FASER: F orw A rd S earch E xpe R iment at the LHC work with Jonathan Feng, Iftah Galon and Sebastian Trojanowski arXiv: 1708.xxxxx Felix Kling DPF 2017 August 3rd 2017
Introduction transverse region: high pT Milliqan, Mathusla - searches for heavy strongly coupled physics ATLAS, CMS - typical rates σ ~ fb - pb forward region - mostly used for SM measurement LHCf, TOTEM, ALFA, CASTOR σ inel ∼ 75 mb ∼ 10 17 - enormous event rates: ( inelastic pp collisions ) even extremely weakly-coupled particles may be produced sufficiently - most decay products have small pT ∼ Λ QCD energetic particles highly collimated for θ ∼ Λ QCD /E ∼ mrad E ∼ TeV ∼ 1 m 3 - we propose small ( ) inexpensive detector a few 100 m downstream FASER: F orw A rd S earch E xpe R iment at the LHC Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
Outline LHC Infrastructure - where can we place the experiment Dark Photons - a physics example Detector Considerations - what detector design do we need Backgrounds - and why we do not worry about them Expected Reach - how do we perform Summary and Outlook Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
LHC Infrastructure IP - particles produced at ATLAS/CMS Interaction Point TAS - Front Quadrupole Absorbers absorbs particles with θ > 0 . 85 mrad DI - inner beam separation dipole magnet charged particles ( ) get deflected µ, π ± TAN - forward absorbed by Target Neutral Absorbers n, γ Arc - beam starts to curve at L = 272m Intersection Intersection Arc D IP D2 TAS D1 TAN Arc off-axis on-axis 0 100 200 300 400 L[m] Detector Locations off-axis : L=100m on-axis : L=400m m m 0 0 1 1 = = ∆ ∆ inner radius R in = 10 cm outer radius outer radius R out = 20 cm R out = 20 cm Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
A Physics Example - Dark Photons Dark Photons - (broken) dark U(1) gauge group mixing with the SM photon X ¯ L � � 1 µ ν F 0 µ ν + 1 2 m A 0 2 + 4 F 0 f ( i 6 @ � ✏ eq f 6 A 0 ) f ✏ ∼ 10 − 6 − 10 − 4 - FASER aims to probe and m A 0 ∼ 10 − 500 MeV Production Modes p π 0 [ GeV ] - meson decays: mainly , π 0 → γ A 0 η → γ A 0 10 4 π 0 EPOS - LHC - proton Bremsstrahlung: pp → pA 0 X Fermi-Weizsäcker-Williams approximation 10 3 q → gA 0 , qg → qA 0 - (direct production): q ¯ 10 2 PDFs at low and low highly uncertain Q 2 x 10 16 p T , A ' = Λ QCD 10 Meson Production 10 15 - use forward tools/models 1 10 14 EPOS-LHC, SIBYLL 2.3, Q GSJETII-04 10 13 - boosted mesons highly collimated 10 - 1 10 12 p · θ = p T ∼ Λ QCD L = 300 fb − 1 10 - 2 - large rates at 10 - 5 10 - 4 10 - 3 10 - 2 10 - 1 1 π L = 300 fb − 1 2 θ π 0 Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
A Physics Example - Dark Photons Meson Decay to Dark Photons ◆ 3 1 − m 2 ✓ - branching fractions: BR( ⇡ 0 → � A 0 ) = 2 ✏ 2 A 0 m 2 - even small large sizable rate ✏ ∼ 10 − 5 π Dark Photon Decay - A’ is long lived: A 0 / (12 ⇡ BR( A 0 → ee )) Γ A 0 = ✏ 2 e 2 m 2 - decay length � 2 E A 0 � 2 10 − 5 � 100 MeV p A ' [ GeV ] d [ m ] ¯ d ≈ 80m B e π 0 →γ A' EPOS - LHC 10 3 10 4 TeV m A 0 ✏ m A ' = 100 MeV 10 2 ϵ = 10 - 5 10 3 10 10 2 1 p T , A ' p T , A ' 10 5 10 = = Λ QCD Λ QCD 10 4 10 - 1 1 m A ' 2 / m π 10 3 2 10 - 2 10 - 1 10 2 L = 300 fb − 1 10 - 3 10 - 2 10 - 5 10 - 4 10 - 3 10 - 2 10 - 1 1 π 2 θ A ' Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
A Physics Example - Dark Photons Meson Decay to Dark Photons ◆ 3 1 − m 2 ✓ - branching fractions: BR( ⇡ 0 → � A 0 ) = 2 ✏ 2 A 0 m 2 - even small large sizable rate ✏ ∼ 10 − 5 π Dark Photon Decay - A’ is long lived: A 0 / (12 ⇡ BR( A 0 → ee )) Γ A 0 = ✏ 2 e 2 m 2 - decay length � 2 E A 0 � 2 10 − 5 p A ' [ GeV ] d [ m ] � 100 MeV ¯ d ≈ 80m B e π 0 →γ A' EPOS - LHC 10 3 10 4 TeV m A 0 ✏ m A ' = 100 MeV 10 2 ϵ = 10 - 5 10 3 - probability to decay inside detector: L = 300 fb − 1 d h i P = e − L/ ¯ e ∆ / ¯ 10 d − 1 10 2 Θ ( L θ A 0 − R ) 1 p T , A ' = Λ QCD - only A’ with E~TeV will reach detector 10 2 10 on - axis detector - A’ very forward θ A 0 < 1 mrad 10 10 - 1 1 small detector radius 1 10 - 2 10 - 1 on - axis 10 - 1 L far = 400m 10 - 3 10 - 2 10 - 5 10 - 4 10 - 3 10 - 2 10 - 1 1 π 2 θ A ' Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
Detector Considerations 10 4 Detector Position and Size Distance to the IP Δ = 10m, R out = 20cm, R in = 10cm - ideally as close as possible to IP E A ' > 100 GeV 10 3 - small detector radius R~20cm sufficient 10 2 - off-axis design benefits from low distance, N sig but suffers from reduced angular coverage off - axis on - axis 10 1 10 - 4 10 - 5 Kinematic Features of Signal ϵ : m A ' : 20 MeV 100 MeV π 0 → γ A' 1 - two oppositely charged energetic tracks: E>500 GeV → γ A' η Bremsstrahlung - vertex inside detector volume 0 0.2 0.4 0.6 0.8 1 - combined momentum points towards IP L far [ km ] 10 4 Detector Radius: on axis L far = 400m, Δ = 10m Proposed Detector Apparatus E A ' > 100 GeV 10 3 - tracking based technology - small opening angle θ ee ∼ m A 0 /E A 0 ∼ 10 µ rad 10 2 N sig - magnetic field required to obtain sizable splitting � 2 1 TeV � � ` B 10 - 4 10 - 5 ϵ : 10 1 h B = 3 mm m A ' : 20 MeV 100 MeV π 0 → γ A' E 10 m 0 . 1 T η → γ A' Bremsstrahlung can be obtained by conventional magnets 1 0.01 0.1 1 10 R out [ m ] Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
Backgrounds Signal - 2 simultaneous high energy tracks - combined momentum points towards IP - both tracks have similar energy - tracks start inside detector Tracks starting outside detector - particles from IP kinematic features reduce these BG deflected/absorbed by D1/TAS/TAN possible scintillating layer for veto - cosmic/beam induced high energy μ s 10 − 4 Hz/cm 2 expected rate: ATLAS: 1203.0223 simultaneous tracks/year < 10 − 2 Neutrino Event Yield per kg for E ν > E ν ,min Tracks starting inside detector 10 ν N →μ ± X - mainly from , but also heavy mesons π ± 1110.1971 ν µ N ν [ Events / kg ] 1 - : ~8 events with E>100GeV ν N → µ ± X simultaneous CC interaction highly unlikely 10 - 1 ν N →μ ± π ∓ X ν N → µ ± π ⌥ X ∼ 10 − 1 - : events pion usually soft E π /E µ . 0 . 05 10 - 2 L far = 400m, R out = 20cm analysis is basically BG free 10 - 3 10 100 1000 E ν ,min [ GeV ] Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
Expected Reach Signal Rate - signal acceptance almost 100% A 0 → ee, µµ, π ± π ⌥ - includes modes - low ε : limited production rate - high ε : A’ decay before detector - high mass: improvement via direct production? π 0 on - axis L far = 400m, Δ = 10m, R out = 20cm L = 300fb - 1 , E A ' > 100GeV * 10 - 4 Bremsstrahlung A ϵ 10 4 * 10 - 5 10 3 1 1 10 2 10 10 η 1 10 - 6 10 - 2 10 - 1 1 m A ' [ GeV ] Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
Expected Reach Reach Signal Rate - almost background free - signal acceptance almost 100% A 0 → ee, µµ, π ± π ⌥ - reach similar to SeaQuest, SHiP - includes modes - low ε : limited production rate ( m A 0 ✏ ) 2 | max ∝ L/E Beam A 0 - high ε : A’ decay before detector - high mass: improvement via direct production? 10 - 3 π 0 on - axis LHCb D * L far = 400m, Δ = 10m, R out = 20cm HPS L = 300fb - 1 , E A ' > 100GeV * 10 - 4 LHCb A' →μμ 10 - 4 Bremsstrahlung 10 - 5 A ϵ A ϵ 10 4 * 10 - 5 10 3 300 fb - 1 1 10 - 6 3000 fb - 1 1 SeaQuest 10 2 10 ShiP FASER: on - axis 10 η 1 L far = 400m, Δ = 10m, R out = 20cm 10 - 7 10 - 6 10 - 2 10 - 1 10 - 2 10 - 1 1 10 1 m A ' [ GeV ] m A ' [ GeV ] Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
Summary and Outlook Forward Physics Intersection Intersection Arc D IP TAS D1 TAN D2 - large event rates in forward direction off-axis on-axis 0 100 200 300 400 L[m] - energetic particles very forward θ < 1 mrad - search for light extremely weakly coupled particles p A ' [ GeV ] d [ m ] π 0 →γ A' EPOS - LHC 10 3 10 4 m A ' = 100 MeV FASER 10 2 ϵ = 10 - 5 10 3 - small size detector ∼ 1 m 3 10 10 2 - placed few 100 m downstream of the ATLAS/CMS IP 1 p T , A ' p T , A ' 10 5 10 = = Λ QCD Λ QCD - equipped with tracking system + magnetic field 10 4 10 - 1 1 m A ' 2 / m π 10 3 2 - operates parasitically 10 - 2 10 - 1 10 2 10 - 3 10 - 2 Physics Example: Dark Photons 10 - 5 10 - 4 10 - 3 10 - 2 10 - 1 1 π 2 θ A ' - A’ 2 energetic charged tracks, 10 - 3 E ∼ TeV LHCb D * - basically background free HPS LHCb A' →μμ 10 - 4 - reach: , m A 0 ∼ 10 − 500 MeV ✏ ∼ 10 − 6 − 10 − 4 10 - 5 A ϵ Outlook - explore more physics opportunities/models 3 0 0 10 - 6 f b - 1 3 0 0 0 f b - 1 SeaQuest ShiP FASER: on - axis We look forward to feedback from experimentalists! L far = 400m, Δ = 10m, R out = 20cm 10 - 7 10 - 2 10 - 1 1 10 m A ' [ GeV ] Felix Kling FASER : F orw A rd S earch E xpe R iment at the LHC
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