FASER: ForwArd Search ExpeRiment at the LHC

Transcription

1 work with Jonathan Feng, Iftah Galon and Sebastian Trojanowski arxiv: Searches for long-lived particles at the LHC Second Workshop of The LHC LPP community October 9th 7

2 Introduction transverse region: high pt Milliqan, Mathusla,Codex-b - searches for heavy strongly coupled physics ATLAS, CMS - typical rates σ ~ fb - pb N H = 7 at 3fb forward region - mostly used for SM measurement LHCf, TOTEM, ALFA, CASTOR - enormous event rates: inel 75 mb : N = 7 at 3fb extremely weakly-coupled long-lived particles may be produced sufficiently - most particles have small pt QCD energetic particles highly collimated QCD /E mrad for E TeV - we propose small ( m 3 ) inexpensive detector a few m downstream

3 Outline LHC Infrastructure Dark Photons Detector Considerations Backgrounds Expected Reach - where can we place the experiment - a physics example - what detector design do we need - and why we do not worry about them - how do we perform Summary and Outlook

4 LHC Infrastructure Arc Intersection IP TAS D TAN D Intersection Arc D 3 4 L[m] x[cm] +5 + IP TAS Q Q Q3 D TAN D Q4 proton beam +5-5 proton ~ TeV neutral particles dark photon near location - proton ~ 4.5 TeV proton beam L[m] IP particles produced at ATLAS/CMS Interaction Point D & Q Magnets charged particles get deflected µ, ± TAN forward xxxx n, absorbed by Target Neutral Absorbers Arc beam starts to curve at L = 7m

5 LHC Infrastructure Arc Intersection IP TAS D TAN D Intersection Arc D 3 4 L[m] IP particles produced at ATLAS/CMS Interaction Point Detector Locations D & Q Magnets charged particles get deflected µ, ± TAN forward xxxx n, absorbed by Target Neutral Absorbers LHC Infrastructure acts as natural filter : L=4m - after tunnel curves, surrounded by rock - L = 4 m, = m, R= cm near location: L=m - between TAN and D, embedded in infrastructure - L = 5 m, =5m,R=4cm Arc beam starts to curve at L = 7m

6 A Physics Example - Dark Photons Dark Photons - (broken) dark U() gauge group mixing with the SM photon L 4 F µ F µ + m A + X f(i6@ eqf 6A )f - FASER aims to probe m A 5 MeV and 6 4 Production Modes - meson decays: mainly! A,! A - proton Bremsstrahlung: pp! pa X Fermi-Weizsäcker-Williams approximation - (direct production): q q! ga,qg! qa PDFs at low Q and low x highly uncertain p π [GeV] 4 π EPOS-LHC Meson Production - use forward tools/models 5 EPOS-LHC, SIBYLL.3, QGSJETII boosted mesons highly collimated - 3 p = p T QCD L = 3 fb - large rates at L = 3 fb π θ π

7 A Physics Example - Dark Photons Meson Decay to Dark Photons - branching fractions: BR(! A )= m A - even small large sizable rate m 5 Dark Photon Decay - A is long lived: A = e m A /( BR(A! ee)) - decay length apple 5 apple apple EA MeV p A' [GeV] d 8m B e TeV m A 4 π γa' 3 3 EPOS-LHC m A' = MeV ϵ= L = 3 fb π - -3

8 A Physics Example - Dark Photons Meson Decay to Dark Photons - branching fractions: BR(! A )= m A - even small large sizable rate m 5 Dark Photon Decay - A is long lived: A = e m A /( BR(A! ee)) - decay length apple 5 apple apple EA MeV p A' [GeV] d 8m B e TeV m A 4 π γa' - probability to h decay inside detector: i P = e L/ d e / d (L A R) 3 3 m A' = MeV ϵ= -5 L = 3 fb 3 - only A with E~TeV will reach detector - A very forward A < mrad small detector radius L max =4m π

9 Detector Considerations Detector Position and Size - ideally as close as possible to IP - small detector radius R~cm sufficient - near location benefits from low distance, but suffers from reduced angular coverage Kinematic Features of Signal - two oppositely charged energetic tracks: E>5 GeV - vertex inside detector volume - combined momentum points towards IP Proposed Detector Apparatus - tracking based technology - small opening angle ee m A /E A µrad - magnetic field required to obtain sizable splitting apple apple apple TeV ` B h B =3mm E m. T can be obtained by conventional magnets Nsig Nsig Distance between detector and IP near location R=4cm Δ=5m π γa' η γa' Bremsstrahlung ϵ: m A' : R=cm Δ=m -4 MeV -5 MeV L max [km] 4 Detector Radius: L max =4m, Δ=m E A' > GeV ϵ: m A' : π γa' η γa' Bremsstrahlung -4 MeV -5 MeV.. R [m]l max

10 Backgrounds Signal - simultaneous high energy tracks - tracks start inside detector - combined momentum points towards IP - both tracks have similar energy Beam Induced Backgrounds (at ) - best estimated with simulations or exp. data - detector shielded by surrounding rock - mainly muon arrive expected rate: 3 Hz/cm ~. simultaneous muon tracks/year Neutrino Induced Backgrounds - mainly µ from ±, but also heavy mesons - N! µ ± X : ~8 events with E>GeV simultaneous CC interaction highly unlikely - N! µ ± X : events pion usually soft E /E µ..5 analysis is basically BG free ATLAS: kinematic features reduce these BG possible scintillating layer for veto Nν [Events/kg] νn μ ± X νn μ ± π X Neutrino Event Yield per kg for E ν >E ν,min L far =4m, R out =cm E ν,min [GeV]

11 Signal Rate - signal acceptance almost % - includes A! ee, µµ, ± modes - low ε: limited production rate - high ε: A decay before detector - high mass: direct production? -3-4 π FASER: L max =4m, Δ=m, R=cm L=3fb -, E A' >GeV Expected Reach Aϵ Bremsstrahlung η - - m A' [GeV]

12 Expected Reach Signal Rate - signal acceptance almost % - includes A! ee, µµ, ± modes - low ε: limited production rate - high ε: A decay before detector - high mass: direct production? -3-4 π FASER: L max =4m, Δ=m, R=cm L=3fb -, E A' >GeV Reach - almost background free - reach similar to SeaQuest, SHiP (m A ) max / L/EA Beam -3-4 LHCb D HPS LHCb A' μμ Aϵ m A' [GeV] 3 Bremsstrahlung η Aϵ fb - 3 fb - FASER: L max =4m,Δ =m, R=cm - - m A' [GeV] SHiP SeaQuest

13 Summary and Outlook Intersection Forward Physics Arc - large event rates in forward direction - energetic particles very forward < mrad - search for light extremely weakly coupled particles FASER - cheap small size m 3 detector, operates concurrently - placed few m downstream of the ATLAS/CMS IP - equipped with tracking system + magnetic field Physics Example: Dark Photons - A energetic charged tracks, E TeV - basically background free - reach: m A 5 MeV, 6 4 IP TAS D TAN D Outlook and Current Developments - explore more physics opportunities: scalars, axions, HNL - find ideal detector location, GEANT4 simulations together with experimentalists We look forward to feedback and suggestions Intersection 3 4 L[m] Aϵ p A' [GeV] 4 π γa' fb - 3 fb - Arc LHCb D HPS FASER: L max =4m,Δ =m, R=cm π LHCb A' μμ - - m A' [GeV] D EPOS-LHC m A' = MeV ϵ= -5 SHiP SeaQuest

14 Backup: Dark Higgs at FASER Light Dark Higgs - weakly couples to SM fermions L = m + m f ff v - mainly produced in Kaon and B-meson decay - can be probed by FASER p B [GeV] 4 B-meson 3 FONLL p ϕ [GeV] 4 3 B ϕx s FONLL m ϕ = GeV θ= -4 Aθ K πϕ 4 3 MATHUSLA B ϕx s FASER: L max =4m, Δ=m, R=m L=3 ab -, E ϕ > GeV 3 3 B X s ϕ SHiP - m ϕ [GeV] p ϕ [GeV] FONLL m ϕ = GeV θ= π θ B pt = m b L=3 ab R=cm R=m pt = m b L max =4m L=3 ab π θ ϕ pt = m b L=3 ab π θ ϕ

15 Backup: Forward Physics Models Particle Multiplicity: /σ dσ/dn Comparison of Forward Physics Models - traditionally relied on data from ultra-high-energy cosmic-ray experiments - new models are tuned to match LHC data - predictions are consistent π [GeV] 4 π EPOS-LHC p π [GeV] 4 π QGSJETII π η EPOS-LHC QGSJETII-4 SIBYLL.3 p π [GeV] n 4 π SIBYLL π π π θ π θ π θ π

16 Backup: Signal Contributions p A' [GeV] 4 π γa' 3 EPOS-LHC m A' = MeV ϵ= -5 3 p A' [GeV] 4 η γa' 3 EPOS-LHC m A' = MeV ϵ= -5 3 p A' [GeV] 4 Bremsstrahlung 3 m A' = MeV ϵ= -5 3 pt,a' = GeV p A' [GeV] π π γa' m A' = MeV ϵ= p A' [GeV] π η γa' m A' = MeV ϵ= p A' [GeV] 4 3 pt,a' = m A' π 4 Bremsstrahlung m A' = MeV ϵ= -5 pt,a' = GeV L max =4m π L max =4m π L max =4m π

17 Backup: fear vs near location pt -,A ' = Λ Q CD Lmax=4m - -3 π - - pt near location ,A ' = Λ Q CD near location Lmax=5m θa' -,A ',A ' = = G ev Λ Q CD -3-4 ms str a Lmax=4m - pt,a ',A ' = = Λ Q CD -3 π G ev θa' Br em ss tra h lun -3 g π FASER: near location Lmax=5m,Δ=5m,R=4cm L=3fb-, EA' >GeV near location Lmax=5m η - ma' [GeV] -6 hlu ng Br e pt FASER: Lmax=4m, Δ=m, R=cm L=3fb-, EA' >GeV π θa' pa' [GeV] -3 π 3 4 Bremsstrahlung ma'= MeV ϵ= pt π pt - ma'= MeV ϵ= θa' pa' [GeV] 3 4 π γa' ma'= MeV ϵ= Aϵ ma'= MeV ϵ=-5 Aϵ 3 pa' [GeV] 4 Bremsstrahlung near location pa' [GeV] 4 π γa' - - ma' [GeV] η