francisco Zurita (IFIC - Univ. of Valencia and CSIC (ES)), Mason Proffitt (University of Washington (US))
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Coscattering in micrOMEGAs: LLP implications in the singlet-triplet dark matter model
In scenarios with very small dark matter (DM) couplings and small mass splittings between the DM and other dark-sector particles, so-called "coscattering" or "conversion-driven freeze-out" can be the dominant mechanism for DM production. They hence also tend to feature long-lived dark-sector particles with longer lifetimes than in the well-known coannihilation case. In this talk, we present the inclusion of this mechanism in micrOMEGAs together with a case study of the phenomenological implications in the singlet-triplet model. We observe that coscattering is needed to describe the thermal behaviour of the DM for very small couplings and it opens up a new region in the parameter space of the model. Long-lived particle constraints from the LHC, evaluated with SModelS, are found to exclude a large part of this region, up to DM masses of about 500 GeV for the smallest lifetimes considered.
Speaker: Gael Alguero -
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Searching for Heavy QCD Axions via Dimuon Final States
Heavy QCD axions are well-motivated BSM candidates that can address both the strong CP problem and the axion quality problem. The defining gluon coupling can lead to significant production of such axions in beam dump and forward facilities. Additionally, if axions couple to SM leptons, as can easily happen within UV frameworks, the produced axions can exhibit long-lived decay into a pair of leptons. In particular, above the dimuon threshold and below a GeV, dimuons can be a dominant decay channel. We utilize this possibility to constrain new regions of heavy QCD axion parameter space using existing ArgoNeuT data, and project what a future analysis (e.g., at DUNE and FASER) might be able to achieve.
Speaker: Soubhik Kumar (UC Berkeley)
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15:50
Coffee
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New ideas for LLPs at LHCbConveners: Audrey Katherine Kvam (University of Massachusetts (US)), Federico Leo Redi (CERN)
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Selecting LLP in the first level trigger at LHCb
The LHCb is starting to take data in Run 3 with a completely renewed DAQ system, allowing it to take data at 30 MHz, analyzing in real time the full LHC non-empty collision rate, at an instantaneous luminosity 5 times larger than the one of the past run. One novel opportunity offered by this system is triggering on long-lived particles at the earliest stages of the trigger, thus increasing efficiency with respect to previous runs.
To test the feasibility of such triggers, I have focused on moving the reconstruction of V$^0$'s from the second trigger level (HLT2) to the first (HLT1), and studied the attainable efficiency improvement.
To this purpose, I focused on some specific channels of interest for flavor physics that produce $K^0_S$ or $\Lambda^0$ in the final state; some of them having exclusively long-lived particles in the final state, like $D^0 \rightarrow K^0_SK^0_S$ and $B^0 \rightarrow K^0_SK^0_S$. Selections based on either one or two $K^0_S$ have been fully developed, optimized and tested on LHCb Run 3 simulated samples.
Results show large increases in selection efficiency for these benchmark channels (up to 2.6x for the $D^0 \rightarrow K^0_SK^0_S$ channel), at the price of a very small HLT1 computational load, and a modest increase of trigger rates. These selections have therefore been included in the default HLT1 reconstruction and trigger sequence for physics data taking in Run 3.
These improvements were obtained with a selection that is limited to tracks originating inside the tracking volume of the VELO, which limit the flight distance acceptance. We conclude with a discussion of the prospects for extending the trigger to tracks decaying outside the VELO volume ("downstream tracks"), that are expected to bring even further improvements in acceptance for LLP.Speaker: Lorenzo Pica (SNS & INFN Pisa (IT)) -
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Following the muon track of hierarchical sectors at LHCb
B decays into multiple muons are predictions of well motivated BSM theories shuch as Composite Higgs models. In this talk, I will present the results of the phenomenologycal analysis developed in order to probe the sensitivity of the LHCb detector to those decay chains, showing that the proposed search could probe extensive regions of the parameter space which could explain the commented anomalies. By exploiting the use of tracks only reconstructed in subsystems of the detector at the high-level LHCb trigger, B(B0
s → a1a2) < 10−8 and B(B+ → K+a1a2) < 10−9 could be reached in the muon channel across seven orders of magnitude in the lifetime of the Goldstone bosons. Additionally, the reach of the proposed CODEX-b experiment is studied as well in the long-lived scenario, whilst the heaviest scalar is always considered a prompt resonance.Speaker: Emilio Xose Rodriguez Fernandez (Universidade de Santiago de Compostela (ES)) -
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Impact of the High Level Trigger for detecting long-lived particles at LHCb
Long-lived particles (LLPs) show up in many extensions of the Standard Model, yet are challenging to search for with current detectors, due to their very displaced vertices. In this talk, I will evaluate the ability of the trigger algorithms used in the LHCb experiment to detect long-lived particles and work to adapt them in order to enhance the sensitivity of this experiment to undiscovered long-lived particles. Sensitivity and efficiency to reconstruct /Lambda^O and K_s^0 SM particles are analyzed. Moreover, two particles regarding physics Beyond the Standard Model model are tested, and the sensitivity reach is discussed. I will also present the farthest tracking station of the LHCb tracking system from the collision point, the SciFi detector. One of the challenges in the track reconstruction is to deal with the large amount and combinatorics of hits in this detector. A dedicated algorithm has been developed to cope with the large data output. When fully implemented, this algorithm would greatly increase the available statistics for any long-lived particle search in the forward region, and would additionally improve the sensitivity of analyses dealing with Standard Model particles of a large lifetime.
Speaker: Diego Mendoza (Univ. of Valencia and CSIC (ES))
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