Search for long-lived particles at the LHC LianTao Wang U. Chicago Stone turning workshop, Utah. August 10, 2019
Guardian
Road ahead at the LHC
We are here.
LHC is pushing ahead. Exp. collaborations are pursuing a broad and comprehensive physics program: SUSY, composite H, extra Dim, etc.
As data accumulates m = 2 TeV 14 TeV / 8 TeV low 2.5 qq q q qg 2 gg low m 1.5 / high m 1 0.5 0 0 10 20 30 40 50 60 70 80 90 100 -1 luminosity (fb ) Rapid gain initial 10s-100 fb -1 , slow improvements afterwards. Progress will become slower, harder
New directions
The potential of a lot of data - Very rare signal E.g. dark sector, rare decays, ... - Data can help with reducing systematics Precision measurements.
stronger coupling covered by current searches heavier NP particle
stronger coupling covered by NP too heavy for LHC current searches with direct production dark sector heavier NP particle
stronger coupling covered by NP too heavy for LHC current searches with direct production dark sector heavier NP particle
Example: Long Lived particles (LLP) - Very weakly coupled to the SM. Connection with dark matter, neutrino, etc. - Displaced-Long lived, soft, kink, … Covered by LHC searches already. Curtin and Sundrum Here, I focus on: decay length >> 10 meters Generic constraint from cosmology: τ < 0.1 s
tons of models General LLP Map
Far detectors les on � MATHUSLA � ayers � ectrons � new detectors far Letter of intent: � away from the interaction region � – – � “demonstrator” � CODEX-b � DELPHI CODEX-b box � � SM SM ϕ x shield veto FASER UXA shield Pb shield IP8 Data acquisition will be moved to surface for run 3
Far detectors claim: zero background MATHUSLA
Far detectors les on � MATHUSLA � ayers � ectrons � Have we fully optimized LLP searches at Letter of intent: � the interaction points ATLAS, CMS, LHCb? � – – � “demonstrator” � CODEX-b � DELPHI CODEX-b box � � SM SM ϕ x shield veto FASER UXA shield Pb shield IP8 Data acquisition will be moved to surface for run 3
Optimal place to catch LLP ΔΩ L Δ L Number of particle decayed within detector volume: # in ≃ # produced × ΔΩ 4 π × Δ L d e − L / d d = γ c τ decay length d ≫ Δ L , L Very long lived: d ≥ 100s meters
Optimal place to catch LLP Number of particle decayed within detector volume: # in ≃ # produced × ΔΩ 4 π × Δ L d e − L / d d = γ c τ ATLAS/CMS (LHCb) Far detectors ∼ 4 π < 0.1 ΔΩ Δ L 1 − 10 meters 1 − 10 meters L 1 − 10 meters 10 − 100 meters
Optimal place to catch LLP # in ≃ # produced × ΔΩ 4 π × Δ L d e − L / d d = γ c τ ATLAS/CMS (LHCb) Far detectors ∼ 4 π < 0.1 ΔΩ Δ L 1 − 10 meters 1 − 10 meters L 1 − 10 meters 10 − 100 meters Advantage of far detector? Far away from interaction point, less background. Room for new ideas: suppression bkgd near interaction point. We played with one: using timing information
Time delay a b Timing layer ` a ` SM L T 2 ` X L T 1 SM X Good for massive LLP produced with small or moderate boost β X < 1
Basic topologies X = LLP SM X SM X Y SM X or SM SM X or SM γ ≃ m Y boost: boost: γ ∼ 1 2 m X challenging for m X ≪ m Y slow moving, sizable Δ t benchmark: SUSY benchmark: Higgs portal Y = Higgs X = neutralino χ 0 → gravitino + . . . Long lived Long lived X → SM
Higgs portal. 1 μ XH † H H = ( v + h ) 2 m b → μ vXh → μ v v Xb ¯ Last step: integrating out Higgs b m 2 h X → b ¯ At the LHC: pp → h → X . . . , b m b μ v v ∼ 10 − 7 → c τ ∼ m If m 2 h - Too small a mixing with the Higgs?
̂ ̂ ̂ A class of model α v h G μν ̂ ℒ ⊃ G μν 6 π f f Dark sector dark QCD. Higgs couples to dark QCD through TeV new physics. α : dark QCD coupling, f ∼ TeV ∼ m NP , v / f : Higgs NP mixing Dark QCD confines around m 0 = 10 GeV, produces bound states X (e.g. glueball). m X ∼ m 0 ∼ 10 GeV
̂ ̂ ̂ A class of model α v h G μν ̂ ℒ ⊃ G μν 6 π f f α : dark QCD coupling, f ∼ TeV ∼ m NP , v / f : Higgs NP mixing ∼ 10 − 8 c τ ≃ 18m × ( 7 m 3 ) 4 m b m b μ v 1 v ( 750 GeV ) 10 GeV f 0 v ∼ m 2 8 π 2 f ⋅ m 2 v f m 0 h h BR ( h → dark glueballs) < 1 % A bit model building, but not so unreasonable Signal pretty generic: hidden valley, twin Higgs... Other LLPs with small mixings to Higgs: ALPs, relaxion, extra-singlet... With various degrees of motivation. Similar signal.
Signal ISR jet (time stamp) ISR jet (time stamp) SM X SM X Y SM X or SM SM X or SM 1. ISR jet provides the time for the hard collision 2. LLP decay before reaching timing layer. measurement of Δ t
background Same hard interaction Pile up ISR jet ISR jet Trackless jet 2 Time stamping PV Time stamping PV No need to fake signal Trackless jet Trackless jet 1 Fake displaced obj Fake displaced obj Time delay from Time delay from resolution of timing detector. spread of the proton bunch ∼ 190 ps
Examples: b a Timing layer ` a ` SM L T 2 ` X L T 1 SM X • timing layers considered here: • CMS EC search: LT1 = 0.2 m, LT2 = 1.2 m (EC = Electromagnetic Calorimeter) • Resolution: δ t = 30 ps • MS search (hypothetical): LT1 = 4.2 m, LT2 = 10.6m (MS = Muon Spectrometer) • Resolution: don’t need to be as good (detail later)
Search based on EC delay at EC from LHC 10 0 10 - 1 / bin ) 10 - 2 / Δ t 10 - 3 1 / 10 - 4 0. 0.5 1. 2 5 10 20 50 100 200 Δ t ( ns ) c τ = 10 m After timing cut: Δ t > 1 ns # background ∼ 1 Back ground dominated by pile up
Search based on MS delay at MS from LHC 10 0 10 - 1 / bin ) 10 - 2 / Δ t 10 - 3 1 / 10 - 4 0. 0.5 1. 2 5 10 20 50 100 200 Δ t ( ns ) Pile up background smaller, shielded by HCAL etc. Before timing cut: ∼ 50 After timing cut: Δ t > 1 ns # background ∼ 1 Further away, larger for signal. Δ t
Search based on MS delay at MS from LHC 10 0 10 - 1 / bin ) 10 - 2 / Δ t 10 - 3 1 / 10 - 4 0. 0.5 1. 2 5 10 20 50 100 200 Δ t ( ns ) no need for super Pile up background smaller, shielded by good timing resolution HCAL etc. Δ t > 1 ns # background ∼ 1 δ t ∼ 200 ps will do Further away, larger for signal. Δ t
Sensitivity to Higgs portal Jia Liu, Zhen Liu, LTW Precision Timing Enhanced Search Limit ( HL - LHC ) 10 0 10 - 1 h < 3.5 % BR inv 10 - 2 BR ( h → XX ) 10 - 3 h → X X, X → j j MS ( 30ps ) , Δ t > 0.4ns 10 - 4 MS ( 200ps ) , Δ t > 1ns EC ( 30ps ) , Δ t > 1ns 10 - 5 MS2DV, noBKG MS1DV, optimistic 10 - 6 m X in [ GeV ] 10 40 50 10 - 7 10 - 3 10 - 2 10 - 1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 c τ ( m ) For example, for BR( h → XX ) ∼ 10 − 3 EC(MS) reach can be c τ ∼ 10 3 (10 4 ) meters
Sensitivity to SUSY Jia Liu, Zhen Liu, LTW Precision Timing Enhanced Search Limit ( HL - LHC ) 10 5 F = 10 5 TeV GMSB Higgsino 10 4 Δ t > 1.2 ns 10 3 Δ t > 2 ns Δ t > 1 ns 10 4 10 2 Δ t > 10 ns c τ ( m ) MS 10 1 n bkg = 100 n bkg = 0 10 3 EC 10 0 n bkg = 100 n bkg = 0 10 - 1 10 - 2 8 TeV 13 TeV Diplaced Dijet 10 - 3 200 400 600 800 1000 1200 1400 m X ( GeV ) Slower moving LLP , timing cuts can be further relaxed.
Neutrino 𝒫 SM = HL See-Saw model sin θ ν λ ν XHL + MX c X + h . c . X × ( 0.01 eV ) ( ) m ν 10 GeV Basic See − Saw : sin 2 θ = 10 − 12 m X Larger mixing possible for extended models: inverse, linear...
Neutrino 𝒫 SM = HL See-Saw model sin θ ν λ ν XHL + MX c X + h . c . X × ( 0.01 eV ) ( ) m ν 10 GeV Basic See − Saw : sin 2 θ = 10 − 12 m X Larger mixing possible for extended models: inverse, linear... c τ ≃ 1 m × ( sin 2 θ ) ( 5 10 − 8 ) 10 GeV m X 10 − 8 ) ( sin 2 θ 3 ab − 1 × σ ( pp → W ± ) ⋅ BR ( W ± → ℓ ± X ) ≃ 2 × 10 3 With trade-off between production and decay, LLP signal possible. Difficult to reach the basic see saw model due to low production rate.
Liu, Liu, Wang, Wang, 1904.01020
New directions and ideas - Apply timing to current LLP searches should already help. e.g. muon-RoI based searches - Removing the ISR jet for MS searches. Higher rate. Larger Δ t = 1 ns cut, don’ t need precise hard collision time. - High granularity, better pointing and vertexing Would be at least as useful as timing. HGCAL, MS RPC upgrade. - Using timing info with the calorimeters, HGTD.
Other rare processes - Rare W, Z, top decays. Sensitive to very rare and distinct signals. - More attention needed.
Conclusion - LHC still has a lot to say. 15+ years of operation, 95+% of data to come. - Need to think about how to new searches with this data. (In addition to looking else where. ) - I Long lived particles, with timing information. - More work (and originality) needed.
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