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FASER: ForwArd Search ExpeRiment at the LHC
Felix Kling
Searches for long-lived particles at the LHC Second Workshop of The LHC LPP community
October 19th 2017
arXiv: 1708.09389
work with Jonathan Feng, Iftah Galon and Sebastian Trojanowski
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Introduction
forward region - mostly used for SM measurement LHCf, TOTEM, ALFA, CASTOR - enormous event rates: : extremely weakly-coupled long-lived particles may be produced sufficiently - most particles 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
�inel ⇠ 75 mb
✓ ⇠ ⇤QCD/E ⇠ mrad E ⇠ TeV⇠ ⇤QCD
⇠ 1 m3
NH = 107 at 300fb�1
transverse region: high pT Milliqan, Mathusla,Codex-b - searches for heavy strongly coupled physics ATLAS, CMS - typical rates σ ~ fb - pb
N⇡ = 1017 at 300fb�1
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 InfrastructureIntersection
ArcIP D1 D2TAN
ArcIntersection
0 100 200 300 400 L[m]
DTAS
far location
x[cm]
0
+5
+10
+15
-5
-10
-15
0 50 100 150 L[m]
Q1 Q2 Q3TASIP D1 TAN D2 Q4
ne
ar
loca
tio
n
proton beam
proton beam
proton ~ 4.5 TeV
proton ~2 TeV
neutral particles
dark photon
µ,⇡±
IP particles produced
at ATLAS/CMS Interaction Point
D & Q Magnets charged particles
get deflected
TAN forward xxxx
absorbed by Target Neutral Absorbers
n, �Arc
beam starts to curve at
L = 272m
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
LHC InfrastructureIntersection
ArcIP D1 D2TAN
ArcIntersection
0 100 200 300 400 L[m]
DTAS
far location
x[cm]
0
+5
+10
+15
-5
-10
-15
0 50 100 150 L[m]
Q1 Q2 Q3TASIP D1 TAN D2 Q4
ne
ar
loca
tio
n
proton beam
proton beam
proton ~ 4.5 TeV
proton ~2 TeV
neutral particles
dark photon
µ,⇡±
IP particles produced
at ATLAS/CMS Interaction Point
D & Q Magnets charged particles
get deflected
TAN forward xxxx
absorbed by Target Neutral Absorbers
n, �Arc
beam starts to curve at
L = 272m
LHC Infrastructure acts as natural filter
Detector Locations
far location: L=400m - after tunnel curves, surrounded by rock - near location: L=100m - between TAN and D2, embedded in infrastructure -
R = 20 cmR = 4 cm
�
L = 150 m, � = 5 m, R = 4 cm
L = 400 m, � = 10 m, R = 20 cm
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
A Physics Example - Dark PhotonsDark 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
⇡0 ! �A0 ⌘ ! �A0
pp ! pA0X
qq̄ ! gA0 , qg ! qA0
Meson Production - use forward tools/models EPOS-LHC, SIBYLL 2.3, QGSJETII-04 - boosted mesons highly collimated - large rates at
p · ✓ = pT ⇠ ⇤QCD L = 300 fb�1
L = 300 fb�1
pπ0 [GeV]
10121013101410151016
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104 π0 EPOS-LHC
pT,A' = Λ
QCD
θπ0
Q2x
L � �1
4F 0µ⌫F
0µ⌫ +1
2mA0
2 +X
f̄(i 6@ � ✏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
BR(⇡0 ! �A0) = 2✏2✓1� m2
A0
m2⇡
◆3
Dark Photon Decay - A’ is long lived: - decay length
d̄ ⇡ 80m Be
10�5
✏
�2EA0
TeV
�100 MeV
mA0
�2�A0 = ✏2e2m2
A0/(12⇡ BR(A0 ! ee))
✏ ⇠ 10�5
pA' [GeV] d [m]
102
103
104
105
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103π0→γA' EPOS-LHCmA'=100 MeV
ϵ=10-5
pT,A' = Λ
QCD
θA'
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⇡
◆3
Dark Photon Decay - A’ is long lived: - decay length
d̄ ⇡ 80m Be
10�5
✏
�2EA0
TeV
�100 MeV
mA0
�2�A0 = ✏2e2m2
A0/(12⇡ BR(A0 ! ee))
✏ ⇠ 10�5
P = e�L/d̄he�/d̄ � 1
i⇥ (L✓A0 �R)
✓A0 < 1 mrad
pA' [GeV] d [m]
10-11
10
102
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103π0→γA'mA'=100 MeV
ϵ=10-5
farlocation
pT,A' = Λ
QCD
far locationLmax=400m
θA'
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Detector ConsiderationsDetector Position and Size - ideally as close as possible to IP - small detector radius R~20cm sufficient - near location 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
✓ee ⇠ mA0/EA0 ⇠ 10 µrad
hB = 3 mm
1 TeV
E
�`
10 m
�2 B
0.1 T
�
Nsig
0 0.2 0.4 0.6 0.8 1
104
105
103
102
101
11
Distance between detector and IP
near locationR=4cmΔ=5m
far locationR=10cmΔ=10m
ϵ:mA':
10-420 MeV
10-5100 MeV
π0 → γA'η → γA'
Bremsstrahlung
●
●●
●
●
●
Lmax [km]
Nsig
0.01 0.1 1 10
103
104
102
101
11
Detector Radius: far locationLmax=400m, Δ=10m
EA'>100 GeV
ϵ:mA':
10-420 MeV
10-5100 MeV
π0 → γA'η → γA'
Bremsstrahlung
R [m]Lmax
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
BackgroundsSignal - 2 simultaneous high energy tracks - tracks start inside detector
- combined momentum points towards IP- both tracks have similar energy
Neutrino Induced Backgrounds - mainly from , but also heavy mesons - : ~8 events with E>100GeV simultaneous CC interaction highly unlikely - : events pion usually soft
Beam Induced Backgrounds (at far location) - best estimated with simulations or exp. data - detector shielded by surrounding rock - mainly muon arrive expected rate: ~0.1 simultaneous muon tracks/year
kinematic features reduce these BG possible scintillating layer for veto
Nν[Events/kg
]10 100 1000
10-3
10-2
10-1
1
10
Neutrino Event Yield per kgfor Eν>Eν,min
Lfar=400m, Rout=20cm
νN→μ±X
νN→μ±π∓X
Eν,min[GeV]
1110.1971
⌫N ! µ±X
ATLAS: 1203.0223
⌫µ ⇡±
⌫N ! µ±⇡⌥X ⇠ 10�1
E⇡/Eµ . 0.05
analysis is basically BG free
� ⇠ 10�3 Hz/cm2
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Expected ReachSignal Rate - signal acceptance almost 100% - includes modes - low ε: limited production rate - high ε: A’ decay before detector - high mass: direct production?
A0 ! ee, µµ,⇡±⇡⌥
Aϵ
10-2 10-1 1
10-6
10-5
10-4
10-3
110102
103
104
π0
110η
1
Bremsstrahlung
FASER: far locationLmax=400m, Δ=10m, R=20cm
L=300fb-1, EA'>100GeV
*
*
mA' [GeV]
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Expected ReachSignal Rate - signal acceptance almost 100% - includes modes - low ε: limited production rate - high ε: A’ decay before detector - high mass: direct production?
Reach - almost background free - reach similar to SeaQuest, SHiP
A0 ! ee, µµ,⇡±⇡⌥
(mA0✏)2|max
/ L/EBeam
A0
Aϵ
10-2 10-1 1
10-6
10-5
10-4
10-3
110102
103
104
π0
110η
1
Bremsstrahlung
FASER: far locationLmax=400m, Δ=10m, R=20cm
L=300fb-1, EA'>100GeV
*
*
mA' [GeV]
Aϵ
10-2 10-1 110-7
10-6
10-5
10-4
10-3
FASER: far locationLmax=400m,Δ =10m, R=20cm
300 fb-13000 fb-1
LHCb D*
LHCb A'→μμ
HPS
SHiP
SeaQuest
mA' [GeV]
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Intersection
ArcIP D1 D2TAN
ArcIntersection
0 100 200 300 400 L[m]
DTAS
far location
x[cm]
0
+5
+10
+15
-5
-10
-15
0 50 100 150 L[m]
Q1 Q2 Q3TASIP D1 TAN D2 Q4
ne
ar
loca
tio
n
proton beam
proton beam
proton ~ 4.5 TeV
proton ~2 TeV
neutral particles
dark photon
Summary and OutlookForward Physics - large event rates in forward direction - energetic particles very forward - search for light extremely weakly coupled particles
Physics Example: Dark Photons - A’ 2 energetic charged tracks, - basically background free - reach: ,
FASER - cheap small size detector, operates concurrently - placed few 100 m downstream of the ATLAS/CMS IP - equipped with tracking system + magnetic field
⇠ 1 m3
mA0 ⇠ 10� 500 MeV ✏ ⇠ 10�6 � 10�4
Outlook and Current Developments - explore more physics opportunities: scalars, axions, HNL - find ideal detector location, GEANT4 simulations together with experimentalists
E ⇠ TeV
We look forward to feedback and suggestions
✓ < 1 mrad
Aϵ
10-2 10-1 110-7
10-6
10-5
10-4
10-3
FASER: far locationLmax=400m,Δ =10m, R=20cm
300 fb-13000 fb-1
LHCb D*
LHCb A'→μμ
HPS
SHiP
SeaQuest
mA' [GeV]
pA' [GeV] d [m]
102
103
104
105
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103π0→γA' EPOS-LHCmA'=100 MeV
ϵ=10-5
pT,A' = Λ
QCD
θA'
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Backup: Dark Higgs at FASER
pB [GeV]
1091010101110121013
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
L=3 ab-1
B-meson FONLL
pT = m
b
θB
pϕ [GeV] d [m]
102103104105106
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103
L=3 ab-1
B→ϕXs FONLLmϕ=2 GeV
θ=10-4
pT = m
b
θϕ
pϕ [GeV] d [m]
10-1110102103
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103
L=3 ab-1
B→ϕXs FONLLmϕ=2 GeV
θ=10-4farlocationR=20cm
farlocationR=1m
pT = m
b
far locationLmax=400m
θϕ
Aθ
10-1 1 1010-6
10-5
10-4
10-3
10-2
B→Xsϕ
K→πϕ
3
10102
103
FASER: far locationLmax=400m, Δ=10m, R=1m
L=3 ab-1, Eϕ>100 GeV
*
*
SHiP
MATHUSLA
mϕ [GeV]
L = m2��
2 + ✓mf
v�f̄f
Light Dark Higgs - weakly couples to SM fermions
- mainly produced in Kaon and B-meson decay - can be probed by FASER
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Backup: Forward Physics Models
pπ0 [GeV]
10121013101410151016
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104 π0 EPOS-LHC
pT,A' = Λ
QCD
θπ0
pπ0 [GeV]
10121013101410151016
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104 π0 QGSJETII-04
pT,A' = Λ
QCD
θπ0
pπ0 [GeV]
10121013101410151016
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104 π0 SIBYLL 2.3
pT,A' = Λ
QCD
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 10010-4
10-3
10-2
10-1
1Particle Multiplicity: 1/σ dσ/dn
π0 η
n
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Backup: Signal ContributionspA' [GeV] d [m]
102
103
104
105
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103BremsstrahlungmA'=100 MeV
ϵ=10-5
pT,A' = Λ
QCD
pT,A' = 10 GeV
pT,A' = m
A'
θA'pA' [GeV] d [m]
10-11
10
102
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103BremsstrahlungmA'=100 MeV
ϵ=10-5
farlocation
pT,A' = Λ
QCD
pT,A' = 10 GeV
far locationLmax=400m
θA'
pA' [GeV] d [m]
10-11
10
102
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103π0→γA'mA'=100 MeV
ϵ=10-5
farlocation
pT,A' = Λ
QCD
far locationLmax=400m
θA'
pA' [GeV] d [m]
10-11
10
102
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103η→γA'mA'=100 MeV
ϵ=10-5farlocation
pT,A' = Λ
QCD
far locationLmax=400m
θA'
pA' [GeV] d [m]
102
103
104
105
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103π0→γA' EPOS-LHCmA'=100 MeV
ϵ=10-5
pT,A' = Λ
QCD
θA'
pA' [GeV] d [m]
102
103
104
105
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103η→γA' EPOS-LHCmA'=100 MeV
ϵ=10-5
pT,A' = Λ
QCD
θA'
Felix Kling FASER: ForwArd Search ExpeRiment at the LHC
Backup: fear vs near locationpA' [GeV] d [m]
10-11
10
102
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103BremsstrahlungmA'=100 MeV
ϵ=10-5
farlocation
pT,A' = Λ
QCD
pT,A' = 10 GeV
far locationLmax=400m
θA'
pA' [GeV] d [m]
10-11
10
102
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103π0→γA'mA'=100 MeV
ϵ=10-5farlocation
pT,A' = Λ
QCD
far locationLmax=400m
θA'pA' [GeV] d [m]
10-1110102103104105
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103π0→γA'mA'=100 MeV
ϵ=10-5
nearlocation
pT,A' = Λ
QCD
near locationLmax=150m
θA'
pA' [GeV] d [m]
10-1110102103104105
10-5 10-4 10-3 10-2 10-1 1π2
10-2
10-1
1
10
102
103
104
10-3
10-2
10-1
1
10
102
103BremsstrahlungmA'=100 MeV
ϵ=10-5nearlocation
pT,A' = Λ
QCD
pT,A' = 10 GeV
near locationLmax=150m
θA'Aϵ
10-2 10-1 1
10-6
10-5
10-4
10-3
110102
103
104
π0
110η
1
Bremsstrahlung
FASER: far locationLmax=400m, Δ=10m, R=20cm
L=300fb-1, EA'>100GeV
*
*
mA' [GeV]
Aϵ
10-2 10-1 1
10-6
10-5
10-4
10-3
110
102103
104
π0
110
η
1
Bremsstrahlung
FASER: near locationLmax=150m,Δ=5m,R=4cmL=300fb-1, EA'>100GeV
*
*
mA' [GeV]