FASER: F orw A rd S earch E xpe R iment at the LHC work with - - PowerPoint PPT Presentation

FASER: ForwArd Search ExpeRiment at the LHC

Felix Kling DPF 2017


August 3rd 2017

arXiv: 1708.xxxxx

work with Jonathan Feng, Iftah Galon and Sebastian Trojanowski

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

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
• enormous event rates: ( inelastic pp collisions )

even extremely weakly-coupled particles may be produced sufficiently

• most decay products have small pT

energetic particles highly collimated for

• we propose small ( ) inexpensive detector a few 100 m downstream

FASER: ForwArd Search ExpeRiment at the LHC σinel ∼ 75 mb ∼ 1017 θ ∼ ΛQCD/E ∼ mrad E ∼ TeV ∼ ΛQCD ∼ 1 m3

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

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

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

LHC Infrastructure

Intersection Arc IP D1 D2 TAN Arc Intersection

100 200 300 400 L[m] D

TAS

• n-axis
• ff-axis
• particles produced at ATLAS/CMS Interaction Point
• Front Quadrupole Absorbers absorbs particles with
• inner beam separation dipole magnet

charged particles ( ) get deflected

• forward absorbed by Target Neutral Absorbers
• beam starts to curve at

Detector Locations

• ff-axis: L=100m on-axis: L=400m

IP TAS DI TAN Arc n, γ µ, π± θ > 0.85 mrad ∆ = 1 m Rin = 10 cm Rout = 20 cm inner radius

• uter radius

∆ = 1 m Rout = 20 cm

• uter radius

L = 272m

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

A Physics Example - Dark Photons

Dark Photons

• (broken) dark U(1) gauge group mixing with the SM photon
• FASER aims to probe and

mA0 ∼ 10 − 500 MeV ✏ ∼ 10−6 − 10−4 Production Modes

• meson decays: mainly ,
• proton Bremsstrahlung:

Fermi-Weizsäcker-Williams approximation

• (direct production):

PDFs at low and low highly uncertain π0 → γA0 η → γA0 pp → pA0X q¯ q → gA0 , qg → qA0 Meson Production

• use forward tools/models

EPOS-LHC, SIBYLL 2.3, QGSJETII-04

• boosted mesons highly collimated
• large rates at

p · θ = pT ∼ ΛQCD

L = 300 fb−1

L = 300 fb−1

pπ0 [GeV] 1012 1013 1014 1015 1016 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 π0 EPOS-LHC

pT,A' = ΛQCD

θπ0

Q2 x L 1 4F 0

µνF 0µν + 1

2mA02 + X ¯ f(i6@ ✏eqf 6A0)f

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

A Physics Example - Dark Photons

L = 300 fb−1

Meson Decay to Dark Photons

• branching fractions:
• even small large sizable rate

pA' [GeV] d [m] 102 103 104 105 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 π0→γA' EPOS-LHC mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD pT,A' = ΛQCD mA'

2 /mπ 2

θA'

BR(⇡0 → A0) = 2✏2 ✓ 1 − m2

A0

m2

π

◆3 Dark Photon Decay

• A’ is long lived:
• decay length

¯ d ≈ 80m Be 10−5 ✏ 2 EA0 TeV

• 100 MeV

mA0 2 ΓA0 = ✏2e2m2

A0/(12⇡ BR(A0 → ee))

✏ ∼ 10−5

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

A Physics Example - Dark Photons

• probability to decay inside detector:
• only A’ with E~TeV will reach detector
• A’ very forward

small detector radius

L = 300 fb−1

Meson Decay to Dark Photons

• branching fractions:
• even small large sizable rate

BR(⇡0 → A0) = 2✏2 ✓ 1 − m2

A0

m2

π

◆3 Dark Photon Decay

• A’ is long lived:
• decay length

¯ d ≈ 80m Be 10−5 ✏ 2 EA0 TeV

• 100 MeV

mA0 2 ΓA0 = ✏2e2m2

A0/(12⇡ BR(A0 → ee))

✏ ∼ 10−5 P = e−L/ ¯

d h

e∆/ ¯

d − 1

i Θ (LθA0 − R) θA0 < 1 mrad

pA' [GeV] d [m] 10-1 1 10 102 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 π0→γA' EPOS-LHC

• n-axis detector

mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD

• n-axis

Lfar=400m

θA'

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Detector Considerations

Nsig

π0 → γA' η → γA' Bremsstrahlung

0.2 0.4 0.6 0.8 1 103 104 102 101 1

• ff-axis
• n-axis

Distance to the IP

Δ=10m, Rout=20cm, Rin=10cm EA'>100 GeV ϵ: mA': 10-4 20 MeV 10-5 100 MeV

Lfar[km] Nsig 0.01 0.1 1 10 103 104 102 101 1 Detector Radius: on axis

Lfar=400m, Δ=10m EA'>100 GeV ϵ: mA': 10-4 20 MeV 10-5 100 MeV π0 → γA' η → γA' Bremsstrahlung

Rout [m]

Detector Position and Size

• ideally as close as possible to IP
• small detector radius R~20cm sufficient
• off-axis design benefits from low distance,

but suffers from reduced angular coverage Proposed Detector Apparatus

• tracking based technology
• small opening angle
• magnetic field required to obtain sizable splitting

can be obtained by conventional magnets Kinematic Features of Signal

• two oppositely charged energetic tracks: E>500 GeV
• vertex inside detector volume
• combined momentum points towards IP

θee ∼ mA0/EA0 ∼ 10 µrad hB = 3 mm 1 TeV E

• 

` 10 m 2 B 0.1 T

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Backgrounds

Signal

• 2 simultaneous high energy tracks
• tracks start inside detector
• combined momentum points towards IP
• both tracks have similar energy

Tracks starting inside detector


• mainly from , but also heavy mesons
• : ~8 events with E>100GeV

simultaneous CC interaction highly unlikely

• : events

pion usually soft Tracks starting outside detector

• particles from IP

deflected/absorbed by D1/TAS/TAN

• cosmic/beam induced high energy μs

expected rate: simultaneous tracks/year kinematic features reduce these BG possible scintillating layer for veto < 10−2

Nν [Events/kg] 10 100 1000 10-3 10-2 10-1 1 10 Neutrino Event Yield per kg

for Eν>Eν,min Lfar=400m, Rout=20cm νN→μ±X νN→μ±π∓X

Eν,min[GeV]

1110.1971

νN → µ±X

ATLAS: 1203.0223

10−4 Hz/cm2 νµ π± νN → µ±π⌥X ∼ 10−1 Eπ/Eµ . 0.05 analysis is basically BG free

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Expected Reach

Signal Rate

• signal acceptance almost 100%
• includes modes
• low ε: limited production rate
• high ε: A’ decay before detector
• high mass: improvement via

direct production?

Aϵ 10-2 10-1 1 10-6 10-5 10-4

1 10 102 103 104

π0

1 10

η

1

Bremsstrahlung

• n-axis

Lfar=400m, Δ=10m, Rout=20cm L=300fb-1, EA'>100GeV

* *

mA' [GeV]

A0 → ee, µµ, π±π⌥

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Expected Reach

Signal Rate

• signal acceptance almost 100%
• includes modes
• low ε: limited production rate
• high ε: A’ decay before detector
• high mass: improvement via

direct production?

Aϵ 10-2 10-1 1 10-6 10-5 10-4

1 10 102 103 104

π0

1 10

η

1

Bremsstrahlung

• n-axis

Lfar=400m, Δ=10m, Rout=20cm L=300fb-1, EA'>100GeV

* *

mA' [GeV] Aϵ 10-2 10-1 1 10 10-7 10-6 10-5 10-4 10-3

FASER: on-axis Lfar=400m,Δ =10m, Rout=20cm

300 fb-1 3000 fb-1 LHCb D* LHCb A'→μμ HPS ShiP SeaQuest

mA' [GeV]

Reach

• almost background free
• reach similar to SeaQuest, SHiP

A0 → ee, µµ, π±π⌥ (mA0✏)2|max ∝ L/EBeam

A0

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Summary and Outlook

Forward Physics

• large event rates in forward direction
• energetic particles very forward
• search for light extremely weakly coupled particles

Aϵ 10-2 10-1 1 10 10-7 10-6 10-5 10-4 10-3

FASER: on-axis Lfar=400m,Δ =10m, Rout=20cm

3 f b-1 3 f b-1 LHCb D* LHCb A'→μμ HPS ShiP SeaQuest

mA' [GeV]

Intersection IP D1 D2 TAN Arc Intersection

100 200 300 400 L[m] D

TAS

• n-axis
• ff-axis

Physics Example: Dark Photons

• A’ 2 energetic charged tracks,
• basically background free
• reach: ,

FASER

• small size detector
• placed few 100 m downstream of the ATLAS/CMS IP
• equipped with tracking system + magnetic field
• operates parasitically

∼ 1 m3

pA' [GeV] d [m] 102 103 104 105 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 π0→γA' EPOS-LHC mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD pT,A' = ΛQCD mA'

2 /mπ 2

θA'

mA0 ∼ 10 − 500 MeV ✏ ∼ 10−6 − 10−4 Outlook

• explore more physics opportunities/models

E ∼ TeV We look forward to feedback from experimentalists! θ < 1 mrad

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Backup: Forward Physics Models

pπ0 [GeV] 1012 1013 1014 1015 1016 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 π0 EPOS-LHC

pT,A' = ΛQCD

θπ0 pπ0 [GeV] 1012 1013 1014 1015 1016 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 π0 QGSJETII-04

pT,A' = ΛQCD

θπ0 pπ0 [GeV] 1012 1013 1014 1015 1016 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 π0 SIBYLL 2.3

pT,A' = ΛQCD

θπ0

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
• ● ● ● ●●●●●
• ●
• ■

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• ■

■ ■ ■ ■ ■ ■ ■ ■ ■■■■■■■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲

• ■

▲

• EPOS-LHC

■

QGSJETII-04

▲

SIBYLL 2.3

1 10 100 10-4 10-3 10-2 10-1 1 Particle Multiplicity: 1/σ dσ/dn

π0 η

n

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Backup: Signal Contributions

pA' [GeV] d [m] 102 103 104 105 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 Bremsstrahlung mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD pT,A' = 1 G e V pT,A' = mA'

θA' pA' [GeV] d [m] 102 103 104 105 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 η→γA' EPOS-LHC mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD pT,A' = ΛQCD mA'

2 /mη 2

θA' pA' [GeV] d [m] 102 103 104 105 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 π0→γA' EPOS-LHC mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD pT,A' = ΛQCD mA'

2 /mπ 2

θA' pA' [GeV] d [m] 10-1 1 10 102 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 Bremsstrahlung

• n-axis detector

mA'=100 MeV ϵ=10-5

p

T , A '

= Λ

Q C D

p

T , A '

= 10 GeV

• n-axis

Lfar=400m

θA' pA' [GeV] d [m] 10-1 1 10 102 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 η→γA' EPOS-LHC

• n-axis detector

mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD

• n-axis

Lfar=400m

θA' pA' [GeV] d [m] 10-1 1 10 102 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 π0→γA' EPOS-LHC

• n-axis detector

mA'=100 MeV ϵ=10-5

p

T , A '

= Λ

Q C D

• n-axis

Lfar=400m

θA'

Felix Kling FASER: ForwArd Search ExpeRiment at the LHC

Backup: on-axis vs off-axis

pA' [GeV] d [m] 10-1 1 10 102 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 Bremsstrahlung

• n-axis detector

mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD pT,A' = 10 GeV

• n-axis

Lfar=400m

θA' pA' [GeV] d [m] 10-1 1 10 102 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 π0→γA' EPOS-LHC

• n-axis detector

mA'=100 MeV ϵ=10-5

pT,A' = ΛQCD

• n-axis

Lfar=400m

θA'

Aϵ 10-2 10-1 1 10-6 10-5 10-4

1 10 102 103 104

π0

1 10

η

1

Bremsstrahlung

• n-axis

Lfar=400m, Δ=10m, Rout=20cm L=300fb-1, EA'>100GeV

* *

mA' [GeV]

pA' [GeV] d [m] 10-1 1 10 102 103 104 105 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 103 Bremsstrahlung mA'=100 MeV ϵ=10-5

• ff-axis detector

pT,A' = ΛQCD pT,A' = 10 GeV

• ff-axis

Lfar=100m

θA' pA' [GeV] d [m] 10-1 1 10 102 103 104 105 10-5 10-4 10-3 10-2 10-1 1π

2

10-2 10-1 1 10 102 103 104 10-3 10-2 10-1 1 10 102 π0→γA' EPOS-LHC mA'=20 MeV ϵ=10-4

• ff-axis detector

pT,A' = ΛQCD

• ff-axis

Lfar=100m

θA'

Aϵ 10-2 10-1 1 10-6 10-5 10-4

1 10 102 103 104 105

π0

1 10 102

η

1 10

Bremsstrahlung

• ff-axis

Lfar=100m,Δ=10m Rout=20cm,Rin=10cm L=300fb-1, EA'>100GeV

* *

mA' [GeV]