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YOUNGST@RS - Colours in darkness: towards improved modelling of strongly interacting dark-sector showers

→ Europe/Berlin
Description

All discussions have been summarised in a workshop summary report: arXiv:2311.16330

 

In recent years, there has been an increase in the number of search programmes exploring the possiblity of a "dark sector" beyond the Standard Model (BSM) using LHC data. To date, dark-matter searches at the LHC have usually focused on WIMPs, but since the standard signatures have found no compelling evidence, several recent phenomenology papers have explored the possibility of accessing the dark sector with unique collider topologies. If dark mesons exist, their evolution and hadronization procedure are currently little constrained. They could decay promptly and result in a very Standard Model (SM) QCD-like jet structure, even though the original decaying particles are dark-sector ones; they could behave as semi-visible jets; or they could behave as completely detector-stable hadrons, in which case the final state is just the missing transverse momentum. Furthermore, depending on whether the dark hadrons decay promptly or not, emerging jet signatures can also arise.

 

Owing to the associated experimental challenges, these classes of models are still under developed and mildly explored. Recent developments in reconstruction and identification techniques have made it possible to probe such models at the Large Hadron Collider, and the first limits on some of these signatures are public from both ATLAS and CMS. However, there's still a lot of ground left to cover, in terms of shower/hadronisation approach, and benchmarking the models for future iterations of the searches as we step into an era of unprecedented data, with LHC Run-3 well underway.

 

This workshop aims to foster collaboration between the experimental and theory community dedicated towards developing and understanding the strongly interacting dark sector. The workshop will feature talks from the leading experts in the field, and extensive discussion sessions, to understand the current status of the dark showering module within Monte Carlo generators like Pythia and Herwig, as well as establishing a set of realistic benchmark models that will drive future search strategies. 

 

The following Zoom room will be used for all days and all sessions: https://zoom.us/j/97148725055?pwd=ckYyWFByVkNiSWlzajlMV3Y5V2ozQT09

 

Contact @ MITP : Guest Relations Team
  • Tuesday 17 October
  • Wednesday 18 October
    • 13:00 → 13:05
      Introduction 5m
      Speaker: Sukanya Sinha (University of Manchester (GB))
      MITP WS intro day 2.pdf
    • 13:05 → 14:05
      Overview talks: Experimental perspective
    • 14:05 → 14:15
      Coffee break 10m
    • 14:15 → 14:55
      Overview Talks (Part 2)
      • 14:15
        ATLAS: semi-visible jets t-channel 15m
        Speaker: Deepak Kar
        dk-dsWS.pdf
      • 14:35
        ATLAS: dark jet resonance 15m
        Speaker: Dilia Maria Portillo Quintero
        ATLAS DJR
    • 14:55 → 15:25
      ECS Session
      • 14:55
        HEPData for dark jet resonances 7m

        ECS Lightning talk

        Recently, the first search for a resonance arising from the dark sector in the fully hadronic channel, using the ATLAS detector, has been made public. Events containing at least two large-radius jets with high track multiplicity are selected, and a resonant search is performed over the invariant mass distributions of the multi-jet background. The analysis considered four benchmark models, to span a broad parameter space that results in the desired signature. However, this analysis is not an exhaustive exploration of all possible dark QCD parameter combinations or BSM theories to which ATLAS is sensitive to in the analysis search region. To ensure the implications of this dark jet resonance search is beneficial for other BSM models, it's crucial to store the relevant data in HEPData. HEPData is a public online database containing data from HEP publications, such that the data is easily accessible and reusable. We present the proposed information from this analysis to preserve, including model dependent and independent limits, a cutflow table, and selected observable distributions.

        Speaker: Danielle Joan Wilson-Edwards
        DJR _ HEPDATA-2.pdf
      • 15:05
        Simulating near-conformal Hidden Valleys 7m

        ECS Lightning talk

        We explore the behaviour of the running coupling within the Hidden Valley module of Pythia at a high number of flavours, finding that the current implementation cannot accurately simulate the expected behaviour. The unique IR behaviour at a high number of flavours allows us to demonstrate the first steps for finding a running coupling which matches the expected behaviour.

        Speaker: Joshua Lockyer
        Lockyer_MITPDarkSectors_2023.pdf
      • 15:15
        New experimental techniques for dark sectors 7m

        The nature of dark matter (DM) remains one of the biggest open questions in physics and has eluded astrophysical and cosmological scientists searching for indirect evidence of its existence. In recent years at the Large Hadron Collider (LHC), there has been an increase in efforts to explore the dark sector using LHC data. New studies explore the possibility of accessing the dark sector containing DM with unusual collider topologies.
        This talk explores the recent DM model of dark sector jets with observable signatures called Semi-Visible Jets (SVJ), jets with some fraction of invisible DM particles, and Emerging Jets (EJ), jets with displaced vertices.
        Due to the constraint of recording information from every proton-proton (pp) collision event at the LHC, the ATLAS experiment at LHC uses a trigger and data acquisition (TDAQ) system that selects and sends interesting events to the data storage system while throwing away the rest. The challenge lies in situations where large backgrounds bury the interesting events and they are thrown out and not identified as signals by the trigger system.
        Partial Event Building (PEB) poses a solution by storing only part of the detector raw information, together with high level information. This leads to smaller event sizes and allows us to record larger datasets using the same storage space. This report conducts a preliminary feasibility study on triggering on the dark sector and leveraging PEB to search for dark sector models containing the unusual SVJs and EJs.

        Speaker: Angelica Aira Araw Ayalin
        YOUNGST@RS Workshop - Ayalin.pdf
    • 15:25 → 15:35
      Coffee break 10m
    • 15:35 → 17:05
      Open discussion session
      Strassler_Mainz23_SomeAnswersDay1.pdf
      Strassler_Mainz_Jets_Subjets_Day2.pdf
      Workshop Live Notes
  • Thursday 19 October
    • 13:00 → 13:05
      Introduction 5m
      Speaker: Sukanya Sinha (University of Manchester (GB))
      MITP WS intro day 3.pdf
    • 13:05 → 14:10
      Overview talks: Reinterpretability/reproducibility of experimental results, and new final-state signatures
    • 14:10 → 14:30
      Coffee break 20m
    • 14:30 → 15:20
      ECS Session
      • 14:30
        Emerging jet probes of strongly interacting dark sectors 7m

        A strongly interacting dark sector with long-lived dark mesons (lifetimes between few centimeters and few meters) can give rise to emerging jets, which have been sought by the CMS collaboration.In this talk I would describe the validation of the CMS emerging jet search using the publicly available material. We will interpretate this search in the context of Exotic Higgs decays, setting constraints to the branching fraction of a Higgs boson into two dark quarks.

        Speaker: Juliana Carrasco
        EJs_mitp.pdf
      • 14:40
        The Exploration of Bottom-quark-philic Semi-visible Jets 7m

        ECS Lightning talk

        Proposing strongly interacting massive particles as dark matter candidates introduces a fascinating collider signature known as semi-visible jets. This study is a continuation of the first search for non-resonant production of SVJs, setting the first upper limits for strongly coupled dark sectors for a bi-fundamental mediator mass up to 2.7 TeV. The new search strategy for semi-visible jet production, in contrary to looking at democratic production of all five quark flavors along with dark matter particles, the focus is on semi-visible jet production along with just bottom quarks. The first step was to probe if this signal has been excluded by any current search at the LHC, involving MET and b-jets. A thorough literature review yielded few potential papers which probes a similar final state as this signal, namely, the search for dark matter produced in association with a Standard Model Higgs boson decaying into b-quarks and the search for SUSY in final states with MET and three or more b-jets. These searches are not sensitive to our signal. The second step was to make use of variable-R jet clustering to better reconstruct the signal.

        Speaker: Wandile Nzuza
        Young_stars_Wandile_Nzuza.pdf
      • 14:50
        Leptons lurking in semi-visible jets at the LHC 7m

        ECS Lightning talk

        Hidden Valley models propose alternative BSM scenarios to explain the nature of Dark Matter evading the phase-space currently probed by WIMPs searches. Under the assumption of a QCD-like confining dark sector, novel experimental signatures emerge, characterized by sprays of particles resembling hadronic jets containing stable invisible dark matter bound states. These semi-visible jets have been studied theoretically and experimentally in the fully hadronic signature where the unstable dark bound states can only decay promptly back to Standard Model quarks. We present a simplified model based on two messenger fields separated by a large mass gap allowing dark bound states to decay into pairs of oppositely charged leptons [Eur. Phys. J. C 82, 793 (2022)]. We propose a search strategy targeting this new signature leveraging the enhanced leptonic content of these anomalous jets, and discuss the orthogonality with respect to the existing searches.

        Speaker: Cesare Tiziano Cazzaniga
        presentation_DS_workshop.pdf
      • 15:00
        Tau leptons-enriched semi-visible jets at the LHC 7m

        ECS Lightning talk

        This Letter proposes a new signature for confining dark sectors at the Large Hadron Collider. Under the assumption of a QCD-like hidden sector, hadronic jets containing stable dark bound states could manifest in proton-proton collisions. We present a simplified model with a Z′ boson yielding the production of jets made up of dark bound states and subsequently leading to the decays of those that are unstable to τ leptons and Standard Model quarks. The resulting signature is characterised by non-isolated τ lepton pairs inside semi-visible jets. We estimate the constraints on our model from existing CMS and ATLAS analyses. We propose a set of variables that leverage the leptonic content of the jet and exploit them in a supervised jet tagger to enhance the signal-to-background separation. Furthermore, we discuss the performance and limitations of current triggers for accessing sub-TeV Z′ masses, as well as possible strategies that can be adopted by experiments to access such low mass regions. We estimate that with the currently available triggers, a high mass search can claim a 5σ discovery (exclusion) of the Z′ boson with a mass up to 4.5TeV (5.5TeV) with the full Run2 data of the LHC when the fraction of unstable dark hadrons decaying to τ lepton pairs is around 50%, and with a coupling of the Z′ to right-handed up-type quarks of 0.25. Furthermore, we show that, with new trigger strategies for Run3, it may be possible to access Z′ masses down to 700 GeV, for which the event topology is still composed of two resolved semi-visible jets.

        Speaker: Tobias Fitschen
        SVJtau.pdf
      • 15:10
        Set-Up for Semi-Visible Jets with Leptons 7m

        ECS Lightning talk

        Semi-visible jets (SVJs) arise in strongly-interacting dark matter scenarios. Fol- lowing a recent publication on leptons in SVJs [1], we have looked at a simpler model of generating Dark Photons in SVJs with leptons. We used the Pythia Hidden Valley module to generate a Z’ mediator that de- cays to two dark quarks. These then decay to a neutral dark sector pion that decays into a strange quark and a charged dark pion. The charged dark pion decays into a stable dark hadron and a dark photon, which produces a lepton pair. This results in leptons cloaked by the SVJ. We look at some basic kinematic variables to see if we can reconstruct the invariant mass of the mediator.

        [1] Cesare Cazzaniga and Annapaola de Cosa. Leptons lurking in semi-visible jets at the LHC. The European Physical Journal C, 82(9), Sep 2022.

        Speaker: Clarisse Prat
        Youngstars_CPrat_Final.pdf
    • 15:20 → 15:30
      Coffee break 10m
    • 15:30 → 17:00
      Open discussion session
      Strassler_Mainz23_SomeAnswersDay1.pdf
      Strassler_Mainz_Jets_Subjets_Day2.pdf
      Workshop Live Notes
  • Friday 20 October
    • 14:30 → 16:30
      Workshop summary report meeting 2h
      Speaker: Sukanya Sinha (University of Manchester (GB))
      MITP Darkshowers workshop Live notes

      The way I envisioned the report is:

      • We summarise each days talk, using a combination of the slides and the minutes, focusing on the main discussion points raised during the open discussion session
      • We provide a list of community agreed action items for each topic
      • Upload it on zenodo or a similar platform, for a reference document when we want to discuss things or perform studies in the future,

       

      It would be good if we can identify editors for specific topics who would want to write that up within a specified time frame, and then we can collate all the topics together in the report, in a coherent manner. I’m happy to take other suggestions for ways to move forward with the summary report! 😊

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