Searching for long-lived particles at the LHC: Seventh workshop of the LHC LLP Community

25 May 2020, 09:00 → 27 May 2020, 19:10 Europe/Zurich

Virtual only (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)), James Beacham (Duke University (US)), José Francisco Zurita (KIT), Juliette Alimena (Ohio State University (US)), Matthew Daniel Citron (Univ. of California Santa Barbara (US)), Michelangelo Mangano (CERN), Nishita Desai (TIFR, Mumbai), Rebeca Gonzalez Suarez (Uppsala University (SE)), Ryu Sawada (University of Tokyo (JP))

https://cern.ch/longlivedparticles

UPDATE: Due to the ongoing COVID-19 pandemic, the seventh LHC LLP Community workshop will be virtual only!  The dates are the same -- 25-27 May -- but the sessions will be limited to three half-days instead.

The seventh workshop of the LHC LLP Community, 25-27 May 2020 at CERN, will undoubtedly be another raucous and vibrant gathering, this time via videoconference only.

As we inch closer and closer to the beginning of LHC Run 3, there are several urgent LLP-related questions to be addressed:

• What triggering strategies are we missing at ATLAS, CMS, and LHCb?
• What signatures are we overlooking?
• What new models have been introduced that give rise to signatures we haven't searched for yet?
• How can machine learning improve our ability to discover LLPs?
• What about new dark shower phenomenology?
• What's the latest with MoEDAL?
• How soon can we get all of the dedicated LLP detectors (FASER, MATHUSLA, CODEX-b, MilliQan, AL3X, ANUBIS) fully installed and running?
• What decisions need to be made now to ensure that the Phase 2 upgrades definitively improve our ability to discover LLPs?
• What are the latest results or studies from related experiments (fixed-target, future collider, neutrino-related, etc.) that can also search for LLPs?
• Why isn't your brand new idea in this list?

The agenda is now nicely solidified.  To best accommodate the virtual-only format, the program is composed of only plenary talks, with plenty of time for discussion.

Please register now!

Additionally, recall that our LLP workshop was designed to sit right next to FIPs 2020, a very closely-related workshop about feebly-interacting particles across multiple disciplines.  FIPs, however, has been rescheduled to 2-4 September 2020.  We look forward to coordinating with them in the future, as well.

NEW: As you're aware, the Snowmass process is underway.  Because it's such an important and timely project with many topics relevant to the LLP Community, we're holding an informal, brainstorming-style satellite session dedicated to possible Snowmass contributions on Friday, 29 May 2020, at 4 PM Geneva time.

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Finally, remember that the eighth workshop of the LHC LLP Community will be held in Tokyo in November of 2020, with the exact dates to be announced very soon.

Monday, 25 May

Plenary talks: Session 1 -- Intro, dedicated detectors at the LHC, and new theory developments

Conveners: James Beacham (Duke University (US)), Nishita Desai (LUPM, Montpellier)

1 Introduction and welcome

Speaker: James Beacham (Duke University (US))

Beacham_LHC_LLP_Seventh_Virtual_Intro_v2_2020May25.pdf

2 CODEX-$\beta$: opening the book for CODEX-b

Speaker: Philip Ilten (University of Birmingham (GB))

codexb.pdf

3 MATHUSLA

Speaker: Mason Proffitt (University of Washington (US))

LLP Workshop May 2020 MATHUSLA Update (full).pdf

4 The MoEDAL experiment and MAPP & MALL extensions

Speaker: Dr Vasiliki Mitsou (Univ. of Valencia and CSIC (ES))

Mitsou-MoEDAL-LLP-may2020.pdf

5 Discussion

6 Collider probes of real triplet scalar dark matter

Speaker: Yong Du (University of Massachusetts-Amherst)

LHC-LLP-Yong Du.pdf

7 Displaced physics at colliders and pre-BBN cosmology

Displaced events at colliders are a promising way, and in a large region of the
parameter space the only way, to test dark matter produced via freeze-in. Typical decay lengths as obtained from relic density calculations are way too large to observe anything in our detectors if the freeze-in production happens in a radiation dominated universe. However, after inflation, the universe gets reheated through the decay of the inflaton during a matter dominated era. If the freeze-in production of dark matter happens (partially) during this era, the typical decay lengths involved can become accessible for current detectors. If the observation of such a displaced event happens, the characteristics of this event might provide hints about the pre-BBN universe.

Speaker: Sam Junius (ULB & VUB)

LLP_workshop_SJ.pdf

8 Light hidden mesons inspired by neutral naturalness

Confining hidden sectors are an attractive possibility for physics beyond the Standard Model (SM). They are especially motivated by neutral naturalness theories, which reconcile the lightness of the Higgs with the strong constraints on colored top partners. We study hidden QCD with one light quark flavor, coupled to the SM via effective operators suppressed by the mass of new electroweak-charged particles. This effective field theory is inspired by a new tripled top model of supersymmetric neutral naturalness. The hidden sector is accessed primarily via the Z and Higgs portals, which also mediate the decays of the hidden mesons back to SM particles. We find that exotic Z decays at the LHC and future Z factories provide the strongest sensitivity to this scenario, and we outline a wide array of searches. For a larger hidden confinement scale ~GeV, the exotic Z decays dominantly produce final states with two hidden mesons. ATLAS and CMS can probe their prompt decays up to 3 TeV at the high luminosity phase, while a TeraZ factory would extend the reach up to 20 TeV through a combination of searches for prompt and displaced signals. For smaller confinement scale, the Z decays to the hidden sector produce jets of hidden mesons, which are long-lived. LHCb will be a powerful probe of these emerging jets. Furthermore, the light hidden vector meson could be detected by proposed dark photon searches.

Speakers: Christopher Verhaaren (University of California, Irvine), Ennio Salvioni (CERN), Hsin-Chia Cheng (University of California, Davis ), LINGFENG LI (HKUST), Lingfeng Li (HKUST)

Talk_LLC7.pdf

9 Discussion

15:15 Coffee

Plenary talks: Session 2 -- Theoretical overview, PBC & FIPs, HL-LHC, new theory/pheno ideas

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

10 Physics Beyond Colliders initiative & preview of FIPs 2020

Speaker: Joerg Jaeckel (ITP Heidelberg)

LLP3.pdf

11 Discussion

12 Bigger picture and new theoretical perspectives on LLPs

Speaker: Nathaniel Craig (UC Santa Barbara)

LHC_LLP_Craig.pdf

13 Discussion

14 Prospects for an LLP search in a CMS Forward Spectrometer

We are developing a proposal to search for neutral particles with masses up to a few GeV, produced at $\eta$ = 6 - 7, penetrating 42m of steel and decaying in a large diameter 27m-long vacuum pipe. This would be a new subsystem for CMS in Run 4 with high luminosity. There is sensitivity to lifetimes in the range $\gamma.c.\tau$ from about 10m to several km. Decays to lepton pairs (including $\tau+\tau^-$) and hadrons (including $c\bar{c}$) can be measured in a 10m-long spectrometer (Forward Multiparticle Spectrometer, FMS) with tracking, calorimetry and muon chambers using CMS endcap Upgrade technology. The FMS can also measure multi-TeV charged hadron spectra in low pileup runs.

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

Albrow-FMS-EXO-0525.pdf

Albrow-FMS-EXO-0525.pptx

15 Long-lived particle searches with the CMS High Granularity Calorimeter

The search for long-lived particles is an exciting physics opportunity in the upcoming runs of the Large Hadron Collider. We uniquely study the potential of using the High Granularity Calorimeter (HGCAL), part of the upgrade of the CMS detector, in such searches. In particular, we demonstrate that the precise pointing capability coming with this upgrade can play a crucial roll in identifying the signal and suppressing the background. We study the reach of HGCAL in a simplified model with SM Higgs decay into a pair of long-lived particles $X$. After carefully estimate the Standard Model QCD and the misconnected fake track backgrounds, we give the projected reach both for a more conservative vector boson fusion trigger and a novel displaced-track-based trigger. Our results show that the best reach for vector boson fusion channel is about $\mathcal{O}(10^{-4})$ for SM Higgs decay branching ratio at lifetime of $c\tau \sim 0.1$--$1$ meters, while for the gluon gluon fusion channel it is about $\mathcal{O}(10^{-5}\text{--}10^{-6})$ for similar lifetime. Alternatively, for $c\tau \sim 10^3$ meters, it should be able to probe the branching ratio down to a few $\times 10^{-2}$($10^{-4}$) for the two channels, respectively.

Speaker: Jia Liu (University of Chicago)

2020-05-25-LLP-7th-v2-JiaLiu.pdf

16 Discussion

17 Baryogenesis and dark matter from freeze-in

Speakers: Brian Shuve (SLAC National Accelerator Laboratory), David Tucker-Smith (Williams College)

lhc_llp_05_25_20.pdf

18 Using white dwarfs to constrain atomic dark matter

A subcomponent of dark matter could in the form of "dark atoms", which emit dark radiation and could have cooled to form a second "dark disk" in our galaxy. Dark atoms are predicted in a variety of models, in particular the Mirror Twin Higgs model. I will present new constraints on this type of dark matter from white dwarf cooling -- if white dwarfs have a captured nugget of dark atoms in their cores, the energy loss to dark radiation can alter predictions for white dwarf cooling rates. We are able to extend existing constraints on the kinetic mixing parameter by at least an order of magnitude across a wide range of dark matter masses.

Speaker: Dr Jack Setford (University of Toronto)

Using white dwarfs to constrain atomic dark matter -- LLP.pdf

19 Soft displaced leptons at the LHC

Speaker: Abanti Ranadhir Sahasransu (Vrije Universiteit Brussel (BE))

LHC_LLP_2020_SoftDisplacedLeptons_AR.pdf

20 Discussion

Tuesday, 26 May

Plenary talks: Session 3 -- More dedicated LLP detectors at the LHC and other LLPs at CERN

Conveners: Albert De Roeck (CERN), Ryu Sawada (University of Tokyo (JP))

21 Heavy neutral leptons at ANUBIS

Speaker: Zeren Simon Wang (APCTP, Korea)

slides.pdf

22 Producing and detecting long-lived particles at different experiments at the LHC

Speaker: Yue Zhao (University of Utah)

ATLAS-LHCb-ALICE.pdf

23 Discussion

24 CLIC

Speaker: Erica Brondolin (CERN)

20200526_LLPatCLIC_EricaBrondolin.pdf

25 NA64

Speaker: Paolo Crivelli (ETH Zurich (CH))

NA64_LHC_LLP_2020_Crivelli.pdf

26 Status and prospects for $Br(K^+ \rightarrow \pi^+ \nu \bar{\nu})$ measurement at NA62

Speaker: Francesco Brizioli (Universita e INFN, Perugia (IT))

LHC_LLP_NA62_Brizioli_def.pdf

27 Discussion

28 FASER

Speaker: Claire Antel (Universite de Geneve (CH))

LLPworkshop_May2020_FASER_CAntel.pdf

29 The SHiP-SND experiment at the LHC

Speaker: Giovanni De Lellis (Universita e sezione INFN di Napoli (IT))

SND_LHC.pdf

30 Search results from the milliQan demonstrator

Speaker: Ryan Schmitz (Univ. of California Santa Barbara (US))

Search for millicharged particles in proton-proton collisions using the milliQan demonstrator (2).pdf

31 Discussion

15:55 Coffee

Plenary talks: Session 4 -- New results from ATLAS and CMS, dark shower / dark QCD phenomenology

Conveners: José Francisco Zurita (KIT), Juliette Alimena (Ohio State University (US))

32 ATLAS search for a displaced vertex and a muon

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

2020.05.26.kdp.DVmu_LLPWorkshop.pdf

33 ATLAS displaced jets: Solving the LLP re-interpretation challenge using RECAST

Speaker: Alice Morris (UCL (GB))

AMorris_CalRatioRECAST_LLPWorkshop.pdf

34 CMS search for disappearing tracks

Speaker: Brian Francis (Ohio State University (US))

bfrancis_disappTrks_llp7.pdf

35 Discussion

36 Casting a ParticleNet to catch dark showers

Speaker: Elias Bernreuther (RWTH Aachen University)

ml_darkshowers.pdf

37 Challenges of searching for low mass LLPs from strongly interacting dark sectors

Speaker: Patrick Tunney (King's College London)

LLP_SIMP.pdf

38 Discussion

39 Dark showers with jet substructure

Speaker: Dr Marat Freytsis (Rutgers University)

LLPVirt0520.pdf

40 A robust measure of event isotropy at colliders

Speaker: Cari Cesarotti (Harvard University)

LLPisotropyCesarotti.pdf

41 Discussion

Wednesday, 27 May

Plenary talks: Session 5 -- Triggering ideas for ATLAS and CMS and a new result from CMS

Conveners: Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), Rebeca Gonzalez Suarez (Uppsala University (SE))

42 Search for long-lived heavy neutrinos at the LHC with a VBF trigger

The charged current production of long-lived heavy neutrinos at the LHC can use a prompt charged lepton for triggering the measurement of the process. However, in order to fully characterize the heavy neutrino interactions, it is necessary to also probe Higgs or Z mediated neutral current production. In this case the charged lepton is not available, so other means of triggering are required.
In this work, we explore the possibility of using a vector boson fusion trigger in the context of a GeV-scale Type I Seesaw model. We consider a minimal model, where both Higgs and Z-mediated contributions produce one heavy neutrino, as well as an extended model where the Higgs can decay into two heavy ones. Both scenarios are tested through displaced dilepton and displaced multitrack jet searches.

Speaker: Dr Joel Jones-Perez (PUCP)

LLP-2020.pdf

43 A displaced vertex trigger following the CMS Phase II upgrade

The CMS track trigger may enable a dedicated trigger for a displaced, multi-track vertex. This would open up qualitatively now parameter space for e.g. Higgs decays to LLP, which in turn decay hadronically.

Speaker: Simon Knapen (CERN)

LLP_worshop.pdf

44 Muon shower L1 trigger: Expanding CMS’s long-lived particle lifetime coverage

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 present studies aimed to upgrade the muon system in advance of Run-3 to trigger on muon showers.

Speaker: Sven Dildick (Rice University (US))

LLPWorkshop_20200523_SD.pdf

LLPWorkshop_20200523_SD_v2.pdf

45 Discussion

46 CMS search for displaced jets

Speaker: Jingyu Luo (Princeton University (US))

DisplacedJets_LLP7.pdf

47 Triggering long-lived particles in HL-LHC at level-1

Triggering long-lived particles at the first stage of the trigger system is very crucial in LLP searches to ensure that we do not miss them at the very beginning. The future High Luminosity runs of the Large Hadron Collider will have increased number of pile-up (PU) events per bunch crossing and there will be major upgrades in hardware, firmware and software sides, like tracking at level-1 (L1) as well as inclusion of the MIP timing detector to deal with the increasing amount of PU. The L1 trigger menu will also be modified to cope with pile-up and maintain the sensitivity to physics processes. In our study we found that the usual level-1 triggers, mostly meant for triggering prompt particles, will not be very efficient for LLP searches in the 140 PU environment of HL-LHC, thus pointing to the need for dedicated L1 triggers in the menu for LLPs. We consider the decay of the LLP into jets and develop dedicated jet triggers using the track information and if available, the regional timing information at L1 to select LLP events. We show in our work that these triggers give promising results in identifying LLP events with moderate trigger rates.

Speaker: Rhitaja Sengupta (Indian Institute of Science)

LLP_L1_Rhitaja.pdf

48 Discussion

14:40 Coffee

Triggers for Run 3 for ATLAS, CMS, and LHCb

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

49 Introduction

Speaker: David Curtin (University of Toronto)

50 Triggering at ATLAS

Speaker: Kunihiro Nagano (High Energy Accelerator Research Organization (JP))

ATLASTrigger_LLPWS.pdf

51 Triggering at CMS

Speaker: Sam James Harper (STFC - Rutherford Appleton Lab. (GB))

llpWorkshop7CMSTriggerV3.pdf

52 Triggering at LHCb

Speaker: Olli Lupton (University of Warwick (GB))

LLPLupton-200527.pdf

53 Why can't we trigger for X? / Discussion and idea-tossing

Google slides (can view & leave comment using link only):
https://docs.google.com/presentation/d/13yImk15XsbMK95lnDuTeOIF3o2aIQ2G_dgpwSPnZxFY/edit#slide=id.g85c001cedf_2_35

We will keep notes on discussion for each topic in 'speaker notes' of corresponding slide. After discussion we'll make PDF record of slides including notes.

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

LLP WG

Conveners: Albert De Roeck (CERN), Carlos Vazquez Sierra (Nikhef National institute for subatomic physics (NL)), 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)), Juliette Alimena (Ohio State University (US)), Sascha Mehlhase (Ludwig Maximilians Universitat (DE))

Session Indico page