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Long-lived Particles at CODEX-b, FASER, MATHUSLA (and more)

Dean Robinson

Snowmass RF6 Kick-Off

Aug 2020 Cross-Frontier Discussion

Disclaimer: This is a short (and necessarily incomplete) LLP summary talk.

A more extensive set of LLP Snowmass talks were given at the recent Cross-frontier meeting (AF - EF - RF) https://indico.fnal.gov/event/44030/

A few other key references:

• Searching for long-lived particles beyond the at the Large Collider, 1903.04497

• Physics Beyond Colliders at CERN: Beyond the Standard Model Working Group Report, 1901.09966

• ...

Dean Robinson [email protected] LLPs RF6 2 | 15 Why Long-Lived Particles? Long-lived particles are generic phenomenological consequence of • Small couplings or • scale (or loop) hierarchies or • phase space suppression

m  M, typically n ≥ 4 broken sym loop factors weak mixing/ marginal operator technically natural !n 2 m Γ ∼ ε PS squeezed spectra M approx sym multibody decays

+ E.g. in the SM: KL, π , n, µ. No reason same phenomenology cannot occur in a dark sector.

Dean Robinson [email protected] LLPs RF6 3 | 15 How can we look for them?

LLP theory space LLPs occur over a huge theory and parameter space. Examples:

SUSY: DARK: MISC:

R-parity violation Asym. Dark Matter Baryogenesis

Gauge mediation Freeze-in masses

(mini-)split SUSY Composite Dark Matter Flavor puzzle

stealth SUSY Neutral Naturalness

Hidden Valleys • LLP lifetimes τ . 1 s (BBN) • Masses from sub-MeV to TeV. • A large parameter space to explore!

Dean Robinson [email protected] LLPs RF6 4 | 15 LLP theory space LLPs occur over a huge theory and parameter space. Examples:

SUSY: DARK: MISC:

R-parity violation Hidden Asym. Dark Matter LHC interactionBaryogenesis Standard Sector Model Hidden Gauge mediation (new physics)Freeze-in Standard NeutrinoSector masses Model (new physics) (mini-)split SUSY Composite Dark Matter Flavor puzzle New forces, interactions LLP Decay (Higgs, other heavy or stealth SUSY light states, ...?) Neutral Naturalness

Hidden Valleys • LLP lifetimes τ . 1 s (BBN) • Masses from sub-MeV to TeV. • A large parameter space to explore! How can we look for them?

Dean Robinson [email protected] LLPs RF6 4 | 15 L Intuition

interaction Idea: Look point (IP) for displaced decays-in-flight

Shielding/Rock LLP Detector

cτ L :  eff cτ Ldet/γβ Leff: Lnear/cτ Lfar/cτ L /cτ ≡ e− eff e− eff e− eff exponential suppression − ∼ δLeff/cτ linear regime

• Prompt search: always in linear regime. Prompt Detectors near IP always have search power, coverage even at long lifetimes!

• Displaced search: peak at cτ ∼ Leff •

Advantage: Displaced/shielded detectors SCHEMATIC Branching Ratio Displaced/shielded can achieve lower/zero BGs, higher coverage sensitivities even with smaller acceptances cτ

Dean Robinson [email protected] LLPs RF6 5 | 15 Schematic Complementarity

• ATLAS/CMS will set best limits for charged, colored and/or heavy LLPs∗ • LHCb: O(GeV) neutral LLPs with large muon BR and cτ . 0.1 m • But large hadronic BGs: lighter, neutral, longer-lived LLPs are hard to see → → LHC coverage LHC coverage (ATLAS, CMS, LHCb) (ATLAS, CMS, LHCb) 10 GeV 10 GeV & &

LLP Transverse M (MATHUSLA, Transverse Forward Forward (FASER, SHiP, CODEX-b, . . . ) (MATHUSLA, (FASER, SHiP, NA62, . . . ) CODEX-b, . . . ) NA62, . . . ) 10 MeV 10 MeV . . SCHEMATIC SCHEMATIC ← ← near m far light cc¯, b¯b, ττ¯ h, t heavy ← ∼ ← → cτ→ √sˆ • Apart from LLP mass and lifetime, characterize sensitivity wrt parton CoM energy: production through light vs heavy portals

∗See millicharge talk! Dean Robinson [email protected] LLPs RF6 6 | 15 LLP Proposals/Experiments FORWARD PHYSICS FACILITY • A few experiments are under construction or proposed for this location. But they are severely limited by the tunnels and infrastructure that were created long before the physics potential of this space was appreciated.

FASER, FASERn Beam Collision Axis

Tunnel TI12

Cavern UJ12 30 m Dougherty (2020) The FASER experiment Long-Lived Particle Searches * light LLPs could be copiously produced in very forward direction * FASER looks for LLPs decays ~500 m downstream from ATLAS * , dark Higgs, HNLs, ALPs, … 15 July 2020 Feng 5 * FASER References: LOI, Physics Case, TP decay

FASERnu Neutrino Measurements

* ATLAS provides intense forward neutrino beam i) collimated ii) E ~ TeV iii) all flavors: π→νμ, K→νe, D→ντ * FASERnu will see ~104 νμ, ~103νe, ~10 ντ during LHC Run 3

* FASERnu References: Proposal,TP F Kling | J Feng Cross-frontier Meeting (AF - EF - RF) Notes: • Figure not to scale! • FASER approved for Run 3. Larger FASER2 in planning for HL-LHC

Dean Robinson [email protected] LLPs RF6 7 | 15 LLP Proposals/Experiments

4

Large area surface detector above CMS IP dedicated to detection of ultra long-lived particles - air decay volume with tracking chambers. ❑ Decay volume 100m2X25m ❑ Robust tracking and good background rejection - five tracking layers at top and two more ~ 5 m below top layers ❑ Two scintillator layer of floor detectors to reject cosmic ray inelastic backscattering, muon decays and interactions near the surface. ❑ Detector planes consist of extruded coupled to SiPMs - provides good time/space resolution needed for cosmic ray rejection and vertex reconstruction. ❑ Cosmic ray rate ~ 1.7 MHz ❑ Test installed at P1 above ATLAS to understand muon rate from LHC pp collisions and cosmic ray backgrounds that result in upward going tracks (inelastic backscattering and muon decays) – arXiv:2005.02018

Snowmass H. Lubatti 15 -16 July 2020

H Lubatti Cross-frontier Meeting (AF - EF - RF)

Notes: • In planning for HL-LHC era

Dean Robinson [email protected] LLPs RF6 8 | 15 LLP Proposals/Experiments CODEX-b in a Nutshell

DELPHI CODEX-b box

SM SM

'

x

shield veto UXA shield Pb shield IP8

CODEX-b 2/12 Notes: S Knapen Cross-frontier Meeting (AF - EF - RF) • Demonstrator version in (part of) Run 3 • In planning for HL-LHC era Dean Robinson [email protected] LLPs RF6 9 | 15 LLP Proposals/Experiments Beam-dump and fixed-target experiments can also play a big role. E.g. REDTOP NA62

SHiP Several more LLP proposals: • AL3X (converted ALICE interaction point) • ANUBIS (in ATLAS vertical access shaft) • MAPP (MOEDAL affiliate in LHCb tunnel near beamline) Also: Belle II, NA64, LDMX can/will perform (inv.) LLP

searches.Dean Robinson [email protected] LLPs RF6 10 | 15 Example Benchmarks

A large number of benchmarks were considered/developed for the Physics Beyond Colliders BSM report [1901.09966]. Including:

• Dark photons • Higgs mixed scalars • Invisible Higgs BR • Heavy neutral leptons • -like particles In most cases, several sub-benchmarks were considered.

Following are two example minimal model benchmarks. There are many more!

Dean Robinson [email protected] LLPs RF6 11 | 15 Minimal Dark Photon

Portal: F Fe

Very light, short life-time: Better suited to forward detectors.

Dean Robinson [email protected] LLPs RF6 12 | 15 Higgs-mixed scalar Generates effective mixing h → h cos θ + S sin θ.

Portal: µH†HS

Dominant production through b → sS.

Dean Robinson [email protected] LLPs RF6 13 | 15 Higgs-mixed scalar Generates effective mixing h → h cos θ + S sin θ. λ Portal: µH†HS + H†HS†S, λ = 1.6 × 10−3 2

Including quartic allows huge production from Higgs decays. Low η detectors do better. Dean Robinson [email protected] LLPs RF6 13 | 15 Caveats & Thoughts • These two examples are minimal/simplified models benchmarks. Also many well-motivated ‘complete model’ benchmarks! [See e.g. MATHUSLA 1806.07396 and CODEXb 1911.00481]

• In some cases, further theory development is important. E.g. gluon coupled ALP Initial analysis in PBC With parton shower contributions ALP w/ gluon couplings,Λ=1TeV 100 CODEX-b, 300/fb 10-3 10-1 CHARM Excl. 1811.03474 10-4 10-2 FASER2, 3/ab 17 REDTop, 10 pot ] -5 10 - 1 10-3 CODEX-b w/calo MATHUSLA200, 3/ab, G -6 [ GeV

c -5 ϵfloor=10 10 10-4 PBC

10-7 1 / f -5

10 1911.00481 10-8 10-6 10-9 10-7 0.05 0.10 0.50 1 5 10

ma[GeV] • Suggests: A clear policy for indicating where ‘known unknown’ theory inputs might significantly change a story Dean Robinson [email protected] LLPs RF6 14 | 15 Caveats & Thoughts

• Minimal model benchmarks are merely metaphors for underlying (dark sector) phenomenology/physics; complete model benchmarks often ‘bake in’ many assumptions or theory priors.

• We should be cautious about over-emphasis on coverage of benchmark spaces versus coverage of the space of dark sector phenomenology/ signatures. (Eg for LLPs: displaced decays in flight)

Thank you!

Dean Robinson [email protected] LLPs RF6 15 | 15